GB2122124A

GB2122124A - Circular form tool with plurality of alternative cutting edges

Info

Publication number: GB2122124A
Application number: GB08215598A
Authority: GB
Inventors: Roy Sidney Ernest Chettleburgh
Original assignee: Svenska Kullagerfabriken AB
Current assignee: SKF AB
Priority date: 1982-05-27
Filing date: 1982-05-27
Publication date: 1984-01-11

Abstract

A circular form tool for machining workpieces has a core 30 formed with a plurality of ribs 31, 33, 35 spaced around the core, each rib having a cutting edge 31a, 33a, 35a. In operation, one of the cutting edges is used to machine a workpiece and when the cutting edge becomes worn or damaged another cutting edge is moved into the same cutting position relative to the workpiece by angular movement of the tool about its axis. Each rib may be cut away after its cutting edge has become worn to provide clearance for swarf when machining the workpiece with the cutting edge on the next succeeding rib. <IMAGE>

Description

SPECIFICATION Improvements in circular form tools This invention relates to circular form tools for machining workpieces in succession to cut the same profile on each workpiece.

A conventional circular form tool is made from a cylindrical tool-steel blank by machining away a segment from the periphery of the blank to produce a form or shape having a single cutting edge and a space for swarf clearance. The tool is usually made of high speed steel which is heat treated to provide the optimum of life for the cutting edge. In operation the workpiece is usually rotated and the circular form tool is held in a stationary position.

When the cutting edge of a conventional circular form tool becomes damaged or worn during use, part of the tool can be ground away along the top rake edge until an undamaged and unworn cutting edge is exposed. Such refurbishing of the cutting edge by grinding the top rake edge can take place repeatedly until so much material has been removed from the periphery of the tool that the root portion connecting the cutting edge to the shank of the tool will not provide sufficient strength to support the cutting loads. The service life of the tool will of course depend on the degree of damage to the tool and the skill of the machinist in removing the worn or damaged cutter material.If a great deal of material needs to be removed from along the top rake edge of the form tool, then it is feasible that the heat developed in removing the material will generate sufficient heat to change the material structure and/or its hardness. A change of the material structure and/or its hardness from the optimum state originally imparted to the tool has been found to lead to increased tool wear and damage and subsequent reduction of the life of the cutting edge and tool.

It is known to coat the entire surface of a circular form tool made of high-speed-steel with a hard wearing coating of titanium. A form tool coated with titanium can be operated at higher cutting speeds and feed rates than can be achieved with an uncoated high-speed-steel form tool, and moreover the cutting edge has a longer life than that on the cutting edge of an uncoated form tool. A coated form tool has however the disadvantage that once the first cutting edge life has been exhausted and the tool is re-ground to provide another cutting edge, the hard wearing coating is removed from the top rake edge in the re-grinding process. Although the coating remains on the periphery of the tool and provides protection for the front rake face, the advantage of the protective coating on the top rake edge is lost.

The life obtained from the refurbished cutting edges and the speed and feed advantages over the original titanium coated cutting edge are therefore reduced.

The object of the invention is to provide an improved construction of a circular form tool and a method of machining workpieces with the form tool which can extend the life of the tool without the need for repeated refurbishing of the cutting edge of the tool.

According to the present invention there is provided a method of machining workpieces in succession with a circular form tool in a power driven machine to cut the same profile on each workpiece, wherein the circular form tool is provided with a plurality of cutting edges spaced around the tool and having substantially the same profile arranged at substantially the same distance from the axis of the tool, and each cutting edge is moved into the same cutting position relative to a workpiece in the machine by angular movement of the tool about its axis whenever the cutting edge previously in use has become worn or damaged.

The method of the invention avoids the necessity, with conventional circular form tools, of refurbishing a cutting edge everytime it becomes worn or damaged, before machining can be continued. In the method of the invention the circular form tool is preferably provided with a plurality of legs having substantially the same profile arranged at substantially the same distance from the axis of the tool, each leg having one of the cutting edges.

