GB2205513A

GB2205513A - Manufacture of form cutting tool tip

Info

Publication number: GB2205513A
Application number: GB08713841A
Authority: GB
Inventors: Alan B Riach; Alexander F Shaw
Original assignee: FLEMING THERMODYNAMICS Ltd
Current assignee: FLEMING THERMODYNAMICS Ltd
Priority date: 1987-06-12
Filing date: 1987-06-12
Publication date: 1988-12-14
Anticipated expiration: 2007-06-12
Also published as: GB2205513B; GB8713841D0

Abstract

The method comprises a rough forming stage by moulding and a fine finishing stage using computer controlled electric discharge machining or grinding. The final finishing method produces a tool tip with a cutting form 5 to 7 accurately placed with respect to accurate location datum feature(s) 9, 10 to enable the tip to be accurately mounted on a carrying base or tip holder. The features are apertures, as shown, or recesses in the sides and rear of the tip. <IMAGE>

Description

METHOD FOR MANUFACTURING HIGH ACCURACY FORM CUTTING TOOLS This invention relates to a method for manufacturing high accuracy form cutting tools.

Form tools are well known as a method of producing shapes in workpieces by passing a tool of the required shape over or through the workpiece or by moving the workpiece past the tool in order to replicate the tool shape in the workpiece.

To produce an accurate shape in the workpiece, the form tool shape must in turn be accurate. This type of high accuracy form tool is especially difficult to make if the tool is of complex shape.

There are various recognised methods for producing the accurate shape in the tool, e.g. rough milling or moulding to an approximate shape and then high accuracy finishing by grinding or by electric discharge machining (EDM).

The main difficulty is in achieving the final accurate shape since the grinding machines or EDM machines must work on the tool accurately.

This implies slow material removal in order to cut down the deflections in the machine and in the tool being worked on. The slow rate of work throughput increases the machining cost.

A further disadvantage with these tools is the difficulty of sharpening since the form is often of such shape that a new cutting edge cannot easily be reconstructed. In such cases it is more economical to make tips which can be mounted on a tool carrying base since these use up less material than a full tool. The tool tip can then be discarded when it becomes too blunt to cut effectively and a new tip mounted on the carrying base. There is however considerable difficulty in mounting the tool tip accurately on the carrying base.

A typical example of a form tool tip is shown in Figures 1, 2 and 3 in which 12 is the tool tip mounted in tip carrying base 13 and 19 is the cutting edge form. The tip 12 is located by form 14 resting against recess 15 in carrying base 13. This method of location does not locate the tip very accurately on its carrying base since small movements in or out of the recess may allow small radial movements of the tip. It is retained by clamp 16 which is secured by clamp bolt 17. Figure 2 shows a plan view of tip 12 and Figure 3 is a section through tip 12 taken at YY and showing the cutting edge 19 with top clearance angle M and front and side clearance angle N.

According to the present invention there is provided a 2 stage method of manufacturing high accuracy form tool tips comprising a first stage in which an approximation to the required form is moulded into the cutting portion of the tool and a second stage in which an accurate location datum feature plus an accurate cutting edge form placed accurately with reference to the datum feature is machined into the tool by electric discharge machining, using a computer controlled EDM machine tool and/or a computer controlled grinding machine with the computer working to a pre-defined instruction set which has been prepared by considering the requirements of the final workpiece shape and the requirements of the tool cutting edge clearances.

A specific embodiment of a tool tip made by the method described in the invention will now be described by way of example with reference to the accompanying drawings in which Figure 4 shows in perspective a cutting tool assembly Figure 5 shows a plan view of the tool tip Figure 6 shows a section through the cutting edge of the tool tip at section XX.

Figure 7 shows a plan view of the tool tip with an alternative form of open slot datum feature Figure 8 shows the tip shown in Figure 7 mounted on a suitable carrying base Referring to the drawings, the tool is comprised of a piece of hard material 1 of relatively thin section, hereinafter referred to as the tool tip, which is located accurately on carrying base 2 by circular spigots 3 and 4 which are rigidly mounted on base 2 engaging in spigot holes 9 and 10 in tip 1 and fixed securely to carrying base 2 by securing clamp 20 and fastening screw 21.

