A tool portion of a forming tool and a method for manufacturing such a tool portion

THE BACKGROUND OF THE INVENTION AND PRIOR ART

The present invention relates to a tool portion of a forming tool and a method for manufacturing such a tool portion. The tool portion comprises a material piece having a specifically shaped surface.

Hydroforming is a process which mainly is used for manufacturing components of metal, which many times have a complicated geometric shape. A conventional tool for hydroforming of tubular products usually consists of two tool halves which are movably arranged in relation to each other between an open position and a closed position. Each of the tool halves comprises a portion with a recess having a specifically shaped surface. When the tool halves are in an open position, a tubular blank is applied in one of the tool halves. Thereafter, the tool halves are closed whereupon a liquid at a very high pressure is supplied inside the tubular blank. The tubular blank expands radially outwardly and is formed plastically after the surfaces of the recesses in the respective tool halves wherein a tubular product is provided.

A conventional hydroforming tool for forming of sheet-shaped products comprises a first tool half provided with a portion comprising a recess with a specifically shaped surface and a second tool half which comprises a space for supplying of a liquid with a very high pressure. A sheet-shaped blank is applied in a parting line between the tool halves, whereupon the liquid is supplied to the first tool half with a high pressure. Thereby, the liquid presses the sheet-shaped blank down into the recess of the

second tool half such that the sheet-shaped blank is plastically formed after the surface of the recess wherein a sheet-shaped product is provided.

The tool surfaces, which are used for giving hydroformed products a desired shape, are subjected to very high pressures and thus large mechanical stresses. In order to enable hydroforming of a large number of products to products with an even and high quality, it is required that the tool surfaces maintain its struc- ture. Consequently, the surfaces must not be worn. Conventional tools for hydroforming of products in large series are therefore manufactured of hard materials which are very resistant to wear. Such materials are normally expensive to procure at the same time as the strength properties of the materials make the manufacturing of the tool surfaces difficult to perform. The cost for manufacturing of conventional hydroforming tools is therefore high.

Also the costs for manufacturing of other kinds of forming tools, such as pressing tools and tools for forming of plastics, are also relatively high.

SUMMARY OF THE INVENTION

The object with the present invention is to provide a tool portion of a forming tool which can be manufactured to a relatively low cost at the same time as it can be used for forming a large number of products.

This object is achieved by the tool portion of the initially mentioned kind, which is characterised in that it comprises a material layer which is formed after the specifically shaped surface of the material piece during a hydroforming process, and that the material layer comprises a surface which is intended to come in contact with and form blanks which are formed by means of the tool portion. Hydroformning is a manufacturing process in which

it is possible to manufacture a material layer such that it obtains a desired shape and thickness with a very high precision. By using the specifically shaped surface of the material piece for hy- droforming the material layer, it provides a surface which very exactly corresponds to the specifically shaped surface of the material piece. Thereby, the material layer can be applied in the recess of the material piece and the final forming tool can be used for hydroforming products, press forming products or forming plastics. The material layer protects thereby the specifically shaped surfaces of the material piece such that they are not worn. Advantageously, the material layer is manufactured of a hard material having good properties against wear. Thereby, the material layer may be used for forming a large number of products. The material layer may also be exchanged and replaced by a new one in a simple manner if it becomes worn.

According to a preferred embodiment of the present invention, the material layer comprises a strain hardened material. The fact that the material layer is strain hardened implies that it has been manufactured of a material having strain hardening properties when it is loaded above its yield point during a cold working process which in this case is a hydroforming process. The material layer thereby has been subjected to a plastic deformation during which dislocations in the material layer provide mutual motions. When the dislocations are moving, they gradually prevent each other from performing further motions. In this manner, a successively increased grade of strain hardening is provided which is related to the plastic deformation of the material layer. By choosing to manufacture the material layer of a material hav- ing good strain hardening properties, it is possible to give the material layer a considerable hardness and a good capacity to withstand wear also when the material layer is relatively thin. Hydroformning is a cold working process in which it is possible, with a very high precision, to manufacture a material layer with a desired grade of strain hardening.

According to an embodiment of the present invention, the material layer comprises a strain hardened metal material. The most metals provide at least a certain strain hardening during a hy- droforming process and thereby obtain properties such that they advantageously can be used as material layer in the tool portion. Preferably, the material layer is a strain hardened steel material. Steel materials are normally hard materials with good properties against wear also in a non-strain hardened state. In a strain hardened state, the majority of steel materials may pro- vide a very hard surface which provides very good properties against wear. Advantageously, the material layer comprises a strain hardened austenitic stainless steel. Austenitic stainless steels are a group of steels which provide very good strength properties in a strain hardened state. Also a very thin material layer, which consists of a strain hardened austenitic stainless steel, may form a material layer having a very hard and wear resistant surface.

