EP2259883B1 - Method for controlling the flow of material when deep-drawing a workpiece, and deep-drawing device - Google Patents

Description

The invention relates to a method for material flow control during deep drawing of a workpiece. The method can be carried out by means of a deep-drawing device with a deep-drawing die, which has a guide portion and a mold portion, with a hold-down, which supports the positioning of the workpiece during the deep drawing operation on the guide portion, and with a deep-drawing die, which exerts the force required for deep drawing ,

Methods of the type mentioned are already known. The problem with these methods is that during the deep-drawing process in the flange portions of the workpiece, a material accumulation can form. This possibly leads to the fact that the flow of material from the flange portion of the workpiece is reduced or even prevented, so that the material from the already deep-drawn areas, such as the frame or the floor, thins with continued deep drawing operation and thus the risk of a crack in these areas is. This is particularly the case when the drawing depth is very large or when the workpiece is to be deep drawn to a drawn part with more curved areas such as corners.

On the other hand, can be impaired by a occurring during the deep drawing process constriction of the bottom portion of the drawn part of the frame, the dimensional accuracy of the soil. Because in the training of soil structures are in In this case there are hardly any areas of pre-stretched material. This can have a disadvantageous effect, in particular, when the bottom surface is significantly smaller than the frame surface.

In order to avoid reisser, workpieces can be processed whose diameter does not exceed the maximum diameter specified by the respective drawing-off ratio relative to a well-shrinking test. However, the deep drawing process can then be used only for the production of drawn parts in certain size ranges. In addition, the flange portions of the workpiece are comparatively narrow, so that increased care must be taken during the deep drawing operation. In order to prevent breakage, it is also possible to carry out the deep drawing operation in several steps, during which the cross section of the deep-drawing die is successively reduced. In this way, the predetermined by the Grenzziehverhältnis condition can be maintained longer even when using workpieces with large diameters. However, the tooling is increased by this approach. Furthermore, the cycle time in production is extended, which reduces the efficiency of the process. Facilitating the flow of material from the flange area into the deep-drawn areas by reducing the flow-inhibiting friction of the workpiece on the deep-drawing die and / or hold-down by the use of lubricants can indeed assist, but not fully guarantee, correct process control. In addition, when using lubricants additional cleaning measures on the drawn part and the thermoforming tools are required. In the flange area of the workpiece, the flow direction of the material during the Deep drawing process be braked by appropriately arranged Bremswülste over a certain section. As a result, the material of the workpiece can be stretched even before the actual deep-drawing process. However, this procedure only achieves the uniformity of ironing of the material. The enlargement of the run-in radius of the workpiece from the guide portion into the mold portion of the deep-drawing die is also not given. This can lead to undesirable wrinkling on the drawn part.

According to the patent EP 1 526 931 B1 a material flow control is made in the deep drawing of sheets by embossing a Z-shaped shut-off in the sheet edge, which inhibits the flow of material. During the deep-drawing process, the shut-off stage is reduced again so that the flow of material from the flange area into the die is facilitated. However, an additional deflection of the material and correspondingly expensive tools, which must exert high additional forces required for this procedure. In addition, the friction is increased by the deflection.

From the publication JP-A-01027726 In addition, a deep drawing method is known in which good formability is achieved and springback in pressing operations is avoided by forming a first and then a second bead in the flange region during the continuous lowering of the die.

The present invention is therefore based on the object to provide a method by which or with which the Pulling capacity of a workpiece better utilized and better dimensional accuracy, in particular the bottom of the drawn part can be achieved.

According to a first teaching of the present invention, the object is achieved by a method for material flow control during deep drawing of a workpiece, wherein the Deep drawing operation is performed incrementally, and in which at least one bead is incorporated in the flange portion of the workpiece before each Tiefziehvorgangsinkrement.

By doing so, the dimensional accuracy of the drawn part can be improved. Because by the incorporation of the bead, a pre-stretching of the bottom regions is first achieved, which favors the interaction of the deep-drawing die with the bottom region taking place in the course of the deep-drawing process increment following the incorporation of the bead. In addition, more material from the flange portion of the workpiece can flow into the frame as it approaches the frame. As a result, the risk of material fracture, for example in the region of the frame or the floor, which may be caused in particular by a material accumulation, reduced. Thus, it is possible to achieve a drawing depth with predetermined workpieces, which in particular goes up to a factor of 2.5 beyond the drawing depth predetermined by the known drawing-off ratio.

