DE102014221423B4 - Process for the production of large hot forming tools using a generative manufacturing process - Google Patents

Abstract

Method for producing a hot forming tool (100) for press hardening, the method comprising the following steps:
a) Layer-by-layer production of at least one shell element (10) of the hot forming tool (100) by means of a generative manufacturing process, wherein a first outer surface (12) of the shell element (10) is formed with a contour (14) in such a way that the first outer surface (12) of the shell element (10) with the contour (14) forms an active surface of the hot forming tool (100), wherein during layer-by-layer production at least one channel-shaped cavity (15) between the first outer surface (12) and a second outer surface (13) of the shell element (10) is introduced into the shell element (10) by means of the generative manufacturing process, wherein several shell elements (10) are produced layer-by-layer by means of a generative manufacturing process, wherein the second outer surface (13) of the shell element is also formed with a contour and wherein on the second outer surface (13) of the shell element (10) by means of the generative manufacturing process, transition elements (16) are applied which protrude from the second outer surface (13) of the shell element (10) and are formed in such a way that a material of the base body (11) can flow partially behind the transition elements (16) when the shell element (10) is back-cast;
b) back-casting the shell element (10) to produce a base body (11) of the hot-forming tool (100), such that the base body (11) forms a positive and/or material-locking connection with the shell element (10) in the region of its second outer surface (13), wherein the composite of the at least one shell element (10) and the base body (11) forms the hot-forming tool (100) or a segment of the hot-forming tool (100).

Description

The invention relates to a method for producing a hot forming tool for press hardening. Furthermore, the invention relates to a hot forming tool with a base body and at least one shell element connected thereto.

Form hardening or press hardening is a process for hot forming components, such as sheet metal, and is used in automobile construction, for example. A component, such as sheet metal, is heated to a temperature of over 800 degrees Celsius and cooled during the forming process. Hot forming tools are usually used for this, which can be clamped in a press. Hot forming tools can consist of an upper tool part and a lower tool part, between which the component is pressed. For the purposes of this invention, both upper and lower tool parts are generally understood to be hot forming tools. When pressing the component or when forming the heated component, the component is cooled as quickly as possible to a temperature in the range of approximately 200 degrees Celsius. Cooling channels are usually provided in the hot forming tool for this purpose.

State of the art

For example, it is known in the prior art to construct hot forming tools from individual segments, whereby the individual segments can consist of a tool steel and the cooling channels are drilled through the individual segments. The individual segments are then assembled and connected to one another, for example screwed, thus producing a hot forming tool.

In the DE 10 2010 017 014 A1 A method and an arrangement for producing contour-related tempering channels in tools or tool inserts is described. For this purpose, tempering channels are produced and then spatially fixed in the tool.

Through the DE 10 2006 056 160 A1 A molding tool body and a method for its production are known. The molding tool body, in particular a bending tool body, is produced by building up the tool body layer by layer from powdered material, whereby the tool body is produced in segments with segments in the form of columns lying next to one another and separated from one another by narrow gaps on a base structure.

The DE 199 25 541 C1 relates to a permanent forming tool, in particular for light metal die casting and the production of plastic, glass and ceramic parts, as well as a method for its production. The permanent forming tool produced has the advantages of metal laser sintered tool parts with a shaping contour, without the usual size restrictions and is superior in terms of production time to conventional methods such as machining (e.g. milling) and/or erosion. This is achieved by assembling the permanent forming tool from two categories of tool parts. The tool parts belonging to a first category, which have a complicated geometry of the shaping contour and/or smaller dimensions, are produced by means of metal laser sintering. The tool parts belonging to a second category, which have a simple geometry of the shaping contour and/or larger dimensions unsuitable for production by means of metal laser sintering, are produced by means of conventional methods such as milling, erosion and the like from tool blanks cast to a near-net shape. These near-net-shape cast tool blanks are produced by casting intermediate molds, which can also be designed as lost molds due to the low demands on their service life. The tool parts of both categories produced in this way are joined to form the permanent primary mold tool.