According to another preferred embodiment of the present in- vention, the tool portion comprises a material piece which comprises a surface forming an underlying support surface for the material layer. At least when the material layer is relatively thin, it is required that it has an underlying support surface which provides stability to the material layer. Advantageously, the ma- terial piece comprises a material having the property that it is softer and more easy to work than the material used in the material layer. Consequently, the material piece is not intended to come in direct contact with the products which are formed by means of the tool. It can thus be manufactured of a softer and more easy to work material than that used in the material layer. However, the material piece must have the property of being able to form a stable underlying surface for the material layer. The material piece thus ought to be considerably thicker than the material layer. Advantageously, the material piece may comprise aluminium. Aluminium is an easy to work material which in an easy manner may be given a support surface with a

desired shape by means of conventional working methods such as milling. A material piece of aluminium may also provide a support surface with a relatively complex shape in a relatively uncomplicated manner and to a low cost. Alternatively, the ma- terial piece may, for example, comprise a plastic material or a composite material.

According to an embodiment of the present invention, the tool portion comprises a material piece and a material layer which are loosely connected to each other. Consequently, the material piece has a support surface having a shape corresponding to the abutting surface of the material layer. A form fitting is thus obtained between said surfaces which can be used for holding the material layer in a desired position in relation to the material piece. In many cases, such a loose connection between the material piece and the material layer is fully enough to enable the tool portion to be used at hydroformning processes. Alternatively, the tool portion may comprise a material piece and a material layer which are fixedly connected to each other by means of a fastening means. In order to guarantee that the material piece and the material layer are maintained in an intended mutual position in relation to each other during a large number of forming processes, such a fastening means may be applied between the contact surfaces of the material pieces and of the ma- terial layer. The fastening means may be a glue having suitable properties.

According to another preferred embodiment of the present invention, the forming tool comprises at least two tool parts where at least one of the tool parts comprises a tool portion according to the above. However, two tool parts are normally used for hy- droforming of both sheet shaped products and tubular products. Consequently, the tool portion according to the invention may be used both for, for example, hydroforming sheet-shaped products and tubular products.

The above mention object is also achieved by the method which comprises the steps of working a material piece such that it provides a recess with a specifically shaped surface, using the material piece with its specifically shaped surface for hydroforming a blank such that a product is formed which comprises a material layer, and connecting the material layer and the material piece such that they form a tool portion where the material layer comprises a surface which is intended to come in contact with and form blanks which are formed by means of the tool. Pref- erably, the tool portion here comprises a material piece which is manufactured of an easy to work material. It is thus simple, with conventional working methods, such as milling, to provide the material piece with the specifically shaped surface. Thereafter to hydroform a material layer by means of the specifically shaped surface of the material piece is a manufacturing step which also is easy to perform. The material layer thus provides a surface with a shape corresponding to the specifically shaped surface of the material piece. Advantageously, the material layer comprises a material which has been strain hardened during the hy- droforming process. The strain hardened material layer of the tool portion thus forms a hard and wear resistant surface for hydroforming of tubular and sheet-shaped products. Such a material layer may be used for forming a very large number of sheet- shaped and tubular products substantially without being worn. If the material layer is being worn, it can easily be replaced by a new material layer which is hydroformed by means of the specifically shaped surface of the material piece.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following preferred embodiments of the invention are described as examples with reference to the attached drawings, in which:

Fig. 1 shows a tool with a tool portion according to the present invention for hydroforming of a sheet-shaped product,

Fig. 2-4 shows different steps of a method for manufacturing of the tool portion in Fig. 1 ,

Fig. 5 shows a tool with two tool portions according to the present invention for hydroforming of a tubular product,

Fig.6-9 shows different steps of a method for manufacturing of the two tool portions in Fig. 5 and

