METHOD AND MACHINE FOR HIGH ENERGY RATE FORMING

Abstract: Method of high energy rate forming of metals and other ductile materials, wherein a transmission medium is used for transferring a discharge of power for acting on a blank with a force sufficient for forming the blank. In the method the discharge of power is provided by imparting kinetic energy to the transmission medium by rotating the medium, in the form of a liquid, and by essentially momentarily converting kinetic energy into a pressure that acts on the blank. A machine for carrying out the method comprises a container (9, 10, 11) which together with a liquid contained in it can be caused to rotate. A discharge pipe (16) is arranged to guide the liquid, once said liquid has obtained a predetermined kinetic energy, essentially momentarily, in a direction towards a tool (28, 28A, 28B) that contains the blank (e.g. 26) to thereby exert, in a simple manner and without any risk, a predetermined pressure against the blank to form it.

Description: Method and machine for high energy rate forming This invention relates to a method of high energy rate forming of metals and other ductile materials. High energy rate forming is a forming method by which the necessary amount of deformation energy is intro¬ duced over a relatively short time interval ranging from micro- to milliseconds. In the litterature is described explosive forming where an explosive charge is detonated transferring energy to the blank via water or another suitable transmitting media. This process is often used in the stretch or draw forming of sheet metal, e.g. in the production of tank heads. A related process is electrohydraulic form¬ ing where, instead of being provided by detonation of explosives, the power is prcvid.ed by discharge of elec¬ tric energy from a capacitor bank o-;er £_, spark gap sub¬ merged in the medium of transmission. Other high energy rate forming methods use compressed gases to accelerate a piston with a tool acting on a stationary tool part. This method, termed indirect high energy rate forming, is mostly used in swaging and pow¬ der-pressing as well as punching and cropping operations, Explosive forming has the drawback that it requires spe¬ cially trained personnel for safety reasons. In additi- on, the efficiency is relatively low because only part of the energy spent can be directed towards the blank to be deformed. Electrohydraulic forming requires ex¬ cessive investments in the bank of capacitors, electric control etc., and again, the efficiency is low. Fur- O PI / , VIFO . thermore, in the methods mentioned the deformation ener¬ gy is introduced in such a brief interval that most of¬ ten it is necessary to evacuate the space behind the blank, which complicates the procedure to some extent. The object of the invention is to provide a method of high energy rate forming which as opposed to the prior art allows a more flexible preadjust ent of the form¬ ing course and which can be carried out by a machine which is sa er and cheaper than the known machines for high energy rate forming. This object is achieved by carrying out the method as stated in the characterizing portion of claim 1, it being possible to control the forming e.g. in depen¬ dence upon the density, speed, and viscosity of the transmission medium (e.g. water) used and upon the flow conditions provided for the liquid. The method defined in claim 2 provides advantages in terms of installation because it obviates the necessity of adding and discharging liquid. The same liquid may thus be used again and again. The invention also relates to a machine for carrying out the method, said machine being constructed as de- scribed in the characterizing portion of claim 3« Claims 4-6 provide preferred embodiments of the tool for the machine of claim 3« The invention will be explained in greater detail in the following description of some embodiments with re¬ ference to the drawings, in which 0?-IPI_ fig. 1 is a vertical section of an embodiment of a ma- chine according to the invention, with a tool for stretch or draw forming of sheet blanks, fig. 2 a horizontal section of same, fig. 3 another tool for the machine of figs. 1 and 2 for forming a tubular blank, fig. 4 a tube as formed, fig. 5 a vertical section of an indirectly acting tool for the machine of figs. 1 and 2, and fig. 6 an object produced by the tool of fig. 5. The machine is built around three heavy plates 1, 2, and 3_ which are maintained in suitable spaced relation¬ ship by means of columns 4. The plates 1 and 2 are pro¬ vided with bearings 5 and 6 for a shaft 7 provided with a flange 8. On the flange 8 is fitted a cylindrical container consisting of a circular bottom 9, a shell 10, and a ring-shaped plate 11 whose internal diameter is considerably smaller than that of the shell. The container may be rotated in the direction of the arrow A by means of a motor 12 via a transmission 13. The plates 2 and 3 are furthermore provided with bear¬ ings ' 14 and 15 for a pipe 16, whose bottom* part is form¬ ed with a 90 bend in the vertical plane and another bend of about 60° in the horizontal plane. The latter bend is oriented with its opening pointing towards the direction of rotation of the container. The pipe 16 may be turned approx. 