US2299105A - Method and apparatus for forging billets - Google Patents

Description

Oct. 20, 1942. V I w. P. MUIR 2,299,105

METHOD AND APPARATUS FOR FORGING BILLETS Filed March 18, 1940 6 Sheets-Sheet 1 35 13 F W A A INVENTOR W-PMUIR ATTOBNE S FIG. i

Oct. 20, 1942. w. P. MUIR METHOD AND APPARATUS FOR FORGING BILLETS 6 Sheets-Sheet 3 Filed March 18, 1940 @MVEF m m-FH w I ///l ris/ i m J $\\M H A 6 INVENTOR WIARMUIR Oct. 20, 1942. w. P. MUlR 2,299,105

METHOD AND APPARATUS FOR FORG-[NG BILLETS Filed March 1 1940 s Sheets-Sheet 5 Patented Oct. go, 1942 I METHOD AND APPARATUS FOR FORGING BILLETS William P. Muir, Ham assignor to Dominion pstead, Quebec, Canada, Engineering Works Limited, Lachine, Quebec, Canada Application March 18, 1940, Serial No. 324,604 1 Claim. I (Cl. 78-81) This invention relates to a method and apparatus for forging blanks from billets and has been especially devised to meet the requirements in the field of manufacture of artillery shells. The invention, however, isnot confined to this particular application but is also useful in other relations.

The old method of forging blanks for artillery shells was to pierce the blank by forcing a punch down through the middle of the billet, after which the billet was stripped from this punch and usually drawn through one or more dies to remove the taper caused by the fact that the billet was pierced in aclosed die pot. This method usually entailed a 3-operation forging. The first operation being to push the forging into the die pot, spreading it slightly to centre it; the second operation, piercing the forging; and the third, drawing same. Due to the change in volumes, the forging was usually upset into the'die and considerable extrusion around the punch occurred as the punch was being forced into the billet. This entaileda very considerable hydrostatic pressure in the plastic steel below the tip of the punch which has been called the plastic stress or deformation stress in the steel. This stress ran to a very high figure arid caused rapid destruction of the punch on its surface with consequent rough bores and the necessity for finished boring of the shell during machine operations.

A further process for shell forging was developed which eliminated a large portion of this excessive pressure. The cost of replacing the punch used in the piercing operation was excessive and it was felt that if the friction of the shell forging die during extrusion, particularly during the piercing operation, could be eliminated the excessive pressure on the punch would be considerably reduced and thus maintain a reasonable life of the punch. This led to the invention of an apparatus which was essentially a closeddie pot free to move in an axial direction with the bottom of the pot formed by a pin which completely filled the bottom end of the die pot and was supported firmly during the punching operation on the bottom platen of the press. During the extrusionpart of the operation, the die pot would rise with the shell, relieving, to some extent; the back pressure against extrusion and lessening to a large degree the fluid pressure on the end of the punch and, therefore, reduce the destruction of the punch surface. This operation Was very successful and the punch life was greatly lengthened. However, no attempt was made to forge shells with finished cavities.

A recent development has been made which consists of a method of forging which eliminates, to a large extent, the extrusion found in the above mentioned processes. This recent method is based on the idea of finished forged cavities without any subsequent boring. It was found that if the piercing operation was carried to the stage where extrusion took place the piercing punch could not be maintained in sufllciently good condition on the surface to give the smooth cavity required and that scoring and destruction of the surface in the piercing operation could not be removed in the subsequent drawing operation.

This led to the adoption of a process of using a square billet of such dimensions that the punch pierced through the centre of the square billet and formed it into a round one without-any lengthening in the piercing operation. This was very satisfactory from a piercing point of view and the life of the punch was considerably increased.- However, this necessitated an excessive reduction in the drawing operation. The reduction in the diameter of a. 4.5 inch shell in the drawing operation amounted to approximately 1 /4 inches in diameter. This led to a very extensive and cumbersome drawing press and precluded the possibility of using multiple punches in the drawing press, thereby greatly reducing production.

A further development has taken place along the same lines except that a lesser amount of drawing is used which enables the use of multiple punches in the drawing press, thereby increasing production.

