WO1998035126A1

WO1998035126A1 - A method of mounting a cutting member in a tool body

Info

Publication number: WO1998035126A1
Application number: PCT/DK1998/000044
Authority: WO
Inventors: Mogens Bjarne Nielsen
Original assignee: American Tool Companies A/S
Priority date: 1997-02-10
Filing date: 1998-02-04
Publication date: 1998-08-13
Also published as: AU5749398A

Abstract

Cutting tools, such as drills, may comprise a cutting member (11) which is made from cemented carbide and mounted in an open channel (13) formed in a tool body (10) made from steel or another metal. The cutting member (11) is fixed in a position by means of a braze metal which together with the inner part of the cutting member and the adjacent channel walls is heated to a fusing temperature. In order to reduce thermal stresses created in the cutting member due to the brazing process the open channel (13) is shaped such that at least along a substantial part of the channel depth the channel width is decreasing continuously from the opening of the channel towards the bottom thereof.

Description

A METHOD OF MOUNTING A CUTTING MEMBER IN A TOOL BODY

The present invention relates to a method of mounting a cutting member made from cemented carbide or a similar hard metal in a tool body made from a different metal, such as steel. The tool being made may, for example, be a drill, such as a hammer drill or another drill of the percussive type.

Such drills are conventionally made from a fluted steel drill body and from a plate- like cutting member made from cemented carbide. A slot or channel defined between a pair of paral- lei, opposite side walls is formed at one end of the drill body, and the cutting member is arranged in this channel and fused together with the channel walls by a brazing process. The characteristics, such as the coefficient of linear thermal expansion, of the material from which the drill body and the cutting member or drill bit, respectively, are made are quite different. Therefore, when during the brazing process the cutting member and the adjacent parts of the drill body are heated to a fusing temperature and subsequently cooled substantial tensile and compressive stresses are induced in the cutting member, in the brazing metal and in the adjacent parts of the drill body.

The cemented carbide from which the cutting member is made is very hard and wear resistant, but also very brittle, which means that the cutting member is able to resist only rather limited stresses. In order to enable the cutting member to resist the stresses induced by the brazing process and under subsequent operational conditions the brittleness of the material from which the cutting member is being made and, consequently, also the hardness and wear resistance of the cutting member has to be kept within certain limits.

EP 0353214 A2 , EP 0516581 A2 , EP 0669448 Al and DE 3426977 Al disclose various proposals for solving the above problem. Thus, EP 0353214 A2 proposes the use of support plates made of cemented carbide for positioning the cutting member in the channel of the drill body during the brazing process, while EP 0516581 A2 and EP 0669448 Al propose the use of a channel being widened at the channel bottom. Finally, DE 3426977 Al suggests a substantial spacing between the bottom of the channel and the lower end of the cutting member inserted therein.

It has been found that the hardness and wear resistance of the cutting member may be substantially increased if the cross-sectional shape of the channel or slot formed in the tool body and/or the cross-sectional shape of the cutting member received in the channel is/are designed so as to minimize the maximum tensile stress induced in the cutting member during the brazing process.

A substantial reduction of the maximum tensile stress induced in the cutting member by fusing the cutting member and the tool body together may be obtained by the method according to the invention comprising forming in the tool body an open channel which at least along a substantial part of the depth of the channel has a width decreasing continuously from the opening of the channel towards the bottom thereof, positioning an inner part of the cutting member in the channel, an outer part of the cutting member extending outwardly from the channel opening, and fusing the inner part of the cutting member together with metal defining adjacent wall parts of the channel by heating to a fusing temperature and subsequently cooling said inner part of the cutting member and said adjacent wall parts.

By using such inwardly tapering shape of the channel the maximum tensile stress induced in the brittle material of the cutting member may be substantially reduced. Consequently, a type of cemented carbide having an increased hardness and wear resistance may be used, whereby the operational lifetime of the tool thus produced may be prolonged and/or the efficiency of the tool may be substantially improved. The cutting member may be fused together with the tool body by any suitable method, such as by resistance welding. Preferably, however, the cutting member and the tool body are interconnected by brazing, and it has been found that the maximum tensile stress induced in the material of the cutting member is reduced when the width of the space defined between the inner part of the cutting member and the adjacent channel wall parts, which is filled by braze metal, is increased. Therefore, the width of this space or brazing seam should preferably be chosen at a maximum value. The braze metal may be introduced in said space, for example in the form of sheet metal or metal wires, prior to heating and fusing. Alternatively, the brazing metal may be introduced into the said space in a molten condition.

In order to position the cutting member correctly in the channel when the tool parts are being brazed or fused together spacing means may be arranged between the inner part of the cutting member and the adjacent channel wall parts prior to heating. Such spacing means may be of any suitable type and is preferably made from metal. The brazing means may be made from a metal with a melting point exceeding the fusing temperature to which the inner part of the cutting member and the adjacent channel wall parts are heated, and the spacing means will then be able to position the cutting member correctly also when fusing or brazing is taking place. Alternatively, the spacing means may be made from braze metal, and in such case the spacing means may constitute or form part of the braze metal used for fusing the cutting member and the tool body together.

The cross-sectional shape of the inner part of the cutting member needs not necessarily completely correspond to the inwardly tapering cross-sectional shape of the channel, which means that the width of the space defined between the inner part of the cutting member and the adjacent channel wall parts may vary to some extent. However, in the preferred embodiment the cross-sectional shape of the inner part of the cutting member is substantially complementary to the cross- sectional shape of the channel so as to define a substantially uniform spacing between the inner part of the cutting member and the adjacent channel wall parts.

