US20040134249A1

US20040134249A1 - Method and device for making intricately-shaped axisymmetric parts from hardly deformable polyphase alloys

Info

Publication number: US20040134249A1
Application number: US10/338,681
Authority: US
Inventors: Farid Utiashev; Oskar Kaibyshev; Viacheslav Plekhov; Vener Valitov
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 2003-01-09
Filing date: 2003-01-09
Publication date: 2004-07-15

Abstract

A method for making an intricately-shaped axisymmetric part having a central portion and a peripheral portion, comprises simultaneously rotating a blank structure fixed on a shaft and forming a peripheral portion of the blank using a forming tool having at least three degrees of freedom (i) at a temperature above 0.4 the blank melting point but below the temperature of secondary recrystallization, (ii) at a rate of from 10⁻³to 10²s⁻¹, and (iii) for a rotation period to effect stress relief in the portion being formed. A device for making intricately-shaped axisymmetric part having a central portion and a peripheral portion, comprising an axial blank structure fixing and rotating unit including a fixture for interchangeably installing a mandrel including a built-up mandrel; at least one roll with a carrier; actuating mechanism for rotating and displacing the roll relative to a blank structure fixed by the unit; a furnace for heating the blank structure fixed by the unit, the furnace having a movable portion disposed around a window for introducing the roll into the furnace; wherein the movable portion of the furnace is axially movable together with the roll over an entire working stroke length of the roll.

Description

BACKGROUND OF THE INVENTION

The invention relates to plastic metal working, more specifically to a method for producing a precision blank for parts such as intricately-shaped disks that feature considerable variations in thickness and diameter and deep non-forgeable undercuttings. Particularly, the invention relates to producing an intricately-shaped axisymmetric part from a blank of hardly deformable polyphase alloy, particularly from a heat-resistant nickel alloy.

“GatorizingTM” is a method for making a part from a hardly deformable alloy by die-forging of a fine-grained blank under superplasticity conditions. At a first stage of the method, a superplastic intermediate product is produced by intense plastic deformation (deep-drawing extrusion), and the at a second stage of the method, the product is subjected to die-forging. The method can produce an axisymmetric part of a relatively intricate shape, e.g., small-diameter bladed disks. However, the capabilities of said method is much restricted due to a disadvantage inherent in the die-forging technique and consisting in that virtually each part is made in its own die set. Thus, the greater the number of parts to be produced, the greater number of expensive die sets is required. In addition, the method requires use of powerful press-forging equipment and expensive sturdy forging dies.

A more versatile and less power-consuming rolling method for producing an intricate part, comprises local forming by rolling a blank having a central and a peripheral portion. In this method, an intricately shaped part is attained by using a polyphase alloy blank made from a structure prepared for superplastic deformation. Local forming of the blank is effected under controlled thermomechanical conditions at temperatures within a range exceeding 0.4 the melting point but below the temperature of secondary recrystallization of the blank material, and at deformation rates of from 10 ⁻³to 10²s⁻¹. The central blank portion is deformed by compression or by compression and torsion, using tools appearing as quills, while a peripheral portion is deformed by rolls having at least three degrees of freedom and operating with a specific force:

σ_s>q≧σ_τ (1)

where σ _τ is the flow stress of the blank material in the deformation zone of the peripheral blank portion; σ_sis the deformation resistance of the blank material in the deformed zones of the blank central and peripheral portions and q is the pressure (specific force) exerted by the tool on the blank.

Die-forging cannot be used directly to produce a disk part having a variable cross section. Forging such a part requires forming a hot-type projection composition at the stages preliminary to the forging. The local forming method enables making an axisymmetric part that is too complicated constructionally to be made by the die-forging technique. A distinguishing feature of the local forming method is a deformation condition that establishes favorable distribution of stress-and-deformation states over the blank. When forming intricately shaped parts, the value of deforming loads must be very specific to avoid deformation of an already formed thin-walled blank portion, inasmuch as the thin wall blank portion is liable to deform even at low stress values, especially when in a state of superplasticity. In a generalized aspect, favorable distribution of a stressed state in a blank is represented by relationship (1).

However, there are axisymmetric parts that have a central portion and a peripheral portion, wherein the peripheral portion not only has an intricate profile and a well developed surface, but also a volume and surface area that substantially exceed the volume and surface area of the central portion. In addition, a narrow shape of the peripheral portion may be non-forgeable or undercuttings may prevent forging. Forming such an intricately shaped peripheral portion of a blank involves rolling of with large degrees of deformation. However, this is attainable only under hot deformation conditions, including superplasticity conditions. Despite the fact that under such conditions flow stress of the material is rather low, deformation (displacement) of a sturdy peripheral blank portion requires heavy loads, i.e., forces and specific forces, which are even larger at the so-called “rigid end” of the blank As a matter of fact, such rigid end in the rolling procedure under consideration is the zone of constrained (hindered) deformation characterized by a distance between an outside and an inside diameter of said rigid end. During the rolling process the rolls exert pressure on the rim inner surface, but in order that the blank diameter increase, the deformation center should be developed to the rim external surface. The longer said distance, the greater pressure (specific force) must be exerted on the blank. The size of the blank rigid end can be evaluated by the ratio between the above said diameters. When said ratio exceeds 1.5 to 1.8, it is necessary to apply such pressure and force that will change the size and shape of the already formed thinner disk portion (web) as well. The ratio between the axial dimensions of the central and peripheral portions (i.e., the disk rim being rolled and the disk web having been rolled) is limited to approximately the same value. Hence the volume and weight of peripheral disk portion being rolled are also restricted on the whole.

Web deformation preventing techniques fail to solve the problem of rolling a blank having a robust. Thus, web resistance must be increased for a local forming method by hardening the material by intercooling. However, the degree of practicable intercooling is restricted to the thermal conductivity factor of the material and the danger of overcooling the portion being deformed to critical temperatures at which plasticity of the alloy is badly affected and the flow stress increases which in turn leads again to an increase in deforming forces. Otherwise, uncontrolled cooling will result in grain size variations. The radial deformation rate may not be reduced substantially as well, since in this case the tool-to-blank contact pattern is decreased and hence the deformation center is decreased, too, which to a greater extent will add to the influence of the rigid end. One of the conditions for carrying into effect local forming process, according to the prototype, is the provision in the blank of a structure prepared for superplastic deformation. Preparation of a fine-grained structure is carried out according to a separate rather labor-consuming technological process concerned with a necessity for carrying out an intense blank deformation.

Thus there is a need for a local forming method to produce intricately-shaped large-size axisymmetric parts from hard-to-deform polyphase alloys to make precision parts having an intricately shaped well developed peripheral portion.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a local forming method for the production of intricately-shaped large-size axisymmetric parts from hard-to-deform polyphase alloys. According to the invention, a method for making an intricately-shaped axisymmetric part having a central portion and a peripheral portion, comprises simultaneously rotating a blank structure fixed on a shaft and forming a peripheral portion of the blank using a forming tool having at least three degrees of freedom (i) at a temperature above 0.4 the blank melting point but below the temperature of secondary recrystallization, (ii) at a rate of from 10 ⁻³to 10²s⁻¹, and (iii) for a rotation period to effect stress relief in the portion being formed.

Also the invention provides a device for making intricately-shaped axisymmetric part having a central portion and a peripheral portion, comprising an axial blank structure fixing and rotating unit including a fixture for interchangeably installing a mandrel including a built-up mandrel; at least one roll with a carrier; actuating mechanism for rotating and displacing the roll relative to a blank structure fixed by the unit; a furnace for heating the blank structure fixed by the unit, the furnace having a movable portion disposed around a window for introducing the roll into the furnace; wherein the movable portion of the furnace is axially movable together with the roll over an entire working stroke length of the roll.

