EP1715066B1 - Device for forming and press hardening metal sheet, with integrated heating elements - Google Patents

Description

The invention relates to a device for forming metal sheets, which has a forming tool with a forming space, wherein the metal sheet in the forming space is partially heated by at least one heating element.

The hot forming of metal sheets as such is known, for example by the DE 24 52 486 A1 as well as through the GB 1 490 535 A , Here, the metal sheets, preferably sheet steel blanks, heated in a heat treatment plant, then placed hot in the press tool and reshaped. Still clamped in the press tool, the sheet-metal profile components are hardened. A significant advantage of this approach is that hardened sheet metal profile components can be produced with a complicated shape, and with high dimensional accuracy.

Certain thermoformed components, especially made of high-strength sheet steel, such as B-pillars, must still be trimmed at the edge in order to comply with the specified dimensional tolerances. In addition, many mold components are still punched after hot forming. Since the thermoforming process brings about a very hard martensitic microstructure state, a conventional edge / hole trimming of the shaped components carried out with cutting knives is very wear-resistant and cost-intensive. Alternative cutting methods, such as The trimming by means of laser radiation are also extremely expensive due to the high system costs.

In order to be able to carry out a conventional edge / hole trimming, the areas in which trimming must take place should have a much softer texture. There are various starting points for this.

One possibility is to subject the mold component to an additional heat treatment after the hot forming in order to soften the material structure in the areas to be machined. Due to the necessary additional process, however, this inevitably leads to an increase in manufacturing costs, which adversely affects the economics of the overall process.

The second possibility is to design the hot forming or hardening process in such a way that a slower cooling during hardening takes place in the areas to be trimmed. This is only possible to a limited extent in the currently used conventional hot forming tools, which are aimed at cooling the moldings as quickly as possible. Suggestions for this are from the DE 197 23 655 A1 known. Here inserts or additional heating elements are provided in the press tool in order to achieve reduced cooling during hardening in targeted areas, so that these areas have a softer material structure at the end of the process.

Also the DE 101 62 441 A1 describes a method for producing motor vehicle components from metal sheets in a forming tool having a mold space, wherein for controlling the material flow mold space areas can be tempered specifically by heat and / or heat dissipation.

Out PATENT ABSTRACTS OF JAPAN vol. 009, No. 107 (M-378), May 11, 1985 (1985-05-11 ) - & JP 59 229242 A (SUMITOMO KINZOKU KOGYO KK), December 22, 1984 (1984-12-22) discloses a device for forming metal sheets, which has a forming tool with a forming space, wherein the metal sheet in the forming space is heated in regions by at least one heating element. The heating element is arranged in a recess of the forming tool and projects partially into the forming space.

However, the particular difficulty is fundamentally that very different cooling gradients with the lowest possible transitions between hard and soft Zones, so to realize within a few millimeters of the same mold component.

The invention is based on the prior art, the object to provide a plant and application technology improved device for forming metal sheets, in particular, very different cooling gradients can be realized in tight spatial limits on the molding to be circumcised and / or punched areas in To leave a soft well-cut microstructural state.

The solution of this problem consists according to the invention in a device according to the features of claim 1.

The main point of the invention is the measure to heat-control the heating element integrated in the forming tool completely or in sections relative to the adjacent walls of the forming tool by means of an insulating layer. In this way, the effectiveness of the heating element can be increased with a targeted heat transfer to specific narrow or locally limited areas or zones of the molded component. The influence of the material structure on the molded part can thus be made significantly better. A heat flow into adjacent areas of the forming tool is avoided.

The heating element is limited by a cover to the forming space. The cover expediently closes off the heating element and the insulating layer toward the shaping space, so that the tool surface on which the sheet metal blank to be formed slides during the forming process is designed to be homogeneous. The cover is made of a material with good thermal conductivity, such as copper. This ensures good heat transfer in the direction of the mold component in the forming space. Basically, the material of the cover should have a thermal conductivity λ of ≥ 10 W / Km.