Fig. 10 shows a tool for hydroforming of two sheet blanks and

Fig. 1 1 shows a tool for hydromechanical forming.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 shows a tool for hydroforming of sheet-shaped products which comprises a first tool part 1 and a second tool part 2. However, the tool can comprise more tool parts. The tool parts 1 and 2 are movably arranged in relation to each other between an open position and a closed position. Fig. 1 shows the tool parts 1 , 2 in the closed position. A sheet-shaped blank 3 has here been applied in a plane having an extension between the tool parts 1 , 2. The second tool part 2 consists in this case of a unit in the form of a tool portion 4. The tool portion 4 comprises a recess 5 which is defined by a surface 6 which is intended to come in contact with and form sheet-shaped blanks 3 which are hydroformed by means of the tool. The surface 6 of the recess 5 is formed by a material layer 7 of a strain hardened material. Advantageously, the material layer 7 is manufactured of a material having good strain hardening properties. Such a material can be a metal material in the form of an austenitic stainless steel which is a group of steel materials having very good strain hardening properties. Except said material layer 7, the tool portion 4 consists of a material piece 8. The material piece 8 can

consist of a homogeneous material body. The material piece 8 thus forms an underlying support for the material layer 7. Preferably, the material piece 8 consists of a material which is considerably softer and more easy to work than the material which is used in the material layer 7. Advantageously, the material piece 8 can consist of aluminium. Aluminium is a relatively inexpensive material which is very formable and easy to machine work to a desired shape.

The first tool half 1 comprises a space 9 which is connected to openings, not shown, for the supply of a liquid with a very high pressure. The tool parts 1 , 2 are during a hydroforming process held together in the closed position by a power member, not shown, with a very large force. The tool parts 1 ,2 thus hold the edge portions of the sheet-shaped blank 3 in a fixed position during a hydroforming process. When the hydroforming process is started, liquid is supplied to the space 9. Since the liquid has a very high pressure, it presses the sheet-shaped blank 3 down into the recess 5 of the second tool part 2. Thereby, the sheet- shaped blank 3 is deformed plastically and is formed after the surface 6 of the recess 5.

Fig. 2-4 show a method for manufacturing the above described tool portion 4. A material piece 8 of an easy to work material is initially provided with a recess 10 having a specifically shaped surface 1 1 . Such a material piece 8 is shown in Fig. 2. Consequently, the material piece 8 consists suitably of an easy to work material, which may be aluminium. It is thus relatively simple to provide the material piece 8 with a recess 10 having a specifi- cally shaped surface 1 1 by means of conventional working methods. Thereafter, the material piece 8 with its recess 10 and specifically shaped surface 1 1 is used as a second tool part for hydroforming a sheet-shaped blank 12, which is shown in Fig. 3. In this case, a thin sheet blank 12 manufactured of a material having good strain hardening properties is suitably used. When a liquid with a high pressure is supplied to the space 9 of the

first tool half 1 , the sheet blank 12 is pressed down in the recess 10 of the material piece 8 and formed after the specifically shaped surface 1 1 . Since hydroforming is a cold working process, the sheet-shaped blank 12 provides a strain hardening such that a sheet-shaped product is formed in the form of a strain hardened material layer 7 which covers the recess 10 of the material piece 8. The strain hardened material layer 7 thus provides a hard surface 6 having good properties against wear.

The manufactured tool portion 4 is shown in Fig. 4. When a thin sheet-shaped blank 12 has been used, an even thinner material layer 7 is obtained which at least covers the specifically shaped surface 10 of the material piece 8. Such a material layer 7 can have a thickness of 0,05 mm - 1 mm. In the cases, when the ma- terial layer 7 is very thin, it provides a recess 5 and an inner surface 6 which have a substantially completely identical shape as the recess 10 and inner surface 1 1 of the material piece 8. The material layer 7 is here loosely connected to the material piece 8. Since the shape of the material layer 7 corresponds to the shape of the recess 10 of the material piece 8, they are held form fit together in a desired mutual position in which they form said tool portion 4. If thicker material layers 7 are used, consideration ought to be taken to the thickness of the material layer 7 since the surfaces 1 1 of the recess 10 are formed in the material piece 8 such that the final recess 6 and inner surface 5 of the tool portion 4 obtains a desired dimension.

Consequently, the tool portion 4 comprises a material layer 7 of a strain hardened material which is intended to comprise the surface 6 of the tool portion 4 for forming of sheet-shaped products. Since the strain hardened material layer 7 is very hard and resistant, the strain hardened surface 6 can be used to form a very large number of sheet-shaped products substantially without the surface 6 being worn. Consequently, the tool portion 4 comprises also a material piece 8 which is manufactured of an easy to work material. With such a choice of material, it is rela-

tively easy to provide the material piece 8 with the recess 10 and the specifically shaped surface 1 1 by means of conventional working methods such as milling. Thereafter hydroforming a material layer 7 on the material piece 8 is a manufacturing step which also is easy to perform. The material layer 7 thus provides a surface 6 which substantially has the same shape as the specifically shaped surface of the material piece 1 1. The tool portion 4 can thus in a simple manner be provided with a strain hardened hard surface 6 having a desired form.

