EP0055421A2 - Procédé pour réduire le retour élastique de tôles pressés - Google Patents

Procédé pour réduire le retour élastique de tôles pressés Download PDF

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Publication number
EP0055421A2
EP0055421A2 EP19810110488 EP81110488A EP0055421A2 EP 0055421 A2 EP0055421 A2 EP 0055421A2 EP 19810110488 EP19810110488 EP 19810110488 EP 81110488 A EP81110488 A EP 81110488A EP 0055421 A2 EP0055421 A2 EP 0055421A2
Authority
EP
European Patent Office
Prior art keywords
panel
pressing
strain
female molding
molding member
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP19810110488
Other languages
German (de)
English (en)
Inventor
You Chao Liu
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Ford Werke GmbH
Ford France SA
Ford Motor Co Ltd
Ford Motor Co
Original Assignee
Ford Werke GmbH
Ford France SA
Ford Motor Co Ltd
Ford Motor Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Ford Werke GmbH, Ford France SA, Ford Motor Co Ltd, Ford Motor Co filed Critical Ford Werke GmbH
Publication of EP0055421A2 publication Critical patent/EP0055421A2/fr
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D5/00—Bending sheet metal along straight lines, e.g. to form simple curves
    • B21D5/01—Bending sheet metal along straight lines, e.g. to form simple curves between rams and anvils or abutments
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D—WORKING OR PROCESSING OF SHEET METAL OR METAL TUBES, RODS OR PROFILES WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
    • B21D11/00—Bending not restricted to forms of material mentioned in only one of groups B21D5/00, B21D7/00, B21D9/00; Bending not provided for in groups B21D5/00 - B21D9/00; Twisting
    • B21D11/20—Bending sheet metal, not otherwise provided for

