Process and Installation for Producing a Component from Sheet Magnesium

Abstract

The invention relates to a method and an installation for producing a component from sheet magnesium, comprising a forming tool, which comprises a punch and a die, for forming a semi-finished product made of sheet magnesium, in particular a semi-finished product in the form of a sheet magnesium blank, and a device for heating the semi-finished product to an elevated temperature, preferably to a temperature of at least 200° C., prior to the forming. In order to reduce the component costs, the invention proposes that the forming tool is designed without an internal heat source, is provided with a semi-finished product holder on which the heated semi-finished product can be placed in the forming tool without direct contact with the punch and the die, and comprises a drive which brings about a closing speed of the punch and the die in the range of 15 mm/s to 500 mm/s.

Description

The invention relates to a method for producing a component from sheet magnesium by forming a semi-finished product made of sheet magnesium, in particular a semi-finished product in the form of a sheet magnesium blank, in which the semi-finished product is heated to an elevated temperature, preferably to a temperature of at least 200° C., prior to the forming and is formed in a forming tool comprising a punch and a die. The invention further relates to an installation for producing a component from sheet magnesium.

Owing to the hexagonal lattice structure of magnesium, magnesium sheets can only be formed with difficulty at room temperature. In particular, components made of sheet magnesium which are to have a complex three-dimensional shape must be hot formed to avoid cracks. In general, magnesium blanks are formed in the heated state using tempered tools.

In the prior art, various configurations of tempered tools for forming magnesium sheets are known. For example, Korean patent application 10 2006 00 57 901 A discloses a press for hot forming sheet magnesium, which press is provided with an electric resistance heating device. In this case, the resistance heating device is integrated in an upper tool part (die) and in an associated sheet holder.

In comparison with conventional tools used in cold forming, tempered forming tools involve a higher level of technical complexity and thus higher investment and higher operating costs. This has a negative impact on the costs of components made of magnesium.

The object of the present invention is to provide a method and an installation for producing a three-dimensional component from sheet magnesium which allow low component costs.

According to the invention, this object is achieved by a method having the features of claim 1 and by an installation having the features of claim 9.

The method according to the invention is characterised in that a forming tool designed without an internal heat source being used for forming the semi-finished product heated to an elevated temperature, preferably to a temperature of at least 200° C., the heated semi-finished product being placed in the forming tool without direct contact with the punch and the die and is then formed at a forming speed in the range of 15 mm/s to 500 mm/s.

The installation according to the invention is accordingly characterised in that the forming tool thereof being designed without an internal heat source and being provided with a semi-finished product holder on which the semi-finished product heated to an elevated temperature, preferably to a temperature of at least 200° C., can be placed in the forming tool without direct contact with the punch and the die, and comprising a drive which brings about a closing speed of the punch and the die in the range of 15 mm/s to 500 mm/s.

Owing to the present invention, the additional complexity caused by the tempering of the forming tool by means of an internal heat source does not apply. The invention provides for the processing of a heated magnesium semi-finished product in a forming tool without an internal heat source.

The tool and operating costs and thus ultimately the component costs are reduced considerably as a result, In particular when producing components in relatively small quantities, the profitability of the component can be increased substantially owing to the reduction of the tool costs.

Through tests, the inventors were able to show that a three-dimensionally shaped component can be produced without cracks from a magnesium blank, which for example is heated to 250° C., in an untempered forming tool when excessive temperature losses are avoided prior to the actual forming process by preventing the heated plate from being deposited directly'on the punch or the die when the blank is placed (laid) in the forming tool, and the subsequent forming takes place at a relatively high forming speed (15-500 mm/s).

The average cooling speed for a 2.00 mm thick magnesium sheet which is heated to a temperature in the range of 200° C. to 250° C. is, for example in air at room temperature of 20° C., between 2 and 12 K/s. Owing to this relatively small temperature loss, it can be ensured in a suitable transfer system that the heated semi-finished product or the heated blank has, prior to the forming, a sufficiently high starting temperature to allow a error-free, in particular crack-free component with given degrees of deformation.

The use according to the invention of an untempered tool for forming heated magnesium blanks also has positive effects with regard to the dimensional accuracy and the handling of the components produced in this manner. This is because, owing to the considerably reduced temperature which the component has when it is removed from the untempered forming tool, the component has greater dimensional stability in comparison with a component produced in a tempered tool and is thus less susceptible to undesired deformations when it is removed from the forming tool and during subsequent handling, and this has a positive effect on the dimensional accuracy of the component. In addition, the components produced according to the invention are easier to handle owing to the considerably reduced temperature which they have when they are removed from the untempered forming tool. In this case, conventional transfer systems can be used which are not temperature-stable or have comparatively low temperature stability.