From the DE 10 2007 054 723 B4 A molded part with at least one mold surface is known, wherein a region of the mold surface is designed as a mold surface insert produced by a separate process and contour-adapted to a non-flat surface of the molded part, wherein the mold surface insert is inserted into a recess in the molded body and forms a surface section of the molded part with its upper side, wherein at least one mold surface comprises a flatly cooled or heated region and for this purpose has an arrangement of channels arranged close to the region behind the mold surface for guiding a cooling or heating medium, wherein the mold surface insert can be permanently or removably attached to a molded body of the molded part after its production, characterized in that the mold surface insert is produced by a selective laser melting process (SLM) and has a system of cooling or heating channels which adjoin outlets of cooling or heating channel sections of the molded body at the ends.

The DE 10 2012 000 633 A1 relates to a console element for holding a steering column of a motor vehicle, in particular a passenger car, via which a steering wheel can be coupled to at least one steerable wheel of the motor vehicle, wherein the console element is designed as a hybrid component with at least one base body which is supplemented with at least one plastic to form the hybrid component, and a method for producing such a console element.

Description of the invention: task, solution, advantages

The object of the present invention is to further improve a method for producing a hot forming tool in such a way that particularly large hot forming tools can be produced in the simplest and most cost-effective manner possible.

1. a) Schichtweises Herstellen mindestens eines Schalenelements des Warmumformwerkzeugs mittels eines generativen Fertigungsverfahrens, wobei eine erste Außenfläche des Schalenelements mit einer Kontur ausgebildet wird, derart, dass die erste Außenfläche des Schalenelements mit der Kontur eine Wirkfläche des Warmumformwerkzeugs bildet, wobei beim schichtweisen Herstellen mindestens ein kanalförmiger Hohlraum zwischen der ersten Außenfläche und einer zweiten Außenfläche des Schalenelements in das Schalenelement mittels des generativen Fertigungsverfahrens eingebracht wird;
2. b) Hintergießen des Schalenelement zur Herstellung eines Grundkörpers des Warmumformwerkzeugs, derart, dass der Grundkörper beziehungsweise das Gussmaterial mit dem Schalenelement im Bereich dessen zweiten Außenfläche eine formschlüssige und/oder stoffschlüssige Verbindung eingeht, wobei der Verbund aus dem mindestens einen Schalenelement und dem Grundkörper das Warmumformwerkzeug oder ein Segment des Warmumformwerkzeugs bildet.

For this purpose, the invention provides a method for producing a hot forming tool for press hardening, wherein the method comprises at least the following steps:

1. a) producing at least one shell element of the hot forming tool layer by layer by means of a generative manufacturing process, wherein a first outer surface of the shell element is formed with a contour such that the first outer surface of the shell element with the contour forms an active surface of the hot forming tool, wherein during layer-by-layer production at least one channel-shaped cavity between the first outer surface and a second outer surface of the shell element is introduced into the shell element by means of the generative manufacturing process;
2. b) Back-casting the shell element to produce a base body of the hot-forming tool, such that the base body or the casting material forms a positive and/or material-locking connection with the shell element in the region of its second outer surface, wherein the composite of the at least one shell element and the base body forms the hot-forming tool or a segment of the hot-forming tool.

The above-mentioned steps a) and b) are preferably carried out one after the other in the above-mentioned order.

The hot forming tool produced by this process therefore consists of at least one shell element and the base body. The base body forms the core of the hot forming tool. The at least one shell element forms at least the active surface or the pressure surface of the hot forming tool, which is pressed against the component, for example the sheet metal to be formed, during press hardening. This active surface is the first outer surface of the shell element and has the desired contour of the active surface.

The at least one shell element is relatively narrow compared to the base body. By back-casting the at least one shell element in step b), a firm connection is created between the base body and the at least one shell element. This creates a positive and/or material connection between the base body and the at least one shell element.

A generative manufacturing process is an additive manufacturing process in which production is carried out on the basis of computer-internal data models from formless or form-neutral material using chemical and/or physical processes. No special tools, such as molds, are required that have the respective geometry of the workpiece. In particular, this refers to a 3D printing process.

