US2305336A - Hydraulic blank holder - Google Patents

Description

Dec. 15,1942, L; R. wlL AMsw 2.305.33

' HYDRAULIC BLANK HOLDER Filed April 20, 1939 2 Sheets-Sheet l INVENTORL LARK/N fF. WILLIAMSON RNY.

Dec. 15, 1942. 1.. R. WILLIAMSON HYDRAULIC BLANK HOLDER Filed A ril 20, 1939 2 sheets-sham 2 R v ON M mm M E 0 R w W M W III M Fig.5

Patented Dec. 15, 1942 Uri-ire -HYDRAULIC BLANK HOLDER Larkin R. Williamson, Brooklyn, N. Y., assignor to E. W. Bliss Company, Brooklyn, N. Y., a corporation of Delaware Application April 20, 1939, Serial .No. 268,961

5 Claims.

Inpresses of this type-heretofore used'it has I,

been customary to provide toggles to operate the blank holder .and gearing connecting the toggles and main drive of the press. Similarly, in triple action presses additional gearing, shafts and levers were required over that utilized to operatethe blank holder. These prior constructions were expensive to build and were difiicult tosynchronize in such a manner that the load was uniformly applied in accord with a predetermined ratio. This has been particularly true in toggle-operated blank holders where it was necessary to control the time and amount of pressure applied ateach corner of the blank holder and the time it was applied.

The general object of my invention has been to provide a press in which the expensive and unwieldy gearing is eliminated and to employ hydraulic means to actuate the blank holder and related mechanism in either a double or triple action press. An additional obiect has been to provide mechanism associated with a blank holder to permit accurate control of the pressure applied at the corners thereof. Still another object has been-to provide adjustments by which the relation between the force applied to the blank holder at any given point and the power means of the press may be varied as desired.

To the accomplishment of the foregoing and related ends, said invention, then, consists of the means hereinafter fully described and particularly pointed out in the claims; the annexed drawings and the following descriptionsetting forth in detail certain structure embodying the invention, such disclosed means constituting, however, but one of various structural forms in which the principle of the invention may be used.

In said annexed drawings- Fig. 1 is a perspective view of my improved press;

Fig. 2 is a view showing the hydraulic system employed;

Fig. 3 is a section through one of the pressure applying pistons and the supply reservoir therefor;

Fig. 4 is a detail the system;

Fig. 5 shows a unit of the system by which an increased stroke is applied to the blank holder showing an adjustment of over the stroke appliedto-the actuating piston; Fig. 6 is a similar view showing a construction by which an increased pressure at the blank holder is obtained over the pressure at the actuating piston; V

Fig. '7 is a detailof the safety mechanism; and Fig. 8 is a graphshowing how the pressure applied to the blank holder may be controlled.

In general, my invention is preferably employed in connection with the blank holder -of a press. In such case four independent hydraulic systems are employed which act at the four corners of the blank holder to push the same downwardly to grip a sheet. The systems are independent of each other to prevent one corner from acting as a-hydraulic fulcrum for another. It will be apparent that more or fewer systems maybe employedandthat the blank holder may receive the thrust of the hydraulic systems at other thanthe'four corners. An air piston is provided to aid in -moving the blank holder against the work and to returnthe blank holder at the end of the drawing operation. Each separate system comprises an actuating piston driven from the press drive shaft, and a second piston acting onthe blank holder which is moved upon actuation of the first'piston. A column of oil fills the space between the two pistons.

My invention contemplates varying the ratio between the actuating piston and its related piston in each system, such that the ratio be tween the pressure applied and the pressure derived therefrom may be varied. Similarly, I contemplate varying the stroke of the blank holder with respect to the stroke of the actuating piston. Additionally, the various systems which function as a unit to operate the blank holder may be varied, one with respect to the other.

Referring now to the drawings, my press comprises the usual bed I!) and uprights II and I2 surmounted by a crown l5. A die slide 16 to sup-,

port the movable die is slidingly supported from the crown. The mating die is carried in the customary manner on the bed.

The slide is reciprocated by a crankshaft l8 extending from right to left and provided with two eccentric portions 20. The eccentrics carry pitmans 2!, which in turn engage the die slide to raise and lower the same. A blank holder 23 is slidably carried in the uprights in ways 22 secured thereto. The blank holder is of the usual configuration surrounding the die slide.

Both the die slide and the blank holder are driven from the crankshaft [8 as hereafter described. The crankshaft in turn carries a pair of twin gears 24 and 25 at opposite ends of the press. Each gear is provided with a counterweight 2! to balance the crankshaft eccentrics. These gears are driven by pinions mounted in the usual manner on a back shaft extending across the press parallel to the crankshaft. The back shaft in turn is driven by a clutch shaft. A combined pulley wheel and flywheel til is idly carried on the clutch shaft and is driven by a suitable source of power. A clutch and brake mechanism is provided to drive the clutch shaft from the flywheel or to act as a brake to hold the clutch shaft with respect to the press frame.

