DEEP-DRAWING DEVICE TO PREVENT WRINKLING DEFECTS IN THE PRODUCTION OF THIN-WALLED DEEP-DRAWN PARTS

Abstract

A deep-drawing device for the production of a thin-walled deep-drawn part from a sheet-metal blank includes a drawing die with a drawing edge and a sheet-metal holder, which together form a flange feed zone of the deep-drawing device, and a deep-drawing punch. The deep-drawn part includes a wall inclined toward a working direction. The deep-drawing device has at least sectional controlled wrinkle-generation elements in the flange feed zone.

Description

TECHNICAL FIELD

The invention relates to a deep-drawing device and a method for the production of thin-walled deep-drawn parts.

BACKGROUND

For the production of thin-walled containers or three-dimensionally shaped parts such as sinks, body parts or also food and pharmaceutical packaging, the so-called deep-drawing method is used. Within the scope of this method, a sheet or sheet foil is clamped between a sheet-metal holder and a drawing die (also known as a drawing ring) with a drawing edge and then deep-drawn across the drawing edge into the desired shape using a deep-drawing punch, which moves in a working direction relative to the drawing die. Depending on the required geometry of the end part, this drawing-die method can also be repeated during the course of a plurality of stages, wherein the tool geometry must then be specifically adapted.

The drawing in of the sheet induces tensile stresses (“radial” tensile stress) in the flange area of the sheet in the “radial” direction. In the areas where the circumferential length is compressed, compressive stresses are generated in the circumferential direction (“tangential” compressive stress). This always occurs with round shapes and with square shapes in the (round) corners. Due to a low level of flexural rigidity, these then result in the formation of undesirable wrinkles.

In the following, a working direction refers to the direction in which the deep-drawing punch and the drawing die move relative to each other. This applies regardless of whether the die or the deep-drawing punch is static. In the case of rotationally symmetrical drawn parts, the working direction is parallel to the rotational axis.

If the wrinkles occur in the flange area, they are referred to as wrinkles of the first type. In the case of part shapes in which a wall (i.e., a wall of the deep-drawn part) is not vertical (i.e., parallel to the working direction) but under an angle of inclination to the working direction, such wrinkles can also occur in the wall area. These occur in free zones, i.e., in areas that temporarily have no contact with tool surfaces and are referred to as wrinkles of the second type (see FIG. 1).

To prevent the wrinkles of the first type in the flange area, the sheet-metal holder is used. This prevents wrinkle formation by building up pressure in this zone. In the wall area, however, the sheet metal is free so that wrinkle formation cannot be prevented directly by means of supporting using a tool wall. Up until now, such wrinkles have primarily been counteracted by increase formation the sheet-metal holding force and thus by increase formation the radial stress, which results in the reduction of tangential compressive stresses. In many cases, however, this measure is insufficient. This second type of wrinkle formation is visible, for example, in a round cylindrical/conical shape in the area of the entire wall or in square shapes with round corners in the area of the corners.

The problem described above occurs in both single-stage as well as multiple-stage forming methods. Depending on the design of the tools, these are referred to as forming in a progressive production process (a plurality of successive tool stages with part transport) or forming in an overall composite process (forming in a stacked tool without part transport). Regardless of the type of stage sequence, wrinkles always occur when the inclination of the wall exceeds a certain angle, for example, in the case of conical deep-drawn parts with a uniform inclination or in the case of dome- or hemispherical deep-drawn parts with a continuously increasing inclination.

In the case of conical deep-drawn parts, wall inclinations of between 5 and 15 degrees are often used. This angle is chosen, for example, for reasons of the stackability of the parts. For conventional conical containers, the angle is about 7.5 degrees.

Wrinkle formation results in an unattractive appearance (cf. FIG. 2A) as a consequence, which is classified as a surface defect and often does not meet the quality requirements (e.g., in the case of car body parts).

Especially in the case of deep-drawn parts, where double-sided tool contact occurs at the end of the process, such unwanted wrinkles are compressed (squeezing of the material). This induces a so-called wrinkling defect due to vertical material wrinkles, which can cause cracks when compressed (see FIG. 2B). Deep-drawn parts with cracks are detected in a subsequent quality inspection and disposed of as rejects. Depending on the deep-drawn part, the scrap can be in the low single-digit percentage range.

As described, the wrinkle formation of the second type is caused by the inclination of the wall and thus by the geometry of the end part. The previous technical forming procedure of reducing wrinkle formation by increasing sheet-metal holding force has its limits, since this increases the thinning of the sheet metal, which then results in so-called bottom tears more quickly (defect due to necking).