Fig. 5 shows a tool for hydroforming of tubular products. The tool comprises a first tool part 21 and a second tool part 22, which are movably arranged in relation to each other between an open position and a closed position. However, the tool can comprise more than two tool parts. The tool parts 21 , 22 are in the closed position in Fig. 5. The first tool part 21 comprises a first tool portion 24a which comprises a recess 25a defined by a surface 26a. The second tool half 22 comprises in a corresponding manner a second tool portion 24b which comprises a recess 25b defined by a surface 26b. The surface 26a of the first tool portion 24a and the surface 26b of the second tool portion 24b are intended to come in contact with and form tubular blanks 23 which are applied in the space which is formed by the recesses 25a, b of the tool portions 24a, b.

The surface 26a of the first tool portion 24a and the surface 26b of the second tool portion 24b are formed by material layers 29a, b which comprise a strain hardened material. Advantageously, the material layers 29a, b are manufactured of materi- als having good strain hardening properties. The material layers 29a, b can thus, for example, consist of a strain hardened steel material in the form of a strain hardened austenitic stainless steel. Except the material layers 29a, b, the respective tool portions 24a, b consist of a material piece 30a, b. The respective material pieces 30a, b can consist of a homogeneous material body which forms an underlying support for the material layers

29a, b. The material pieces 30a, b consist suitably of a material which is softer and more easy to work than the material used in the material layers 29a, b. Advantageously, the material pieces 30a, b can consist of aluminium. When a hydroforming process is to be performed, a liquid with a very high pressure is supplied to an inner space 31 of the tubular blank 23. The tool parts 21 , 22 are held together during the hydroforming process in the closed position by means of power members, not shown. The liquid pressure presses the tubular blank 23 radially outwardly such that it is deformed plastically and is formed after the surfaces 26a, b of the tool portions 24a, b.

Fig. 6-9 shows a method for manufacturing of the above described tool portions 24a, b. The method comprises the step of working two material pieces 30a, b such that each of them is provided with a recess 32a, b having a specifically shaped surface 33a, b. Two such worked material pieces 30a, b are shown in Fig. 6. The material pieces 30a, b consist suitably of an easy to work material, such as aluminium, such that they in a rela- tively simple manner can be provided with said recesses 32a, b and specifically shaped surfaces 33a, b. Fig. 7 shows a tubular blank 34 which has been applied inside the space which is formed by the recesses 32a, b of the material pieces 30a, b. The tubular blank 34 is suitably manufactured of a material with good strain hardening properties. The tubular blank 34 can be manufactured of a steel material, such as an austenitic stainless steel material. The tool parts 30a, b are held together in the closed position by means of power members, not shown. The tubular blank 34 is connected to openings, not shown, for the supply of a liquid with a very high pressure to the inner space 35. Since such a liquid is supplied with a very high pressure, the walls of the tubular blank 34 are pressed radially outwardly. Thereby, the tubular blank 34 is deformed plastically and is formed after the specifically shaped surfaces 33a, b of the material pieces 30a, b.

Fig. 8 shows a tubular product 37 which has been formed by means of the above described hydroforming process. In this case, the product 37 is cut in two parts along the shown dividing line d such that two products are created in the form of two ma- terial layers 29a, b. Each of the material layers 29a, b have an outer surface 36a, b with a shape corresponding to the respective specifically shaped surfaces 33a, b of the material pieces 30a, b. The material layers 29a, b are relatively thin and they have a substantially constant thickness. The inner surfaces 26a, b of the material layers 29a, b thus obtain a shape substantially corresponding to the outer surfaces 36a, b and the specifically shaped surfaces 33a, b. The tubular blank 34 was subjected to a cold working when it was hydroformed to said tubular product 37. Since the tubular blank 34 consisted of a material with good strain hardening properties, the hydroformed material layers 29a, b, which were created by the tubular product 37, will comprise a strain hardened material and have very good strength properties.

