Patent GB-550230-A (GB)
Title: Improvements in or relating to a method of and means for forming recesses, depressions or the like in thin material such as sheet metal
IPC: B21D22/04
Filed: 1941-06-26
Abstract: 550,230. Countersinking &c. by stamping. HILL, J. A., and CUNUFFE-OWEN AIRCRAFT, Ltd. June 26, 1941, No. 8047. [Class 83 (iv)] Recesses are stamped in thin sheet metal, particularly dimples for use in flush riveting in aircraft construction by a device employing free transmitting means extending through the aligned holes. A die 8 is removably carried by a mandrel 6 handled at 9 for insertion through the hole in the work 47, 48. The forward end of the mandrel is serrated for gripping in a chuck 121 normally open to permit insertion of the mandrel but closed on the commencement of the operative stroke by being drawn into a bevel edged sleeve 11. In modifications the connection may be screwed, or a bayonet joint, or the mandrel may be plain with a head to pass beyond the chuck jaws. A guide rod 14 screws into the end of the chuck and attaches it to a block 15 sliding in a recess in the body 1 and having screwed to it a piston 18 normally held in the position shown by a spring 21. Compressed air &c. admitted at 40 passes by a port 45 in a spring pressed valve with a head 44 for finger control, to the rear of a piston 26 normally held in the position shown by a spring 31. The piston rod 33 is fitted with a cup leather 35 working in a small bore 34 connected at 37 with the cylinder 19 the space between the pistons 35 and 18 being filled with oil. The die 3 screwed into the body 1 is held against the work and the intensified pressure on the piston 18 draws up the counter die 8 to effect the dimpling. Relief valves may be fitted to prevent the development of excessive pressure and the cylinder parts containing the springs may be vented. In a modification the valve 42 may admit air pressure to the ends of the cylinders containing the springs to effect return of the pistons either instead of or additionally to the springs. The device may be activated by pressure hammer mechanism. In a modification the die 53, Fig. 4, is carried by the rod 59 of the piston 60 fluid actuated through the passage 69 by the ram 69<SP>1</SP> directly connected to the air actuated piston 74 controlled by a valve 79 and grip handle 81. An additional port 85 in the valve connects a relief passage 84 to a port containing a spring loaded ball 87 acting as a supply valve. The gripper 67 for the mandrel is screwed into the body of the tool and is closed by a shoulder in the hollow end 59 on the first part of the working stroke. If the metal is soft enough a plane abutment die may be used in combination with the convex dimpling punch. In other modifications referred to in the Provisional Specification the closing of the chuck jaws may be effected by a compressed air operated sliding collar ; the die 3 may be movable and forced outwards ; the mandrel may be carried by the tool, both the die 8 and abutment 7 being then detachably secured to the mandrel ; two pistons may move outwardly in a single cylinder on admission of air between them one effecting the working of the mandrel and the other forcing the die 3 outwards. Specification 544,603 is referred to.