US3592032A

US3592032A - Control means for hydrostatic extrusion

Info

Publication number: US3592032A
Application number: US837537A
Authority: US
Inventors: Ingemar Stromblad
Original assignee: ASEA AB
Current assignee: ABB Norden Holding AB
Priority date: 1968-07-02
Filing date: 1969-06-30
Publication date: 1971-07-13
Anticipated expiration: 1988-07-13
Also published as: FR2012139A1; GB1263490A; SE326932B; DE1932662B2; DE1932662A1

Abstract

For the control of a press which includes a press stand, an operating cylinder carried by the stand and having an operating piston therein, a pressure chamber arranged in the stand and an extrusion die in the chamber, with a pressure-generating punch connected to the operating piston and inserted in the pressure chamber for compressing a pressure medium isostatically around the billet, a position indicator and a pressure indicator are provided which are connected to a calculating unit to sense when extrusion starts and to calculate, depending on the size of the billet, the allowable movement of the pressure-generating punch, which is interrupted just before the last of the billet is extruded.

Description

United States Patent [72] Inventor Ingemar Stromhlad Vasteras, Sweden [2]] Appl. No. 837,537

[22] Filed June 30, 1969 [45] Patented July 13, 1971 [73] Assignee Allmauna Soenska Electriska Aktiebolaget Vasters, Sweden [32] Priority July 2, 1968 [3 3 Sweden [54] CONTROL MEANS FOR HYDROSTATIC EXTRUSION 10 Claims, 2 Drawing Figs.

52 US. Cl 72 20, 72/35, 72/270, 72/710 51 int. Cl B2lc 31/00 50 Field of Search 72/60, 35,

[56] References Cited UNITED STATES PATENTS 2,558,035 6/l95l Bridgman 72/60 3,491,565 1/1970 Birman 72/60 Primary Examiner-Richard J. Herbst Attorney-Jennings Bailey, Jr.

ABSTRACT: For the control of a press which includes a press stand, an operating cylinder carried by the stand and having an operating piston therein, a pressure chamber arranged in the stand and an extrusion die in the chamber, with a pressuregenerating punch connected to the operating piston and inserted in the pressure chamber for compressing a pressure medium isostatically around the billet, a position indicator and a pressure indicator are provided which are connected to a calculating unit to sense when extrusion starts and to calculate, depending on the size of the billet, the allowable movement of the pressure-generating punch, which is interrupted just before the last of the billet is extruded.

PATENTEflJuualsn I 3,592,032

INVENTOR INGEMA R STROM BLAJ) I BY 3%? mfi w CONTROL MEANS FOR HYDROSTATIC EXTRUSION BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a means for controlling the extrusion process during hydrostatic extrusion in such a way that complete extrusion of the billet through the die is avoided and so that the production rate is high, that is, that only a small quantity of material remains in the die when the extrusion is interrupted.

2. The Prior Art For hydrostatic extrusion a billet is enclosed in a pressure chamber having a die with an opening of desired cross section and subjected to high-hydrostatic pressure all round so that the material is extruded through the opening. The equipment usually consists of a wire or strip-wound high-pressure cylinder which is inserted in a hydraulic press. The cylinder is closed at one end by a die having an opening with the desired cross section of the component. The pressure is generated by a punch which is pressed by a hydraulic operating piston into the high-pressure cylinder filled with liquid. Usually pressures of between and 25 kilobar are used. At these high pressures the liquid compression is also considerable, often more than percent, and the energy in the compressed liquid is great. If a billet is completely pressed out through the die the liquid expands rapidly when the billet leaves the die and accelerates the rod produced so that this can be deformed or cause damage to surrounding or adjacent equipment. The liquid is forced out with explosive speed and may thus also directly or indirectly cause serious damage. The extrusion must thus be interrupted before the billet is completely extruded and the remaining material scrapped. It is thus advantageous to adjust the press so that the material can be exploited to the fullest extent while complete extrusion is safely avoided. With the high pressures in question it is extremely difficult to arrange bushings for signal conduits in the wall of the high-pressure cylinder and emitters cannot therefore be used inside the cylinder to indicate a suitable moment for the interruption of the extrusion process, for example by measuring when the end surface of the billet has passed a certain point. The great quantity of metal in the cylinder also makes it impossible to measure the volume or position of the billet in the cylinder by inductive methods with sufficient accuracy. The required determination of a suitable moment for interruption of the extrusion must therefore be carried out indirectly by measuring and making use of the available magnitudes.