In an embodiment of the invention, a method for making a part having a central portion and a peripheral portion, comprises preconditioning a blank structure for superplastic deformation; forming the blank structure into the shape of a sleeve having a monotonically narrowing shape in a first step, forming a complete peripheral portion of the sleeve in a single second step (i) at a temperature above 0.4 the blank melting point but below the temperature of secondary recrystallization, (ii) at a rate of from 10 ⁻³to 10²s⁻¹, and (iii) for a rotation period to effect stress relief in the portion being formed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 represents the diagram of a device adapted for carrying the proposed method; [0012]
FIGS. [0013] 2-11 represent type of parts which can be produced by the proposed method;
FIG. 12 illustrates the photographs of parts the types presented in FIGS. 3, 7, and [0014] 9;
FIG. 13 illustrates photographs of the part, which is presented in FIG. 11; [0015]
FIG. 14 illustrates a photograph showing the instant of completing a technological process for production of a part; [0016]
FIG. 15 illustrates a photograph showing the working zone proper during the process for producing a part (the furnace top being out of position); [0017]
FIG. 16 represents the diagram of performing essentially first operation of forming a sleeve-type part using a single roll and a forming mandrel. [0018]
An original shape of the blank peripheral portion and an initial roll position are indicated with a dotted line; [0019]
FIG. 17 illustrates a diagram of a final forming operation of a sleeve-type part having a monotonically varying shape using a single roll. [0020]
FIG. 18 illustrates a diagram of forming a sleeve-type part having a monotonically varying taper shape using a single roll and a forming mandrel. [0021]
FIG. 19 illustrates a sketch of a part following the forming procedure using a built-up forming mandrel; [0022]
FIG. 20 illustrates a diagram of a forming procedure of a flange in the peripheral portion of a sleeve-type part having a monotonically varying shape using a single roll and a built-up forming mandrel. [0023]
FIG. 21 illustrates a diagram of a forming procedure of part having the peripheral portion bilateral relative to the central portion thereof and having a monotonically varying shape using a single roll and built-up forming mandrels. [0024]
FIG. 22 illustrates a diagram of a forming procedure of a sleeve-type part having a monotonically varying shape using an external forming mandrel and a single roll; and [0025]
FIG. 23 illustrates a diagram of a forming procedure of a sleeve-type part having a monotonically varying shape using rollers disposed on opposite sides of the peripheral blank portion.[0026]

