Method and tool for redrawing

Claim 1

A method of redrawing a pre-drawn metal cup having a sidewall of predetermined initial thickness, to increase its length and reduce both its diameter and its thickness, wherein the cup is engaged internally by a punch and by a guide ring coaxially surrounding the punch, and in this condition is urged forward by the punch along the punch axis so that the material of the cup sidewall is progressively urged radially inwardly past a forward face of the guide ring and, subsequently, axially through an annular die having the same axis, the sidewall material of the cup being subjected in turn to: (i) elastic radially-inward bending around a curved edge of the guide ring and in intimate contact with the guide ring only; (ii) elastic bending in the reverse direction through an angle substantially greater than 45 degrees but less than 90 degrees, around a curved edge of the die; and (iii) passing convergently along a convergent bore of the die towards a die throat, whilst the guide ring exerts on the sidewall and an axial pressure sufficient only to guide the sidewall radially past the forward face of the guide ring but insufficient to provide a clamping force, and the sidewall being in contact with only the die throughout steps (ii) and (iii), whereby the thickness of the sidewall is reduced by simple stretching induced by back tension whilst its diameter is reduced by said bending.

Claim 2

A method of redrawing a pre-drawn metal cup having a sidewall of predetermined initial thickness, to increase its length and reduce both its diameter and its thickness, wherein the cup is engaged internally by a punch and by a guide ring coaxially surrounding the punch, and in this condition is urged forward by the punch along the punch axis so that the material of the cup sidewall is progressively urged radially inwardly past a forward face of the guide ring and, subsequently, axially through an annular die having the same axis, the sidewall material of the cup being subjected in turn to: (i) elastic radially-inward bending around a curved edge of the guide ring and in intimate contact with the guide ring only; (ii) elastic bending in the reverse direction through an angle substantially greater than 45 degrees but less than 90 degrees, around a curved edge of the die; and (iii) passing convergently along a convergent bore of the die towards a die throat, whilst the guide ring exerts on the sidewall and an axial pressure sufficient only to guide the sidewall radially past the forward face of the guide ring but insufficient to provide a clamping force, and the sidewall being in contact with only the die throughout steps (ii) and (iii), whereby the thickness of the sidewall is reduced by simple stretching induced by back tension whilst its diameter is reduced by said bending.

Claim 15

A method of redrawing a pre-drawn metal cup having a side wall and an end wall of predetermined initial thickness and a predetermined axial length to reduce the sidewall thickness and increase the axial length comprising the steps of establishing an annular path of travel for the sidewall which in axial cross-section is generally of a funnel-shaped configuration, the funnel-shaped annular path being defined by a cylindrical path portion of a predetermined major diameter merging with a first radiused path portion progressively reducing the major diameter and merging with a radial path portion in turn merging with a second radiused path portion merging with a convergent path portion converging toward a predetermined minor diameter, positioning a pre-drawn metal cup within the cylindrical, first radiused and radial path portions in the absence of mechanical clamping forces; applying an axial force against the end wall to progressively move the latter in and through the convergent path portion while simultaneously bending and stretching the sidewall during its movement through the first radiused, radial and second radiused path portions again in the absence of mechanical clamping forces; and maintaining the size of the annular path as measured generally normal thereto at the cylindrical, first radiused and radial path portions at all times no less than said sidewall predetermined initial thickness whereby the metal cup is reduced in sidewall thickness and increased in axial length.

Claim 16

A method of redrawing a pre-drawn metal cup having a side wall and an end wall of predetermined initial thickness and a predetermined axial length to reduce the sidewall thickness and increase the axial length comprising the steps of establishing an annular path of travel for the sidewall which in axial cross-section is generally of a funnel-shaped configuration, the funnel-shaped annular path being defined by a cylindrical path portion of a predetermined major diameter merging with a first radiused path portion progressively reducing the major diameter and merging with a radial path portion in turn merging with a second radiused path portion merging with a convergent path portion converging toward a predetermined minor diameter, positioning a pre-drawn metal cup within the cylindrical, first radiused and radial path portions in the absence of mechanical clamping forces; applying an axial force against the end wall to progressively move the latter in and through the convergent path portion while simultaneously bending and stretching the sidewall during its movement through the first radiused, radial and second radiused path portions again in the absence of mechanical clamping forces; and maintaining the size of the annular path as measured generally normal thereto at the cylindrical, first radiused and radial path portions at all times no less than said sidewall predetermined initial thickness whereby the metal cup is reduced in sidewall thickness and increased in axial length.