Tool made from plastic

Abstract

The invention relates to tools (11, 12), made from plastic and a material with slide bearing properties inlaid in the plastic, whereby the plastic tools further comprise a component of inlaid aluminium. Said plastic tools are suitable for the moulding, in particular the deep-drawing of metallic workpieces (10), such as for example components of automobiles. The tools have a high pressure-resistance and wear resistance and permit deep-drawing with essentially small amounts of, or no, lubricants as a result of said slide bearing properties.

Description

The present invention relates to a tool made of a plastic and a material with lubricant properties embedded in the plastic. Tools within the meaning of the present invention are, in particular, forming tools, such as deep-drawing tools for the forming of metal components, such as automobile components.

Tools made of steel or gray cast iron are conventionally used for deep-drawing. For some time, plastics, such as plastics containing metallic fillers, have also been used for deep-drawing. An advantage of these plastics is that they are more cost-effective materials. However, it has been found that, for certain applications, such plastic-based tools can be used as deep-drawing tools not at all, or can only be used with restrictions. This is especially applicable to deep-drawing applications in which workpieces must be formed in large numbers, so that the tool is subject to substantial wear. Tools made of plastics also exhibit insufficient resistance to pressure in these application cases.

DE 93 18 272.4 U1 describes a tool for the non-cutting forming of workpieces, with the tool per se being made of a metallic material, especially gray cast iron, while a guide component of the tool, which has a slide face, is made of a duroplastic with a fiber or woven material insert and embedded laminar graphite. This is done to improve the lubricant properties and reduce wear.

The object of the invention lies in providing a tool made of plastic which, on the one hand, exhibits favorable lubricant properties and, on the other hand, also exhibits improved wear properties and high resistance to pressure.

This object is attained by providing a tool according to the invention having the features of the principal claim. According to the invention, the synthetic tool contains a component of embedded aluminum to achieve greater resistance to pressure and wear resistance, and, furthermore, an embedded material with lubricant properties, so that the tool essentially possesses a self-lubricating capacity. As a result, the use of an additional lubricant in the region between the forming tool and the workpiece to be formed is generally unnecessary. Experiments have shown that the serviceable life of the tool can be significantly improved by the embedded materials. Examples of possible materials with lubricant properties are graphite or molybdenum sulfide. The use of graphite powder is especially preferred. Aluminum can be contained in the synthetic tool as a filler, for example, in the form of aluminum powder or large-grained aluminum particles. Tools of this nature are preferably made with a correspondingly composed cast resin or from a block material.

According to a preferred embodiment of the invention, the tool contains a weight component of more than approximately 50% aluminum filler. The weight component of aluminum filler in the plastic mass used to produce the tool can be several times that of the plastic component. This weight component is preferably at least about 60%, preferably about 70% aluminum filler, preferably aluminum powder, relative to the total weight of the plastic compound.

The weight component of the material with lubricant properties embedded in the plastic is generally lower than the plastic component and/or the aluminum component of the plastic compound. The tool preferably contains a weight component of at least 20% to approximately 50% graphite powder relative to the weight component of the plastic contained in the tool, i.e.,. not relative to the total weight of the plastic compound, but relative to the pure plastic component. The weight component of the graphite, relative to the total weight of the material of which the tool is made, is preferably at least approximately 3% to approximately 15% graphite. The weight ratio between the graphite component and the aluminum component is preferably between 1:15 and 1:6.

Within the scope of the present invention, the production of tools for forming processes is preferred, especially of deep-drawing tools made of the plastic compound of the type stated above. They can be dies or hold-down devices for the deep-drawing of metal parts, for example. Embedding the material with lubricant properties prevents, during the deep-drawing of a metal plate, for example, which is stressed in this process in a tensile direction perpendicular to the direction of motion of the deep-drawing tool, particles, especially filler particles, from being torn out of the plastic matrix, resulting in cracks in the tool. It has already been mentioned that graphite in the form of graphite powder can be embedded in the plastic, as a material with lubricant properties. The use of graphite powder with a particle size between approximately 50 μm and approximately 250 μm has proven to be especially advantageous.

The tools according to the invention can essentially be made entirely of plastic having the stated embedded material; in other words, they are consistently made of a homogeneous plastic compound, thereby distinguishing them from the tools described in DE 93 18 272.4 U1 mentioned at the outset, in which only a front layer of the tool, referred to as a guide component, is made of a plastic with certain lubricant properties.

The features specified in the subclaims relate to preferred embodiments of the object attained according to the invention. Further advantages of the invention can be found in the following detailed description.

In the following, the present invention will be explained in greater detail, using exemplary embodiments with reference to the attached drawings, which show

FIG. 1 a highly schematically simplified perspective view to explain a deep-drawing process by means of a tool according to the invention;

FIG. 2 a second schematically simplified view to explain the deep-drawing process;

FIG. 3 a diagram, which shows the change in the modulus of elasticity when plastics with various fillers are used;

FIG. 4 a male die for deep-drawing valve covers for motors in perspective view;

FIG. 5 the corresponding female die for deep-drawing valve covers with a male die according to FIG. 4;

FIG. 6 valve covers deep-drawn by means of the male and female dies shown in FIGS. 4 and 5.

