WO2007129980A1

WO2007129980A1 - A forming tool portion and a method for manufacturing the same

Info

Publication number: WO2007129980A1
Application number: PCT/SE2007/050315
Authority: WO
Inventors: Martin HOLMSTRÖM
Original assignee: Hydroforming Design Light Ab
Priority date: 2006-05-08
Filing date: 2007-05-08
Publication date: 2007-11-15
Also published as: SE0601022L

Abstract

The present invention relates to a tool portion for a forming tool and a method for manufacturing such a tool portion. The tool portion comprises a material piece (2, 21) which has a specifically shaped surface (4, 4') and a material layer (8, 8') which is formed after the specifically shaped surface (4, 41) of the material pieces (2, 2') during a superplastic forming process. The material layer (8, 8') comprises a surface (9, 9') which is in- tended to come in contact with and form blanks which are formed by means of the tool portion.

Description

A forming tool portion and a method for manufacturing the same.

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 which has a specifically shaped surface.

Superplastic forming is a process which mainly is used for manufacturing components of metal which many times have a complicated geometric shape. A conventional tool for superplastic forming comprises a surface with a specific shape for forming a blank which usually is plate-shaped. In connection with the applying of the plate-shaped blank in the tool, it is heated to a temperature at which the material will be considera- bly softer than at room temperature. Thereafter, a gas is supplied with an overpressure to a closed space on one side of the plate-shaped blank. The gas pressure will make the plate- shaped blank to expand slowly in direction towards and be formed by the specifically shaped surfaces of the tool. The form- ing process of the plate-shaped blank takes usually 30 to 120 minutes. However, only few metals and metal alloys have such properties that they can be used for superplastic forming.

Forming tools of different kinds are in many cases subjected to very high pressures and thus large mechanical stresses. In order to enable manufacturing of a large number of products by a forming tool, it is required that the specifically shaped surfaces of the forming tool maintain its structure substantially without being worn. Conventional forming tools for manufacturing of products in large series are therefore manufactured by 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 specifically shaped surfaces of the tool difficult to perform. The cost for manufacturing conventional forming tool is therefore high.

SUMMARY OF THE INVENTION

The object of 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 mate- rial layer which is formed after the specifically shaped surface of the material piece during a superplastic forming 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. Superplastic forming is a manufactur- ing process in which it is possible to manufacture a material layer such that it obtains a desired shape with a very good precision. By using the specifically shaped surface of the material piece for superplastic forming of the material layer, a surface is provided which very exactly corresponds to the spe- cifically shaped surface of the material piece. Thereby, the material layer may be applied form fitly on the material piece and the final forming tool can be used for, for example, hydroforming products, pressforming products or forming plastics. The material layer thus protects the specifically shaped surfaces of the material piece such that they do not be worn. Advantageously, the material layer is manufactured of a hard material which has good properties against wear. Thus, the material layer can be used for forming a large number of products. The material layer can also be easy exchanged and be replaced by a new one in a simple manner if it will be worn.

According to a preferred embodiment of the present invention, the material layer comprises aluminium, titanium or a stainless steel material. The above-mentioned materials or alloys which contain these materials are often possible to use in an superplastic forming process. However, it is a relatively restricted number of materials having properties such that they can be used in a superplastic forming process. Such metals or metal alloy must be fine grained and have a grain size less than 5-8 micron. The grain size will not either be allowed to increase when the material is heated to a temperature of about 90% of the melting temperature of the material during a superplastic forming process which can be up to two hours long. Advantageously, the material layer is hardened after that it has been formed during the superplastic forming process. Thereby, the material layer can be subjected to a heat-treating process resulting in that it is age-hardened. Thus, a hard-wearing material layer with a high strength may be obtained.

According to another preferred embodiment of the present in- vention, the tool portion comprises a material piece comprising a surface creating an underlying support surface for the material layer. At least when the material layer is relatively thin, it requires that it has an underlying support surface which supplies stability to the material layer. Consequently, the material piece itself is not intended to come in direct contact with the products formed by means of the tool. Thus, it may 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 that it shall be able to form a stable underlying surface for the material layer. Thus, the material piece ought to be considerably thicker than the material layer. The material piece may comprise aluminium. Aluminium is an easy to work material which in a simple manner can be given a support surface with a desired shape by means of conventional working methods such as milling. Alternatively, the material piece may, for example, com- prise 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 a loosely connected to each other. Consequently, the material piece has a support surface having a corresponding shape as the abutting surface of the material layers. Thus, a form fitting is obtained between said surfaces which can be used to maintain the material layer in a desired position in relation to the material piece. In many cases, such a lose connection between the mate- rial piece and the material layer is quite sufficient for that the tool portion shall be able to be used in a pressforming process. 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 secure 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 piece and the material layer. The fastening means may be a glue with suitable properties.

