US1844250A - Draw press - Google Patents

Description

Feb. 9, 1932. J wK s 1,844,25U

DRAW PRESS Filed Feb. 1, 1950 2 Sheets-Sheet 1 A5 6 H A5 Feb. 9, 1932. s. H HAWKINS v 11,844,250

DRAW PRES 5 Filed Feb. 1, 1950 2 Sheets-Sheet 2 l. l A 0 mEm nnmm-M gnmwfoc 'rlatented Feb. 9, 1932 ITED STATES ATENT OFFlCE BERT H. HAWKINS, F ROYAL OAK, MICHIGAN, ASSIGNOB, TO MCCORD RADIATOR & MANUFACTURING COMPANY, OF DETROIT, MICHIGAN, A CORPORATION OF MAINE DRAW PRESS Application filed February 1, 1930. Serial No. 425,339.

In double acting draw presses as heretofore constructed, a screw and nut arrangement is provided between the blank-holder and the toggle shafts for adjusting the ram 5 to hold the material from wrinkling while being drawn. In setting the ram for a die the practice has been to manually tighten the ram against the blank through the manipulation of the nuts on the adjusting screws. By ll this method there is no means of determlning the pressure at which the ram is tightened against the die, and the matter has been more or less left to the guess of the operator, depending on the material used and the depth of the draw. It frequently happens that the ram is set too tight, that is, beyond the capacity of the press, and the latter is likely to be broken in the repeated forcing of the ram and its associated parts against the die.

i The object of my invention is to provide means whereby the load exerted by the blankholder to hold the material against wrinkling during the drawing operation may be accurately regulated, and thus overcome the d1ff ficulty as heretofore encountered in having the load on the hold-down exceed the capacity of the press. I accomplish this object by providing means which acts in COIIJHIIC- tion with the screw and nut device already on the press to accurately determine the pressure required for the blank-holder to hold the material or blank against the die while being drawn, without wrinkling.

One form of means for carrving out this result is herein disclosed int-he form of a fluid actuated means so constructed and arranged that a predetermined fluid pressure may be interposed between the ram and the screws to regulate the load on the ram or hold-down to hold the material properly against the die without wrinkling during the drawing operation.

Briefly stated, this fluid actuated means comprises the combination of an air cylinder and its piston, and a hydraulic cylinder and 59 act load which must be placed on the ram to hold the material against wrinkling while being drawn by the plunger of the press,

The adjusting screw is made in two parts, one of which is provided with the cylinder of the hydraulic element, and the other pro- Vided with the piston of the hydraulic element so that the pneumatic element may exert the pressure on the hydraulic medium between the two parts of the screw to move them with respect to each other the distance required to obtain the required load on the ram or hold-down when drawing the material. By knowing the pressure areas of the pistons in the pneumatic and hydraulic units, and also the units of pressure exerted by these devices, it can be readily and easily determined, by mathematical calculations, what the total load exerted by the hold-down on the blank will be, and thus provide for the operator means by which the pressure required on the hold-down to load it for any particular die may be accurately determined while set-ting a die and be kept within the capacity of the press.

The invention consists further in the mat ters hereinafter described and claimed.

In the accompanying drawings:

Fig. 1 is a front elevation view of a double acting drawing press embodying the features of my invention;

Fig. 2 illustrates an adjusting screw assembly as heretofore employed; and

Fig. 3 is a vertical sectional view taken through one of the loading devices of my invention.

In the drawings, I have shown a double acting draw press of the type employed for drawing relatively large sheets of various forms. Generally, the press comprises a bed or base 1 and a super-structure thereon having upright side members 2, 2 between which the ram 3 and plunger 4 have vertical movement in the operation of the press. The plunger 4 is connected to and reciprocated by the crank shaft 5 of the press in the usual manner. The ram 3 is connected to and reciprocated by toggle shafts 6, 6 arranged on the front and rear sides of the press and journaled in the superstructure thereof adjacent to and parallel with the crank shaft,

as shown in Fig. 1. Shafts 6, 6 are oscillated to effect the required up and down movement of the ram by being connected to the crank shaft 5 through the usual cam and toggle mechanism as employed in presses of this general type. Die 7, made to the shape required for the particular articles being drawn,is secured to the bed 1,beneath the ram 3 and the plunger 4. An adapter 8 is secured to the under side of the ram 3 and carries a hold-clown plate 9 which conforms to the shape of the die 7.