The wrinkles of the second type are not to be confused with indentations, which are intentionally inserted as design or reinforcement elements.

WO2012140266 reveals a device for deforming a hexagonal sheet-metal blank from an originally flat to a cylindrical cup shape. In order to achieve a stronger redrawing of the sheet material in the corner regions of the blank, the drawing die can comprise a drawing edge with different rounding radii in sections so that a reduced retention force results in the six corner regions. The rounding radii must be correspondingly large in order to compensate for the longer path on the front side of the drawing die in the corner regions. Due to the cylindrical cup shape, there is no wrinkle formation of the second type, nor can it be controlled with the proposed embodiment of the drawing edge.

SUMMARY

One aspect of the invention relates to a deep-drawing device and a deep-drawing method with which a wrinkling defect is prevented or at least greatly reduced.

Accordingly, embodiments of a deep-drawing device and a method are disclosed herein.

The deep-drawing device for the production of a thin-walled deep-drawn part from a sheet-metal blank comprises a drawing die with a drawing edge and a sheet-metal holder, which together form a flange feed zone of the deep-drawing device, and a deep-drawing punch. The deep-drawn part comprises a wall inclined toward a working direction. In the flange feed zone, the deep-drawing device at least comprises sectional controlled wrinkle-generation means.

The controlled wrinkle-generation means are dimensioned in such a way that they do not result in any sectional change in sheet metal feeding in the radial direction but only control the arrangement of the resulting wrinkles.

The invention is based on the knowledge that wrinkle formation of the second type is not to be prevented but is to be directly influenced. By controlled wrinkle-generation means, the wrinkles of the second type are introduced into the wall with a controlled, regular distribution. Due to this regularity, in the event of double-sided tool contact, which leads to flattening of the wrinkles, a wrinkling defect with crack formation is prevented or at least significantly reduced. In addition, the wrinkles are no longer perceived as surface defects.

Accordingly, the solution is based on the use of a deep-drawing device with controlled wrinkle-generation means. These are designed in such a way that they trigger an optimal wave disturbance for the respective part geometry and thus specifically influence the shape but also the number of wrinkles of the second type. The wrinkles are shaped in such a way that at the end of the process there is no wrinkling defect due to uncontrolled wrinkles of the second type.

This wave fault can be integrated into the drawing die of the nth stage in the case of multiple-stage processes and directly into the drawing die of the first stage in the case of single-stage processes. The number and extent of the wave-like indentations depends on the geometry of the part, for example, the inclination of the wall, the ratio of sheet thickness to the drawing die radius or the curvature of the wall by one axis parallel to the working direction.

A change in the pressure of the sheet-metal holder and/or a resulting change in the retention force is not significantly influenced by the controlled wrinkle-generation means.

As a reference for the number of wave-like indentations, a free number of wrinkles calculated using the FEM (finite element method) can be used. This number serves as the minimum number. Sheet-metal holding forces should not be affected by this, otherwise the drawing die process will be changed. For example, good results can be achieved with as little as 10 wave-like indentations.

The controlled wrinkle-generation means can comprise a plurality of wave-like indentations along the drawing edge of the drawing die and/or a plurality of oblong radial recesses on a surface of the drawing die facing the sheet-metal holder or on a surface of the sheet-metal holder facing the drawing die. The drawn sheet metal can deviate into such spatial expansion areas in the flange feed zone, thus controlling the formation and arrangement of the second type wrinkles in the wall. The oblong recesses can be inclined relative to the surface so that the recess tapers radially toward the outside. Ideally, the recesses reach up to the drawing edge. Recesses and indentations can be combined with each other.

Preferred embodiments of the invention are also disclosed herein.

In some embodiments, the wave-like indentations and/or oblong recesses can be evenly spaced from each other. The wave-like indentations and/or the oblong recesses can each have the same shape (length, width, depth). The depth is chosen as small as possible in order to reduce the visibility of the controlled introduction of second type wrinkles as much as possible. In addition, other parameters such as the pressure of the sheet-metal holder or the additional retention force of the sheet-metal blank influenced by drawing die/edge rounding radius should not be affected.

Good results are achieved, for example, with a rotationally symmetrical deep-drawn part with a diameter of about 25-30 mm and a sheet thickness of, for example, 0.06 to 0.12 mm with 10 to 35 controlled wrinkle-generation means. Preferably, the number of controlled wrinkle-generation means is at least 16 (at least 4 per 90° enclosing angle).

