AU754548B2 - Method and device for forming metals - Google Patents

Abstract

The deforming process involves clamping the metal part (2) in a clamping device (4) to form a forging cavity (13) in the swage (5) with the part clamped to take forging forces directly; applying a forging hammer (7) to force metal into the forging cavity, exerting pressure on the hammer so that the mechanical stress is within the Hooke elastic region, applying a pulse with the hammer so that the metal passes into the flowing region and repeating the last two stages.

Description

Method and Device for Forming Metals This invention relates to a metal working method, in particular a compressive deformation method, for metal workpieces such as pipes, wires or sections, and a compressive deformation device.

According to the state of the art, swellings are accomplished, as a rule, in such a way that a pipe or a metal section having the largest wall thickness is provided, and the thickness is reduced at the desired places through targeted cutting out or hammering out. This cutting out or hammering out starting from the thickest sections is a tedious process, in particular when the proportion of swelling is only small compared to the remaining portion of the pipe or section.

Various attempts to thicken sections through direct compressive deformation have failed so far. Attempts to thicken pipes or rods have often caused the sections to widen laterally or yield to buckling already in the initial phase of the compressive deformation, whereby pile-ups and overlaps result. Furthermore, a non-homogeneous, crystalline structure of the reshaped material thereby results, which is undesirable with respect to stability. Wrinkles also thereby occur in the section, like in an elephant's trunk.

Resolving the phenomenon through formation of folds has been attempted in that various die stages of different shape are put in, which is a rather time-consuming method.

It is therefore the object of the present invention to make available a metal working method by means of which swellings in pipes, rods or other sections can be produced quickly and economically.

It has been found that desired, targeted places in pipes, rods and other sections can be thickened through compressive deformation if the workpiece to be thickened is prestressed in the Hooke range, and the workpiece is processed with a compressive deformation hammer in a pulsating way.

Through the impulses of the compressive deformation hammer, the material of the workpiece undergoes a transition for a short time from the Hooke range into the plastic range. The impulse causes the material in the compressive deformation zone to be brought to flow, the deformation space is thereby filled a little, the compressive deformation hammer follows the movement, the pressure drops, the workpiece once again returning to the crystalline state, but still being under prestressing, however. Further periodic compressive deformation impulses are subsequently delivered to the workpiece, a transition into the plastic range and a recrystallization occurring again each time. By means of this procedure, a homogeneous, thickened section with homogeneous structure can be obtained.

The subject matter of the present invention is thus the compressive deformation method according to the definition in claim 1 and the compressive deformation device according to the definition in claim The method according to the invention is referred to as "stutter compressive deformation." It is thereby important that the active thrust forces 1o are directed in such a way that they come to bear only in the deformation space and serve only the transport of material.

To this end it is necessary that the profile to be compressively deformed be free in the deformation space and the remaining section held in such a way that the compressive deformation forces are equalized outside the deformation space or are neutralized, ineffective against the walls. Owing to the prevailing pressure relations, the material is exposed to increased temperatures. The energy thereby brought in must be correspondingly carried off in the region of the clamping so that the transition zone does not flow at the same time and the material is not able to expand in an uncontrolled way.

Prior to the actual compressive deformation action, the material to be reshaped has to be prestressed with corresponding hydraulic pressure so that the stutter pulses come to bear correctly. The prestressing takes place preferably in a region located just before the transition into the plastic range.

The material is therefore still in the prestressed state in the elastic phase.

Through suitable measures, the prestressing is maintained during the entire compressive deformation action, i.e. the metal part to be worked remains under prestressing between the individual impulses. The stressed material is preferably preheated up to just before the yielding state, in particular in the case of larger sections. The energy to be supplied and the frequency are determined according to Brillouin (first Brillouin zone). The preheating preferably takes place locally in the deformation space by means of microwaves. With thin sections, the preheating can be omitted. The pressure pulse can now be applied to the prestressed and preheated material, the prestressed material being brought to flow. Because the material becomes soft, the pressure piston is able to move forward, and the pressure subsides; the material can recrystallize. The prestressing of the material is maintained between the individual pressure pulses. This can take place in that a hydraulic system is used for the application of force, which system comprises two hydraulic pumps, namely a prestressing pump for the prestressing pressure for example at 40 bar (4 10 6 Pa) and a smaller impulse pump for a pressure up to 700 bar (7 107 Pa). The pipelines of these pumps to the piston ("stutter piston") must be provided with a return valve.

