US3007427A

US3007427A - Press for hot forming metal

Info

Publication number: US3007427A
Application number: US540971A
Authority: US
Inventors: Floyd E Bryan; William D Mitchell; Orville A Wheelon
Original assignee: Douglas Aircraft Co Inc
Current assignee: Douglas Aircraft Co Inc
Priority date: 1955-10-17
Filing date: 1955-10-17
Publication date: 1961-11-07
Anticipated expiration: 1978-11-07

Description

Nov. 7, 1961 F. E. BRYAN ETAL PRESS FOR HOT FORMING METAL 2 Sheets-Sheet 1 //V/ /Y7'0z5 Flo/0E 56! Mum/Ma lW/Z/fll 4N0 ail 415 4. @5540 Ml, Anne/vs) Nov. 7, 1961 F. E. BRYAN EI'AL 3,007,427

PRESS FOR HOT FORMING METAL Filed Oct. 17, 1955 2 Sheets-Sheet 2 United States Patent 3,007,427 PRESS FOR HOT FORMING METAL Floyd E. Bryan, Pacific Palisades, William D. Mitchell, Los Angeles, and Orville A. Wheelon, Pacific Palisades, Calif., assignors to Douglas Aircraft Company, Inc., Santa Monica, Calif.

Filed Oct. 17, 1955, Ser. No. 540,971

5 Claims. (Cl. 113-44) This invention relates to high pressure hydraulic presses of the diaphragm type and 'itsprincipal aim is to adapt this general type of press that it can form, draw, or form and draw hard alloy metallic sheet-material into various shapes, contours, etc. into which they previously could not be formed acceptably.

Currently, presses of this general type cannot be employed to draw-form metallic alloys harder than 3ST aluminum alloy without cold-cracking at least some of the short-radii bends of the formed material or failing to meet the criteria as to the integrity, internal stress conditions, and surfiace conditions established for the finished article. For one reason, contemporaneous presses work .cold, that is, take in unheated metallic sheet material and apply forming pressure to the cold sheet. If bends are to be formed on short radii, the metal ruptures, or cold cracks, in the bend. Hence alloy sheets of a hardness of the order of 7 5 ST aluminum alloy and beryllium and titanium alloys cannot be formed for very many purposes in current hydraulic diaphragm presses.

Deep drawing of metallic alloy sheets with any degree of success is replete with difli'culties and even the softer metallic alloy sheets cannot be acceptably deep-drawn in current hydraulic diaphragm presses.

This invention adapts the current general type of high pressure hydraulic diaphragm press so that it can form and draw such hard alloys as 75ST aluminum alloy, beryllium alloys and titanium alloys without producing any of the aforementioned, or other, defects. It also enables the deeper drawing of sheets of these alloys than heretofore feasible in such presses. -At the same time, it provides these improvements without appreciably augmenting the overall volume or bulk of a hydraulic diaphra gm press of a given capacity-rating and without Weakening any component of the press.

Generally to achieve these, and other, ends, the invention provides an otherwise substantially conventional press with novel work-heating means capable of raising the temperature of metallic alloy sheets to a temperature of the order of 600 F. 900 F. before the diaphragm is powered formingly against these sheets while they are resting on form blocks. In this range of temperature, nearly all commercial metallic alloy sheets can be formed on quite short radii without cracking, rupturing, oilcanning, or the like. Further, the eificacy of the press is not limited to thin sheets. The depth of drawing is also augmented by virtue of this heating feature in conjunction with a novel configuration of a work-carrying trayand floor-piece. Means are also provided for preventing impairment of any of the metallic parts of the press by the rather high degree of heat employed, as Well as means for preventing impairment of the work-supporting means, or platen, itself.

In one embodiment of these concepts, the conventional two-piece roof unit and two-piece floor unit are replaced by a single piece hemicylindric roof unit anda singlepiece, hemicylindric floor unit, these two pieces being mounted concentrically in a hollow, horizontally disposed cylindric shell. The outer cylindric surface of each of these pieces fits directly against the inner cylindric surface of the shell, and the planeal inner face of the roofpiece carries the hydraulically powered expandible bag and the diaphragm powered by the bag.

