DE102015220231B4 - Device for deep-drawing a sheet metal blank with forming tools - Google Patents

Abstract

Device for deep-drawing a sheet metal blank with forming tools with a drawing punch (4), a drawing ring or a die (3) and a hold-down device (1), with the drawing ring or die (3) and hold-down device (1) in the sheet metal blank to be formed (2nd ) facing the flange area have a plurality of projecting shaped elements (6, 7) spaced apart from one another, the shaped elements (6, 7) acting approximately in a punctiform manner being offset from one another on or in the drawing ring or die (3) and on or in the hold-down device (1) and/or are arranged in alignment with each other.

Description

The invention relates to a device for deep-drawing sheet metal blanks (blanks, foils, plates, panels, blanks).

According to DIN 8584, deep drawing is the tensile compression forming of a sheet metal blank into a hollow body that is open on one side or a preformed hollow body into one with a smaller cross-section without intentionally changing the sheet metal thickness.

Deep drawing is one of the economically most important sheet metal forming processes in both small series and mass production. When deep-drawing with forming tools, the necessary forming force is applied to the bottom of the deep-drawn part to be manufactured with the aid of a stamp. The sheet metal blank is pulled through the forming die or die with the punch. The hold-down device, which acts on the sheet metal blank under a defined pressure, is intended to prevent wrinkles from forming on the deep-drawn part.

Lubricants such as Aqua-Form or Raziol are regularly used due to the strong friction between the sheet metal blank, the hold-down device and the drawing die. To do this, the sheet metal blanks to be processed must first be wetted with the lubricant and then cleaned in a laborious process once the forming process is complete.

From the prior art, hold-down devices are also known which have a drawing bead or braking bead in order to improve the effect of the hold-down device. Corresponding analogous representations are, for example US 2009/0 049 886 A1 or can be found in the textbooks by Jahnke or Lange.

During the forming of rotationally symmetrical workpieces, the drawing bead is a circular, projecting, continuous strip in the hold-down device, which has a constant distance to the drawing edge, which protrudes from the flat surface of the hold-down device, with a shaped ideal recess in the drawing die as a counterpart in the form of a drawing bead circumferential, continuous annular groove is arranged.

When forming rectangular cross-sectional shapes, the drawing bead is formed from projecting, straight strips in the hold-down device, the length of which essentially corresponds to the size of the component, with recesses in the drawing die that are ideal in shape being arranged as a counterpart in the form of continuous grooves.

During the deep-drawing process of rotationally symmetrical workpieces, the annular drawing bead presses on the underlying area of the sheet metal blank and forces the material to flow into the trough-shaped counterpart in the drawing die before the material is drawn into the final shape via the drawing ring. A corresponding device is for example DE 24 50 624 A1 disclosed.

1 shows a deep-drawing tool with a brake ring according to the prior art.

The left-hand part of the figure shows the hold-down device 1 with a circumferential, continuous annular groove 5a in a sectional view.

The drawing ring 3 arranged underneath has a circular, continuous strip 5b (drawing bead) at the same position. The stamp 4 is in the starting position before the forming process and touches the surface of the sheet metal blank 2.

The right part of the figure from 1 shows the start of the forming process in a sectional representation. The hold-down device 1 presses on the sheet metal blank 2. At the same time, the punch 4 moves downwards and pulls the sheet metal blank 2 over the drawing ring 3. Due to the contact pressure of the punch 4, the material of the sheet metal blank 2 flows between the annular, continuous bar 5b in the drawing ring 3 and the circumferential, continuous annular groove 5b in the drawing ring 3 arranged vertically aligned above it. For clarification is at the right edge of the picture 1 a section of the area between hold-down device 1, sheet metal blank 2 and drawing ring 3 with the annular, continuous strip 5b in the drawing ring 3 and the circumferential, continuous annular groove 5a in the hold-down device 1 arranged vertically above it is shown enlarged.

The material flow is controlled area by area by using the pulling or braking bead. The disadvantages of this are the comparatively high forming forces, the need to use lubricants and the higher risk of component failure due to bottom tears.

the DE 195 04 264 A1 reveals the grooved design of the contact surfaces of the clamping frame. The forming tool has a contact surface that has at least two continuous beads and a corresponding number of continuous grooves in the opposite contact surface. That works DE 195 04 264 A1 not about the disclosure of the DE 24 50 624 A1 out.