After considering these various machines and the reasons for their use, I have made numerous experiments in order to overcome the problems which others have heretofore been faced with. I adopted the idea of using a square billet and then placed it in a loose fitting die. Contrary to expectations I found that the billet, upon being pierced, was not upset all the way down until the punch was nearly at the bottom of its stroke, at which time the die was completely filled and a slight amount of extrusion took place. This seemed to be a method of forging which would eliminate, to a large extent, the extrusion found in other methods and therefore wouldeliminate the destruction of the punch. However, it was soon discovered that a long slender square billet could not be held central in the die because the die must be tapered if it is solid and the square billet could not be properly centred without an upsetting operation to distort it into the die to hold it in position to receive the punch. This upsetting operation defeated it own end as it shortened the billet so that extrusion became necessary. It was also noted that, at the time extrusion took place, the force necessary to push the punch into the billet increased about three times even though the so.-called floating die pot arrangement was used.

The present invention is the result of a careful study of the previous methods and the problems encountered as well as the numerous experiments which I have made in this field.

A particular feature of this invention is in a process of operation which eliminates extrusion and the undesirable high pressures due to such extrusion. By this particular process of operation, the life of the forging punch is greatly extended and the punch is allowed to be depressed into the billet to its required depth with a minimum amount of back pressure onthe punch.

A further feature of the invention resides in the manner in which the billet is centered with reference to a guide in which the punch is positively guided during the billet piercing or forging operation. This eliminates eccentric forgings by ensuring that the punch will enter the billet in the centre;

A still further feature of the invention consists in providing die pots which maybe easily cleaned.

According to the present invention the bottom of the die pot is free to move relatively to the body of the pot and is hydraulically controlled so that, during the forging operation, said bottom is forced outwardly as the punch nears the end of its working stroke, the outward movement of the bottom being, against the resistance of an opposing hydraulic pressure which is regulated to give suflicient back pressure to ensure that the punch will complete the upsetting of the billet and cause the same to fill the mold without extrusion and without subjecting the punch to undesirable high pressures.

In the preferred embodiment of the invention the die pot comprises two hingedly connected sections which are closed together to grip and. centre the billet with reference to the guide in which the punch works during the piercing or forging operation. The bottom of the die pot consists of a pin carried by a piston element working in a hydraulic cylinder located beneath the pot. Oil under pressure is supplied to said cylinder to raise and hold the bottom of the pot in an elevated position at the commencement of the forging operation. As the punch descends and commences to pierce the upper end of the billet, the metal of this portion of the billet is spread with considerable pressure against the sides of the die chamber and the spread portion of the billet is thus forced to take the shape of the die on its outer surface. Further movement of the punch tends, in addition to spreading the billet against the sides of the die pot, to force the metal from the centre of the billet downwardly and this increases-the force acting on the movable bottom of the pot. When this force reaches a predetermined magnitude, determined by the hydrostatic pressure in said cylinder, the fluid beneath the piston attached to tht bottom of the pot is allowed to escape through an adjustablerelieve valve so that the bottom of the pot is allowed to recede ahead of the punch as the latter continues toward the end of its stroke. The adjustable relieve valve is set so that the hydraulic back pressure acting against the bottom of the pot as the latter recedes ahead of the punch is Just enough to enable the punch to complete the upsetting and spreading of the billet without extrusion and without subjecting the punch to undesirable high pressures. Other characteristic features of the present invention will be readily understood from the following detailed description taken in connection with the accompanying drawings, in which:

Fig. 1 is a front elevational view, partly in section, of my improved apparatus.

Figure 2 is a sectional plan view taken along the line AA of Fig. 1. This view shows one of the die pot sections in what may be termed the open position, while the other section is shown in what may be termed the closed position. This is merely to indicate the relation between the die pot sections and the punch guide in the open and closed positions of the die pot, since, in actual practice, both sections of the die pot will be operated to their open and closed positions simultaneously. I

Fig. 3 is a sectional plan view taken along the line BB of Fig. 1.

Fig. 4 is a sectional plan view taken along the line CC of Fig. 1.

Fig. 5 is a vertical sectional view taken along the line D-D of Fig. 1.

Figs. 6 to 10 inclusive are sectional views of the die pot showing the successive formations of the billet during the punching operation.

Fig. 11 is a sectional plan view of the split die pot in its closed position.

Fig. 12 is a diagrammatic view of the apparatus showing one form of hydraulic control circuit which may be employed in reducing the invention to practice.