First reference is made to FIG. 1. The drawing shows, in a highly schematically simplified perspective view, an array of tools for deep-drawing a sheet metal component 10. An upper tool part 11 is provided for forming the sheet metal component 10 in a deep-drawing process, as well as a lower tool part 12 in the form of a female die that accepts the upper tool part 11. The upper tool part 11 is made of a plastic of the type according to the invention, which contains embedded aluminum particles 13, as well as embedded graphite powder 14, to achieve a self-lubricating effect during forming of the sheet metal component 10.

The upper tool part 11 was made with a cast resin composed of plastic, aluminum powder as filler, and graphite powder. In this process, 1 kg of plastic, 3 kg of aluminum powder and 200 g of graphite powder were used to produce a compound of this material totaling 4.2 kg. The particle size of the graphite powder varied between 50 and 250 μm. The plastic tool had very good lubricant properties and a 40% increase in resistance to pressure. The cracking that occurs in the front layer of tools made of other plastics with conventional fillers, such as sand and iron, which is caused by filler particles being torn out of the underlying matrix of the plastic compound during the deep-drawing process, did not occur when using tools made of the plastic according to the invention.

It was found that the deep-drawing tools made of the abovementioned plastic compound are suitable for forming workpieces in higher numbers, such as up to 100,000 or more.

FIG. 2 illustrates the forces acting on the tool that cause the stated cracking during deep-drawing with materials lacking adequate lubricant properties. In a highly schematically simplified sectional view, an upper tool part 11 is shown which, according to the invention, was made of a full cast material composed of a plastic of the invention containing aluminum and graphite powder as fillers. The lower tool part 15 was also cast from the plastic compound of the invention. Before entering the deep-drawing process, the sheet metal component 10 to be formed is located in the gap 16 between the upper tool part 11 and the lower tool part 15. During deep-drawing, the sheet metal component 10 to be formed is deformed, with forces acting in the direction of the arrow 17, perpendicularly to the direction of motion. As a result, the front surfaces 18, 19 of the two tools 11, 15 are subjected to shearing action. The graphite powder embedded in the plastic of the tools 11, 15 provides a lubricant effect and favorable sliding properties in the interface zone among the front surfaces 18, 19, the tools 11, 15 and the deep-drawn sheet metal component 10.

FIG. 3 illustrates the percentage change in the modulus of elasticity of tools made of various plastics, which was determined on the basis of compression tests within the scope of the invention. The modulus of elasticity of a plastic filled only with aluminum is shown in column 20 in the far left of the diagram, and is assigned a value of 100 as a relative reference quantity for the other plastics. The relative value of the modulus of elasticity for a PTFE filled with aluminum is shown in the second column from the right, which is identified by reference number 22, and it is evident that this value only amounts to about 60% of that of the plastic shown in column 20 in FIG. 3. For purposes of comparison, the moduli of elasticity for two plastics manufactured according to the invention are shown in FIG. 3. Column 23, at far right in the figure, shows the value for a plastic filled with aluminum and MoS₂ as the lubricant. It is evident that the modulus of elasticity is more than 20% greater than that of the plastic filled with aluminum, which is shown in column 20. The relative value of the modulus of elasticity for a plastic filled with graphite and aluminum is shown in column 21 (second from left in the figure). As is evident in the figure, this value is 40% higher than the modulus of elasticity for a plastic filled with aluminum, as shown in column 20 at the far left of the figure. The value shown in column 21 in FIG. 3 was reached by adding 20% graphite power to an aluminum-filled plastic, for which the value is shown in column 20. For deep-drawing experiments, a deep-drawing tool 30, shown in perspective in FIG. 4, was used to design, lay out and manufacture valve covers for a three-cylinder motor. FIG. 4 shows the underside of a deep-drawing die for valve covers 30, which is made with a plastic according to the invention. Deep-drawing experiments were conducted with this tool 30. Based on these experiments, it was determined that dimensional accuracy, serviceable life and the self-lubricating effect were significantly improved in comparison to tools made with other plastics. Tools made with conventional plastics were worn after a short period of time. As a result of the embedding of only about 20% graphite powder in a plastic filled with aluminum powder, significantly better friction and wear conditions were achieved with the tool 30 shown in FIG. 4. As is evident in FIG. 4, the deep-drawing die features two characteristic forming elements 31, 32 to produce the depressions and raised areas typical of the shape of the valve cover.

FIG. 6 shows examples of valve covers made of various materials, which were manufactured by means of the deep-drawing tool 30 shown in FIG. 4. The valve covers 40, 41, 42 shown in FIG. 6 were manufactured by forming sheets of titanium, aluminum and galvanized steel, each having a material thickness of 1 mm. The characteristic formed regions, namely the flat cylindrical depression 43 (or elevation, when the deep-drawn valve covers 41 shown in FIG. 6 are viewed from below), are easily recognizable in the depiction shown in FIG. 6. This formed region 43 can be matched to the forming element 32 of the deep-drawing tool 30 shown in FIG. 4. Accordingly, the formed region 44 can be matched to the forming element 31 of the deep-drawing tool 30 shown in FIG. 4. When the valve cover shown in FIG. 6 was deep-drawn with the tool 30 according to the invention, it was possible to achieve very good results with all three materials, sheet titanium, sheet aluminum, and galvanized sheet steel.

