GB2250703A

GB2250703A - Forming or cutting press tools

Info

Publication number: GB2250703A
Application number: GB9119436A
Authority: GB
Inventors: John Clifford Phillips
Original assignee: Marrill Engineering Co Ltd
Current assignee: Marrill Engineering Co Ltd
Priority date: 1990-12-12
Filing date: 1991-09-12
Publication date: 1992-06-17
Anticipated expiration: 2011-09-12
Also published as: GB2250703B; GB9027008D0; GB9119436D0

Abstract

A forming or cutting press tool is made by a moulding or casting process using a polymer concrete comprising a dense hard aggregate such as granite, an optional filler such as sand and a cured polymer matrix such as epoxy resin. The tool may comprise a press tool 10, a punch and die set 16, 17 for forming sheet metal 18; or a cropping tool set 24, 25 having cutting edges 26, 27. Fine surface finishes and detail can be achieved in the finished tool which has good dimensional stability, strength and durability. <IMAGE>

Description

Forming or cutting press tools This invention relates to forming or cutting press tools.

In forming or cutting sheet material for example metal, various types of tool are used depending on the properties of the material to be formed, the nature of the operation to be carried out and the number of products required to be made from each tool.

Where very difficult profiles are to be formed or large production runs are to be achieved, especially in hard-to-form alloy steels, the mould or die used needs to be very strong and hardwearing. Such press tools are usually made by machining high grade cast iron. Cutting tools also require strength and durability and are usually made of high grade steel.

Less difficult profiles can be formed in light alloys or thin steel sheet using tools made of a low melting point metal alloy, for example that known as Kirksite, an alloy which includes zinc and lead.

In a typical example, a car body panel may be made by forming a pattern and using this to make a reverse mould which, in turn, is used to cast a Kirksite form. The sheet metal is drawn over the form by a press to produce the shaped panel.

Low melting point alloys such as Kirksite can also be used to make die and mould pairs for press forming of sheet.

However, low melting point alloys have various disadvantages.

They are expensive, require expensive foundry plant and process heat to form then into tools, and they contain heavy metals which are environmentally harmful. Another major disadvantage in use is that they tend to shrink on cooling so that it is difficult to achieve a tool having good dimensional tolerances. Fine surface finishes are also difficult to achieve because of the hot casting process and shrinkage during cooling.

In an attempt to overcome this shrinkage problem, a Kirksite or similar low melting point alloy core has been used with a finishing skin of epoxy resin which can be moulded to fine tolerances with excellent surface finish. However this brings its own drawbacks since the durability of the epoxy resin is not great. The tool needs to be stripped and refaced at frequent intervals with fresh epoxy resin.

Neither- Kirksite nor epoxy resin is hard enough for use in cutting tools.

It is an object of the present invention to provide a forming or cutting press tool which overcomes or reduces some or all of these disadvantages.

According to the invention there is provided a forming or cutting press tool comprising a moulded polymer concrete which comprises a dense hard aggregate in a cured polymer matrix.

The polymer concrete may also comprise sand as a filler.

The aggregate is preferably a dense hard mineral aggregate such as granite particles. Alternatively or in addition, it may comprise particles or fibres of metal, glass or other minerals.

The polymer matrix may comprise an epoxy resin.

The tool may comprise a mould or a die. The mould or die may be adapted for forming sheet material or for forming an amorphous material in a plastic state, for example fibrous composites, synthetic plastics or ceramic pastes.

The mould or die may include heating or cooling means embedded in the polymer concrete.

The tool may alternatively or in addition include cutting means comprising a pair of cropping edges adapted to be moved past each other to cut a material placed therebetween.

The invention also provides a method of making a forming or cutting press tool comprising the steps of taking a reverse impression of the desired shape of said tool and forming a polymer concrete therein from a two-component settable polymer system and a dense hard aggregate and causing or allowing the concrete to set. The method may include the additional step of applying vibration to the polymer concrete during setting.

The method may further include the step of inserting permanent or temporary inserts into the polymer concrete during setting.

Permanent inserts may include for example heating elements, electrical power supplies, cooling tubes, structural reinforcements, magnetic inserts, mould air release vents, ejector pins or the like. Temporary inserts may include cores to be withdrawn to leave voids in the tool after setting.

Forming and cutting press tools embodying the invention will now be described by way of example only with reference to the accompanying drawings in which Figure 1 illustrates a stage in forming a press tool, Figure 2 illustrates a further stage in forming the press tool, Figure 3 diagrammatically illustrates the manner of use of the press tool made by the method illustrated in Figures 1 and 2, Figure 4 is a scrap sectional view of part of a die and punch set embodying the invention, Figure 5 is a diagrammatic sectional view of a heated press tool embodying the invention, Figure 6 is a scrap sectional view of a cutting tool embodying the invention.