In this context, an advantageous configuration of the method according to the invention provides that, as a forming tool, a forming tool is used in which the punch and/or die comprise an active cooling apparatus. As a result, the removal temperature of the component can be lowered more rapidly, the dimensional accuracy of the component can be improved further and the handling of the component can be simplified further. This active cooling of the punch and/or the die is advantageous in particular when comparatively large quantities are to be formed in a predetermined time, that is to say when the desired forming capacity is to be relatively high. However, heating of the forming tool owing to the heated semi-finished product during production can also be tolerated when there are no negative effects on the dimensional accuracy of the finished component as a result.

An advantageous configuration of the invention, allowing that the heated sheet magnesium semi-finished product must not deposited directly on the punch or the die, consists in that the heated semi-finished product is placed on a semi-finished product holder associated with the forming tool, and therefore the essential surface region of the heated semi-finished product is arranged in a self-supporting manner in the ambient atmosphere between the punch and the die and with spacing therefrom prior to the actual forming process. In this case the ambient atmosphere, preferably ambient air, acts as a heat insulator. This ensures that the heated semi-finished product undergoes only very slight cooling prior to the actual forming process. In this case the semi-finished product holder is designed, for example, as an active sheet holder which is positioned above a punch associated with the die.

Another advantageous configuration of the method according to the invention is characterised in that, as a semi-finished product holder, a semi-finished product holder is used, the surface region of which touching the heated semi-finished product has a surface structure which is porous or comprises indentations. This reduces the heat or temperature loss of the heated semi-finished product caused by conduction of heat from the heated semi-finished product to the semi-finished product holder.

Additionally or alternatively, another advantageous configuration of the method according to the invention provides that, as a semi-finished product holder, a semi finished product holder is used, the surface region of which touching the heated semi-finished product is made of a material, or is provided with a coating, which has a thermal conductivity of at most 20 W/mK at 30° C. to 100° C. ambient temperature. This, too, reduces the heat or temperature loss caused by conduction of heat from the heated semi-finished product to the semi-finished product holder.

Another advantageous configuration of the method according to the invention is characterised in that, as a die, a die is used which has, in its forming face which faces the heated semi-finished product to be formed, indentations which bring about a reduction of the contact face which faces the heated semi-finished product. The indentations or the air contained therein has/have a heat-insulating effect, and therefore the heat or temperature loss of the heated semi-finished product can be reduced in this manner.

Another advantageous configuration of the method according to the invention provides that the semi-finished product is transported directly into the forming tool by means of a transfer device which is provided with a conductive heat source. As a result, the semi-finished product to be formed can be given a sufficiently high starting temperature prior to the forming and at the same time the temperature loss of the semi-finished product prior to the forming can be minimised.

Owing to the use of an untempered forming tool, cost-effective integrated component trimming during the forming of the semi-finished product which consists of sheet magnesium is also conceivable. Another advantageous configuration of the method according to the invention is accordingly characterised in that, during the forming, the semi-finished product is simultaneously trimmed by means of at least one cutting member integrated in the forming tool.

Other preferred and advantageous configurations of the installation according to the invention are given in the dependent claims.

The invention will be described in detail below with reference to drawings showing a plurality of embodiments, in which:

FIG. 1 shows schematically an installation or a process line for producing three-dimensionally shaped components from magnesium semi-finished products;

FIG. 2 shows schematically another embodiment of a process line for producing three-dimensionally shaped components from magnesium semi-finished products; and

FIG. 3 is a schematic vertical sectional view of a forming tool according to the invention.

The installation shown in FIG. 1 basically comprises a device 1 for heating a semi-finished product 2 made of sheet magnesium and a forming tool 3, without an internal heat source, for forming the heated semi-finished product 2. The semi-finished product 2 to be formed may for example be in the form of a sheet magnesium blank.

In this case, the device 1 for heating the semi-finished product 2 is designed as a continuous furnace, preferably as a roller hearth furnace. The continuous furnace or roller hearth furnace 1 is provided with inductors, radiant heaters, hot-air burners and/or recuperator burners. It is also conceivable to use infra-red radiators to heat the semi-finished product 2 to be formed.

In the embodiment shown, sheet magnesium blanks 2 to be formed are removed from a conveyor belt or a supply stack 4 and heated in the continuous furnace 1 to an elevated temperature which is selected such that the workpiece temperature is substantially still above 180° C. to 220° C. at the end of the forming. For this purpose, the sheet magnesium blank or the semi-finished product 2 is heated for example to a temperature in the range of 230° C. and 260° C.