Copper, for example, has a thermal conductivity λ. from 394 W / Km up. The use of a cover made of iron is possible. Iron has a thermal conductivity λ. from 73 W / Km.

The heated in the forming space areas of the mold component cool in the hardening process, so while they are clamped in the forming tool, not from. Only after the deformation tool has been opened do the spots cool at a considerably lower cooling rate in air. Due to the slow cooling rate, no hard martensitic structure is produced in the molded component at the previously heated locations. It can be at these points a component hardness similar to the unmilled material state achieve, so that downstream processing steps, ie in particular cutting or punching operations, better and of higher quality can be performed. Even the processing tools used, such as knives or punching tools, are subject to significantly lower wear and achieve significantly longer service lives.

Advantageous developments of the basic concept of the invention are the subject of the dependent claims 2 to 7.

In the apparatus according to the invention spatially highly limited microstructural adjustments of the material of a molded part in the thermoforming process are possible. This is done by the targeted heating of the mold component during the forming process to keep the respective area of the sheet metal blank or the mold component during the forming process at an elevated temperature and then cooled relatively slowly in air. In this way, the area to be trimmed is left in a soft, well-cut microstructural state.

According to the invention, at least one, preferably a plurality of heating elements are integrated in recesses of the forming tool, wherein the heating element is thermally insulated from the adjacent walls of the forming tool by an insulating layer, so that a heat dissipation into the forming tool is avoided and the heat is released primarily only in the direction of the tool surface.

The configuration of the heating elements is in particular geometrically tuned in such a way that those areas of the mold component which are intended to remain soft are tempered in a targeted manner. In the forming tool for this purpose depressions, grooves or similar recesses are provided, in which a heating element is introduced.

As an insulating layer, ceramic insulating materials or glass fiber materials can be used. Insulating layers of mica are also suitable for the purpose according to the invention. Since air also has good insulation or thermal insulation properties, the insulating layer can also be formed as an air gap. Also possible is a combination of the insulation of an insulating material and an air gap. As a material for the insulating layer is a technical ceramic with a thermal conductivity λ ≤ 2 W / Km offers.

As the heat source, electric heating elements, e.g. High-performance heating cartridges, just as conceivable as small pipes through which a hot medium flows. It should be noted that for the electrical heating of large tool areas relatively high power densities must be provided.

In the context of the invention, it is particularly intended to heat-insulate the heating element at all sides adjacent to the forming tool by an insulating layer, ie at the bottom and at the side walls. In principle, however, depending on the embodiment, only a bottom-side insulation or insulation of the side walls may be provided.

Figur 1

in perspektivischer Darstellungsweise, technisch vereinfacht, einen Ausschnitt aus einem Umformwerkzeug mit einem integrierten Heizelement;

Figur 2

den Ausschnitt A der Figur 1 in vergrößerter Darstellungsweise;

Figur 3

eine alternative Ausführungsform eines Umformwerkzeugs mit integriertem Heizelement in perspektivischer Darstellungsweise und

Figur 4

eine weitere alternative Ausführungsform.

The invention is described below with reference to exemplary embodiments. Show it:

FIG. 1

in perspective representation, technically simplified, a section of a forming tool with an integrated heating element;

FIG. 2

the section A of FIG. 1 in an enlarged representation;

FIG. 3

an alternative embodiment of a forming tool with integrated heating element in perspective representation and

FIG. 4

another alternative embodiment.

In the FIGS. 1 to 4 each corresponding components carry the same reference numerals.

The FIG. 1 shows a perspective view of a technically schematized a section of a forming tool 1 of a device according to the invention, for example a press. From the basic structure, the forming tool 1 has an upper tool 2 and a lower tool 3, which are matched to one another in the contour. Between upper tool 2 and lower tool 3, a forming space 4 is formed. In the forming space 4, a previously heated to a certain forming temperature sheet metal plate can be added and then pressed by Gegeneinanderverlagern of upper tool 2 and lower tool 3 shaping. Still clamped in the forming tool 1, the mold component is cooled and cured. Here, a hard martensitic microstructure state is fundamentally set on the molded component.

