US2974708A - Method and apparatus for stretch forming metal stock - Google Patents

Description

March 14, 1961 H. PERKWS 2,974,708

METHOD AND APPARATUS FOR STRETCH FORMING METAL STOCK Filed Aug. 18, 1959 3 Sheets-Sheet 1 L2: INVpENTOR.

gu w' BY I mrmelvsx March 14, 1961 ERKlNs 2,974,708

METHOD AND APPARATUS FOR STRETCH FORMING METAL STOCK Filed Aug. 18, 1959 3 Sheets-Sheet 2 INVENTOR.

1 474 I BY March 14, 1961 G. H. PERKINS METHOD AND APPARATUS FOR STRETCH FORMING METAL STOCK Filed Aug. 18, 1959 3 Sheets-Sheet 5 \WIW v United States Patent METHOD AND APPARATUS FOR STRETCH FORMING METAL STOCK George H. Perkins, Euclid, Ohio, assignor to The Cyril This invention relates to an improved method of stretch forming metal stock and to an'improvement in stretch forming apparatus for rendering it effective for practicing the improved method.

The improvement in the method broadly resides in the manner in which the stretch forming cycle is initiated and continued without subjecting the stock to suddenly applied high or excessive tensioning stresses, and particularly in tensioning thev stock initially by holding one end fixedly in position and gradually moving the other end away from the one end until the slack in the stock is removed and preselected tensioning force is applied to the stock by said movement and then releasing said one end for movement in opposition to yieldable resisting force applied to said one end, and continuing the movement of said other end in opposition to said yieldable resisting force until the stock is stretch formed. 7 A further specific improvement useful when each piece of stock is to be separately monitored and formed under more precise conditions, resides in continuing the initial movement of the other end until the ratio of elongation of the stock to the applied tensioning force increases disproportionately, then releasing said one end for movement while restraining that movement by a yieldable resisting force applied to said one end and which is less than that which caused the disproportionate increase in said ratio, thereby to maintain said ratio within proper preselected limits, and then continuing the movement of said other end, in opposition to said yieldable resisting force until the stock is stretch formed.

More specifically, the present invention relates to an improvement in a rotary table type stretch forming machine such as disclosed in United States Letters Patent No. 2,514,830, issued July 11, 1950, to Cyril J. Bath, and further to an improvement in the table drive disclosed in connection with such machines in my copending application, Serial No. 792,304, filed February 10, 1959.

As mentioned in my copending application, the elastic limit, yield point, and ultimate strength of the higher alloys are relatively close together'so that a small change in the applied tensioning force can overstress and ruin the stock being formed. This change in metals has introduced new problems in the field of stretch forming. To appreciate the problems, certain prior practices must be noted.

The earliest prior practice, with machines of this type, is to connect one end of the-length of stock to the turntable for rotation therewith and one end to the stretch forming piston and cylinder assemblage for movement therewith, while the table is held stationary by its mechanical drive. Fluid pressure is then admitted to the assemblage to tension the stock to the degree preselected for the particular operation. While this tension is maintained, table rotation is started and continued until the stock is formed.

However, as machines of this character became larger and heavier, it became increasingly difiicult to start the table without imposing a sudden jerk on the stock being 2 formed and thus causing a sudden and excessive increase in the applied tensioning force.

This prior practice is improved, in accordance with my copending application, by utilizing a hydraulic drive for the table and removing as much slack as possible from the table drive preparatory to actuating the stretch forming piston and cylinder assemblage. This slack removal causes the table to start more smoothly and thereby reduces the sudden jerk on the stock and the resulting amount of undesirable tension imposed.

