EP0055435A2 - Verfahren zum Vermindern des Rückspringens von mechanisch gepresstem plattenförmigem Material - Google Patents

Verfahren zum Vermindern des Rückspringens von mechanisch gepresstem plattenförmigem Material Download PDF

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Publication number
EP0055435A2
EP0055435A2 EP19810110579 EP81110579A EP0055435A2 EP 0055435 A2 EP0055435 A2 EP 0055435A2 EP 19810110579 EP19810110579 EP 19810110579 EP 81110579 A EP81110579 A EP 81110579A EP 0055435 A2 EP0055435 A2 EP 0055435A2
Authority
EP
European Patent Office
Prior art keywords
striking
bend
springback
male
female
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Withdrawn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
EP19810110579
Other languages
English (en)
French (fr)
Inventor
You Cao 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 EP0055435A2 publication Critical patent/EP0055435A2/de
Withdrawn legal-status Critical Current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
    • 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
    • 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

Definitions

  • Springback is a phenomenon always present in the bending of metal. Bending operations for sheet metal are typically carried out by the use of presses broadly classified by the source of power as hydraulic or mechanical. Certain alternatives are available when using hydraulic presses to control springback, within tolerable limits, because of the lower strain rate involved. However, more efficient and rapid production can be achieved with mechanical presses which use higher strain rates resulting from high speed ram movement.
  • Springback is the natural tendency of the material to revert to its original shape after the bending force has been removed. It has been generally believed heretofore that the springback is proportional to a certain group of parameters which include the bending radius, the thickness of the product material and the hardness of the material. It has been conventional for tool designers to correct such springback by (a) overcompensating through an overbend whereby the product will relax to a shape that is more precisely desired upon relief of the bending force, or (b) restriking the material in the same die at the same bend point to encourage the material to more closely conform to the desired die configuration.
  • the invention is a method of mechanically deforming sheet material to eliminate or substantially reduce the apparent springback of the material, irrespective of a variance of material properties, chemical composition, thickness of the material and speed of the deforming member.
  • the invention uses progressive pressing of sheet material at adjacent but spaced bend radii to achieve this result. Residual springback from the first striking action subtracts from the springback of the second striking action to significantly reduce the resultant springback in the product.
  • the method comprises (a) striking together male and female forming members through a first increment of travel to firstly bend the sheet material placed therebetween about at least a first locus to define a first deformed sheet material member having a positive springback angle, and (b) striking together male and female forming members through a second increment of travel to secondly bend said first deformed sheet material member about at least a second locus spaced from said first locus a distance to provide a reduced resultant springback angle.
  • One mode employs repeated striking movements to separately provide the first and second bending; each female member and male member is changed in cross-sectional size for the second striking movement to create the spacing needed between the first and second bend radii.
  • Such change may be an enlargement or reduction because the second bend radius can be located to either side of the first bend radius but within a controlled spacing, preferably of 0.5 to 6. 4 mm.
  • the gap can be in a wide range for the first striking action, preferably about 1.5 x 2.0 times the thickness of the material.
  • the gap for the second striking increment is optimally equal to the thickness of the material and operably in a range of 1.0-1.5 times the thickness of the material. It has been found desirable to limit the corner radius of said members to about the thickness of the material.
  • Another mode is to form the female die with tapered walls and to carry out the first and second bending as part of a continuous pressing motion.
  • bending of the sheet material at a first locus would occur during the initial increment of travel of the male member into the tapered female member and the second or subsequent bendings would occur as the male member moves through additional increments of travel down along the tapered walls of the female member, creating bending at different loci.
  • bending will occur about a plurality of loci as the male die is moved during a single striking action to mate with the female member.
  • Springback is always present in a bending operation performed on sheet materials that have an elongation of at least 1.5% and have a melting temperature at least twice the temperature at which pressing occurs. Springback cannot be theoretically eliminated since there is little one can do to alter the Young's modulus of a material.
  • the types of sheet metal materials that respond to the method of this invention include all sheet materials that accept a permanent bend as a result of its elongation and solid structure during pressing. This invention is particularly useful for sheet metals such as mild steels (cold rolled, low carbon, hereinafter CRLC), high strength, low alloy steels (hereinafter HSLA), and alloys of aluminum, magnesium and copper.