Fig. 13 is' a view similar to Fig. 12 but showing certain elements in a diiierent operating position.

Fig. 14 is a longitudinal sectional view of a modified form of apparatus in which the punch operates in a horizontal direction, the plane of the section being substantially along the line I4--'I4 of Fig. 15.

Fig. 15 is a transverse sectional view taken substantially along the line I 5-45 of Fig. 14.

The invention will first be described in detail with reference to the construction shown in Figures 1 to 13 inclusive. In these figures I have shown a shell forging machine including a cap member ID, upper side frame members II, a cross member I2, lower side frame members I3 and a base I I, these parts being bolted together as indicated at I5.

The cap I0 forms part of a down stroking hydraulic press comprising a ram I6 operating in a vertical cylinder I1. The upper end of cylinder I1 extends intoa prefill tank I'Ia and is fitted with a conventional prefill valve Ill). The lower end of ram I6 is attached to a platen I8 which carries a rotary turret I9, the latter being secured to the underside of the platen in a position slightly to the rear of the central portion of the platen, as indicated at 20 in Figure 3. A plurality of punches 2I are secured to and depend from the underside of the turret I9. The platen I8 is also fastened to push back rams 22 working in the push back cylinders 23.

The cross member I2 is provided with three vertical openings designated 24, 24' and 25. The openings 24 and 24' are respectively aligned with tubular pipes 26 and 26' extending upwardly from a tank 21. The tank is filled with water which rises in the tubular members 26 and 26',

the latter sewing as cooling chambers in which the two idle punches 2| extend when the third punch is moving downwardly on its working stroke. The opening 25 is fitted with a tubular punch guide 28 which projects below the cross member I2.

A die pot generally indicated at 29 is mounted below the cross head l2. The body portion of the pot comprisestwo half sections 29a and 29b hinged to swing about a common vertical hinged pin 30, the ends of said pin being mounted in openings in the cross head l2 and the base l4, as shown to advantage in Figure 5. The die pot sections 290 and 29b are provided with lined semi-circular recesses 290 which conjointly provide a cylindrical billet receiving chamber 3| when the two halves of the die pot are closed together, as shown in Figure 11. In their closed positions the die pot sections 29a and 29b encircle the lower end of the punch guide 28 as shown to advantage in Figure 1. In this connection, it will be also noted that the lower portions of the die pot sections 29a and 29b close about a collar 32 which serves as a guide collar for the pin 48 which constitutes the movable bot om of the pot, 25 as clearly indicated in Figures 1 and 5 to inclusive. I

The two halves of the die pot 29 are moved to and locked in the closed position shown in Figures 1 and 11 by wedge members 33 working 30 in suitable guides 34, each wedge member being provided with a sloping surface 33a adapted for wedging engagement with a complementary sloping surface 29d formed on one of the die pot sections. Each wedge member 33 is attached to an operating plunger 35 working in a cylinder 36. In Figure 2, one of the wedges is shown in a die pot closing position while the other is shown in a die pot opening position. In practice, however, both wedges are operated simultaneously to their die pot opening or closing positions. When it is desired to close the die pot fluid pressure is supplied through pipes 36a and 36b to one end of each of the cylinders 36 to move the wedges 33 into wedging'engagement withfthe die pot sections 29a and 29b so that the latter are swung to and locked in their closed position. To open the die pot fluid pressure is supplid through pipes 360 and 36d to the opposite end of each cylinder 36 to effect a return stroke of the wedges 33. The wedges 33 are connected to the die pot sections 29a and 29b by chains 43 which serve to pull the die pot sections to open position during the return stroke of the wedges.

The previously mentioned collar 32 serves to centre the movable bottom pin 48 of the die pot with reference to the punch guide 28. Pin 48 is carried by a ram or piston element 44 working in a cylinder 45, the lower portion of which is enlarged to provide a pressure chamber 46. The movable piston or ram 44 is cored out to provide a cylinder 41 in which is fitted a stationary ram or piston 48 extending upwardly from the bottom of cylinder 45. The stationary piston orram 48 5 is provided with a central fluid passage 49 connected at its lower end to a fluid supply and exhaust line 58. The upper portion of cylinder is provided with two ports 5| and 52 connected respectively to fluid lines 53 and 54.