Definitions

  • Complex formed sheet materials usually refers to panels that have some degree of reverse bending involved.
  • forces have been applied to the sheet material which cause spaced, but oppositely oriented, bend radii to be formed. If the sheet material is formed in a press with a single straight line stroke, the bends will be formed sequentially and the section of the sheet material between the bend radii will be subjected to progressive bending and unbending which may include some rubbing or shearing forces on one side. Such bending and unbending forces produce a type of springback which curls the separating section.
  • a T-shaped male punch member would be struck downwardly upon the panel lying atop a female molding member.
  • the skirt of the panel is folded upwardly (at a first bend) until the panel edge margins are restrained by the overhanging head of the T-shaped punch.
  • the head of the punch imparts a second bend opposite to the first bend, but spaced therefrom. Because such bends are formed sequentially, curling strain is involved.
  • the panel is drawn more deeply into the female molding member. The panel edges become progressively more restrained as the punch head approaches closely the female molding member.
  • the intermediate panel section With the panel edges increasingly restrained and the panel continuing to be pulled into the female molding member, the intermediate panel section will be progressively bent and unbent along with being rubbed vigorously on one side.
  • the bending and unbending occurs by sliding contact of the intermediate section against the edge or mouth of the female molding member which acts as a fulcrum, creating differential stress and strain across the thickness of the intermediate section (between the inner and outer surfaces of the panel).
  • the intermediate section Upon removal of the male punch and withdrawal of the complex formed sheet panel, the intermediate section.will assume a curled condition, not conforming to the configuration of the female molding member in which it was struck.
  • This invention relates to a method of overcoming curling in sheet materials subjected to progressive opposed bending.
  • the first step of this method comprises pressing a panel of material to sequentially form opposite and separated bend radii therein.
  • the separating section of the panel between the bend radii is subjected to progressive bending and unbending about a fulcrum which relatively slides along one side of the panel to impart a first strain in the separating section.
  • the panel is counter rubbed on its opposite side to impart a strain opposite to the first strain to remove the curling.
  • the counter rubbing is carried out either simultaneously or subsequent to the first pressing.
  • the resulting sheet material panel will adopt the configuration imparted by the press with reduced curvilinear springback in the separating section.
  • This method has particular utility in forming hat sections having pairs of opposed bending radii and bend angles of about 90°.
  • Such forms typically comprise a high percentage of automotive sheet metal requirements in chassis construction.
  • the intermediate section of the sheet material panel (in which curling is a particular problem) has a length of at least 12,7mm and the bend radii are within the range of 3, 18 mm to 6, 35 mm
  • the die gap (space between the mated male punch member and female molding member) is preferably controlled during first pressing to 1.5 - 3.0 times the thickness of the sheet metal and, during counter rubbing, the die gap is preferably controlled to about the thickness of the material. Die gap is decreased in proportion to an increase in strength of the sheet metal.
  • One desirable mode for carrying out the method is to carry out a first pressing with one pair of male punch and female molding members, and to carry out the counter rubbing by use of a second, oversized male punch member in a second pressing or restrike.
  • a binder element may be employed adjacent the entrance opening of the female molding member to guide the movement of the sheet material panel in a direction transverse to the pressing motion, thereby to insure a continuous and uniform bending and unbending during pressing.
  • This mode may be further modified by incorporating a bead or knuckle on the binder element to impart a continuous pressure which strains the sheet metal panel on both sides causing the bending and unbending and counter rubbing to occur simultaneously during pressing.
  • Yet another mode comprises using a male punch member with negatively tapered sidewalls so that the necessity for a restrike is eliminated.
  • the corner radius of the entrance opening to the female molding member imparts bending and unbending to one side of the sheet material panel during pressing, as in the preferred mode.
  • the corner radius on the male punch member formed by its negatively inclined walls and a flat punch face, counter rubs the other side of the sheet material panel during withdrawal of the male punch member from the female molding member.
  • Elimination or optimized reduction of curling can be obtained by reducing the residual die gap between the male and female members (minus the thickness of the material) to a value which is not substantially zero, but about 0,254 mm.
  • a press is the machine used most often for cold working of sheet material.
  • a press consists of a machine frame supporting a bed and a ram, a source of power and a mechanism to cause the ram to move in line with and at right angles to the bed.
  • a press in and of itself, is not sufficient as a production machine, but must be equipped with tools commonly called punches and molds, each of which are designed for certain specific operations and forming contour.
  • a male punch member is carried by the ram and is moved in a downward direction to contact the upper surface of a flat sheet metal panel which sits atop a female molding member designed to allow the male punch member to penetrate thereinto.
  • Presses can be conveniently classified into two broad types, including hydraulic and mechanical presses. This invention is applicable to the use of either type of such presses. Mechanical presses are desirable from a production standpoint because of their higher speed of cycling and more rapid production.
  • this invention has discovered that if the sheet material is strained or stressed by counter rubbing on the surface of the sheet material opposite to the surface to which strain or stress was applied by bending and unbending during pressing to create curling, the curvilinear springback (or curling) can be eliminated or significantly reduced.
  • Springback which results in an out-of-shape curled section may be due in part to (a) bending springback by progressive bending and unbending about a fulcrum of one of the pressing members, and (b) deformation strain imposed by shearing or surface rubbing forces creating a strain gradient across the metal thickness.
  • Curling is defined herein to mean curvilinear springback residing in a sheet material panel which has been subjected to separated and opposed sequential permanent bending during pressing, causing the panel to be bent and unbent about a fulcrum contacting one panel side as it is pulled into the female molding member during pressing. Sequential permanent bending is involved since one bend is imparted prior to the completion of the other bend which necessitates feeding and curling of the panel around the form (fulcrum) for the second bend. Bend radii is used herein as referring to the bend in the sheet material resulting from pressing a corner of the male punch member or female molding member thereagainst.
  • a preferred method for carrying out the present invention comprises interposing a panel 10 of undeformed sheet metal between a male punch member 11 and a female molding member 12 carried by a press of the type described in "Techniques of Pressworking Sheet Metal", by D.F. Eary and E.A. Reed, 2nd Edition, Prentice-Hall, Inc., 1974.
  • the members 11 and 12 are moved together, such as by a rapid striking or pressing, to form progressively opposite and separated bend radii 13 and 14 in the sheet metal (see Figure lc).
  • the section 15 of the panel between the bend radii is subjected to bending and unbending about the fulcrum 30, as well as rubbing or shear forces, on one side, here being the outer surface 10a.
  • an unbalanced strain gradient is imparted across the thickness of the sheet metal material in this section.
  • the other or inside surface 10b of the separating section 15 of the sheet metal panel is counter rubbed (engaged by a fulcrum 33) to impose a strain generally equal and opposite to the first strain resulting in a reduction of curvilinear springback in the separating section.
