GB2157989A - Rotary cutting tool - Google Patents

Abstract

A rotary cutting tool e.g. drill or end mill is disclosed wherein a concave part (23) is formed at a tip (2) which is plate-like and polygonal, and has a bottom cutting edge (10) and a circumferential cutting edge in a position including the axis of the shank body (1). The concave part extends in the direction from the flat part (21) of the above-mentioned tip toward the side face (22) thereof. The ridgeline created by the concave part, the above- mentioned flat face, and the above- mentioned side face is made to be a cutting edge (24) at the centre of revolution, and this cutting edge has a non-cutting zone of 0.1-3 mm set aside around the centre of the axis of the tool. The concave part can have a second further concave portion within the main portion. <IMAGE>

Description

SPECIFICATION Rotary cutting tool This invention relates to rotary cutting tools such as drills, end mills, and the like which chiefly conduct cutting in the axial direction of the tool (drilling working) or in the axial and radial directions thereof (planing working.

There are known various kinds of cutting edges used in drills which mainly conduct axial cutting, or rotary cutting edges such as end mills which mainly conduct radial cutting. An example of a cutting edge for drills, is one where a negative-angle chisel is formed on the central part of the tool, connected with a linear cutting edge. Another exmaple of such a cutting edge is a throwaway type where the end part of the tip is situated on the axis of the tool and the cutting edges are arranged radially, extending from the central part of the tool toward the outer circumferential side. An example of a rotary cutting edge for end mills is one where a linear cutting edge is formed extending from a position over the axis of the tool to the outer circumferential part thereof.

Another example of a rotary cutting edge is one where any cutting edge is not provided at the central part of the tool.

However, the drill having the chisel is disadvantageous because the centripetalism is disturbed, the thrust load and the mechanical horsepower required for the purpose of drilling are increased, and the precision of the worked hole is poor. The throwaway type has the disadvantage that chipping in the cutting edge of the central part due the difference between the cutting edge of the central part and the cutting edge of the circumferential side increases the abrasion of the circumferential cutting edge, because all cutting edges are linear from the central part of the tool to its circumference.As for the end mill, it has the disadvantage that, although it can perform radial cutting efficiency on the basis of the cutting edge being linear and further because of its being over the axis of the tool or its not being formed at the central part of the tool, it is unsuitable for axial cutting.

This invention has been made with a view to overcoming the disadvantages mentioned above.

According to the invention there is provided a rotary cutting tool where a concave part is formed at a tip, plate-lie and polygonal, having a bottom cutting edge or a circumferential cutting edge and a bottom cutting edge, which concave part is made situated in a position including the central part of the axis of the shank body fixing the tip in the direction from the flat face of the tip toward the side face thereof; where the ridgeline part created by the concave part, the flat face of the tip, and the side face thereof is made to be a cutting edges used for cutting round the part of the center of revolution of the tool; and where the ridgeline of the cutting edges has a non-cutting zone of 0.1-3 mm set aside round the center of the axis of the tool.

The invention also provides a rotary cutting tool where a concave part is formed at a tip, plate-like and polygonal, having a bottom cutting edge or a circumferential cutting edge, which concave part is made situated in a state where the tip is fixedly secured on a shank body in a position including the central part of the axis of the above body and in the direction of from the flat face of the above tip toward the side facethereof; the concave part being made up of at least more than two dents; and where the ridgeline part created by the concave part, flat face of the tip, and the side face thereof is made to be a cutting edge used for cutting round the centre of revolution of the tool.

The rotary tool of the invention, if used in end mills, allows not only the usual radial cutting but also axial cutting, thereby enlarging the field of application of this tool, reducing the breakage of the cutting edge, and enhancing the efficiency of the cutting operation. If the rotary tool is used in drills, it greatly reduces the thrust load and the amount of the horsepower used in the machine at the time of drilling, prevents the breakage of the cutting edge which is to cut round the central part of the tool and the deposition of chips on the cutting edge, and diminishes the abrasion of the circumferential edge.

In this way, the rotary cutting tool increases the precision of the worked hole while maintaining its centripetalism, has a high working efficiency, and prolongs the life of the tool.

An embodiment of the invention will now be described in detail, by example only, with reference to the accompanying drawings, wherein: Fig. 1 shows an end mill, (a) of which is a front view and (b) is a bottom view of (a); Fig. 2 is an enlarged view of (b) of Fig. 1; Fig. 3 shows a drill, (a) of which is a front view and (b) is a bottom view of (a); Fig. 4 shows a throwaway tip, (a) of which is a front view and (b) is a bottom view of (a); Fig. 5 shows a throwaway tip having a different form, (a) of which is a front view and (b) is a bottom view of (a); Fig. 6 shows an end mill, (a) of which is a front view and (b) is a bottom view; Fig. 7 shows a throwaway tip, (a) of which is a front view and (b) is a bottom view; Fig. 8 shows a throwaway tip having a different form, (a) of which is a front view and (b) is a bottom view;; Fig. 9 is an enlarged view of the concave part of a throwaway tip, (a) of which shows a variation in design, and (b) is an enlarged view of part of Fig. 7; and Fig. 10 shows a drill, (a) of which is a front view and (b) is a bottom view.