Each leg may then be moved into the same cutting position relative to a workpiece in the machine by angular movement of the tool about its axis whenever the cutting edge on a leg previously in use has become worn or damaged.

The number of legs which can be provided on the form tool will depend on the required strength of each leg and will therefore be dependent on the length of the cutting surface and the permitted maximum diameter of the cutter. In a case in which the legs are spaced symmetrically around the axis of the tool, the maximum number of legs will also be dependent on the minimum spacing required between adjacent legs to avoid interference between the workpiece and legs not in use and to provide for swarf clearance.

The number of legs on the tool may however be increased by providing the minimum spacing between two of the legs necessary to avoid interference between the tool and workpiece when the cutting edge on one of the legs is in cutting engagement with the workpiece, and spacing the remaining legs closer together. It will then be necessary to cut away each leg after its cutting edge has become worn in use in order to expose the cutting edge on the adjacent leg for cutting operations.

Thus according to the invention there is also provided a method of machining workpieces in succession with a circular form tool in a power driven machine to cut the same profile on each workpiece, wherein the circular form tool is provided with a plurality of legs each having a cutting edge, said legs having substantially the same profile arranged at substantially the same distance from the axis of the tool, the spacing between a first of said legs and an adjacent leg in one direction around the tool being sufficient to permit the cutting edge on said first leg to machine a workpiece without interference between the workpiece and the other legs on the tool and provide adequate swarf clearance, but the spacing between each adjacent pair of legs in the opposite direction around the tool from said first leg being insufficient to permit the cutting edge on the second or subsequent leg to cut a workpiece, said method comprising the steps of machining workpieces with the cutting edge on said first leg, cutting away the first leg after its cutting edge has become worn or damaged to provide sufficient clearance for the cutting edge on the second leg to machine the next workpiece, and then cutting away each of the remaining legs in turn after their cutting edges have become worn of damaged to provide sufficient clearance for the cutting edge on the succeeding leg to machine a workpiece.

Each of the cutting edges on the tool, or the entire surface area of the tool, is preferably provided with a coating of titanium or other wear resisting material.

The invention will now be described with reference to the accompanying drawings, in which: Figures 1-3 are diagrammatic views illustrating the construction, operation, and refurbishing of conventional circular external and internal forming tools, Figure 4 is a perspective view of one construction of a multi-legged circular form tool according to the invention, Figure 5 is an end view of the tool of Figure 4 in cutting engagement with a surface of a bore in a rotating workpiece, Figure 6 is a perspective view of another construction of a multi-legged circular form tool according to the invention, and Figure 7 is an end view of the tool of Figure 6 shown in cutting engagement with the surface of a bore in a rotating workpiece.

Figure 1 is a diagrammatic end view of a conventional circular form tool 10 in cutting engagement with the external surface of a rotating workpiece 1 The tool is made by machining the periphery of a cylindrical blank in a direction parallel to the axis of the blank to remove a segment so as to provide a cutting edge 12 having a top rake surface 13. In operation, the workpiece is rotated continuously about its axis, and the circular form tool is held against rotation in the position shown and is fed towards the workpiece so as to bring the cutting edge 12 into cutting engagement with the external surface of the workpiece.

Figure 2 is a diagrammatic end view of a conventional circular form tool 15 in cutting engagement with the surface of a bore in a rotating workpiece 16. The tool 15 is similar in construction to that of the tool 10 and has a cutting edge 17 formed with. a top rake surface 1 8. A part of the tool facing the top rake surface is however cut away as shown at 19 to avoid interference between the tool and workpiece.

As shown in Figure 3, when the cutting edge 20 of a conventional form tool becomes worn, the original top rake surface 21 is ground away as shown in cross hatching in Figure 3 to form another cutting edge 20a and top rake surface 21 a. The form tool can be repeatedly refurbished to form new cutting edges 20b-20g and new top rake surfaces 21h-21g, until the root portion 22 connecting the cutting edge to the shank will not provide sufficient strength to support the cutting loads.

