Patent GB-789641-A (GB)
Title: Improvements in apparatus for working sheet metal
IPC: B21D11/02
Filed: 1956-02-08
Abstract: 789,641. Stretching; drawing; stamping. ANDERSON, F. Feb. 8, 1956 [Feb. 8, 1955], No. 3979/56. Class 83 (4). A machine for curving a metal sheet in two directions by differential stretching comprises means for drawing the sheet firstly through a pair of opposed work - engaging elements arranged to determine a general path of movement of, and to exert a restraining force on, the work and having means to reciprocate one of the elements to vary the gap between them and secondly over a forming element reciprocable in a path parallel to that of the restraining element and cams actuated by the drawing means for controlling the reciprocation of one or both of the said elements. The machine comprises three main parts, a sheet-forming structure, the draw-bench and carriage and the draw-mechanism for pulling the sheets through the forming elements. A sub-base 11 serving as a reservoir for hydraulic fluid and having its longest dimension extending transversely of the machine supports, at one end, the main power unit M1 and gear-box 14 for driving the carriage which is reciprocated by a bull-gear 31 engaging a rack 36 on the underside of the carriage. The drawbench is an elongated channel-member supported at its centre on the gear-box and at its ends by legs 33 and has guides 32a which overlie the carriage. The carriage is provided with upper and lower formica wearing strips 41, 44, Fig. 44, and also with bronze wearing strips 37 at the sides to take the lateral thrust which occurs in operation. At the bottom of the gearbox is a lubricating-oil sump 23 from which a pump 26 distributes oil to the gear-box and also through passages such as 45a, 46a and 47, Figs. 22 and 44, to oil grooves formed in the wearplates of the carriage. For dealing with longer sheets than usual, both the draw-bench and the carriage may be fitted with extensions. The forming structure is mounted on a main base 65, Fig. 12, secured on the sub-base 11 to the right of the gear-box 14 as seen in the direction of travel of the work and is positioned between two uprights 89, 90 upstanding from the base. The base supports a guide structure for the third stage forming assembly and at its rear end provides a trunnion support 77, 78 for a guide structure 79, Fig. 13, for the first stage assembly. In the first stage forming mechanism the sheet S is drawn between elements 121 and 124 of a lower member and elements 110, 113 of an upper member. A top-plate 97 adjustable in height for sheets of different thicknesses spans secondary uprights 92 and carries an hydraulic cylinder 104 which operates through toggle mechanism 102 the ram 99 to which member 110 is clamped. Plate 113 is secured to a carrier 114 having a lost-motion and resilient connection with the ram. A typical opening movement of the ram is one inch and the lost-motion may be of the order of half-an-inch, the adjustment of the parts being such that the plates 113 and 124 do not touch the sheet except to determine its plane of movement. A rearwardlyextending leg 94 of the first stage assembly extends through a guide 84 of the structure 79 and at its rear is connected by links 132 to a crank 134 pivoted on a pin 135 extending between trunnion plates 137 secured to the rear of bars 85 and 86 of the structure 79. The crank may be racked by an hydraulic cylinder 139 to reciprocate the first stage assembly in the structure 79. The point of connection between the cylinder and crank-arm 134 can be varied for different thicknesses of sheet. A universal mounting for the first stage assembly comprises a cradle hung on the main base trunnion arms 77 and 78 in which it seats and rocks the bottom of the guide 84 whilst the front ends of bars 87, 88 of structure 79 are connected to hydraulic cylinders 148 and 149 so that if both cylinders are operated equally the assembly'will be rocked about a transverse axis while if they are differentially operated there will be a component of movement about the longitudinal axis. Overlying the guide structure and main base is a feed table comprising rear channel sidebars 151, 152 and shorter front channels 153, 154, all of which carry horizontal guide rollers 167 and vertical rollers 168 to engage the edges of the sheet S. Anti-friction balls 169 are provided on the top plates 128, 129 and 130. The channels are adjustably secured to transverse guide-plates and may be set at an angle to the longitudinal axis of the machine. Before the sheet enters between the plates 113 and 124 both surfaces are supplied with oil which is pumped from a sump in the main base to openings beneath the sheet and also through secondary uprights 92 into the hollow interior of plate carrier 114 and thence through openings above the sheet. Used oil drips back into the sump, falling first on surfaces 80, 81 and 82 of the guide structure 79 and surfaces 70 and 70a of the base 65. Spanning the main uprights 89, 90 is