In the U.S. 6,196,043 B1 "Double Vee lockbead for sheet metal forming" is the use of V-shaped draw beads (lockbeads) to control the Material flow revealed in sheet metal forming. These "lockbeads" form one or more continuous draw beads parallel to the board blank.

subject of DE 28 28 431 A1 is a deep-drawing device in which the sheet metal part to be processed is clamped between a first and a second holder (blanket and matrix). The first holder has a recess on its holding surface and the second has a pin that can be operated hydraulically or pneumatically. A variable pressure can be applied to the pin while the holder is being closed or during the deep-drawing process. The pin is opposite the recess. The recess is preferably designed as a groove. the DE 28 28431 A1 sees it as essential to the invention that each pin is opposite a recess.

The object of the invention is to propose a device that makes it possible to significantly increase the range of parts to be manufactured in order to open up new areas of application or to shift existing process limits.

In addition, the device according to the invention should largely dispense with the use of lubricants in order to reduce the costs for the auxiliary materials, the pre- and post-treatment of the sheet metal blanks or the formed deep-drawn parts and thus the environmental impact.

According to the invention, the object is achieved by a device according to patent claim 1. Preferred configurations and developments of the device are the subject matter of dependent claims 2 to 11.

In the device according to the invention, the necessary forming force is applied to the sheet metal blank via a drawing die. The flow movement of the workpiece to be formed is controlled by a hold-down device in connection with a drawing ring.

In the area of the component flange, the hold-down device and drawing ring/die have several projecting, spaced-apart shaped elements. The shaped elements of the hold-down device and the drawing ring/the die are arranged in alignment with one another or offset.

The contact surface between the tool and the workpiece in the flange area of the deep-drawing tool is significantly reduced in comparison to known drawing and braking beads due to the protruding, spaced-apart and quasi-punctiform shaped elements.

With a staggered arrangement of the forming elements of the hold-down device and the drawing ring or the die, the metal sheet to be formed undergoes alternating bending in the radial and tangential direction, which stabilizes it against wrinkling as a result of the targeted increase in and thus prevents wrinkling.

In an alternative arrangement of the shaped elements of the hold-down device and the drawing ring or the die, aligned in the direction of the punch movement, the metal sheet to be formed is guided at the same contact points on both sides. This minimizes the friction between the tool and the workpiece.

In a further, equally preferred embodiment, individual shaped elements of the hold-down device and the drawing ring or the die are aligned with one another in the punch feed direction and other shaped elements of the hold-down device and the drawing ring or die are arranged offset with respect to one another in the punch feed direction. On the one hand, this minimizes the friction between the tool and the workpiece compared to the known solutions of the prior art. At the same time, the partially offset arrangement of form elements of the hold-down device and the drawing ring or the die, which is partially offset in the direction of the punch feed, prevents the undesired formation of creases.

The use of the shaped elements according to the invention not only allows the energy-efficient production of sheet metal components without the use of lubricants, but in particular the forming of irregularly shaped components with increased process reliability, i. H. with enlarged process window. Here, the material flow can be specifically controlled by the fixed or preferably rotatably mounted, particularly preferably flexibly positionable form elements.

The form elements are firmly or detachably connected to the hold-down device and the drawing ring/die. The hold-down device and the drawing ring with the projecting shaped elements are manufactured using known machining processes, such as e.g. B. by milling.

The shaped elements are preferably designed as hemispherical or dome-shaped projections. Depending on the size and geometry of the workpiece to be manufactured, the form elements are fixed at a defined distance from one another. In a preferred embodiment, the shaped elements are at an identical distance from one another, although this is not absolutely necessary.

2 shows a deep-drawing tool according to the invention before the forming process in which the The surface of the hold-down device 1 and the drawing ring/die 3 in the area of the component flange has a plurality of equally spaced, spaced, fixed, cantilevered shaped elements 6 which touch the surface of the sheet metal blank 2 .