SUMMARY OF THE INVENTION The press is provided with a position-indicator which senses the position of the pressure-generating punch and a pressureemitter which senses the pressure in the operating cylinder which drives the punch. According to the invention the press contains a calculator with at least one memory unit and at least one calculating unit, which calculator receives the output signals of the indicator and emitter and, with the guidance of these signals, senses when extrusion starts and, depending on the size of the billet, calculates the allowable movement of the pressuregenerating punch and interrupts the extrusion when the desired volume has been extruded. The pressure in the pressure cylinder itself is thus measured indirectly since the high pressure does not permit connections to the pressure chamber through the wall of the cylinder or the punch. In order to enable correct calculation the entire extrusion equipment can be calibrated by registering the output signals of the indicator and the emitter at known volumes of the billet in the pressure chamber and storing these signals in the memory unit. During calibration the high-pressure cylinder is suitably either completely filled with oil, that is, the billet volume V=0 andthedieprovided with a plug to prevent pressure medium from leaking out through the die opening, or a billet of approximately the size of those to be later extruded may be inerted in the high-pressure cylinder. Thus a relationship is obtained between the cylinder pressure and the punch movement. This is dependent on the spring action in the press stand, the increase of the cylinder volume due to the pressure, the volume and compressibility of the liquid enclosed and the volume and compressibility of the billet of known size in the cylinder, and so on. The volume of the billets intended to be extruded need not be known. Because during the extrusion the output signals of the indicator and emitter are supplied to the calculator and compared with the values of the output signals stored in the memory part which were obtained during the calibration with known billet volumes, the calculator determines the volume of the billet in question according to a pro gram which has been fed in and the difference between the measured values. The start of the extrusion is indicated by at least one emitter which senses when the extrusion is indicated by at least one emitter which senses when the extrusion starts and the output signal of this emitter is also supplied to the calculator. The previously mentioned indicator and emitter are suitably also used to indicate the start of the extrusion process, the calculator for example analyzing the relationship between the punch position and the pressure and sensing a certain point at the start of the extrusion process because the derivative of the function then rapidly decreases towards zero. The calculator is programmed to determine how much further the punch must be inserted into the cylinder in view of the calculated volume of the billet after the start of the extrusion process has been indicated and to interrupt the feeding or reverse the movement of the punch when the calculated infeeding has been obtained.

Calculators of both digital and analogue type can be used. A single calculator may control one, two or more presses.

The invention enables much better utilization of the material than was previously possible. The measurements can be rapidly reproduced and the volume of the billet in question can be determined with great accuracy. The position of the punch when the extrusion process should be interrupted can therefore also be determined with great safety. At a high ratio between the billet volume and pressure cylinder volume the error in calculation may be 5 percent or lower. Even when great safety against complete extrusion is desired, it is possible to utilize percent of the material or more.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is further described with reference to the accompanying drawings.

FIG. 1 shows the ratio between the pressure in a pressure cylinder and the movement of a punch inserted into the cylinder to generate the pressure for extrusion of a billet inserted in the pressure cylinder.

FIG. 2 shows schematically the parts essential for the invention in a press for hydrostatic extrusion and certain auxiliary equipment for adjusting the press.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the diagram according to FIG. 1 the punch movement is indicated along the abscissa and the pressure in the pressure cylinder along the ordinate. The curve A indicates the pressure in the cylinder as a function of the punch movement and the curve B the pressure in an operating cylinder which drives the punch, also as a function of the punch movement. Before the punch has reached the position 5,, where there is a seal between the punch and the washer in the cylinder, no pressure increase is obtained. When the punch is inserted further into the cylinder a distance 8 -8 the pressure increases substantially in a straight line. The slope of the curve is in this part a function of the spring action of the press stand, the volume increase of the cylinder due to its suspension, the compression of the punch, die and billet and of the volume and compressibility of pressure medium enclosed in the pressure cylinder. The volume of the pressure medium is in turn a function of the billet volume under otherwise constant conditions. At the position S l of the punch the slope of the curve alters noticeably and a maximum is obtained at The derivatives of the curve thus alter from a constant value to O at this part. At the position 8 such a pressure has been attained that a certain deformation of the front part of the billet projecting into the die is obtained. At the position S of the punch the pressure has reached such a value that the extrusion process through the die opening is initiated. When the material has started to move the resistance decreases and the pressure drops until, when the punch is in position a constant state is achieved, after which the pressure remains constant during the continued movement of the punch to a position where only a conical part of the billet remains in the die and, when the extrusion process is continued, the area reduction is decreased, and thus the driving pressure required is also decreased. The flow of material through the die then increases and the pressure drops when the speed of the punch is unaltered and at point S the last of the material leaves the die and the pressure medium is expelled through the die with considerable force. The expansion of the pressure medium causes the last of the material to be accelerated to great speed. This may then be damaged and surrounding equipment may also be damaged, and even the press itself because of the recoil. The pressure medium, which has a pressure of -20 kilobar may also directly damage those parts with which it comes into contact. In order to prevent complete extrusion the movement of the punch is interrupted at S,,. If the punch is only stopped the extrusion continues under decreasing pressure and stops when the pressure has dropped to a certain level. If, however, the movement of the punch is at a reversed at position S the extrusion is stopped almost instantaneously. During the return movement of the punch the cylinder pressure drops so that it is zero at position S Curve B indicates the pressure in the pressure cylinder as a function of the pressure in the operating cylinder for the punch. This pressure is proportional to the pressure in the cylinder and can therefore be utilized to determine the pressure in the extrusion cylinder.