Tip 1 has an accurate cutting edge 6 extending from point 7 to point 8 and 2 accurate datum holes 9 and 10, one circular and one slotted. The cutting edge is constructed in a position which is accurate relative to datum holes 9 and 10.

In order to get the tool to cut successfully it may have to have top rake angle A and side or front clearance angle D. These angles will vary depending on the material being cut and/or the speed of cutting.

Depression 5 is a chipbreaking feature for breaking the cut swarf into small pieces which can be more easily handled and disposed of.

To produce this form accurately it is proposed to make the tool in two distinct stages.

In stage 1 the tool tip is moulded into an approximate shape including the datum feature leaving a minimum of material for removal in stage 2.

The amount of material which is left on the tip during stage 1 will depend on the moulding or forming accuracy. Because various moulding techniques may be used which are amenable to low cost high production volume methods this stage of manufacture can be made very economical.

An added advantage is that intricate shapes can be moulded into the tip form very simply by using appropriately shaped moulding tools.

Stage 2 involves producing the accurate datum location holes and related high accuracy cutting edge from the less accurate moulded form. The method used in stage 2 is high accuracy electric discharge machining (EDM) using a machine of the die sinking or wire discharge variety and/or high accuracy grinding as appropriate. In order to achieve complex tool forms computer controlled machines are used.

The tool tip is clamped onto the EDM worktable and the EDM machine is used to produce the accurate datum features 9 and 10. The accurate cutting edge form 6 can then be produced at the same time or the tip may be relocated on this or another machine's worktable by means of the accurate datum holes 9 and 10 in order that the edge 6 can be produced accurately in relation to the datum feature. This enables the tool tip at a later stage to be mounted on its carrying base 2 with its cutting edge in an accurate known position. If required further work is carried out on the cutting edge 6 with a grinding machine, the tool tip during this operation being located accurately on the grinding machine worktable via the previously machined datums 9 and 10.

Fig 7 shows a form of the tool tip which has open datum holes to make it more amenable for manufacture by an EDM wire erosion machine where 22, 23 and 24 are three location slots with semi-circular inner profiles and Fig 8 shows this form of the tip mounted in a suitable carrying base with circular spigots 25, 26 and 27 which locate in said slots, spigots 25 and 27 bearing against the semi-circular inner profiles of slots 22 and 23 and spigot 26 bearing against the sides only of slot 24 as shown.

This variation of the tool tip is retained on the carrying base by a clamp and fastening screw in a similar manner to that shown for Tip 1 in Fig 4.

Claims

1. A two stage method of manufacturing high accuracy form tool tips comprising a first stage in which an approximation to the required form is moulded into the cutting portion of the tool and a second stage in which an accurate location datum feature plus an accurate cutting edge form placed accurately with reference to the datum feature is machined into the tool by electric discharge machining (EDM machining), using a computer controlled EDM machine tool and/or computer controlled grinding machine with the computer working to a pre-defined instruction set which has been prepared by considering the requirements of the final workpiece shape and the requirements of the tool cutting edge clearances.

2. A two stage method of manufacturing high accuracy form tools as claimed in claim 1 wherein the stage 1 moulding process is isostatic powder moulding.

3. A two stage method of manufacturing high accuracy form tool tips as claimed in claim 1 wherein the stage 1 moulding process is liquid metal casting.

4. A two stage method of manufacturing high accuracy form tool tips as claimed in claim 1 wherein the stage 1 moulding process is squeeze forging.

5. A two stage method of manufacturing high accuracy form tool tips as claimed in claim 1 when the stage 1 moulding process is hot or cold metal forging.

6. A two stage method of manufacturing high accuracy form tool tips as claimed in claim 1-5 wherein the stage 2 ED machining is by wire eroding machining.

7. A two stage method of manufacturing high accuracy form tool tips as claimed in claim 1-5 wherein the stage 2 ED Machining is by shaped electrode, in a die sinking type of machine.

8. A two stage method of manufacturing high accuracy form tool tips as claimed in claim 1-7 in which the datum feature is composed of a circular hole and a slotted hole.

9. A two stage method of manufacturing high accuracy form tool tips as claimed in claim 1-7 in which the datum feature on the tool tip is composed of two open slotted holes.