CA1055680A - Method for making metallic sandwich structures - Google Patents
Method for making metallic sandwich structuresInfo
- Publication number
- CA1055680A CA1055680A CA238,141A CA238141A CA1055680A CA 1055680 A CA1055680 A CA 1055680A CA 238141 A CA238141 A CA 238141A CA 1055680 A CA1055680 A CA 1055680A
- Authority
- CA
- Canada
- Prior art keywords
- stack
- workpieces
- chamber
- metal
- inert gas
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
- B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D26/00—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces
- B21D26/02—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces by applying fluid pressure
- B21D26/021—Deforming sheet bodies
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D26/00—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces
- B21D26/02—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces by applying fluid pressure
- B21D26/053—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces by applying fluid pressure characterised by the material of the blanks
- B21D26/055—Blanks having super-plastic properties
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D26/00—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces
- B21D26/02—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces by applying fluid pressure
- B21D26/053—Shaping without cutting otherwise than using rigid devices or tools or yieldable or resilient pads, i.e. applying fluid pressure or magnetic forces by applying fluid pressure characterised by the material of the blanks
- B21D26/059—Layered blanks
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21D37/00—Tools as parts of machines covered by this subclass
- B21D37/16—Heating or cooling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
- B23P—METAL-WORKING NOT OTHERWISE PROVIDED FOR; COMBINED OPERATIONS; UNIVERSAL MACHINE TOOLS
- B23P15/00—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass
- B23P15/26—Making specific metal objects by operations not covered by a single other subclass or a group in this subclass heat exchangers or the like
Landscapes
- Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Physics & Mathematics (AREA)
- Fluid Mechanics (AREA)
- Pressure Welding/Diffusion-Bonding (AREA)
- Shaping Metal By Deep-Drawing, Or The Like (AREA)
Abstract
METHOD FOR MAKING METALLIC SANDWICH STRUCTURES
ABSTRACT
A method for fabrication of metallic sandwich structures in which metal blanks, preferably of a titanium alloy, are joined at selected areas and expanded superplastically to form a desired sandwich structure. Various techniques for joining, preferably diffusion bonding, selected areas of the metal blanks are disclosed.
These include treating the metal blanks at selected areas to prevent bonding at those areas and selective application of pressure during bonding. In the preferred enbodiment, the metal blanks are positioned in a stack after being treated at selected areas. The stack is positioned relatives to shaping members and heated to a temperature suitable for superplastic forming and diffusion bonding. Compressive pressure is applied for the selective diffusion bonding. The stack is expanded into contact with the shaping members by increasing the internal pressure therein, preferably with inert gas, thus forming the desired shaped sandwich structure in one operation.
ABSTRACT
A method for fabrication of metallic sandwich structures in which metal blanks, preferably of a titanium alloy, are joined at selected areas and expanded superplastically to form a desired sandwich structure. Various techniques for joining, preferably diffusion bonding, selected areas of the metal blanks are disclosed.
These include treating the metal blanks at selected areas to prevent bonding at those areas and selective application of pressure during bonding. In the preferred enbodiment, the metal blanks are positioned in a stack after being treated at selected areas. The stack is positioned relatives to shaping members and heated to a temperature suitable for superplastic forming and diffusion bonding. Compressive pressure is applied for the selective diffusion bonding. The stack is expanded into contact with the shaping members by increasing the internal pressure therein, preferably with inert gas, thus forming the desired shaped sandwich structure in one operation.
Description
-` 1055680 BACKGROU~D OF THE INV~NTION
For many years it has been known that certain metals, such as titanium and many of its alloys, exhibit superplasticity. Superplasticity is the capa-bility of a material to develop unusually high tensile elongations with reduced tendency toward necking. This capability is exhibited by only a few metals and all~ys and within a limited temperature and strain rate range. Titanium and titanium alloys have been observed to exhibit superplastic characteristics equal to or greater than those of any other metals. With suitable titanium alloys, overall increase in surface areas up to 300/~ are possible.
The advantages of superplastic forming are numerous: very complex -shapes and deep drawn parts can be readily formed; low deformation stresses are required to form the metal at the superplastic temperature range, thereby permitting forming of parts under low pressures which minimize tool deformation and wear, allows the use of inexpensive tooling materials, and eliminates creep in the tool; single male or female tools can be used; no sprlng-back occurs;
:, no ~auschinger efEect develops; multiple parts of different geometry can be made during a single operation; very small radii can be formed, and no problem with compression buckles or galling are encountered. However, when superplastic forming of titanium and similar reactive metals, it is necessary to heat and form in a controlled environment to ensure cleanliness of the titanium which ; is particularly sensitive to oxygen, nitrogen, and water vapor content in the air at elevated temperatures. Unles3 the titanium is protected, it becomes embrittled and its integrity destroyed, Diffusion bonding refers to the metallurgical joining of surfaces of similar or dissimilar metals by applying heat and pressure for a time duration so as to cause co-mingling of atomg at the joint interface. Diffusion .1 ~; bonding is accomplished entirely in the solid-state at or above one-half the ;~ base metal melting point (absolùte). Actual times, temperatures, and pressures will vary from metal to metal. The joining surfaces must be brought within ,~, , .
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For many years it has been known that certain metals, such as titanium and many of its alloys, exhibit superplasticity. Superplasticity is the capa-bility of a material to develop unusually high tensile elongations with reduced tendency toward necking. This capability is exhibited by only a few metals and all~ys and within a limited temperature and strain rate range. Titanium and titanium alloys have been observed to exhibit superplastic characteristics equal to or greater than those of any other metals. With suitable titanium alloys, overall increase in surface areas up to 300/~ are possible.
The advantages of superplastic forming are numerous: very complex -shapes and deep drawn parts can be readily formed; low deformation stresses are required to form the metal at the superplastic temperature range, thereby permitting forming of parts under low pressures which minimize tool deformation and wear, allows the use of inexpensive tooling materials, and eliminates creep in the tool; single male or female tools can be used; no sprlng-back occurs;
:, no ~auschinger efEect develops; multiple parts of different geometry can be made during a single operation; very small radii can be formed, and no problem with compression buckles or galling are encountered. However, when superplastic forming of titanium and similar reactive metals, it is necessary to heat and form in a controlled environment to ensure cleanliness of the titanium which ; is particularly sensitive to oxygen, nitrogen, and water vapor content in the air at elevated temperatures. Unles3 the titanium is protected, it becomes embrittled and its integrity destroyed, Diffusion bonding refers to the metallurgical joining of surfaces of similar or dissimilar metals by applying heat and pressure for a time duration so as to cause co-mingling of atomg at the joint interface. Diffusion .1 ~; bonding is accomplished entirely in the solid-state at or above one-half the ;~ base metal melting point (absolùte). Actual times, temperatures, and pressures will vary from metal to metal. The joining surfaces must be brought within ,~, , .
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atomic distances by application of pressure. Ad~quate pressure must also be provided to cause some plastic flow to fill normal void areas. If pressures are too low, small voids will remain at the joint interface and the joint strength will be less than the maximum obtainable. The application of pressure also breaks up the surface oxides an~ surface asperities so as to present ; clean surfaces for bonding. The elevated temperatures used for .
diffusion bonding serve the functions of accelerating diffusion of atoms at the joint interfaces and providing a metal softening which aids in surface defor~ation so as to allow more intimate contact for atom bonding and movement across the joint interface.
~, The elevated temperature and application of pressure also results in diffusion o~ the surface contaminants into the base metal during bonding which allows metal atom-to-atom bonding and thereby strengthens the bond. Suicient time mu5t be allowed ~1 ,.
to ensure the 3trsngthening o the bond by diffusion of atoms across the joint interface,~ A protective atmosphere for bonding is required when titanium and other similar reactive metals are to be bonded.
The process of superplastic forming of metals and diffusion bonding have individually been disclosed in the prior art. U.S.
patent No. 3,340,101 to Fields, Jr., et al. discloses a method of superplastic forming where a metal is conditioned to exhibit its effective strain rate sensitivity and then formed by applica-tion of vacuum soIely or in combination with a metal dye.
Patents relating to solid-state or diffusion bonding include U.SO
patent No. 3,145~466; 3,180,022; 3~044,160; 2,850,798; and 3,1700234.
However, the prior art does not disclose combining these two processes.
j 30 In my co-pending Canadian ~ plication ~o. 233,354 there
)5561~
atomic distances by application of pressure. Ad~quate pressure must also be provided to cause some plastic flow to fill normal void areas. If pressures are too low, small voids will remain at the joint interface and the joint strength will be less than the maximum obtainable. The application of pressure also breaks up the surface oxides an~ surface asperities so as to present ; clean surfaces for bonding. The elevated temperatures used for .
diffusion bonding serve the functions of accelerating diffusion of atoms at the joint interfaces and providing a metal softening which aids in surface defor~ation so as to allow more intimate contact for atom bonding and movement across the joint interface.
~, The elevated temperature and application of pressure also results in diffusion o~ the surface contaminants into the base metal during bonding which allows metal atom-to-atom bonding and thereby strengthens the bond. Suicient time mu5t be allowed ~1 ,.
to ensure the 3trsngthening o the bond by diffusion of atoms across the joint interface,~ A protective atmosphere for bonding is required when titanium and other similar reactive metals are to be bonded.
The process of superplastic forming of metals and diffusion bonding have individually been disclosed in the prior art. U.S.
patent No. 3,340,101 to Fields, Jr., et al. discloses a method of superplastic forming where a metal is conditioned to exhibit its effective strain rate sensitivity and then formed by applica-tion of vacuum soIely or in combination with a metal dye.
Patents relating to solid-state or diffusion bonding include U.SO
patent No. 3,145~466; 3,180,022; 3~044,160; 2,850,798; and 3,1700234.
However, the prior art does not disclose combining these two processes.
j 30 In my co-pending Canadian ~ plication ~o. 233,354 there
3 -~L055680 ;`.
is disclosed a method for superplastic forming of metals with concurrent diffusion bondingO The crux of that invention is :
the superplastic forming of a metal blank against a shaping member and another metal workpiece so that the metal blank is ~ :
formed and diffusion bonded to the other metal workpiece in one ,. : .
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"` 105~68~ , a hollow metal structure bonded at peripheral edges can be formed as disclosed in that application, the process is not designed ior the forming of sandwich structures. The forming of sandwich structures according to the present invention requires separate superplastic forming and joining stages and a technique for joining only selecti~e areas of the metal blanks employed.
