US2368603A - Apparatus for forging billets - Google Patents

Description

length and does not have the same crowding and pressure increasing effect as the tapered punch.

, When a tapered punch is used the body wall of the die pot will be moved in a die pot lengthen-;

ing direction by its frictional contact with the flowing metal but, since the velocity of motion imparted to the metal is not uniform over the in its lowermost position with the lugs 23 resting on the supporting enlargements 25 of the guide rods l9, the-lower ends of said guide rods being screwed into sockets 26 provided in the length of the punch or throughout the area of l contact between the metal and said wall, the die pot lengthening motion of the latter cannot relieve all of the plastic pressure increase due to the previously mentioned crowding action'of the tapered portion of the punch. The present invention overcomes this difliculty since it provides a means whereby the body wall of the die pot may be moved in a die pot lengthening direction at a rate such that the frictional contact between said wall and the billet metal is utilized to assist flow of metal over the surface of the advancing punch. When a tapered punch is used the velocity of motion imparted to the body wall of the die pot in a die pot lengthening direction is at least equal to the maximum velocity of motion of the metal flowing over the tapered portion of the punch. v

The present application is a division of our co-pending United States application Serial No. 342,530, filed June 26, 1940.

Proceeding now to a more detailed description of thi invention reference will be had to the accompanying drawing-in whichv Fig. 1 is a view, partly in section and partly in elevation, of one form of shell forging apparatus which may be used for, carrying out the present invention.

Fig. 2 is a diagrammatic view illustrating the conditions obtained when a tapered billet piercing punch is employed in the forging operation.

Referring more particularly to Fig. 1, '5 designates the upper movable platen and 6 the lower stationary platen of a forging press. The billet piercing punch is indicated at This punch is provided with a threaded upper end 8 which is screwed into a threaded socket 9 formed in the central projection H] of a punch holder H which is fastened to the underside of the platen 5. The unch 1 is provided with a shoulder forming portion |2 which is jammed tightly against the lower end of the projection when the threaded portion 8 of the punch is screwed home.

A vertically movable plunger carrying plate I3 is positioned below and in the path of movement of the die holder so that this plate is forced to move downwardly with the die holder during a portion of the downward working stroke of the billet piercing punch I. Plate |3 carries two plungers l5 arranged at opposite sides of the punch 1, said plungers being provided with threaded upper portions l6 which are screwed into the plate sockets ll until the shoulder forming portions I8 of the plungers are jammed tightly against the underside of the plate, Plate I3 is guided by a pair of guide rods l9 which pass upwardly through the guide openings 20 provided adjacent the ends of said plate. Springs 2|, encircling the guide rods l9 below plate l3, act

upwardly against the lower surface of said plate lower tationary platen 6. Casting 24 is also provided with additional guide lugs 21 which slide on the portions of the guide rods located below the enlargements 25.

The central portion of casting 24 is pierced by a central cylindrical bore 29, the wall of which constitutes the body wall of the die pot chamber A in which the billet B is forged during the working stroke of the punch I. The bottom of chamber A is formed by a cylindrical member 30 which is fixed to the stationary platen 6 and is slidably fitted in the lower portion of the bore 29. Member 30 is provided with a stripper pin 3| working in the guide bore 32.

The plungers l5 are slidably fitted in guide bores 33 which are provided in the upper portion of the casting 24 and which communicate, at their lower ends, with chambers 34 provided in the lower portion of said casting. Stationary plungers 35 are fastened to the platen 6 so that they extend upwardly into the chambers 34. These plungers 35 are provided with cavities 36 into which the lower portions of the movable plungers l5 are forced by the downward movement of the plate I3. The upper portions of the chambers 34 are reduced in diameter to provide shoulders 31 which rest on'the upper ends of the stationary plungers 35 when casting 24 is disposed in the lowermost position which it occupies prior to commencement of the forging operation.

When plate l3 and casting 24 are in the position which they occupy prior to commencement of the forging ope1"ation,'the chambers 34 and the communicating cavities '33 are completely filled with liquid which is supplied from tank 39 by way of pipes 4| and 42, the pipe 4| being pro- 'vided with a pressure relief'valve 43 and a manually operable filling valve 44, the latter being located between valve 43 and the tank 45.

The plate l3 and the casting 24 remain in their initial positions during the downward or working stroke of the punch 1 until the die holder contacts the upper surface of plate l3. When this occurs the plate I3 moves downwardly with the punch I until the latter has completed its working stroke and is retracted to its starting position above and clear of the die pot chamber A. During the downward movement of plate l3 the plungers l5 are advanced into the chambers 34 and into the cavities 36 of the stationary plungers 35. The hydraulic pressure in the chambers 34 and cavities 36 is thus intensified so that the casting 24 is forced to move upwardly in a die pot lengthening direction against the slight resistance of the springs 2| and this lengthening of the die pot continues until the punch 1 has completed its working stroke. The parts are preferably designed so that the upward die pot lengthening movement of casting 24 proceeds at a velocity which is at least equal to the maximum velocity of the billet metal which is caused to flow upwardly around the tapered portion Ia of the punch as the punch proceeds beyond that point of its working stroke at which the full length of the billet is expanded into frictional contact with the die pot wall 29 as shown, for example, in Fig. 2.