This is accomplished by keeping the hydraulic drive of the table sufliciently under the influence of the power supply to reduce slack in the power transmission while the assemblage is being activated to tension the stock to the preselected value, and then, when the preselected value is reached, starting the table at a creeping speed and increasing the speed by minute increments until it is brought up to full speed. However, for such performance, some means are required for locking the table against rotation in the reverse direction by the pull of the stretch forming assemblage, acting through the stock, against the force of the hydraulic table drive during initial operation. This need arises because the pull of the stock is soon increased to a degree suflicient to rotate the table backwards because the power applied by a hydraulic drive for rotating the table at creeping speed is very limited. If the power. were applied in a suflicient amount to withstand the full tensioning force, imposed on the table by the stock, before activation of the stretch forming assemblage and resultant. restraint of table rotation thereby, that power would cause the unrestrained table to rotate at too great a speed and suddenly take up the slack in the stock when the assemblage was activated, with a result that the applied tensioning force would become excessive. For that reason, the hydraulic drive of the table is supplemented by expensive braking devices and control mechanisms therefor, arranged to lock the table positively against reverse rotation during the period that only sufficient power is being supplied to eliminate slack in the drive.

In accordance with the present invention, additional advantages are obtained by locking the stretch forming piston and cylinder assemblage, instead of the table, in fixed position, either hydraulically or mechanically, then removing any original slack in the stock and initially tensioning the stock by rotation of the table at a creeping speed until the desired preselected forming tension is obtained, meanwhile maintaining the assemblage locked.

In some forming operations it is desirable to monitor each piece of stock to preselect the forming tension to be used. In such cases, the initial tensioning of the stock by table rotation with the assemblage locked may be continued until the stock is stressed so that the ratio elongation to tensioning force increases disproportionately. With this information, the tensioning force to be used is preselected, and continued stressing of the stock, at the preselected tension below that causing excessive yield, can be effected in either of two ways.

This may be done by stopping the table and, through its hydraulic drive, maintaining suflicient force so that it does not move forwardly appreciably, if at all, and so that it cannot be rotated in reverse by the stock. With the table thus arrested, the stock elongates slightly and thus relieves the stress and reduces the tension. When the tension falls to that preselected, hydraulic pressure fluid is supplied to the stretch forming assemblage to cause it to yieldably maintain the preselected tension during the forming operation and the assemblage is thereupon released under the restraint of the fluid pressure. The table, being prevented by its hydraulic drive from being rotated in reverse by the tension applied to the stock, is started so smoothly and with increments so slight that it does not impose any sudden jerk on the stock, and the speed is then gradually increased by minute incrementsof increase in the speed of the drive.

On the other hand, this transition may be effected without stopping the table. For example, with the table creeping, as soon as the tension applied to the stock by table rotation is such as to cause the excessive rate of elongation, fiuid pressure is supplied to the stretch forming cylinder so as to provide the preselected tension less than that which caused the excessive elongation, whereupon the tensioning assemblage is released from its hydraulic or mechanical latched condition and operates against the resistance of the controlled fluid pressure supplied thereto so as to maintain the stock at the lower preselected tension. This transition is made while the table is creeping so that the stock is not subjected to any severe shock or sudden jerk, after which the table speed is smoothly increased by minute increments.

Thus a new method of forming is provided and the method is one which can be performed quite readily on the particular type of apparatus as modified.

One of the principal advantages of the present invention resides in the fact that it provides effective control of the forces applied to the stock during the entire stretch forming cycle without sudden jerks and excessive stresses and strains.

For the purposes of illustration the present invention is described in connection with a combined stretching and wipe forming machine such as disclosed in my above identified copending application and which is ilustrated in the present drawings wherein:

Fig. 1 is a diagrammatic graph illustrating one of the principal problems in connection with such machines;

Fig. 2 is a top plan view of a combined wipe and stretch forming machine embodying the principles of the present invention; part thereof being broken away for elearness in illustration;

Fig. 3 is a front elevation of the apapratus illustrated in Fig. 2; and,

Fig. 4 is a diagrammatic illustration of the apparatus and a hydraulic circuit and flow diagram, illustrating a preferred form of control of the present invention.

Referring to Fig. l, a graph is shown, illustrating the earlier prior practice described above, in which the pull exerted on the stock is plotted on the ordinate as against time on the abscissa. A curve 1 indicates the pull applied to the stock at different times during the forming operation. Starting at the origin, it is assumed that the table 15 stationary, the stock has been placed under tension sufiicient to determine its yield point and the tension has been decreased to a selected point between the yield point and the elastic limit, at which the stock is to be formed. Thus, power has been applied to the stock by the yieldable stretch forming means for initially stretching it to its yield point. This power has been reduced to that il esired for stretch forming-a point above the elastic imlt.