In a first example embodying the invention and shown in Figures 1-3, it is desired to make a mould 10 for aluminium vehicle body panels 11 to be made by drawing a sheet of metal over a single male mould 10 using a press. A pattern 12 is firstly made to the desired shape of the panel and including any surface features required. A reverse impression 13 is taken of the pattern 12 and this is then used to cast an epoxy resin two component system havi##ng a sand filler and a fine particulate granite aggregate. The aggregate forms a high percentage of the polymer concrete cast in the reverse impression. The polymer concrete 14 is compacted using vibration either by carrying out the casting process on a vibrating bed or by using a vibrating poker 15 inserted in the concrete 14 before curing.

The resulting cured polymer concrete mould 10 has a fine surface finish and sufficient strength and durability to be used for the desired purpose.

In a second embodiment shown in Figure 4, a punch 16 and die 17 for stamping sheet metal 18 in a press are formed by the same general technique. In this case, however, the fine surface finish of the punch 16 and die 17 are impressed on the sheet metal 18 being stamped and can be used for transferring fine detail to the finished article.

In a further embodiment shown in Figure 5, a pair of large complimentary dies 19, 20, are formed by the same technique but using inserted electrical heating elements 21, 22 which are set into the polymer concrete 14 during the curing process. The complimentary mould and die set 19,20 is then suitable for use in preforming vehicle linings which are made of a heat curable resin impregnated fibrous felt 23. The felt is press formed and heated by the elements 21, 22 to a temperature of the order of 1500 Celsius in order to cure the resin impregnation in the felt 23 so as to form the vehicle lining.

In a still further embodiment shown in Figure 6, a pair of complimentary tools 24, 25 are provided with edges 26, 27 so shaped that the sheet material 28 placed between them is sheared as the tools 24 and 25 are moved together. The tools 24, 25 may be forming tools having cutting edges 26, 27 for example for trimming the edge of a sheet material blank 28 or for punching one or more holes or slots in it.

Polymer concretes having dense hard mineral aggregates are known to be suitable for use in for example the manufacture of machine tool bases, in which context they have been found to have great strength and load bearing capabilities, vibration and noise absorption and resistance to the effects of chemicals and corrosive materials. However it has not been previously proposed to utilise a polymer concrete as a tool.

Epoxy resins have been proposed as finishing skins of tools but, in themselves, do not appear to have the potential strength or durability for use as forming or cutting press tools.

Claims

1. A forming or cutting press tool comprising a moulded polymer concrete which comprises a dense hard aggregate in a cured polymer matrix.

2. A tool according to Claim 1 wherein the polymer concrete further comprises sand as a filler.

3. A tool according to Claim 1 or Claim 2 wherein the dense hard aggregate comprises a mineral aggregate such as granite particles.

4. A- tool according to any preceding claim wherein the aggregate comprises particles or fibres of metal.

5. A tool according to any preceding claim wherein the aggregate comprises particles or fibres of glass.

6. A tool according to any preceding claim wherein the polymer matrix comprises an epoxy resin.

7. A tool according to any preceding claim comprising a mould.

8. A tool according to any one of Claims 1-6 comprising a die.

9. A tool according to Claim 7 or Claim 8 adapted for forming sheet material.

10. A tool according to Claim 7 or Claim 8 adapted for forming amorphous material in a plastic state.

11. A tool according to any one of Claims 7-10 and including heating or cooling means embedded in the polymer concrete.

12. A tool according to any preceding claim and including cutting means comprising a pair of cropping edges adapted to be moved past each other to cut a material placed between the edges.

13. A method of making a forming or cutting press tool comprising the steps of taking a reverse impression of the desired shape of said tool and forming a polymer concrete therein from a two-component settable polymer system and a dense hard aggregate and causing or allowing the concrete to set.

14. A method according to Claim 13 including the additional step of applying vibration to the polymer concrete during setting.

15. A method according to Claim 13 or Claim 14 including the step of inserting permanent or temporary inserts into the polymer concrete during setting.

16. A tool substantially as hereinbefore described with reference to and as illustrated in Figures 1-3 of the accompanying drawings.

17. A tool substantially as hereinbefore described with reference to and as illustrated in Figure 4 of the accompanying drawings.

18. A tool substantially as hereinbefore described with reference to and as illustrated in Figure 5 of the accompanying drawings.

19. A tool substantially as hereinbefore described with reference to and as illustrated in Figure 6 of the accompanying drawings.