The above mentioned object is also achieved by the method which comprises the steps of working a material piece such that it provides a specifically shaped surface, using the material piece with its specifically shaped surface for forming a blank during a superplastic forming process such that a product in the form of a material layer is formed, 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. Preferably, the tool portion comprises here a material piece which is manufactured of an easy to work material. Thus, it is simple with conventional working methods such as milling to provide the material piece with the specifically shaped surface. Thereafter to form a material layer by means of a superplastic forming process is a manufacturing step which also is relatively easy to perform. The material layer thus provides a surface with a corresponding shape as the specifically shaped surface of the material piece. Such a material layer may be used to form a very large number of products substantially without being worn. If the material layer is being worn, it can easily be replaced by a new material layer formed by a superplastic forming process be 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 -3 shows different steps for manufacturing a tool portion according to a first embodiment of the present invention and

Fig. 4-6 shows different steps for manufacturing a tool portion according to a second embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Fig. 1 -3 show different manufacturing stages of a female tool portion 1 . Initially, a material piece 2 is provided with a recess 3 having a specifically shaped surface 4, see Fig. 1 . The material piece 2 suitably consists of an easy to work material, which may be aluminium. With such an easy to work material, the material piece 2 can relatively easy be provided with a recess 3 having a specifically shaped surface 4 by means of conventional working methods.

Thereafter, the material piece 2 with its recess 3 and specifically shaped surface 4 is used as a tool part together with another tool part 5 for superplastic forming of a plate-shaped blank 6, which is shown in Fig. 2. Advantageously, the plate-shaped blanket 6 is relatively thin and it is manufactured of a material with properties which makes it suitable to be formed superplastically. After the plate-shaped blanket 6 has been attached between the tool parts 2, 5, it is heated, in a suitable not shown manner, to a temperature at which the material will be considerably softer than at room temperature. Such a temperature may be within a temperature range which corresponds to 70 - 90 % of the melting temperature of the plate-shaped blanket 6. Thereafter, a gas is supplied with an overpressure to a closed space 7 formed by the second tool part 5 and the plate-shaped blanket 6. The overpressure in the space 7 will make the plate- shaped blanket 6 to expand slowly in direction towards the spe- cifically shaped surface 4 of the first material piece 2. The air located in the recess 3 is guided, during this course, out through non-shown channels. Alternatively, a negative pressure can be formed in the recess 3 which will make the plate-shaped blanket 6 to expand slowly in direction towards the specifically shaped surface 4 of the material piece 2. The superplastic forming process is ended when the plate-shaped blanket 6 has been completely formed after the specifically shaped surface 4 of the material piece 2. The forming process of the plate-shaped blanket 6 by means of the tool parts 2, 5 can take 30 minutes to 2 hours.

The final manufactured tool portion 1 is shown in Fig. 3. The plate-shaped blanket 6 forms, after the forming process, a plate shaped product in the form of a material layer 8 which has a form such that it at least covers the specifically shaped surface 4 of the material piece 2. After the forming process, the material layer 8 is with advantage subjected to a temperature treatment such that it provides an age hardening. Thus, the material layer 8 obtains a hard surface 9 having good properties against wear.

Since a relatively thin plate shaped blank 6 has been used as starting material, an even thinner material layer 8 is obtained which at least covers the specifically shaped surface 4 of the material piece 2. In the cases when the material layer 8 is very thin, it provides a recess 10 having a surface 9 which has a substantially completely identical shape as the specifically shaped surface 4 of the material piece 2. Since the shape of the material layer 8 corresponds to the shape of the recess 3 of the material piece 2, they can be held together form fitly in a desired mutual position in which they form said tool portion 1 . Alternatively, a binding means, for example, in the form of a suitable glue 1 1 can be arranged between the contact surfaces of the material layer 8 and material body 2. Thus, the material layer 8 and the material body 2 will be kept safely together in an intended mutual position when the tool portion 1 is used. If a thicker material layer 8 is used consideration ought to be taken to the thickness of the material layer 8 as the specific surface 4 is formed in the material piece 2 such that the final surface 9 of the tool portion 1 , which is intended to form products, obtains a desired dimension.

Consequently, the tool portion 1 comprises preferably a material layer 8 of a preferably hardened material which is intended to comprise the surface 9 of the tool portion 1 for forming of products. Since such a hardened material layer 8 is strength and wear resistant the surface 9 can be used to form a very large number of products substantially without that the surface 9 be worn. If a less wear resistant material is used, it can instead be exchanged more frequently. The tool portion 1 comprises a material piece 2 which is manufactured of an easy to work material. Such a material piece 2 can be provided with the specifically shaped surface 4 by means of conventional working methods such as milling. Thereafter, forming a material layer 8 super- plastically by means of the material piece 2 is a manufacturing step which also is relatively easy to perform. The material layer 8 thus provides a surface 9 having substantially the same shape as the specifically shaped surface 4 of the material piece 2. Thereafter, the material layer 8 can be provided with an age- hardened surface 9. The final tool portion 1 can be used as or consist a part of a press tool, a hydroforming tool or tool for forming of plastics.