In a preferred embodiment of the method, the bead is incorporated only in the region to be formed corners of the workpiece. In this way, the inventive method can be implemented more efficiently. Because in principle, the risk of material jams occurs only in more curved areas such as corners reinforced. In contrast, in largely rectilinear areas of a drawn part, for example on the long side of a rectangular box, the flow behavior of the material may be sufficient, even without the additional provision of a bead, in order to achieve a satisfactory deep drawing result. On In this way, in particular the tool and process costs can be reduced.

Furthermore, can be partially or completely reshaped by the following on the incorporation of the bead Tiefziehvorgangsinkrement the bead. In this way, the Tiefziehvorgangsinkrement and the incorporation of the bead are optimally matched. This ensures that each material section is subjected at least once to a pre-stretching effected by the incorporation of the bead.

In a further preferred embodiment of the method, the bead is incorporated with rounded contours. In this way, the inventive method for use on workpieces made of sensitive materials can be made suitable. Because the roundness of the contours gently modifies the flow behavior of the material. Material impairments due to sharp-angled contours are thus avoided.

Preferably, the bead is incorporated with parallel to the deep drawing and / or inclined walls. As a result, the pre-stretching effected by the incorporation of the bead is advantageously carried out essentially in the deep-drawing direction. As a result, the process control of the deep drawing process increment following the incorporation of the bead can be improved.

The method according to the invention can be carried out with a deep-drawing device, which is particularly suitable for carrying out a method as described above Method is suitable, with a deep-drawing die, which has a guide portion and a mold portion, with a hold-down, which supports the positioning of the workpiece during the deep-drawing operation on the guide portion, and with a deep-drawing die, which exerts the force required for deep drawing, performed a is independently operable bead stamp is provided, whose contour is adapted to the contour of the guide portion.

By means of the independently operable bead punch, the beads can be worked into the flange area of the workpiece without having to use a drive coupled to the deep-drawing punch, to the deep-drawing die and / or to the blank holder. In this way, the operation of the bead punch can be very flexibly tuned to the operation of the other components of the device. This facilitates in particular the process control of the deep-drawing process.

Preferably, the punch of the thermoforming device has two or more projections. In the guide section of the deep drawing die, two or more depressions are then arranged opposite the projections, into which the projections can be inserted upon actuation of the bead punch. In this way, more than one bead can be incorporated into the material in the flange region of the workpiece with simple means.

Fig. 1a-g

ein Ausführungsbeispiel des erfindungsgemäßen Verfahrens an einer schematisch abgebildeten, Vorrichtung in einer Querschnittsansicht.

There are now many possibilities for designing and developing the method according to the invention. In the following the invention will be explained in more detail with reference to an embodiment shown in a drawing. In the drawing show:

Fig. 1a-g

An embodiment of the method according to the invention to a schematically illustrated, device in a cross-sectional view.

Fig. 1a shows a portion of a thermoforming device 2 in a schematic cross-sectional view. The deep-drawing device 2 comprises a deep-drawing die 4, a deep-drawing die 6, whose shaped portion 8 is adapted to the deep-drawing die 4, a hold-down 10 and an independently operable bead punch 12. The bead punch 12 has two projections 16 on its side facing the guide portion 14 of the deep-drawing die 6 which can be inserted into two recesses 18 arranged on the guide section 14. In this example, both recesses 18 and both projections 16 each have the same contour. However, the contours can be designed differently with each other when several recesses 18 and projections 16, if appropriate. It is of course also possible to provide only a single recess 18, to which the bead punch 12 is then adapted accordingly.

The single hold-down 10 is arranged in this example on the side facing away from the deep-drawing die 4 side of the bead punch 12. However, it is also conceivable to provide a plurality of hold-downs 10, one being arranged, for example, between deep-drawing punches 4 and bead punches 12. If several separate bead punches 12 are to be present, downholders 10 can also be arranged between the bead punches 12. The depressions 18 in the guide section 14 of the deep-drawing die 6 have a wall surface which slopes in an inclined manner relative to the deep-drawing direction and which is in this example is arranged on the side of the recess 18 further spaced from the deep-drawing die 4, whereas the wall surfaces arranged on the side of the depression 18 closer to the deep-drawing die 4 extend substantially parallel to the deep-drawing direction. In principle, however, another contour is conceivable.

