US3670545A - Bulge-forming apparatus - Google Patents

Abstract

Power cylinders at each end of a tubular workpiece having a force transmitting medium therein operable by the cylinders to force the workpiece into mold cavities. The force transmitting medium is an incompressible plastic such as a polyurethane plug with a memory which returns to its original configuration when the pressure is removed. The retention force between the opposing cylinders is transmitted through the mold die.

Description

United States Patent Kent et al. [4 1 June 20, 1972 s41 DULCE-FORMING APPARATUS OTHER PUBLICATIONS [72] In e Ronald KQIIQ f Alvin Tips to Successful Bulging With Urethane Rod" by Joseph Rothell rl R ling 8, h of C Turner; pp. 14- 16 of The Tool 8 Manufacturing Engn; Sept. [73] Assignee: McDonnell Douglas Corporation 1968; 61

[ Filed: on. 1970 Primary Examiner-Richard J. Herbst [21] APP] NOJ 85,103 Attorney-Walter J. Jason, Donald L. Royer and Robert O.

- Richardson [52] LS. Cl ..72/58, 29/157 T 57 ABSTRACT [51] Int. (I 21d 9/05 l [58] Field of Search ..72/54, 58, 60, 61, 62; Power cylinders at each end of a tubular workpiece having a 29/157 T force transmitting medium therein operable by the cylinders to force the workpiece into mold cavities. The force trans- Refmnm Cited mitting medium is an incompressible plastic such as a polyu- UNITED STATES PATENTS rethane plug With a memory which returns to its ong nal configuration when the pressure 1s removed. The retention force 2,603,175 7/1952 Wurzburger ..29/ 157 T between h opposing li d i t a mitted through the 2,975,510 3/1961 Heuss et a]. ....29/157 T mold i 2,713,314 7/1955 Leuthesser, Jr. et al.. ..72/58 3,220,098 1 1/1965 Arbogast ..29/421 3 China, 7 Drawing Figures a a2 7 n 0 W2 BULGE-FORMING APPARATUS BACKGROUND OF THE INVENTION Ducts other than straight tube or tubing bent on a tube bender are nonnally formed in two or more half shells and welded together to make a completed duct. Ducts fabricated by this method are high cost items to make and in many cases the quality of the parts results in failures and rejections. Material costs are high due to extra material required for drop-hammer forming.

Bulge formed parts make a stronger, better quality part that will substantially reduce the number of rejected parts and total cost. One such apparatus uses a resilient material such as rubber for pushing the workpiece into the mold cavity. However, at extreme pressures and at the heat thus generated the resilient material deteriorated and its useful life was too short to be practical. A liquid medium such as hydraulic fluid was tried but at high pressures leakage problems made this approach unworkable. In one application oil pressure ruptured the workpiece before the part could be defonned the desired amount.

When high pressures are used in the deformation of a workpiece, and in particular when opposing power cylinders are used, great structural strength is needed in the interconnection of the parts exerting the force and the parts having the force exerted thereon.

SUMMARY OF THE PRESENT INVENTION A pair of opposing power cylinders with an interconnecting polyurethane plug within the workpiece is used to exert an outward force on the plug and deform the workpiece outwardly into the cavities of the die into which the workpiece had been positioned. The power cylinders are interconnected through tension plates and the die itself. In one forming setup heavy tension plates serve as a base to which the lower die half and the actuating mechanisms are attached. The base plates are positioned on the bed of a press, and the upper die half interconnects the tension plates attached to the ram of the press. The actuating mechanisms may be spaced apart in accordance with the length of the dies used. The press provides the necessary clamping pressure during the forming operafions. The innerlocking design of the forming structure permits all thrust loads to be confined within the setup, protecting the press from damage that can occur from the extremely high pressures which can be exerted.

The polyurethane plug has a memory and, after a pressure of 20,000 psi, will return to its original shape in less than seconds. However, it must have a shore hardness of 90-95 on the D scale of a shore hardness machine such as that widely accepted in industry and marketed by Shore Instruments and Manufacturing Company, Jamaica, New York. The plug also must be free from air bubbles to prevent explosion. The plug can be cast by pouring it in liquid form into tubing of standard production sizes. lt shrinks slightly as it cures, and fits production tubing perfectly for the forming operations. After about 1,000 deformations the plug finally becomes permanently defonned but can be easily machined back to the proper diameter and reused indefinitely.