  • a mechanical press is the machine used for most cold working operations of sheet metal material.
  • Such 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 punch and molding members which together 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 the sheet metal lying on a female molding member. The male punch member moves the sheet metal out of its normally flat plane against the contour of the female molding member requiring deep penetration of the male punch member into an opening of the female molding member, forming such complex sections as a U-shape or hat section.
  • Presses can be'conveniently classified into two broad types, including hydraulic and mechanical presses.
  • Mechanical presses are desirable, particularly in the automotive industry, because of the improved speed of cycling and thereby greater production.
  • Mechanical presses that are associated with the method of this invention can have a variety of mechanical means for applying power to the ram such as through a crank, a cam, an eccentric, a power screw, a rack and pinion, a knuckle joint, a toggle, and even pneumatic means.
  • This invention has discovered that by deforming sheet metal with a press at two spaced bend loci (or bend radii), the resultant springback can be substantially reduced and optimally eliminated.
  • the prerequisite for this achievement is the existence of two bend corners which are spaced apart a small distance typically not easily observable, but in some cases observable.
  • the relative locations of the two corners is not a limitation.
  • This invention achieves such result by way of a mechanical press using typically a male punch member and a female molding member. After a first bending action is completed at a first bend locus, one or both of the members is changed in shape or size to bend the sheet metal at a closely spaced second bend locus.
  • the increments of travel to create both bending actions may be part of a common striking action or may be separated and repeated striking actions.
  • This invention is of particular significance to the pressing of sheet metal by mechanical means as opposed to hydraulic presses. Deformation in a mechanical press is carried out with considerable energy which exerts a strong influence on springback in the formation of complex shapes.
  • the term epsilon which is related to the Young's modulus of materials, controls the springback. As the press speed or strain rate is increased, the overall stress/strain curve is displaced toward higher stress levels. Thus, for a given bending geometry, elastic strain or springback increases with increasing press speed.
  • the present invention has particular significance with respect to high strength steel. Excessive springback is encountered in production parts made of high strength steels because of the compound effect of high strength and high mechanical press speed.
  • the first step of the method comprises pressing or striking together, through a first increment, complimentary shaped male punch member 11 and a female molding member 12 with a flat sheet metal panel 10 therebetween.
  • the female molding member has an opening 13 with a mouth 13a provided with rounded edge.
  • the opening may be variously shaped such as a slot or other regular geometric configuration.
  • the male punch member has a body with a substantially flat bottom face 14 provided with rounded edges 14a at opposite sides.
  • the transverse width 15 of face 14 is designed to be slightly smaller than the width 16 of opening 13, producing a residual die gap 17 after allowance is made for the thickness 18 of the sheet metal panel.
  • the speed of striking is preferably in excess of 5.08 m/min optimally 9. 15 m/min.
  • the striking action bends the sheet metal at least at a pair of bend loci identified as A.
  • the male punch member 11 is designed to form an overall U-shaped configuration in the sheet metal in cooperation with the female molding member 12.
  • the preferred range of bending at locus A is 45-95°.
  • the sidewalls 19 of the U are to be desirably parallel after deformation; however, springback from the first bending action causes the sidewalls to be canted outwardly an angle e.
  • the sheet metal form resulting from the first increment of striking action may have a crown or curvilinear section 20 formed at the base of the U, between the first bend loci A.
  • This curvilinear section is due to the 4-point bending moment applied to section 28.
  • the sidewalls 24 possess a nonparallel condition because of springback about locus A.
  • the curvilinear section may be avoided by maintaining a positive counter pressure through a counterpad operated inside the female molding member.
  • the second step ( Figure 4b) of the process is to strike the members 11 and 12 together through a second increment of travel with the first bent sheet metal therebetween (having bends at loci A).
  • This step is preferably carried out by restriking the members, using a different sized male punch member and using different sized female molding member responding to the change in size of the male member.
  • the sheet metal is secondly bent at a pair of bend loci B, each spaced a small distance from a bend locus A.
  • the transverse dimension of the male punch member is changed preferably by 0. 5 to 6. 35 mm when working with most sheet metals.
  • a smaller male punch member was employed.
  • the pairs of bend loci B were thus located inside the pair of bend loci A.