For clarification is at the right edge of the picture 2 a section of the area between hold-down device 1, sheet metal blank 2 and drawing ring 3 with a plurality of cantilevered, spaced-apart shaped elements 6 in hold-down device 1 and in drawing ring 3 is shown enlarged.

The cantilevered, fixed form elements 6 are arranged on several concentric circular paths and have the same distance from one another.

In a particularly preferred embodiment, the flow of material is controlled by a plurality of movably mounted mold elements 7 . As a result, the frictional forces occurring between the preferably rotatably mounted, projecting shaped elements 7 on the hold-down device 1 and on the drawing ring/die 3 and the surface of the sheet metal blank 2 can be significantly reduced.

In a further, likewise preferred embodiment, the shaped elements 6, 7 are at different distances from one another. In a further, likewise preferred embodiment, the shaped elements 6, 7 have a different distance from one another, specifically for the processing of complex-shaped, asymmetrical workpieces, which corresponds to the stress profile to be expected during deep-drawing. The arrangement of the shaped elements 6, 7 and the distances to one another are determined using known analytical and semi-analytical design methods.

In a further, likewise preferred embodiment, the shaped elements 6, 7 are arranged uniformly on at least two different tracks 9. In the context of this invention, a path 9 is understood to mean a line on which the spaced-apart form elements 6, 7 of the hold-down device 1 and the drawing ring 3 are located. The form elements 6, 7 of the hold-down device 1 and the drawing ring or the die 3 are arranged in alignment with one another or offset with respect to one another in the punch feed direction (Z-direction).

In a further, likewise preferred variant, the shaped elements 6, 7 are arranged irregularly on at least two different webs 9.

3 shows the left part of the figure in a sectional representation of the hold-down device 1 with a plurality of equally spaced, cantilevered and rotatably mounted shaped elements 7 which touch the surface of the sheet metal blank 2 in a quasi-punctiform manner.

The drawing ring 3 arranged underneath has staggered, equally spaced, cantilevered and movably mounted, preferably rotatably mounted shaped elements 7 which touch the surface of the sheet metal blank 2 . The movably mounted form elements 7 are preferably designed as spheres which partially protrude from the surface of the hold-down device 1 and the drawing ring 3 .

The stamp 4 is in the starting position before the forming process and touches the surface of the sheet metal blank 2.

The right part of the figure from 3 shows the start of the forming process in a sectional representation. The hold-down device 1 presses the sheet metal blank 2 with a pressure of 2 MPa -10 MPa. At the same time, the punch 4 moves downwards and pulls the sheet metal blank 2 over the drawing ring 3. The material of the sheet metal blank 2 flows through the contact pressure of the punch 4 between the equally spaced, cantilevered and rotatably mounted shaped elements 7 of the hold-down device 1 and the cantilevered and rotatably mounted shaped elements 7 of the drawing ring 3 which are arranged offset thereto in the xy plane.

For clarification is at the right edge of the picture 3 a section of the area between hold-down device 1, sheet metal blank 2 and drawing ring 3 with the cantilevered and rotatably mounted form elements 7 of hold-down device 1 and drawing ring 3, which are offset from one another in the xy plane, is shown enlarged.

The enlarged view shows the material flow of the sheet metal blank 2 controlled by the projecting, movably mounted form elements in the hold-down device 1 and in the drawing ring 3.

The projecting, movably mounted, preferably rotatably mounted form elements 7 on the hold-down device 1 and on the drawing ring/the die 3 are offset from one another in the x-y plane. This results in an alternating bending load on the material during the forming process, which causes strain hardening of the flange area and possibly the frame area.

By using the protruding form elements 7 on the hold-down device 1 and on the drawing ring/the die 3, it is also possible to produce components with complex shapes by deep-drawing without lubricant. An otherwise expected tearing of the sheet metal blank due to the limited formability of the material is as cantilevered form elements 7 preferably used, effectively prevented rotatably mounted balls.

In a further, likewise preferred embodiment, fixed and movably mounted, preferably rotatably mounted, mold elements 6, 7 are arranged on the blank holder 1 and on the drawing ring/die 3 for the forming of large and complex-shaped workpieces. As a result, preferably asymmetrical parts can be produced.