DETAILED DESCRIPTION OF THE INVENTION

In this specification, the recitation of one element, feature or step shall mean one or more of the element, feature or step. A “blank” is an unfinished metal or alloy such as a billet. The term “titanium” includes titanium metal, alloy, composite and other titanium-containing compositions. The term “aluminum” includes aluminum metal, alloy, composite and other aluminum-containing compositions. A “quill” is a hollow shaft. A process of “stress relief” is a low temperature annealing process to reduce residual stress in a blank that may result from work hardening or quenching. The term “generatrix direction” means a direction toward the center of a blank structure away from a peripheral portion. [0027]
The present invention has for its object to provide a method for making, from polyphase alloys, intricately-shaped axisymmetric parts having a central portion and a well-developed peripheral portion, and to ensure high production output of the forming process. [0028]
In addition, one more object of the invention is to extend processing capacities due to the use of blanks having a fine- and coarse-grained structure and of the deformation conditions corresponding to the blank structure. [0029]
The aforesaid object is accomplished in a method for making intricately-shaped axisymmetric parts from hardly deformable polyphase alloys, said parts having a central portion and a peripheral portion, which method consisting in that an appropriately shaped blank having a structure prepared for superplastic deformation, is set fixably and rotatably in a quill and that the blank peripheral portion is subjected to local forming at temperatures exceeding 0.4 the melting point but below the temperature of secondary recrystallization, at a rate of from 10[0030] ⁻³to 10²s⁻¹, using a local forming tool having at least three orders of freedom, CHARACTERIZED in that use is made also of a blank having a structure not prepared for superplastic deformation, wherein at least part of the already shaped peripheral blank portion, irrespective of the structure thereof, has the outside diameter exceeding the diameter of the finished part, or the inside diameter less than the diameter of the finished part, and local forming is performed using at least a single roll by reducing the blank peripheral portion in the direction of the generatrix thereof, and the period of blank rotation relative to the local forming tool is preset to be not less than the time of intense relaxation of stresses in the areas being deformed; used as quills at the first step for at least the blanks having a coarse-grained structure, is a forming mandrel having a diameter corresponding to the inside or outside diameter of the peripheral portion of the shaped blank or of the finished part.
Some of the aspects or embodiments of the invention include: [0031]
rotating an aluminum alloy blank structure relative to a forming tool for a period of rotation not in excess of 0.25 s; [0032]
rotating a titanium alloy and heat-resistant nickel alloy blank structure relative to a forming tool for a period of rotation between 0.25 and 100 s; [0033]
rotating a coarse-grained blank structure relative to a forming tool for a period of rotation between 50 and 100 s; [0034]
rotating a fine-grained blank structure relative to a forming tool for a period of rotation between 10 and 50 s; [0035]
rotating a submicrocrystalline blank structure relative to a forming tool for a period of rotation between 0.25 and 10 s; [0036]
forming in a number of steps depending on profiling and structure of a blank; [0037]
single step forming of a sleeve-shaped blank structure prepared for superplastic; [0038]
two step forming of a central portion and peripheral shaped portion shaped blank structure prepared for superplastic steps, wherein a sleeve-shaped blank is formed in a first step; [0039]
forming a coarse-grained original blank structure having a central portion and a thin-walled peripheral projection,, wherein forming is performed by first preparing a sleeve-shaped blank and then by subjecting the peripheral portion to 50-75% reduction under temperature and deformation rate conditions of superplasticity; [0040]
forming an original blank by performing several steps of reversal roll motion; [0041]
local forming of a peripheral portion of a blank with a forming mandrel is used to produce a part having wide variations of thickness and diameter in adjacent sections; [0042]
a forming mandrel is used to form an interior surface; [0043]
a forming mandrel is used to form an exterior surface; [0044]
a built-up forming mandrel is used; [0045]
maintaining mandrel forming surface temperature within a range of superplasticity of the blank material; [0046]
local forming of the peripheral portion using a single roll to produce a sleeve-type part having a monotonously narrowing profile, [0047]
local forming of the peripheral portion using a single roll and a forming mandrel having an outside diameter equal to a minimum inside diameter of the peripheral portion to produce a sleeve-type part having a monotonously narrowing profile, [0048]
two rolls disposed on opposite sides of a wall being formed for local forming of the peripheral portion is carried out using; [0049]
two rolls disposed on opposite sides of the wall being formed, and a forming mandrel, wherein one roll and the mandrel are used in a first step, and both rolls are used in a second step; and [0050]
heating temperature of the surface being deformed of the peripheral portion of the part within a range of from the deformation temperature to a temperature exceeding the lower temperature threshold of superplasticity for performing a fine-grained heat-resistant nickel alloy; [0051]
Carrying the herein-proposed method into effect is possible in a device comprising units that provide for axially fixing the blank and its rotation, at least one roll with its carrier, a working furnace with openings in the walls for part of the fixing unit and the roll to bring into the furnace, and actuating mechanisms for the roll to rotate and displace. In addition the furnace walls have a movable portion disposed around the opening for bringing the roll into the furnace, said device being characterized in that the blank fixing unit is provided with fixtures for installing change mandrels, built-up ones inclusive, and the movable portion of the working furnace wall is axially movable, together with the roll, over the entire length of the preset roll working stroke. [0052]
The method can also be carried into effect provided that: [0053]
the blank fixing unit has a shaft and sleeves for imparting torque to the blank; [0054]
the roll carrier further comprises a heat shield. [0055]
A combination of features of the proposed invention provides for solving its problem due to the provision of a favorable distribution of the stressed-strained states in the blank, with which states, as has been pointed out before, the stresses in the zone of deformation are high enough for plastic flow of material in the direction predetermined by the tool, while in other zones the stresses are below the level initiating plastic deformation. In this case, the favorable stressed-strained states are understood to mean not only correspondence of deformation values to the shape assumed but also forming or retaining a required deformation structure, in particular, without accumulating flaws dangerous to the forming process or operating conditions, and whenever possible, provision of homogeneity of said structure. [0056]
Now let us assess the effect of the geometric factors, i.e., the dimensions of the blank volume being displaced and the deformation rate, on the relationship (1) which represents, in a generalized aspect, a favorable distribution of the stressed-strained states. [0057]
An average pressure value q exerted by the roll on the blank is defined as [0058]
q=F/S, (2)
where S is the area of the tool-to-blank contact pattern; and F is a complete force exerted by the tool on the blank on the contact pattern area. [0059]
The value of said force can also be expressed by virtue of internal stresses in the body being deformed [0060]
F=n_σσ_iS, (3)
where n[0061] _σ is the stressed state factor, which depends on the size of rigid blank end and σ_iis the intensity of internal stresses.
With a sufficient correctness for an engineering analysis one may assume that deformation at a preset rate in the peripheral blank portion being deformed occurs whenever the stress intensity σ[0062] _ireaches a certain flow stress value σ_τ, said value depending on the deformation rate ξ.
σ_τ=Kξ^m (4)
where K is an empirically determined coefficient; and m is the flow stress rate response. [0063]
Having used expressions (2), (3), and (4), we obtain the following equality: [0064]
q=nKξ^m (5)
In the precedent equations ξ denotes an average deformation rate of each local area per blank revolution (i.e., the period of blank rotation relative to the roll). Instantaneous value of the deformation rate of each local area may be defined as follows: [0065]
ξ_m =V/L, (6)
where V is the velocity of metal crowding onto the tool; and L is the length of blank-to-tool contact in the direction of metal crowding. [0066]
With a constant amount of reduction by the tool (in a direction towards the axis in the proposed method, and between the rolls in the prototype), V consists of two components. viz., V[0067] _τ—blank peripheral velocity and V_a—axial rate of tool displacement (which is the radial rate V_τ for the prototype). In the scalar representation the equation of linear velocities may be written as V_τ ²=V+V_a ²)^1/2. Taking the latter in consideration we obtain:
ξ_m =V/L=(V _τ ² +V _a ²)^1/2 /L (7)
An average velocity per blank revolution equals [0068]
ξ=ξ_m Δt/T, (8)
where Δt is the residence time of a local area (contact pattern) under the tool; and T is the blank rotation period. [0069]
In its turn, T=Δt+τ, where τ is the time of idle run of the area being deformed; since τ>>Δt, it may be assumed that T≅τ, whereby ξ≈ξ[0070] _mΔt.
The parameters used are associated with one another as follows: Δt=L/V[0071] _r; V_r=ωR; ω=2π/T, where ω is angular velocity, R is the current deformation radius of the peripheral blank portion, π≈3.14.
Hence the instantaneous and average velocities may be represented respectively as follows: [0072]
ξ_m =V _r /L×[1+(V _a /V _τ)²]^1/2 ≈Δt ⁻¹×[1+(V _a /V _τ)²]^1/2 (9)
ξ=τ⁻¹×[1+(V _a /V _τ)²]^1/2 (10)
and substituted expression (10) to expression (5) we obtain: [0073]
q≅K×n _σ×τ^−m×[1+(V _a /V _τ)²]^m/2 (11)
or else, when taking into account that V[0074] _τ=ωR and ω=2π/T the expression (11) may appear in another aspect:
q≅K×n _σ×τ^−m×[1+(V _aτ/2πR)²]^m/2 (12)
Expression (12) holds true both for the proposed method and the prototype, but in the latter case velocity V[0075] _r. is to be substituted in expression (12) instead of V_a.
In expression (12) the value enclosed in square brackets approximates unity, since in forming large-size parts the circumference (2πR) exceeds substantially the tool feed rate per revolution ((V[0076] _aτ) and hence the relation (V_aτ/2πR)²is a small value.
Having simplified expression (12), we obtain: [0077]
q≅K×n_σ×σ^−m (13).
Thus, equation (13) common to both the herein-proposed method and the prototype demonstrates that when leaving out of account the coefficients K and m representing the effect of the structure which is quite admissible in case of hot deformation under the ÑÏÄ conditions, while the pressure depends on the period of τ . . . Insofar as τ is located in the denominator so with its rise q decreases, and with reduction of q the value of τ increases. However, a change in the period □ influences but dissimilarly the value of q in the proposed method and in the prototype, this being due to the coefficient n[0078] _σ. Thus, reduction of said period in the proposed method leads to an inversely proportional increase in the value of q, because the rigid blank end does not influence in this case the value of q and the coefficient n_σ which is practically a constant number approximating unity.
In the prototype the pressure depends on the size of the blank rigid end and the deformation center. The coefficient n[0079] _□ depends on said parameters nonlinearly. As the deformation rate increases the values of the stresses effective in the region being deformed increase, too. As a result, intensity σ₁of said stresses is changed so that in order that said intensity reaches again a higher value of the flow stress σ_τ corresponding to a higher deformation rate, it is necessary to further increase the tool pressure.
Therefore when the deformation rate increases, the pressure rises not only due to an increase in the flow stress resultant from said deformation rate but also due to the effect produced by the blank rigid end. It is said effect that the coefficient n[0080] _σ represents which ranges within 2 and 5. Hence the same specific tool force applied to the blank corresponding to the condition of the expression (1), in the proposed method provides for higher level of flow stress σ_τ in the blank peripheral portion and accordingly a higher deformation rate and output of the process as compared to the prototype.
Thus, absence of a mutual effect of the period and the stressed state factor enables one to substantially enhance the effect of stress increase due to a reduced period of blank rotation, according to the proposed method provided that the condition of expression (1) is observed. [0081]
Besides, according to the proposed method, the output may be increased not only due to a reduced period of blank rotation but also due to a change in the ratio between velocities V[0082] _A/V_τ, which cannot be done, as has been pointed out before, in the prototype, since when V_eris decreased the effect of the stressed state is increased, and when V_tis increased, there is augmented, as will hereinafter be demonstrated, the moment of force resulting in deformation of the already formed blank portion.
