Patent GB-1117398-A (GB)
Title: Safety device for a stamping machine
IPC: B21D55/00
Filed: 1967-04-06
Abstract: 1,117,398. Punching. H. SCHMID. 6 April, 1967 [15 April, 1966], No. 15748/67. Heading B3W. A safety device, for a blanking and piercing press having at least two piercing punches cooperating with die openings formed in the blanking punch, piston operated ejector pins operating in each die opening and a travel limiting stop for the piston, comprises an intermediate member between the piston and the pins which can be moved relative to the pins to a predetermined rest position if the die openings are clear, means for determining whether the intermediate member is in its rest position and a control switch operated by said means where. by the press is stopped if the intermediate member is not in the rest position at the end of a press cycle. The press comprises a fixed platen 10 and an up-stroking ram 21, which carries a die 23 and two piercing punches 30, which pass through a plate 29 and rest on a block 28. An ejector 24 is secured by guide rods 25 to a counter-ram 26. The punch 11 is fixed in the platen 10 and is surrounded by a hold-down 13 which has an annular V-section projection 14, and is connected by rods 15 to a disc-shaped thrust member 16 which is slidable within a thrust ring 18 fixed in the platen. Each of the die openings 31 in the punch 11 contains an ejector pin 32, the upper ends of which bear against the thrust member 16, and the downward movement of which is limited by a shoulder on the pin engaging the top surface of the punch 11. A cylinder 35 mounted on the upper surface of the platen 10 contains a piston 36, and between the piston and the thrust member 16 is the intermediate member 37. The downward movement of the piston is limited by a shoulder 38. The total axial length of the thrust and intermediate members is such that they have a limited movement " K ". Gravity and a spring 39 bias the parts downwardly. The intermediate member 37 is loosely coupled to the piston 36 by a pin and screw 40, 41. A groove 45 round the intermediate member has inclined sides and receives the rounded end of a spring-loaded pin 46. A conical shoulder 49 on the pin engages the actuating roller 50 of an electric switch 52. Operation.-A workpiece S is blanked from a strip M by upward movement of the ram 21, the counter-ram 26 remaining stationary during the first part of the movement. Simultaneously the punches 30 pierce the work. As the punch penetrates the strip, the hold-down 13 is moved upwardly relative to the punch and lifts the thrust member 16 and the intermediate member 37, so that the pin 46 is displaced horizontally and actuates the switch 52. At this stage of the press-cycle the actuation of the switch does not stop the press. The ejector pins 32 are able to move upwards in the die openings, to receive the piercing slugs, due to the upward movement of the thrust member 16. The ram 21 retracts and the part S is ejected by upward movement of the counter-ram 26. Pressure fluid admitted above the piston 36 moves it downwards against the stop 38, moving with it the thrust member 16 and the hold-down 13 which strips the webbing off the punch. The ejector pins are also actuated to clear the dieopenings and provided that this is effected properly the intermediate member 37 is then able to move down freely to its predetermined rest position in which the end of the pin 46 enters the groove 44. If for any reason the ejector pins jam the intermediate member maintains the pin 46 in a position to actuate the switch 52 and this prevents a control signal being emitted which would enable the press to continue running.