The circular form tool according to the invention shown in Figures 4 and 5 comprises a core 30 provided with three identical legs 31,33, 35 spaced symmetrically around the core, a shank 36 co-axial with the core, and a cylindrical shoulder 37 interconnecting the ends of the legs adjacent the shank, the core 30, legs 31, 33, 35, shank 36 and shoulder 37 being an integral structure. The leg 31 has a cutting edge 31 a and a top rake surface 31 b. Similarly, the legs 33,35 have cutting edges 33a, 35a and top rake surface 33b, 35b respectively.The tool is made from a cylindrical blank having the same diameter as the shoulder 37, the blank being machined axially to form the individual legs 31, 33, 35. The entire surface of the tool apart from the shank 36 is provided with a hard wearing coating of titanium.

In operation, the leg 31 is used first for cutting the surface of a bore in a rotating workpiece 39 as shown in Figure 5. When the cutting edge 31 a on the leg 31 is worn or damaged, the form tool is rotated anti-clockwise through 1 200 about its axis (in the view shown in Figure 5) to bring the cutting edge 33a on the leg 33 into cutting engagement with the rotating workpiece. When the cutting edge 33a is worn or damaged, the form tool is again rotated anti-clockwise through 1 200 about its axis to bring the cutting edge 35a on the tooth 35 into cutting engagement with the workpiece.

Since the legs 31, 33, 35 are identical, their cutting edges 31a, 33a, 35a have the same profile spaced at the same distance from the axis of the tool, so that each cutting edge 31a, 33a, 35a is movable into the same cutting position relative to the workpiece by angular movement of the tool about its axis.

The circular form tool according to the invention shown in Figures 6 and 7 has features which are the same as corresponding features of the form tool of Figures 4 and 5 and like parts are denoted by like reference numerals.

The form tool of Figures 6 and 7 has a core 30, five legs 31, 32, 33, 34, 35, a shank 36 and a circular shoulder 37. The legs 31, 33, 35 are identical to the correspondingly numbered legs in the form tool of Figures 4 and 5 and are spaced at the same angular relationship around the axis of the tool. The additional leg 32 on the form tool of Figures 6 and 7 is positioned between the legs 31, 33 and the additional leg 34 is positioned between the legs 33. 35. The legs 32, 34 are identical to the other legs 31, 33, 35 and have cutting edges 32a, 34a respectively.

In the operation of the circular form tool of Figures 6 and 7, the leg 31 is used first for cutting the surface of a bore in a rotating workpiece 39 as shown in Figure 7. When the cutting edge 31a on the leg 31 is worn or damaged, the form tool is removed from the bore in the workpiece, the entire leg 31 is cut off along the line A-B as shown in broken lines in Figure 7, the form tool reinserted in the same position in the bore in the workpiece, and the form tool then rotated anticlockwise through 600 about its axis to bring the cutting edge 32a on the leg 32 into cutting engagement with the rotating workpiece.It is necessary to cut away the leg 31, or at least a substantial part of the leg 31, to avoid interference between the leg 31 and the workpiece when the leg 32 is in the cutting position and to provide clearance for swarf removed from the workpiece by the cutting edge on the leg 32. When the cutting edge 32a is worn or damaged, the leg 32 is cut away along the line B-C to avoid interference with the workpiece and provide clearance for swarf cut from the workpiece by the cutting edge on leg 33 when that cutting edge is brought into cutting engagement with the workpiece. Similarly leg 33 is cut away along the line C-D when its cutting edge is worn or damaged, and leg 34 is cut away along line D-E when its cutting edge is worn or damaged. When the cutting edge on leg 35 is worn or damaged, the tool is discarded.

A circular form tool according to the invention may have any suitable number of legs provided that there is sufficient spacing between the first and the last leg to be used to provide the necessary clearance when cutting a workpiece with the cutting edge on the first leg.

In the circular form tools shown in the drawings the legs have a straight profile as viewed in side elevation, but the legs and their associated cutting edges can of course have any suitable curved or irregular profile as viewed in side elevation.