To begin with, the description will be directed to the throwaway tip (hereinafter referred to simply as the "tip") on the basis of Figs. 4 and 5.

The tips 2, 2, are plate-like and polygonal, having a flat face 21 which becomes a rake face at the toolfitting time and a side face which becomes a relief face, and have ridgelines created by the intersections of these faces as the cutting edges 10, 1 Oa. The concave parts 23, 23, of the tips are provided adjacent the noses 27, 27 and incline from the flat face 21 toward the side faces 22, 22. The ridgelines created by the above-mentioned concave parts, the flat face 21, and the side faces 22 are the cutting edges 24, 24, of the centre of revolution. It does not matter if the relief faces 25, 25, including the side faces 22, 22 are formed at one or all sides in positive angles or negative angles or zero angles, but in this example they are all consistently made in positive angles.Reference numeral 26 indicates a hole through which a clamp screw 3 for fastening the tip to the tip seat 12 on the shank body 1 (fig. 1) penetrates.

It is not of importance whether the bottoms of the above-mentioned concave parts 23, 23, are formed of a curved surfaces or of a combination of a curves and plane surfaces.

In the tip 2, shown in Fig. 5 (a) and (b), there are formed at the concave parts 23, 23, chamfers 126, 126b having the prescribed angles of inclination 6, 8,. . In this respect, it is different from the tip shown in Fig. 4(a) and (b). It should be noted that, it is satisfactoryforthe concave parts 23, 23, to be formed other than on the flat face 21 independently as shown in the figure, namely to be formed so as to include the noses 27, 27. Again, the form of the tip may be another polygonal form such as a trigonal form.

The tip constructed as above is fixedly but detachably secured by a clamp screw on the tipfitting seat of the shank body 1 which is provided at its end part with a notched part 11 for removing the chips and also tip seat 12, as shown in Figs. 1 to 3.

Further the tip is situated in a position where the concave part 23 of the tip includes the axis 13 of the above-mentioned body, and moreover the tip is fitted on the shank body in such a manner that the ridgeline 24 of the cutting edges may form a reference circled within a range of 0.1-3 mm around the central axis 13 of the above-mentioned body when the tool rotates.

If the above ridgeline of the cutting edge is situated less than 0.1 mm from the axis 13 of the tool body, the thrust load augments and the cutting edge is damaged in the axial cutting, so that smooth cutting is obstructed. On the other hand, the ridgeline of the cutting edge is situated further away than 3 mm, the non-cutting zone becomes larger and a large uncut area is left so that a core is produced which can collide with the tip and break the tip.

In contrast, the tool now being described has the ability to perform the working efficiency even when the rotation of the central part of the tool is extremely slow at the time of the axial cutting, because the concave part 23 is formed in a position corresponding to the axis 13 of the body, and the ridgelines created by the concave parts, the flat face 21 of the tip, and the side faces 22 thereof act as the cutting edges 24, 24,. Moreover, although the previously mentioned known tool requires an under-hole for conducting the axial cutting, the tool now described does not need any under-hole and enables the drilling working to be done none the less. More than that, the cutting edge formed in the concave part provided on this tool may be curved in the central part of the tool, thereby having a long effective cutting edge.Thus, the deposition of chips on the cutting edge of the central part is prevented, and though chips are generated effectively, the chips are easily divided so that they are easily removed. This means that the thrust load at the time of the cutting is reduced, the centripetalism is increased, and the precision of the worked hole is enhanced.

Further, if using the tip 2, with the chamfers 126, 126b, it is possible to reduce the abrasion of the relief face and thereby to prolong the life of the tip.

Also, by using the tips having the concave parts 23, 23i formed so as to include the sides of the noses 27, 27, the same effects as mentioned above are obtainable. Of course, these advantages can also be applied to the drill, as shown in Fig. 3. It is to be noted that the central part of Fig. 3(b) corresponds to the central part of the enlarged view in Fig. 2.

Description will be now directed to the tips in Figs.

7-9; as these figures are the same as Figs. 4 and 5 except for the concave parts 23, 231,the same reference numerals are used.

The concave parts 23, 23, in these tips are made up of two dents, one being 23a and another being 23b (see Fig. 9(b)), and the ridgelines created by these dents, the above-mentioned flat face, and the above-mentioned side faces intersecting one another form the cutting edges 24, 24,, 242 about the centre of rotation.

By fitting the above-mentioned tips on to end mills or drills, as shown in Fig. 6 or Fig. 10, it is possible to do effectively the cutting of the part rotating slowly to an extreme round the centre of axis 13 of the tool, and it can also improve the drilling capability of the tool, that is, cutting edges can be made in a longish form on the basis of the concave parts constructed by the two dents, whereby chips which are generated round the central part of the tool are thin, are easy to divide in pieces, and are small in width. Accordingly, it becomes possible by the use of the tool described to prevent the deposition of chips on the cutting edges to facilitate the removal of chips, thereby allowing the cutting around the central part of the tool to be conducted smoothly and reducing the cutting resistance by a large margin.

