US2981136A - Apparatus for modulating punch and die - Google Patents

Description

April 25, 1961 E. E. LEGGE APPARATUS FOR MODULATING PUNCH AND DIE Filed April 18, 1955 FIG-2 PIC-3- I All l V 6. V

INVENTOR ELMER E- LEGGE BY W7 WM ATTORNEYS APPARATUS FOR MODULATING PUNCH AND DIE Elmer E. Legge, West Hartford, Conn, assignor, by mesne assignments, to Koehring Company, Milwaukee, "Wis., a corporation of Wisconsin Filed Apr. 18, 1955, Ser. No. 501,835 8 Claims. (Cl. 83-632) The present invention relates to the class of machines that are commonly employed for stamping, punching, dieing, blanking or other similar operations, and more particularly to mechanism for modulating or damping the relief or release of the load on such machines'as the work portion of operation is completed.

In punching and dieing operations, the load on the die or punch builds up to a maximum at the break-through point at which the work piece no longer offers appreciable resistance to the tool and is cut or sheared whereupon the load created on the machine by the tool and the Work piece drops abruptly. This abrupt load drop occasioned by the shearing or'cutting operation should not be confused with. the gradual load relief occasioned in a coining, drawing or stretching operation where less than complete shear, if any, is effected.

- Depending upon the slack or play in the machine and its bearings and upon the stresses created in its components by the load, with abrupt relief or release of the load, the

tool will tend to over-travel or overshoot the normal travel of its work stroke before reversing and traveling the return or back stroke.

This overtravel of the tool on the load or work stroke occasions numerous disadvantages, not the least of which is excess wear on the tool and necessitates frequent tool sharpening or dressing.

Moreover, it is virtually impossible to set the machine to consistently punch or die-cut the work piece and at the same time not dislodge the severed portion or cutout from within the hole from which punched. Overtravel of the die completely dislodges the cutout, rather than leaving it displace-d within, but frictionally retained by the work piece.

Heretofore, so -called striking blocks or contact pads have been provided to prevent overtravel of the punching or dicing tool. These blocks. or pads are hardened steel members which engage and load the pressing or dieing machine before the tool bottoms or reaches the end of its work stroke. The striking blocks gradually build up andrelieve the load on the presses the tool finishes the work stroke and starts its back or retraction stroke, thereby preventing the 'machine from traveling unloaded through the end of the work stroke and also preventing overtravel' of the tool despite abrupt relief of the load created by the tool when the work piece fails in shear before completion of the work stroke.

Considerable care must be taken to prevent overloading and breaking the press with the striking blocks.

This danger has been lessened by substituting one or more springs for the striking blocks or spring cushioning the blocks in place of more conventional and relative unyielding mounting of the blocks. However, the fallibility of springs to repeated loading considerably imp-airs their effectiveness.

-' It is an object of the present invention to provide improved method and apparatus of the type indicated for punching and die cutting in which the punch or die is subject to a minimum of wear.

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2. A further object is to provide hydraulically cushioned loading means in combination with a punch or die apparatus which loads the apparatus progressively to the end of the work stroke and thereafter progressively unloads the apparatus on the back or return stroke so that undesirable overtravel of the punch or die is precluded.

Another object is to provide a device of the type indicated including means for adjustably selecting the load applied to the dieing apparatus.

A still further object is to provide a hydraulically cushioned loading device of the type indicated wherein the hydraulic cushion is progressively increased by automatically greater throttling of a hydraulic system which is effected as the punch or other tool advances in its workv stroke.

These and other objects and advantages of the invention and the means for accomplishing them will be apparent from the following description of a preferred embodiment of the invention which is described with reference to the accompanying drawings, in which:

Fig. l is an elevation view partly in cross-section of a dieing machine on which adjustable oil cushion blocks are installed in accordance with the present invention;

Fig. 2 is an enlarged view, the lower portion of which is in cross-section, showing details of one of the oil cushion blocks shown in Fig. 1; and

Fig. 3 is an enlarged cross-section view taken on line 3-3 of Fig. 2.