  • use of an enlarged male punch member will also be successful.
  • the springback angle 6 B is reduced by the residual springback e l resulting from the flattening of the original bend at A during the formation of the new bend at B.
  • the die gap (the separation between the side wall of the male punch member and the side wall of the female molding cavity, said walls being parallel to the direction of striking) has some effect in controlling the amount of resultant springback when the male or female member is increased in size for the second striking increment.
  • the bottom die gap during restrike becomes controlling with respect to minimizing resultant springback.
  • Bottom die gap is the distance between the bottom wall or face of the male punch member and the upper face or wall of the counterpad used as part of the female molding member, the walls being transverse to the direction of pressing.
  • pressing and striking is defined to mean the bending of sheet metal involving only very limited metal flow, usually restricted at the bend to one side of the sheet being subjected to tension, the other side, of course, being subjected to compression.
  • This phenomenon of bending is to be distinguished from drawing, where the entire cross-section of the sheet metal or member to be shaped is subjected to forces that exceed the elastic limit and thereby permit plastic flow of the metal throughout the entire cross-section.
  • the male punch member 11 was shaped to have a width between corner radii 14a of about 25.4mm, a length along its face of about 127 mm, and a height along the line of movement of about 76.2 mm .
  • the corner radii 14a of the male punch member was 3.18 mm .
  • the female molding member 12 had an opening 13 complimentary in shape to the male member allowing it to pass thereinto.
  • the edge radii 13a of the mouth entrance to opening 13 was about 6. 35 mm.
  • the members when struck together formed a U-shaped cross-section in the sheet metal member having 90° angles at its bend loci.
  • the die gap was set at varying widths by changing backup shims supporting the split halves of the female molding member.
  • a single action mechanical press was used to carry the members.
  • the press ram had an average calculated punch speed of 0.15 in/sec.
  • SAE 30 motor oil was coated on the sheet metal to function as a lubricant during pressing. Springback was measured; the overall experimental error due to variation of sheet metal properties was estimated to be about + 1/2 degree.
  • Sheet metal pressings were first made using only a single striking action in accordance with the prior art.
  • the die gap (defined to mean the distance between the sidewalls 20 of the male punch member and the sidewall of the opening in the female molding member, when mated) and the pressure applied to a counterpad 21 (see Figure 5) were varied in the hope of substantially reducing springback.
  • springback decreases with increasing counterpad pressure to a plateau.
  • the plateau varied according to sheet material and die gap.
  • the plateau started at about 2. 5 bar at the 0. 89 mm die gap and about 4. 2 bar at the 1. 27 mm die gap.
  • For the HSLA material it was about 3.5 bar at the 0. 89 mm die gap and about 1.
  • springback could not be eliminated by a variation in counterpad pressure. Also, as shown in Figure 8, springback could not be eliminated by a variation in die gap for HSLA steels and substantially so for AKDQ steels.
  • Sheet metal pressings were then made using the method of Figure 4 whereby a smaller male punch member was used during a restrike action.
  • a first pressing was carried out using a male punch with a transverse dimension of 29.5 mm at a die die gap of 1. 25 mm.
  • the measured wall inclination was 9° for HSLA and 3° 55' for AKDQ steel channels.
  • the channels were restruck with a narrower punch having a transverse dimension of 25.4 mm at varying die gaps, see Figure 9.
  • Springback decreased initially with increasing restrike die gap and reached a minimum at a die gap of about 1. 9 mm in AKDQ steel, but was less in HSLA 110 steel channels (about 1. 4 mm).
  • the second bending or restrike action was carried out using an oversized male punch member.
  • the starting channels were preformed with a male punch having a transverse dimension of 25.4 mm at a die gap of 1.25 mm.
  • the width of punch used for restrike was 29.5 mm.
  • Figure 10 shows the observed springback as a function of restrike bottom die gap.
  • Figure 6 Still another mode for carrying out the method is shown in Figure 6, which comprises the use of a tapered female molding member. Only a single striking action is necessary for this mode, but the concept of a double bend or plural bend technique is still employed.
  • the arrangement of progressively performing a series of bends with one striking operation is graphically represented in tandem in Figure 6. If a line is drawn tangent to the corners of the female molding dies 31 and 32, the resulting configuration is a single female molding member with a tapered wall 33 having an inclination angle as indicated. Resultant springback is reduced by such tapered die.
  • the effect of die gap on springback in female molding members having a wall inclination of 3° and 5° is shown in Figures 13 and 14.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • Bending Of Plates, Rods, And Pipes (AREA)
EP19810110579 1980-12-29 1981-12-18 Verfahren zum Vermindern des Rückspringens von mechanisch gepresstem plattenförmigem Material Withdrawn EP0055435A2 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US22047980A 1980-12-29 1980-12-29
US220479 1988-07-18