Selection of the period of blank rotation is concerned with some specific features of deformation during local forming of the blank peripheral portion. [0083]
The nature of deformation in the proposed technical solution is such that each area of the blank peripheral portion being deformed is many times subjected to a cyclic action of the tool due to the fact that the blank rotates relative to the tool and the latter performs translation motion towards the generatrix of the blank peripheral portion. During direct tool exertion on the blank within the local site of deformation, shear stresses are therein effective which displace the blank material in the direction predetermined by the tool. Once any blank area has come out of contact with tool, and during the tool idle run till a next tool contact with the blank relaxation of the blank material occurs so that the stresses caused by the tool are reduced. At the microstructure level density of defects is reducing during said relaxation of the material, which is due to, e.g., annihilation of dislocations. Insofar as the deformation center exceeds the zone of direct blank-to-tool contact on the area of the tool action, especially for a fine-grain structure, i.e., the extent of the deformation center in the direction towards said generatrix is perceptibly larger than the rate of tool feed per blank revolution, part of the blank material is subjected repeatedly by the tool action during blank rotation relative to the tool. When the blank rotates for a period of time not in excess of the time of intense relaxation, stress values are reduced several times so that defects that change substantially the structural state and mechanical characteristics of the blank material, in particular, shear stress and plasticity have no time to accumulate therein. A number of specially performed experiments are the evidence of the fact. In said experiments there were determined the time of intense relaxation of flow stresses after releasing the test specimen from the load during tensile test. The experiment also included comparing the levels of plasticity and flow stresses of test specimens subjected to continuous and intermittent (cyclic) tension. In this case, intermittent tensile test involved releasing the test specimen from load for a period of rest exceeding the time of intense relaxation of stresses. It was established that stresses in a high heat-resistant alloy dropped several times for a time lapse of the order of 1 to 5 seconds. In addition, the stress level in a test specimen cyclically deformed with a predetermined period was approximately the same as in the test specimen subjected to continuous deformation, and percentage elongation was 1.5 to 2 times higher. [0084]
In the prototype, when a period of blank rotation relative to the tool is reduced, the tangential force component F[0085] _□ constituting a moment is increased. Said moment together with the radial force component F_racts in the same rolling plane, thus twisting and tensioning, respectively, the web in its minimum cross-section. To substantially reduce the component F_ris impossible, since the deformation center should be well developed. Therefore with a reduced period the sum of forces acting on the deformed blank portion is increased.
According to the proposed method, an increase in F[0086] _□ due to a fast-rate hardening tells but insignificantly on the rise of stresses in the blank formed portion, since said force is less than in the prototype, inasmuch as the contact area in the respective direction is smaller. The other component, i.e., the axial force F_aalso falls short of being rather large and may therefore be preset within a required value using two ways of which the first one involves an appropriate selection of the value of q in accordance with the above-considered relationships, while the other procedure is based on varying the value of S, forasmuch as the method can be carried out either at a single step (in case of a higher value of S) or at a number of steps (with a lower value of S), since in this case there is no effect of the blank rigid end (1).
Thus, the feature consisting in that blank rotation period is not in excess of the time of intense relaxation of the blank deformed portions is one of the principal and adequate features for providing favorable deformed state of the blank material allowing deformation of said material with high degrees of deformation without accumulation of defects, and one of the features indispensable for accomplishing the object of the invention. [0087]
To attain higher output and adhere to the relationship (1), i.e., to provide favorable stressed-strained state, it is reasonable to reduce the blank rotation period until it is equal to the relaxation time and decrease the axial tool displacement speed for the period of blank rotation, i.e., the tool rate of feed per blank revolution. Linear velocity of tool displacement is in this case determined by the product of the number of blank revolutions per minute by the rate of tool feed per blank revolution. In addition, reduction of the axial tool displacement speed will result in reduction of the respective force acting as a tensile force with respect to the formed zone of the blank peripheral portions, that is, conditions for obeying the relationship (1). [0088]
Use of quills as a forming mandrel, according to the proposed method, improves stressed-strained state at least when the peripheral portion of coarse-grained blanks is deformed, said portion featuring flow stress exceeding that in said portion of fine-grained blanks. This is also promoted by friction forces acting in the opposite direction relative to the aforementioned forces, tending to change the shape and size of the deformed blank peripheral portion. [0089]
Finally, it is worth noting that forming the blank peripheral portion in the direction towards its generatrix is in fact neither a single nor unambiguous way of local forming parts having well developed peripheral portion. Such parts may be made according to another production process technique and from a blank shaped differently than in the proposed method. In particular, such parts may be manufactured from a blank having its peripheral portion shaped in the plane of the central portion thereof which can then be “laid” onto the mandrel using rotary reduction technique. However, such a method fails to solve the problem. Moreover, all disadvantages inherent in the prototype will interfere with it during the preforming process the blank peripheral portion with the aid of, e.g., rolling the blank to the required dimensions. [0090]
In the subordinate claims the relaxation time depends on a number of factors, such as temperature, nature of the alloy used, and its structure. Thus, the higher the temperature of superplastic deformation and the lower the grains size, the faster proceeds the stress relaxation process. For instance, a longer relaxation period is required for heat-resistant alloys in case of deformation at a temperature corresponding to the lower superplastic deformation range, whereas for usual fine-grained alloys deformable at high superplastic deformation temperature a shorter period (5 s)is required, for titanium alloys, 5 s, and for aluminum alloys, 0.25 s. [0091]
Relatively short periods of repeated action in forming the blank peripheral portion are especially favorable for local deformation of fine-grained structure blanks, since relaxation processes proceed rapidly in such structure and the latter provides for high technological plasticity of the blank material. The influence exerted by the nature of an alloy on the period of blank rotation and the relaxation time is ambiguous; thus, for instance, the relaxation time in polyphase nickel- or titanium-base heat-resistant alloys is longer than in, e.g., aluminum alloys. However, the former alloys have lower thermal conductivity as compared to the latter one, so that a deformation-induced local temperature rise may expedite relaxation, though the heat released should not be causative of an inadmissible overheating. Experimental checking has evidenced that the rotation period in forming titanium-base and heat-resistant blanks should not be in excess of 100 s. [0092]
Further additional essential features also develop and define more exactly possibilities of accomplishing the object of the present invention. [0093]
According to the proposed method, the blank peripheral portion is formed with the aid of a forming mandrel. [0094]
The presence of friction between the blank and the mandrel on a developed contact surface, according to the proposed method, as distinct from the prototype, makes possible, with lower contact stresses (hold-down pressure), providing blank rotation during local forming. Moreover, according to the proposed method, only one out of three vectors of deformation forces acts, as a moment of force, on the blank central portion. However, stresses resulting from said moment are but insignificant, since as distinct from the prototype, they are reduced by rather high value of a high polar moment of resistance of the central cross-section. [0095]
When making parts having their peripheral zone shaped as a sleeve tapering with respect to the web, the peripheral bank portion is subjected to forming in two steps; first a straight sleeve is formed, having a diameter not less than the diameter of the bottom, then by reduction on a sectional forming mandrel or without such a mandrel, by drawing the walls until the finished size is obtained. [0096]
Local forming is effected at a several steps the number of which is determined depending on the degree of the blank preforming and on the blank structure, which is concerned with that an original blank can be obtained by the various metallurgical techniques, such as casting, die-forging, powder metallurgy, or a combination thereof. [0097]
In particular, when a possibility is provided for use of a blank preformed as a sleeve and having a structure prepared for superplastic deformation, the number of operations of local forming may be practically as little as one. [0098]
At the same time, the method is also realizable if use is made of a blank having its structure prepared for superplastic deformation and preformed as a central portion and a peripheral projection. [0099]
Furthermore, to use a blank preformed in the way mentioned above is expedient if said blank has an original coarse-grained structure. Herein an indispensable prerequisite is the provision of a thick-walled projection which ensures, during subsequent deformation, conversion of a microstructure of the blank into a micro- or submicrocrystalline. [0100]
Regardless of the final profile of the part it is recommended that at the first step of the local forming process the blank be shaped as a sleeve, using a forming mandrel. In some cases said shape may be the final one of the part to be obtained. [0101]
Whenever it is necessary to obtain a part having an extended thin-walled peripheral portion, it is recommended that the forming process be performed at a number of steps which provides for optimum conditions for applying the deforming load. It is due to varying the pathway of the tool (i.e., roll), changing it he angle of incline to the blank rotation axis, as well as the roll penetration depth that one can effect control over the degree of deformation within a wide range at each step, thereby providing the most favorable conditions for deforming the blank peripheral portion. This is of paramount importance when a blank is used, wherein a coarse-grained structure is established in the original state of the peripheral portion thereof. As it is common knowledge [3], a coarse-grained structure is characterized by a much restricted resource of technological plasticity in case of hot deformation which might result in disturbing the continuity of the blank material in attempting to make axisymmetric parts having a well-developed thin-walled peripheral portion from hardly deformable materials. Therefore when using a blank whose peripheral portion has a coarse-grained structure, it is necessary that at the initial steps said structure be transformed into a microcrystalline one with a particle size of 1 to 10 □m or into a submicrocrystalline structure with a particle size less than 1 □m so as to prepare a structure amenable to superplastic deformation. [0102]
A proper selection of the specific values of the degrees of deformation and the temperature-and-rate conditions for at least part of the steps required for preparing the blank structure for superplastic deformation depends on a number of factors, viz., chemical and phase composition of the alloys used, final shape of the part peripheral portion, requirements imposed on the structure and mechanical characteristics of the finished part. The degree and temperature-and-rate conditions of deformation are selected to be adequate for dynamic recrystallization to occur in the blank material, in the course of which a microcrystalline structure is established. It is worth noting that a microcrystalline structure may be established in the blank peripheral portion at a number of steps. At a first step a partially recrystallized structure is established, then at a second step (which may be the final) a completely recrystallized structure is established in the blank peripheral portion. Such a technique makes possible substantially reducing the value of specific forces, as well as promoting more complete stress relaxation, which is especially important for polyphase alloys. In particular, for instance, as far as dispersion-solidifying nickel alloys are concerned, at a first step it is necessary to eliminate the hardening effect of a second phase due to its coagulation, disturbing coherent association with the matrix and its partial dissolution. An insignificant degree of deformation at the first step expedites substantially the processes of coagulation of the second phase, and selection of maximum values of the period of blank rotation provides for more favorable conditions for stress relaxation due to processes of dynamic polygonization and recrystallization leading to formation of a partially recrystallized structure. [0103]