Referring to the drawings, the invention is illustrated in conjunction with a Henry & Wright dieing machine of well-known construction and operation. Generally, the machine comprises a frame F which includes a base 1 and upwardly projecting supports 2 on the top of which is a table 3. A crank shaft 4 is rotatably mounted in the frame F and power driven in any suitable way, as by a belt driven fly wheel 5 through a clutch-brake combination 6. T he crank shaft 4 is operatively connected to and reciprocates a punch, generally designated P, and its crosshead holder '7. The crosshead 7 is secured to the upper ends of rods 8 which are slidably mounted in the frame F and the lower ends of which are fastened to a crosshead 9 that is mounted for vertical reciprocating movement below crank 4a of the crank shaft 4. Reciprocating movement is imparted to the crosshead 9 by the crank 4a through a connecting rod 10 the length of which is adjustable in a, manner common to machines of this type to raise and lower the extreme positions of travel of the crosshead 7 and the punch P mounted thereon.

The weight of the punching mechanism, including the punch P, the upper crosshead or punch holder 7, the rods 8, the lower crosshead 9 and the connecting rod 1i preferably is counterbalanced by a counterbalancing spring assembly 11 which is located beneath and resiliently supports the lower crosshead 9 and the components of the punching assembly which are secured to the lower crosshead.

As shown in Fig. 1, the punch P is adapted to cooperate with a die D and punch a corresponding hole in sheet stock or similar work piece 14. Lengthening the connecting rod 10 serves to lower the crosshead 7 so that the punch P earlier in its stroke engages the work piece 14 and descends farther into the die D. Conversely, shortening the rod 10 raises the crosshead '7 and punch P so the contact with the work piece 14 is made later in the stroke and the punch P does not descend as far relative to the die D.

More particularly, the die D is securely fastened on the dieing machine table 3 and is provided with a hole or passageway 15 which is aligned with and conforms to the shape of the punch P so that on the downstroke the punch P cuts the desired opening 16 in the workpiece 14 and displaces the portion 14a therein or entirely removes the portion 14a from the work piece 14.

In this cutting or punching operation, the load on the die D and punch P buildsup to a maximum which cuts the work piece 14, whereupon the load on the punch P drops abruptly. This abrupt drop in resistance occasioned by the shearing or cutting operation causes the punch P to overtravel or overshoot the normal travel of its work stroke before reversing and traveling the return or back stroke. The extent of this overtravel varies with the slack or play in the machine and its bearings and upon the stresses created in the machine by the load.

The overtravel of the punch P on the load or work stroke causes excessive wearing and dulling contact with the die D so that both punch and die have to be frequently dressed or sharpened.

In accordance with the present invention, oil cushioned units, generally designated 18, are provided between the table 3 and crosshead 7 to prevent abrupt load release and the excessive wear on the punch and die set. Identical units may be provided at each of the four corners of the table 3, or elsewhere, as may best serve to distribute the load in the several units.

More particularly, as best shown in Figs. 2 and 3, each oil cushioning unit 18 includes a base or well block 19 which is securely fastened to the table 3 by screws 20.

The block 19 has a vertically disposed generally cylindrical well 21 containing a cylindrical floating piston 22 which is guided for vertical travel by rib members 23 which are secured to the well wall 21.

The piston 22 is supported by springs 24, three of which are employed in the illustrative embodiments and on which the weight of the piston is equally distributed so that the bottom surface 22a of the pistons 22 is evenly spaced from the bottom surface 25 of the well 21.

The springs 24 are located within suitable cylindrical recesses 26 in the bottom of the well 21 so that the bottom 22a of the piston 22 can be pressed down against the force of the springs 24 into close abutting relationship to the well bottom 25. 7

As shown in Fig. 2, the upper portion of the piston 22 has an annular shoulder 27 which engages a capping plate 28 which is secured by screws 29 to the top of the well block 19 and determines the upper position to which the floating piston 22 is pressed by the springs 24. Projecting upward from the piston shoulder 27 is a cylindrical portion 30 of the piston of lesser diameter. The cylindrical portion 30 slidably extends through a conforming aperture 31 in the cap plate 28.