Thereupon, the table is started at point 2 on the curve. Due to the inertial stresses, the table cannot be started Without a sudden jerk, particularly inasmuch as tension is being applied to the stock tending to rotate the table in the direction opposite to that in which it is to be rotated for stretch forming. Accordingly, this sudden jerk applied on the stock causes an abrupt rise in the pull exerted on the stock, so that the curve rises rapidly to a point indicated at 3. By this time, the static inertia of the table has been overcome and the continued application of power maintains the table at the proper speed. The sudden jerk imposed by the starting of the table does not continue but drops oif rapidly to a point indicated at 4, at which point the table has steadied down to the proper forming speed, and thereafter the pull is maintained substantially steady during the remainder of the operation, or, if increased or decreased mam to adjust to changes in configuration of the die and the like, the increase or decrease is gradual. These changes in later tensions are predetermined and gradually applied and can be allowed for, and are not sudden changes.

Referring therefore to the specific apparatus for carrying out this procedure, a'combined wipe and stretch forming machine, such as illustrated in my above identified application, is shown for purposes of illustration. The machine comprises a frame 10 having a main portion 10a on which is mounted a stretch forming piston and cylinder assemblage and a lateral portion 1012 on which is mounted a wipe forming piston and cylinder assemblage, so that the stock can be subjected either to Wipe forming or stretch forming, or to both concurrently.

Mounted on the frame 10 for rotation about an upright axis or post 11 is a rotary table 12 on which is mounted a side face die 13. A suitable clamp 14 is provided on the table for securing one end of a length of stock S to be formed in fixed position relative to the die.

For stretch forming the stock, a stretch forming piston and cylinder assemblage 15 is provided on the frame main portion 10a. This stretch forming assemblage comprises a cylinder 16 in which is reciprocably mounted a piston 17 having a piston rod 18. The rod 18 is connected to a pedestal 19 of a slide 20 which is arranged to travel parallel to the axis of the piston and cylinder assemblage toward and away from the table 12. On the pedestal 19 is a stretch forming head 21 which is adapted to grip the other end of the length of stock S for applying tension thereto. The entire assemblage, in cluding the slide 20, is mounted on a carriage 23 which is rotatable about an upright pivot 24 so that the assemblage can align itself properly with the point of tangency between the stock and the side face die during stretch forming.

Mounted on the frame portion 10b is a wipe forming piston and cylinder assemblage 30 comprising a cylinder 31 with a piston 32 reciprocable therein and having a rod 33 connected to a pedestal 34 of a slide 35. The slide 35 is mounted in a slideway 36 for movement in a direction parallel to the axis of the piston and cylinder assemblage 30. A suitable wipe forming shoe 37 is mounted on the pedestal 34.

In order to drive the table 12 in opposite directions about its axis, as desired, the table is provided with a ring gear 38 coaxial with the bearing post 11.

The structure thus far described is fully disclosed in the above entitled Patent No. 2,514,830.

In accordance with the present invention, the ring gear 38 is in mesh with a plurality of pinion gears 40 which are distributed circumferentially of the table 12. In the form illustrated, two such gears 40 are used, though more may be used, depending upon the torque to be applied to the table. The two gears 40 shown are arranged at opposite sides of a plane through the axis f the table and the axis of the assemblage 30 in the normal centered operating position of the assemblage 30, the gears 40 being placed about 37 to each side of such plane.

Pressure fluid for operating the piston and cylinder assemblages is supplied from a suitable pump 41 driven by an electric motor 42. This pump may also supply the hydraulic motors which drive the operating gears 40.