The present invention obviates the prior art problems of forming sandwich structures. A sandwich structure normally comprises a core between face sheets. Previous to Applicants' invention, fabrication o~ sandwich structures typically took the approach of first rolling metal foil or ribbon, forming and joining the foil sheet into the desired cellular core, and then attaching the core to face sheets by brazing or spot welding. Problems with the prior art method include the cost of the core due to excess material usage and the great difficulty, excess time consumption, and cost of fabrication of the sandwich shape. Additionally, a separate operation is required to join a close out or attachment to the sandwich strllcture.
Fabricatlon of an unusual shape for the sandwich structure such as a taper, is nearly impossible.
~5568~D
SUMMARY OF THE INVENTION
, It is, therefore, an object of the present invention to combine the processes of metal joining and superplastic forming to form metal sandwich structures.
Is is another object of the present invention to form metal sandwich structures in one operation, thereby significantly lowering the cost, difficulty, and time involved.
It is yet another object of the present invention to form a sandwich structure and join an attachment or close-out in the same operation.
It is still another object of the present invention to heat, superplas- ` -tically form, and join the sandwich in the same apparatus, thereby saving fabrication time and equipment costs.
Briefly, in accordflnce with the invention, there is provided a method ; for making a metallic sandwich structure from a plurallty of metal blank work-pieces initially positioned in a stacked position. The blanks are joined at ; selectad areas. At least one of the blanks is superplastically formed against a shaping member to form the desired sandwich structure. The core configuration is determined by the location, size, and shape of the joined areas.
Other objects and advantages of the invention will become apparent ; 20 upon reading the following detalled description and upon reference to the drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
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Figure 1 is an exploded view of a three-piece metal sheet assembly treated for selective diffusion bonding prior to insertion in the forming .
apparatus;
Figure 2 is a cross-sectional elevational view of a preferred .~ ~;
embodiment of a forming apparatus used for fabrication of metal sandwich structures with the three piece metal sheet assembly of Figure 1 inserted :~ therein;
. Figure 3 illustrates the fully expanded three-piece metal sheet assembly within the forming apparatus of Figure 2 with broken lines added - to delineate the final position of the component metal sheets of the expanded joined assembly;
Figure 4 is a detail view of an inflation tube connection to the three-sheet assembly;
i 15 TFigures 5 and 6 are cross-sectional elevational views oE a modified forming apparatus with a three-piece metal sheet assembly inserted therein in its initial position in Figure 5 and in its final expanded position in Figure 6;
Figures 7 and 8 are cross-sectional elevational views of a modified forming apparatus with a two-piece metal sheet assembly inserted therein in '. its inltial position in Figure 7 and in its final expanded position in Figure 8;
. Figure 9 is a cross-sectional elevational view of a modified forming apparatus illustrating a tapered three-piece metal sheet assembly in final formed position with an attachment ~oined to the sandwich structure at the broken lines;
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1~)556~10 ,-Figure 10 is a perspective view with the ends cut off of the formed sandwich structure of Figure 9; ~ ```
. Figure 11 is a frag~entary cros~-sectional elevational view of a modified forming apparatus illustrating the positioning of an inflation tube relative to a four-piece metal sheet assembly;
Figure 12 is a cross-sectional elevational view of a sandwich structure formed from a four-piece metal sheet aasembly; and Figure 13 is a fragmentary perspective view of the sandwich structure shown in Figure 12.
While the invention will be described in connection with the preferred procedures, it will be understood that it is not intended to limit the inventionto those procedures. On the contrary, it is intended to cover all alternatives, modifications, and equlvalents that may be included within the ~pirit and scope of the lnvention as defined by the appended claims, ,,' , .~ '' ~ .
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~ ~OS56130 DETAILED DESCRIPTION OF THE INVENTION
In order for superplastic forming to be successful, it is necessary to use a material that is suitable. The extent to which the material selected will exhibit superplastic properties is predictable in general terms from a determination of the strain rate sensitivity and a ~lesign determination of the permissible variation in wall thickness. Strain rate sensitivity can be defined as m where m equals ~ and cr is stress in pounds per square inch and ~ is strain rate in reciprocal minutes. Strain ~ate sensitivity may be determined by a simple and now well recognized torsion test described in the article, "Detenmination of Strain Hardening Characteristics by Torsion Testing," by D. S. Fields, Jr., and W. A. Backofen, published in the Proceedingsof the A.S.T.M., 195~, Volume 57, pages 1259-1272. A strain rate sensitivity of about 0.5 or greater can be expected to produce satisfactory results. The larger the value (to a maximum oi one) the greater the superplastic properties.
! 15 Maximum strain ra~e sensitivlty in metals is 8een to occur, if at all, as metals are deformed near the phase transformation temperature. Accordingly, the temperature immediately below the phase transiormation temperature can be expected to produce the greatest strain rate sensitivity. For titanium alloys, the temperature range in which superplasticity can be observed is about 1450 F. to about 1850F. depending on the specific alloy used.
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Other variables have been found to effect strain rate sensitivity and therefore should be considered in selectin~ a suitable metal material. t ~ Decreasing grain size results in correspondingly higher values for strain rate - sensitivity. Additionally strain rate and material texture effect the strain rate sensitivity. It has been found that for titanium the m value reaches a - peak at an intermediate value of strain rate (approximately 10 ~ in./in./sec.).
For maximum stable deformation, superpIastic forming should be done at or near this strain rate. Too great a variance ~rom the optimum strain rate may result ~;; in loss of superplastic properties.
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Diffusion bonding,where separate elements form a single unitary mass therefrom, may be practiced in a wide variety of metals and alloys.
However, the quality of the bond and the parameters employed will necessarily vary for each particular choice of workpiece material. Among the metals or alloys which may be joined by solid state diffusion bonding are aluminum, strainless steel,titanium, nickel, tantalum, molybdenum, zirconium, columbium, and beryllium.
The present invention is particularly directed to the reactive métals whose surfaces would be contaminated at the elevated temperatures required for superplastic forming and diffusion boncling. Titanium and its alloys are examples of such metals which have also been found to be particularlywell suited ~or a process of the present invention in that these alloys exhibit very high superplastic properties in a temperature range suitable for diffusion bonding, i.e., 1450F~ to about 1850F. depending on the speciELc alloy used.
Turning Eirst to Figure 1, there is ~hown an exploded view of a three-piece metal sheet assembly to be formed into a sandwich structure according to the present invention. The assembly is made up of metal blanks 10, 12, and 14, all preferably in the form of sheets having upper and lower opposed principal surfaces 15 and 16, 17 and 18, and l9 and 20, respectively (see also Figure 4). The number of sheets used will vary depending on load conditions : and design requirements. However, a minimum of two sheets must be utilized and normally no more than four sheets would be used. The metal sheets must have the ability to be ~oined by such methods as brazing, welding, or diffusion bonding. Depending on the number of sheets to be expanded, at least one of the sheets must exhibit superplastic properti~s. Any metal that exhibits i. suitable superplastic properties within a workable temperature range can be used for such sheet, but the present invention is particularly concerned with metals that exhibit superplastic properties within the temperature range ,? required for diffusion bonding and that are subject to contamination at forming .~., .
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temperature, as titanium or an alloy thereof such as Ti-~1-4V. When using Ti-6Al-4V, the forming temperature is preferably approximately 1700 F.
Initial thickness of metal blanks 10, 12, and 14 are determined by the dimen-sions of tbe part to be formed.
In order to join only selected areas of the metal sheets, a preferred step is to apply a suitable stop-off material to those areas within the stack where no attachment or joining between the sheets is desired. Thus, areas 30, 32, and 34 are covered with a stop-off material to prevent bonding in those areas. ~ther areas on surfaces lS~ 18, and 20 could also be so covered for prevention of joining. Alternatlvely, the metal sheet st~ucture could be spot welded or brazed at those areas where ~oining is desired.
Additionally, as hereinafter explained, the metal sheçt structure or stack 40 could be diffusion bonded at selected area~ by ~elective application of pressure.
lS Figure 2 illustrates a preEerr~d forming apparatus generally indicated at 42 for carrying out the invention, Upper ~ooling frame 44 has preferably integral side walls 45 in the form of a ring which can be of any desired shape. Lower tooling frame 46 whic~ preferably has the same outer area dimensions as upper frame 42 can bç flat and act as a base as illustrated for supporting the stack of metal blanks 40. For purposes of the clalms, both upper tooling frame 44 and lower tooling fra~e 46 are to be con~idered shaping members as both combine to form the desired shaped structure. The inner surface of upper tooling frame 4~ defines an inner chamber 48 and a female die surface. One or more male die members (not shown) can be provided in chamber 48 to vary the shape of the part to be formed. The stack of metal blanks 40, which is supported on lower tooling ~ frame 46, covers chamber 48. The metal blanks of the stack must all be c of a material suitable for joining such as by welding, brazing, or diffusion bonding. At least one of the outer metal blanks, and most likely the inner blanks, must have an effective strain rate sensitivity for exhibiting superplastic properties at a desired forming temperature and preferably ; within a temperature range required for diffusion bonding of the stack.
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This is shown in Figure 3 by the expanded stack 40 where both sheets 12 and 14 have been superplastically expanded, while sheet 10 of the formed stack has been substantially unchanged. Initial thicknesses of the sheets of stack 40 are determined by the dimensions of the parts to be formed.
The joining method to be used, namely welding, brazing, or diffusion bonding, depends on the material selected for the metal blanks, the tempera~ure required for superplastic forming, and the desired strength. ~owever, especially for titanium, diffusion bonding is preferred as this results in the strongest joining and the bonding temperature is generally suitable -for superplastic forming.
As previously mentioned, stop-off can be used at areas 30, 32, and 34 to prevent bonding at those areas. The particular stop-off selected must prevent bonding and be compatible with the metal or metals of ~he stack (nonreactive with the stack metals and minimal diffusion into the stack ;; lS metals). For titanium metal blanks, suitable stop-off materials are graphite, boron nitride, and yttria. Typically, when using yttria stop-off, the , stop-off pattern on the blanks is sprayed with a solution of yttria and a binder thereEor, The binder holds the yttria in position during bonding and eventually vaporizes below forming temperature.
i' 20 Joining the stack 40 at selected locations, when by braæing orspot welding is normally accomplished outside of the forming apparatus 42 ~ before the stack is placed therein. When diffusion bonding, the unjoined .~ stack 40 is preferably bonded after placement in the ~orming apparatus 42, 1, !
thereby saving fabrication time and equipment costs (although the stack could be diffusion bonded as by press bonding or roll bonding before placing it in the forming apparatus 42). The weight of upper tooling frame 44 acts ; as a clamping means for the stack 40. A single continuous edge of the stack 40 ;~ i8 effectively constrained between the upper tooling frame 44 and the lower , tooling frame 46. This insures t4at those portions of the blanks of the stack ~, .