, 3,001,427 Patented Nov. 7, 1961 ice The planeal inner face of the floor-piece is provided with a centered, stepped depression almost coextensive in area with the diaphragm, and in this depression there is concentrically mounted a substantially coextensive metallic platen for supporting the work mounted on heat-conductive form blocks. The periphery of the platen is insulated from the floor-piece. Heating means, such as electric-resistance heating elements, are incorporated in the platen for raising it to temperatures of the order of 600 F. to 900 F. so as to render the hard alloy sheet material safely workable.

In order to prevent the occurrence of too high a gradient rate of heat transfer between the metallic platen and the metallic single-piece tray-and-fioor member," with consequent serious warping of the platen and even slight annealing or loss of the strength-characteristics of the floor piece itself, means are interposed between the bottom face of the platen and the bottom of the depression in the floor piece for preventing chilling of said bottomface. Such chilling of course would set up lateral and longitudinal unbalanced stresses in the bottom face that would warp the platen. As now contemplated, these preventive means include means for laterally and longitudinally interrupting the stresses set up by cooling this bottom surface of the platen and for automatically breaking the contact of the platen with the bottom of the floor-piece as soon as the diaphragm is retracted from the work.

7 In one of the species of the invention, the means for transferring heat from the platen to the floor-piece comprise a metallic waflle-plate having a planeal upper face fixed in facewise contact to the bottom face of the platen, the lower face of this plate being of a checkered configuration, having a plurality of protuberances alternating with depressions therebetween. An identical waffleplate has its planeal bottom surface fixed in facewise contact with the bottom of the depression, its upper surface, checkered similarly to the aforesaid one, having protuber- -ances and depressions registering with the corresponding formations on the confronting checkered face of the firstsaid plate. Resilient means, such as the well-known Baumbach springs, are mounted upright to the depressions bottom and extend through the lower grid plate into unattached contact with' the upper grid-plate. These Baumbach springs yield downwardly with the platen under the forming pressure of the diaphragm, but expand up wardly and restore the platen to its original position as soon as the diaphragm is retracted from contact with the platen, thus breaking the heat-transferring contact of the platen and upper wafile plate with the lower wafiie plate and the floor-piece.

Thus the bottom face of the platen-unit is rendered discontinuous as is the surface to which it transfer heat, and contact of the waffie-plates is broken as soon as the forming operation is terminated, so that warp-producing lateral and longitudinal stresses cannot be established in the platen-unit, nor can the heat-head of the platen be dissipated by prolonged contact thereof with the floor-piece. Electric-power loss is also minimized since continuous or excessive transfer of heat from the platen to the floorpieee is obviated. By the same token, any actionin the head, suificient to cause it to lose its characteristics to such complishments of the invention, that one of the many presently contemplated embodiments which is most concrete is representationally depicted in the accompanying drawings and is generally described hereinafter in conjunction with said drawings. However, it is to be understood that this showing and said description are typical merely and in no wise constitute the invention itself nor limit the scope of the concept, which latter is as defined in the subjoined claims.

In said drawings,

FIGURE 1 is a perspective view, partly in longitudinal section, of a high pressure hydraulic press incorporating the present advances;

FIGURE 2 is a paired cross-sectional view of the lower one of the rigid bodies enclosed by the press of FIGURE 1, the left-hand of the section showing the platen and its associated elements in one condition of operation and the right-hand half of the section depicting the same plated in another condition of use;

FIGURE 3 is a fragmentary longitudinal, substantially central section of the improved tray=and-floor member of the press with the platen and its associated elements in retracted position; 1

FIGURE 4 is a top plan view of the platen itself, the associated electrical instnunentalities for heating same and controlling the degree to which it is heated being shown diagrammatically; 7

FIGURE 5 is a fragmentary enlarged detail cross-section of the tray and the platen unit taken on a transverse plane lying back of the transverse plane on which the section of FIGURE 2 was taken;

FIGURE 6 is an enlarged fragmentary sectional detail of the lower lefthand side of FIGURE 2, and

FIGURE 7 is an enlarged perspective sectional detail view of a part of one of the grid elements of the press.

