US3685337A

US3685337A - Shaping of hollow workpieces

Info

Publication number: US3685337A
Application number: US889218A
Authority: US
Inventors: Betzalel Avitzur
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-12-30
Filing date: 1969-12-30
Publication date: 1972-08-22
Anticipated expiration: 1989-08-22

Abstract

A hollow workpiece to be ironed is subjected to a relatively large frictional force at its interior engaged by a punch, and to a smaller frictional force at its outside engaged by a die, whereby tensile stresses in the ironed portion of the workpiece are decreased and larger reductions in wall thickness are rendered possible per die. Deep drawing may be combined with ironing and both performed during a single stroke of the punch.

Description

Unlted States Patent 1151 3,685,337 Avitzur 51 Aug. 22, 1972 [54] SHAPING OF HOLLOW WORKPIECES 807,085 6/1951 Germany ..72/60 72 Inventor: Betzalel Avitzur, 17 N 31 St 834,626 5/1960 Great 131112111 ..72/82 lemown, p 1 104 625,01 1 6/1949 Great Bntam .....72/349 [22] Filed: Dec. 30, 1969 OTHER PUBLICATIONS [21] Appl. No.: 889,218 Promotion of Fluid Lubrication in Wire Drawing" by Christopherson et al.; pp. 643 653; Proc. Inst. 52 us. c1 ..72/347 Mech- Eng-i 1955- [51] Int. Cl. ..B2ld 22/20 [58] Field of Search ..72/347, 348, 349, 370, 467, P Herbs 72/468, 253; 29/12, 1.21, 1.3 AmmekEr'c Michelson [56] References Cited 1 1 ABSTRACT UNITED STATES PATENTS A hollow workpiece to be ironed 1e subjected to a relat1vely large fr1ct1onal force at its mterlor engaged Fuchs, Jr. a punch to a maller frictional force at out- 211,342 1/1879 Palmer ..72/347 side engaged by a die whereby tensile Stresses i the 3,360,157 12/1967 Bolt 61 a1. ..1 13/ 120 A ironed portion of the workpiece are decreased and 1123,095 3/1949 K8116! ..72/349 larger reductions in wall thickness are rendered p Lyon ble p p drawing y be combined with iron LangCWlS 1 ing and perfonned during a Single Stroke of FOREIGN PATENTS OR APPLICATIONS P 1,468,073 12/ 1966 France ..72/60 l8 CIaims, 26 Drawing Figures E l I 1 I I I 32 l R 1 7 i R. 1 ZONE 1-/ PATENTEDwszz m2 3,685.33 7

sum 02 or 25 F/a. lb

i Y .IXVEXTOR. BETZALEL AV/TZU/P BY PATENTEDwszz I972 SHEET URUF 25 ZONE I lNvE N TOR. BETZALEL Al ITZUR PATENTEIJA um 3.335.337

I SHEET OSUF 25 ik LIMITED DUE TO WALL TENSION m .05 0' L O 3.0?

WEIGHTED IRONING FORCE SEMI-CONE ANGLE FIG. 30 WEIGHTED IRONING FORCE AS A FUNCTION BETZALEL AVITZUR IINVENTOR.

PATENTED M1922 I973 sum as or 25 SEMI-CONE ANGLE FIG. 3b WEIGHTED IRONING FORCE AS A FUNCTION IBETZALEL AVITZUR INVENTOR.

OF (1 AND m $3 74 7 1 MY/M PATENTEDwczz 1912

sum

07 or 25 er LIMITED DUE TO WALL TENSION WEIGHTED IRONING FORCE SEMI -CONE ANGLE FIG.40 WEIGHTED IRONING FORCE AS A FUNCTION 7 OF 0 AND 1 A,.

BETZALBL' AVITZUR INVENTOR.

PATENTEDmszzmz 3.685337 sum near 2 1k LIMITED DUE TO WALL TENSION m, 0-, L 5

EQ.(9b

WEIGHTED IRONING FORCE SEMI-CONE ANGLE FIG. 4b WEIGHTED IRONING FORCE AS A FUNCTION OF 0 AND 1 A,.

BETZALEL' AVITZUR INVENTOR.

'1 lIIITIII SHEET OSUF 25 PATENTED M922 1972 womom @220: QwFIQEB SEMI-"CONE ANGLE FIG.5 WEIGHTED IRONING FORCE AS A FUNCTION OF a AND m BETZALBL RVITZUR INVENTOR.

I L KYLVLQ-V g PATENTEDAUG 22 I972 SEMI-CONE ANGLE FlG.6c| RELATIVE WALL TENSION AS A FUNCTION OF (2 AND m BBTZALEL .AVITZUB INVENTOR.

PATENTEflAuczz m2 SHEET llUF 25 SEMI-CONE ANGLE F|G.6b RELATIVE WALL TENSION AS A FUNCTION BETZALEL AVITZUR INVENTOR.

OF a AND m PATENTEDmcza m2 SHEET 120F 25 SEMI-CONE ANGLE FIG.70 RELATIVE WALL TENSION AS A FUNCTION OF 0 AND r /t BETZALEL AVITZUR INVENTOR.

PATENTED ms 22 I972 SHEET 13UF 25 SEMI -CONE ANGLE FlG.7b RELATIVE WALL TENSION AS A FUNCTION BETZALEL. AVITZUR OF 0 AND 1 /1,.

' INVENTOR.

SHEET l [1F 25 PATENTED M1822 I972 SEMI-CONE ANGLE FIG.8 RELATIVE WALL TENSION AS A FUNCTION OF a AND m BETZALEL AVITZU'R INVENTOR.

PATENTED M1522 I972 SHEET ISUF 25 MAXIMUM POSSIBLE THICKNESS RATIO SEMI- CONE ANGLE FIG.9 MAXIMUM POSSIBLE THICKNESS RATIO AS A FUNCTION OF 0 AND m BETZALEL Avmzun INVENTOR.

I r I I L. 5 (MM.

PATENTED M1222 I972 SHEET 16 0F 25 SEMI-CONE ANGLE F|G.IO MAXIMUM POSSIBLE THICKNESS RATIO AS A FUNCTION OF 0 AND m BETZALBL Avnzun INVENTOR.

PATENTEIIAUBZZIHTZ I 3.685337 SHEET 170T 25 POSSIBL'E THICKNESS RATIO IMPOSSIBLE THICKNESS RATIO b I I (I) IIHIIIW "rrvv-rrrrv-r r rrlrllrrri I I, I 'I'IIIIIIIIII/I SEMI-CONE ANGLE FIG.|I THICKNESS RATIO AS A FUNCTION OF a AND m I BBMALEL AVITZUR INVENTOR.

' POSSIBLE IMPOSSIBLE SHEET 180F 25 THICKNESS RATIO BETZALEL AVITZUR INVENTOR.

gg/ f/ flm PATENTEDwszz I972 SEMI-CONE ANGLE AND rn F|G.l2 THICKNESS RATIG AS A FUNCTION OF a PATENTEnnuazz m2 SEMI-CONE ANGLE SHEET 19 0F 25 WALL TENSION 0 s s 1 6 EQ.(l3c) EXISTS W ELIMINATED MANDREL FRICTION FIG.I3 CRITICAL SEMI-CONE ANGLE OF THE DIE TO PREVENT WALL TENSION.

BET ZALEL AVITZUR INVENTOR.

Claims

1. 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.

2. 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.

3. 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.

4. 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.

5. 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

6. 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

7. 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

8. 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.

9. 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 ).

10. 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.

11. 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.

12. 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.

13. 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.

14. 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.

15. 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.

16. 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.

17. 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.

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