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` -- lqDSS65l~ , to be formed, will be stretched rather than drawn. Should i~ be desired9 additional tightening means such as bolts (not shown) can be employed to more effectively constrain the stack 40. Another aclditional tightening means that could be employed is a press tnot shown), preferably hydraulic, having platens 50. Forming apparatus 42 is positioned between platens 50 and compressed thereby assuring that stack 40 is effectively constrained and chamber 48 sealed from the air. This arrangement is particularly advantageous as the platens 50 can be made of ceram:ic material and resistance heated wires 52 can be pravided therein for heating stack 40 to the forming temperature. Other heating methods could be used with the forming apparatus 42 ordinarily surrounded by a heating means if the heatlng platens are not used.
, For contamination preve~tion and diffu~ion bonding of the stack 40 when un~oined within the Eorming Apparatus 42, an ~nvironmental con~rol ; 15 system i8 provided. The purpose of the system i8 to expose the stack 40 only to inert gas or vacuum while heating, forming, and bonding, and option-ally, to diffusion bond the stack by fluid pressure. The metal blanks of stack 40 will not react with inert ga3 due to the nature of inert gas, even at the elevated forming and bonding temperatures. In a high vacuum, there are substantially no elements for the stack 40 to react with. Thus, in this environment, contamination of the ~tack 40 will be prevented.
Line 52 i~ connected to a source of pressurized inert gas at one end (not shown) and to chamber 40 through orifice 54 in upper tooling frame 44. A valve 56 for governing the flow of inert gas throu~h line 52 into chamber 48 and a pressure gauge 58 to indicate pressure are provided.
The inert gas used i9 preferably argon in liquid form. ~ine 52 also functions as an outlet for inert gas in chamber 48 and could also be ~, . .: , . ,: : .
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connected to a source of vacuum, such as a suction pump (not shown) for creatingvacuum in chamber 48. When line 52 is used as an outlet, valve 56 governs flow of inert gas from chamber 48. An additional line 60 is optimally provided on the opposide side of tooling frame 44 and functions as an outlet for inert gas in chamber 48. Line 60 is connected to chamber 48 through orifice 62 in upper tooling frame 44. Line 60 has a valve 64 provided therein for regulation of inert gas flow from chamber 48. Line 60 can si~ply function as a vent or be connected to a source of vacuum, such as a suction pump (not shown).
As previously stated, the contamination prevention system can also function as a means for gas pressure diffusion bonding stack 40. Thus, when i~ stack 40 is placed in forming apparatus 42 ~s illustrated in Figure 2, the stack can be heated in an inert gas atmosphere to a suitable diffusion bonding temperature (approximately 1700F. when the metal blanks of s~ack 40 are of Ti-6~1-4V) by heat generated from heatin8 pl~tens 50, and then applying press~reto stack 40 by increasing the pressure in chamber 48 by adding additional pressuri7-ed inert gas through line 52 while maintaining line 60 closed by valve 64. In this manner, the untreated areas of stack 40 will be diffusion bonded by the application of such presæure, which is preferably approximately 500 psi for Ti-6Al-4V, for a suitable forming time, which depends on the thickness of stack 40 and may vary from 30 minutes to 12 hour~. The edges of the blanks of stack 40 may also be diffusion bonded iE desired by virtue of ~ealing pressure thereon in the form of the weight o upper tooling 44 ; and optionally pressure from a press and/or a clamping means. ~fter diffusion bonding qtack 40, excess inert gas would be removed from chamber 48 through lines 52 and 60 to allow for in~lation of stack 40.
For expansion of stack 40 to the configuration shown in Figure 3 expansion tubes 72 and 74 are provided, the details of which are best illustrated in Figures 1 and 4. Expansion tube 72 (and likewise expansion tube 74 located on the opposide side of stack 40) is positioned between metal blanks 10 and 14 and protrudes into a channel 75 defined by recesses 76 and 78 and that portion of surface 20 of metal blank 14 which overlies .. . .. , . ~ . . .
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recess 78. Recesses 77 and 79 are provided on the opposite sides of blanks 10 and 12 respectively to provide a channel for inflation tube 74. The positioning of expansion tube 72 in such a channel 75 prevents compression of tube 72 by the tooling frames 44 and 46. Also, by locating ~ube 72 so that it protrudes only partially into channel 75, inert gag will flow fairly evenly between the metal blanks of stack 40, in thil~ case on either side of t blank 12 as shown by arrows 80 and 82. As shown in Figure 2 expansion tubes 72 and 74 have valves 84 and 86 therein respectively for governing ; flow of inert gas therethrough, and pressure gauges 88 and 90 for indicating pressure.
Expansion tubes 72 and 74 can also serve to draw off vaporized ` binder. To this end, tube 72 could act as an inlet and tube 72 an outlet ,.- with inert gas flow being transmitted through stack 40 prior to expansion of stack 40 to draw off the vaporized binder.
A pair of lateral grooves 71 (not shown~ and 73 are preferably provided on opposite sides of lower tooling frame 4~ with groove 71 in alignment with recess 77 and groove 73 in alignment with recess 76. The -; :
.. grooves 71 and 73 are provided to insure that passage of inert gas from , inflation tubes 72 and 74 between the metal blanks of stack 40 is not ~ 20 prevented from reaching treated areas 30 and 34 by pinçhing of the stack ;~ due to the pressure exerted by upper and lower tooling frames 44 and 46.
The width of groo~es 71 and 73 are preerably the same as recesses 76 and 77, bu~ grooves 71 and 73 terminate further inward in stack 40 so that pinching does not occur before the inert gas flow reaches treated areas 30 and 34.
As shown in Figure 1 when treating as by stop-off selected areas : .
, of stack 40 to prevent diffusion bonding thereon, additional areas such : ~
as that shown at 92 and 94 should likewise be treated to prevent bonding :
thereon so that the gas from inflation tubes 72 and 74 will reach the selected treated areas for expansion of stack 40. Apertures 96 are provided in treated areas 3~, 32 and 34 for further transmitting the inert gas from inflation tubes 72 and 74 inside stack 40 to the other treated a:reas and to ,: ' , ' ' ' . ' ~L~5~6511D , ~ ~
insure equal pressure inside stack 40 (in this case on çither side of metal A~ blank 12). If pressure is unequal, the resulting core of the sandwich, metal blank 12 in the configuration illustrated in Figure 3, would be distorted with a consequent effect on load carrylng ability on the final sandwich structure.
In order to make the expanded metallic sandwich structure as shown ; in Figure 3 according to Applicants' inventive method, metal blank workpieces 10, 12 and 14 are provided. Both sheets 12 and 14 must be of a material having an effective strain rate sensitivity for superplastic formlng. Optimally one or more oi the blanks are treated at specified locations such as 30, 32, and 34 so that when the metal blanks are arranged in a stack ~0 and diffusion bonded, only selected areas of the stack will be joined thereby. Alternately, the stack 40 could be spot welded or brazed for selective joining. When joining by diffusion bonding, the stack 40 would optimally be placed in the forming apparatu~ ~2 before forming. The pres~ure in ~hamber 48 would be increased by flow of pressurized inert gas through line 5~ into chamber 48. Once ehamber 48 had an inert gas atmosphere, the stack 40 would be heated by resistance wires 52 in hea~ing platens 50 to a temperature which optimally would be sultable for both diffusion bonding and superplastic forming, although the temperature could later be raised or lowered if a different temperature is required for superplastic forming. The pressure in chamber 48 ; would be increased by additional pressurized inert gas through line 52 to a pressure suitable Eor diffusion bonding of ~tack 40. That pressure would be maintained for a time duration sufficient for diffusion bonding. ~len the : 25 metal blanks of stack 40 are of Ti-4V-6Al alloy, the temperature used would be approximately 1700F. and the pressure about 500 psi. These values can of course be varied during forming and bonding as long as they are maintained within a suitable range. The time duration will vary depending upon the alloys used, temperature, pressure, and thickne~s of stack 40. Duration may vary from 30 minutes to 15 houre, but three hours is a fairly representative expectation. As previously stated, bondlng tempera-ture may vary from 1450F to about 1850 F. Bonding .
~L~556~ ' t pressure may vary from about 100 psi to 2000 psi or more with the preferred i range being 150 psi to 600 psi.
Before expanding stack 40, the pressure in chamber 48 is reduced through lines 52 and 60, When stack 40 is joined prior to insertion in forming apparatus 42, the preceding diffusion bonding step in forming apparatus 42 would be omitted. At superplastic fo~ming temperature, which is approximately 1700 F for Ti-4V-6Al alloy ~generally 1650-1750 F), stack 40 is expanded by flowing pressurized insert gas through lines 72 and 74 while optimally a vacuum is applied to chamber 48 through lines 52 and 60. The pressurized inert gas, which protects the interior of stack 40 from contsm-ination at the elevated forming temperatures, flows from tubes 72 and 74 into channels 75, preferably on opposite sides of stack 40, whereupon the inert gas flows within stack 40. Such pressurized inert gas wLthin stack 40 Eorces the expansion of stack 40 due to the pressure diEferentLal between the interlor of stack 40 and chamber 48. The pre~s~re dl~ferential normally used Eor superplastic forming of ~i-6Al-4V is normally in a range of from 25 to 250 psi.