The assemblage 15 is connected to the pressure source supplied by the pump through a suitable control valve 43, controlled by a servo-motor 43a, later to be described. The assemblage 30 correspondingly is connected through a suitable valve 44, these valves being the customary valves by which pressure fluid can be supplied to either end of the associated assemblage and the opposite end vented concurrently, and, by which, when desired, both ends can be vented or blocked, concurrently, in accordance with the desires of the customer. The specific manipulations of the piston and cylinders for the forming operation are fully set forth in the above entitled patent and form no part of the present invention.

As mentioned, the tables in machines of this type have reached large sizes, four to five tons and larger being not uncommon. Likewise, these tables are of large diameter. Since they-are designed to form various large sheets of metal and subject it to extremely high forces, they are usually driven at comparatively slow speeds, and, for economical drive, are driven through reduced speed transmissions in which the speed reduction from the driving motor to the table may be reduced to as much as one revolution of the table to 4300 revolutions, or more, of the motor. 7

Each driving mechanism comprises a speed reduction power transmission 45 which may be of the conventional reduction gear type. The transmission 45 has a driving shaft 46 and an output shaft 47 which is drivingly connected to a worm gear 48 to which, in turn, is drivingly connected a pinion gear 49 keyed to a shaft 50 to which the gear 40 is also keyed in coaxial relation. Thus the drive of the table is through the speed reduction transmission 45, and if the shaft 46 is turning 4300revolutions per minute, the speed of the gear 40 is such thatthe table 12 is turned one revolution per minute. The transmission 45 is driven by a pair of hydraulic motors 51 and 52 which are connected in coaxial relation on the shaft 46.

The hydraulic circuit leading from the pump to the motors is such that the motors can be connected in parallel, or one of the motors can be used alone, thus providing motive power morein keeping with extremely heavy forming operations and relatively light forming operations, respectively. Fluid pressure is supplied to the motors, as will be more fully described hereinafter.

It is desired that the hydraulic motors operate at the proper speed and, for this purpose, suitable controls may be provided. As illustrated, the power supplied to the motors is from a variable volumetric delivery hydraulic pump 54 driven by an electric motor 55. The preselected pressure fluid supplied by the pump is delivered to the main lines 56 and 57 through a suitable reversing valve 58. A suitable supplementary pump 59 may be provided for maintaining the system loaded with pressure fluid during periods when it is inoperative or idling. The pressure fluid is conducted from the lines 56 and 57 to suitable control valves 61 arranged one control valve illustrated to block the lines 56 and 57 at a point be tween the motor 52 and pump 54 and beyond the leads to the motor 51. At'the same time, it connects the input and discharge of the motor 52 together so that the motor 52 can idle. Thus, only the motor 51 is operable in response to valve 58. When, however, the plug 62 is shifted so that the portions 62b become operative,

then both of the motors 51 and 52 are connected in parallel to the pressure line 57 and to the line 56, and, again,

' both of them are responsive to the valve 58.

Mounted on the shaft 46 is a tachometer 64 which supplies electric signals in accordance with the speed of the motors 51 and 52 through an amplifier 65 to a signal responsive control 66 on the pump 54, thus changing the volumetric delivery of the pump in accordance with the tachometer reading. This control is of a well known type which can readily be setso that, if the speedsignal indicated by the tachometer varies appreciably from that preselected, the volumetric discharge of the pump 54 will be varied accordingly so as to increase or decrease the 6 pump delivery and bring the motors 51 and 52 to the proper speed. The pressure of the delivered fluid is pre selected and set by a pressure control valve 67 which may, if desired, be set to ditferent valves during stretch forming if dictated by the requirements of the particular piece being formed.

Since it is desirable to operate the apparatus from a central control panel, the valve 61 may be operated by a suitable solenoid, such as indicated at 68, and the valve 58 may be operated by a suitable solenoid such as indicated at 69.

As mentioned, it is desirable to preload all of the driving mechanisms including the motors 51 and 52, the speed reduction transmission 45, the mechanism connected between it and the gear 40, the gear 40, the ring gear 38, and table 12. This can be accomplished by supplying pressure fluid to the motors 51 and 52 in a quantity sufiicient to drive them in the selected table driving direction sufficiently to rotate the table slightly. Since reduction is 4300 motor revolutions to one table revolution, the motorscan operate slowly to drive without moving the table appreciably. Thus slack is eliminated and static inertia is partially overcome. Accordingly, the starting of the table can be effected by gradually increasing the delivery of the variable delivery pump 54. pressure is being maintained and the table either is creeping by negligible increments, or is merely subject to slight torque suflicient only to balance 'the friction, the stock is connected at one end to the clamp 14 and-at the other end to the stretch forming head 21.