In addition to the use of cantilevered shaped elements 6, 7, which are designed as hemispheres or rotatably mounted spheres, the use of cantilevered ellipsoids of revolution or cylinders, which allow material to flow along a limited path, is also preferred. Due to the projecting shaped elements 6, 7, the contact surface between the tool and the workpiece is significantly reduced in the flange area of the deep-drawing tool compared to the known brake beads.

Due to the preferably used, movably mounted form elements 7, a further reduction in the frictional forces and the necessary drawing force resulting therefrom is achieved in comparison to the fixed form elements 6. Between the workpiece and the tool there is only rolling friction in the flange area, which is significantly lower than the sliding friction when using fixed form elements.

The preferably used, movably mounted, particularly preferably rotatably mounted form elements 7 can be used in numerous different designs with regard to their design, size and permissible load capacity. Spheres, cylinders, rollers, roller rings, cones, truncated cones or barrels are particularly preferred as shaped elements 7 .

During the drawing process with the deep-drawing tool according to the invention, the metal sheet to be formed undergoes alternating bending in the radial and tangential direction, which stabilizes it against wrinkling as a result of the targeted increase in and thus prevents process instability such as wrinkling. The force to overcome the alternating bending in the flange area is used as a restraining force to control the flow of material.

4 shows a sectional representation of the hold-down device 1 with a plurality of equally spaced, cantilevered and fixed shaped elements 6 which touch the surface of the sheet metal blank 2.

For this purpose, the drawing ring 3 arranged underneath has equally spaced, cantilevered and stationary shaped elements 6 which are aligned in the x-y plane and touch the surface of the sheet metal blank 2 . This preferred configuration leads to a minimization of the contact area between the tool and the workpiece and thereby to a minimization of the frictional forces.

5 shows further preferred embodiments of the invention.

The left-hand part of figure a) shows the hold-down device 1 with a plurality of equally spaced, cantilevered and fixed or rotatably mounted shaped elements 6, 7, which touch the surface of the sheet metal blank 2, in a highly schematic, sectional view. For this purpose, the drawing ring 3 arranged underneath has projecting, fixed or rotatably mounted shaped elements 6, 7 which are arranged in alignment and are equally spaced, which touch the surface of the sheet metal blank 2. This preferred configuration leads to a minimization of the contact area between the tool and the workpiece and thereby to a minimization of the frictional forces.

5 shows in the middle image b) in a highly schematic, sectional representation of the hold-down device 1 with several, equally spaced, cantilevered and fixed or rotatably mounted form elements 6, 7, which touch the surface of the sheet metal blank 2. The drawing ring 3 arranged underneath has offset, cantilevered, stationary or rotatably mounted shaped elements 6, 7 which touch the surface of the sheet metal blank 2. This preferred embodiment enables the resulting alternating bending to control the flow of material in a targeted manner and prevents the formation of folds.

5 shows in the right ) in a highly schematic, sectional view, the hold-down device 1 with several, differently spaced, cantilevered and fixed or rotatably mounted form elements 6, 7, which touch the surface of the sheet metal blank 2.

For this purpose, the drawing ring 3 arranged underneath has in the left area aligned, cantilevered, stationary or rotatably mounted shaped elements 6 , 7 which touch the surface of the sheet metal blank 2 . In the right-hand area, the drawing ring 3 has offset, cantilevered, stationary or rotatably mounted shaped elements 6, 7 that touch the surface of the sheet metal blank 2.

This likewise preferred, combined arrangement of mutually aligned and staggered shaped elements 6, 7 on or in the hold-down device 1 and on or in the drawing ring (die) 3 is made possible by the changes resulting therefrom bends a targeted control of the material flow and prevents possible fold formation. At the same time, the frictional forces that occur are reduced compared to the known solutions of the prior art.

In order to be able to set the material flow and the friction in a targeted manner in the case of the macrostructured tools according to the invention, the tool geometry must be adapted to the component geometry. The geometry of the tools can be determined by the immersion depth (e), the span (A) of the adjacent shaped elements, the design and fixation of the shaped elements (fixed or movably mounted shaped elements 6, 7) and the geometric arrangement on or in the hold-down device 1 and the drawing ring 3 are defined. 6 shows the relevant tool parameters in a schematic sectional view.