In the in Fig. 1a In the position shown, a workpiece 20, for example a steel blank in the deep-drawing device 2, is arranged between the guide section 14 of the deep-drawing die 6 on one side and the punch 12 and the blank holder 10 on the other side. The Sickenstempel 12 is in a raised position, whereas the hold-10 is already applied to the workpiece 20 under slight pressure. The deep-drawing die 4 is located in such a position over the deep-drawing die 6 that it is preferably in light contact with the workpiece 20.

Fig. 1b now shows in a first step, as the beads 22 are incorporated into the flange portion of the workpiece 20. The bead punch 12 is lowered onto the guide section 14 independently of the other components 4, 6, 10. By inserting the projections 16 in the on the guide portion 14 arranged recesses 18 two beads 22 are incorporated into the workpiece 20. As a result, an advantageous pre-stretching of the workpiece 20 is effected, because the material flows to the beads 22 on the one hand from the outer part of the flange portion on the other hand from the arranged between deep-drawing die 4 and deep-drawing die 6 portion of the workpiece 20, which is at least partially used for the formation of the soil, to. Further, the material is prepared by incorporating the beads 22 for the following deep drawing operation increment. In this simple schematic representation and in the following, a possible change in the thickness of the workpiece 20 is not shown for the sake of clarity.

After incorporation of the beads 22, the bead punch 12 is again brought into the raised position, so that it is preferably no longer in the plane of the workpiece 20.

Fig. 1c shows the first thermoforming increment. The deep-drawing die 4 is moved by a certain distance in the direction of the mold section 8 of the deep-drawing die 6. In this case, the workpiece 20 is detected by the deep-drawing die 4 and drawn into the mold section 8 by the appropriate distance. In this example, the distance is just dimensioned such that the material used to form the bead 22, which is closer to the deep-drawing die 4, is completely expended for the deep-drawing operation increment. As a result, the said bead 22 is largely reshaped from the workpiece 20. In this way, the material can flow well both in largely rectilinear and in more curved areas, for example at corners. One Material accumulation in the flange area is thus substantially avoided. After the movement remains the thermoforming stamp 4 in the in Fig. 1c shown position.

Fig. 1d shows how once again the punch 12 is actuated independently of the other components 4, 6, 10 of the thermoforming device 2 and the beads 22 are worked into the remaining flange region of the workpiece 20. The material is fed to the beads 22 substantially from the outer part of the flange. After actuation, the punch 12 is returned to the raised position.

Fig. 1e shows the next deep drawing increment. The thermoforming punch 4 is moved further toward the mold section 8. The deep drawing die 4 closer bead 22 is again almost formed out. The thermoforming punch 4 remains in the position shown.

Fig. 1f shows the next operation of the bead punch 12. The flange area has become so narrow by the deep drawing process that only one bead 22 can be incorporated.

Fig. 1g shows the last thermoforming increment. The thermoforming punch 4 is moved in this example to the stop on the mold section 8 of the deep drawing die 6. The workpiece 20 is thereby almost completely pulled out of the area between the guide section 14 and the punch 12. The thermoforming process is over. The thermoforming punch 4 can now be raised to remove the finished drawn part of the deep-drawing die 6.

Claims (5)

1. Method for controlling the flow of material when deep-drawing a workpiece, characterised in that the deep-drawing process is performed incrementally, and in that at least one bead is incorporated into the flange region of the workpiece prior to each increment of the deep-drawing process.
2. Method according to Claim 1, characterised in that the bead is only incorporated into the region of corners of the workpiece which corners are to be formed.
3. Method according to Claim 1 or 2, characterised in that the bead shape is partly or fully taken out again by the deep-drawing process increment which follows the incorporation of the bead.
4. Method according to any one of Claims 1 to 3, characterised in that the bead is incorporated with rounded contours.
5. Method according to any one of Claims 1 to 4, characterised in that the bead is incorporated with walls running parallel and/or inclined to the deep-drawing direction.

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