The invention is embodied in structure that transforms the contemporary high pressure hydraulic diaphragm press capable only of cold-working and only the soft metals, and of the general type shown in FIGURE 1, into a type of press that is also capable of forming and deepdrawing the harder" metals and alloys; briefly, by reorganization thereof to include, in a single piece floor configuration, means for heating the work and means for dissipating excess heat without warping the platen or 1m: pairing the strength of the floor of the press.

To these, and other, ends the working chamber of the press is defined by a pair of

castings

18 and 21 whlch are essentially hemicylindric and arranged concentrically n the open-ended shell 12 in radially spaced relat onship with their cylindric surfaces conformingly contiguous to the inner surface of the shell, 12. The working chamber 13 essentially includes, in its upper ma or surface, material-working means that include a metal-form ng diaphragm 14, a pressure-fluid expandible bag 15, a bag liner or backing plate 16, and a pressure fluid conduit 17 connected to a source of pressure fluid and conducting same a stherein. I h e l t wer one, 18, of the working chamber defin1 main components is a shell-floor type tray; that is, itls both a floor defining component and an endwise movable work-carrying tray. Dual-nature member 18 bears, 111 its upper, or chamber-defining, face an ellipsoidal planifor-m depression or sink 19 that extends as nearly from s1deto-side of 18 and from end-to-end of 18 as is consistent with the concomitant working-stress-takmg purpose of this floor piece. Disposed longitudinallyand laterally centrally of this first, or major, sink is an ellipsoidal countersunk formation 20, which extends as nearly coextensively of the bottom of the major depression, both laterally and longitudinally, as is consistent with the strength of the floor-piece. The depth of the ma or depression is such, preferably, as to provide head-room between sheets of metal mounted on deep metallic form blocks for deep drawing, and the diaphragm when the tray-andfloor piece is endwise moved into and o t of he p nended shell. The depth of the minor depression need be only such as to receive and encompass the novel dropcenter work-supporting and work-heating means constituting one of the most vital portions of this invention.

These means essentially include a generally elliptical work-supporting and heating platen 22, shown in the left-hand portion of FIGURES 2 and 5 in the depressed, heat-transferring position into which it is urged, bearing the work by the powered diaphragm on the working stroke of the latter. Platen 22 is shown in the right-hand side of this view in the elevated, or non-heat-transfern'ng position which it occupies on the retraction, or de-powered, stroke of the diaphragm. The platen 22 is directly heated, in controlled degrees and periods of heating, in order to correspondingly heat the metallic form blocks and the sheet metal resting thereon, by means including a continuous electric-resistance type heating element 23, shown diagrammatically in planform in FIGURE 4 and in section in FIGURE 5. The platen 22 is preferably composed of some such metallic alloy as a stainless steel and the heating element, of any suitable resistance-type now on the open market, is built into the platen in the fabrication of the latter. Element 23 is so configured with platen 22 as to distribute its heating effects uniformly of the platen, both surfacewis'e and thicknesswise. This embodiment-contemplates that the platen be thermally elevated to a temperature of the order of 600 F.900 F., beingmaintained thereat by suitable electro-thermal control means", arid by heat-transferring means, later described. In order to provide both energy and control for the heating element, the latter is associated with an energy source and with standardized control means, not shown, by means of a conductor path 24. A conventional temperature pickup device, such as thermostat 27, is carried in the platen and is electrically connected to a pyrometer 28 by means of conductor means 29, the pyrometer being connected to path 24 by path 30. The heating element 23, the thermal pickup 27, and the pyrometer are associatable with and disassociatable from, the energy source by means of a single-throw, bi-pole switch 25. Switch 25 is a solenoid operated switch and is manually opened. Conductor path 24 shunts through the pyrometer and if the latters reading is low and the platen ready to be heated, this current energizes a solenoid 50 which is adapted to close the switch 25. When the reading of the pyrometer reaches a predetermined high, the attendant manually opens switch 25.