Metal blank 14 is initially lifted by the pressure differential and pulls with it at the selected joined areas metal blank 12. Such expansion allows the ~;
pressurized inert gas to flow through apertures 96 to provide an equal pressure within stack 40 so that the core (workpiece 12) is formed uniformly. The equal pressure also retains metal blank 10 of stack 40 ln its initial position, it being forced against the base or lower tooling frame 46.
i Figures 5 and 6 illustrate the use o$ a differently configured lower tooling frame 100 having preferably integral sidewalls 102, 104 which define a chamber 106. Tube lines 108 and 110 are provided in lower tooling frame 100 for creating an inert gas environment in chamber 106 and to act as vents or vacuum lines when superplasticall~ expanding stack 40. If stack 40 is diffusion bonded in forming apparatus 120, the pressure in both chambers 48 and 106 would have to be increased, preferably equally, so that a suitable pressure is applied to stack 40 for diffusion bonding. For superplastically expanding stack 40, the pressure wlthin stack 40 would be increclsed by allow-ing flow of inert pressurized gas into stack 40 through lines 72 and 74 so 05568al , that the pressure within stack 40 is greater than that in chambers 48 and 106. Additionally, the pressure in chambers 48 and 106 would have been reduced and optimally exposed to vacuum through lines lOô, 110, 52, and 60.
i/ As shown in Figure 6, since all three of the metal blanks of stack 40 would be superplastically expanded, each of the blanks must bç of a material with an effective strain rate sensitivity for superplastic forming. As illustrated, 'j metal blank 14 is forced upwards into chamber 48, metal blank 10 is forced ; downward into chamber 106, and metal blank 12, by virtue of being selectively , joined at specified lorations to both metal blank 10 and metal blank 14 is deformed in both directions and forms the rore of the sandwich structure as shown.
Figures 7 and 8 illustrate a modified forming apparatus 130 and the use of a different technique for selective ~oining. The u~e of a two sheet stack 132 with metal blankS134 and 136 i8 also illustrated. Stack 132 could be Joined as by difEusion bonding, brazing, or spot welding prior to insertion in forming apparatus 130. If diffusion bonded, the metal blanks 134 and 136 would first be selectively treated with a suitable stop-off so that only certain predetermined areas of the stack would be joined. Optimally, however, the stack 132 would be unjoined prior to insertion in the forming apparatus 130. When such is the case, stop-off need not be applied.
Forming apparatus 130 utilizes an upper tooling frame 140 having a lower arcuate surface defined by a plurality of protuberances 142 spaced from each othar by intermediate recesses or chamber~ 144. Lower tooling frame 150 has a complimentary upper arcuate surface 152 to that defined by protuberances 142.
Inflation tubes 160 and 162 are positioned between the two metal blanks 134 and 136. Similar to recesses 76 and 77 in metal blank 10 (Figure 1) blanks 134 and 136 are provided with aligned recesses tnot shown) which define a cylindrical chamber (not shown) in which tubes 160 and 162 ara loca~ed. Lines 164 and 166, like lines 52 and 60 of Figure 2, provide an inert gas environment in chambers 144 and act as vents or connection to sources of vacuum for drawing out the ,,~ . .... ;- - .
5568~ ~, inert gas from chambers 144 for superplastically expanding metal blank 134 within those chambers. Each of tubes 164 and 166 would be provided with a valve (not shown) and pressure gauge (not shown) to control addition and removal of inert gas in chambers 144. Tubes .
164 and 166 are connected to bores 170 and 172 respectively which provide access to chambers 144. . :
Depending on the thickness and desired curvature of stack :
132, the stack can be preformed to this shape prior to insertion in forming apparatus 130 by conventional sheet metal forming, as roll forming or superplastic forming, or subsequent to insertion in for~
ming apparatus 130 by pressure applied to stack 132 by the protuber- ~
: ances 142 of upper tooling frame 140 and surface 152 of lower tool- :-ing frame 150. Preforming in the forming apparatus 130 is prefer- .
able as the preforming and selective diffusion bonding are accom~
plished simultaneously when the stack is also unjoined prior to in- .
sertion in forming apparatus 130, thereby saving fabrication time and equipment costs.
Using this forming apparatus 130, the unjoined stack can be diffusion bonded by application of pressure from upper tooling frame 140 and lower tooling frame 150 at required temperature for a suitable time duration. By virtue of protuberances 142, the pres-sure is only applied to selected areas of stack 132 so that only .
those areas are diffusion bonded, thereby allowing for expansion ;
in the unbonded areas.
After diffusion bonding ~or insertion into forming appa-ratus 130 if the stack 132 has already been joined) and preforming, stack 132 is inflated by flow of inert gas through lines 160 and 162 so that the unjoined areas of metal blank 134 are expanded into chambers 144. Optimally a vacuum would be applied to chambers 144 through lines 164 and 166. As the only space provided for expan- .
sion is chambers 144, only metal blank 134 is expanded and conse- : .
quently only that blank must be of a material suitable fo:r super-plastic forming. It is seen from the above that diffusion bonding, pre-forming, and superplastic expansion can all be done in the same apparatus in one operation.
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5~i61510 It should be noted that the superplastic expansion could be done .
prior to diffusion bonding of stack 132 by sealing the surrounding area . around stack 132 without applying pressure to stack 132. Thus~ upper tooling - frame 140 could be applied to stack 132 contacting at its protuberances 142 ` 5 without sufficient pressure for diffusion bonding. Wlth this procedure, stack 132 would be expanded into chambers 144 by superplastic inflation with pro-, tuberances 142 preventing expansion at other areas without application of pressure by virtue of the position of tooling frame 140. After such expansion, . sufficient pressure would be applied by tooling frames 140 and 150 at areas corresponding to the lower surface of protuberances 142 to diffusion bond those corresponding areas of stack 132.
Figure 9 illustrates the forming of a variably shaped structure, here shown as a tapered sandwich structure with an attachment Joined thereto.
Applicant accomplishes tapering of the sandwich structure by guitably designing ; lS the corresponding shaping surface of the upper tooling frame. In Figure 9, upper tooling frame 170 has an upper shaping surface 172 which angles down-wardly from one side to the other (shown as left to right). Thus, when the upper metal blank 174 of stack 176 is superplastically expanded against surface 172, it is shaped into the taper of such surface. The core formed by blank member 178 of stack 176 is also tapered by virtue of its dependence , upon the movement of upper blank 174.
Attachment 180, shown in an arbitrary design, i8 joined to the stack 176 on the upper member 174 along bond line 182 during the superplastic expansion of stack 176 in the same forming apparatus, thereby lowering fabrication time, apparatus cost, and forming difficulty. As set out in our prior co-pending application, Serial No. 511,900, attachment 180 could be positioned within a suitably shaped groove, here shown at 182, where the attachment may or may not protrude from such groove, or be located in the forming chamber, without the use of a groove so that it forms either a ':
male or female shaping surface itself. For purposes of the claims, when a groove is used, it is considered part of the forming chamber, so that the ,~
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-- attachment is positioned within the chamber when in the groove. In the embodiment illustrated, when stack 176 is superplastically expanded, it contacts attachment 180 along bond line 182. By virtue of the superplastic ~ ;
forming temperature, which attachment 180 is also heated to, and the S pressure expanding stack 176 which eventually force3 upper member 174 to bear against surface 172 and attachment 182, attachment 182 is diffusion bonded to stack 176 along bond line 182 when the temperature and pressure ~.
- are maintained at a required diffusion bonding level for a suitable time duration. Optimally, the temperature and pressure for superplastic forming of members 174 and 178 would also be suitable for diffusion banding so ~hat the pressure or temperature would not have to be increa~ed or dçcreased after forming in order to diffusion bond. The material selected for attachment 182 should be one that is suitable for diffusion bonding to the material of member 174, preferably a like material. As the superplastic forming gas pre~sure typically used is 150 psi, a pressure considerably less than tho 2000 psi used normally in dlffusion bonding, the bond which result~ may not develop full parent metal strength, but would likely be analogous to a high quality braze joint. However, once the sandwich structure is fully expanded, as shown in Figure 9, the pressure can be increased within the expanded sandwich through i~flation tubes 190 and 192 to a level more suitable for complete diffusion bonding.
A close-out such as shown at 194 can also be formed to the expanded sandwich structure in the same operation by diffusion bonding the close out 194, which comprises an unexpanded end of stack 176, by heating stack 176 to the diffusion bonding temperature with application of pressure by upper and lower tooling frames 170 and 171 respectively. The expanded sandwich structure 200 of Figure 9 removed from the fonming apparatus is shown at Figure 10 with the side ends cut off.
Figure 11 illustrates the positioning of an inflation tube 10 relative to a four-piece metal sheet assembly or s~ack 212 in a forming apparatus having upper and lower chambers 214 and 216 resPectively.
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.~ ... : . ~ , Inflation tube 210 is positioned between the upper metal blank 217 and lower metal blank 218 with the lower metal blank 213 having a recess 220 at its periphery such as recess 76 shown in Figure 1. Inner metal blanks 221 and 222 of stack 212 have a recess such as that shown at 78 in Figure 1 which allows for positioning oE inflation tube 210 between members 217 and 218. Apertures 230, for transmitting inflating gas, and stop-off 232 at areas for which no bonding is desired, are also illustrated. Illustrative views of the final formed sandwich structure 240 of Figure 11 are shown at Figures 12 and 13.
Thus it is apparent that there has been provided, in accordance with the invention, a method for making metallic sandwich structures from a pluralityof workpieces that fully satisfies the objectives, aims, and advantages set forth above. While the invention has been described in conjunction with specific ~mbodiments thereof, it i9 evident that many alternatives, modifica-}5 tions, and variations, will be apparent to those skilled in the art in light of the foregoing descriptlon. Accordingly, it is intended to embrace all such alternatives, modifications, and variations which fall within the spirit and scope of the appended claims.
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is disclosed a method for superplastic forming of metals with concurrent diffusion bondingO The crux of that invention is :
the superplastic forming of a metal blank against a shaping member and another metal workpiece so that the metal blank is ~ :
formed and diffusion bonded to the other metal workpiece in one ,. : .
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"` 105~68~ , a hollow metal structure bonded at peripheral edges can be formed as disclosed in that application, the process is not designed ior the forming of sandwich structures. The forming of sandwich structures according to the present invention requires separate superplastic forming and joining stages and a technique for joining only selecti~e areas of the metal blanks employed.
The present invention obviates the prior art problems of forming sandwich structures. A sandwich structure normally comprises a core between face sheets. Previous to Applicants' invention, fabrication o~ sandwich structures typically took the approach of first rolling metal foil or ribbon, forming and joining the foil sheet into the desired cellular core, and then attaching the core to face sheets by brazing or spot welding. Problems with the prior art method include the cost of the core due to excess material usage and the great difficulty, excess time consumption, and cost of fabrication of the sandwich shape. Additionally, a separate operation is required to join a close out or attachment to the sandwich strllcture.
Fabricatlon of an unusual shape for the sandwich structure such as a taper, is nearly impossible.