Moreover, use of a number of steps make possible step-to-step temperature reduction which contributes to further refining of microstructure of the blank peripheral portion down to a submicron grain size. Provision of a submicrocrystalline structure in the blank peripheral portion makes it possible to substantially shorten the stress relaxation period, thereby enhancing the output of the process involved. [0104]
Process capabilities of the proposed method can be extended due to a technique, wherein the forming process is effected revering the roll motion. [0105]
In this case repeated deformation is carried out by analogy with backward extrusion, thus enhancing the output of the process. [0106]
One of the recommended conditions of making a part with considerable variations in thickness and diameter in adjacent sections is performing local forming of the blank peripheral portion using a forming mandrel. This facilitates meeting the conditions of relationship (1), which eventually adds to the production accuracy of a part as to geometry and dimensions. [0107]
Constructionally, a forming mandrel may be either solid or built-up, which can be made use of depending on the shape of the blank peripheral portion. Whenever the blank peripheral portion has a decreasing outside diameter and terminates with a flange, i.e., when the forming mandrel fails to be withdrawn from the interior space of the part after the forming process, use is to be made of a built-up forming mandrel. [0108]
The mandrel may be either external or internal depending on the shape of the external and internal surface thereof. [0109]
As a rule, mandrels are made of a more heat-resistant material than that of a blank to be worked, e.g., from a cast high nickel alloy. To provide adequate construction strength of the mandrel the latter is to be more robust than the blank. Inasmuch as the mandrel is in permanent contact with the blank being deformed, an intense heat transfer occurs, especially in cases where local intercooling of the mandrel is used through the unit of fixing the blank central portion to the mandrel. In such a case it is recommendable to effect a strict control over the mandrel heating temperature so that the temperature of the mandrel forming surfaces corresponds to a temperature range of superplasticity of the blank material. [0110]
When making thin-walled parts such as a sleeve with monotonically varying shape, local forming of the blank peripheral portion is practicable using a single roll, or a single roll and a forming mandrel. In some cases the mandrel may be constructionally shaped in such a manner as not to follow the internal shape of the blank peripheral portion, but has such a size that are sufficient to fix the blank in position and retain the already formed cantilevered blank portion sand prevent it from distortion. That is why the mandrel has an outside diameter equal to a minimum inside diameter of the blank peripheral portion. [0111]
When manufacturing large-diameter parts having a well-developed peripheral portion, it is recommended that local forming of the blank peripheral portion be performed using two rolls disposed on opposite sides of the wall being formed, or be made at a preceding step using a roll and a forming mandrel. [0112]
It is expedient that making parts having a bilateral blank peripheral portion, relative to the central blank portion, be effected by local forming the blank peripheral portion with two rolls at a time, said rolls moving in opposite directions from the blank central portion. Using such a technique is instrumental in substantially increasing the output of the process, or alternatively, local forming of the blank peripheral portion may be performed consecutively with a single roll using reversal of the roll motion. Choosing between said two techniques depends both on economic advantage of their use and on the shape of the part obtained. [0113]
When forming blanks from heat-resistant alloys, resort may be made, with a view to increasing tool endurance and mandrel rigidity, to intercooling of both. However, a difference may occur between the temperature of the blank heated up to the deformation temperature and the less heated roll and mandrel. Therefore it is necessary in such cases to maintain the temperature of heating the surface of the peripheral portion being deformed within the range from the deformation temperature to a temperature exceeding the temperature threshold of superplasticity for a fine-grained material. Otherwise with a preset deformation rate the overcooled surface layers will be deformed under non-optimum superplasticity conditions. Hence strain hardening of the surface layers of the blank peripheral portion will result from local forming. On performing final heat treatment of such parts with a view to enlarging, by one or two orders of magnitude, the grain size, zonal grain size variations are liable to occur which impairs badly mechanical characteristics of the finished part. [0114]
When a blank is deformed, especially a nickel alloy blank, upon stress relaxation, even occurring under most favorable conditions, some residual stresses are likely to remain which are concerned with a change in the blank geometry but produce no influence on the forming process of a part but may result in zonal grain size variations developing upon subsequent high-temperature heating. For completely eliminating residual stresses and ruling out any possibility for developing grain size variations following the process of forming parts from nickel alloys, it is recommendable to preheat blanks from the alloy ageing temperature to a temperature below that of complete dissolution of the strengthening phase, followed by holding at that temperature for 1 to 24 hours. [0115]
To obtain parts with a maximum accuracy and shape and size stability, it is also recommendable to combine the last step of the final forming of the blank peripheral portion with calibration which is conducted at a deformation temperature and involves penetration of rolls into the blank for a depth not exceeding the size tolerance value for the finished part. [0116]
The proposed method can be realized in a device whose distinguishing feature consists in that the fixing unit is provided with positioners of change mandrels, the built-up ones inclusive, and the movable portion of the working furnace is axially displaceable together with the roll throughout the length of the preset roll working stroke. [0117]
In the known technical solution the fixing unit appearing as two quills is adapted for fixing the blank central portion in position and imparting torque and its replacement involves dismantling the entire device. In the proposed device all the above listed functions of the fixing unit are retained and, in addition, whenever necessary said unit is imparted the functions of a tool. The construction arrangement of the furnace provides for local forming of the blank peripheral portion in the direction towards its generatrix. [0118]
Thus, construction arrangement of the proposed device enables one to manufacture intricately shaped parts having a well-developed peripheral portion. [0119]
The operating capabilities of the device can be further extended due to the following additional features. [0120]
When the working furnace is additionally provided with a separate chamber adapted for accommodating the tool, while inoperative, and preheating it, the production cycle will thereby cut down substantially. Besides, since the roll weight is cardinally less than the weight of the mandrel and blank before the local forming procedure, so the roll is expedient to be preheated to a temperature lower than that in the working furnace. [0121]
A construction arrangement wherein communication between said chamber and the interior space of the working furnace is established through an opening in the movable portion of the furnace wall renders the device more space saving. [0122]
In cases where the roll is introduced into the furnace together with its carrier it is expedient that the roll-to-carrier attachment unit be provided with ducts for the refrigerant to supply and withdraw, as well as that the roll carrier be provided with a heat shield. [0123]
When making parts having a central hole and an extended peripheral portion, use is made of shaft provided with sleeves for higher rigidity, said sleeves serving also for torque transmitting purpose. [0124]
When effecting local forming with two rolls disposed on opposite sides of the blank peripheral portion, it is suggested that use be made of rolls adapted to move radially and axially in step with each other and to mutually turn through an angle of from zero to π/2. [0125]
Features of the invention will become apparent from the drawings and following detailed discussion, which by way of example without limitation describe preferred embodiments of the invention. [0126]
FIG. 1 represents the diagram of a device adapted for carrying the proposed method. FIGS. [0127] 2-11 represent type of parts which can be produced by the proposed method, FIG. 12 illustrates the photographs of parts the types of are presented in FIGS. 3, 7, and 9. FIG. 13 illustrates photographs of the part the type of which is presented in FIG. 11. FIG. 14 illustrates a photograph showing the instant of completing a technological process for production of a part (the furnace top being out of position). FIG. 15 illustrates a photograph showing the working zone proper during the process for producing a part (the furnace top being out of position). FIG. 16 represents the diagram of performing essentially first operation of forming a sleeve-type part using a single roll and a forming mandrel. An original shape of the blank peripheral portion and an initial roll position are indicated with a dotted line. FIG. 17 illustrates a diagram of a final forming operation of a sleeve-type part having a monotonically varying shape using a single roll. An initial roll position is indicated with a dotted line. FIG. 18 illustrates a diagram of forming a sleeve-type part having a monotonically varying taper shape using a single roll and a forming mandrel. An initial roll position is indicated with a dotted line. FIG. 19 illustrates a sketch of a part following the forming procedure using a built-up forming mandrel. FIG. 20 illustrates a diagram of a forming procedure of a flange in the peripheral portion of a sleeve-type part having a monotonically varying shape using a single roll and a built-up forming mandrel. An initial roll position is indicated with a dotted line. FIG. 21 illustrates a diagram of a forming procedure of part having the peripheral portion bilateral relative to the central portion thereof and having a monotonically varying shape using a single roll and built-up forming mandrels. An initial roll position is indicated with a dotted line. FIG. 22 illustrates a diagram of a forming procedure of a sleeve-type part having a monotonically varying shape using an external forming mandrel and a single roll. FIG. 23 illustrates a diagram of a forming procedure of a sleeve-type part having a monotonically varying shape using rollers disposed on opposite sides of the peripheral blank portion. Ref. No. 5 in FIGS. 16-23 denotes a blank, Ref. No. 11 denotes a roll, Ref. No. 19 denotes a solid forming mandrel, and Ref. Nos. 20, 21, and 22 denote the component of a built-up forming mandrel. Curved arrows in FIGS. 16-22 indicate the senses of rotation of the blank and rolls.
The following Examples are illustrative and should not be construed as a limitation on the scope of the claims unless a limitation is specifically recited. [0128]
The device (FIG. 1) for carrying the herein-proposed method into effect comprises fixing [0129] units 1 and 2 which are coaxially arranged and are provided with drives (not shown in FIG. 1) for being displaced with respect to each other along ways 3 and 4 provided on a bed (not shown in FIG. 1) and for imparting rotation to a blank 5, reversible rotation inclusive. The fixing units are interconnected through a shaft 6 provided with sleeves 7 through which torque is transmitted to the blank 5. The bedway 9 mounts a carriage 8 provided with a drive of its own (not shown in FIG. 1) for its being displaced along a bedway 9, i.e., lengthwise the axis of the blank rotation. The carriage 8 mounts a roll carrier 10 with a roll 11. Drives for the roll to displace are not shown in FIG. 1. Indicated at Ref. No. 12 is a high-temperature furnace for heating the blank and maintaining a preset temperature thereof during the deformation procedure. The furnace is provided with a movable shutter 13 having an opening 14 for the roll to introduce. The furnace also has windows 15 and 16 for the components of the fixing units 1 and 2 to pass through. The roll carrier 10 is equipped with a heat shield 17. The device is further provided with a separate chamber 18 adapted to accommodate the tool, while inoperative, and for preheating.
For forming the blank [0130] 5 shown in FIG. 1 the device further comprises forming mandrels 19 and 20.
The following Examples are illustrative and should not be construed as a limitation on the scope of the claims unless a limitation is specifically recited. [0131]