As shown in Figures 12 and 13 the flaw of fluid to and from the die pot cylinders 36, as well as the flow of fluid to and from the cylinder 41 of piston 44, is controlled by a manually operable valve generally indicated at 56. This valve com- 7 previously mentioned line prises a casing 51 and a movable valve member 58. Casing 51 is provided with ports 59, 68, 6| and 62. The casing ports 59 and 88 are respectively connected to opposite ends of the dash pot cylinders 36 by way of the previously mentioned pipes 36b and 36d. Pipe 36b is also connected by way of the previously mentioned pipe 50 to the fluid passage 49 of the stationary piston 48 contained in cylinder 45. The casing port 6| is con: nected by lines 63, 64, 65, stop valve .66 and line 61 to a pump or other source offluid under pressure. I Casing port 62 is connected by line 68 to an exhaust line 69 leading from the prefill tank. He. The movable valve element 58 of valve 56 is provided with an annular port 18 and a central port 1|. I

The port 5| of cylinder 45 is connected by the He, it being noted that line 53 is provided with a suitable check valve 18'. The port 52 of cylinder 45 is connected by the previously mentioned line 54 to the casing port 12 of a pressure regulating relief valve 13. Valve 13 is provided with a secf ond casing port 14 which is connected through line 65 and stop valve 66 to pressure supply line' 61. Communication between ports 12 and 14 of valve 13 is normally disrupted by a movable valve member 15 which isnormally held to its seat 16 by a valve closing spring 11 which exerts 'a predetermined pressure on said valve. The spring, 11 is opposed by a-spring 18 which may be placed under any suitable degree of compression by means of the regulating screw 19. When screw 19 is turned in the proper direction, compression is applied to spring 18 which, by opposing the valve closing pressure of spring 11, reduces the effective load on valve 15 to give a reduction in relief. In other words, the valve closing pressure of spring 11 may be balanced to any desired extent by increasing the opposing pressure offered by the spring 18.

The operation of the main ram l6 and the push I back rams 22 is controlled by a main control valve generally indicated at 8|. This valve comprises a casing element 82 and a movable valve element 83a. Casing 82 is provided with ports 83, 84, and 86. Port 83 is connected by line 81 to the upper end of the main pressing cylinder 1. Port 84 is connected by line 88 and branch lines 89 to the lower'ends of the push back cylinders 23. Port 84 of valve casing 82 is also connected, by line 99, to the prefill valve lib. Port 85 of valve casing 82 is connected to the previously men-.

tioned line 64 while port 86 is connected to the previously mentioned line 68. The movable'valve member 83 of valve 8| is provided with an annular port 9| and a central port 92.

The apparatus described herein is used in the following manner. Assuming the various elements to be positioned as shown in Figure 12, a long slender square billet 4|, Figures 6 to 11 inclusive is placed on the bottom pin 40 of the die pot and is then clamped in place .by closing the die pot sections 29 and 29a. The closing of the die pot is effected y shifting the movable valve element 58 of valve 56 from the position shown in Figure 12 to the position shown in Figure 13,. In this latter position of valve member 58 line 63 is connected to line 36b by the valve ports 6|, 18 and 59. Pressure fluid from supply line. 61 is thus admi -ted to one end of ca"h of the die pot cylinders 36 and acts against the p stons 35 to swing the die pot sections 29a. and 29b to the closed position shown in Figure 13. A portion of the pressure fluid thus supplied to line 36b 53to the prefill tank passes through line 50 and fluid passage 48 of stationary piston 48 and acts against the movable piston 44 to raise the latter to the position shown in Figure 13. Pin 48 is thus. raised to its starting position, represented by dotted lines in Figures 1 and 5 and by full lines in Figure 6. As the movable piston 44 is moved upwardly by the fluid pressure supplied through line 58 to cylinder 4! check valve I opens and cylinder 45 is filled with fluid supplied through the prefill tank Ha through line 53a, check valve 18' and port 5|. The oil thus supplied to cylinder 45 is trapped therein by the valves and 13 and assists in holding the pin 40 in its elevated position during the initial upsetting of the billet 4|.