In FIG. 2, 1 designates a press table, 2 an operating cylinder in a hydraulic press not otherwise shown. In the press is a highpressure cylinder 3 formed by a steel cylinder 4, a strip sheath 5 of wire having rectangular cross section and great strength wound on under prestressing, and ends 6 and 7. In the cylinder are a lining 8, a die 9 and sealing rings 10 and III which seal between the cylinder 4 and the die 9 with respect to a pressure-generating punch 12. In the end 7 is a seal 113 which seals between the end and the punch 12 while the cylinder is being filled with pressure medium from the cylinder space 14 through a channel 15 in the end 7 before the punch 112 is inserted to generate the pressure necessary for the extrusion process. The press is of the type which has a horizontal, axially movable pressure cylinder in which a billet l6 and a new die 9 are inserted from the side of the press table in the space 18 and where the billet l6 and die 9 are held in the correct position by a piston 17 freely movable in the lining 8, the piston pressing the billet and the die against the table I while the cylinder 3 is returned to the press table. The pressure force is obtained by pressure medium in the space 14 influencing the piston 17 which is pressure determined by spring-loaded overflow valves in the piston 17. The punch 12 is joined to the piston 19 which is influenced in the direction of the press table 1 by the pressure in the space 20. The punch is operated in the opposite direction by operating cylinders, not shown. The space 20 communicates through conduit 27 and a valve 21 operated by an electromagnet 22 with either a pump 23 and a pressure medium container 24 or a collection container 25. If a continuously operating pump is used the pressure medium can be transferred through the same valve directly to the collecting container 25. A pressure-emitter 28 is connected by a tube 29 to the tube 27 and thus measures the pressure in the space 20 and thus indirectly the pressure inside the cylinder 3. In the press, for example, is a resistive position-indicator 30 having a stationary part 31 in the press stand and a part 32 joined to the piston 19, with a trailing contact 33 which fol lows the piston 19 and the punch 12 during their movement.

The pressure-emitter 28 and the position-indicator 30 are connected to a calculator which is connected both to an operating table 35, a recorder 36 and the operating unit 22 of valve 21, as well as other operating units for the press, not shown.