The immersion depth e defines how far the individual form elements can penetrate in the normal direction of the sheet metal. The span λ defines the distance between two adjacent form elements from each other in the originally flat plane of the sheet metal.

However, a greater immersion depth e also increases the restraining force in the flange and thus the required pulling force, which can lead to component failure in the form of a crack in the bottom. Accordingly, the immersion depth e and span λ can be varied locally in relation to the component geometry in order to set a homogeneous material flow in the flange area and prevent component failure due to bottom tears.

In contrast to the conventional deep-drawing process, in which the blank holder is usually power-controlled, when deep-drawing with the macrostructured tools according to the invention, the distance between the blank holder and the die is path-controlled to set the immersion depth (as a setting parameter). This can be done with the help of a spacer ring (also known as a pulling aid).

7 shows a schematic sectional view of the spacer ring 8 as a mechanical path limiter when pressing the hold-down device 1. The spacer ring 8 causes the distance a between the fixed shaped elements 6 of the pressed-on hold-down device 1 and the fixed shaped elements 6 of the drawing ring 3 to be equal to or greater than the sheet thickness s of the sheet metal blank 2 is.

8th shows a section of the work area between hold-down device and drawing die in a schematic, sectional plan view.

The figure on the left shows four spherical shaped elements 7n of the holding-down device which are equally spaced apart and are rotatably mounted. A rotatably mounted spherical shaped element 7z is arranged in the drawing die symmetrically and offset to the shaped elements 7n. Such an arrangement is preferably used to produce rotationally symmetrical workpieces.

The figure on the right shows four spherical shaped elements 7n of the hold-down device which are equally spaced apart from each other and are rotatably mounted. A rotatably mounted spherical shaped element 7z is arranged in the drawing die asymmetrically and offset to the shaped elements 7n. Such an arrangement is preferably used for the production of workpieces without an axis of symmetry.

9 shows a top view of the drawing die 3 of a deep-drawing tool according to the invention for the production of a cup for pan-shaped parts (oil pan for cars, wash basins and sinks).

The form elements 6, 7 spaced apart from one another are arranged on three webs 9 which are equally spaced apart from one another. The stationary, cylindrical shaped elements 6 protrude from the drawing die 3 . The rotatably mounted, spherical shaped elements 7 in the corner area of the cup reduce the forming stresses and forces that occur in this highly stressed zone and prevent the sheet metal blank from tearing.

The arrows marked with "W" show the course of the material flow.

The use of the deep-drawing tool according to the invention in the deep-drawing of a rotationally symmetrical cup with spherical structuring of the drawing ring 3 and the hold-down device 1 is described in more detail on the basis of an exemplary embodiment. The basic structure of the deep-drawing tool is in 3 shown:

In the tool parts holding-down device 1 and drawing ring 3 rotatably mounted, cantilevered and mutually spaced spherical shaped elements 7 are arranged in the flange area. These form elements 7 are each located on three concentric circles which run around the axis of rotation of the tool. The circles of hold-down device 1 and drawing ring 3 are arranged offset. The shaped elements 7 of the hold-down device 1 and the drawing ring 3 are also arranged tangentially in such a way that they each engage in a gap in the counterpart.

• Zuerst wird ein rundes Blech (Ronde, Durchmesser: 180 mm, Dicke: 1,0 mm, Werkstoff: DC04) eingelegt und mittig auf dem Ziehring 3 (Innendurchmesser: 103 mm, Einlaufradius: 10 mm) zentriert. Dann schließt sich der Niederhalter 1 und die auskragenden, drehbar gelagerten kugelförmigen Formelemente 7 drücken einen definierten Weg ins Blech hinein (Eintauchtiefe: 1,0 mm). Dabei wird das Blech radial und tangential durch die versetzt angeordneten Formelemente 7 wellenförmig gebogen.
• Danach bewegt sich der Stempel 4 (Durchmesser: 100 mm, Kantenradius: 10 mm, Geschwindigkeit: 10 mm/s) in Richtung Ziehring 3 und der eigentliche Tiefziehprozess beginnt.