In operating the press, the flat blank to be drawn is placed in proper position on the die 7 after the ram 3 and plunger 4 have been raised therefrom, whereupon the clutch is engaged or thrown in to move the ram and the plunger toward the die. The action of the press is so timed that the ram 3 moves gg down in advance of the plunger 4 and forces to the die.

the hold-down plate 9 against the marginal portion of the blank about the cavity in the die to hold the blank while it is being drawn by the plunger. The ram remains stationary in its lowered position during the drawing operation and is not lifted from the die until after the plunger has left the same, whereupon the ram is raised to release the drawn piece, and a knock plate (not shown) is raised from beneath the die to lift the drawn article therefrom and permit the operator to remove it from the press. These operations are repeated for each drawing operation, a blank being inserted in the press,

drawn and removed after the piece has been formed. Inasmuch as the ram 3, adapter 8 and hold-down plate 9 all serve to hold the blank against the die to prevent wrinkling of the blank during the drawing operation,

the parts referred to may be termed the blankholder, and I have used this term in the appended claims to indicate whatever form the means may take to hold the blank against the die.

The ram 3, in the type of press illustrated, is provided on each of its front and rear sides with the usual pair of integral lugs 10, 10 through which the ram is connected with the toggle shafts 6, 6. In the presses as heretofore constructed, a single adjusting screw 11 (Fig. 2) has been employed with each lug 10, the screw extending vertically through a hole in the lug as shown in Fig. 2. The upper end of each screw 11 has been connected by a toggle link 12 with the outwardly extending arms 13 rigid on the toggle shaft 6. A pair of clamp nuts 14;, 14 are provided on each screw with one nut above the lug and the other below the lug for the purpose of adjusting the ram vertically when setting the ram to the die. After the required die has been placed on and secured to the bed of the press, and the hold-down plate 9 has been secured to the ram, the practice is to adjust the ram This is done after the ram has been brought to its lowest position with the screwed out of engagement with the lugs whereupon the nuts above the lugs are screwed down as tight as possible to force the plate 9 against the die and to take up all lost motion in the toggle shaft bearings and connections with the ram. Then the ress is started to raise the ram 3 and holdown plate 9 away from the die. A blank of the desired metal and havin the required size and gauge is then place on the die, the press started, and the first shell drawn. After removing the first shell from the die, it is usual to find that the blank has not been held tight enough between the hold-down and the die to avoid wrinkles. To overcome this, it is necessary to further tighten the nuts on the upper sides of the lugs 10. This can only be done by raising the ram away from the die and any further tightening of these nuts to force the ram further toward the die is pure guess work, and if they are tightened too tight so as to be beyond the capacity of the press 1, the press is liable to be broken when the ram again comes in contact with the die, because further ti htening of the nuts has a tendency to over oad the press due to the fact that there is a positive distance between the die and the toggle shaft bearings, and screwing down the upper nuts lengthens the distance between the toggle shaft and the lower face of the ram while the ram is raised off the bed. When the ram again descends, the toggle arrangement forces this excess length between two fixed distances and when a point is reached where there is no further give or spring to the parts, the press will be broken. Heretofore, there had been no method of determining the exact load required to draw a shell wrthout wrinkles, and if the press has been adjusted to drawing a perfect blank, there has been no way of telling what the load is on the press and it may be very close to the breaking point, with a likelihood of spreading the press to the breaking point. For example, if the press and toggle arran ement is designed to withstand a load of fifty tons on each adjustlng screw, and the load on each adjusting screw has been adjusted to fifty tons, the continued operation of the press under this condition would be liable to break the press. To guard against this, it is essential that the load on the adjusting screws be less than the capacity of the press, and with the practice as heretofore employed in adjusting the ram, it has been impossible to determine whether the load on the adjusting screw is greater or less than the capacity of the press, with the result that presses are frequently broken, due tothe guess work in adjusting them.

In accordance with my invention, I provide means whereby the load on the ram or the lank-holder may be accurately determined at the time of setting the die so that there is no opportunity afforded for overloadmg the press, and thus breakage is positively prevented through adjusting the blank-holder when setting the die. One form of devlce for accomplishing this object is shown in the drawings.