In some embodiments, the number of the plurality of wave-like indentations and/or oblong recesses across a wall segment with an enclosing angle of 90° C. an be at least four. In other words, any non-linear drawing die rounded area, which is provided with wrinkle-generation means can comprise at least four wave-like indentations and/or oblong recesses per 90° enclosing angle.

In some embodiments, the controlled wrinkle-generation means can be arranged along the entire perimeter of the flange feed zone. In particular, this is provided if it is an overall round or rotationally symmetrical deep-drawn part (e.g., a conical or hemispherical container or hollow body). In the case of a deep-drawn part with straight sides (e.g., a rectangular container with rounded corners and straight areas), the controlled wrinkle-generation means can be arranged at least or only in sections of the flange feed zone that are curved around an axis parallel to the working direction. These sections each form a rounded wall (non-linear drawing die rounded area), for example, in the case of a circular or oval container or in the round corners of a rectangular container (wherein the wall is inclined toward the working direction in each case).

In some embodiments, the wave-like indentations can be formed by a variation in the edge radius of the drawing edge. For example, the edge radius along the drawing edge can vary within a certain range between at least the sheet thickness used and 2.5 mm, preferably between 0.2 and 2.5 mm, creating a wave-like drawing edge. Such values are suitable, for example, for containers made of foils with a sheet thickness of approx. 0.1 mm.

The optimal minimum and maximum edge radius of the area of variation depends on the sheet thickness, the radius of the drawing die rounding and the curvature of the wall. For rotationally symmetrical deep-drawn parts with a diameter of about 25-30 mm and a sheet thickness of, for example, 0.06 to 0.12 mm, a variation of the edge radius between 0.2 and 0.4 mm has proven to be good. Depending on the size of the deep-drawn part and/or the thickness of the sheet-metal blank, the radii must be adapted to the specific forming.

The wave-like indentations along the drawing edge, arranged in sections, can form a uniform wavy line with a constant amplitude and wavelength. The amplitude as well as the wavelength can vary depending on the rounding of the drawing die and/or the curvature of the wall.

In the present case, the drawing die rounding or curvature of the wall refers to a curvature around an axis parallel to the working direction, for example, in the round corners or in the case of a round shape of the drawn part. As viewed in the working direction, the wall can be straight (e.g., in the case of a conical deep-drawn part) or curved (e.g., in the case of a dome-shaped or hemispherical deep-drawn part).

In some embodiments, the oblong recesses in the surface of the drawing die or the sheet-metal holder can form a uniformly corrugated surface. The depth of the recesses can be about 0.05 to 2.5 mm, depending on the thickness of the sheet.

In some embodiments, the inclined wall can have an angle of at least 3 degrees, preferably 5 to 15 degrees, toward the working direction.

In some embodiments, the deep-drawn part can be a thin-walled container or hollow body with or without a flange, with a wall inclined toward the drawing axis and with a bottom.

The invention also relates to a deep-drawing method for the production of a thin-walled deep-drawn part by means of a deep-drawing device described above, comprising the steps: (a.) provision of the deep-drawing device that comprises controlled wrinkle-generation means; (b.) clamping of the sheet-metal blank in the deep-drawing device; (c.) deep drawing of the sheet-metal blank across the drawing edge, wherein wrinkles are introduced into the wall of the deep-drawn part in a controlled manner at least in sections by the controlled wrinkle-generation means.

In some embodiments, the deep-drawing method can be a single or multiple-stage process with one or a plurality of forming stages, wherein at least one of the forming stages is carried out with a drawing die or a deep-drawing punch according to any one of the preceding claims.

In some embodiments, in the case at least one forming stage, the controlled wrinkles can be compressed by means of double-sided tool contact.

The invention also relates to a deep-drawn part, which is produced using the deep-drawing device or the deep-drawing method described above, wherein the deep-drawn part comprises an inclined wall and the wall comprises a plurality of evenly arranged wrinkles in sections, which are orientated in the working direction.

