Patent GB-775160-A (GB)
Title: Coin dimpling apparatus and method
IPC: B21D22/04
Filed: 1955-05-16
Abstract: 775,160. Dimpling. CHICAGO PNEUMATIC TOOL CO. May 16, 1955 [May 25, 1954], No. 14055/55. Class 83 (4). Apparatus for forming a dimple around a preformed hole in a metal sheet comprising a punch, a die for engaging the sheet around the peripheral area of the dimple, a ram engaging the edge of the dimple immediately around the hole, and pressure means for resisting the downward or forward movement of the ram in response to the pressure of the dimple is characterized in that said pressure means urges the ram upwardly or rearwardly with a pressure that remains substantially constant as the pressure on the die rises abruptly. The apparatus comprises a yoke 11 having upper and lower jaws 12 and 13 respectively. The upper jaw supports a reciprocable plunger 14 which carries an adjustable punch holder 17 and a dimpling punch 21. The adjustable stationary dimpling die 19 is supported by a die holder 26 secured to an adjusting screw 27 threadably mounted on a sleeve 28 disposed in a bore 29 in the yoke jaw 13. The adjusting screw is rotated by a knurled knob 31 and a graduated ring 33 indicates the position of the screw. The die is bored to slidably receive a ram 36 (Fig. 3), which has a flat upper end engaging the lower edge of the formed dimple 37 causing the metal to flow upwards and to form a sharp corner adjacent the punch. The ram is supported on a post 38 which is slidably mounted in the bore of the adjusting screw 27 and the die-holder 26. The lower end of the post rests on an adjusting screw 40 threadably mounted in the short arm of a lever 41 pivoted at 42 on a cylinder member 44. An indicator 52 gives the location of the adjusting-screw 40, which is retained in position by a spring-loaded ratchet-pin 56. The long arm of lever 41 engages with a piston 61 operating in a cylinder 62 in the member 44. Compressed air is supplied to the cylinder 66 via a pressure regulator 69 (Fig. 8). A drain valve 92 (Fig. 9) is provided in the cylinder member 44 for rapidly relieving the pressure in the piston chamber 60 at the end of the dimpling. In operation compressed air is supplied to the pressure regulator 69, the diaphragm 85 of which is raised against the pressure of a preset spring 88. Upon attainment of a predetermined pressure, for which the regulator is set, a valve member 78 is closed by a spring 83, thus preventing further pressure rise in a chamber 81 which communicates with the piston chamber 60. The preformed hole in the sheet metal is aligned with the punch and when the punch projection 24 drops into the hole the power stroke is initiated automatically by known means. As the punch dimples the sheet metal the reaction is transmitted back through the yoke to the rigid die 19 and the yielding ram 36. At the lower end of the dimple, downward movement is resisted by engagement with the flat upper face of the compressed-air loaded ram 36, and the metal flows around the projection 24 and fills the space between the punch and die, thus preventing drawing, thinning or cracking of the metal at the mouth of the dimple. The apparatus may be portable and may be used for hot or cold dimpling.