FIG. 5 shows the female die 50 corresponding to the deep-drawing die 30 shown in FIG. 4, for the production of valve covers 40, 41, 42, as shown in FIG. 6. The die 30 is lowered into the deep-drawing female die 50 shown in FIG. 5. The shape of the female die 50, approximately rectangular and rounded at the edges, which corresponds to the die 30, is recognizable in FIG. 5. Also recognizable is the formed region 51, which matches the approximately cylindrical forming element 32, as a depression in the deep-drawing tool serving as a female die 50. The female die 50 shown in FIG. 5 was also made with the plastic of the invention, which contains aluminum and graphite powder.

The advantages of the plastic tools made with the materials according to the invention, in comparison to conventional steel tools, lie, for example, in the material costs, which are reduced by up to about 70%. The plastics used to manufacture the tools are more easily machined, reducing the use of machinery in production of the tools. Energy and output requirements during the machining work required to produce the tools can be reduced by 65%, for example. The break-in time is also shorter than with steel tools, by up to 60%, for example. The use of plastics according to the invention for production of the tools leads to a substantial reduction in weight of up to 60%, for example, and thus to a reduction in loads on crane equipment. The tools can be modified more flexibly and cost-effectively, thereby achieving a high degree of cost, time, and energy savings. The tools are also suitable for recycling, because they can be fully recycled as filler material in the production of new plastic tools, thus eliminating disposal costs.

The elastic behavior of the plastics results in improvement of the quality of the formed workpieces. Embedding graphite in the plastic of the tools produces a self-lubricating effect on the contact surfaces of the tool. If it is even necessary to additionally use liquid lubricants during forming, the amount of lubricant necessary can be significantly reduced, such as by approx. 3 g/m². The frictional conditions during deep-drawing are improved by incorporating graphite powder into the plastic. As a result of the elimination of or reduction in liquid lubricants during deep-drawing, dirt accumulation in the work area is significantly reduced, thereby benefiting the environment.

LIST OF REFERENCE CHARACTERS

10 Sheet metal component

11 Upper tool part

12 Lower tool part

13 Aluminum particle

14 Graphite powder

15 Lower tool part

16 Gap

17 Arrow

18 Front surface

19 Front surface

20 Column

21 Column

22 Column

23 Column

30 Deep-drawing tool

31 Forming element

32 Forming element

40 Valve cover

41 Valve cover

42 Valve cover

43 Depression

44 Forming region

50 Deep-drawing female die

51 Deep-drawing region

Claims

1-14. (Canceled).

15. A tool made from a plastic compound, wherein said compound comprises a plastic component having embedded therein a material with lubricant properties and a component of aluminum.

16. The tool according to claim 15, wherein the component of aluminum comprises a filler selected from the group consisting of aluminum powder and aluminum particles.

17. The tool according to claim 15, wherein the material with lubricant properties is graphite or molybdenum sulfide.

18. The tool according to claim 17, wherein the material with lubricant properties is graphite.

19. The tool according to claim 18, wherein the graphite is graphite powder.

20. The tool according to claim 15, wherein the tool is made with a block material or a cast resin.

21. The tool according to claim 16, wherein the tool contains a weight component of more than approximately 50 percent aluminum filler.

22. The tool according to claim 16, wherein the aluminum filler is at least approximately 60 percent by weight relative to the total weight of the plastic compound.

23. The tool according to claim 22, wherein the aluminum filler is at least approximately 70 percent by weight relative to the total weight of the plastic compound.

24. The tool according to claim 22 or 23, wherein the aluminum filler is aluminum powder.

25. The tool according to claim 18, wherein the graphite is at least approximately 20 to approximately 50 percent by weight relative to the weight of the plastic component of the plastic compound.

26. The tool according to claim 18, wherein the graphite is at least approximately 3 to approximately 15 percent by weight relative to the plastic compound.

27. The tool according to claim 25 or 26, wherein the graphite is graphite powder.

28. The tool according to claim 18, wherein the weight ratio of the graphite component to the aluminum component is between approximately 1:15 and approximately 1:6.

29. The tool according to claim 28, wherein the graphite and the aluminum are in powder form.

30. The tool according to claim 19, wherein the graphite powder has a particle size between approximately 50 μm and approximately 250 μm.

31. The tool according to claim 15, wherein the tool is a forming tool.

32. The tool according to claim 15, wherein the tool is a deep-drawing tool.

33. The tool according to claim 15, wherein the tool is a die, a hold-down device or a female die for the deep-drawing of metal components.

34. A process for the formation of a part comprising the steps of obtaining a workpiece and subjecting the workpiece to the action of a tool according to claim 15.

35. A process according to claim 34, wherein the process is a deep-drawing process, and the workpiece is sheet metal.