Shaping of hollow workpieces

Claim 2

In a method of shaping a hollow workpiece with the aid of a punch and a die having an aperture extending therethrough, said aperture including a conical portion having a semi-cone angle Alpha ; the steps of providing said workpiece with a side wall having an inner and an outer surface; causing said punch to engage said inner surface of the side wall of the hollow workpiece so that the latter is positioned on said punch; moving said punch with said workpiece thereon relative to said die and into said conical portion of the aperture thereof to iron said side wall and thereby reduce the thickness and increase the length thereof to a predetermined degree while subjecting said workpiece to differential frictional forces including a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch, and a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die, said differential frictional forces being effective to limit tensile stresses in the ironed portion of said side wall during ironing; and controlling said differential frictional forces in part by said semi-cone angle Alpha being in agreement with the equation wherein m1 constant friction factor at conical portion of the die aperture, m2 constant friction factor at punch, to original wall thickness of side wall of workpiece, tf final wall thickness of side wall of workpiece after ironing.

Claim 3

A method as defined in claim 1, wherein said die has a single Ironing portion, and said workpiece is ironed to a predetermined final degree during passage through said single ironing portion.

Claim 4

A method as defined in claim 1, including the step of providing said punch with a surface rougher than the inner surface of said tapered aperture of the die, the relatively rough surface of said punch being caused to engage said interior surface of the side wall of the workpiece.

Claim 5

A method as defined in claim 1, in which said aperture of the die includes a substantially cylindrical portion, and the magnitude of said relatively large frictional force is in accordance with the expression L length of substantially cylindrical portion of die, sigma xb back pull stress in side wall of workpiece, sigma xf front pull stress in ironed portion of side wall, sigma o yield stress of workpiece material.

Claim 6

A method as defined in claim 4, wherein the ironed portion of said side wall is kept substantially free of tensile stresses during the ironing step and, accordingly, said expression is reduced to

Claim 7

A method as defined in claim 5, wherein said semi-cone angle Alpha of the conical portion of the die aperture is smaller than approximately 55* and thus the reduced expression is approximately equal to

Claim 8

A method as defined in claim 4, wherein the portion of said side wall emerging from said conical portion of the die aperture is subjected to tensile stresses in accordance with the equation

Claim 9

A method as defined in claim 4, in which the thickness of said side wall is reduced in accordance with the equation wherein exp exponential function of; and remaining symbols are as set forth in claim 7.

Claim 10

A method as defined in claim 8, in which the ironed portion of said side wall is kept substantially free of tensile stresses during the ironing step and, accordingly, the last-cited equation is reduced and modified to wherein Alpha < or = Alpha cr ( Alpha cr critical value of Alpha ).

Claim 11

In a method of shaping a hollow workpiece with the aid of a punch and a die having an aperture extending therethrough, said aperture including a conical portion and a substantially cylindrical portion; the steps of providing said workpiece with a side wall having an inner and an outer surface; causing said punch to engage said inner surface of the side wall of the hollow workpiece so that the latter is positioned on said punch; moving said punch with said workpiece thereon relative to said die and into said conical portion of the aperture thereof to iron said side wall and thereby reduce the thickness and increase the length thereof to a predetermined degree while subjecting said workpiece to differential frictional forces including a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch, and a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die, said differential frictional forces being effective to limit tensile stresses in the ironed portion of said side wall during ironing; and controlling said smaller frictional force by providing hydrodynamic lubrication in the area in which said outer surface of the side wall of the workpiece passes through said aperture of the die, said hydrodynamic lubrication being obtained under conditions represented by the equation wherein Nu viscosity of lubricant, sigma o yield or flow stress of workpiece material, vf final velocity of workpiece material, to original thickness of side wall of workpiece, tf final thickness of side wall of workpiece after ironing, Alpha semi-cone angle of conical portion of aperture of die, L length of substantially cylindrical portion of die, epsilon thickness of lubricant film at die exit, ( epsilon /tf)cr critical value of relative thickness of lubricant film at die exit.

Claim 12

In a method of shaping a hollow workpiece with the aid of a punch and a die having an aperture extending therethrough, said aperture including a conical portion and a substantially cylindrical portion; the steps of providing said workpiece with a side wall having an inner and an outer surface; causing said punch to engage said inner surface of the side wall of the hollow workpiece so that the latter is positioned on said punch; moving said punch with said workpiece thereon relative to said die and into said conical portion of the aperture thereof to iron said side wall and thereby reduce the thickness and increase the length thereof to a predetermined degree while subjecting said workpiece to differential frictional forces including a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch, and a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die, said differential frictional forces being effective to limit tensile stresses in the ironed portion of said side wall during ironing; and controlling said smaller frictional force by providing hydrodynamic lubrication in the area in which said outer surface of the side wall of the workpiece passes through said aperture of the die, said hydrodynamic lubrication being obtained under conditions represented by the equation wherein Nu viscosity of lubricant, sigma o yield or flow stress of workpiece material, vf final velocity of workpiece material, to original thickness of side wall of workpiece, tf final thickness of side wall of workpiece after ironing, Alpha semi-cone angle of conical portion of aperture of die, L length of substantially cylindrical portion of die, epsilon thickness of lubricant film at die exit, ( epsilon /tf)cr critical value of relative thickness of lubricant film at die exit.