  • the press is preferably of a mechanical type having a power linkage to the ram which may be a crank, a cam, an eccentric, a power screw, a rack and pinion, a knuckle joint, a toggle, and even a pneumatic coupling means.
  • the male and female members are each contoured to ultimately form a hat section (see Figure lg) having pairs of oppositely opposed bend radii 13-14 and 16-17 separated by a desirably flat webbing 18.
  • the male punch member 11 is preferably T-shaped, having a central punch body 19 with an overhanging head 20.
  • the body 19 is adapted to seat within the cavity 21 of the female molding member to create one bend 14 and the head 20 is adapted to seat against the shoulder 30 surrounding the entrance to the opening or cavity of the female molding member to form a second bend 13.
  • the opening or cavity 21 of the female molding member 12 receives the body of the male member with a predetermined spacing or die gap 22 therebetween to accommodate not only the thickness 23 of the material, but also to provide a predetermined residual space 24.
  • the depth of the opening within the female molding member is designed to be greater than the depth 25 of the body of the male punch member so that upon complete penetration of the male punch member within the female molding member, the head 20 will seat fully.
  • a counterpad 27 is preferably used to grip the sheet metal in cooperation with the punch member; counterpad 27 is typically stationed flush with the entrance to cavity 21 and resists the punch with a force of about 300 psi applied via a pin 28 and hydraulic or pneumatic actuator 29.
  • Sheet materials which respond to this method include metallic and nonmetallic materials having (a) an elongation of at least 1.5% permitting the material to be permanently bent, and (b) a melting temperature at least double the temperature at which pressing occurs (so that the material can be cold worked at conventional room temperature in a solid rigid form).
  • the sheet material must have sufficient structural rigidity to withstand the shearing or rubbing in some modes. Typically, this necessitates a thickness of about 1 , 27mm inches for conventional carbon steel and for HSLA steel when subjected to the mode of Figures 1 and 3.
  • the outer margin 10c of the sheet metal panel is free and out of contact with the head or body of the male punch member.
  • the panel is drawn into the opening 21 of the female molding member 12 and is caused to be bent at first radii 14.
  • the sections 15 flare outwardly out of contact with the male punch member.
  • the flared margins 10c will contact the head. 20 of the male punch member; the margins of the sheet metal panel will be restrained from freely folding upwardly and will bend downwardly. This increases the rubbing contact of the panel outer surface on the corner radius 30 of the female molding member.
  • Counter rubbing is preferably carried out with the deformed or pressed sheet metal panel remaining within the female molding member and the first punch member is withdrawn.
  • a second, but oversized, male punch member 31 (see broken outline in Figure lc) within a predetermined oversizing of 1,575 mm is restruck or pressed into the female molding member. This time, the inner surface 32 of the sheet metal panel will be engaged and rubbed by punch surface 31, imparting approximately equal and opposite strain to the first strain.
  • the surface 31 of the oversized punch member 31 applies shearing or rubbing forces.
  • the sheet metal Upon removal of the sheet metal panel from the female molding member after the restrike operation, the sheet metal will adopt substantially the configuration of the tooling members 11 and 12.
  • Uncompensated curling is due in part to two phenomena, one is the springback due to the progressive bending and unbending about a sliding fulcrum, and to the unbalanced rubbing strain after the sheet metal has contacted the overhanging head of the male punch member.
  • To facilitate total removal of such curling there must be fairly accurate oversizing of the male punch member to produce substantially comparable.and opposite straining of the interior surface. This is difficult to accomplish throughout the entire height of the separating section 15.
  • a modification of the method can be carried out as shown in Figures 2 and 2a.
  • a binder or restraining element 34 is mounted atop the female molding member 12.
  • Such binder element guides the sheet metal panel 10 in a horizontal direction 36 transverse to the line of movement 35 of the punch member.
  • the panel is fed to the pressed center zone, it is restrained against folding freely upwardly (flaring) to later engage the overhang of the head of the male punch member.
  • Such restraint is afforded by the binder 34 which forms a slot 37 through which the panel may pass in a horizontal direction.
  • the outer surface 10a of section 15 is uniformly rubbed throughout the entire stroke of the male punch member thereby facilitating equal a counter rubbing during restriking with an oversized male punch member.
  • the first strain is now uniform throughout the section 15 so that the strain resulting from uniform counter rubbing during restriking is more accurately equal to the first strain.
  • FIG. 3a-3d Another alternative mode for the method is shown in Figures 3a-3d, which mode eliminates the necessity for a restrike motion.
  • the male punch member 40 is formed with negatively inclined sidewalls 41 to the body 43 of the punch. This permits the corner radius 43 (formed between the negatively inclined walls 41 and the bottom face 44 of the punch) to have particular utility during withdrawal of the punch member.
  • the male punch member contacts a fixed portion of the panel during the first downward pressing motion; contact is by the punch face 44 and corner radii 45 only. There is no relative rubbing action between the male punch member and the sheet metal as it is drawn with it. There is bending and unbending as well as rubbing of the outside surface 46 on the corner radius 43 of the female molding member to impart the curling strain.
  • FIG. 4 An alternative mode shown in Figure 4 retains the virtue of a single strike action while permitting the use of straight walled punches.
  • a conventional male punch member 11 is employed having a straight-sided body 19.
  • the binder element 53 has a bead 54 depending from the inner edge to impose a predetermined pressure upon the inner surface 10b of the sheet metal panel 10 as it is progressively drawn through the binder element into the opening 21 of the female molding member 12.
  • equal and opposite strain is imparted simultaneously to the inner and outer surfaces 10a and 10b of the sheet metal panel, preventing any curling tendency. This is accomplished during the downward striking motion of the male punch member.
  • the withdrawal of the male punch member does not enter into the sequence of removal of strain and thus can be extremely rapid.
  • a counterpad 27 to assist in eliminating both curling and bending springback can be employed as shown in Figure 5a.
  • the binder element is again used having a bead 54 to impose a continuous pressure during the downward striking of the sheet metal panel.
  • the counterpad 27 is positioned a distance 55 below the mouth 56 of the female molding member 12.
  • a curvilinear form is imparted to web 18 of the panel.
  • the web in the sheet metal Upon confrontation of the male punch member with the counterpad, the web in the sheet metal will be flattened to spread apart the first bend loci A.
  • the panel will be bent at a new loci B (spaced a slight distance from A).
  • a first pressed specimen was prepared utilizing HSLA steel having a thickness of 1,45mm and a tensile strength of 3515 bar.
  • the bend radii were 3, 18mmfor the male punch member and 6,35mm for the female molding member.
  • the male punch member, used for the first strike had a width of 29,4mm and a die gap of 3,15 mm
  • Specimen 60 was not restruck (see Figure 6) and exhibited severe curling.
  • Specimen 61 was restruck with an oversized male punch member having a width of 26, 97 mmand resulted in a desirable hat section as shown in Figure 7.
  • the die gap during pressing was varied to 1,016 to 1,778 mm the optimum 0,254mm added to the thickness of the material.
  • the section between the bend radii should preferably be at least 12, 7 mm to achieve noticeable elimination of curling.
  • the residual die gap ( ⁇ d) that proved to reduce curling the most was in the range of 0, 20 mm to 0, 559 mm and optimally at 0, 3.0 mm, the metal thickness being about 1,448mm.