~5568~D
SUMMARY OF THE INVENTION
, It is, therefore, an object of the present invention to combine the processes of metal joining and superplastic forming to form metal sandwich structures.
Is is another object of the present invention to form metal sandwich structures in one operation, thereby significantly lowering the cost, difficulty, and time involved.
It is yet another object of the present invention to form a sandwich structure and join an attachment or close-out in the same operation.
It is still another object of the present invention to heat, superplas- ` -tically form, and join the sandwich in the same apparatus, thereby saving fabrication time and equipment costs.
Briefly, in accordflnce with the invention, there is provided a method ; for making a metallic sandwich structure from a plurallty of metal blank work-pieces initially positioned in a stacked position. The blanks are joined at ; selectad areas. At least one of the blanks is superplastically formed against a shaping member to form the desired sandwich structure. The core configuration is determined by the location, size, and shape of the joined areas.
Other objects and advantages of the invention will become apparent ; 20 upon reading the following detalled description and upon reference to the drawings.
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BRIEF DESCRIPTION OF THE DRAWINGS
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Figure 1 is an exploded view of a three-piece metal sheet assembly treated for selective diffusion bonding prior to insertion in the forming .
apparatus;
Figure 2 is a cross-sectional elevational view of a preferred .~ ~;
embodiment of a forming apparatus used for fabrication of metal sandwich structures with the three piece metal sheet assembly of Figure 1 inserted :~ therein;
. Figure 3 illustrates the fully expanded three-piece metal sheet assembly within the forming apparatus of Figure 2 with broken lines added - to delineate the final position of the component metal sheets of the expanded joined assembly;
Figure 4 is a detail view of an inflation tube connection to the three-sheet assembly;
i 15 TFigures 5 and 6 are cross-sectional elevational views oE a modified forming apparatus with a three-piece metal sheet assembly inserted therein in its initial position in Figure 5 and in its final expanded position in Figure 6;
Figures 7 and 8 are cross-sectional elevational views of a modified forming apparatus with a two-piece metal sheet assembly inserted therein in '. its inltial position in Figure 7 and in its final expanded position in Figure 8;
. Figure 9 is a cross-sectional elevational view of a modified forming apparatus illustrating a tapered three-piece metal sheet assembly in final formed position with an attachment ~oined to the sandwich structure at the broken lines;
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1~)556~10 ,-Figure 10 is a perspective view with the ends cut off of the formed sandwich structure of Figure 9; ~ ```
. Figure 11 is a frag~entary cros~-sectional elevational view of a modified forming apparatus illustrating the positioning of an inflation tube relative to a four-piece metal sheet assembly;
Figure 12 is a cross-sectional elevational view of a sandwich structure formed from a four-piece metal sheet aasembly; and Figure 13 is a fragmentary perspective view of the sandwich structure shown in Figure 12.
While the invention will be described in connection with the preferred procedures, it will be understood that it is not intended to limit the inventionto those procedures. On the contrary, it is intended to cover all alternatives, modifications, and equlvalents that may be included within the ~pirit and scope of the lnvention as defined by the appended claims, ,,' , .~ '' ~ .
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~ ~OS56130 DETAILED DESCRIPTION OF THE INVENTION
In order for superplastic forming to be successful, it is necessary to use a material that is suitable. The extent to which the material selected will exhibit superplastic properties is predictable in general terms from a determination of the strain rate sensitivity and a ~lesign determination of the permissible variation in wall thickness. Strain rate sensitivity can be defined as m where m equals ~ and cr is stress in pounds per square inch and ~ is strain rate in reciprocal minutes. Strain ~ate sensitivity may be determined by a simple and now well recognized torsion test described in the article, "Detenmination of Strain Hardening Characteristics by Torsion Testing," by D. S. Fields, Jr., and W. A. Backofen, published in the Proceedingsof the A.S.T.M., 195~, Volume 57, pages 1259-1272. A strain rate sensitivity of about 0.5 or greater can be expected to produce satisfactory results. The larger the value (to a maximum oi one) the greater the superplastic properties.
! 15 Maximum strain ra~e sensitivlty in metals is 8een to occur, if at all, as metals are deformed near the phase transformation temperature. Accordingly, the temperature immediately below the phase transiormation temperature can be expected to produce the greatest strain rate sensitivity. For titanium alloys, the temperature range in which superplasticity can be observed is about 1450 F. to about 1850F. depending on the specific alloy used.
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Other variables have been found to effect strain rate sensitivity and therefore should be considered in selectin~ a suitable metal material. t ~ Decreasing grain size results in correspondingly higher values for strain rate - sensitivity. Additionally strain rate and material texture effect the strain rate sensitivity. It has been found that for titanium the m value reaches a - peak at an intermediate value of strain rate (approximately 10 ~ in./in./sec.).
For maximum stable deformation, superpIastic forming should be done at or near this strain rate. Too great a variance ~rom the optimum strain rate may result ~;; in loss of superplastic properties.
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Diffusion bonding,where separate elements form a single unitary mass therefrom, may be practiced in a wide variety of metals and alloys.
However, the quality of the bond and the parameters employed will necessarily vary for each particular choice of workpiece material. Among the metals or alloys which may be joined by solid state diffusion bonding are aluminum, strainless steel,titanium, nickel, tantalum, molybdenum, zirconium, columbium, and beryllium.
The present invention is particularly directed to the reactive métals whose surfaces would be contaminated at the elevated temperatures required for superplastic forming and diffusion boncling. Titanium and its alloys are examples of such metals which have also been found to be particularlywell suited ~or a process of the present invention in that these alloys exhibit very high superplastic properties in a temperature range suitable for diffusion bonding, i.e., 1450F~ to about 1850F. depending on the speciELc alloy used.
Turning Eirst to Figure 1, there is ~hown an exploded view of a three-piece metal sheet assembly to be formed into a sandwich structure according to the present invention. The assembly is made up of metal blanks 10, 12, and 14, all preferably in the form of sheets having upper and lower opposed principal surfaces 15 and 16, 17 and 18, and l9 and 20, respectively (see also Figure 4). The number of sheets used will vary depending on load conditions : and design requirements. However, a minimum of two sheets must be utilized and normally no more than four sheets would be used. The metal sheets must have the ability to be ~oined by such methods as brazing, welding, or diffusion bonding. Depending on the number of sheets to be expanded, at least one of the sheets must exhibit superplastic properti~s. Any metal that exhibits i. suitable superplastic properties within a workable temperature range can be used for such sheet, but the present invention is particularly concerned with metals that exhibit superplastic properties within the temperature range ,? required for diffusion bonding and that are subject to contamination at forming .~., .
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temperature, as titanium or an alloy thereof such as Ti-~1-4V. When using Ti-6Al-4V, the forming temperature is preferably approximately 1700 F.
Initial thickness of metal blanks 10, 12, and 14 are determined by the dimen-sions of tbe part to be formed.
In order to join only selected areas of the metal sheets, a preferred step is to apply a suitable stop-off material to those areas within the stack where no attachment or joining between the sheets is desired. Thus, areas 30, 32, and 34 are covered with a stop-off material to prevent bonding in those areas. ~ther areas on surfaces lS~ 18, and 20 could also be so covered for prevention of joining. Alternatlvely, the metal sheet st~ucture could be spot welded or brazed at those areas where ~oining is desired.
Additionally, as hereinafter explained, the metal sheçt structure or stack 40 could be diffusion bonded at selected area~ by ~elective application of pressure.
lS Figure 2 illustrates a preEerr~d forming apparatus generally indicated at 42 for carrying out the invention, Upper ~ooling frame 44 has preferably integral side walls 45 in the form of a ring which can be of any desired shape. Lower tooling frame 46 whic~ preferably has the same outer area dimensions as upper frame 42 can bç flat and act as a base as illustrated for supporting the stack of metal blanks 40. For purposes of the clalms, both upper tooling frame 44 and lower tooling fra~e 46 are to be con~idered shaping members as both combine to form the desired shaped structure. The inner surface of upper tooling frame 4~ defines an inner chamber 48 and a female die surface. One or more male die members (not shown) can be provided in chamber 48 to vary the shape of the part to be formed. The stack of metal blanks 40, which is supported on lower tooling ~ frame 46, covers chamber 48. The metal blanks of the stack must all be c of a material suitable for joining such as by welding, brazing, or diffusion bonding. At least one of the outer metal blanks, and most likely the inner blanks, must have an effective strain rate sensitivity for exhibiting superplastic properties at a desired forming temperature and preferably ; within a temperature range required for diffusion bonding of the stack.
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This is shown in Figure 3 by the expanded stack 40 where both sheets 12 and 14 have been superplastically expanded, while sheet 10 of the formed stack has been substantially unchanged. Initial thicknesses of the sheets of stack 40 are determined by the dimensions of the parts to be formed.
The joining method to be used, namely welding, brazing, or diffusion bonding, depends on the material selected for the metal blanks, the tempera~ure required for superplastic forming, and the desired strength. ~owever, especially for titanium, diffusion bonding is preferred as this results in the strongest joining and the bonding temperature is generally suitable -for superplastic forming.
As previously mentioned, stop-off can be used at areas 30, 32, and 34 to prevent bonding at those areas. The particular stop-off selected must prevent bonding and be compatible with the metal or metals of ~he stack (nonreactive with the stack metals and minimal diffusion into the stack ;; lS metals). For titanium metal blanks, suitable stop-off materials are graphite, boron nitride, and yttria. Typically, when using yttria stop-off, the , stop-off pattern on the blanks is sprayed with a solution of yttria and a binder thereEor, The binder holds the yttria in position during bonding and eventually vaporizes below forming temperature.
i' 20 Joining the stack 40 at selected locations, when by braæing orspot welding is normally accomplished outside of the forming apparatus 42 ~ before the stack is placed therein. When diffusion bonding, the unjoined .~ stack 40 is preferably bonded after placement in the ~orming apparatus 42, 1, !
thereby saving fabrication time and equipment costs (although the stack could be diffusion bonded as by press bonding or roll bonding before placing it in the forming apparatus 42). The weight of upper tooling frame 44 acts ; as a clamping means for the stack 40. A single continuous edge of the stack 40 ;~ i8 effectively constrained between the upper tooling frame 44 and the lower , tooling frame 46. This insures t4at those portions of the blanks of the stack ~, .