Claim 13

A method as defined in claim 10, in which with friction at the die being negligible the portion of said side wall emerging from said conical portion of the die aperture is subjected to tensile stresses in accordance with the equation wherein sigma xf front pull stress in ironed portion of side wall, sigma xb back pull stress in side wall, m2 friction factor at punch; and remaining symbols are as set forth in claim 10.

Claim 14

In a method of shaping a cup-like workpiece from a substantially flat blank with the aid of a punch and die means having an aperture extending therethrough, said aperture including a conical portion having a semi-cone angle Alpha ; the steps of causing said blank to abut said die means; advancing said punch relative to said die means so as to draw said blank into said aperture and impart thereto the form of a cup having a side wall and a bottom integral therewith, said side wall having an outer and an inner surface; continuing the movement of said punch relative to said die means to introduce said workpiece into said conical portion of the aperture of the die means and iron said side wall and thereby reduce the thickness and increase the length thereof to a predetermined degree while subjecting said workpiece to differential frictional forces including a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch, and a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die means, said differential frictional forces being effective to minimize application of forces to said bottom of the cup-shaped workpiece and thereby limit tensile stresses in the ironed portion of said side wall during ironing; and controlling said differential frictional forces in part by said semi-cone angle Alpha being in agreement with the equation wherein m1 constant friction factor at conical portion of the die aperture, m2 constant friction factor at punch, to original wall thickness of side wall of workpiece, tf final wall thickness of side wall of workpiece after ironing.

Claim 15

In a method of shaping a cup-like workpiece from a substantially flat blank with the aid of a punch and die means having an aperture extending therethrough, said aperture including a conical portion having a semi-cone angle Alpha ; the steps of causing said blank to abut said die means; advancing said punch relative to said die means so as to draw said blank into said aperture and impart thereto the form of a cup having a side wall and a bottom integral therewith, said side wall having an outer and an inner surface; continuing the movement of said punch relative to said die means to introduce said workpiece into said conical portion of the aperture of the die means and iron said side wall and thereby reduce the thickness and increase the length thereof to a predetermined degree while subjecting said workpiece to differential frictional forces including a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch, and a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die means, said differential frictional forces being effective to minimize application of forces to said bottom of the cup-shaped workpiece and thereby limit tensile stresses in the ironed portion of said side wall during ironing; and controlling said differential frictional forces in part by said semi-cone angle Alpha being in agreement with the equation wherein m1 constant friction factor at conical portion of the die aperture, m2 constant friction factor at punch, to original wall thickness of side wall of workpiece, tf final wall thickness of side wall of workpiece after ironing.

Claim 16

A method as defined in claim 12, including the steps of starting said ironing substantially immediately after formation of said bottom while keeping the ironed portion of said workpiece generally free of tensile stresses during ironing.

Claim 17

In apparatus for shaping a hollow workpiece provided with a side wall having an inner and an outer surface; die means having an aperture extending therethrough, said aperture including a conical ironing portion; a punch movable relative to said die means and arranged to engage said inner surface of the side wall of the workpiece for advancing the latter into said ironing portion of the die aperture so as to iron said workpiece; first means for subjecting said workpiece to a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch; and second means for subjecting said workpiece to a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die means; said first and second means being effective to limit tensile stresses in said side wall during ironing; and said conical portion of the aperture of the die means having a semi-cone angle Alpha in accordance with the equation wherein Alpha semi-cone aNgle of ironing portion of die means, m1 constant friction factor at ironing portion of die means, m2 constant friction factor at punch, to original thickness of side wall of workpiece, tf final thickness of side wall of workpiece after ironing.

Claim 18

In apparatus for shaping a hollow workpiece provided with a side wall having an inner and an outer surface; die means having an aperture extending therethrough, said aperture including a conical ironing portion; a punch movable relative to said die means and arranged to engage said inner surface of the side wall of the workpiece for advancing the latter into said ironing portion of the die aperture so as to iron said workpiece; first means for subjecting said workpiece to a predetermined, relatively large frictional force resulting from contact of said inner surface of the side wall with said punch; and second means for subjecting said workpiece to a smaller frictional force acting on said outer surface of the side wall and resulting from movement of said side wall relative to said die means; said first and second means being effective to limit tensile stresses in said side wall during ironing; and said conical portion of the aperture of the die means having a semi-cone angle Alpha in accordance with the equation wherein Alpha semi-cone aNgle of ironing portion of die means, m1 constant friction factor at ironing portion of die means, m2 constant friction factor at punch, to original thickness of side wall of workpiece, tf final thickness of side wall of workpiece after ironing.

Claim 19

Apparatus as defined in claim 14, wherein said first means includes a punch surface rougher than the surface of said aperture of the die means, said rougher surface of the punch being arranged to engage said inner surface of the side wall of the workpiece.

Claim 20

Apparatus as defined in claim 15, wherein said second means includes an actuating device for moving said punch and workpiece relative to said die means at a rate sufficient for hydrodynamic lubrication of the area in which said outer surface of the side wall of the workpiece passes through said ironing portion of the die aperture.

Claim 21

Apparatus as defined in claim 14, wherein said aperture of the die means includes a drawing portion preceding said ironing portion and cooperating with said punch for drawing said workpiece from a substantially flat blank to the shape of a cup and for thereby producing said side wall and a bottom integral therewith prior to and in series with the ironing operation; and wherein said drawing and ironing portions of the aperture of the die means are arranged so close to each other that ironing will commence as soon as said bottom of the workpiece emerges from said drawing portion of the aperture of the die means.

Claim 22

Apparatus as defined in claim 17, wherein said drawing portion merges into said ironing portion.