A hydraulic system is preferably used for exerting a pressure pulse upon 1o the compressive deformation hammer. The impulse is thereby transmitted from the hydraulic or stutter piston to the compressive deformation hammer. The stutter piston is moved with oil up to the material to be compressively deformed, then the pressure increases such that the stressed oil causes the desired prestressing in the workpiece. The lines between pumps and stutter pistons are to be designed non-elastic, and for the pulse frequency anechoic. The pressure pulses are modulated upon the prestressed oil, for example with a frequency-controlled piston control, so that an unattenuated transmission of the pulse from the hydraulic piston to the compressive deformation hammer can take place (compressibility of the hydraulic oil approximately 101.

2o The time of the compressive deformation is determined according to the Hooke Law; the first half cycle of the stutter frequency is established thereby.

For the second half cycle, it is only to be checked whether the available time suffices for the recrystallization. With this method, the stutter frequency is always matched to the material. After the last tension release of the material in the compressive deformation region, the material is still in the Hooke range, that is prestressed. It is to be seen to it that the material can relax in the compressive deformation region through removal of the compressive deformation hammer since otherwise undesired swellings can arise adjacent to the compressive deformation region.

The invention will be explained more closely in the following, with reference to the attached drawings. Shown are: Figure 1 a sectional drawing of a compressive deformation device for carrying out the method according to the invention: state prior to the compressive deformation action, Figure 2 the same compressive deformation device as in Figure 1, however after the compressive deformation action, Figure 3 an alternative embodiment of a compressive deformation device, namely a head compressive deformation device for carrying out the method according to the invention, applied to a different material or product, Figure 4 a configuration of hydraulic pumps on the stutter piston, Figure 5 a pressure/course diagram of the compressive deformation action, Figure 6 a pressure/time diagram of the method according to the invention, io Figure 7 an enlarged cutout of a compressive deformation device similar to Figure 1, Figure 8 another embodiment of a compressive deformation device designed for compressively deforming a hollow section in a region between its ends, Figure 9 the detail D of Figure 7 and 8 on an enlarged scale, Figure 10 in a depiction similar to Figure 7, a device for producing a nonrotational-symmetrical swelling at the end of a pipe, Figure 11 in a depiction similar to Figure 8, a device for producing a nonrotational-symmetrical swelling between the ends of a pipe, 2o Figure 12 a diagrammatic section through a pulse generator.

Figure 1 shows a stutter compressive deformation device 1, which is intended for compressively deforming a pipe 2 at its end, while forming a greater wall thickness. Inserted in the pipe 2 is a pin 3 which serves to hold the section of the pipe in that the material is prevented from being able to escape into the section interior. The pipe is held through a dclamping device 4, which exerts a counter-pressure upon the pin 3. The clamping device exerts a pressure around the pipe on all sides. Prevented thereby is that material can escape in an uncontrolled way. The pipe 2 to be compressively deformed projects further into the die 5 which is provided with a cooling coil 6 which is fed with a cooling medium 14. The temperatures arising through the high pressures are thereby dissipated, as far as necessary. The pin 3 projects through the pipe 2 to be compressively deformed partially into the die 5. A bore 9 is provided at the end of the pin 3 penetrating into the die, which bore serves as a guide for the extension 8 of the compressive deformation hammer 7. This extension, together with the die, defines the deformation space 13 into which the material of the pipe can spread during the compressive deformation action. The pressure or respectively the required impulses on the compressive deformation hammer 7 are exerted by the stutter piston 10. This is hydraulically operated, 11 designating the hydraulic line and 12 the chamber for the expanding hydraulic oil. Before the compressive deformation action can begin, the pipe to be compressively deformed, with the pin 3 inserted, is 1o brought into the desired position in the clamping device 4, and the clamping device is tightened as much as necessary. The compression deformation hammer 7 is applied on the face of the pipe located in the die 5. Then the pipe to be compressively deformed is prestressed to the extent that the material is still in the elastic range (Hooke range).