For selective adjustment of a softer material structure in certain areas, the pressed-out mold component in the forming space 4 can be heated in certain regions. For this purpose, a heating element 6 or 7 is integrated in a recess 5 of the forming tool 1.

The FIG. 2 shows a heating element 6 with a circular cross-section, whereas the heating element 7 as shown in the FIGS. 3 and 4 have a square cross section with an edge length of for example 4 mm to 8 mm.

The length of the heating elements 6, 7 can be selected according to the particular requirements on the molded component. The heating elements 6, 7 can be bent, so that even curved curved tool areas can be heated.

The heating element 6, 7 is separated from the adjacent walls 8, 9, 10 of the forming tool 1 and the lower tool 3 through an insulating layer 11, 12, 13 and thermally insulated. In the embodiments according to the FIGS. 2 and 3 an insulating layer 11 is provided below the heating element 6, 7 at the bottom 8 of the recess, Furthermore, an insulating layer 12 is also arranged at the edge between the heating element 6, 7 and the side walls 9, 10 of the recess 5. The insulating layer 11, 12 is made of ceramic, a glass fiber mat or mica.

In the embodiment according to FIG. 4 an insulating layer 11 made of ceramic or mica is integrated on the bottom 8 of the recess 5. Between the heating element 7 and the side walls 9, 10 of the recess 5 is provided as an insulating layer 13 each have an air gap for thermal insulation.

On the upper side to the forming space, the heating element 6 according to the embodiment of FIG. 2 closed by a cover 14 made of a material with good thermal conductivity, such as copper. The material of the cover has a thermal conductivity λ which is greater than or equal to 10 W / Km.

By means of the heating elements 6, 7, a controlled temperature control of the molded component in the forming space 4 can take place. The isolation or thermal insulation of the heating elements 6, 7 according to the invention for the forming tool 1 prevents an adverse heat flow into the tool, so that the heating of the mold component is carried out effectively. In the device according to the invention also extremely different Abkühlgradienten be realized within only a few millimeters on the mold component. The areas of the molded component heated in the forming tool 1 do not cool or barely cool when the press is closed. Only after the opening of the forming tool 1 is a cooling of the molded component with a low cooling rate in air. Due to this slow cooling rate, these previously heated areas have a softer material structure, so that cutting or punching operations can be carried out more simply and dimensionally true with less tool wear.

Claims (7)

1. Apparatus for forming sheet metal, comprising a forming tool with a forming cavity, the sheet metal being adapted to be heated in regions in the forming cavity by at least one heating element which is arranged in a recess of the forming tool, and the heating element (6, 7) being insulated from the forming tool (1) by an insulating layer (11, 12, 13), characterised in that the heating element (6) is delimited by a cover (14) relative to the forming cavity (4), and the cover (14) consists of a material with a heat conductance λ≥ 10 W/Km.
2. Apparatus according to claim 1, characterised in that an insulating layer (11) is provided between the heating element (6, 7) and the bottom (8) of the recess (5).
3. Apparatus according to claim 1 or 2, characterised in that an insulating layer (12, 13) is provided between the heating element (6, 7) and the side walls (9, 10) of the recess (5).
4. Apparatus according to one of claims 1 to 3, characterised in that the insulating layer (11, 12) consists of ceramics.
5. Apparatus according to one of claims 1 to 3, characterised in that the insulating layer (11, 12) consists of mica.
6. Apparatus according to one of claims 1 to 3, characterised in that the insulating layer (11, 12) consists of fibreglass material.
7. Apparatus according to one of claims 1 to 3, characterised in that the insulating layer (13) is formed by an air gap.

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