a bar 198, Fig. 3, supporting through toggles 202 a ram comprising an upper bar 199 and a lower element-carrying bar 200 adjustably connected thereto by turn-buckles 201. The ram is counterbalanced by a weight 206 guided by rails 209 and operated through the toggles 202 by an hydraulic cylinder 204. To the bottom of the bar 200 is secured a downwardly curved forming element 211 of the second stage mechanism. Guided on the surfaces 70 and 70a of the main base and reciprocated longitudinally of the machine by an hydraulic cylinder 218 is the third stage body member comprising a crosshead 215 and a rearwardly extending leg 216 which is connected with the cylinder 218. Crosshead 215 supports a crosshead 213 carrying a forming element 221 which is substantially complementary to the former 211 of the second stage. Although the forming elements 211 and 221 of the second and third stages have been shown as inflexible plates, a flexible construction is also contemplated. In this form, the bar 200, Fig. 31, has a dove-tailed slot to receive a channel-sectioned abutment member 345 to which is clamped by a plate 347 and screws 348, a channel-sectioned work-engaging member 346, the upper flange of which is disposed between the two flanges of member 345. Member 346 has a series of longitudinal slots extending down to a relatively thin and flexible bottom strip to which is secured a hardened steel workface 346a. Flexing of the working face to the required form is done by means of hollow screws 350 threaded through the lower flange of the abutment member 345 into which are threaded smaller screws 352 with heads which abut the top of the working strip. A similar flexible forming element is secured to the lower crosshead 215. The operation of the several hydraulic cylinder devices is controlled by tracer mechanism which follows cam-tracks comprising six flexible rods or wires 225a- 230a, one for each hydraulic cylinder. Angular frames 224 on the draw-bench carriage 35, Fig. 25, support six cam bars 225-230 and each bar carries a vertically adjustable support 231 having a clamp 232 for a cam rod. As the cams move with the draw-bench they actuate six similar tracer valves 237-242 associated with the hydraulic cylinders. One such valve 240, described by way of example, is mounted on a carriage 243 running on tracks in an arm 244 attached to a fixed plate 236 bolted to the upright 89 so as to overlie the draw-bench. The valve stem 247 is urged in one direction by a spring 248 against a weighted tracer arm 249 to which is attached the arm 253 of a cam follower roll 254. The connection between arms 253 and 249 can yield under abnormal force. Three of the tracer valves, 239, 241 and 242, Fig. 59a, also incorporate a solenoid for supplemental control to allow interruption of the cam operation of the valve when required. A spring 257 acting on a cup 258 slidable on the valve stem 247 is strong enough to overcome spring 248 and move the stem 247 away from the tracer arm 249. The action of the solenoid 53 is to move an inner cup 261 so as to compress spring 257 and place the valve stem under the influence of the spring 248. A pump P2 (not shown) driven by a motor M2 supplies fluid at 1000 lbs. per square inch to cylinder 139 through a valve 266 (not shown) and all the other cylinders are supplied at 300 lbs. per square inch by a pump P3 (not shown) driven by a motor M3 through tracer valves 237, 238, 240, 241 and 242. Pump P3 also supplies fluid through tracer valve 239 to control valve 266. Each of the parts moved by the cylinders is coupled by a push-pull cable operating within a fixed sheath to the casing of its controlling tracer valve so that, in the case of the first stage assembly, for example, the horizontal movement imparted by cylinder 139 is transferred to the casing of valve 239 which, acting through valve 266, shuts off hydraulic pressure when the assembly has been displaced by the required amount. The sheet pulling mechanism, Fig. 45, is carried by a laterally-extending tapering arm 355 comprising a flat plate 357 reinforced by a concave top cover sheet 360. The arm is secured to the top of the carriage 35 at its widest end and supported on a rail 362 at its narrow end. On the underside of the plate 357 are two pairs of channel-shaped guides 363, 365, which receive the cross-plates 369, 368, respectively, of converging bars 366, 367 secured at their rear ends to a vertical plate 371 and a horizontal plate 372. Plate 371 has four slots 377, Fig. 46, through which pass bolts 376 to secure a jaw holder bar 378, adjustable vertically by means of hand wheels 380. Screwed and keyed to the top and bottom of the bar 378 are plates 384, 385 which retain a series of twelve screws 389 each of which passes through and secures the threaded hub of a jaw carrier comprising a body 390, Fig. 48, screwed into the hub 388, side-plates 392 and converging top and bottom plates 396, 397 forming backing members and guides for the gripping plates 398, 399 which are actuated by a