Since the hydraulic oil likewise has an elastic lower pressure range, the prestressing has the advantage here that not only is the metal piece to be worked prestressed, but also the hydraulic oil. During the compressive deformation action, the oil is thus in a range in which it has practically no elasticity.

2o Figure 2 shows the same stutter compressive deformation device as in Figure 1, however after completed compressive deformation action. The reference numerals have the same meaning as in Figure 1. In this figure it can be seen that the stutter piston 10 has moved to the right, compared to Figure 1.

The stutter piston 10 has thereby been driven into the die 5, the part of the pipe to be compressively deformed turned toward the compressive deformation hammer being compressively deformed and the deformation space according to Figure 1 now being filled up by the entire compressively deformed part 15 of the pipe 2 to be compressively deformed.

Figure 3 shows an alternative embodiment of a stutter compressive deformation device for carrying out the method according to the present invention. The device 20 is a head compressive deformation device. The device serves to compressively deform a metal rod or metal wire at one end with formation of a head. A metal wire (not shown) is inserted into the bore 21 of the clamping device 22 until the one end projects into the hemispherical depression 23 of the compression deformation hammer 24 until the limit stop.

The compressive deformation hammer 24 can exert a pressure on the workpiece through the piston 25, whereby during the compressive deformation action, which takes place the same way as described above, the material is able to escape into the die 26 and the hemispherical depression 23 in the compression deformation hammer 24. The piston 25 is actuated hydraulically.

Details of the clamping device and also of the hydraulic system are not depicted in this figure, since they are obvious for one skilled in the art.

Figure 4 shows a typical configuration of hydraulic pumps 31, 32 at the to piston (Figures 1 and 2) or respectively 25 (Figure which exerts pressure on a compressive deformation hammer (not shown). The larger hydraulic pump 32 serves to maintain a permanent prestressing pressure during the compressive deformation action, e.g. 40 bar. The smaller pump 31 serves to exert periodic impulse pressures, with a higher pressure, e.g. of 700 bar, which is sufficient for the transition of the material from the Hooke into the plastic range. The lines 34, 35 of the pumps 31, 32 to the piston are provided with return valves 36, 37. Shown, for better clarity, above the pump symbols are little diagrams 38, 39 with a schematic indication of the course of pressure.

Figure 5 shows a pressure/course diagram a for a compressive deformation action according to the present invention. h shows the Hooke range and A the prestressing point.

Figure 6 shows a pressure/time diagram b for a compressive deformation process for steel according to the present invention. Clearly visible is the pulsating pressure course during the impulses. In the area h, the material is prestressed in the Hooke range until the prestressing point A. As soon as this point is reached, a first impulse is exerted upon the material to be compressively deformed, whereby the first peak of the curve arises. During this impulse, the material to be reformed undergoes transition from the elastic range into the yielding range f, in which a reforming takes place since the material is brought to flow. The piston is thereby able to move further forward, and the pressure subsides until (it reaches) the prestressing pressure, the material being able to recrystallize. The recrystallization phase is shown by the area r. Then an impulse is again delivered to the material to be reformed, until the summit of the second peak. The same thing thereby happens as with the first peak: The pressure piston is able to move further forward, the material undergoing transition into the plastic range, which allows a reforming. Then the pressure diminishes again, a renewed recrystallization of the material being made possible. This action is repeated until the desired reforming is achieved.

Further indicated on the diagram is the pressure difference Apressure; this is a material-dependent constant which has to be calculated or found out otherwise.

Figure 7 shows important details of a compressive deformation device which is constructed in a similar way to the compressive deformation device of Figure 1, on a larger scale compared to Figure 1. Same parts are given the io same reference numerals in Figure 7 as in Figure 1. The clamping device generally designated by 4 comprises a plurality of hydraulic cylinders which act upon clamping jaws 16. Shown in Figures 1 and 7 are only two sets of hydraulic cylinders situated next to each other in the longitudinal direction of the pipe and distributed on the periphery of the clamping jaws. In practice, however, three or more sets of hydraulic cylinders are preferably provided. It has been shown namely that good reforming results are achieved if the clamping force is high in the vicinity of the end of the pipe 2 to be reformed, and decreases, then increases again, in the direction of the opposite end of the pipe 2. With such a clamping course, undesired flowing of the material of the 2o pipe 2 in the clamping region is avoided. Therefore the hydraulic cylinders of the embodiment according to Figure 7, situated behind one another in the longitudinal direction of the pipe to be reformed, have separate supply lines for the pressure medium, in contrast to the embodiment according to Figure 1.