When the punch '1 has completed its working stroke it is raised above and clear of the die pot chamber A by the return stroke of the press platen so that the billet B may be expelled from the die pot chamber by operation of the stripper pin 3|. As the die holder H is raised to its initial starting position the plate I3 is forced upwardly by the springs 2! to withdraw the plungers l5 from the cavities 36 and the chambers 34 so that the hydraulic pressure acting against the 34 and the cavities 36 by the downward movement of the plungers l5 serves to take the weight of the axially movable body portionof the. die

pot off the billet and, at the same time, utilizesv the friction between the billet metal and the upwardly moving wall of the die pot chamber to assist in drawing the metal upwardly over the surface of the punch.

In the It may be pointed out here that it is the decrease in volume from B to A with consequent increase in the velocity of motion of the .particles of the metal from B to A which defeats, to a large extent, the beneficial effect of using a die pot provided with an axially movable body wall which is carried upwardly solely by the flowing action of the displaced billet metal in frictional contact therewith. In this instance the axially movable body wall of the die pot will be carried upwardly by the extruded or upwardly flowing metal in frictional contact therewith but, as the velocity of the metal is not constant from B to A, such upward movement of the body wall of the die pot cannot relieve all of the crowding effect of decreasing areas from B to A. The

present invention is based on the discovery that It is thought that the following explanation of the conditions obtaining when the forging operation is carried out with the aid of apunch having a tapered tip portion will be conducive to a clearer understanding of the functioning and advantages of the invention described herein. In this connection reference will be had to Fig. 2

in which the punch l is shown advanced to that point of its working stroke at which the billet B is upset or expanded so that the-whole length of the billet is in frictional engagement with the surrounding portion of the body wall of the die pot. As the punch advances beyond thispoint the resulting diminution of the space between the bottomlwall of the die chamber A and the advancing tip of the punch causes the metal of the billet to flow upwardly along the surface of the punch. The shape of the'tapered portion 1a prescribes that the metal at a point B must be further compressed to flow toward the point A and this results in a rise or upward flow of the metal between A and B at varying velocities relative to the punch and in a direction opposite to the billet piercing motion of the punch. Ob-

viously, as the punch advances the metal must rise with increasing velocity relative to the tapered portion of the punch and the surrounding wall of the die pot until it reaches the point A and passes to the zone between the body wall of the die pot and the cylindrical surface of the punch where no further reduction ofthe shell wall takes place by reason of the advancingmotion of the punch. Due to the fact that the metal flowing directly from zone B to zone A is forced to do so by reason of the plastic pressure causes a building up of such pressure between A and B.

this difficulty may be overcome by imparting to the axially movable body wall 24 of the die pot a motion relative to the bottom member 30 which is in excessof that motion which the body wall-would have solely by reason of its frictional contact with the retarded or upwardly flowing metal. To this end the present invention, as previously explained, provides means whereby the upward movement of the body wall of the die pot is effected by the application of a controlled force other than the force exerted by the upwardly flowing metal in contact with said wall. In the latter instance the friction grip of the metal on thedie pot wall is utilized to assist the motion'of the metal relative to the punch from zone B to A. With this arrange-. ment a state of tension is. created in the metal which partially oifsetsthe compression of the 8 metal due to the reducing areas of cross section which the metal is forced to traverse in flowing from B to A and the result of this is to effect a considerable reduction in the plastic pressure under the tip of the punch and in zone B with consequent further reduction in the frictional resistance to flow of the metal on the surface of the punch. This, in turn, has the effect of reducing the scoring effect on the punch surface so that the useful life of the-punch is considerably prolonged, in addition to making feasible. in a single forging operation, the roduction of forgings having full length smooth or finished cavities.

Having thus described our invention, what we claim is:

Apparatus for forging shells or other hollow articles comprising a billet receiving die pot pro vided with relatively movable bottom and body wall portions, a piercing punch and means including a power actuated punch holder for advancing and .retracting said piercing punch so that, during the advancing movement thereof, the punch is forced against a billet contained in said die pot to form a cavity in said billet and to expand the billet into frictional contact with the body wall of the die pot, hydraulic pressure applying means operable to effect relative movement of the bottom and body wall portions of the die pot in a die pot lengthening direction during the forging operation, and means actuated by said punch holder for operating said hydraulic pressure applying means when the holder has advanced the piercing punch to a predetermined point of its working stroke.

HUBERT G. WELSFORD. WILLIAM P. MUIR.

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