The equipment operates in the following way. It is calibrated before the extrusion process is started so that the spring constant" of the equipment is known by determining the relationship between the punch movement and the pressure in the cylinder 3 at a known volume of the billet 116. The cylinder may be completely filled with pressure medium of the type used for the extrusion, that is the billet volume V=0 or a billet of arbitrary volume may be inserted. A billet is preferably used which has approximately the same volume as those to be used for the extrusion. The pressure in the cylinder 3 is measured indirectly through the emitter 28 which measures the pressure of the pressure medium in the space 20 which influences the operating piston 19 which drives the pressure-generating punch 12 into the cylinder 3. The movement of the punch 12 is measured by the resistive position-indicator 30. The output signals of both emitter and indicator are supplied to the calculator 34 and inserted in its memory unit. For the extrusion a billet 16 is inserted in the pressure cylinder. This may be of arbitrary size, within certain limits. The press is started and the values of the pressure-emitter 28 and the position-indicator 33 are supplied to the calculator 34 and the ratio between pressure and punch movement is compared with the calibration values stored in the memory unit. Because the compressibility of the pressure medium is greater than that of the metallic billet (approximately 15 percent and 2 percent, respectively at 10 kilobar), different volumes of the billet and pressure medium cause the slope of the curve in the area S S to differ from that of the curve registered during the calibration. The difference in slope, the derivative of the curve, is a gauge of the difference between billet volumes. If the equipment has been calibrated with the cylinder completely filled with pressure medium the difference will be great. However, ifit has been calibrated with a billet of the size to be used for the extrusion, there will be no difference, or very little. According to a program fed in the calculator calculates the billet volume or the difference between the calibration billet and the billet in the cylinder. When the punch reaches position S the billet starts to be deformed. This means that a certain movement of the punch causes less pressure increase and thus curve A or B, respectively, levels off and gradually ob tains a maximum value at The beginning of extrusion is complete approximately when the punch reaches the position S With most materials a pronounced peak is obtained in the curvejust at the start of the extrusion, after which the pressure drops to a somewhat lower level. When the punch is in position 5;, the pressure has dropped, in spite of constant speed of the punch, to a value which continues to be constant. The alteration of the curve derivatives can be used to determine the position of the punch 16 when the extrusion starts. When material is extruded which provides a well-defined pressure peak at the start of the extrusion the calculator may be programmed, when the curve derivatives pass zero, to calculate, with the help of the calculated billet volume, the distance 5 -8. the punch must travel further into the cylinder so that, with the desired degree of safety against complete extrusion of the material, the least possible material is left which must be scrapped. The calculator 34 may be programmed to give a control signal to a valve unit which interrupts the supply of pressure medium to the space 20 so that the pressure remains and the extrusion continues until the flow of material ceases at a certain lower pressure. Alternatively a control signal may be sent to the operating member 22 in a valve 2] according to FIG. 2, which immediately unloads the cylinder 2 by placing it in communication with a collecting container 24 for the pres sure medium. During the first part of the return movement of the piston 19 and punch 12, that is from position S. to position S the pressure drops to p=0.

The calculator 34 is connected to an operating panel with operating buttons and adjusting knobs for operating the press,

ACT example for start, stop, emergency stop, selection of program, correction of program during operation, and so on, and to indication devices for faults, alarm and so on. The calculator may also be connected to a recorder for recording production statistics from the calculator.

The invention is of course not limited to the embodiment shown in the figures. Many variations are feasible within the scope of the following claims.

I claim:

1. In combination with a press comprising a press stand, an operating cylinder arranged in the stand and having an operating piston, a pressure chamber arranged in the stand and an extrusion die arranged in the chamber, a pressure-generating punch connected to the operating piston to generate the required pressure in a pressure medium enclosed in the pressure chamber which isostatically influences a billet in the pressure chamber and a position-indicator which senses the position of the punch and a pressure-emitter means which senses the pressure in the operating cylinder, the improvement comprising a calculator with at least one memory unit and at least one calculating unit, means to supply to the calculator the output signals of the indicator and emitter, said calculator including means responsive to these signals to sense when extrusion starts and, depending on the size of the billet, to calculate the allowable movement of the pressure-generating punch and to interrupt the extrusion when the desired volume has been extruded.

2. Means according to claim 1, in which the calculator has a memory unit, comprising means to supply the output signals of the pressure-emitter means at a known volume of billet in the pressure chamber to the calculator and to store such signals in its memory unit.

3. Means according to claim 2, in which the output signal at a billet volume of zero is supplied to the calculator and stored in its memory unit.

4. Means according to claim 2, said calculator comprising means to compare the output signals of the pressure-emitter means produced by billets of unknown volume with the values of the output signals at known volumes, so that the calculator calculates the volume of the billet with the help of the diffcrence.

5. Means according to claim 4, which has at least one emitter which senses when the extrusion starts and means to supply the output signal of said emitter to the calculator.

6. Means according to claim 5, in which said emitter is constituted by said pressure-emitter means.

7. Means according to claim 6, in which the output signal comprises an alteration in the slope of the curve for the relationship between punch position and pressure.

8. Means according to claim 5, in which the calculator includes means to determine according to a program which is fed distance the pressure-generating punch is to be inserted into the pressure chamber and to deliver an output signal which interrupts the feeding when the punch has been fed in the calculated distance.

9. Means according to claim 2, in which the calculator is of digital type.

10. Means according to claim 2, in which the calculator is of analogue type.

Claims

4. Means according to claim 2, said calculator comprising means to compare the output signals of the pressure-emitter means produced by billets of unknown volume with the values of the output signals at known volumes, so that the calculator calculates the volume of the billet with the help of the difference.

9. Means according to claim 2, in which the calculator is of digital type.

10. Means according to claim 2, in which the calculator is of analogue type.