The device operates on a combmedpneumatic and hydraulic principle, and m the drawings I have shown a separate device for each of the adjusting screws. As the devlces at the several screws are the same in construction and operation, a description of one Wlll answer for all.

The adjusting screw for each lug, in accordance with my invention, 1s made into sections 15, 16 (Fig. 3). The upper sectlon 15 is connected to the link 12 while the lower section 16 extends downward through the lug 10 as shown in Fig. 3. The-lower adjusting screw 16 is provided at its upper end with an integrally formed cylinder 17 in which fits and moves a piston 18 formed on the lower end of the upper screw 15. A cupshaped packing 19 is located against the lower face of the piston 18 and engages the side walls of the cylinder 17 to prevent leakage of the hydraulic medium which is confined 1n the cylinder for the purpose to be hereinafter described. A steel plate 20 is held against the inside of the packing 19 by a coiled spring 21 which surrounds a cylindrical boss 22 extending upward into the cylinder from its bottom wall. The boss 22 not only provides a support for the spring, but also limits the distance that the piston 18 is required to move into the cylinder to contact with the boss in setting the hold-down to the die to be presently described. A cap plate 23 closes the upper end of the cylinder 17 and is securely fastened thereto by one o r more bolts as shown. The upper screw 15 extends through the cap plate 23 as shown. The cap provides a guide for the screw section and holds it in axial alinement with the lower screw 16 as required and limits the upward movement of the piston 18, when the hydraulic medium is forced into the cylinder.

Clamp nuts 14, 14 are employed on the lower screw section 16 above and below the lug 10, the same as before.

The pneumatic element of the device comprises an air cylinder 24, which, as shown in Fig. 1, is secured to the outer face of the ram 3, at one side of the lug 10. This cylinder may be arranged elsewhere on the press if desired, but for the convenience of illustration I have shown it mounted on the ram as described. A piston 25 fits within the cylinder 24 and is provided on its pressure side witha cup-shaped packing or other sealing member 26 to prevent leakage of the pressure fluid from the front to the rear side of the piston. An inlet port 27 is provided in the end wall 28 of the cylinder opposite the pressure side of the piston 25 and provides means whereby a conduit 29 may be connected with the cylinder for supplying pressure fluid, such as compressed air, thereto in the operation of the device. When the cylinder 24 is mounted on the ram 3, the conduit 29 is of the flexible type so that the cylinder may move up and down with the ram during the operation of the press without straining the conduit. The latter is connected with the supply line 30, which is in the form of a pipe fastened to one of the uprights 2 of the press, as shown in Fig. 1. A pressure gauge 31 is connected with the'pipe in a position to be conveniently seen by the operator and the purpose of such gauge is to indicate the load on the ram when'the press is in operation. The gauge will be of the type which will indicate through the movement of a single pointer or hand pressure in pounds per square inch on the pressure surface of the piston 25, and tons on the pressure surface of the hydraulic piston 18.

A plunger 32 is connected with the piston 25 and extends therefrom through the end wall 33 of the cylinder 24 opposite the pressure face of the piston. The plunger 32 extends into a cylinder 34 located between the cylinders 17 and 24. The plunger fits snugly in the cylinder 35 and said cylinder opens at its inner end into'the cylinder 17, as shown in Fig. 3. The cylinder 34 is connected to the cylinder 24 in the manner shown in the drawings, there being stufling box 35 provided at the outer end of the cylinder 34 to prevent leakage of hydraulic medium against which the inner end of the plunger operates. A cupshaped packing 36 is secured to the inner or pressure end of the plunger 32, as shown.

With a press equipped with my devices, one at each adjusting screw, the press is set in the following manner. Ram 3 is brought to its lowermost position to contact the holddown plate 9 with the die 7 and the upper adjusting nuts 14, 14, (after the lower ones are loosened) are screwed down on each lower screw section 16 to tighten the plate 9 against the die, the same as before. As the plate 9 contacts with the die a continued tightening of the upper nuts 14 moves the lower screws 16 upward and causes the bosses 22 to contact with the pistons 18 to raise the upper screws 15 to take up all looseness in the toggle shaft bearings and in the connections between said shafts and the upper screws 15. The nuts are screwed down as tight as possible with a wrench or bar to take all of the loose motion out of the mechanism. In forcing the screw sections 15, 16, together, the w oil or other non-compressible fluid medium employed in each cylinder 17 is displaced out of the space which was between the two sections at the pistons 18 and bosses 22 when the parts were in separated relation. In displacing this fluid it is forced outward against the plungers 35, moving them outward and impartin a like movement to the air pistons 25, there eing no air pressure in the cylinders 24 at this time.