The bulge-forming procedure eliminates the pressure sizing and secondary metal deposits which were problems in drophammer forming. Special trimming, weld smoothing, and other time-consuming hand operations are no longer required. Material thinning, which was a serious problem with drophammer forming, is inconsequential with this process.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a duct made by prior art methods;

FIG. 2 is a perspective view, partly broken away, showing the incompressible plastic plug within a tube to be formed;

FIG. 3 is a perspective view of a tube after the first stage bulge-forming operation;

FIG. 4 is a perspective view of the formed tube after final bulge and the tube is ready for use;

FIG. 5 is a perspective view of another tube shape alter the bulge-forming operation;

FIG. 6 is an elevational view partly in section of the bulgeforrning apparatus in its pre-compression position; and

FIG. 7 is a similar view with the apparatus in compressed position.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS Reference is now made to FIG. 1 wherein is shown a prior art tubular duct consisting of two halves l0 and 12 which have been formed by a drip-hammer technique. The drop-hammer forming operation stamps the metal into a female die to form a semi-cylindrical section with a T opening portion 14 extending outwardly from the'axis of the cylinder. The two sections are then welded along their mating edges 16 and 18. After the half sections have been welded, tool coordination, trimming and other handling operations are required which affect the quality and cost.

A similar T shaped duct may be formed in accordance with the present invention in which illustrative steps are shown in FIGS. 2, 3 and 4. In FIG. 2 there is shown an annealed tubular blank 20 which may be of some forrnable material such as titanium, stainless steel, aluminum or high strength material known as lnconel. Within this tubular blank is an incompressible plastic, such as a polyurethane plug 22. One such plug is made by'Aerolast Company, Inc., 3235 San Fernando Road, Los Angeles, California 90065, and is now available under the trademark of Aerolast 2001A. In the bulge-forming process, the blank 20 and plug 22 in FIG. 2.are placed into a female die of appropriate shape. Hydraulic pressure is applied to the ends of the plug, forcing the material into the cavities of the die and makingthe tube wall conform to the desired shape. Split dies with internal cavities are generally used for bulge-forming to provide the shape into which the wall of the tubular blank is forced. If multiple operations are required, the die is made to the final configuration and spacers are provided which are removed individually after each operation until the material is incrementally forced to the maximum depth required. Simple shapes can be formed in a single operation at reasonable production rates.

FIG. 3 shows the tubular blank 20 after the bulging operation has been performed and a portion 24 of the tube has been expanded into a female die. The bulge may be cut or ground out and re-annealed before final forming. FIG. 4 shows the part after the final trimming and ready for use.

A wide variety of parts can be produced by the bulge-forming technique. The workpieces need not have a straight axis but may be curved or angular or have compound or multiple bulges. Deformable material in sheet form may also be. used. The various cross-sections of the workpiece may be of any configuration before forming, although obviously the plug,

workpiece and die must be of compatible shape for the bulgeforming process to be efiective. By way of example,.a titanium ring adapter is shown in FIG. 5 wherein the midsection 26 has been bulged out and has a larger diameter than its ends 28 and 30.

Exemplary apparatus for the bulge-forming operation is shown in FIGS. 6 and 7. A pair of tension plates 32, 34 are positioned on the bed 36 of a punch press. The upper surface of the plates has grooves 38, 40, 42 and 44 to receive flanges 48, 50, 52 and 54 of a pair of opposed power cylinders 56 and 58. These power cylinders may be hydraulically or pneumatically actuated through conduit lines 57 and 59. These power cylinders have pistons 60 and 62 which, when actuated, move inwardly in the direction of the arrows 64, 66. The lower half of a female die 68 has grooves 70 and 72 thereon which fit over the tongues 74, 76 in the tension plates 32 and 34.

The tension plates 32 and 34 may be spaced any desired length apart depending upon the length of the female die 68' and a spacer block 78 is positioned therebetween. This block takes bending moments out of the die 68 during the bulgeforming operation.