After the die pot has been closed about the billet 4l, as previously described, the movable element 83a of the press control valve 82 is shifted from the position shown in Figure 12 to the position shown in Figure 13. In this latter posi-- tion of valve member 83 the fluid line 84 is connected to fluid line 8'! by the valve ports 85, 8| and 83. Pressure fluid is thus supplied to the upper end of the main pressing cylinder I! to move the ram l8 downwardly on its working stroke. The punch 2| is thus moved downwardly through the guide 28 which ensures that the punch will engage the centre of the billet, as

shown in Fig. 6. As the punch continues its downward movement it pierces the upper portion of the billet, as shown in Fig. 7, and causes this portion of the billet to be spread with considerable pressure against the sides of the die chamher and thus forces'the spread portion of the billet to take the shape of the die on its outer surface. Further downward movement of the punch tends to force the metal from the centre of the billet downward and this increases the force acting on the pin 48. When this force reaches a predetermined magnitude, determined by the setting of the relieve valve I3, fluid is allowed toescape from cylinder 45 through valve 13, the movable member of which is opened against the resistance of spring I! to establish communication between the pipes 54 and 85. In this connection it will be understood that the valve 13 is set so that the fluid pressure required in cylinder 45 to open this valve must be considerably greater than the pump pressure in line 61. It may also be pointed out here that a suitable accumulator (not shown) is connected to line 8'! at some suitable point between the shut-off valve 88 and the pump or other suitable source of fluid under pressure. The escape of fluid through relief valve 13 is regulated by he setting of valve member 15 so that the back pressure resisting the recession of pin" 48 is just sufiicient to enable the punch to complete the upsetting and spreading of the billet as the punch reaches the end of its working stroke. As shown in Figure 10 when the punch reaches the end of its working stroke the billet is pierced to the required depth and has been completely expanded to fill the die pot, producing a finished forging. When the forging step is completed the press is reversed by shifting the movable element 83a of the press control valve 8! from the position shown in Figure 13 to the position shown in Figure 12. In this position of valve member 82a the fluid previously supplied to the upper end of press cylinder I1 is relieved to exhaust line 89 through line 81, valve ports 83, 92, 88 and line 88.

At the same time pressure fluid from supply line 81 passes through line 84, valve ports 85, 9], 84 and lines 88 and 89 to the lower end of the push back cylinders 23 so that the push back rams 22 are raised to restore the press ram. l8 and the .punch 2| to the starting position shown in Figure 12. p g

During this upward or return'movement the punch 2| is stripped from the forged billet 4|. The movable valve element 88 of the die pot control valve 88 is now shifted from the position shown in Figure 13 to the position shown in Figure 12. In this position of valve member 48 the pistons are moved in a die pot opening direction by fluid pressure admitted to cylinders 38 through lines 81, 84, 88, valve ports 8|, 10, 80 and line 88d. At the same time, the fluid previously admitted to the opposite ends of cylinders 88 is exhausted through lines 38a, 38b, valve ports 58 and82 and lines 88 and 89. Since line 88 is connected to the line 3812 it will be evident that said line 50 serves bothas a supply and exhaust line for the cylinder 41 of the piston 44.

It is important to note that, during the progress of the forging operation illustrated in Figures 6 to 10, inclusive the plastic steel of the billet never flows in a direction opposite to the direction of movement of the punch 2|. In other words there is no upward flow or extrusion of the metal displaced by the punch. This absence of upward flow or extrusian is important since it reduces the pressure on the punch to a fraction of the pressure to which the punch is subjected where such' upward throw or extrusion occurs and materially prolongs the life of the punch.

The use of a sectional die pot arranged and operated as described herein has several advantages. It provides a convenient means for firmly clamping the billet so that it is accurately centered with reference to the punch. It also enables the die pot to be fully opened for inspection between forgings and permits the pot to be kept perfectly clean by means of an air lance.

A further advantage of the methodhere described is that cleaner bores can be had if it is possible to forge on one punch for the reason 'that any small pieces of scale or other foreign matter adhering to the punch, or the gas entrapped in the cavity upon insertion of the drawing punch, are necessarily eliminated with their subsequent marking of the bore on the finished forging, It has also been found that with heavy drawing operations, subsequent to the initial punch, it is necessary to cool the inside of the cavity to prevent the second punch from being punched through the bottom of the shell. This cooling entails'a chilling of the inside surface of the cavity which might very well cause a tearing of the metal on the surface of the second punch due to it not being in a plastic condition when heavy work is being done on the metal adjacent to the cool surface. That is, there is danger of this cooling of the shell and cold work ng of the metal on the inside causing cracks in the inside bore which will not readily be detected by ordinary inspection. These two objections are both eliminated by the use of a single operation forging where one punch only is used to produce the finished cavity.