60° about its vertical axis in such way that its bottom opening in one position (dashed) is disposed within the inner edge of the plate ring 11 and in its other extreme position (dotted) close to the in¬ ternal surface of the shell 10. The upper opening of the pipe 16 is connected to a tool which is fitted on the plate '3 and comprises an openable forming part 28 which may be secured in liquid tight relationship with the plate 3 by means of a hasp 27 , optionally via a seal. The tool is arranged to receive a plate-shaped blank, such as a disc 26, so that one side of the disc is connected to the pipe 16, while the other side faces a cavity defined by the tool 28. The pipe 16 is provided with a control guide 17 which serves to limit the angular rotation as it hits the stop dogs 18 and 19. These are located on the bottom side of the plate 3 before the vertical section plane. Normally the pipe is in the position indicated by dash¬ ed line in which the guj.de 17 is held in contact with the dog 19 by means of a spring 20, A compressed air cylinder 21 or another type of actuator is able to turn the guide 17 towards stop dog 18 when the forming is to take place, which will be explained below. After the container has been brought into rotation with the speed required for the forming operation in question, water is introduced through the pipe 22 and the valve 23. Due to the rotation of the container the water is flung outwards and fills the annular part of the con¬ tainer. During the filling procedure the water surface, which is practically vertical, gradually moves inwards and thereby acts on a plate 24 which interrupts the sup¬ ply of water via a switch 25 when the surface approach¬ es the internal edge of the plate ring 11. The blank 26 ' is placed on top of the plate 3 and the tool is closed onto the blank by means of the hasp 27. Forming is brought into effect by activating the cylin-. der 21 whose piston rod is provided with a pin 29 en- GMPI gaging a notch in the guide 17. This causes the pipe 16 to turn-, its lower opening swinging outwards so that its outer edge penetrates the cylindrically shaped water surface. Due to the velocity of the water, the pipe then momentarily turns into the position indicated by dotted line where it is stopped by stop dog 18 which is provid¬ ed with a rubber buffer. From this it appears that the cylinder 21 only performs the first part of the angular rotation effected, and the cylinder is controlled so as to immediately return to the starting position: After the pipe opening has been swung outwards the iner¬ tia in the rotating body of water forces water inwards and upwards through the pipe 16 where it hits the blank 26. " When the water hits the blank a considerable pres¬ sure is created which starts the forming operation by lifting the mid section of the blank free of the inlet opening. As the amount of water in the container has a considerably greater- volume than cavity formed by the tool and the blank, water continues to flow through the pipe 16 until the blank has been fully formed and rests against the internal surface of the tool. This inter¬ rupts the flow through the pipe 16, and the force, which maintained the bottom opening in its position near the periphery of the container, is reduced to zero. At this moment the cylinder 21 has returned and the pipe 16 is returned to its starting position by a spring 20. During forming, the air contained in the tool above the blank is pressed out through a hole 30 and since the speed of forming is low compared with explosive forming, there is no harmful counter pressure build-up which might necessitate evacuation of the tool cavity. After the forming has been completed within few milli¬ seconds, the water runs back into the rotating contain¬ er through the pipe 16. " When the amount of water used returns to the circuit, the speed of rotation is reduc- ed for a while, but then it increases again until the motor 12 has resupplied the amount of energy used to the system. In the meantime the operator has opened the tool, removed the finished part and inserted a new blank, and then the machine is ready for the next cycle. The advantage of having the pressure medium contained in a rotating container is that flow losses are virtual¬ ly eliminated during the comparatively long periods in which the machine is idle. Instead of the shown tool for forming plate blanks, the machine described may be provided with another tool for other high energy rate forming operations. Fig. 3 shows ε tool 28A which is arranged to be fitted on the plate 3 and designed to provide two annular por¬ tions of locally increased diameter in a metal pipe. The metal pipe is inserted in the tool 28A which is cen¬ trally split in a vertical plane and bolted to the plate above the upper opening of the pipe 16. By the same pro¬ cedure as described above may be produced the finished object shown in fig. 4 by high energy rate forming. Fig. 5 shows a tool 28B which is arranged for indirect forming. The tool 28B comprises a hollow, upwardly closed piston 31 which is vertically movable in the pipe 16. The piston is provided with an annular seal 32 and the top of the piston has mounted thereon a tool part 33 on which a blank 34 is placed. The tool part 33 acts . on a stationary tool part 35 which is mounted on a OMFI bridge across the working area. The bridge is clamped on the plate 3 " by means of a bolt 36 which extends through spacer pipe 37. When the pipe 16 is turned, water momentarily fills the hollow piston which is thus given an upward acceleration to forge the blank in the desired shape. Fig. 6 shows a finished object. It appears from the description that a machine for carrying out the invention may be built without great precision requirements and that it contains very few complicated components. It is therefore possible to build very large units at reasonable costs and for the production of tank heads a diameter of the rotating container of 2 meters or more is very well conceiv¬ able. Complete forming in the tool used requires; besides a sufficient amount of water, the presence of