Fig. 4-6 show different manufacturing stages of a male tool portion V. Fig. 4 shows a material piece 2' which initially is provided with a specifically formed surface 4¹. The material piece 2' suitably consists of an easy to work material, which can be aluminium. Thus, it is relatively simple to provide the material piece 2 with a specifically formed surface 4' by means of conventional working methods.

Thereafter, the material piece 2' with its specifically formed surface 4' is used as a tool part together with a lower tool part 5' and an upper tool part 5" for forming a plate shaped blank 6' superplastically, which is shown in Fig. 5. The plate-shaped blanket 6' consists of a metal or a metal alloy having such properties the material can be used in a superplastic forming process. The plate-shaped blanket 6' has here been attached between the lower tool part 5' and the upper tool part 5". Thereafter, it is heated, in a suitable manner, to a temperature at which the material will be considerably softer than at room temperature. A gaseous material is supplied with an overpressure to a space 3¹ located below the plate-shaped blanket 6' for that the plate-shaped blanket 6' will obtain the shape shown in Fig. 5 . Thereby, the plate-shaped blanket 6' is pressed a predetermined extension into a space 7' whereupon the material piece 2' with its specifically formed surface 4' is moved upwardly such that it obtains contact with the plate-shaped blanket 6'. Alternatively, a negative pressure can be formed in the space 7' for giving the plate-shaped blanket 6' the shape shown in fig. 5. Thereafter, gas with an overpressure is guided into the space 7' while the space 3' is connected with surrounding pressure. Thereby, the overpressure in the space 7' will make the plate-shaped blanket 6 to be pressed towards and be formed after the specifically shaped surface 4' of the first material piece 2'.

The final manufactured tool portion 1 ' is shown in Fig. 6. The plate-shaped blanket 6¹ forms, after the forming process, a plate shaped product in the form of a material layer 8' which has a form such that it at least covers the specifically shaped surface 4' of the material piece 2'. Advantageously, the material layer 8' has after the forming process been subjected to a temperature treatment such that it has provided an age hardening. Thus, the material layer 8' has provided a hard surface 9' having good properties against wear. The material layer 8' and the material piece 2' form together the final manufactured tool portion Y where thus the material layer 8¹ comprises the surface 9¹ which is intended to come in contact with and form blanks during a forming process which can be a pressing process, a hydro- forming process or a forming process of plastics.

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

Claims

1. A tool portion for a forming tool, wherein the tool portion comprises a material piece (2, 2') having a specifically shaped surface (4, 4¹), characterised in that the tool portion comprises a material layer (8, 8¹) which is formed after the specifically shaped surface (4, 4') of the material piece (2, 2') during a super- plastic forming process, and that the material layer (8, 8') comprises a surface (9, 9¹) which is intended to come in contact with and form blanks which are formed by means of the tool portion.

2. A tool portion according to claim 1 , characterised in that the material layer (8, 8') comprises aluminium, titanium or a stainless steel material.

3. A tool portion according to claim 1 or 2, characterised in that the material layer (8, 8') has been hardened after that it has been formed during the superplastic forming process.

4. A tool portion according to any one of the preceding claims, characterised in that the material piece (2, 2¹) is connected to the material layer (8, 8') such that it forms an underlying support surface for the material layer (8, 8¹).

5. A tool portion according to any one of the preceding claims, characterised in that the material piece (2, 2') and the material layer (8, 8') are loosely connected to each other.

6. A tool portion according to any one of the preceding claims, characterised in that the material piece (2, 2') and the material layer (8, 8') a fixedly connected to each other by means of a fastening means (11 , 11 ').

7. A method for manufacturing a tool portion of a forming tool, wherein the method comprises the step of working a material piece (2, 2') such that it provides a specifically shaped surface (4, 4¹), characterised in that the method comprises the steps of using the material piece (2, 2¹) with its specifically formed surface (4, 4¹) for forming a blank (6, 6') during a superplastic form- ing process, such that a product in the form of a material layer (8, 8') is formed which is formed after said specifically shaped surface (4, 4'), and connecting the material layer (8, 8') and the material piece (2, 2¹) such that they form a tool portion (4,4') where the material layer (8, 8') comprises a surface (9, 9') which is intended to come in contact with and form blanks which are formed by means of the tool portion.

8 A method according to claim 7 characterised in the step of hardening the material layer (8, 8') after it has been formed during the superplastic forming process.

9. A method according to claim 7 or 8, characterised in the step of connecting the material layer (8, 8') and the material piece (2, 2') such that the material piece (2, 2') forms an underlying support material for the material layer (8, 8').

10. A method according to any one of the preceding claims 7-9, characterised in the step of connecting the material piece (2, 2') and the material layer (8, 8') loosely to each other.

1 1. A method according to any one of the preceding claims 7-9, characterised in the step of connecting the material piece (2, 2') and the material layer (8, 8') fixedly to each other by means of a fastening means (1 1 , 1 1 ').