The invention also relates to a deep-drawn part with a round wall inclined toward the working direction, wherein the wall comprises evenly arranged wrinkles in sections, which are orientated in the working direction.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below on the basis of exemplary embodiments in connection with the draw die(s). The figures show:

FIG. 1 a schematic illustration of a drawing device with wrinkle formation of the second type;

FIGS. 2A and 2B cut-out of an inclined wall under (FIG. 2A) with wrinkle formation of the second type under (FIG. 2B) with crack formation;

FIG. 3 drawing die with corrugated drawing edge, with FIG. 3A detailing the area A of FIG. 3;

FIG. 4 drawing die with corrugated drawing edge, with FIG. 4A detailing the area A of FIG. 4; and

FIG. 5 drawing die with radial recesses

EMBODIMENTS OF THE INVENTION

FIG. 1 shows a schematic illustration of a deep-drawing device with wrinkle formation of the second type. The deep-drawing device comprises a drawing die 2 with drawing edge 5, a sheet-metal holder 4 and a deep-drawing punch 3. The drawing die 2 with drawing edge 5 and the sheet-metal holder 4 define a flange feed zone of the deep-drawing device. A sheet-metal blank 7 made of a sheet metal or sheet foil is clamped between the sheet-metal holder 4 and the drawing die 2 and is deep-drawn into the desired shape using the deep-drawing punch 3 across the drawing edge 5. The deep-drawing device is designed for the production of a deep-drawn part 1 (see also FIGS. 2A and 2B) with (or without) a flange 11, a wall 12 inclined to the working direction A and a bottom 13. Such a deep-drawn part can be, for example, a conical container or a rectangular container with round corners. Particularly in the case of part shapes in which the wall (i.e., a wall of the deep-drawn part) is not vertical (i.e., parallel to the working direction A) but under an angle of inclination to the working direction A, so-called wrinkles of the second type can occur in the wall area 8 which can eventually lead to crack formation in the event of double-sided tool contact 8a (cf. FIGS. 2A and 2B).

In the present case, the working direction A refers to the direction in which the deep-drawing punch and the drawing die move relative to each other. This applies regardless of whether the die or the deep-drawing punch is static. In the case of rotationally symmetrical drawn parts, the working direction is parallel to the rotational axis.

FIG. 2B and FIG. 2A show this uncontrolled wrinkle formation of the second type and the crack formation in a wall of a conical container. This crack formation is also known as a wrinkling defect.

FIG. 3 and FIG. 4 now show a drawing die 2 of a deep-drawing device, by means of which a wrinkling defect can be efficiently prevented or at least significantly reduced. FIGS. 3A and 4A show an enlarged section of the drawing edge 5. The drawing die and/or its drawing edge is provided with controlled wrinkle-generation means.

The drawing die 2 shown is provided for the production of a conical container. For example, the drawing die can be used in the second drawing die stage to prevent a wrinkling defect in the conical container. The drawing die 2 comprises a circular drawing edge 5 on the inside. This drawing edge 5 is provided with controlled wrinkle-generation means in the form of a plurality of wave-like indentations 6, via which a wrinkle formation of the second type is not prevented, but the wrinkles of the second type are introduced into the wall of the deep-drawn part in a controlled manner at regular intervals. Since this prevents the wrinkle formation with narrow and irregular wrinkles, in the case of a subsequent double-sided tool contact, a wrinkling defect is prevented and/or significantly reduced, which occurs due to the squeezing of uncontrolled and therefore irregular, partially closely spaced wrinkles of the second type.

In the example shown, the drawing edge shown for such conical containers comprises a minimum edge radius of about 0.2 mm, but at least about the thickness of the sheet used. The plurality of wave-like indentations 6 of the shown sliding edge 5 are created by periodically changing the edge radius of the drawing edge 5. The edge radius in the embodiment shown varies between about 0.2 and 0.4 mm, resulting in a wave-like drawing edge with uniform amplitude and wavelength.

The drawing die in FIG. 4 differs from the drawing die in FIG. 3 in that its drawing edge 5 has a larger number of wavy indentations. The number of controlled wrinkle-generation means—e.g., in the form of wave-shaped indentations-across a wall segment with an enclosing angle of 90° is at least four (see FIG. 3). In the case of a rectangular moulded part, at least four of the controlled wrinkle-generation means would be arranged in each corner. The embodiment in FIG. 4 shows about 8 controlled wrinkle-generation means per 90° enclosing angle. The embodiment in FIG. 5 is about 10 per 90° enclosing angle.

FIG. 5 shows another way to control the wrinkle formation by designing the controlled wrinkle-generation means in the form of a plurality of radially arranged, oblong recesses 6a. The oblong recesses 6a extend in the flange feed zone partially across the surface of the drawing die 2, which is facing the sheet-metal holder 4, starting at the drawing edge 5 of the drawing die 2. Alternatively, the recesses 6a could also be arranged on a surface of the sheet-metal holder 4 facing the drawing die 2, wherein the recesses then start at the inner edge of the sheet-metal holder. These recesses 6a are also arranged regularly around the entire circumference of the flange feed zone. In the embodiment shown, they have a depth of about 0.1 mm. As a rule, the recesses 6a are inclined toward the surface of the drawing die 2 (or the sheet-metal holder 4) so that the recesses 6a taper radially toward the outside. Ideally, the recesses 6a reach up to the drawing edge 5 and/or are combined with indentations 6.