The tube 80 to be formed, with the incompressible plastic plug 82 within it, is place in the lower half 68 of the female die and then the top half 84 of the female die is placed over it. A pair of top tension plates 86, 88 are positioned over the upper half of the female die 84 and have recesses 90, 92, 94 and 96 for engaging the top portions of the flanges 38, 40, 42 and 44 on the power cylinders 56 and 58. Tension plates 86 and 88 also have tongues98 and 100 for engaging recesses 102 and 104 in the upper half of the die 84. A spacer block 106 positioned between plates 86 and 88, and between the upper half 84 of the die and the head 108 of the punch press, removes the bending moment from the die. Soft metal caps 110 and 112 are at the ends of the plastic plug 82 to prevent flow of the plastic from the plug 82 when under pressure.

A cavity 114 is in the lower portion of the die 68 into which the surface of the tube 80 will be deformed, as shown in FIG. 7. Here is shown mid-portion 112 of the tube 80 depressed into die cavity 1 14 as the plastic material 82 within the tube 80 has been deformed under pressure from the pistons 60 and 62. The retention forces holding the cylinders 56, 58 in a fixed spaced relationship, while the pistons 60, 62 move inwardly, pass through the tension plates 32, 34, 86, 88 and the die halves 68, 84. After the deformation, the pistons 60 and 62 are returned to their pre-compression positions as shown in FIG. 6 and by the time the mold dies are opened, the plastic plug 82 has returned to its original configuration and can readily be removed from the tube 80.

Having thus described an illustrative embodiment of the present invention, it is to be understood that other embodiments will occur to those skilled in the art and that these modifications are to be construed as part of the present invention.

We claim:

1. A bulge-forming apparatus for deforming a workpiece comprising:

a female die having an internal cavity therein, said die being adapted to receive said workpiece therein,

an incompressible plastic plug within said die,

pressure means exerting a pressure on said plug to force said workpiece into said cavity,

said pressure means comprising a pair of opposed power cylinders with pistons protruding into said die and engageable with said plug, and retention means for retaining said cylinders in predetemtined spaced relationship,

said retention means including tension plates interconnecting said power cylinders to said die said tension plates having grooves and said power cylinders having flanges thereon adapted to fit within said grooves to prevent lateral movement therebetween, said die and said plates having coordinating tongues and grooves to prevent lateral movement therebetween, and

means for applying forces normal to said tension plates to retain interlocking of said plates, cylinders and die when pressure is applied to said plug.

2. A bulge-forming apparatus as in' claim 1, and spacer blocks between said tension plates to permit varied spacing of said cylinders to accommodate dies of various lengths and to remove bending moments from said dies.

3. A bulge-forming apparatus as in claim 1 wherein said plug is of a polyurethane plastic material deformable under pressure and has a memory to return to its original configuration when said pressure is released, and

wherein said plug is air bubble free polyurethane having a shore hardness of from to on the D scale.

Claims (3)

1. A bulge-forming apparatus for deforming a workpiece comprising: a female die having an internal cavity therein, said die being adapted to receive said workpiece therein, an incompressible plastic plug within said die, pressure means exerting a pressure on said plug to force said workpiece into said cavity, said pressure means comprising a pair of opposed power cylinders with pistons protruding into said die and engageable with said plug, and retention means for retaining said cylinders in predetermined spaced relationship, said retention means including tension plates interconnecting said power cylinders to said die said tension plates having grooves and said power cylinders having flanges thereon adapted to fit within said grooves to prevent lateral movement therebetween, said die and said plates having coordinaTing tongues and grooves to prevent lateral movement therebetween, and means for applying forces normal to said tension plates to retain interlocking of said plates, cylinders and die when pressure is applied to said plug.

2. A bulge-forming apparatus as in claim 1, and spacer blocks between said tension plates to permit varied spacing of said cylinders to accommodate dies of various lengths and to remove bending moments from said dies.

3. A bulge-forming apparatus as in claim 1 wherein said plug is of a polyurethane plastic material deformable under pressure and has a memory to return to its original configuration when said pressure is released, and wherein said plug is air bubble free polyurethane having a shore hardness of from 90 to 95 on the D scale.

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