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` -- lqDSS65l~ , to be formed, will be stretched rather than drawn. Should i~ be desired9 additional tightening means such as bolts (not shown) can be employed to more effectively constrain the stack 40. Another aclditional tightening means that could be employed is a press tnot shown), preferably hydraulic, having platens 50. Forming apparatus 42 is positioned between platens 50 and compressed thereby assuring that stack 40 is effectively constrained and chamber 48 sealed from the air. This arrangement is particularly advantageous as the platens 50 can be made of ceram:ic material and resistance heated wires 52 can be pravided therein for heating stack 40 to the forming temperature. Other heating methods could be used with the forming apparatus 42 ordinarily surrounded by a heating means if the heatlng platens are not used.
, For contamination preve~tion and diffu~ion bonding of the stack 40 when un~oined within the Eorming Apparatus 42, an ~nvironmental con~rol ; 15 system i8 provided. The purpose of the system i8 to expose the stack 40 only to inert gas or vacuum while heating, forming, and bonding, and option-ally, to diffusion bond the stack by fluid pressure. The metal blanks of stack 40 will not react with inert ga3 due to the nature of inert gas, even at the elevated forming and bonding temperatures. In a high vacuum, there are substantially no elements for the stack 40 to react with. Thus, in this environment, contamination of the ~tack 40 will be prevented.
Line 52 i~ connected to a source of pressurized inert gas at one end (not shown) and to chamber 40 through orifice 54 in upper tooling frame 44. A valve 56 for governing the flow of inert gas throu~h line 52 into chamber 48 and a pressure gauge 58 to indicate pressure are provided.
The inert gas used i9 preferably argon in liquid form. ~ine 52 also functions as an outlet for inert gas in chamber 48 and could also be ~, . .: , . ,: : .
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connected to a source of vacuum, such as a suction pump (not shown) for creatingvacuum in chamber 48. When line 52 is used as an outlet, valve 56 governs flow of inert gas from chamber 48. An additional line 60 is optimally provided on the opposide side of tooling frame 44 and functions as an outlet for inert gas in chamber 48. Line 60 is connected to chamber 48 through orifice 62 in upper tooling frame 44. Line 60 has a valve 64 provided therein for regulation of inert gas flow from chamber 48. Line 60 can si~ply function as a vent or be connected to a source of vacuum, such as a suction pump (not shown).
As previously stated, the contamination prevention system can also function as a means for gas pressure diffusion bonding stack 40. Thus, when i~ stack 40 is placed in forming apparatus 42 ~s illustrated in Figure 2, the stack can be heated in an inert gas atmosphere to a suitable diffusion bonding temperature (approximately 1700F. when the metal blanks of s~ack 40 are of Ti-6~1-4V) by heat generated from heatin8 pl~tens 50, and then applying press~reto stack 40 by increasing the pressure in chamber 48 by adding additional pressuri7-ed inert gas through line 52 while maintaining line 60 closed by valve 64. In this manner, the untreated areas of stack 40 will be diffusion bonded by the application of such presæure, which is preferably approximately 500 psi for Ti-6Al-4V, for a suitable forming time, which depends on the thickness of stack 40 and may vary from 30 minutes to 12 hour~. The edges of the blanks of stack 40 may also be diffusion bonded iE desired by virtue of ~ealing pressure thereon in the form of the weight o upper tooling 44 ; and optionally pressure from a press and/or a clamping means. ~fter diffusion bonding qtack 40, excess inert gas would be removed from chamber 48 through lines 52 and 60 to allow for in~lation of stack 40.
For expansion of stack 40 to the configuration shown in Figure 3 expansion tubes 72 and 74 are provided, the details of which are best illustrated in Figures 1 and 4. Expansion tube 72 (and likewise expansion tube 74 located on the opposide side of stack 40) is positioned between metal blanks 10 and 14 and protrudes into a channel 75 defined by recesses 76 and 78 and that portion of surface 20 of metal blank 14 which overlies .. . .. , . ~ . . .
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recess 78. Recesses 77 and 79 are provided on the opposite sides of blanks 10 and 12 respectively to provide a channel for inflation tube 74. The positioning of expansion tube 72 in such a channel 75 prevents compression of tube 72 by the tooling frames 44 and 46. Also, by locating ~ube 72 so that it protrudes only partially into channel 75, inert gag will flow fairly evenly between the metal blanks of stack 40, in thil~ case on either side of t blank 12 as shown by arrows 80 and 82. As shown in Figure 2 expansion tubes 72 and 74 have valves 84 and 86 therein respectively for governing ; flow of inert gas therethrough, and pressure gauges 88 and 90 for indicating pressure.
Expansion tubes 72 and 74 can also serve to draw off vaporized ` binder. To this end, tube 72 could act as an inlet and tube 72 an outlet ,.- with inert gas flow being transmitted through stack 40 prior to expansion of stack 40 to draw off the vaporized binder.
A pair of lateral grooves 71 (not shown~ and 73 are preferably provided on opposite sides of lower tooling frame 4~ with groove 71 in alignment with recess 77 and groove 73 in alignment with recess 76. The -; :
.. grooves 71 and 73 are provided to insure that passage of inert gas from , inflation tubes 72 and 74 between the metal blanks of stack 40 is not ~ 20 prevented from reaching treated areas 30 and 34 by pinçhing of the stack ;~ due to the pressure exerted by upper and lower tooling frames 44 and 46.
The width of groo~es 71 and 73 are preerably the same as recesses 76 and 77, bu~ grooves 71 and 73 terminate further inward in stack 40 so that pinching does not occur before the inert gas flow reaches treated areas 30 and 34.
As shown in Figure 1 when treating as by stop-off selected areas : .
, of stack 40 to prevent diffusion bonding thereon, additional areas such : ~
as that shown at 92 and 94 should likewise be treated to prevent bonding :
thereon so that the gas from inflation tubes 72 and 74 will reach the selected treated areas for expansion of stack 40. Apertures 96 are provided in treated areas 3~, 32 and 34 for further transmitting the inert gas from inflation tubes 72 and 74 inside stack 40 to the other treated a:reas and to ,: ' , ' ' ' . ' ~L~5~6511D , ~ ~
insure equal pressure inside stack 40 (in this case on çither side of metal A~ blank 12). If pressure is unequal, the resulting core of the sandwich, metal blank 12 in the configuration illustrated in Figure 3, would be distorted with a consequent effect on load carrylng ability on the final sandwich structure.
In order to make the expanded metallic sandwich structure as shown ; in Figure 3 according to Applicants' inventive method, metal blank workpieces 10, 12 and 14 are provided. Both sheets 12 and 14 must be of a material having an effective strain rate sensitivity for superplastic formlng. Optimally one or more oi the blanks are treated at specified locations such as 30, 32, and 34 so that when the metal blanks are arranged in a stack ~0 and diffusion bonded, only selected areas of the stack will be joined thereby. Alternately, the stack 40 could be spot welded or brazed for selective joining. When joining by diffusion bonding, the stack 40 would optimally be placed in the forming apparatu~ ~2 before forming. The pres~ure in ~hamber 48 would be increased by flow of pressurized inert gas through line 5~ into chamber 48. Once ehamber 48 had an inert gas atmosphere, the stack 40 would be heated by resistance wires 52 in hea~ing platens 50 to a temperature which optimally would be sultable for both diffusion bonding and superplastic forming, although the temperature could later be raised or lowered if a different temperature is required for superplastic forming. The pressure in chamber 48 ; would be increased by additional pressurized inert gas through line 52 to a pressure suitable Eor diffusion bonding of ~tack 40. That pressure would be maintained for a time duration sufficient for diffusion bonding. ~len the : 25 metal blanks of stack 40 are of Ti-4V-6Al alloy, the temperature used would be approximately 1700F. and the pressure about 500 psi. These values can of course be varied during forming and bonding as long as they are maintained within a suitable range. The time duration will vary depending upon the alloys used, temperature, pressure, and thickne~s of stack 40. Duration may vary from 30 minutes to 15 houre, but three hours is a fairly representative expectation. As previously stated, bondlng tempera-ture may vary from 1450F to about 1850 F. Bonding .
~L~556~ ' t pressure may vary from about 100 psi to 2000 psi or more with the preferred i range being 150 psi to 600 psi.
Before expanding stack 40, the pressure in chamber 48 is reduced through lines 52 and 60, When stack 40 is joined prior to insertion in forming apparatus 42, the preceding diffusion bonding step in forming apparatus 42 would be omitted. At superplastic fo~ming temperature, which is approximately 1700 F for Ti-4V-6Al alloy ~generally 1650-1750 F), stack 40 is expanded by flowing pressurized insert gas through lines 72 and 74 while optimally a vacuum is applied to chamber 48 through lines 52 and 60. The pressurized inert gas, which protects the interior of stack 40 from contsm-ination at the elevated forming temperatures, flows from tubes 72 and 74 into channels 75, preferably on opposite sides of stack 40, whereupon the inert gas flows within stack 40. Such pressurized inert gas wLthin stack 40 Eorces the expansion of stack 40 due to the pressure diEferentLal between the interlor of stack 40 and chamber 48. The pre~s~re dl~ferential normally used Eor superplastic forming of ~i-6Al-4V is normally in a range of from 25 to 250 psi.
Metal blank 14 is initially lifted by the pressure differential and pulls with it at the selected joined areas metal blank 12. Such expansion allows the ~;
pressurized inert gas to flow through apertures 96 to provide an equal pressure within stack 40 so that the core (workpiece 12) is formed uniformly. The equal pressure also retains metal blank 10 of stack 40 ln its initial position, it being forced against the base or lower tooling frame 46.
i Figures 5 and 6 illustrate the use o$ a differently configured lower tooling frame 100 having preferably integral sidewalls 102, 104 which define a chamber 106. Tube lines 108 and 110 are provided in lower tooling frame 100 for creating an inert gas environment in chamber 106 and to act as vents or vacuum lines when superplasticall~ expanding stack 40. If stack 40 is diffusion bonded in forming apparatus 120, the pressure in both chambers 48 and 106 would have to be increased, preferably equally, so that a suitable pressure is applied to stack 40 for diffusion bonding. For superplastically expanding stack 40, the pressure wlthin stack 40 would be increclsed by allow-ing flow of inert pressurized gas into stack 40 through lines 72 and 74 so 05568al , that the pressure within stack 40 is greater than that in chambers 48 and 106. Additionally, the pressure in chambers 48 and 106 would have been reduced and optimally exposed to vacuum through lines lOô, 110, 52, and 60.
i/ As shown in Figure 6, since all three of the metal blanks of stack 40 would be superplastically expanded, each of the blanks must bç of a material with an effective strain rate sensitivity for superplastic forming. As illustrated, 'j metal blank 14 is forced upwards into chamber 48, metal blank 10 is forced ; downward into chamber 106, and metal blank 12, by virtue of being selectively , joined at specified lorations to both metal blank 10 and metal blank 14 is deformed in both directions and forms the rore of the sandwich structure as shown.