To operate the blank holder, four independent hydraulic systems are provided which coact as a unit with an air counterbalance cylinder 32 and piston rod 33 to shift the blank holder downwardly into engagement with the work. After the work stroke is finished the air counterbalance, carried by the crown in the usual manner, functions through the piston rod secured to the blank holder to draw the same upwardly to the inactive position of Fig. 1.

The air cylinder provides a chamber on each side of the pistons (not shown) which is carried by a piston rod 33. As the operating cycle of the press begins air is admitted to the upper chamber above the piston with sufiicient pressure to push the blank holder down until it is almost in contact with the work. At this time cam mechanism, hereafter described, applies the hydraulic blank holding force to the blank holder. When the drawing operation is completed the air at the bottom of the cylinder, which is of the usual type, brings the blank holder up to its original position as soon as the air pressure above the piston and the hydraulic pressure applied to the blank holder are removed.

Each individual hydraulic system comprises a pair of cylinders with pistons therein and a solid column of oil between the pistons to transmit the force applied at one to the other piston. Four systems are provided and the pistons to which the actuating force is applied are preferably mounted side by side, as shown in Fig. 2. These actuating cylinders, indicated at 35 (Fig. 3) each comprise a, casing 36 capped at the lower end at 3? and at the upper end at 38. The lower cap threadingly receives a pipe ii) passing to the blank holder.

A piston is slidingly received in the cylinder and protrudes through a cap 38 to be engaged and moved by a, cam ii carried by the crankshaft. Each piston is of usual construction and comprises a disc :33 slidingly received in a respective cylinder and held in sealing relation therewith by packing 44. A rod 5% extends upwardly from the disc 63, preferably not integral therewith and is guided by a cap 38. The rod is provided at its end with a ball follower 5! which is in turn engaged by a cam ll carried on the crankshaft [8.

When the crankshaft rotates each of the cams 4i turn with it and once during each revolution will move the respective pistons 43 downwardly through the cylinder 35 to transmit an operating force to a piston 52 in a cylinder 54 carried above the blank holder at one of the four corners thereof. The piston 52 carries a rod 55 which passes down to the blank holder and is bolted to a boss 55 thereof by nuts 57. Its stroke is equal to the stroke of the blank holder when the working dies are in place and thus the length of the cylinders 54 should exceed this amount. The rod is guided in a slideway 58 integral with the machine crown.

It will be apparent that as the piston 43 is actuated it will transmit the force applied to it through a solid column of fluid to its associated piston 52, which in turn will push the blank holder down in the ways 22. The other three individual systems shown are identical to and in timed relation with the system described as an example. The result is to apply a, downward force at the four corners of the blank holder to move the same into gripping relation with the work.

To avoid loss of power each system is kept completely full of'oil, which is supplied through a reservoir 60 connected by piping 6| into each cylinder. In the piping Bl connecting each cylinder is a solenoid controlled valve which governs the passage of oil from the reservoir to the cylinder.

Each cylinder is controlled individually by its separate valve to avoid any possibility of an uneven building up of pressure in the system and to avoid any fulcrum action between different parts of diiferent systems. To this end, each valve and solenoid unit is electrically connected to and controlled by a limit switch 62, which in turn is opened and closed by a cam 64 on the crankshaft l8.

Only one valve is shown in Fig. 2, but it will be understood that a separate valve unit is provided for each fluid system. As the shaft is 1'0- tated the cam acts to operate the switch to close the valves to the reservoir just prior to the time when the respective cam 4i begins to push the respective piston 43 downwardly. After the blank holding stroke is finished the cam 64 allows the limit switch 53 to open, which releases the solenoid and opens the valves and allows oil to flow freely between the reservoir and the respective fluid systems.

To provide a safety mechanism in each fluid system and to control the pressure attained the spring controlled pistons, as shown in Fig. '7, are provided in each system. Each mechanism comprises a cylinder 65 in which is slidingly received a piston til, one side of which communicates through piping 68 with the main pipe leading between two cylinders of the respective systern. Interposed between the piston and a disc iii in the cylinder is a heavy calibrated spring 12 for urging fluid out of the cylinder. The resistanoe offered by the spring to movement of the piston may be varied by adjusting the position of the disc through the medium of abolt (4 threadingly carried in the end of the cylinder wall. If it is desired to render a blank holder piston inactive at any predetermined time, or to decrease the pressure applied, the corresponding spring '12 may be adjusted by the bolt 13 to collapse when this pressure is attained, thus limiting the pressure of that system by the strength of the spring 12. It will be apparent that by means of these pressure cylinders each system may be adjusted independently of the others or to provide a given pressure ratio between the others.

