Patent ID: 7055359

Claim:
A method for forging/molding a coarse blank of an oil cylinder, comprising steps of: (a) placing burn-in softened aluminum material into a preheated mold having a mold cavity, an inner end of the mold cavity having an end cap molding section with a profile corresponding to a first end cap of the oil cylinder, the mold cavity further having a straight tunnel adjacent to the end cap molding section, the cross-section of the straight tunnel corresponds to the cross-section of the cylinder body of the oil cylinder, the straight tunnel having a length shorter than the axial length of the cylinder body, an outer end of the straight tunnel being a molding hole coaxially extending from the straight tunnel, the cross-section of the molding hole corresponding to the profile of the second end cap of the oil cylinder; and (b) using a first punch head to first forge the aluminum material in the mold cavity from outer side of the molding hole so as to form a blank body of the oil cylinder with a first end cap, a second end cap and a shorter cylinder body, one end of the first punch head having a punch rod with a smaller diameter, an end cap molding section being adjacent to the punch rod, one side of the end cap molding section adjacent to the punch rod having a molding configuration corresponding to the profile of the second end cap of the oil cylinder; (c) moving out the first punch head and connecting an extension mold with the mold, the extension mold having an extension hole as an elongated section of the molding hole; and (d) immediately using a second punch head to secondarily forge the blank body in the mold cavity from outer side of the extension hole so as to make the cylinder body of the blank body outward axially extend into a predetermined length to form the oil cylinder, the second punch head being a straight elongated rod with a diameter equal to the diameter of the punch rod, an end section of the second punch head extending into the mold cavity to a position near the inner end of the mold cavity.