Figures 7 and 8 illustrate a modified forming apparatus 130 and the use of a different technique for selective ~oining. The u~e of a two sheet stack 132 with metal blankS134 and 136 i8 also illustrated. Stack 132 could be Joined as by difEusion bonding, brazing, or spot welding prior to insertion in forming apparatus 130. If diffusion bonded, the metal blanks 134 and 136 would first be selectively treated with a suitable stop-off so that only certain predetermined areas of the stack would be joined. Optimally, however, the stack 132 would be unjoined prior to insertion in the forming apparatus 130. When such is the case, stop-off need not be applied.
Forming apparatus 130 utilizes an upper tooling frame 140 having a lower arcuate surface defined by a plurality of protuberances 142 spaced from each othar by intermediate recesses or chamber~ 144. Lower tooling frame 150 has a complimentary upper arcuate surface 152 to that defined by protuberances 142.
Inflation tubes 160 and 162 are positioned between the two metal blanks 134 and 136. Similar to recesses 76 and 77 in metal blank 10 (Figure 1) blanks 134 and 136 are provided with aligned recesses tnot shown) which define a cylindrical chamber (not shown) in which tubes 160 and 162 ara loca~ed. Lines 164 and 166, like lines 52 and 60 of Figure 2, provide an inert gas environment in chambers 144 and act as vents or connection to sources of vacuum for drawing out the ,,~ . .... ;- - .
5568~ ~, inert gas from chambers 144 for superplastically expanding metal blank 134 within those chambers. Each of tubes 164 and 166 would be provided with a valve (not shown) and pressure gauge (not shown) to control addition and removal of inert gas in chambers 144. Tubes .
164 and 166 are connected to bores 170 and 172 respectively which provide access to chambers 144. . :
Depending on the thickness and desired curvature of stack :
132, the stack can be preformed to this shape prior to insertion in forming apparatus 130 by conventional sheet metal forming, as roll forming or superplastic forming, or subsequent to insertion in for~
ming apparatus 130 by pressure applied to stack 132 by the protuber- ~
: ances 142 of upper tooling frame 140 and surface 152 of lower tool- :-ing frame 150. Preforming in the forming apparatus 130 is prefer- .
able as the preforming and selective diffusion bonding are accom~
plished simultaneously when the stack is also unjoined prior to in- .
sertion in forming apparatus 130, thereby saving fabrication time and equipment costs.
Using this forming apparatus 130, the unjoined stack can be diffusion bonded by application of pressure from upper tooling frame 140 and lower tooling frame 150 at required temperature for a suitable time duration. By virtue of protuberances 142, the pres-sure is only applied to selected areas of stack 132 so that only .
those areas are diffusion bonded, thereby allowing for expansion ;
in the unbonded areas.
After diffusion bonding ~or insertion into forming appa-ratus 130 if the stack 132 has already been joined) and preforming, stack 132 is inflated by flow of inert gas through lines 160 and 162 so that the unjoined areas of metal blank 134 are expanded into chambers 144. Optimally a vacuum would be applied to chambers 144 through lines 164 and 166. As the only space provided for expan- .
sion is chambers 144, only metal blank 134 is expanded and conse- : .
quently only that blank must be of a material suitable fo:r super-plastic forming. It is seen from the above that diffusion bonding, pre-forming, and superplastic expansion can all be done in the same apparatus in one operation.
~, .. . . . . . . .
5~i61510 It should be noted that the superplastic expansion could be done .
prior to diffusion bonding of stack 132 by sealing the surrounding area . around stack 132 without applying pressure to stack 132. Thus~ upper tooling - frame 140 could be applied to stack 132 contacting at its protuberances 142 ` 5 without sufficient pressure for diffusion bonding. Wlth this procedure, stack 132 would be expanded into chambers 144 by superplastic inflation with pro-, tuberances 142 preventing expansion at other areas without application of pressure by virtue of the position of tooling frame 140. After such expansion, . sufficient pressure would be applied by tooling frames 140 and 150 at areas corresponding to the lower surface of protuberances 142 to diffusion bond those corresponding areas of stack 132.
Figure 9 illustrates the forming of a variably shaped structure, here shown as a tapered sandwich structure with an attachment Joined thereto.
Applicant accomplishes tapering of the sandwich structure by guitably designing ; lS the corresponding shaping surface of the upper tooling frame. In Figure 9, upper tooling frame 170 has an upper shaping surface 172 which angles down-wardly from one side to the other (shown as left to right). Thus, when the upper metal blank 174 of stack 176 is superplastically expanded against surface 172, it is shaped into the taper of such surface. The core formed by blank member 178 of stack 176 is also tapered by virtue of its dependence , upon the movement of upper blank 174.
Attachment 180, shown in an arbitrary design, i8 joined to the stack 176 on the upper member 174 along bond line 182 during the superplastic expansion of stack 176 in the same forming apparatus, thereby lowering fabrication time, apparatus cost, and forming difficulty. As set out in our prior co-pending application, Serial No. 511,900, attachment 180 could be positioned within a suitably shaped groove, here shown at 182, where the attachment may or may not protrude from such groove, or be located in the forming chamber, without the use of a groove so that it forms either a ':
male or female shaping surface itself. For purposes of the claims, when a groove is used, it is considered part of the forming chamber, so that the ,~
.
~s~
-- attachment is positioned within the chamber when in the groove. In the embodiment illustrated, when stack 176 is superplastically expanded, it contacts attachment 180 along bond line 182. By virtue of the superplastic ~ ;
forming temperature, which attachment 180 is also heated to, and the S pressure expanding stack 176 which eventually force3 upper member 174 to bear against surface 172 and attachment 182, attachment 182 is diffusion bonded to stack 176 along bond line 182 when the temperature and pressure ~.
- are maintained at a required diffusion bonding level for a suitable time duration. Optimally, the temperature and pressure for superplastic forming of members 174 and 178 would also be suitable for diffusion banding so ~hat the pressure or temperature would not have to be increa~ed or dçcreased after forming in order to diffusion bond. The material selected for attachment 182 should be one that is suitable for diffusion bonding to the material of member 174, preferably a like material. As the superplastic forming gas pre~sure typically used is 150 psi, a pressure considerably less than tho 2000 psi used normally in dlffusion bonding, the bond which result~ may not develop full parent metal strength, but would likely be analogous to a high quality braze joint. However, once the sandwich structure is fully expanded, as shown in Figure 9, the pressure can be increased within the expanded sandwich through i~flation tubes 190 and 192 to a level more suitable for complete diffusion bonding.
A close-out such as shown at 194 can also be formed to the expanded sandwich structure in the same operation by diffusion bonding the close out 194, which comprises an unexpanded end of stack 176, by heating stack 176 to the diffusion bonding temperature with application of pressure by upper and lower tooling frames 170 and 171 respectively. The expanded sandwich structure 200 of Figure 9 removed from the fonming apparatus is shown at Figure 10 with the side ends cut off.
Figure 11 illustrates the positioning of an inflation tube 10 relative to a four-piece metal sheet assembly or s~ack 212 in a forming apparatus having upper and lower chambers 214 and 216 resPectively.
.
: .
.
1~)5568~
.~ ... : . ~ , Inflation tube 210 is positioned between the upper metal blank 217 and lower metal blank 218 with the lower metal blank 213 having a recess 220 at its periphery such as recess 76 shown in Figure 1. Inner metal blanks 221 and 222 of stack 212 have a recess such as that shown at 78 in Figure 1 which allows for positioning oE inflation tube 210 between members 217 and 218. Apertures 230, for transmitting inflating gas, and stop-off 232 at areas for which no bonding is desired, are also illustrated. Illustrative views of the final formed sandwich structure 240 of Figure 11 are shown at Figures 12 and 13.
Thus it is apparent that there has been provided, in accordance with the invention, a method for making metallic sandwich structures from a pluralityof workpieces that fully satisfies the objectives, aims, and advantages set forth above. While the invention has been described in conjunction with specific ~mbodiments thereof, it i9 evident that many alternatives, modifica-}5 tions, and variations, will be apparent to those skilled in the art in light of the foregoing descriptlon. Accordingly, it is intended to embrace all such alternatives, modifications, and variations which fall within the spirit and scope of the appended claims.
. .
Claims (13)
PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of making a metallic sandwich structure from a plurality of workpieces comprising:
providing a plurality of metal blank workpieces, each of said workpieces having two opposed principal surfaces, at least one of said workpieces having superplastic characteristics;
positioning said workpieces in a stack contacting at their principal surfaces, at least one of the outer workpieces of said stack having superplastic characteristics;
joining preselected areas of said stack of workpieces;
providing at least two shaping members;
enclosing at least one chamber by positioning said stack of workpieces relative to said shaping members;
heating said at least one outer workpiece to within a temperature range suitable for superplastic forming, and inducing tensile stress in said at least one outer work-piece causing at least a portion of said at least one outer workpiece to expand superplastically into said at least one chamber and to form against, and into intimate contact with, at least one of said shaping members.
providing a plurality of metal blank workpieces, each of said workpieces having two opposed principal surfaces, at least one of said workpieces having superplastic characteristics;
positioning said workpieces in a stack contacting at their principal surfaces, at least one of the outer workpieces of said stack having superplastic characteristics;
joining preselected areas of said stack of workpieces;
providing at least two shaping members;
enclosing at least one chamber by positioning said stack of workpieces relative to said shaping members;
heating said at least one outer workpiece to within a temperature range suitable for superplastic forming, and inducing tensile stress in said at least one outer work-piece causing at least a portion of said at least one outer workpiece to expand superplastically into said at least one chamber and to form against, and into intimate contact with, at least one of said shaping members.
2. The method as set out in claim 1 also including after the step of providing a plurality of metal workpieces, the step of treating said workpieces at selected areas to prevent bonding at those areas,
3. The method as set out in claim 2 also including after the step of enclosing at least one chamber, the step of providing an inert gas environment in said chamber.
