GB782944A - A method of press-forming hollow members - Google Patents

Abstract

782,944. Extruding; forging. BOSCH GES., R. May 31, 1955 [June 11, 1954], No. 15518/55. Classes 83 (2) and 83 (4). Making sparking-plug casings. A method of making hollow members with stepped walls, more particularly sparking-plug casings, comprises forming a cup-shaped blank 21, Fig. 3, with internal and external stepped surfaces in the region of its mid-length, backwardly extruding the solid base portion 16 of the blank by means of a ram 28 and in a separate subsequent pressing stage, forwardly extruding the head portion at the other side of the stepped surfaces by means of a ram 38, Fig. 4, to form the blank 40, whereby the axial length of the blank is extended on both sides of the stepped surfaces. In the manufacture of a sparking-plug casing, a blank 1, Fig. 1, cut from cylindrical bar stock, is inserted in a die 2 yieldably movable against springs 3, and supported therein against an ejector 5. A ram 6 with a conical nose 7 is pressed into the blank whilst simultaneously an annular pressure member 8 pushes the die forward against its springs, the ejector remaining stationary. The blank is thus pierced and enlarged laterally to cup-shape. The blank is then annealed and phosphated. It is then inserted in a second die 11, Fig. 2 (not shown), in which it is elongated by a ram pressed into the bore of the blank, and the stepped surfaces are formed internally and externally at the mid-length of the blank; the latter now has the shape 21, Fig. 3. The blank 21 is then inserted in the die 23 within which the centre and head portion of the blank are slidable. The base portion is closely fitted in a cylindrical die section 24 closed by an ejector 26. The ram 28 having an enlarged collar 29 is then pressed into the base portion 16 to backwardly extrude the latter, the centre and head portions sliding backwardly unchanged. The ejector 26 carries a boss 27 which forms a recess 30 in the end of the extruded blank 31. The ejector 26 and a stripper plate 32 remove the blank from the die 23. After insertion in the next die 33, Fig. 4, a mandrel 37 is fitted into the blank, and the head portion thereof is extruded forwardly by an annular ram 38; the mandrel moves forwardly with the ram during the extrusion. An ejector 36 removes the extruded blank 40 from the die. The blank is then inserted in a further die 42, Fig. 5 (not shown), a mandrel is passed into the bore of the blank and an annular ram presses on the open end of the blank to form the head 39 thereof into hexagonal cross section; the casing may also be pressed to size during this operation. The disc of metal remaining in the closed end of the blank is then removed by a punch 52, Fig. 6 (not shown), the end of the hexagonal head is turned down by a cutting tool 56, Fig. 7 (not shown), and a thread cut on the base portion of the casing. The surfaces of the plug may then be phosphated, coloured or provided with a rust-protecting coating. The various pressing operatsions are preferably performed cold on a five-stage press.