These supply lines are not shown in Figure 7. By means of these separate supply lines, it is possible to supply adjacent hydraulic cylinders with different pressure in order to achieve the clamping course described above. To further improve the holding force exerted on the pipe 2 by the clamping device 4, the surfaces of the clamping jaws 16 that come into contact with the pipe 2 are provided with a friction-increasing coating, in particular of tungsten carbide, and at least the surface areas of the pipe 2 that come into contact with the clamping jaws 16 are roughened.

A further measure to increase the holding force, directed in a way opposing the reforming force in the longitudinal direction of the workpiece, consists of a small, encircling shoulderl 9 provided between the die 5 and the clamping jaws 16. The shoulder 19 is shown in Figure 9, which shows on an enlarged scale the cutout designated D in Figures 7 and 8. During the reforming action, a small accumulation of the working material of the pipe forms on this shoulder, whereby the pipe 2 is also held in a form-fitting way in longitudinal direction.

Shown in Figure 7 is the compressive deformation device immediately prior to the compressive deformation action. The deformation space 13 is delimited in this embodiment by the contact surface 17 of the compression deformation hammer, the extension 8 of the compression deformation hammer 7, the face 29 of the pin 3 and of course the die 5. The compression 1o deformation hammer 7 is situated with its contact surface 17 on the face of the pipe 2 to be reformed. In simplified terms, the crosshatched end region of the pipe 2 is shifted in the direction of arrows 18 into the deformation space 13 through the reforming action. So that the force transmitted by the compressive deformation hammer 7 onto the pipe is really directed toward the deformation space 13, the contact surface 17 of the compression deformation hammer does not run at a right angle to the longitudinal axis of the pipe 2, but is instead slightly inclined plate-like in direction toward the pipe. If it is important for the finished, reformed pipe 2 to have a face deviating from the shape of the contact surface 17, which is, for example, precisely orthogonal, this face is brought into its final form by means of the compression deformation hammer in a further working step.

Shown in Figure 8 is an embodiment of the compressive deformation device designed for compressively deforming a pipe 2 in a region between its ends. The left half of the device according to Figure 8 corresponds substantially to the right half of Figure 7. Visible at the far left in Figure 8 is in addition a bottom 27 on which the pipe 2 abuts. On the right side of the die 5 is a further clamping device 4, which holds firmly the end of the pipe 2. The compressive deformation hammer 7 here is stepped twice. The first step is formed by a contact surface 17, which transmits the compressive deformation force to the pipe 2 to be reformed at the beginning of the reforming action.

Since the compressive deformation force has to be transmitted within the right damping device 4 through the pipe 2 to the deformation space 13 and the pipe must shift itself in this clamping device to the left toward the deformation space 13, corresponding to the degree of reforming, it is important that the clamping force of the right clamping device 4 be adjustable. Together with the extension 8, the face 29 of the pin 3 and the die 5, the second step, formed by the slightly inclined surface 28, delimits the deformation space 13. As soon as the working material begins to deform on the surface 28, this surface also transmits part of the compressive deformation force to the pipe 2. Of course it is advantageous if the surfaces 28 and 29 are inclined in such a way that their normal lines are directed toward the deformation space 13, as has been described further above for the contact surface 17.

It is clear that both the compressive deformation hammer 7 and the pin 3 and/or its bore 9 can be designed in almost any desirable way, for example io with multiple steps, in order to give the deformation space 13 a desired shape.

One must only see to it that compressive deformation hammer 7 and pin 3 are designed such that they are also able to be driven apart again after the forming, without the formed workpiece being damaged. Furthermore, in all the embodiment examples described above of the stutter compressive deformation device, the parts to be reformed are rotationally symmetrical. It is easily possible, however, within the framework of the present invention, to reshape non-rotationally-symmetrical sections or pipes or to form non-rotationallysymmetrical regions on rotationally symmetrical sections or pipes. Two examples of this are shown in Figures 10 and 11.