4. The method as set out in claim 3 wherein said tensile stress is induced by applying an inert gas pressure loading across the principal surfaces of said at least one outer workpiece for a substantial period of time inversely related to the induced tensile stress, and said at least one outer workpiece is stretched substan-tially in excess of its original surface area.
5. The method as set out in claim 4 wherein said treating is accomplished by the application of a suitable stop-off material.
6. The method as set out in claim 4 wherein said pressure loading is applied by establishing a higher inert gas pressure in the intersticies between unjoined areas of said workpieces of said stack than in said chamber.
7. The method as set out in claim 3 also including the step of preforming said stack of workpieces.
8. The method as set out in claim 1 wherein said joining is accomplished by diffusion bonding.
9. The method as defined in claim 6 wherein said at least one chamber is vented to allow for efflux of inert gas as said at least one outer workpiece expands and thereby reduces the size of said at least one chamber.
10. The method as defined in claim 4 wherein said pressure loading comprises application of vacuum to said at least one chamber while maintaining a positive pressure of inert gas in the inter-sticies between unjoined areas of said workpieces of said stack.
11. The method as defined in claim 4 wherein said inert gas is argon, said metal workpieces are titanium alloy sheet, and said temperature range is about 1650-1750°F.
12. The method as defined in claim 4 also including the step of providing at least one metal attachment to be diffusion bonded to said at least one outer workpiece, and wherein said at least one attachment is located within said at least one chamber, and said at least one outer workpiece also deforms against and diffusion bonds to said at least one attachment.
13. The method as set out in claim 3 wherein first and second chambers are enclosed by positioning said stack of workpieces and wherein tensile stress is induced in both outer workpieces of said stack causing at least a portion of one outer workpiece to expand superplastically into said first chamber and at least a portion of the other outer workpiece to expand superplastically into said second chamber.
Priority Applications (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA305,514A CA1052081A (en) | 1975-03-20 | 1978-06-15 | Method for making metallic sandwich structures |
| CA305,515A CA1050250A (en) | 1975-03-20 | 1978-06-15 | Method for making metallic sandwich structures |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US560437A US3927817A (en) | 1974-10-03 | 1975-03-20 | Method for making metallic sandwich structures |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1055680A true CA1055680A (en) | 1979-06-05 |
Family
ID=24237828
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA238,141A Expired CA1055680A (en) | 1975-03-20 | 1975-10-20 | Method for making metallic sandwich structures |
Country Status (7)
| Country | Link |
|---|---|
| JP (1) | JPS5924893B2 (en) |
| CA (1) | CA1055680A (en) |
| CH (1) | CH622191A5 (en) |
| DE (1) | DE2611859A1 (en) |
| FR (1) | FR2304438A2 (en) |
| GB (1) | GB1495655A (en) |
| SE (1) | SE414591B (en) |
Families Citing this family (34)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5656739A (en) * | 1979-10-16 | 1981-05-18 | Yasuo Ikeda | Production of hollow lightweight metal plate |
| JPS5666337A (en) * | 1979-11-01 | 1981-06-04 | Yasuo Ikeda | Manufacture of lightweight metallic sheet |
| DE3104919A1 (en) * | 1980-02-15 | 1981-12-17 | British Aerospace Public Ltd. Co., London | METHOD FOR PRODUCING METAL ITEMS |
| DE3121126C1 (en) * | 1981-05-27 | 1983-01-27 | Messerschmitt-Bölkow-Blohm GmbH, 8000 München | Device for superplastic deformation |
| GB2109711B (en) * | 1981-11-24 | 1985-07-31 | Grumman Aerospace Corp | Method for superplastic forming and diffusion bonding complex continuous structures |
| US4588651A (en) * | 1983-02-16 | 1986-05-13 | Rockwell International Corporation | Accordion expansion process |
| GB8411611D0 (en) * | 1984-05-05 | 1984-06-13 | British Aerospace | Superplastic forming of panels |
| GB8802738D0 (en) * | 1988-02-06 | 1988-03-09 | British Aerospace | Apparatus & method for fabricating superplastically formed structures |
| GB8821222D0 (en) * | 1988-09-09 | 1988-12-14 | British Aerospace | Double curvature structures by superplastic forming & diffusion bonding |
| US4934580A (en) * | 1988-12-27 | 1990-06-19 | Barnes Group, Inc. | Method of making superplastically formed and diffusion bonded articles and the articles so made |
| US5139887A (en) * | 1988-12-27 | 1992-08-18 | Barnes Group, Inc. | Superplastically formed cellular article |
| GB8912025D0 (en) * | 1989-05-25 | 1989-07-12 | British Aerospace | Diffusion bonding |
| US5385204A (en) * | 1989-08-25 | 1995-01-31 | Rolls-Royce Plc | Heat exchanger and methods of manufacture thereof |
| JP2738971B2 (en) * | 1990-04-10 | 1998-04-08 | 三菱重工業株式会社 | How to make a metal sandwich panel |
| US5287918A (en) * | 1990-06-06 | 1994-02-22 | Rolls-Royce Plc | Heat exchangers |
| US5505256A (en) * | 1991-02-19 | 1996-04-09 | Rolls-Royce Plc | Heat exchangers and methods of manufacture thereof |
| US5253419A (en) * | 1991-02-20 | 1993-10-19 | Societe Nationale D'etude Et De Construction De Moteurs D'aviation "S.N.E.C.M.A." | Method of manufacturing a hollow blade for a turboshaft engine |
| GB9104156D0 (en) * | 1991-02-27 | 1991-04-17 | Rolls Royce & Ass | Heat exchanger |
| GB9104155D0 (en) * | 1991-02-27 | 1991-04-17 | Rolls Royce Plc | Heat exchanger |
| FR2694900B1 (en) * | 1992-08-19 | 1994-10-21 | Hispano Suiza Sa | Method of manufacturing assemblies composed of two glued parts and comprising a forming step. |
| DE19714989A1 (en) * | 1997-04-10 | 1998-10-15 | Matthias Prof Dr Ing Kleiner | Biaxial multi=layer component manufacture, especially in metal sheet |
| DE19714888A1 (en) * | 1997-04-10 | 1998-10-15 | Kleiner Matthias Prof Dr Ing | Production of three=dimensional object in sheet, e.g. deep-drawn, closed vessels |
| GB0006734D0 (en) | 2000-03-20 | 2000-05-10 | British Aerospace | Superplastic forming method |
| FR2817954B1 (en) * | 2000-12-11 | 2003-01-10 | Pechiney Rhenalu | METHOD FOR MANUFACTURING ALUMINUM PANELS WITH INTEGRATED CIRCUIT |
| DE10103131C2 (en) * | 2001-01-24 | 2002-11-21 | Daimler Chrysler Ag | Process for producing hollow bodies from at least two superimposed boards |
| ES2267368B1 (en) * | 2004-12-30 | 2008-06-01 | Airbus España S.L. | COMPOSITE MONOLITICAL PANEL WITH MULTICELLULAR DRAWER SHAPE. |
| RU2291019C2 (en) * | 2005-03-23 | 2007-01-10 | Институт проблем сверхпластичности металлов РАН | Method of manufacture of article by superplastic moulding and diffusion welding |
| DE102007045739B4 (en) * | 2007-09-25 | 2012-10-25 | Technische Universität Chemnitz | Three-dimensionally formable sandwich core for hollow body sandwich components |
| CN102990300B (en) * | 2012-11-21 | 2015-04-29 | 中国航空工业集团公司北京航空制造工程研究所 | Preparation method of titanium alloy three-dimensional lattice sandwich structure |
| CN102990299B (en) * | 2012-11-21 | 2015-04-29 | 中国航空工业集团公司北京航空制造工程研究所 | Preparation method for X-type titanium alloy three-dimensional lattice sandwich structure |
| GB2531518A (en) * | 2014-10-20 | 2016-04-27 | Rolls-Royce Power Eng Plc | Heat exchanger |
| EP3873851A1 (en) * | 2018-11-02 | 2021-09-08 | Rhodia Operations | Compositions based on yttrium, cerium and an organic compound, and stop-off use thereof |
| CN114289594B (en) * | 2021-12-21 | 2024-04-19 | 北京星航机电装备有限公司 | Superplastic forming method for structural part with interlayer |
| EP4209289B1 (en) * | 2022-01-10 | 2024-06-19 | Benteler Automobiltechnik GmbH | Method and hot forming tool for manufacturing a heat exchanger plate |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2850798A (en) * | 1954-05-03 | 1958-09-09 | Fred E Bowman | Method of bonding zirconium |
| US3044160A (en) * | 1958-03-03 | 1962-07-17 | Battelle Development Corp | Method of producing ribbed metal sandwich structures |
| US3145466A (en) * | 1959-11-27 | 1964-08-25 | Westinghouse Electric Corp | Diffusion bonding of metal members |
| NL268834A (en) * | 1960-09-02 | |||
| US3170234A (en) * | 1962-09-17 | 1965-02-23 | Charles O Tarr | Jointing of refractory metals by solidstate diffusion bonding |
| US3340101A (en) * | 1965-04-02 | 1967-09-05 | Ibm | Thermoforming of metals |
| US3920175A (en) * | 1974-10-03 | 1975-11-18 | Rockwell International Corp | Method for superplastic forming of metals with concurrent diffusion bonding |
-
1975
- 1975-10-17 GB GB42761/75A patent/GB1495655A/en not_active Expired
- 1975-10-20 CA CA238,141A patent/CA1055680A/en not_active Expired
- 1975-11-10 FR FR7534351A patent/FR2304438A2/en active Granted
-
1976
- 1976-01-05 CH CH1576A patent/CH622191A5/en not_active IP Right Cessation
- 1976-01-14 SE SE7600331A patent/SE414591B/en not_active IP Right Cessation
- 1976-02-12 JP JP51014794A patent/JPS5924893B2/en not_active Expired
- 1976-03-20 DE DE19762611859 patent/DE2611859A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| FR2304438A2 (en) | 1976-10-15 |
| SE7600331L (en) | 1976-09-21 |
| FR2304438B2 (en) | 1980-07-18 |
| CH622191A5 (en) | 1981-03-31 |
| SE414591B (en) | 1980-08-11 |
| GB1495655A (en) | 1977-12-21 |
| JPS51111465A (en) | 1976-10-01 |
| JPS5924893B2 (en) | 1984-06-13 |
| DE2611859A1 (en) | 1976-10-07 |
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