REFERENCE LIST

• • 1 deep-drawn part
  • 11 flange
  • 12 wall
  • 13 bottom
  • 2 drawing die
  • 3 deep-drawing punch
  • 4 sheet-metal holders
  • 5 drawing edge
  • 6 wave-like indentation
  • 6 a oblong recess
  • 7 sheet-metal blank
  • 8 wrinkle formation of the second type in the wall area
  • 8 a crack formation
  • A working direction

Claims

1. A deep-drawing device for the production of a thin-walled deep-drawn part from a sheet-metal blank, the deep-drawing device comprising a drawing die with a drawing edge and a sheet-metal holder, which together form a flange feed zone of the deep-drawing device, and a deep-drawing punch; wherein the deep-drawn part comprises a wall inclined toward a working direction; and wherein the deep-drawing device comprises at least sectional controlled wrinkle-generation means in the flange feed zone.

2. The deep-drawing device according to claim 1, wherein the controlled wrinkle-generation means comprise a plurality of wave-like indentations along the drawing edge of the drawing die and/or a plurality of oblong, radially running recesses on a surface of the drawing die facing the sheet-metal holder or on a surface of the sheet-metal holder facing the drawing die, wherein the recesses extend up to the drawing edge.

3. The deep-drawing device according to claim 2, wherein the wave-like indentations and/or the oblong recesses are evenly spaced from each other.

4. The deep-drawing device according to claim 2, wherein the number of a plurality of wave-like indentations and/or oblong recesses across a wall segment with an enclosing angle of 90° is at least four.

5. The deep-drawing device according to claim 1, wherein the controlled wrinkle-generation means are arranged along the entire circumference of the flange feed zone.

6. The deep-drawing device according to claim 1, wherein the controlled wrinkle-generation means are arranged at least or only in sections of the flange feed zone which are curved by an axis parallel to the working direction.

7. The deep-drawing device according to claim 2, wherein the wave-like indentations are formed by a variation of the edge radius of the drawing edge.

8. The deep-drawing device according to claim 7, wherein the edge radius varies within a range between at least the thickness of the sheet used and 2.5 mm.

9. The deep-drawing device according to claim 8, wherein the edge radius varies within a range between 0.2 mm and 2.5 mm.

10. The deep-drawing device according to claim 7, wherein the wave-like indentations arranged in sections along the drawing edge form a uniform wavy line.

11. The deep-drawing device according to claim 2, wherein the oblong recesses form a uniformly wavy surface.

12. The deep-drawing device according to claim 1, wherein the inclined wall comprises an angle of at least 3 degrees.

13. The deep-drawing device according to claim 12, wherein the inclined wall comprises an angle of 5 to 15 degrees.

14. The deep-drawing device according to claim 1, wherein the deep-drawn part is a thin-walled container or hollow body with or without flange with a wall inclined toward the working direction and with a bottom.

15. A deep-drawing method for the production of a thin-walled deep-drawn part by means of the deep-drawing device according to claim 1, the method comprising: provision of the deep-drawing device which has controlled wrinkle-generation means;clamping of the sheet-metal blank in the deep-drawing device;deep drawing of the sheet-metal blank across the drawing edge, wherein wrinkles are introduced into the wall of the deep-drawn part in a controlled manner, at least in sections by means of the controlled wrinkle-generation means.

16. The deep-drawing method according to claim 15, wherein the method is a single or multiple-stage process comprising one or a plurality of forming stages, wherein at least one of the forming stages is carried out using the drawing die or the deep-drawing punch.

17. The deep-drawing method according to claim 16, wherein at least one forming stage compresses the wrinkles introduced in a controlled manner by means of double-sided tool contact.

18. A deep-drawn part produced by the deep-drawing device according to claim 1, wherein the deep-drawn part comprises an inclined wall, wherein the wall comprises a plurality of evenly arranged wrinkles in sections, which are orientated in the working direction.

19. A deep-drawn part produced by the deep-drawing method according claim 15, wherein the deep-drawn part comprises an inclined wall, wherein the wall comprises a plurality of evenly arranged wrinkles in sections, which are orientated in the working direction.