In accordance with the present improvement the foregoing structure described in my copending application Ser. No. 792,304 is modified by the addition thereto of additional control, shown in Fig. 4, by which, instead of initially tensioning the stock by activation of the stretch forming assemblage 15, the assemblage 15 is locked to prevent the head 21 from approaching the table 12.

In the illustrative example, this locking is effected by the valve 43 which normally is in an intermediate idle position, shown in Fig. 4. The valve 43 is moved to its different operating positions by a servomotor 70 which, upon receiving a selected signal, operates the valve 43 to connect the assemblage 15to the pump 41 for operation by fluid pressure to yieldably urge the head 21 away from the table 12 for tensioning the stock.

In those instances in which the yield of each length of stock is to be established before forming, means are provided for determining the ratio of elongation of the stock to the applied tensioning force, and for initiating the stretch forming cycle by operating the valve 43 when preselected stretch forming tension to be used in forming the stock is established. For this purpose an additional control circuit of a combined hydraulic and electric type is shown for purposes of illustration, it being apparent that other types of circuits may be provided.

The preferred circuit illustrated includes a load cell control means comprising a load cell 70 interposed between the head 21 and the assemblage 15 so as to reflect the lineal pull exerted on the stock lengthwise by the assemblage 15. The load cell has connected thereto a signal producing device which is responsive to the elastic elongation and contraction of the load cell. signal device, which may be of a hydraulic or electric type, is shown as a simple electric strain gauge 71 such, for example, as a conventional transducer or the conventional patch type strain gauge. A suitable load cell with the conventional patch type strain gauge is disclosed in US. Letters Patent No. 2,849,048, issued August 26, 1958. The signal from the strain gauge 71 is fed to a tension control unit 72 of the type described in the foregoing patent.

Also, an elongation control means is provided and includes a signal producing device responsive to die position or the distance of travel of the end of the stock attached to the table 12 during the initial movement While this The of the table 12 for tensioning the stock. The elongation control means may be in the form of a self restoring potentiometer 73 driven in predetermined relation to the rotation of the table from any suitable driven element of the tabledrive, such as the shaft 47 of the transmission 45, so that it is driven in fixed relation to the table 15. The drive is through the medium of a spring released clutch 75 which is controlled by an electrically operated servomotor 76 and has its driven disc connected to the clutch 75. The servo-motor 76 is electrically connected through a switch 76a to the tension control unit 72 so as to be responsive to the combined effect of the electric signals received from the strain gauge 71 and potentiometer 73 for applyiing the clutch when the stock is tensioned initially and for releasing the clutch when the ratio of elongation of the stock, reflected by the potentiometer, to the tension applied, reflected by the strain gauge 71, becomes excessive.

' When the clutch 75 is released, the potentiometer restores itself to starting position.

For the purpose of giving a signal indicating the ratio of elongation to the applied tensioning force, the strain gauge 71 and potentiometer 73 are connected in a null balance circuit, as disclosed in the above Patent No.

I 2,849,048. Thus the clutch 75 is disengaged at all times except during starting of the table 12 and initial tensioning of the stock. A reduction gear device 77 is interposed between the clutch 75 and the potentiometer 73 for driving the potentiometer at reduced speeds.

At this point it is to be noted that travel of the table during the creeping movement from the point for initial tensioning the stock to yield point is very slight when the stretch forming head is locked in fixed position. Accordingly, even though the potentiometer 73 moves in direct relation to rotation of the table, regardless of variations in curvature of the die, the difference between such slight distances is so small that their practical effect is identical.