For a trial, I allow a certain amount of compressed air to pass reducing valve 37, filling reservoir 39, and the several air cylinders 24 connected therewith, this pressure being indicated on the gauges 31, the pressure so indicated being below the maximum capacity of the press and being determined by the amount of air pressure allowed to pass the reducing valve. In a press designed for a capacity of two hundred and fifty tons on the ram 3, the maximum capacity on each lug 10 is sixty-two and one-half tons. The reducing valve 37 is set so that the air pressure allowed to pass the same is less than that which would load the ram to the full capacity of the press. The air pressure in passing through the pipe connections from reservoir 39 enters cylinders 24, forcing pistons 25 forward, which, in turn, force plungers 32 against the oil in cylinders 17. The oil pressure is sufiicient to separate the screw sections 15, 16 by forcing pistons 18 upward. This is permitted by reason of the space between each cylinder and its cover cap 23, which is provided in the initial setting of the ram by turning the upper nuts 14, 14. When the oil pressure separates the screw sections 15, 16 at each lug and forces the pistons 18 against the cover plates 23, the load on the rams 3 to hold the blank at the proper pressure to prevent wrinkling is within maximum capacity of the press. With the pres sure areas of the air pistons 25 and the hydraulic pistons 18 and the plungers 32 known, the exact amount of pressure on the ram will be known. This is indicated by each gauge 31, so that the operator in setting the ram to the die will know exactly how much pressure to place on the ram to hold the work without wrinkling and prevent overloading of the ram to damage the press, which has not been possible when setting the ram by the manual method as heretofore employed.

To prevent the operator from overloading the ram, a safety valve 40 is connected with reservoir 39, which valve is set to relieve the air pressure within the capacity of the press. For example, assume that each air piston 25 is fourteen inches in diameter, the area on the pressure face of the piston is 153.9 square inches. At a fifty pound pressure per square inch the piston will exert a pressure of 7,695 pounds. With plunger 32, one and one half inches in diameter, the area at the inner end of the plunger is 1,767 square inches. Dividing the 7,695 pounds pressure exerted by piston 25, by the area 1,767 of plunger 32, will give pounds per square inch exerted by plunger 32 on the oil in cylinder 15. This equals 4,354 pounds per square inch. With piston 18 six inches in diameter, the area of its pressure surface is 28.27 square inches. This, times the pounds per square inch (4,354) exerted by plunger 32 equals 123,087 pounds, or 61 tons exerted on the blankholder through the adjusting screws 15, 16. This is close to the maximum capacity of the press, but is within that capacity so that there is no opportunity aflorded for the breaking of the press by overloading the ram 3.

With fifty pounds pressure per square inch in cylinder 24 on piston 25 a pressure of 61 tons will be exerted on each of the four corners of the ram 3. This load can be changed by simply changing the air pressure in the cylinder 24. When the ram 3 has been set at the pressure required to hold the blank during the drawing operation without wrinkling, pistons 18 are out of contact with the cap plates 23, as shown in Fig. 3, and each plunger 32 and air piston 25 are in the positions shown in the figure. The first period of movement of the toggle shafts 6 to efiect lifting of the ram from the die raises the upper screw sections 15 until the pistons 18 contact with the cap plates 23, whereupon the upper and lower screw sections are coupled and the ram is lifted from the die. In the initial upward movementof each piston 18 the space between the piston and the upper surface of the boss 22 is increased to the extent that the piston has movement without lifting the screw section 16. This increases the volume of the chamber between piston 18 and boss 22, and the pressure on air piston 25 immediately acts to force the oil into this space to fill it. Piston 25 in this movement increases the volume in cylinder 24, and consequently lowers the pressure in the same below that initially supplied to the cylinder. The air pressure is not allowed to build up in the cylinder at this time from the reservoir 39 because the reducing valve 37 is cut olf from the reservoir by the closing of a valve 41, which is closed after the initial loading of the ram. When the next blank is to be drawn the blank is placed into position on the die and the clutch of the press is thrown in to lower the ram. The downward movement of the ram stops when it contacts with the blank on the die 7 and in the continued movement of the toggle connections the upper sections 15, 15 of the adjusting screws are forced downward after the lower sections 16, 16 have stopped by reason of contact of the ram with the blank. The upper sections 15, 15 continue their downward movement, reducing the volume of the space beneath the pistons 18 and plungers 32 are forced outward by the oil displaced from the cylinders 17. Pistons 25 are also moved outward and the reduced pressure in cylinders 24 is restored to that which loads the ram to the initial predetermined pressure. Thus the pressure on the blank-holder during the drawing operation is the same as the initial pressure placed on the holder when setting the same to the die, and this pressure is substantially constant as long as the press is operated at the initial loading pressure.

