RU2242317C1 - Method for braking flange of sheet blank at drawing process - Google Patents

Abstract

FIELD: cold sheet forming.

SUBSTANCE: method for braking flange of sheet blank at drawing process comprises steps of folding flange at moving it through tightening ribs and lips; braking flange of blank due to its alternating sign-variable bending at moving through tightening lip and at least through one next row of tightening ribs; after bending each member of flange in the same direction, straightening and bending said members in opposite direction.

EFFECT: enhanced quality and accuracy of drawn parts, reduced consumption of rolled sheet.

2 cl, 3 dwg

Description

The invention relates to sheet stamping and can be used for drawing products from sheet materials, both metals and non-metals, mainly for drawing body parts of vehicles and other equipment on simple, double and triple presses, as well as on multi-position machines, for example, for extracting door panels, hood, trunk lid and other car body parts.

A known method of braking the flange of a sheet stock during drawing by bending it when moving through two rows of semicircular constriction ribs, selected as a prototype (“Forging and stamping”, Handbook in 4 volumes, T. No. 4 “Sheet stamping”, Moscow, ed. Engineering, 1985-1987, p. 426, Fig. 128).

The disadvantage of this method is the overestimated rate of consumption of sheet metal for one workpiece, due to the following reasons. The first hauling rib is located at a considerable distance from the edge of the matrix, based on the condition of strength of the matrix in this place. And since at the final moment of drawing, the edge of the workpiece cannot extend beyond the first edge of the matrix from the edge of the matrix, otherwise the workpiece will lose stability with the formation of folds, which is considered defective, after drawing, the technological allowance remains oversized. If, however, there are no tension ribs beyond the threshold, as shown in the method described in the following source of information (Romanovsky V.P., Handbook on Cold Stamping, St. Petersburg: Mechanical Engineering, 1979, p. 158, Fig. 158. ), then during the drawing process there will be no alternating alternating bending of the elements of the workpiece flange when moving through one hauling threshold. Due to the absence of such alternating alternating bending of the workpiece flange, after drawing (after reducing the drawing force to zero) in the workpiece, reversible elastic deformations, which, according to the law of elastoplastic deformations, always accompany irreversible plastic deformations, decrease unevenly, as a result of which residual stresses occur in the workpiece significant magnitude and the opposite, in comparison with the stresses in the drawing process, sign. Therefore, after removing the effect of force on the workpiece after drawing, under the influence of residual stresses, the surface of this workpiece is distorted - deviates from the given surface of the exhaust stamp, the accuracy of the drawn workpiece is reduced.

The objectives of the invention are to increase the accuracy and quality of the parts to be drawn, as well as to save sheet metal.

The tasks are solved due to the fact that several rows of waist ribs are installed behind the threshold and the workpiece flange is additionally braked by alternating alternating bending when moving through these several rows of waist ribs, and after each element of the flange is bent in one direction, it is carried out by means of a waist ribs straightening and bending in the opposite direction. In practice, the number of tie ribs is from one to three, which is sufficient for drawing parts on presses of simple, double or triple action, as well as on multi-position machines.

The invention is characterized by figures 1-3. In Fig.1 shows a section of the exhaust stamp in the area of the braking elements on the double-acting press at the time of loading the workpiece, Fig.2 - at the time of pressing the sheet stock, Fig.3 - at the time of completion of the drawing process, where 1 is the punch, 2 - matrix, 3 — the constriction threshold at the edge of the matrix aperture, 4 — constriction ribs on the matrix, 5 — clamp, 6 — constriction ribs of the matrix, 7 — blank.

The method is implemented as follows. When the external press slider moves down, the pressure plate - pressure 5 forms the flange of the workpiece 7 along the pressure surface of the matrix 2, bends the flange around the waist threshold 3 and the waist ribs 4 and 6, stops and remains in this position during the entire drawing process. Then, during the course of the internal press slider, the punch 1 draws the workpiece into the opening of the matrix 2 and the workpiece 7 receives the shape specified by the stamp.

In the process of drawing, the flange of the workpiece 7 is inhibited by its alternating alternating bending when moving through the constriction threshold 3 and several rows of constriction ribs 4 and 6.

In Fig. 3, it is conditionally accepted that if (when considering the flange from the punch 1) the center of the circular arc of the workpiece element after bending is located on the right side, then the bending of the workpiece element is considered in the positive direction and the radius is assigned a “+” sign, that is, R ⁺ . If the center of the arc of the circle of the workpiece element after bending is located on the left side, then the bending of the workpiece element is considered in the negative (reverse) direction and the “-” sign is assigned to the radius, that is, the center of the arc of the circle of the workpiece element after bending is located on the right side, then the bending of the element blanks are considered in the positive direction and the bend radius is assigned the sign “+”, that is, R ^- .

Theoretical and experimental studies by the authors showed that the magnitude of the residual stresses and, accordingly, the springing of the elongated part after unloading are minimal if the workpiece flange is braked by alternating alternating bending (when bending along the radius R ⁺ is replaced by straightening and subsequent bending along the radius R ^- ) when moving the workpiece through the constriction threshold and one or more rows of constriction ribs installed beyond the constriction threshold. In practice, the effect of improving the accuracy of the workpiece due to alternating alternating bending is used when editing sheets in multi-roll (roller) machines; after such editing, non-planar deformed sheets become flat.

By reducing the magnitude of the residual stresses in the workpiece flange and, accordingly, reducing the springing of the workpiece flange after drawing, the accuracy of the elongated part is increased. And due to the use of a tensile threshold in combination with constriction ribs, in comparison with the use of several rows of the same constriction ribs, the dimensions of the workpiece and the rate of consumption of material per part are reduced.

Similarly, this method is implemented when the parts are drawn on a single-action press or on a multi-operation automatic press. In this case, the hood circuit shown in Fig. 1 is turned over: the punch 1 is fixed on the motionless lower die plate fixed to the press table, the die 2 is mounted on the slider, and the pressure plate - clip 5 rests on the press cushion located in the table through the pushers press.

Claims (2)

1. The method of braking the flange of a sheet stock during the drawing process by bending it when moving through the tensile ribs and thresholds, characterized in that the blank of the blank is braked by its alternating alternating bending when moving through the constriction threshold and not less than one next row of tensile ribs, moreover, after bending each element of the flange in one direction, straightening and bending in the opposite direction are carried out. 2. The method of braking the flange of a sheet stock during the drawing process according to claim 1, characterized in that the maximum number of hauling ribs following the hauling threshold is three rows.

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