As mentioned, the signals from the strain gauge 71 and from the potentiometer 73 are fed to the tension control unit 72 and a signal derived thereby from the combination of the two signals is fed to the servo-motor 43a of the valve 43. When the ratio of elongation to tension becomes disproportionate with a resulting too great an unbalance in the null circuit and too great an increase in elongation, showing that the metal has reached its yield point, the servo-motor 43a is caused to shift the valve 43 to the left in Fig. 4, thereby unlocking the piston and cylinder assemblage 15 for elongation and contraction and connecting it simultaneously with the fluid pressure circuit so that the head 21 is yieldably urged by the assemblage 15 in a direction away from the table 12 at pressure to produce the preselected tensioning force.

However, this preselected tension must be controlled during forming of the stock and for this purpose a supplemental circuit is provided. Connected to the valve 43 between its outlet and the rod end of the piston and cylinder assemblage 15 to which fluid pressure is supplied for urging the head 21 away from the table 15, is supplemental circuit including a hydraulic line 80. The line 80 leads through a control valve 81 operable remotely by a solenoid 82. In one position of the valve 81, the fluid from the line 80 is directed to a variable discharge release valve 83 which is controlled by a servomotor 84, the servo-motor, in turn, being connected to the tension control unit 72 through a line 85, so as to receive therefrom a signal derived from the strain gauge.

The variable discharge release valve discharges to a sump. Since it is always desirable to keep the rod end of the cylinder full of oil so that there is no slack due to drainage when starting and stopping, a throttling valve 86, adjustable manually by a handle 87, is provided.

.This throttling valve is connected so that it discharges through the variable discharge relief valve 83 and, at the opposite side is connected to the valve 81. The valve 81 is arranged so that when the pressure fluid is passing directly from the line to the valve 83, the by-pass circuit through the throttling valve 86 is stopped at the inlet end and the throttling valve is inoperative. On the other hand, when the valve 81 is shifted to the right, fluid from the line 80 is directed by the valve 31 through the throttling valve 86 and thence to the variable discharge relief valve 83. The throttling valve is such that it allows only a minute amount of creepage of the assemblage 15 suflicient to offset any loss of fluid by leakage and drainage but insufficient to effect any appreciable movement or operation of the piston and cylinder assemblage for moving ahead in a direction away from the table.

With this structure the stock may be brought up to the tension desired, its yield point determined, the tension dropped back to the preselected tension below yield and the operation thereafter continued at preselected lower tensioning forces.

In order to control the speed of the table, a speed control unit 90 is arranged to receive a signal through the line 91 from the tension control unit 72. The speed control unit operates in response to the combined signal which operates the servo-motor 84 to start the forming cycle. Hence, when the stretch forming assemblage is released and connected for operating under the restraint of the fluid pressure from the pump 41, the table speed control becomes operative. A servo-control 92 is connected to the variable delivery pump 54 so as to vary the delivery thereof and thereby control the table speed. The servo-control '92 is responsive to the signal from the table speed control unit. Thus table speed is increased immediately upon the stock being subjected to yieldable tensioning force by the assemblage 15.

By means of this arrangement, the tension can be applied to the stock, the stock brought up to the desired predetermined tension, or to its yield point and then dropped back to the predetermined tension desired, and the machine started for completing the forming operation.

For example, let it be assumed that the table is stationary and the valve 43 is in the position illustrated in Fig. 4, whereby the hydraulic piston and cylinder assemblage 15 is locked so that the head 21 cannot approach the table. A piece of metal stock is connected at one end to the clamp 14 on the table and at the other end to the stretch forming head 21.

Thereupon the table is started manually. The normal setting of the table speed control 90 is such that the table merely creeps very slowly and this creepage continues until the slack is removed from the stock and tension is developed.

This creepage continues until the tension is built up so that the ratio of elongation to tension becomes proportional within certain limits and the null circuit is balanced. Balance causes the clutch to be engaged. Assuming each piece of stock is to be separately monitored, the creeping rotation of the table continues until the ratio of elongation to tension increases disproportionately. During this period the signal is being delivered by the strain gauge 71 and potentiometer 73 to the tension control unit 72 and a corresponding signal is being delivered by the tension control unit 72 to the servo control 76 of the clutch 75.