Publications (1)

Publication Number Publication Date
EP0055435A2 true EP0055435A2 (de) 1982-07-07

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Family Applications (1)

Application Number Title Priority Date Filing Date
EP19810110579 Withdrawn EP0055435A2 (de) 1980-12-29 1981-12-18 Verfahren zum Vermindern des Rückspringens von mechanisch gepresstem plattenförmigem Material

Country Status (5)

Country Link
EP (1) EP0055435A2 (de)
JP (1) JPS57112926A (de)
AR (1) AR226399A1 (de)
BR (1) BR8108306A (de)
ES (1) ES8304454A1 (de)

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2282090A (en) * 1993-08-27 1995-03-29 Lvd Co Adaptive folding
US6748788B2 (en) * 2001-09-26 2004-06-15 Kobe Steel, Ltd. Method for bending metal plate
CN102989854A (zh) * 2012-11-27 2013-03-27 奇瑞汽车股份有限公司 汽车l型冲压件翻边角度不到位和翻边面不平的整改方法
EP3165297A1 (de) * 2015-11-03 2017-05-10 SSAB Technology AB Biegeverfahren
CN112845748A (zh) * 2021-01-05 2021-05-28 浙江申吉钛业股份有限公司 基于控制弯曲的钛合金板材精密弯曲零件制备方法
CN116984461A (zh) * 2023-09-25 2023-11-03 黑龙江勃锦悍马农业装备制造有限公司 一种用于免耕播种机壳体的冲压装置及方法

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP4015398B2 (ja) * 2001-09-26 2007-11-28 株式会社神戸製鋼所 金属板の曲げ成形方法
JP5855969B2 (ja) * 2012-02-15 2016-02-09 株式会社神戸製鋼所 金属板の曲げ加工方法
CN114769372A (zh) * 2022-04-20 2022-07-22 希罗镜下医疗科技发展(上海)有限公司 一种基底制作定形方法及基底

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2282090A (en) * 1993-08-27 1995-03-29 Lvd Co Adaptive folding
GB2282090B (en) * 1993-08-27 1997-08-06 Lvd Co Adaptive folding
US5829288A (en) * 1993-08-27 1998-11-03 L.V.D. Company N.V. Adaptive folding
US6748788B2 (en) * 2001-09-26 2004-06-15 Kobe Steel, Ltd. Method for bending metal plate
CN102989854A (zh) * 2012-11-27 2013-03-27 奇瑞汽车股份有限公司 汽车l型冲压件翻边角度不到位和翻边面不平的整改方法
CN102989854B (zh) * 2012-11-27 2014-10-01 奇瑞汽车股份有限公司 汽车l型冲压件翻边角度不到位和翻边面不平的整改方法
EP3165297A1 (de) * 2015-11-03 2017-05-10 SSAB Technology AB Biegeverfahren
WO2017076946A1 (en) 2015-11-03 2017-05-11 Ssab Technology Ab Bending method
CN108472705A (zh) * 2015-11-03 2018-08-31 瑞典钢铁技术有限公司 弯曲方法
CN108472705B (zh) * 2015-11-03 2020-03-06 瑞典钢铁技术有限公司 弯曲方法
US11633770B2 (en) 2015-11-03 2023-04-25 Ssab Technology Ab Bending method
CN112845748A (zh) * 2021-01-05 2021-05-28 浙江申吉钛业股份有限公司 基于控制弯曲的钛合金板材精密弯曲零件制备方法
CN116984461A (zh) * 2023-09-25 2023-11-03 黑龙江勃锦悍马农业装备制造有限公司 一种用于免耕播种机壳体的冲压装置及方法
CN116984461B (zh) * 2023-09-25 2023-12-19 黑龙江勃锦悍马农业装备制造有限公司 一种用于免耕播种机壳体的冲压装置及方法

Also Published As

Publication number Publication date
JPS57112926A (en) 1982-07-14
BR8108306A (pt) 1982-10-05
ES506129A0 (es) 1983-03-01
AR226399A1 (es) 1982-06-30
ES8304454A1 (es) 1983-03-01

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