EXAMPLE 1

A sleeve-type part was to be produced with its peripheral portion having a bilateral shape tapered in a direction away from the blank central portion, said part being made of the titanium alloy BT25(Ti-6.5Al-4Zr-2Mo-1.5Sn-1W). Local forming was performed using a preformed blank having a central portion and a peripheral portion shaped as bilateral projection. The blank having an outside diameter of 450 mm and thickness of the projections equal to 25 mm and 30 mm, respectively was prepared by the die-forging procedure, whereby a 5-micron homogeneous globular microcrystalline structure of the microduplex type was established. Used as the original blank for die-forging was a cylindrical blank cut from a 390-mm diameter casting The blank having a cast structure was subjected to a multistep deformation involving a 90-degree turn of the direction of deformation in a diphase region in a 1600-ton press under quasi-isothermal conditions. As a result of such working a microcrystalline structure was established in an upset washer which structure was then deformed using an isothermal die-forging block at 950□. Preparatory to local forming the forged piece was subjected to rough machining in order to remove the oxidized metal layer and making a centering hole. [0132]
A forming diagram of a sleeve-type part with its peripheral portion having a bilateral shape tapered in a direction away from the blank central portion, made of the BT25 titanium alloy is presented in FIG. 3. [0133]
Local forming of the blank was carried out in a device whose schematic diagram is represented in FIG. 1. The blank together with the forming mandrels was secured in the fixing unit, whereupon the furnace was closed and heated to a deformation temperature (950° C.). At the same time rotation was imparted to the blank through the sleeves set on the shaft of the blank fixing unit so as to ensure a uniform blank heating. A first step of local forming of the blank peripheral portion was carried out using the forming mandrels and a single roll, both being made of the alloy grade AEÑ6Ó(Ni-9Cr-9.7W-5.5Al-2.6Ti-1.6Mo-1.1V). The heating temperature of the blank and mandrels in the working furnace was 950° C. The roll was heated in the preheating chamber to a temperature by 100 to 200° C. below that stated hereinafter. The roll was brought into the working furnace together with its carrier through the window provided in furnace movable wall. The roll-to-carrier attachment unit was subjected to intercooling beforehand with compressed air passed through the ducts made in the roll carrier. Local forming procedure was effected at a number of steps using a single roll and a mandrel. The period of blank rotation with respect to the roll was 25 s. [0134]
At a first step one of the projections was locally formed into the shape of the type of cylindrical sleeve. At the first pass the thickness of the first projection was reduced from 25 mm to 15 mm. In a similar way there was performed the local forming of the other projection whose thickness was reduced to 12 mm for two passes using reversal of the roll motion. In this case another mandrel was used, since the inside diameter of the second projection was somewhat smaller than that of the first one. [0135]
Thereupon the cylindrical mandrels were replaced with the built-up ones corresponding to the internal shape of the blank peripheral portion, and local forming of the walls of sleeves formed at the first step was carried out using two tools, that is, built-up mandrels and a roll, under the above stated temperature-and-rate conditions. First final forming of the first projection was performed, then the second projection was formed using the same roll. [0136]
A photograph of the finished part is shown in FIG. 12. As can be seen from said Figure, just after the final forming procedure the part has a homogeneous fine-grained macrostructure over the entire cross-section thereof. [0137]