The heated semi-finished product 2 is then grasped by means of a transfer device 5, preferably a robot, in the region of the outlet of the continuous furnace and laid in the forming tool 3 without direct contact with the punch 3.1 and the die 3.2. For this purpose the forming tool 3 is provided with a semi-finished product holder (sheet holder) 3.3 which, when the forming tool 3 is open, is positioned above the punch head, such that the semi-finished product 2 deposited thereon touches neither the punch 3.1 nor the die 3.2. In FIG. 1 it can be seen that the blank 2 placed in the forming tool is initially deposited on the semi-finished product holder 3.3 and is arranged with spacing from both the punch 3.1 and the die 3.2. This prevents excessively rapid cooling of the heated sheet magnesium blank 2.

The tool 3 is then closed in order to form the heated semi-finished product into a shape which is predetermined by the punch 3.1 and the die 3.2. The forming takes place at a relatively high forming speed, such that the temperature loss of the heated workpiece (semi-finished product) 2 during the forming is also kept low. In order to achieve a correspondingly high forming speed, the forming tool 3 comprises a drive (not shown) which brings about a closing speed of the punch 3.1 and die 3.2 in the range of 15 mm/s to 500 mm/s.

After the forming tool 3 is opened, the component 2′ produced in this manner is removed from the forming tool 3 by means of a suitable transfer device 6, preferably a robot, and optionally deposited or stacked on a transport means, for example a transport plate or the like.

Should the temperature loss be too high for the component geometry or the degree of deformation owing to the use of conventional tool steels, the tool 3 can, at least in sub-regions, consist of materials having relatively low thermal conductivity and/or have a coating which has low thermal conductivity. Besides ceramic materials, special tool steels can also meet these requirements. For example, the punch 3.1 and/or the die 3.2 of the forming tool 3 can, at least in sub-regions, be made of a material which has a thermal conductivity of at most 20 W/mK at 30° C. to 100° C. ambient temperature. Alternatively, the thermal conductivity can also be reduced by means of a suitable coating.

Another preferred configuration of the installation according to the invention involves the surface region 3.31 of the semi-finished product holder 3.3, which surface region touches the heated semi-finished product 2, having a surface structure which is porous or comprises indentations 3.32. This further reduces the temperature loss of the heated semi-finished product 2. Additionally or alternatively, it is provided that the surface region 3.31 of the semi-finished product holder 3.3, which surface region touches the heated semi-finished product 2, is made of a material which has a relatively low thermal conductivity, or is coated with such a material. The thermal conductivity of the material used for the semi-finished product holder 3.3 or of a coating used for the semi-finished product holder 3.3 is preferably at most 20 W/mk at 30° C. to 100° C. ambient temperature.

FIG. 2 shows another embodiment of an installation according to the invention for producing a three-dimensionally shaped component 2′ from sheet magnesium. This installation differs from the installation according to FIG. 1 in that a sheet magnesium blank 2 to be formed is heated not in a continuous furnace but in or by means of a robot-like transfer device 5′. For this purpose, the transfer device 5′ is provided with a heating apparatus or conductive heat source 5.1 such that the magnesium sheet 2 is heated while it is being transported from a supply stack 4 or a conveyor belt into the forming tool 3. In this case, the conductive heat source or heating apparatus 5.1 is integrated into gripping or holding members of the transfer device 5′, by means of which members the magnesium sheet (semi-finished product) 2 is gripped and transported to the forming tool 3 and deposited therein.

The forming tool 3 in the installation shown in FIG. 2 is designed as per the forming tool 3 in the installation according to FIG. 1, and therefore reference is made in this respect to the above description of FIG. 1 in order to avoid repetition.

The installations shown schematically in FIGS. 1 and 2 are process lines which operate substantially continuously. It is not shown that it is also possible to work off a coil, that is to say that the material is wound off a coil and, depending on the existing process line, either rectangular blanks are cut to length, for example when trimming takes place during or after the forming, or shaped blanks, the contour ends of which substantially correspond to specified sizes of the finished component.

FIG. 3 is a schematic vertical sectional view of a forming tool 3 according to the invention which can be used for example in the installation according to FIG. 1 or 2. The forming tool, which is shown open, again comprises a punch 3.1 and a die 3.2 for forming a sheet magnesium blank 2. The forming tool 3 does not contain an internal heat source. It is provided with a semi-finished product holder (blank holder) 3.3 on which the heated blank 2 can be placed without direct contact with the punch 3.1 and the die 3.2. The surface region 3.31 of the semi-finished product holder 3.3, which surface region serves as a depositing surface for the heated blank 2, is initially located above the punch 3.1 when the forming tool 3 is in the open, loading state. The surface region 3.31 of the semi-finished product holder 3.3 has a surface structure provided with groove-shaped recesses or indentations 3.32. In addition, recesses or indentations 3.21 are also formed in the surface of the cavity of the die 3.2, which cavity receives the punch head. The recesses or indentations 3.32 and 3.21 define air gaps or air ducts which have a heat-insulating effect and thus prevent rapid heat or temperature loss of the heated blank 2. By contrast, the surface, facing the blank 2, of the punch 3.1 which is moved into the cavity of the die 3.2 in order to form the blank 2, does not comprise any indentations forming air ducts, since in this case this punch surface is the actual shaping surface of the forming tool 3.