The channel-shaped cavity arranged in the shell element and between its two outer surfaces forms the cooling channel or part of the cooling channel of the hot forming tool. For this purpose, the channel-shaped cavity is arranged between the two outer surfaces of the shell element and at a distance from these outer surfaces, whereby the course of the channel-shaped cavity can be designed in different ways. For example, the channel-shaped cavity can run horizontally, vertically and/or diagonally in the shell element.

Because the channel-shaped cavity is introduced using the generative manufacturing process during layer-by-layer production in step a), no separate channel is necessary, for example no insertion of separate pipes or other parts to form a cavity. The channel-shaped cavity is formed using the generative manufacturing process, leaving areas free during layer-by-layer production of the shell element.

A hot forming tool produced by this method therefore consists of at least two parts, namely the base body and a shell element, whereby the two parts are produced using different processes. The outer area, namely the shell element, of the hot forming tool, namely the area that forms the active surface of the hot forming tool and includes one or more cooling channels, is produced by a particularly flexible manufacturing process, namely the generative manufacturing process. This is particularly important for Particularly suitable for creating the contour and the channel-shaped cavity. The base body or core adjoining the shell element is cast in a simple manner and is therefore particularly cost-effective to produce.

Preferably, the generative manufacturing process is a stereolithography process, a selective laser melting process, a laser deposition welding process, or an electron melting process. Particularly preferably, the generative manufacturing process is a selective laser melting process, wherein the material to be processed is applied in powder form in thin layers and the powdery material is melted locally layer by layer using laser radiation, whereby a solid layer of material is created after solidification. The contours for the outer surface of the shell element can be created in a particularly suitable manner. In the areas in which the channel-shaped cavity is provided, for example, the energy supply for the laser radiation is briefly switched off so that the powdery material does not solidify in this area. This area is thus left free during layer-by-layer processing. The powdery material remaining in the channel-shaped cavities can then be removed, for example blown out.

Furthermore, it is provided that in step a) several shell elements are produced layer by layer using a generative manufacturing process. This makes it possible to produce particularly large hot forming tools, for example particularly long hot forming tools or hot forming tools with a particularly large effective surface, as a monoblock. For this purpose, several shell elements can particularly preferably be produced simultaneously using the generative manufacturing process. After producing several shell elements, the shell elements are placed together before back-casting in step b) and then back-cast. This connects the shell elements to the base body and produces a single monoblock. The hot forming tool produced in this way can, like conventionally known hot forming tools, still be repaired, for example welded, on site, for example in the press.

Several shell elements are preferably connected to one another before back-casting in step b). It is therefore particularly preferred that several shell elements are not only placed next to one another and then back-cast, but are connected to one another by welding or plugging before back-casting in step b). Since a cooling channel in the hot forming tool preferably runs over several shell elements, a section of a cooling channel is arranged in each of several shell elements. These sections of a cooling channel can be used to center and align the shell elements when the shell elements are assembled.

Furthermore, in step a), the channel-shaped cavity is introduced into the shell element following a course of the contour of the first outer surface of the shell element. It is therefore preferably provided that the channel-shaped cavity follows the contour of the first outer surface of the shell element or has an identical or almost identical course. Particularly preferably, the distance between the first outer surface of the shell element and the channel-shaped cavity is constant or almost constant in every area. This makes it possible to achieve a contour-close and at the same time very homogeneous or targeted cooling of the components by the resulting hot forming tool.

In step a), the second outer surface of the shell element is also formed with a contour. The second outer surface of the shell element is therefore not flat but uneven, for example with elevations and/or depressions. This contour is also applied using the generative process. A second surface designed in this way improves the connection to the base body when the shell element or shell elements are back-cast in step b).

The contour of the second outer surface of the shell element has specially designed transition elements for improved connection of the shell element to the base body. For this purpose, in step a) transition elements are applied to the second outer surface of the shell element using the generative manufacturing process, which protrude from the second outer surface of the shell element and are designed in such a way that a material of the base body can flow behind the transition elements in some areas when the shell element is back-cast in step b). This makes it possible to achieve a particularly strong connection between the base body and the at least one shell element. The transition elements can have any suitable shape due to the flexible generative manufacturing process. In particular, the transition elements can be designed as lattice structures. Furthermore, the transition elements can be designed as projections with protruding, widened and/or spread head sections. The transition elements can be T-shaped or needle-head-shaped or can be arranged in sections or completely at an angle to the second outer surface of the shell element.