Thereafter, the material layers 29a, b are applied in the recesses 32a, b of the material pieces 30a, b, which is shown in Fig. 9. Since the material layers 29a, b have an outer surface 36a, b which exactly fits together with the specifically shaped surfaces 33a, b of the recesses 32a, b, the material layers 29a, b can be held together in an intended position in the recesses 32a, b by means of form fitting. However, in order to guarantee that the material layers 29a, b are held in their intended positions, a fastening means, in the form of a glue 38, has been applied between the outer surfaces 36a, b of the material layers 29a, b and the surfaces 33a, b of the material pieces 30a, b. The first material layer 29a and the first the material piece 30a form in a connected state a first tool portion 24a. The second material layer 29b and the second material piece 30b form in a connected state a second tool portion 24b. The first tool portion 24a and the second tool portion 24b are thereafter used for hydroforming of tubular products in the manner shown in Fig. 5.

The strain hardened material layers 7, 29a, b can be very thin and be created by thin-walled blanks 12, 34. The hydroformed surfaces 6, 26a, b of the tool portions 4, 24a, b thus obtain a shape substantially identical to the specific surfaces 1 1 , 33a, b of the material pieces 8, 24a, b. If thicker material layers 7, 29a, b are used, consideration has to be taken to the thickness of the material layers 7, 29a, b as the specifically shaped surfaces 1 1 , 33a, b of the material pieces 8, 24a, b are worked so that the hydroformed surfaces 6, 26a, b of the tool portions 4, 24a, b will obtain a desired size and shape. Sheet-shaped blanks 3 or tubular blanks 23, which later are used for forming hydroformed products, can also be used to create said strain hardening material layers 7, 29a, b.

Fig. 10 shows a tool for hydroforming of products of two sheet blanks 40a, b. The edges of the two sheet blanks 40a, b are here welded together. A liquid with a high pressure is supplied, via an opening 41 , to a space between the sheet blanks 40a, b. The sheet blanks 40a, b thus expand plastically when the liquid is supplied. The sheet blanks 40a, b are formed after a first tool part 21 and a second tool part 22. The tool parts 21 , 22 have a construction corresponding to those which were shown in Fig. 5 and therefore have also been provided with corresponding ref- erences. The respective tool parts 20, 21 thus comprises a material piece 30a, b having a specifically shaped surface 33a, b and a material layer 29a, b which is formed after the specifically shaped surface 33a, b of the material pieces 30a, b during a hydroforming process. The material layer 29a, b comprises a sur- face 26a, b which is intended to come in contact with and form sheet blanks 40a, b which are hydroformed by means of the tool parts 20, 21 . The manufacturing of the tool parts 20, 21 also takes place in a manner corresponding to the manufacturing of the tool parts in Fig. 5.

Fig. 1 1 shows a sheet blank 42 which has been applied in a machine for hydromechanical forming. The machine comprises a construction part 43 having a space 44 connected to an opening, not shown, for the supply of a liquid with a high pressure. The construction part 43 comprises portions 45 which are intended to hold the edge portions of the sheet blank 42 against support surfaces of support element 46 with a large force. After the space 44 has been filled with a predetermined quantity of liquid, a hydromechanical forming tool in the form of a convexly shaped stamping tool 47 is moved against the sheet blank 42. The stamping tool 47 has a surface 48 which is intended to give the sheet blank 42 a specific shape the pressure between the stamping tool 47 and the liquid in the liquid filled space 44. The stamping tool 47 comprises a tool portion which consists of a material piece 49 with a specifically shaped surface 50 and a material layer 51 which is formed after the specifically shaped surface 50 of the material piece 49 during a hydroforming process. The material layer 51 comprises said surface 48 which is intended to come in contact with and form the sheet blank 42 during a hydroforming process.

The stamping tool 47 is manufactured by working the material piece 49 such that it provides a specifically shaped surface 50. Thereafter, the material piece 49 with its specifically shaped surface 50 is used for hydroforming a sheet blank, such that a product in the form of a material layer 51 is formed which is shaped after said specifically shaped surface 50. Finally, the material layer 51 and the material piece 49 are connected such that they form said stamping tool 47 where the material layer 51 comprises the surface 48 which is intended to come in contact with and form sheet blanks 42 which are hydroformed by means of the stamping tool.

The present invention is not in any way restricted to the em- bodiments described above on the drawings but may be modified freely within the scope of the claims. The embodiments

show the manufacturing of tools which are used for hydroform- ing of blanks. However, it is likewise possible to manufacture a material piece with a hydroformed material layer for a tool or tool portion which are used as a pressing tool or a tool for forming of plastics.