Figure 10 shows, in a diagram similar to Figure 7, a device for producing a non-rotationally-symmetrical swelling at the end of a pipe 2. The surface 29' delimiting the deformation space 13 on the side of the pin 3 is not oriented at a right angle to the longitudinal axis of the pipe 2 in this embodiment.

Accordingly, the clamping jaws 16 and the die 5 are also of asymmetrical construction, as can be clearly discerned in the drawing.

Figure 11 shows, in a diagram similar to Figure 8, a device for producing a nonlrotationally-symmetrical swelling between the ends of a pipe. In this embodiment, it is the surface 28' delimiting the deformation space 13 on the side of the compressive deformation hammer 7 which is not oriented at a right angle to the longitudinal axis of the pipe 2. Accordingly, the clamping jaws 16 of the further clamping device 4 and the die 5 are of asymmetrical design.

The frequency with which the compressive deformation hammer pulses is to be established empirically for each workpiece. It is suspected that the best results are achieved if a stationary wave arises in the area to be reformed of the pipe 2 between the contact surface 17 of the compressive deformation hammer 7 and a virtual reflecting wall in the region of the shoulder 19. It is therefore advantageous if the pulse frequency is adjustable and preferably changeable even during the reforming action.

The mentioned impulse pump 31 can be a conventional reciprocating pump. A rotating pulse generator is more effective, however. Figure 12 shows a diagrammatical section through a possible embodiment of such a pulse generator 40. A central rotor 41 has at its center a longitudinal bore 42 which, via a rotary seal, can be pressurized with a high pressure of 700 bar, for example. For the purpose of minimizing friction, the rotor is coated on its cylinder generated surface with a layer 43 of ceramic, for example, and is surrounded by a stator 44. Radial channels 45 in the rotor conduct the high pressure from the longitudinal bore 42 to the outside. Provided in the stator 44 are also radial channels 46, which communicate with the channels 45 of the rotor in each case for short periods during the rotation of the rotor. Each channel 46 of the stator 44 has a retumrn valve at its outer, radial end.

According to this embodiment example, the return valve 47 consists of a ball with a cylindrical extension which is led in the bore of a radial connecting line 48. The ball and the extension are bored through to ensure the flow of the pressure agent through the connecting line 48 into an outer annular chamber 49 in which the prestressing pressure, of 40 bar, for example, prevails. It is this prestressing pressure which also presses the ball of the return valve 47 against its seat as long as the channels 45 and 46 are not in connection with one another. All return valves 47 are held in a valve ring 50. Of course other, known return valves can also be used, however, the valve body of which is a ball, for example, and is pressed against its seat by means of a spring, for instance. Each time when a flow connection between a rotor channel 45 and a stator channel 46 occurs, a pressure impulse arises in the latter. These pressure impulses achieve especially steep edges when the channels have a cross-section delimited by straight lines, i.e. are rectangular, for example, in the transitional region between rotor and stator. In the example shown, all four rotor channels enter into connection with the four stator channels at the same time. A symmetrical load is thereby ensured, and the quantities of pressure agent flowing through the channels add up. Embodiments are also conceivable, however, in which the number and the arrangement of the

I

channels is selected in such a way that the connections take place in succession. With such a configuration, high pulse frequencies can be achieved already at low rpm of the rotor.

Claims (19)

1. A method of working a metal piece by compressive deformation in a compressive deformation device, containing a clamping device, a die and a compressive deformation hammer, characterized by the following steps of the method: a) clamping the metal piece in a clamping device with formation of a deformation space in the die, the piece being clamped outside the deformation space in such a way that the compressive deformation forces are absorbed directly by the surrounding environment, b) applying a compressive deformation hammer to the metal piece in such a way that when a force is exerted thereon, the material of the metal piece is able to penetrate into the deformation space, c) prestressing the clamped metal piece by exerting a pressure on the compressive deformation hammer in such a way that the mechanical stress lies within the elastic (Hooke) range, d) exerting an impulse on the metal piece by means of the compressive deformation hammer, the material of the metal piece undergoing a transition from the elastic range into the yielding range, by means of which material is able to escape into the deformation space, the 2o compressive deformation hammer is able to move forwards, the pressure on the material decreases to the prestressing pressure, and the material is able to return again to the elastic range, and e) repeating periodically steps c) and d) until the compressive deformation action has been completed.