There is no necessity for restricting the number of dents forming the concave parts to two. Three or more dents can be formed depending on the cutting condition or others to be made to be the cutting edges. It is convenient for cutting if the joining parts a, a,; b, b, (see Fig. 9) are made to join together smoothly by giving radii of curvature thereto. Also, the ridgeline cutting edges, if an adequate honing is added thereto, become more effective. As for the form of the dents, the same effectiveness as mentioned above is exhibited if another dent 23d is added to the whole of the dent 23c, as shown in Fig.

9(a).

Description will now be made of the actual results of working conducted by a rotary cutting tool constructed according to the invention: The tool used was 20 mm in diameter and was loaded on a vertical milling machine (7.5 kW). The material to be cut, which was of S55c (HB170~200) and of 50 mm in thickness, was fixed on the table of the machine. The number of revolutions of the machine was 1,200 rpm; the feed per revolution was 0.08 mm/rev with the tips described with regard to Figs.1~5, and 0.1 mm/rev with the tips described with regard to Figs. 610. Drilling to a depth of 10 mm was conducted on the abovementioned material smoothly and successfully.

Next, a single-edged tool of 20 mm diameter equipped with a tip made of cermet belonging to the nitride group was loaded on an automiller (7.5 kW), by means of which radial cutting was conducted on a material HPM1 (HRC37.7) at the same time as the axial feed. The number of revolutions of the machine was 850 rpm, the axial feed F was 60 mm/ min (f=0.08 mm/rev), and the radial feed F was 85 mm/min (f=0.1 mm/rev). Under these conditions, a groove of 3 mm in depth and of 20 mm in width and extending over 35 mm could be cut by both the tips described in Figs. and the tips described in Figs. 610 without difficulty.

Further, a comparative test between conventional end mills and examples of end mills constructed according to the invention was made with respect to the cutting resistance: The material of the tips used in both tools was the same cermet belonging to the nitride group, and each of the tools used was of a single-edge and was of 20 mm in diameter. These tools each were loaded on the automiller (7.5 kW), and the materials to be cut (FC25) were separately cut by dry-way axial cutting.

The measurement of the cutting resistance was made with the feed being raised by stages from 0.05 mm/rev up to 0.15 mm/rev, and the number of revolutions being set within the range of from 600 rpm to 1,200 rpm.

The test result was as follows: In the case of conventional end mills, the cutting torque was about 200 kg/cm on average, and the thrust required for the cutting was about 100 kg on average. In the case of the end mills of this invention with the tips described with respect to Figs.1~5, the torque in question was about 75 kg/cm on average, and the thrust in question was about 60 kg/cm on average. Further, in the case of the end mills of this invention with the tips described in respect to Figs.

610, the torque in question was 60 kg/cm on average and the thrust in question was 50 kg on average.

Claims (9)

1. A rotary cutting tool wherein a concave part is formed at a tip, which is plate-like and polygonal, and has a bottom cutting edge or a bottom cutting edge and a circumferential edge, which concave part includes the axis of a shank body fixing said tip in a direction from the flat face of said tip toward the side faces thereof, wherein a ridgeline created by said concave part, said flat face, and said side faces forms a cutting edge for cutting around the centre of revolution of the tool; and wherein said cutting edge or said ridgeline has a non-cutting zone of 0.1-3 mm around the axis of the tool.

2. A rotary cutting tool wherein a concave part is formed at a tip, which is plate-like and polygonal, and has a bottom cutting edge or a bottom cutting edge and a circumferential cutting edge, which concave part coincides when said tip is fixedly secured on a shank body with the axis of said body and runs in a direction from said flat face of said tip toward the side faces thereof, wherein said concave part is formed of at least two dents, and wherein a ridgeline created by said concave part, said flat face, and said side faces forms a cutting edge for cutting around the centre of revolution of the tool.

3. A rotary cutting tool as set forth in claim 1 to 2, wherein said tip has chambers with a prescribed inclination formed at said concave parts.

4. A rotary cutting tool as set forth in claim 1 or 2, where said concave parts are not independently formed on the rake faces of said tip, but are formed so as to include the nose sides.

5. A rotary cutting tool as set forth in claim 4, wherein said tip has chamfers with a prescribed inclination formed at said concave parts.

6. A rotary cutting tool as set forth in claim 1 or 2, where the form of the bottom of said concave parts is of a straight line or a combination of a curve with a straight line.

7. A rotary cutting tool as set forth in claim 2, where the joining part between the dents is rounded.

8. A rotary cutting tool as set forth in claim 2 or 7, where said concave part has a second dent formed within the whole of the first dent.

9. A rotary cutting tool substantially as herein described and as illustrated in the accompanying drawings.