In accordance with the invention, the bottom 22a of the floating piston or ram 22 is submerged in oil or other .viscous liquid 32 in the well 21, the oil level 33 being above the piston bottom 22a when the ram 22 is in the uppermost position. The oil may be introduced into the well 21 through a hole 34 in the cap plate 28. Preferably the hole 34 is located above one of the ribs 23 so that the latter serves as a baffle preventing escape of splashing oil when the piston 22 is driven to the bottom of the well 21 during the down or work stroke of the crosshead 7 and punch P.

"The piston 22 is driven to the bottom of the well 21 against the resistance of the springs 24 and the oil 32 by an adjustable ram, generally designated 35. As shown in Fig. 2, the ram 35 includes a bracket 36 which is secured as by bolts 37 to the crosshead 7 and to which is fastened the base 38 of a split ring 39 in the vertically disposed threaded bore 40 of which is secured a depending threaded ram 41. Adjustment of the rams 41 in the several hydraulic striking cell assemblies 35, located at the corners of the dieing machine, normally is effected initially while the crosshead 7 is stationary at the bottom of the stroke, at which time each ram 41 may be rotated, as by means of the sockets 41a, and a suitable spanner wrench, so' as to lower the ram 41 into engagement with and force the bottom 22a of the floating piston 22 snugly against the bottom 25 of the well 21.

A calibrated ring 42 threaded on the ram 41 then is rotated to the zero adjustment position relative to the fixed pointer 43 on the split ring 39 and there secured as by set screw 42a. The calibrated ring 42 when so secured preferably is spaced from the split ring 39 so that adjustment of the ram 41 may be made in either direction. As shown in Fig. 2, screw 44 provides means for tightening the split ring 39 and locking the ram 41 in a selected position of adjustment.

Preferably the engaging surfaces of ram 41, piston 22 and well bottom 25 are all polished or finely ground fiat. In adjusting the rams 41 of the several units normally each is each drawn to the same amount of snugness against the fully depressed piston 22 to effect zero adjust ment of the calibrating ring 42 while the crosshead 7 is stationary in the lowermost position. Thereafter, each ram 41 may be readjusted any selected amount from the zero position of the calibrated ring 42. Normally, the adjustment is effected with the crosshead 7 raised from the lowermost position and is in a. direction to effect a greater load on the piston 22 and the dieing machine when the machine is in operation. However, the final adjustment may effect a lesser rather than a greater load than at the zero position of calibration.

It is desirable to effect the zero positioning of the ram 41 and to calibrate the ring 42 with the aid of strain gage-oscilloscope, or other load measuring equipment, so that loading is kept within the permissive maximums of the dieing machine and the hydraulic striking units.

Generally it is desirable to effect equal loads on the several cell units 35.- However, differential loading is contemplated and may be effected by suitable adjustment of the rams 41, particularly where the punch load is unsymmertically applied on the upper crosshead 7.

In operating the dieing machine, the load effected on the punch P by the Work piece 14 increases as the punch descends until the shear strength of the work piece is exceeded and the piece 141: is sheared from the work piece 14 and the load on the punch abruptly drops.

Before the punch load falls to zero, the ram 41 of each of the hydraulic striking cell units 35 engages and depresses its floating piston 22 and asserts an increasing load on the dieing machine. The oil is driven from between the piston 22 and the well bottom 25 as the piston is forced downwardly, thereby hydraulically loading the cell 35. In accordance with the invention, the discharge orifice formed between the periphery of the piston bottom 22a and the well bottom 25 rapidly becomes smaller thus increasing the throttling effect of oil displaced therethrough and thereby automatically progressively increasing the load on the cell unit 35 and the machine.