Landscapes

  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Bending Of Plates, Rods, And Pipes (AREA)
  • Shaping Metal By Deep-Drawing, Or The Like (AREA)
  • Shaping Of Tube Ends By Bending Or Straightening (AREA)
EP19810110488 1980-12-29 1981-12-16 Procédé pour réduire le retour élastique de tôles pressés Withdrawn EP0055421A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US22034680A 1980-12-29 1980-12-29
US220346 1980-12-29

Publications (1)

Publication Number Publication Date
EP0055421A2 true EP0055421A2 (fr) 1982-07-07

Family

ID=22823189

Family Applications (1)

Application Number Title Priority Date Filing Date
EP19810110488 Withdrawn EP0055421A2 (fr) 1980-12-29 1981-12-16 Procédé pour réduire le retour élastique de tôles pressés

Country Status (6)

Country Link
EP (1) EP0055421A2 (fr)
JP (1) JPS57134214A (fr)
AR (1) AR228469A1 (fr)
BR (1) BR8106791A (fr)
CA (1) CA1193145A (fr)
ES (1) ES8305606A1 (fr)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106270032A (zh) * 2016-11-17 2017-01-04 讯龙型材折弯（合肥）有限公司 一种u形折弯机构
CN113118307A (zh) * 2021-03-24 2021-07-16 深圳市亿和精密科技集团有限公司 一种一步式负角结构折弯成型模具

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4693475B2 (ja) * 2005-04-14 2011-06-01 アイダエンジニアリング株式会社 プレス成形方法およびそれに用いる金型
CN112605184A (zh) * 2020-11-27 2021-04-06 四川航天长征装备制造有限公司 一种航天用锥框成形方法

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106270032A (zh) * 2016-11-17 2017-01-04 讯龙型材折弯（合肥）有限公司 一种u形折弯机构
CN113118307A (zh) * 2021-03-24 2021-07-16 深圳市亿和精密科技集团有限公司 一种一步式负角结构折弯成型模具

Also Published As

Publication number Publication date
ES506132A0 (es) 1983-04-16
ES8305606A1 (es) 1983-04-16
AR228469A1 (es) 1983-03-15
JPS57134214A (en) 1982-08-19
BR8106791A (pt) 1982-09-08
CA1193145A (fr) 1985-09-10

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Inventor name: LIU, YOU CHAO