sufficient kinetic energy. If this is not the case, the blank will get an approximately comi-elliptical cross section without reaching the internal tool surface. This is called free forming, and in the field of explosive forming it is used in the production of e.g. tank heads. The advantage of this method in which the degree of deformation is only dependent on the speed of the rotating body of water, is that with one very inexpensive tool it is possible to produce tank heads in a variety of materials and with a height suitable for the job in question. The clamping tool does not have to be ring shaped but may e.g. be elliptical or approximately rectangular according to the purpose. The amount of energy spent in the forming may be cal¬ culated from the cubic volume of the formed blank and the speed of the medium of transmission but as the process consumes energy to overcome flow losses in the medium and between blank and tool etc., it is necessary to have a considerable surplus available. The following example illustrates that the process is suitable for releasing very considerable amounts . of energy. The task is to produce tank heads having a diameter of 1.2 meters and a height of 0.2 meter. The cubic volume of this part is about 150 liters, and if the volume of the supply pipe is 50 liters, the active volume of the transmission medium will be 200 liters or, in the case of water, the active mass will be 200 kg. The diameter of the rotating container is 1.2 meters, and the rotational speed max. 1500 rpm. The mean diameter of the rotating ring of water is 1 meter, and the mean speed is thus maximum 146 meters/second. At this speed 200 liters of water possess a kinetic energy in the range of b x 10 N . If 6 mm aluminum is used for the tank head mentioned, experience shows that the amount of work required to - carry out the deformation is in the range of 2 x 10 4 Nm, and this figure is somewhat higher when mild steel is used, but it will appear from the foregoing that there is more than sufficient energy available for the majority of jobs. The practical limits are decided by the strength of the rotating container and the inlet pipe whose top part is subjected to severe pressure impact and lower part to strong centrifugal forces as water flows through the bends. It is natural to design the com¬ ponents in accordance with the range of work since this permits the higher pressures to be achieved, but OMPI - - a smaller volume is possible in the case of a small rapidly rotating container which is e.g. suited for the tools shown in figs. 3 to 6.

Claims: P a t e n t C l a i m s : 1. A method of high energy rate forming of metals and other ductile materials wherein a liquid is used as medium of transmission to transfer to the blank the amount of energy necessary to form it, c h a r a c t e r ¬ i z e d by the fact that kinetic energy is introduced into the medium of transmission by circulating the medium in a closed circuit, and that the circuit is essentially momentarily interrupted to release the medium of trans- mission in a direction towards a tool (28, 28A, 28B) which contains the blank. 2. A method according to claim 1, c h a r a c t e r ¬ i z e d by the fact that kinetic energy is introduced into the medium of transmission by rotating a container (9 » 10, 1.1) in which it is contained, and that the transmission medium is returned to the container after having exerted a pressure in a direction towards the tool (28, 28A, 28B). 3. A machine for carrying out the method according to claims 1 and 2, having means for defining a transmission medium and means for imparting momentum to the medium of transmission in a direction towards a tool which contains a blank, c h a r a c t e r i z e d by the fact that the transmission medium is contained in a cylin- drical container comprising a bottom (9), shell (10) and ring-shaped plate (11) and which can be caused to rotate about a vertical axis by means of a motor (12) , and that an essentially vertical discharge pipe (16) is fitted within the plate (11) and is downwardly formed as a con- necting piece which terminates in the container with its opening oriented towards the direction of rotation, and that actuator means (21) are provided which are arranged c ∑π to turn the pipe (16) about its longitudihal axis spaced somewhat from the rotary axis of the container so that in a first extreme position the lower opening of the pipe (16) is present within the inner edge of the plate (11), and in another extreme position is located adjacent the inner surface of the shell (10), said discharge pipe (16) being upwardly connected to the tool (28, 28A, 28B) which contains the blank. 4. A machine according to claim 3 » c h a r a c t e r - i z e d by the fact that the tool comprises an upper part (28) which may be opened in relation to an essen¬ tially horizontal plate (13) having a central opening in which the pipe (16) terminates, and that the tool is arranged to receive a plate-shaped blank (26) so that the blank is clamped between the upper part (28) and the plate (13). 5. A machine according to claim 3, c h a r a c t e r ¬ i z e d by the fact that the tool is a diametrically split mould (28A) which is upwardly closed and clamped above the upper free opening of the pipe (16). 6. A machine according to claim 3 c h a r a c t e r¬ i z e by the fact that the tool comprises a piston (31) which is slidably fitted in the pipe (16), and that the upper side of the piston has mounted thereon a tool part (33) for forming a blank (34) against another stationary tool part (35).

Inventors: POULSEN P
Applicants: POULSEN P
Application year: 1980
Main classification: B21D26
IPC codes: B21D26, B21J9, B30B1