The load on the cell cushioned by the oil increases to a maximum at the bottom of the work or down stroke and thereafter is progressively relieved with the return or upstroke of the crosshead 7.

Generally, it has been found desirable to adjust the rams 41 so that after the maximum punch load is reached the total load on the machine decreases to approximately half the maximum load. Thereupon the rate of load build-up on the hydraulic units 35 preferably is of the order of the rate at which the load on the punch P drops so that the load on the machine remains approximately constant at about half peak load throughout the remainder of the downstroke.

While the half peak load value is preferable, it is not essential and other values may be selected. Preferably, however, the load on the hydraulically cushioned striking cells 35 and the dieing machine remains above zero or no-load throughout the entire downstroke and is relieved only after commencement of the upstroke,lwhereby the load on the machine components and bearings are not reversed during the downstroke.

Themes-imam load on the cell's35 scour: at the bottom' of the work or downstroke of'the punch P; Loading is initiated at a relatively low rate and increases rapidly to Substantially the constant rate of the cellswhen operated without oil. The substantially constant portion of the loading rate does not appreciably vary when the adjustment of the rams 41 are changed to increase or decrease the maximum load. I

Accordingly, adjustment of the rams 41 also changes the point in the stroke at which cell loading is initiated.

In accordance with the invention, adjustment of the length of the connecting rod serves to vary the time in the work stroke at which the-load on the punch P is initiated and completed and also the timing of the punch load relative to the cell load. Normally it is desirable to initiate the loading of the cell 18 by the ram 41 after theloading of the punch P is initiated and before it is completed. Moreover, it is desirable that the maximum cell load be attained after the maximum punch load has been relieved. I

If desired, the cell load may be initiated simultaneously or even prior to the punch'load. Normally, however, it will be suflicient to have overlapping concurrent loading so that the cell load prevents the load on the machine dropping to zero at any time during the down stroke when punch load drops to zero.

The present invention provides a simple hydraulically cushioned loading mechanism 35 in dieing machines and the like which prevents overthrow of the punch P and attendant disadvantages while minimizing the danger of overloading the machine.

It is possible to set the machine to consistently punch or die-cut the work piece 14 and at the same time not to dislodge the severed portion or cutout 14a from within the hole from which punched. Overtravel of the punch of course would dislodge the cutout 14a, rather than leaving it displaced within and frictionally retained by the work piece 14.

Having thus described a preferred embodiment of the invention, I claim:

1. In combination with a dieing machine or the like having a base and a tool secured to a cross head which is driven through a work stroke and a return stroke relative to the base, a hydraulically cushioned cell for loading the machine to the end of the work stroke concurrently with loading of the machine by a work piece engaged by the tool and for thereafter progressively unloading the machine on the back or return stroke so as to prevent overtravel of the tool, said loading cell including members relatively movable toward each other on the work stroke and away from each other on the return stroke, said members having confronting surfaces relatively movable toward and away from each other within a liquid medium and from between which the medium is discharged through a progressively smaller orifice to the end of the work stroke, and meansadjustably secured to the cross head and movable therewith into engagement with one of said movable members to force the engaged member toward the other of said members and wherein the other of said members is fixed to said base.

2. In combination with a dieing machine having a stationary frame on which is mounted a stationary die and a reciprocable punch holder having a work stroke and a return stroke and on which a punch is secured for reciprocable movement relative to the die so as to cooperate with the die and load the machine on the work stroke by shearing a portion of a work piece, cushioning means independent of the punch for loading the machine progressively to the end of the work stroke and thereafter progressively unloading the machine on the return stroke and preventing overtravel of the punch, said loading means including hydraulic means for cushioning the loading progressively applied by said loading means and comprising a well casing mounted on the frame, piston-like means movably mounted therein, said casing and said means having confronting surfaces yieldably urged apart and a liquid medium interposed between the confronting surfaces, and a ram which' is movable with the punch and which engages said means and forces the confronting surfaces toward each other on the work stroke concurrently with movement of the punch.