Claims

1. A method of machining workpieces in succession with a circular form tool in a power driven machine to cut the same profile on each workpiece, wherein the circular form tool is provided with a plurality of cutting edges spaced around the tool and having substantially the same profile arranged at substantially the same distance from the axis of the tool, and each cutting edge is moved into the same cutting position relative to a workpiece in the machine by angular movement of the tool about its axis whenever the cutting edge previously in use has become worn or damaged.

2. A method as claimed in claim 1 in which the circular form tool is provided with a plurality of legs having substantially the same profile arranged at substantially the same distance from the axis of the tool, each leg having one of said cutting edges, wherein each leg is moved into the same cutting position relative to a workpiece in the machine by angular movement of the tool about its axis whenever the cutting edge on a leg previously in use has become worn or damaged.

3. A method as claimed in claim 2, wherein said legs are spaced symmetrically around the axis of the tool.

4. A method as claimed in claim 2, including the step of cutting away each leg after its cutting edge has become worn in use and using the cutting edge on the adjacent leg to cut the next workpiece.

5. A method of machining workpieces in succession with a circular form tool in a power driven machine to cut the same profile on each workpiece, wherein the circular form tool is provided with a plurality of legs each having a cutting edge, said legs having substantially the same profile arranged at substantially the same distance from the axis of the tool, the spacing between a first of said legs and an adjacent leg in one direction around the tool being sufficient to permit the cutting edge on said first leg to machine a workpiece without interference between the workpiece and the other legs on the tool and provide adequate swarf clearance, but the spacing between each adjacent pair of legs in the opposite direction around the tool from said first leg being insufficient to permit the cutting edge on the second or subsequent leg to cut a workpiece, said method comprising the steps of machining workpieces with the cutting edge on said first leg, cutting away the first leg after its cutting edge has become worn or damaged to provide sufficient clearance for the cutting edge on the second leg to machine the next workpiece, and then cutting away each of the remaining legs in turn after their cutting edges have become worn or damaged to provide sufficient clearance for the cutting edge on the next succeeding leg to machine a workpiece.

6. A method as claimed in any of the preceding claims, wherein at least the cutting edges on said tool are provided with a coating of titanium or other wear resisting material.

7. A method as claimed in any of the preceding claims, wherein the circular form tool is held stationary and the workpiece is rotated during said machining thereof.

8. A method as claimed in claim 7, in which the tool is used to cut the wall of a bore in each workpiece.

9. A circular form tool suitable for use in machining workpieces by the method as claimed in any of the preceding claims, the tool comprising a core formed with a plurality of legs integral with the core and spaced around the axis thereof, each leg having a cutting edge adapted to cut material from a workpiece when fed into cutting engagement therewith, wherein the cutting edges on said legs have substantially the same profile arranged at substantially the same distance from the axis of the core, and the spacing between the legs is sufficient to enable at least one of the cutting edges to perform a cutting operation on a workpiece while the other cutting edges are out of cutting engagement with the workpiece.

10. A circular form tool as claimed in claim 9, wherein said legs are spaced symmetrically around said core.

11. A circular form tool as claimed in claim 9, wherein the spacing between an adjacent pair of said legs is substantially greater than the spacing between any other adjacent pair of said legs.

12. A circular form tool as claimed in any of claims 9-11, wherein the tool is made from a cylindrical blank by machining the blank in directions parallel to the axis thereof to cut-out segments from the periphery of the blank, the remaining portions of the periphery between the cut-out segments forming the legs of the tool.

13. A circular form tool as claimed in claim 12, wherein one end of said core is formed with a cylindrical shoulder integral with the adjacent ends of the legs, the radially outer surface of the shoulder being flush with the radially outer surfaces of the legs.

14. A circular form tool as claimed in claim 13, wherein said one end of the core is formed integral with a shank co-axial with the core.

1 5. A circular form tool as claimed in any of claims 9-14, wherein the cutting edges on the legs are provided with a coating of titanium or other wear resisting material.

16. A method of machining workpieces as claimed in any of claims 1-8 and substantially as hereinbefore described with reference to the accompanying drawings.

17. A circular form tool substantially as hereinbefore described with reference to Figures 4 and 5 or Figures 6 and 7 of the accompanying drawings.