EXAMPLE 2

A sleeve-type part was to be obtained from a blank made of the BT25 titanium alloy, with its peripheral portion having a bilateral shape tapered in a direction away from its central portion, the blank and the deformation conditions being the same as in Example 1. [0138]
The local forming procedure was effected as follows. [0139]
Use was made of two rolls and two forming mandrels. At a first step the projections were subjected to local forming into the shape of the type of cylindrical sleeve accompanied by penetrating the rolls into the blank material and their displacement in the opposite directions away from the blank central portion. At a second step the projections were subjected to final local forming with two rolls at a time, using built-up forming mandrels. [0140]
The result was the finished part similar as to shape and structure to that of Example 1. [0141]

EXAMPLE 3

A sleeve-type part was to be obtained from a blank made of the BT25 titanium alloy, having its peripheral portion unilaterally tapered in the direction away from the central portion thereof. Local forming was effected using a preformed blank having a central portion and a peripheral portion shaped as a unilateral projection. The blank having an outside diameter of 450 mm and a 25-mm thickness of the projection was prepared by a die-forging procedure, whereby a 5-micron homogeneous globular microcrystalline structure of the microduplex type was established. The structure preparing procedure and the final forming conditions were similar to those of Example 1. [0142]
A forming diagram of a sleeve-type part having its peripheral portion unilaterally tapered in the direction away from the central portion thereof, from the BT25 titanium alloy is presented in FIG. 7. [0143]
The local forming procedure was effected as follows. At a first step the forming was carried out using one roll and one forming mandrel, at the second step use was made of only a single roll. [0144]
The final step of the local forming procedure was combined with calibration. In this case the disk peripheral portion is rolled over its profile at specific forces effective in the contact patter causing plastic deformation of the blank the value of which was not in excess of the tolerance limits specified in the drawing. Performing such an operation made it possible to stabilize the size and shape of a finished part and promoted virtually complete relaxation of residual stresses therein. [0145]

EXAMPLE 4

A first step of the local forming procedure was carried out in a way similar to that of Example 3, whereas a second step was performed using a built-up forming mandrel and a roll. A forming diagram of a disk, according to the present embodiment, is illustrated in FIG. 18. [0146]

EXAMPLE 5

A first step of the local forming procedure was carried out in a way similar to that of Example 3. A second step was effected using a forming mandrel having an outside diameter equal to a minimum inside diameter of the blank peripheral portion. [0147]
As a result of the production process, according to all the three embodiments, there were manufactured disks having a homogeneous microcrystalline structure which satisfies completely, as to shape and size, the requirements imposed by the drawing. [0148]

EXAMPLE 6

A sleeve-type part was to be obtained from a blank made of the BT25 titanium alloy, having its peripheral portion unilaterally expanded in the direction away from the central portion thereof. A first step of the local forming procedure was effected using a single roll and an internal forming mandrel similarly to Example 3. The thickness of the blank peripheral portion after the first step of the procedure was 12 mm. Then the internal mandrel was replaced with an external one, there was also replaced the roll and there was changed the angle of its incline relative to the axis of the blank rotation so that local forming of the inner surface of the blank peripheral portion may be performed. [0149]
As a result of the production process according to the present embodiment, the finished part having well-developed inner and outer surfaces of the peripheral portion thereof was obtained. [0150]

EXAMPLE 7

A part similar to that of Example 6 was to be manufactured. A first step of the local forming procedure was effected as in Example 6, but unlike Example 6 a second step of the local forming procedure was carried out with two rolls which were disposed on the opposite sides of the wall being formed of the blank peripheral portion. [0151]

EXAMPLE 8

A sleeve-type part was to be obtained from a blank made of the BT25 titanium alloy with an original coarse-grained structure, said sleeve-type part having its peripheral portion unilaterally tapered in the direction away from the central portion thereof. [0152]
Local forming was effected using a preformed blank having a central and a peripheral portion which is shaped as a unilateral projection. The blank having an outside diameter of 450 mm and the projection thickness of 50 mm was prepared by virtue of die-forging, whereby a coarse-grained structure was established therein with a particle size of 200 to 500 □m. A first step of the local forming procedure was effected using a forming mandrel and a single roll, both being preheated to 990-960° C. in the working furnace. Local forming of the blank peripheral portion into the shape of the type of a cylindrical sleeve having a constant outside diameter was performed in three steps using reversal of the roll motion. At the first step the thickness of the blank peripheral portion was reduced to 35 mm. At the second and third steps the deformation temperature was decreased by 10-20° C. The period of the blank rotation relative the roll was 100 s at the first step, and 25 and 20 s at the second and third steps, respectively. As a result, the thickness of the blank peripheral portion was reduced to 25 and 12 mm, respectively. An analysis into the microstructure of the blank peripheral portion conducted after the third step demonstrated that a microcrystalline structure with a particle size of 5 to 7 □m similar to Example 1 was established. Further on, the cylindrical forming mandrels were replaced by the built-up ones that follow the internal shape of the blank peripheral portion, whereupon the walls of the sleeves made at the first step were reduced on the built-up mandrels under the same conditions. First the forming mandrel was replaced with a built-up one, whereupon final forming of the peripheral portion was effected as in Example 4. Final operation of local forming was carried out in two steps, the period of the blank rotation with respect to the roll was 25 s, and at the second step, 5 s. During the first operation the period of the blank rotation relative to roll was longer than during the second operation, which is due to the fact that with a coarse-grained structure of the blank material a more prolonged period of time is required for stress relaxation than with a fine-grained structure thereof. In the latter case the extent of the grain boundaries contributing to activation of the grain-boundary slippage is much increased, as well as to efficient stress relaxation in superplastic deformation. [0153]

EXAMPLE 9

A sleeve-type part was to be obtained from a blank made of the ÝÏ962 powder nickel alloy (Ni-13Cr10.1Co-4.3Mo-3.2Al-2.6Ti-3.4Nb-2.8W) and having its peripheral portion unilaterally tapered in the direction away from the central portion thereof. The shape of the finished part and of the forming blank are the same as in Example 3. Used for local forming was a blank with the microcrystalline structure prepared for superplastic deformation, said structure being of the microduplex type with the particle size of 2-3 □m obtained by the powder metallurgical technique. The blank peripheral portion was preformed into the shape of the sleeve type having a wall thickness of 12 mm, ready for final local forming procedure which was effected using a single roll similar to a second operation in Example 3. The preheating temperature of the blank and mandrel was 1050° C. Use was made of a roll similar to that of Example 1. [0154]
As a result of the production process according to a given embodiment, there was made from the hardly deformable ÝÏ962 nickel alloy, practically for one operation of local forming, a part having its peripheral portion unilaterally tapered in the direction away from the central portion thereof. [0155]
As a result, the part produced according to a given embodiment is similar, as to shape, to that obtained in Example 4. [0156]