To improve the drawing of the metal I have found that it is desirable to slightly decrease the blank holding pressure after the slide has commenced the drawing operation. This insures that the proper amount of metal will flow from the region of the blank holder to form the finished product between the dies. Fig. 8 illustrates how the pressure is built up to a maximum point P and then is allowed to decrease slightly as at L during the part of the drawing operation where material is pulled from the part held by the blank holder. Thereafter, during the finishing part of the stroke the blank holding pressure is again built up to the maximum M, after which it is almost instantly released, when the piece is removed from the press.

The pressure applied to the blank holder is controlled by shaping the cams M (Fig. 4) to provide two points 75 where the maximum down stroke is given the pistons 63 and a region H in between where the piston is allowed to rise slightly, thus relieving the blank holder pressure. It will be apparent that the cam configurations may be slightly varied one with the other to obtain various desired pressure characteristics.

It is desirable to provide means to adjust the effective stroke of the pistons in the upper cylinders and in the blank holder cylinders E To this end the cylinders 35 are secured to the crown of the machine in such manner as to be adjustable along the line of the piston axis, which adjustment is effected by bolts 8i). After the particular cylinder 35 is clamped in an adjusted position bythe bolts suitable keys are inserted to prevent any movement of the cylinder during operation of, the machine. The position of the effective stroke of the blank holder may be varied by adjusting the rods 55 in the bosses 55 and locking the rods by the nuts 51.

The pressure applied by a system may be increased or decreased with respect to the pressure applied to the piston 43 through the cams 41 by varying the relative areas of the pistons 43 and 52. Thus, in any given press, blank holder mechanism may be employed which will provide a longer stroke of the blank holder than is indicated by the effective throw of the cams 4|. Conversely, a greater force but shorter stroke may be applied to the blank holder than is applied by the earns 41 if the areas of the pistons 52 is made greater than the area of the pistons 43.

It is some times desirable to apply a greater force at one point of the blank holder than is applied at another. If this is to be apermanent feature of the machine, it may be accomplished by varying the size of the pistons effective at that point on the blank holder over the size of the pistons effective elsewhere thereon. The same result may be attained by varying the effective stroke of the pistons of one system as against the other systems.

Normally, any adjustment of pressure in the respective systems is preferably attained by adjusting the calibrated springs to vary the point at which pressure rise due to cams 6i ceases by reason of collapsing of the springs.

If the press is to be employed as a triple action machine, an additional cam or cams are provided to transmit the requisite force through the additional fluid system or systems to perform the additional drawing operation.

From the foregoing description it will be seen that I have provided a novel press which contains many less moving parts than has heretofore been necessary and which possesses marked advantages of simplicity, synchronism and ease of adjustment of movement over the presses heretofore built.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the structure herein disclosed, provided the means stated by any of the following claims or the equivalent of such stated means be employed.

I therefore particularly point out and distinctly claim as my invention:

1. In a press, a frame, a blank-holder slidably carried thereby, a plurality of hydraulically expansible means for actuating said blank-holder, an individual source of hydraulic pressure for each of said means, a common hydraulic fluid reservoir for supplying hydraulic fluid to all of said sources, and valves for individually sealing each of said sources in either direction from each other and from said reservoir.

2. In a press,,a frame, a blank holder slidably carried thereby, a plurality of hydraulically expansible means for actuating said blank holder, individual sources of hydraulic pressure one for each of said means, a common hydraulic fluid reservoir for all of said sources, and valves for simultaneously and individually completely sealing each of said sources from each other and from said reservoir.

3. In a press, a frame, a reciprocable die slide carried thereby, a blank holder slidably carried thereby, a plurality of hydraulically expansible means for actuating said blank holder, individual sources of hydraulic pressure one for each of said means, a common hydraulic fluid reservoir for all of said sources, and valves responsive to the commencement of the reciprocating cycle of said die slide for simultaneously and individually sealing each of said sources from each other and from said reservoir.

4. In a press, a frame, a blank-holder slidably carried thereby, hydraulic means for actuating said blank-holder, a rotatable cam and a cam follower supported by said frame for actuating said hydraulic means, the cam having two spaced high points for varying the actuating forces, said first high point being adapted to cause a maximum piston stroke at the start of the drawing operation and said second high point being adapted to cause a maximum stroke during the finishing part of the drawing operation, with a depressed portion between said high points adapted to cause release during that part of the drawing operation where material is pulled from the part held by the blank holder, and means for adjustably spacing said cam from said cam follower whereby the effective stroke of the actuating means of the blank-holder is varied.

5. In a press, a frame, a die slide therein, a blank holder slidably carried by said frame, mechanical means to actuate said die slide, piston and cylinder means adapted upon admission of fluid to actuate said blank holder intoposition adjacent to the work and to return it automatically afterwards, hydraulic means to actuate said blank holder into a work engaging position, one end of saidcylinder means being dead whereby actuation of said blank holder by fluid means compresses fluid between said end of said cylinder and said piston and when released by said hydraulic means returns the blank holder to its initial position.

LARKIN R. WILLIAMSON.

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