With a press equipped with the mechanism of my invention, the loading of the ram may be accurately determined and maintained, and may be varied from zero to the maximum capacity of the press, as may be required for drawing various articles depend. ing on shape, thickness and character of material, and all of the other factors thatenter into a drawing operation.

The devices of my invention are simple in construction and operation, and require no particular skill on behalf of the operator to load a die. All that is required is to note the gauge and by the reading thereof, noting whether the load on the die is within or without the capacity of the press. There is no guess work required on the part of the operator, as heretofore, and the result is the press is equipped with a safety device which enables the operator to load the die at. a known pressure and be within the capacity of the press so that the press will not bebroken, as when the ram was loaded beyond the capacity by the old hand method. a

The details of structure and arrangement of parts may be variously changed and modified without departing from the spirit and scope of my invention.

I claim as my invention:

1. In a double acting draw press, the combination with the die and the blank-holder therefor with its adjusting screws, of means for applying a known pressure on the blankholder through the adjusting screws to load the blank-holder within the capacity of the press.

2. In a double acting draw press, the combination of die and blank-holder therefor, of two-part adjusting screws for setting the blank-holder with respect to the die, and means for applying a known pressure between the parts of the screws to load the blank-holder for the die.

3. In a double acting draw press, the combination with the die and the blank-holder therefor, of adjusting means associated with the blank-holder for setting the same with rev spect to the die, and means for applying a known pressure on the blank-holder to load the same through said adjusting means.

4. In a double acting draw press, the combination with the die and the blank-holder therefor, of a combined pneumatic and hydraulic actuated means for applying a known load 011 the blank-holder to load the same for the die.

5. In a double acting draw press, the combination of the die and the blank-holder therefor, of a combined pneumatic and hydraulic actuated means for loading the blankholder by applying a known pressure thereon in the direction of movement of the blankholder with respect to the die.

6. In a double acting draw press, the combination of the die and the blank-holder therefor, of means having differential pressure areas acting one with respect to the other, for applying a known pressure on the blank-holder for loading the same for the die.

7. In a double acting draw press, the combination with the blank-holder and the die therefor, of means for applying a known fluid pressure against the blank-holder to load the same for the die by building up the required pressure from a relatively small initial pressure.

8. In a double acting draw press, the combination with the die and the blank-holder therefor, of means for applyin a known fluid pressure against the blank-holder to load the same for the die by building up the known pressure from an initial smaller pressure through the use of differential pressure areas.

9. In a double acting draw press, the combination with the die and the blank-holding element therefor, of a combined pneumatic and hydraulic means, one acting through the other, for applying a known pressure on the blank-holder to load the same for the die, said means being carried by the blank holding element.

10, In a double acting draw press, the combination with the die and the blank-holder therefor, of adjustable elements for the holder to set the same for the die, and means for forcing a noncompressible fluid medium between said elements for loading the blankholder for the die.

11. In a double acting draw press, the combination with the die and the blank-holder therefor, of a two-part adjusting element for the blank-holder, means forming a piston and cylinder unit between said parts, and fluid pressure actuated means for forcing a noncompressible fluid medium into said unit for loading the holder with respect to the die.

12. In a double acting draw press. the combination with the die and the blank-holder therefor, of a two part adjusting element for the holder, means forming a cylinder and piston unit between said parts, and a pneumatically operated device for forclng a noncompressible fluid medium into said unit for loading the holder with respect to the die.

In testimony whereof I afiix my signature.

BERT H. HAWKINS.

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