The electro-thermal control means quite effectively maintain the sensible-heat temperature of the platen very close to 900 F., that is, prevent oversupply of electric heating energy, but while the diaphragm is pressing the irietallic sheet material and the metallic form blocks forcibly onto the metallic platen, even though the cycle of the press may only extend over a period of 7 seconds, the non-conductive, resilient-elastic diaphragm completely blankets the work and the platen. If the flat-faced metallic platen were merely pressed directly into facewise contact wtih the bottom of the depression in the metallic trayand-fioor by the diaphragm then, since the tray-and-fioor are at a great temperature differential, only the lower face of the platen would be cooled off; in fact, this flat face would be chilled to such an extent that lateral and longitudinal thermal skin stresses would develop that would Warp the plate.

In order to prevent the accumulation of a detrimental heat-head in the floor-piece, as well as to inhibit warping of the platen, an improved balanced-heat transfer group is interposed operatively between the bottom face of the platen and the bottom of the minor depression in the tioor-and-tray piece. Roughly stated, this group includes a plurality of disparate, mutually spaced apart protuberances constituting the lower face of the platen, and a correspondingly nodular sheet or plate-like member fixedly mounted to the shell subadjacent the platen-group and thus having protuberances on its upper face arranged to register with those on the lower face of the platen-group when the diaphragms actuation presses the respective protuberances together. Thus, the area of contact of the platen and the subadjacent fixed plate is evenly and balancedly distributed while reducing the mutual contact from the full-area contact resulting in the past from the use of planar plates to that minimum of contact which is compatible with balanced overall support of the depressed platen. There is no effective difference between the heattransfer rate from the top surface of the platen, which is mainly efiectuated by removing the heated work pieces, and the rate of heat loss from the lower surface of the platen. In fact, the ideal condition would occur when there is no heat extraction at all, or to speak of, from either the lower, or the upper, surface of the platen. In any event, the heat loss differential as to upper and lower surfaces of the platen is not of sufiicient magnitude to effect sudden cooling of the platens lower face with the upper face thereof at or near 600 900 F.

This group includes an upper member 32 which is configured to be a thermal-stress inhibitor that permits heat-transfer from the lower face of the platen without chilling same with consequent warping. Tothese ends, member 32 preferably consists of a sheet, plate, or other planar memberof low chromium Austenitic steel and has a planeal upper face and an opposed, lower, face which is of checkered conformation. The 'checkering, or waffle-plate conformation of the lower face is constituted by a multiplicity of protuberances 47, each having substantially rectangular form and each being faced off by a flat surface, the latter all being coplanar, and an equal number of depressions 48, alternating, in both lateral directions, with the protuberances 47, the protuberances and depressions thus defining a rugose face somewhat resembling that of a wafile iron. This sheet or grid-member is affixed to platen 22 by removable fasteners 33, as shown. Member 32 thus dually constitutes a low-gradient heat-transferring means for conducting heat away from the platen and, at the same time, a means for relieving the lower face of the platen of surface thermal expansion and contraction that, if not interrupted or relieved, would set up unbalanced heat-stresses coextensive with this face therein that would cause warpage of the platen.

Thermally semi-conductive thin sheets 44 of suitable material are interposed between

members

32 and 22 to decelerate the rate of heat transfer from member 22 to 3 2, somewhat, and they also serve as spacing means. They also, by variations in the choice of their thicknesses, can assist in adjusting the normal vertical gap between the platen unit and member 34 and thus can be employed to control or vary the travel distance of 22 with reference to 34.

A complementary sheet or grid-member, 34, having its upper face conformed as is the lower face of member 32, and having a planeal lower face, is matchingly arranged in the bottom of the minor depression in the floor-and-tray piece, tothe bottom of which depression it is afiixed by means of removable fasteners 35.