The forming process is as follows:

• First, a round sheet (blank, diameter: 180 mm, thickness: 1.0 mm, material: DC04) is inserted and centered on the drawing ring 3 (internal diameter: 103 mm, inlet radius: 10 mm). The hold-down device 1 then closes and the protruding, rotatably mounted spherical shaped elements 7 press a defined path into the metal sheet (immersion depth: 1.0 mm). The metal sheet is bent radially and tangentially in a wavy manner by the staggered shaped elements 7 .
• Then the punch 4 (diameter: 100 mm, edge radius: 10 mm, speed: 10 mm/s) moves in the direction of the drawing ring 3 and the actual deep-drawing process begins.

The base of the drawn part forms first. No material flows out of the flange area. If the radial stress then reaches a value that satisfies the yield condition, the material begins to flow out of the flange. The material in the flange experiences radial tensile stress and is compressed tangentially. In order to prevent creases from forming as a result of the tangential compressive stress, the metal sheet is stabilized by the bending that occurs as it passes through the spherical shaped elements 7 . This bending is comparable to that of corrugated sheet metal, which, due to its corrugated geometry, is more resistant to buckling than flat sheet metal. When flowing, the sheet metal bends back and forth several times. It experiences alternating bending over the path in the flange. After the stamp 4 has reached the drawing path, it moves back, the hold-down device 1 is opened and the part can be removed.

Reference List

1

hold-down

2

Ronde/sheet blank

3

drawing ring/die

4

Rubber stamp

5

pulling bead/brake bead

5a

Circumferential, continuous ring groove (drawn bead) in the hold-down device

5b

Circular, continuous bar in the drawing ring

6

Form element, fixed

7

Shaped element, movably mounted

7n

Shaped element of the hold-down device, movably mounted

7z

Shaped element of the drawing ring / drawing die, movably mounted

8th

spacer ring (travel limitation)

9

Rail

a

Distance between the shaped elements 6, 7 of the pressed-on hold-down device 1 and the shaped elements 6, 7 of the drawing ring 3

e

immersion depth

s

Sheet thickness of the sheet metal blank 2

W

material flow

λ

span

Non-patent literature cited

• Jahnke, Retzke, Weber: Forming and cutting, VEB Verlag der Technik, Berlin 1981, p. 245
• Lange, K.: Umformtechnik, Springer Verlag Berlin Heidelberg New York London Paris Tokyo Hong Kong 1990, pp. 402-403

Claims (11)

Device for deep-drawing a sheet metal blank with forming tools with a drawing punch (4), a drawing ring or a die (3) and a hold-down device (1), with the drawing ring or die (3) and hold-down device (1) in the sheet metal blank to be formed (2nd ) facing the flange area have a plurality of projecting shaped elements (6, 7) spaced apart from one another, the shaped elements (6, 7) acting approximately in a punctiform manner being offset from one another on or in the drawing ring or die (3) and on or in the hold-down device (1) and/or are arranged in alignment with each other. Device according to Claim 1, characterized in that the shaped elements (6, 7) are connected in a fixed or detachable manner to the hold-down device (1) and the drawing ring or die (3). Device according to one of Claims 1 or 2 , characterized in that the shaped elements (7) are movably mounted, preferably rotatably mounted. device after claim 3 , characterized in that the shaped elements (7) have the contour of a sphere, a cylinder, a roller, a roller ring, a cone, a truncated cone and/or a barrel. Device according to one of Claims 1 or 2 , characterized in that the projecting areas of the shaped elements (6, 7) are spherical, hemispherical or dome-shaped. Device according to one of Claims 1 until 5 , characterized in that the formula elements (6, 7) have the same distance from one another. Device according to one of Claims 1 until 5 , characterized in that the shaped elements (6, 7) have a different distance from one another. Device according to one of Claims 1 until 7 , characterized in that the shaped elements (6, 7) are arranged uniformly on at least two mutually spaced webs (9). device after claim 7 , characterized in that the shaped elements (6, 7) are arranged non-uniformly on at least two webs (9) spaced apart from one another. device after claim 8 or 9 , characterized in that the tracks (9) are arranged uniformly to each other. device after claim 8 or 9 , characterized in that the webs (9) are arranged non-uniformly to one another.

Images