2. The method according to claim 1, wherein the metal piece is a pipe, a section or a rod.

3. The method according to claim 1 or 2, wherein the metal piece is made of iron, copper, aluminum or alloys thereof.

4. The method according to one of the claims 1 to 3, wherein the compressive deformation hammer is operated by means of a hydraulic system, the impulse being generated through a reciprocating pump and being transmitted to the compressive deformation hammer via a hydraulic piston.

The method according to claim 4, wherein the hydraulic oil in the hydraulic system is prestressed so that the prestressing force is achieved in the workpiece and an attenuation of the impulse is avoided.

6. The method according to one of the claims 1 to 5, wherein the metal piece is heated locally in the deformation space through microwaves before it passes into the yielding state so that recrystallization is ensured.

7. The method according to one of the claims 1 to 6, wherein the excess heat generated through the generation of pressure is dissipated through cooling.

8. The method according to one of the claims 2 to 7, wherein the metal piece is a pipe or a hollow section, a pin or a precisely fitting insert being placed in the hollow space where no compressive deformation is supposed to take place.

9. The method according to one of the claims 1 to 8, wherein at least one portion of the surface of the metal piece is roughened prior to clamping in the compressive deformation device.

A compressive deformation device for working a metal piece, containing a clamping device and a die which accept the metal piece (2) with formation of a deformation space a compressive deformation hammer and means (10, 25) of exerting a thrust force upon the compressive deformation hammer characterized by pulsation means (31, 40) by means of which force impulses are able to be superimposed upon the thrust force periodically in the same direction.

11. The compressive deformation device according to claim 10, wherein the clamping device has a plurality of power sources disposed behind one another in the longitudinal direction of the workpiece the clamping force of which sources, exerted upon the metal piece, is individually adjustable.

12. The compressive deformation device according to claim 10 or 11, wherein the clamping device has clamping jaws (16) whose surfaces coming into contact with the workpiece are provided with a friction-increasing coating, in particular of tungsten carbide.

13. The compressive deformation device according to claim 12, wherein the clamping jaws (16) project on the side of the compressive deformation hammer slightly further inwardly than the adjacent die so that an encircling shoulder is formed on which the workpiece is compressively deformed during working so that the holding force, brought about through the clamping effect and directed in a way opposing the reforming force in the longitudinal direction of the workpiece, is strengthened through form closure.

14. The compressive deformation device according to one of the claims to 13, wherein the contact surface (17) on the face of the compressive deformation hammer which transmits the reforming force to the metal piece (2) to be reformed is inclined in such a way that its normal line (18) is directed io toward the deformation space (13) into which the working material is to penetrate.

The compressive deformation device according to one of the claims to 13 for working a metal piece between its ends, characterized by a further clamping device which is disposed on the side of the deformation space (13) opposite the first clamping device

16. The compressive deformation device according to claim 15, wherein the compressive deformation hammer has at least two steps, a first step being formed by a contact surface (17) with which at least part of the reforming force is transmitted onto the face of the metal piece and a second step being formed by a surface (28) delimiting the deformation space (13).

17. The compressive deformation device according to one of the claims to 16, wherein the deformation space (13) is not designed rotationally symmetrical.

18. The compressive deformation device according to one of the claims 10 to 17, wherein the means of exerting a thrust force upon the compressive deformation hammer consist of a piston (10, 25) able to be pressurized with a hydraulic fluid.

19. The compressive deformation device according to one of the claims to 18, wherein the pulsation means contain switching means (45, 46) which connect periodically a hydraulic fluid from a pressure source with higher pressure to the hydraulic fluid bringing about the thrust. The compressive deformation device according to one of the claims to 19, wherein the pulsation means comprise a rotor (41) with a space (42) 9 able to be pressurized with a first pressure by means of a hydraulic fluid, wherein at least one radial channel (45) is connected to the space (42), wherein the rotor is surrounded by a stator (44) in which at least one radial channel (46) is provided which is connected to a space (49) able to be pressurized with a second pressure by means of a hydraulic fluid, and wherein the channels (45, 46) are disposed in such a way that they communicate periodically with one another during rotation of the rotor.