3; Apparatus as recited in claim 2 and including means for adjusting theram relative to the punch and thereby adjustably selecting the load applied to the dieing ma chine by the hydraulically cushioned loading means.

4.- In combination with a dieing machine having a stationary' frame on which is mounted a stationary die and a reciprocabl'e punch holder having a work stroke and a return stroke and on which a punch is secured for reciprocabl'e movement relative to the die so as to cooperate with the die and load the machine on the work stroke by shearing a portion ofa work piece, cushioning means independent of the punch for loading the machine progressively to the end of the work stroke and thereafter progressively unloadingithe machine on the return stroke and preventing overtravel of the punch, said loading means including hydraulic means for cushioning the loading progressively applied by said loading means and comprising a well casing mounted on the frame, piston-like means movably mounted therein, said casing and said means having confronting surfaces yieldably urged apart and a liquid medium interposed between the confronting surfaces, and a ram which is movable with the punch and which engages said means and forces the confronting surfaces toward each other on the work stroke concurrently with movement of the punch, said loading means further including adjustment means for adjusting the ram rela tive to the punch and thereby adjustably selecting the load applied to the dieing machine by the loading means, and means independent of said adjustment means for selecting the bottom position of the punch.

5. In combination with a dieing machine having a stationary frame on which is mounted a stationary die and a reciprocable punch holder having a work stroke and a return stroke and on which a punch is secured for reciprocable movement relative to the die so as to cooperate with the die and load the machine on the work stroke by shearing a portion of a work piece, cushioning means independent of the punch for loading the machine progressively to the end of the work stroke and thereafter progressively unloading the machine on the return stroke and preventing overtravel of the punch, said loading means including hydraulic means for cushioning the loading progressively applied by said loading means and comprising a well casing mounted on the frame, piston-like vmeans movably mounted therein, said casing and said means having confronting surfaces yieldably urged apart within a liquid medium and from between which the liquid medium is discharged through a progressively smaller orifice to the end of the work stroke, and a ram which is movable with the punch and which engages said means and forces the confronting surfaces toward each other on the work stroke concurrently with movement of the punch.

6. In combination with a dieing machine having a stationary frame on which is mounted a stationary die and a reciprocable punch holder having a work stroke and a return stroke and on which a punch is secured for reciprocable movement relative to the die so as to cooperate with the die and load the machine on the work stroke by shearing a portion of a work piece, cushioning means independent of the punch for loading the machine progressively to the end of the work stroke and thereafter progressively unloading the machine on the return stroke and preventing overtravel of the punch, said loading means including hydraulic means for cushioning the loading progressively applied by said loading means and comprising a well casing mounted on the frame, floating piston means mounted therein with said casing and said means having confronting surfaces spring-urged apart and a liquid medium interposed between the confronting surfaces, and a ram which is movable with the punch and which engages said means and forces the confronting surfaces toward each other on the work stroke concurrently with movement of the punch.

7. In combination with a dieing machine having a stationary frame on which is mounted a stationary die and a reciprocable punch holder having a work stroke and a return stroke and on which a punch is secured for reciprocable movement relative to the die so as to cooperate with the die and load the machine on the work stroke by shearing a portion of a work piece, a plurality of cushioning means independent of the punch for concurrently loading the machine progressively to the end of the work stroke and thereafter progressively unloading the machine on the return stroke and preventing overtravel of the punch, each of said loading means including hydraulic means for cushioning the loading progressively applied by said loading means and comprising a well casing mounted on the frame, piston-like means movably mounted therein, said casing and said means having confronting surfaces yieldably urged apart and a liquid medium interposed between the confronting surface, and individual rams which are movable with the'punch and which engage the individual piston-like means and force the confronting surfaces toward each other on the work stroke concurrently with movement of the punch.

8. Apparatus as recited in claim 7 and including individual adjustment means associated with each ram for adjusting the rams relative to each other and to the punch.

References Cited in the file of this patent UNITED STATES PATENTS Lindgren June 30, 1934

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