When the ratio of elongation to tension becomes disproportionate, the tension control unit 72 signals the servo-motor 76 of the clutch 75 causing it to release the clutch 75. The tension control unit also delivers a signal to the servo-motor 70 of the valve 43 as soon as the ratio of elongation to applied tension is disproportionate or greater than that preselected. Thereupon the valve 43 is operated by movement to the left in Fig. 4 to connect the piston and cylinder assemblage 15 in a hydraulic circuit so that the head end of the cylinder is connected to sump and the rod end is connected to the pump 41.

This, of course, causes reduction in the tension on the stock to that below yield due to presetting of the relief valve 83, whereupon the tension control unit 72 through the line 91 signals the table speed control 90 which delivers a signal to the servo motor control 92 and increases the delivery of the pump 54 to increase the table speed gradually by minute increments nad bring it up to the full speed desired.

Immediately upon the reduction in tension, the ratio of elongation to tension changes so that the clutch 75 becomes inoperative and releases the potentiometer which thereupon returns to starting position.

Meanwhile, in response to the signal from the strain gauge 71 through the tension control unit 72, the servo motor 84 operates the valve 83 to maintain a preselected tension on the stock by varying'the discharge of the valve 83. During all of this operation the valve 81 is in the position in Fig. 4.

If desired, conventional indicating means may be provided in the tension control unit or circuit so that the tension being applied and the point at which disproportionate elongation occurs can be readily observed.

The conventional manual controls, either direct or remote by solenoids, may be provided for starting and stopping the table, and for activating and locking the hydraulic piston and cylinder assemblage 15, all such manual controls being in addition to those herein described.

At the end of the forming cycle, the table may be stopped manually, or it may be stopped automatically by a suitable limit switch, whereupon the formed piece is removed, the valve 43 is manipulated by manual control to bring the assemblage 15 to starting position and lock it hydraulically in position preparatory to repeating the cycle.

The words horizontal, vertical, horizontally, and vertically and the like, are used in the description and claims for convenience in describing the relative positions of the parts and not as absolutes, inasmuch as the invention has been illustrated as used with a machine in which a turntable is arranged with its axis extending vertically. Obviously, the entire machine can be disposed so that the axis of the turntable is other than vertical so long as the relative positions of the parts are maintained.

Having thus described my invention, I claim:

1. In a stretch forming machine, a rotatable table adapted to support, for rotation therewith, both a side face die and means for connecting one end of a length of stock in fixed position relative to the die, a hydraulic stretch forming assemblage, a stretch forming head carried by the assemblage and adapted for connection to the other end of the length of stock for tensioning the stock endwise by the assemblage as the stock is wrapped onto the die by rotation of the table, a variable speed hydraulic drive drivingly connected to the table for rotating the table, said hydraulic drive being variable in speed for varying the table speed by minute increments in a speed range from substantially zero table speed upwardly throughout the entire range of tension applied to the stock, speed control means for varying the speed of the hydraulic drive throughout said speed range and settable initially to cause very slight table creepage, pressure supply means for supplying controlled hydraulic pressure fluid to the assemblage for yieldably urging the head thereby in a direction away from the table for tensioning the stock, pressure control means for varying said pressure supplied to the assemblage, locking means for initially constraining the head from movement toward the table during initial creepage of the table, means to release the locking means and render the assemblage operable by said hydraulic pressure to maintain predetermined forming tension on the stock while the table is constrained from reverse rotation by the hydraulic drive.

2. A structure according to claim 1 and including :means to gradually increase the speed of rotation of the 10 table by minute increments by the hydraulic drive while said predetermined forming tension is maintained.