In order to greatly reduce heat transfer to the floor from the platen when the work is not being formed by the diaphragm, thereby to hold the platen at the optimum 600900 F. temperature at the start of, and nearly entirely throughout, the forming operation, and to prevent heat damage to the floor or other parts of the press, means are also provided for so supporting the platen and upper grid with respect to the lower grid, mounted to the floor, that the platen and its grid plate contact the lower grid plate only when the work is being formed by the diaphragm, the platen-unit being automatically returned by these means to its up posit-ion, out of contact with the floor-grid or surrounding tray, shortly after the end of the forming operation. These resiliently yielding, automatically return-thrusting means may, in one form of the invention, consist of Baumbach spring-units, one such being disposed at each of the four corner-regions of the platen. Each of these spring-units consists of a boltpontion 38 mounted upright in a cavity 36 in the floorcasting; a floating abutment or piston 39 mounted coaxially and loosely of the bolt to reciprocate with the bolt-head as a stop; and a coiled spring 40 also mounted coaxially of the bolt between piston 39 and the cavity bottom. The lower grid plate bears an aperture 51 in each of these corners regions through which member 39 passes, each member 39 being upwardly terminated by a disc 42 of some such insulative material as Micarta, a glass fibre matte, or the like, to prevent continuous heat transfer from the upper grid and the platen. The platen is guided in its movements up and down in the minor cavity of the floor-casting and concurrently insulated from the sides and ends of the cavity by some such means as four spaced inserts 45 of suitable, flexible insulating material such as Micarta. The extrusion of the rubber diaphragm into the gap necessarily left between the platens edges and the cavitys walls is prevented by some such means as a fiat elliptical plan-form ribbon 49, of a flexible, but stress-resistant, material, such as stainless steel. 1 The spring 40 of each Baumbach unit de-compresses upon release of the diaphragm from its pressure stroke on the platen and work and causes these units to return the platen to its normal position, as shown in FIGURES 2 and-5, right-hand side, the platen having a thickness proportioned to the spring-rate adequate 'to prevent its being dislodged from the minor depression.

I It will be apparent to those skilled in the art that various changes and modifications may be made in the construction disclosed herein without departing from the spirit of the invention. a

Weclaim:

1. In a hydraulic diaphragm press including a hollow cylindric shell: a dualnature floor-member and workcarrier, the dual nature article having a centered depression in its inner face; a work-supporting metallic platen movable mounted in said depression; means in the platen for heat-ing same and the work; and a pair of parallel, metallic sheets disposed in vertically mutually spaced relationship in said depression, one of said sheets being fixed facewise to the lower face of the platen and the other sheet being fixed facewise to the bottom of said depression, the sheets normally being in vertically spaced relation to each other; each of the confronting faces bearing a plurality of protuberances and depressions, the protuberances of the confronting faces being adapted to mate to establish balanced heat-transfer from the upper sheet to the lower sheet; and elongate spacer means re- 'siliently mounted upright attitude to the bottom of said depression below said lower plate, said lower plate being formed to receive said spaced means therethrough, said spacer means projecting through said lower plate into contact with said upper plate whereby to enable automatic return of said upper plate and platen to their original mutually spaced positions upon de-powering of said diaphragm.

2. In a hydraulic diaphragm metal working press of the type described: a floor element for receiving working pressures; a work-carrying platen; means yieldably supporting same on said floor-element for movement vertically with respect thereto; a work-forming diaphragm overlying said platen and having a major portion of its body reciproca-ble toward and away from contact with said platen; means carried by the platen for heating same; a first, normally elevated-temperature heatcondncting member mounted facewise to the lower face of the platen and having a plurality of grid-like surface protuberances on its lower face; said protuberances facing away from said platen; and a second, normally relatively cold heat-conducting member mounted to said floorelement and having a plurality of protuberances arranged in a grid-formation complementary to the first said such formations and confronting same; the yieldable platen supporting means normally maintainingsaid two heat conducting members in mutually vertically spaced separation and enabling the diaphragm to press them into mutual contact at said protuberances on occasion.

3. In a hydraulic diaphragm type metal forming press a floor portion for receiving working pressures a workcarrying platen resiliently supported by means including said floor portion so as to enable the platen to be moved vertically; an expansible, work-forming diaphragm overlying said platen and having the major portion thereof free for pressural reciprocative movement toward and away from said platen to depress and release same; means for heating the platen; and a pair of metallic, upper and lower sheets normally resiliently spaced apart vertically, one of said sheets being fixed facewise to the lower face of the platen and the other sheet being fixed to said floor portion in parallelism to the first element; each of the confronting faces of said sheets bearing a multiplicity of protuberances alternating with depressions therebetween, said protuberances on said sheets be ing adapted to be mated by expansion of said diaphragm thus to establish an adequate area support of the lower face of the depressed platen which support incorporates the minimum number and size of contact points compatible with balanced platensupport thereby to prevent substantially greater heat extraction fromthe lower face of the depressed platen than from the upper face thereof; whereby to prevent warpage of the platen.