It is also preferably provided that the second outer surface of the shell element is melted at least in some areas before the back-casting in step b). By melting the second outer surface of the shell element in some areas, not only a positive connection is produced between the base body and the at least one shell element during the back-casting in step b), but also a material connection. This is particularly advantageous for particularly thin-walled shell elements.

The contour of the first outer surface of the shell element is preferably reworked after steps a) and b). The final contour, i.e. the desired contour of the active surface of the hot forming tool, is created. This can be done by milling or lasering, for example. Since material is usually removed from the first outer surface of the shell element, a certain allowance is planned and provided for in step a). This makes it possible to make the generative manufacturing process in step a) simpler. Furthermore, corrections or adjustments can be made easily to the first outer surface after steps a) and b) have been carried out.

According to the invention, a hot forming tool is also provided which has at least one base body and a shell element connected thereto. A first outer surface of the shell element has a contour by which an active surface of the hot forming tool is formed. The hot forming tool according to the invention is produced by a method according to one of claims 1 to 9.

Preferably, the hot forming tool has a plurality of shell elements arranged next to one another and connected to a base body.

It is also preferably provided that the base body and the at least one shell element have the same material and particularly preferably consist of the same material. This is particularly advantageous for a subsequent heat treatment, since the parameters of the two parts, namely the base body and the at least one shell element, are identical and in particular have the same melting points. For example, both the base body and the at least one shell element can have tool steel or consist of tool steel. Alternatively, both the base body and the at least one shell element can have a plastic or consist of plastic. Other materials are also possible.

Short description of the drawings

The invention is explained below using preferred embodiments as examples.

• 1: eine Schnittdarstellung durch ein Schalenelement,
• 2: eine Schnittdarstellung durch zwei aneinander gesetzte miteinander verbundene Schalenelemente,
• 3: eine Schnittdarstellung durch ein Warmumformwerkzeug mit zwei Schalenelementen,
• 4: eine Schnittdarstellung durch ein Warmumformwerkzeug mit Übergangselementen an der zweiten Außenfläche der Schalenelemente, und
• 5: eine Schnittdarstellung durch ein Warmumformwerkzeug beim Nachbearbeiten der Wirkfläche.

They show schematically:

• 1 : a cross-section through a shell element,
• 2 : a sectional view through two interconnected shell elements placed next to each other,
• 3 : a sectional view through a hot forming tool with two shell elements,
• 4 : a sectional view through a hot forming tool with transition elements on the second outer surface of the shell elements, and
• 5 : a sectional view through a hot forming tool during post-processing of the effective surface.

Preferred embodiments of the invention

In 1 a sectional view through a shell element 10 or through a section of a shell element 10 is shown. This shows a top view of a layer during the generative manufacturing process of the shell element 10. The shell element 10 is formed with a contour 14 of the first outer surface 12. After the hot forming tool 100 has been produced, the contour 14 forms the active surface or the pressure surface of the hot forming tool 100. On the inside, the shell element 10 has a second outer surface 13. The shell element 10 is produced layer by layer using the generative manufacturing process, with the channel-shaped cavity 15 being formed at the same time.

2 shows a sectional view through two shell elements 10 connected to one another. The two shell elements 10 are manufactured separately from one another using the generative manufacturing process. The cooling channel of the hot forming tool 100 runs through both shell elements 10. Each shell element 10 thus has a section of the cooling channel as a channel-shaped cavity 15. When the two shell elements 10 are assembled, the respective channel-shaped cavity 15 serves to align or center the two shell elements 10. The hot forming tool 100 can also have several, in principle any number, assembled shell elements 10. The two shell elements 10 are as in 2 shown connected to each other at a joint 17. For example, the two shell elements 10 can be welded together or be plugged into one another. In order to connect shell elements 10 to one another in a plug-like manner, the respective connecting surfaces have suitable contours or structures.