In order to keep the temperature of the component 2′ to be removed from the forming tool 3 low in the case of relatively large quantities of components 2′ to be produced from sheet magnesium, the punch 3.1 and/or the die 3.2 can also be provided with an active cooling system (not shown). A cooling system of this type can be integrated in the punch 3.1 and/or the die 3.2 for example by means of a crown construction and/or by means of cooling ducts.

Claims

1. A method for producing a component from sheet magnesium by forming a semi-finished product made of sheet magnesium in which the semi-finished product is heated to an elevated temperature, prior to the forming and is formed in a forming tool comprising a punch and a die, wherein the forming tool used for forming the heated semi-finished product is designed without an internal heat source, the heated semi-finished product is placed on a semi-finished product holder associated with the forming tool without directly contacting the punch and the die, the semi-finished product holder is designed as an active sheet holder and is positioned above the punch associated with the die, and the heated semi-finished product placed on the semi-finished product holder is then formed at a forming speed in the range of 15 mm/s to 500 mm/s.

2. (canceled)

3. The method according to claim 1, wherein the semi-finished product holder comprises a surface region that touches the heated semi-finished product and has a surface structure which is porous or comprises indentations.

4. The method according to claim 1, wherein the semi-finished product holder comprises a surface region that touches the heated semi-finished product and is made of a material, or is provided with a coating, which has a thermal conductivity of at most 20 W/mK at 30° C. to 100° C. ambient temperature.

5. The method according to claim 1, wherein the die has, in its forming face which faces the heated semi-finished product to be formed, indentations which bring about a reduction of the contact face which faces the heated semi-finished product.

6. The method according to claim 1, wherein a forming tool is used in which the punch, the die, or both comprise an active cooling apparatus.

7. The method according to claim 1, wherein the semi-finished product is transported directly into the forming tool by means of a transfer device which is provided with a conductive heat source.

8. The method according to claim 1, wherein, during the forming, the semi-finished product is simultaneously trimmed by means of at least one cutting member integrated in the forming tool.

9. An installation for producing a component from sheet magnesium, comprising a forming tool, which comprises a punch and a die, for forming a semi-finished product made of sheet magnesium the forming tool being designed without an internal heat source, and a device for heating the semi-finished product to an elevated temperature prior to the forming, wherein the forming tool further comprising a semi-finished product holder, designed as an active sheet holder which can be positioned above the punch and on which the heated semi-finished product can be placed in the forming tool without direct contact with the punch and the die, and a drive which brings about a closing speed of the punch and the die in the range of 15 mm/s to 500 mm/s.

10. The installation according to claim 9, wherein a surface region of the semi-finished product holder, which surface region touches the heated semi-finished product, has a surface structure which is porous or comprises indentations.

11. The installation according to claim 9, wherein a surface region of the semi-finished product holder, which surface region touches the heated semi-finished product, is made of a material, or is provided with a coating, which has a thermal conductivity of at most 20 W/mK at 30° C. to 100° C. ambient temperature.

12. The installation according to claim 9, wherein the punch, the die, or both of the forming tool, at least in sub-regions, are made of a material, or provided with a coating, which has a thermal conductivity of at most 20 W/mK at 30° C. to 100° C. ambient temperature.

13. The installation according to claim 9, wherein the punch, the die, or both of the forming tool comprise an active cooling apparatus.

14. The installation according to claim 9, wherein a transfer device provided with a conductive heat source is associated with the forming tool, by means of which transfer device the semi-finished product to be formed can be placed directly on the semi-finished product holder.

15. The installation according to claim 9, wherein indentations which bring about a reduction of a contact face which faces the heated semi-finished product are formed in the die.

16. The installation according to claim 9, wherein the forming tool is provided with at least one cutting member.

17. The method according to claim 1, wherein the semi-finished product is a sheet of magnesium blank.

18. The method according to claim 1, wherein the semi-finished product is heated to a temperature of at least 200° C.

19. The installation according to claim 9, wherein the semi-finished product is a sheet magnesium blank.

20. The installation according to claim 9, wherein the device heats the semi-finished product to a temperature of at least 200° C.