EXAMPLE 10

A sleeve-type part was to be obtained from a blank made of a nickel alloy (Ni-16Cr-13Co-4Mo-4W-2.1Al-3.7Ti) and having its peripheral portion tapered in the direction away from the central portion thereof. Local forming procedure was carried out using a preformed blank having a central and a peripheral portion appearing as a unilateral projection. The blank having an outside diameter of 410 mm and a projection thickness of 25 mm was produced by die-forging technique, whereby a 5-micron homogeneous microcrystalline structure of the microduplex type was established. Used as an original die-forging blank was a cylindrical blank cut out from a hot-pressed rod 230 mm in diameter. Die-forging was effected in a 1600-ton press under quasi-isothermal conditions. The blank was preheated to 1050° C., the die, to 950° C. [0157]
The operation of local forming of the blank peripheral portion was carried out using a forming mandrel and a single roll similarly to Example 3. The preheating temperature of the blank and mandrel in the working furnace was 1050° C. The roll was heated in the preheating chamber to a temperature 100 to 200° C. below that indicated above. The roll was introduced into the working furnace together with its carrier, while the roll-to-carrier attachment unit was subjected to intercooling with compressed air admitted to pass through the ducts provided in the roll carrier. As a result of local forming there was made the finished part of a preset configuration with the thickness of its peripheral portion equal to 12 mm. An analysis into the microstructure of the blank peripheral portion gave evidence of the fact that just after rotary extrusion the microstructure of the blank peripheral portion retained its fine-grained nature with the particle size of ˜5 μm. With a view to eliminating residual internal stresses caused by a change in the disk geometry, there was carried out annealing of the disk in a diphase γ+γ′-region under the following conditions: heating the disk to 850° C. followed by holding for an hour, then heating to 950° C. followed by holding for two hours, next temperature rise to 1050° C. followed by holding for 8 hours. Whenever it was necessary to obtain a more coarse-grained structure homogeneous over the entire cross-section of the part, temperature was raised to 1150° C., followed by holding for two hours and cooling down to room temperature. As a result of such a heat-treatment procedure, a homogeneous structure with the particle size of 20-30 μm was established in the disk peripheral portion. Thus, when using a cooled tool carrying out additional specified annealing in a diphase γ+γ′-region rules out any possibility of developing grain size variations in the part peripheral portion. [0158]
While preferred embodiments of the invention have been described, the present invention is capable of variation and modification and therefore should not be limited to the precise details of the Examples. The invention includes changes and alterations that fall within the purview of the following claims. [0159]

Claims

What is claimed is:

1. A method for making an intricately-shaped axisymmetric part having a central portion and a peripheral portion, comprising:

simultaneously rotating a blank structure fixed on a shaft and forming a peripheral portion of the blank using a forming tool having at least three degrees of freedom (i) at a temperature above 0.4 the blank melting point but below the temperature of secondary recrystallization, (ii) at a rate of from 10⁻³to 10²s⁻¹, and (iii) for a rotation period to effect stress relief in the portion being formed.

2. The method of claim 1, wherein at least a part of the peripheral blank portion has an outside diameter exceeding the diameter of a finished part or an inside diameter less than the diameter of a finished part.

3. The method of claim 1, wherein the blank structure has not been preconditioned for superplastic deformation.

4. The method of claim 1, comprising preconditioning the blank structure for superplastic deformation.

5. The method of claim 1, wherein forming the blank comprises reducing the blank structure peripheral portion by rolling in a direction toward its central portion.

6. The method of claim 1, comprising forming an aluminum blank structure for a period not in excess of 0.25 s.

7. The method of claim 1, comprising forming a titanium blank structure or heat resistant nickel alloy blank structure for a period of 0.25 to 100 s.

8. The method of claim 1, comprising forming a coarse-grained blank structure for a period of 0.5 to 100 s.

9. The method of claim 1, comprising forming a fine-grained blank structure for a period of 10 to 50 s.

10. The method of claim 1, comprising forming a submicrocrystalline blank structure for a period of 0.25 to 10 s.

11. The method of claim 1, comprising forming the blank structure in a number of steps determined by the preformed condition and material of the blank structure.

12. The method of claim 1, comprising preparing the blank structure for superplastic deformation and preforming the blank structure into the shape of a sleeve, wherein forming the peripheral portion is completed in a single step.

13. The method of claim 1, comprising preparing both a central portion and the peripheral portion of the blank structure for superplastic deformation and forming a sleeve-shaped blank in a first step and forming the shaped part from the blank in a further step.

14. The method of claim 1, comprising performing a coarse-grained blank structure into a central portion and a thin-walled peripheral projection and forming the preformed blank into a sleeve-shaped blank being prepared in a first step and subjecting the sleeve-shaped blank to 50-75% reduction under superplaticity temperature and deformation rate conditions.

15. The method of claim 1, comprising forming in a first step effected by reversal roll motion.

16. The method of claim 1, comprising using a forming mandrel to form a part having varying thickness and diameter dimensions.

17. The method of claim 1, comprising forming in a first step effected by reversal roll motion and using a forming mandrel to form an interior surface of the blank structure.

18. The method of claim 1, comprising forming in a first step effected by reversal roll motion and using a forming mandrel to form an exterior surface of the blank structure.

19. The method of claim 1, comprising forming in a first step effected by reversal roll motion and using a built-up forming mandrel in a further forming step.

20. The method of claim 1, comprising forming in a first step effected by reversal roll motion and using a forming mandrel heated within a superplasticity range of the blank structure in a further forming step.

21. The method of claim 1, comprising preparing the blank structure for superplastic deformation and preforming the blank structure into the shape of a sleeve having a monotonically narrowing shape, wherein forming the peripheral portion is completed in a single step.

22. The method of claim 1, comprising preparing the blank structure for superplastic deformation and forming the blank structure into the shape of a sleeve having a monotonically narrowing shape, wherein forming the peripheral portion utilizes a single roll and a forming mandrel having an outside diameter equal to a minimum inside diameter of the blank peripheral portion.

23. The method of claim 1, wherein forming comprises using a first roll to form on a first side of the blank structure in a first step and using the first roll and a second roll at an opposite side in a second step.

24. The method of claim 1, comprising forming a fine-grained heat-resistant nickel alloy blank stricture at a temperature from the deformation temperature to a temperature of superplascity of the structure.

25. A device for making intricately-shaped axisymmetric part having a central portion and a peripheral portion, comprising

an axial blank structure fixing and rotating unit including a fixture for interchangeably installing a mandrel including a built-up mandrel;

at least one roll with a carrier;

actuating mechanism for rotating and displacing the roll relative to a blank structure fixed by the unit;

a furnace for heating the blank structure fixed by the unit, the furnace having a movable portion disposed around a window for introducing the roll into the furnace;

wherein the movable portion of the furnace is axially movable together with the roll over an entire working stroke length of the roll.

26. The device of claim 25, wherein the blank structure fixing and rotating unit comprises a shaft and sleeve for imparting torque to the blank structure.

27. The device of claim 25, wherein the roll carrier further comprises a heat shield.

28. The device of claim 25, comprising two rolls disposed on the opposite sides of a wall of the blank structure.

30. A method for making a part having a central portion and a peripheral portion, comprising:

preconditioning a blank structure for superplastic deformation;

forming the blank structure into the shape of a sleeve having a monotonically narrowing shape in a first step, forming a complete peripheral portion of the sleeve in a single second step (i) at a temperature above 0.4 the blank melting point but below the temperature of secondary recrystallization, (ii) at a rate of from 10⁻³to 10²s⁻¹, and (iii) for a rotation period to effect stress relief in the portion being formed.

31. The method of claim 30, comprising using a roll and a mandrel to form the sleeve shape in the first step and forming the complete peripheral portion in the single second step by use of two rolls disposed on opposite sides of a forming wall of the peripheral portion.