3 shows a sectional view through a finished hot forming tool 100 or a cross-sectional view through a section of a finished hot forming tool 100. The two interconnected shell elements 10 made of 2 were cast behind, whereby the base body 11 is formed. The shell elements 10 thus represent only the outer region, in particular the region that forms the active surface of the hot forming tool 100 and has the cooling channels. The core of the hot forming tool 100 is formed by the base body 11.

4 shows a cross-sectional view through a section of a hot forming tool 100 with exemplary shapes for transition elements 16 on the second outer surface 13 of the shell element 10. The transition elements 16 serve to connect the base body 11 more firmly to the shell element 10. The transition elements 16 are shaped in a particularly suitable manner such that the material of the base body flows in some areas around and in some areas behind the transition elements 16.

As in 4 As shown, the transition elements 16 can be designed, for example, in the shape of a needle head or T-shaped or in the shape of a lattice structure. Furthermore, sections inclined to the second outer surface 13 of the shell element 10 can be designed as transition elements 16.

5 shows a cross-sectional view through a section of a hot forming tool 100 during the post-processing of the active surface or the first outer surface 12 of the shell element 10. For this purpose, the contour 14 of the first outer surface 12 of the shell element 10 is post-processed with a milling head 18 and the final contour of the desired active surface for the hot forming tool 100 is created.

list of reference symbols

100

hot forming tool

10

shell element

11

base body

12

first outer surface of the shell element

13

second outer surface of the shell element

14

contour of the first outer surface

15

canal-shaped cavity

16

transition elements

17

joint

18

milling head

Claims (7)

Method for producing a hot forming tool (100) for press hardening, the method comprising the following steps: a) producing at least one shell element (10) of the hot forming tool (100) layer by layer by means of a generative manufacturing process, wherein a first outer surface (12) of the shell element (10) is formed with a contour (14) such that the first outer surface (12) of the shell element (10) with the contour (14) forms an active surface of the hot forming tool (100), wherein during layer-by-layer production at least one channel-shaped cavity (15) between the first outer surface (12) and a second outer surface (13) of the shell element (10) is introduced into the shell element (10) by means of the generative manufacturing process, wherein several shell elements (10) are produced layer by layer by means of a generative manufacturing process, wherein the second outer surface (13) of the Shell element is formed with a contour and transition elements (16) are applied to the second outer surface (13) of the shell element (10) by means of the generative manufacturing process, which transition elements protrude from the second outer surface (13) of the shell element (10) and are formed in such a way that a material of the base body (11) can flow behind the transition elements (16) in some areas when the shell element (10) is back-cast; b) back-casting the shell element (10) to produce a base body (11) of the hot forming tool (100) in such a way that the base body (11) forms a positive and/or material-locking connection with the shell element (10) in the region of its second outer surface (13), the composite of the at least one shell element (10) and the base body (11) forming the hot forming tool (100) or a segment of the hot forming tool (100). procedure according to claim 1 , characterized in that the generative manufacturing process is a stereolithography process, a selective laser melting process, a laser cladding process, or an electron beam melting process. procedure according to claim 1 , characterized in that several shell elements (10) are connected to one another before back-casting in step b). Method according to one of the preceding claims, characterized in that the channel-shaped cavity (15) is introduced in step a) following a course of the contour (14) of the first outer surface (12) of the shell element (10). Method according to one of the preceding claims, characterized in that before the back-casting in step b), the second outer surface (13) of the shell element (10) is melted at least in regions. Method according to one of the preceding claims, characterized in that the contour (14) of the first outer surface (12) of the shell element (10) is reworked after steps a) and b). Hot forming tool (100) comprising at least one base body (11) and a shell element (10) connected thereto, wherein a first outer surface (12) of the shell element (10) has a contour (14) by which an active surface of the hot forming tool (100) is formed, characterized in that the hot forming tool (100) is produced by a method according to one of the preceding claims, wherein the base body (11) and the shell element (10) have the same material.

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