4. In a hydraulic diaphragm press that includes a floor portion for receiving the press working pressures: a heated work-carrying platen group supported by means including said portion which means enable reciprocative movement of said platen; an expansible diaphragm overlying said platen and having a major portion free for reciprocative pressural movement toward and away from said platen; said platen-group including first plate-means mounted in contact with, the lower face of the platen, said first plate-means having a lower face which is rendered discontinuous by a plurality of laterally and longitudinally spaced protuberances constituting a wafile-iron formation on its lower face; second plate-means mounted subadjacent to the first plate-means in vertically spaced relationship thereto, the upper face of the second plate means being rendered discontinuous in predetermined loci by a plurality of protuberances in said loci which latter protuberances are arranged to contact and mate with the corresponding formations on the lower face of the first plate-means so as to establish balanced support for the depressed platen to minimize heat loss from the lower face of the platen to said floor portion; and yieldable supporting means mounted upright to said floor portion, said yieldable means extending into engagement with said platen group in such manner as to normally space the platen group vertically away from the second plate-means and to enable expansion of said diaphragm to force the respective sets of protuberances into mutually correspond= ing contact; said yieldable means automatically effecting separation of said two plate means upon removal of diaphragm pressure.

5. In a hydraulic, diaphragm type press of the character described and that includes a working chamber and an expansible, metal-forming diaphragm reciprocatable therein; a metallic shell-element arranged to receive the downwardly directed press-working pressures; a workcarrying platen occupying said chamber and arranged for pressural reciprocation by said diaphragm with respect to said shell; means for expanding the diaphragm into pressural contact with the work-carrying platen to depress the platen in said chamber; a first plate-like mem-, ber, thin relative to the thickness of said platen, said first member being attached facewise to the bottom face of said platen and having, on its lower face, a plurality of protuberances spaced from each other in all directions of a reference plane of the lower face of said thin member, said protuberances constituting a plurality of di screte, evenly distributed supporting points for said platen; means carried by said platen for continuously heating same to a metal-forming temperature; resilient means mounted on the base element and supporting the platen and said thin member as a unit with the unit normally spaced apart from a lower plate-like member; a lower plate-like member fixed to the shell-element and being thin relative to said plate, the upper surface of said lower, plate-like member having a plurality of protuberances spaced mutually apart laterally and longitudinally, the second said protuberances lying at points corresponding to the locations of the aforesaid protuberances on the lower face of the first-mentioned thin member so as to adapt the two sets of protuberances to contact and mutually match when the diaphragm depresses the platen and its carried thin member a predetermined amount; said supporting means resiliently returning said thin members into said spaced apart condition when dia phragm-pressure on the platen is removed; the matching contact of the respective setsof protuberances establishing a balanced support for the depressed platen at the minimum number of contacting bearing-loci elfective for such purpose, thereby to prevent total, sudden extraction of heat from the lower surface of said platen and maintain its temperature substantially equal to that of the upper surface thereof so as to inhibit warpage of said platen consequent upon an otherwise high temperature differential between the upper and lower surfaces of said platen.

References Cited in the file of this patent UNITED STATES PATENTS 877,139 Tatarino'fi Ian. 21, 1908 1,246,740 Haefely Nov. 13, 1917 1,636,111 Rode July 19, 1927 1,942,251 Mains Jan. 2, 1934 2,330,632 Seligman Sept. 28, 1943 2,348,921 Pavlecka May 16, 1944 2,418,393 Bridgens Apr. 1, 1947 2,521,282 Butler Sept. 5, 1950 2,532,501 Johnson Dec. 5, 1950 2,575,734 Schulman Nov. 20, 1951 2,632,207 Mahla Mar; 24, 1953 2,771,850 Wheelon Nov. 27, 1956 FOREIGN PATENTS 714,544 Great Britain Sept. 1, 1954 1,075,570 France Apr. 14, 1954