While I have shown the platen l8 of the press equipped with three punches, it will be understood that only one punch is used in each operaembodied in a horizontal forging machine equipped with a conveyor which facilitates the ,handling of heavy billets. The main ram punch 2|, and push back rams 22 shown in Figure 14, are operated in the same manner as described in connection with Figures 1 to 13 inclusive. There is, however, a modification oi the die pot 29 as well as a slight modification in the relative arrangement of the die pot and the cylinder 45 containing the piston elements 44 and 48 which control the movement of the die pot bottom pin 40. In this connection it will be noted that the die pot section 29a is stationary while the die pot section 29b is free to swing about the connecting pivot 30. The closing of the die pot section 29a is accomplished by a wedge 94 connected to an operating piston 95 in a cylinder 96. The wedge 94 corresponds to one of the previously described wedges 33 and its operating piston 95 is operated inthe same manner as previously described in connection with the wedge operating pistons 35. The opening of the diepot section 291), as shown in Figures 14 and 15, is effected by a cylinder and piston device 91 which is connected between the die pot section 291) and a stationary part of the press frame structure. I have not thought it necessary to show how fluid is alternately supplied to and exhausted from opposite ends of the cylinder and piston device 91 during the opening and closing of the'die pot 29 since this may be accomplished in the same way as previously described in connection with the die pot control cylinders 36. 4

In Figure 14 I have shown a horizontal conveyor A working in a space B reserved between the cross head I2 and the cylinder 45. The billet 4| is placed on this conveyor and is moved to a position in line with the guide collar 32 and the pin 40, the latter being in the retracted position shown. When piston 44 is moved to the left by fluid supplied through fluid passage 49, as previously described, the pin 40 pushes the billet 4| onto the die pot section 290, die pot section 29b being at this time in its open position. When pin 40 has reached the limit of its stroke to the left, the die pot section 29b is closed by operation of the piston 95 and the press ram H is then operated on its working stroke to commence the forging operation which proceeds substantially as described in connection with Figures 1 to 13 inclusive. When the forging operation is completed and the punch 2| is stripped from the forging billet by the return stroke of the press ram Hi, the die pot 29 is opened and the punch 2| is then moved to the right to push the forging billet back onto the conveyor A.

It may also be pointed out that, in some cases, it is preferable to provide a direct connection 99, indicated by dotted lines in Fig. 12, between port 14 of valve 13 and exhaust line 69. These and other modifications are considered to fall within the scope and spirit of the invention as defined 'by the appended claim.

From the foregoing description it will be obvious that I have provided a type of forging press in which the friction betweenthe billet metal and the side or body wall of the die pot actually assists the flow of metal upwardly over the surface of the punch as the latter travels downwardly beyond the point where the pressure beneath the tip of the punch becomes high enough to commence downward displacement of the bottom wall of the die pot. In this connection it will be evident that tension stresses are set up in an upper zone of the billet metal surrounding the descending punch and that said stresses assist the flow of metal from beneath thetip of the punch and thereby tend to keep the plastic pressure beneath the tip of the punch at a relatively low value compared with conventional forging practice.

Having thus described my invention, what I claim is:

The herein described method of forging shells and other hollow articles in a sectional die pot provided with a sectional body wall and'a movable bottom wall which comprises placing a solid billet on said bottom wall and closing the body wall sections inwardly upon the billet so that the latter is tightly seized and held by said body wall sections and then forcing a piercing punch into the upper end of the die pot and into said "billet while applying to the bottom wall of the pot a restraining pressure which is predetermined to permit said wall to be displaced in a die pot lengthening direction by elongation of the billet due to the action of the piercing punch as the latter advances toward the end of its working stroke, said method being characterized in that the restraining pressure applied to said bottom wall is predetermined to give a back pressure against the billet metal which is Just suflicient to permit the punch to complete th upsetting and elongation of the billet without extrusion.

WILLIAM P. MUIR.

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