3. In a stretch forming machine, a table member adapted to support both a side face die and means for connecting one end of a length of stock in fixed position relative to the die, a hydraulic stretch forming assemblage, a stretch forming head member carried by the assemblage and adapted for connection to the other end of the length of stock for tensioning the stock endwise by the assemblage as the stock is wrapped onto the die by predetermined relative'movement of the members, means supporting the members for said predetermined relative movement, a variable speed hydraulic drive drivingly connected to one of the members for effecting said predetermined relative movement, said hydraulic drive being variable in speed for varying the speed of said predetermined relative movement by minute increments from substantially zero speed to full speed, speed control means for varying the speed of the hydraulic drive and settable initially to cause said predetermined relative movement to be very slight relative to creepage of the members, pressure supply means for supplying controlled hydraulic pressure fluid to the assemblage for yieldably urging the head member thereby in a direction away from the table member for tensioning the stock, locking means for constraining the head member initially from movement toward the table member during said initial creepage of the members, tension operated means operable in response to the tension applied to the stock, elongation controlled means operative in predetermined relation to the elongation of the stock, and means responsive to both the tension operated means and elongation controlled means, upon said slight initial creepage of the members to the point at which stock elongation increases at a predetermined selected rate disproportionate to the tension applied by table rotation, to release the locking means and render the assemblage operable by the said hydraulic pressure to maintain lower tension on the stock which is less than that which causes said disproportionate elongation. I

4. In a stretch forming machine, a table member adapted to support both a side face die and means for connecting one end of a length of stock in fixed position relative to the die, a hydraulic stretch forming assemblage, a stretch forming head member carried by the assemblage and adapted for connection to the other end of the length of stock for tensioning the stock endwise by the assemblage as the stock is wrapped onto the die by predetermined relative movement of the members, means supporting the members for said predetermined relative movement, a variable speed hydraulic drive assemblage drivingly connected to one of the members for effecting said predetermined relative movement, said hydraulic drive assemblage being variable in speed for varying the speed of said predetermined relative movement by minute increments from substantially zero speed to full speed, speed control means for varying the speed of the hydraulic drive assemblage, pressure supply means for supplying controlled hydraulic pressure fluid to the stretch forming assemblage for yieldably urging the head member thereby in a direction away from the table member for tensioning the stock, locking means operatively connected to one of the members to prevent initial movement thereof, by tension of the stock, toward the other member in a direction endwise of the stock, tension operated means operable in response to the tension applied to the stock, elongation controlled means operative in predetermined relation to elongation of the stock, and means responsive to both the tension operated means and elongation means upon stock elongation increasing at a predetermined rate disproportionate to the tensioning of the stock to render the assemblages operative to stretch form the stock about the side face of the die at a tension lower than that which caused said disproportionate elongation.

'11 5. A structure according to claim 4 including means to increase the speed of said predetermined relative movement upon application of the hydraulic pressure to maintain said lower tension.

6. A structure according to claim 4 including means to release the locking means and to render the stretch forming assemblage operable by said hydraulic pressure to maintain lower tension on the stock which is less than that which causes said disproportionate elongation, and means to increase the speed of the hydraulic drive assemblage.

7. A structure according to claim 4 wherein the means responsive to the tension operated means and elongation controlled means reduces said predetermined relative speed substantially to zero.

8. In a stretch forming machine, a table member adapted to support both a side face die and means for connecting one end of a length of stock in fixed position relative to the die, a hydraulic stretch forming assemblage, a stretch forming head member carried by the assemblage and adapted for connection to the other end of the length of stock for tensioning the stock endwise by the assemblage as the stock is wrapped onto the die by predetermined relative movement of the members, means supporting the members for said predetermined relative movement, a variable speed drive assemblage drivingly connected to one of the members for effecting said predetermined relative movement, spced control means for varying the speed of the drive assemblage, pressure supply means for supplying controlled hydraulic pressure fluid to the stretch forming assemblage for yieldably urging the head member thereby in a direction away from the table member for tensioning the stock, tension operated means operable in response to the tension applied to the stock, elongation controlled means operative in predetermined relation to an elongation of the stock, and means responsive to both the tension operated means and elon gation means upon stock elongation increasing at a predetermined rate disproportionate to the tensioning of the stock to render the assemblages operative to stretch form the stock about the side face of the die at a tension lower than that which caused said disproportionate elongation.

References Cited in the file of this patent UNITED STATES PATENTS

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