The spacing means may be in the form of sheet metal or sheet metal strips having a thickness corresponding to the desired spacing between the cutting member and the adjacent channel walls. Alternatively or additionally, the spacing means may comprise one or more metal wires extending transversely to the longitudinal direction of the channel. Thus, each metal wire may be positioned along the walls of the inwardly tapering channel in a plane extending substantially at right angles to the longitudinal axis of the channel. The cutting member may then be pressed into the channel and retained in position by the friction between the metal wire or wires and/or sheet metal strips . The metal wires or metal strips may, for example, be made from copper.

In principle, the channel and the inner part of the cutting member received therein may have cross-sectional shapes varying along the length of the channel. However, this is disadvantageous for reasons of manufacture. Therefore, the cross-sectional shapes of the channel and of the inner part of the cutting member received therein are preferably substantially unchanged along the length of the channel.

The inner part of the cutting member is preferably symmetrical about a longitudinal symmetry plane, while the outer part of the cutting member may be symmetrical or asymmetric about that plane. In the presently preferred embodiment the outer part of the cutting member defines a cutting edge extending substantially parallel with and spaced from the symmetry plane .

The open channel formed in the tool body may be defined by a pair of opposite side walls and a bottom wall. Any of the side walls may comprise any combination of plane, convexly curved and/or concavely curved wall parts provided that the channel width is decreasing continuously from the opening of the channel towards the bottom thereof along a major part of the channel depth or along substantially the total channel depth. Thus, the channel side walls may be shaped differently or may be symmetrical about a longitudinal symmetry plane . Any of the side walls may, for example, be substantially plane or concavely or convexly curved. Alternatively, any of the side walls may comprise two or more plane surface parts defining angles therebetween and/or two or more convexly or concavely curved surface parts or any combination thereof.

In a presently preferred embodiment each channel side wall comprises an outer wall part being shaped substantially as a convex section of a circular cylinder surface and an inner plane wall part extending tangentially in relation to the cylindrical outer wall part. In another preferred embodiment each channel side wall is shaped substantially as a concave section of a circular cylinder surface.

It has been found, that the tensile stresses to which the cutting member is exposed may be reduced by increasing the height of the outer part of a cutting member extending outwardly from the channel opening of the tool body in relation to the total height of the cutting member. However, for practical reasons the relationship between the height of the inner and outer part, respectively, has to be kept within certain limits. Preferably, the height of the outer part of the cutting member is 1/5-2/5, preferably 1/3 of the total height of the cutting member.

The present invention also relates to a tool comprising a tool body being made from metal, such as steel, and defining an open channel which at least along a substantial part of the depth of the channel has a width decreasing continuously from the opening of the channel towards the bottom thereof, and a cutting member made from cemented carbide and having an inner part, which is received in the channel and fused together with metal defining adjacent wall parts of the channel, and an outer part extending outwardly through the channel opening.

It has been found that the maximum tensile stress to which the cutting member is exposed due to heating and subsequent cooling during the fusing process may be substantially reduced when the channel has a cross-sectional taper from the channel opening towards the bottom of the channel.

The tool may be of any known type having one or more channels for receiving a cutting member therein, such as a hammer drill which may have a single channel or crossing channels for receiving cutting members of cemented carbide or another hard metal .

The invention will now be further described with reference to the drawings, wherein

Figs. 1 and 2 are side views showing the cutting end of a conventional hammer drill,

Fig. 3 is a perspective view of the cutting member of the hammer drill shown in figs. 1 and 2 where stress zones have been indicated,

Fig. 4 is a diagrammatic longitudinal sectional view of the cutting end of a hammer drill according to the invention, and

Figs. 5 and 6 are diagrammatic side views of two diffe- rent embodiments of the tool according to the invention showing the cross-sectional shapes of the channel of the tool body and of the cutting member received therein.

Figs. 1 and 2 illustrate the cutting end portion of a conventional hammer drill comprising a drill body 10 and a cutting member 11 which is made from cemented carbide. Longitudinally extending helical flutes 12 for transporting bore meal out from a hole being drilled are formed on the outer peripheral surface of the drill body 10. A transversely extending open channel 13 is formed in the free end of the drill body 10 for receiving the cutting member 11. The channel 13 is defined by a pair of opposite, parallel side walls 15 and by a transversely spaced bottom wall 14, and the cross-sectional shape of the cutting member 11 is complementary to the cross- sectional shape of the channel in which it is received. As best shown in Fig. 1 the edge portions of the cutting member 11 extends outwardly from the drill body 10 so as to form the cutting edges of the tool or drill. The cutting member 11 and the adjacent parts of the drill body 10 are brazed together, and the brazing process involves heating of the cutting member 11 and the adjacent parts of the drill body 10 to a high temperature and subsequent cooling. Because the coefficient of linear thermal expansion for steel - from which the drill body is usually made - is much higher than the coefficient of linear thermal expansion of cemented carbide the brazing process induces substantial stresses in the material of the cutting member, in the brazing material and in the material of the adjacent parts of the drill body 10.

Fig. 3 illustrates the stresses induced in the cutting member 11 of a conventional hammer drill as illustrated in Figs. 1 and 2 due to the brazing process. In Fig. 3 the dark zone indicates compression stresses while the light zones indicate tensile stresses. It is apparent that tensile stresses are induced especially along the edges of the cutting member 11. As mentioned above, the cutting member 11 is made from cemented carbide which is a hard and wear resistant, but rather brittle material which is unable to resist substantial tensile forces. Therefore, the tensile stresses induced by the brazing process are very disadvantageous and preclude the use of a harder, more wear resistant, but also more brittle material for the cutting member 11.

Fig. 4 diagrammatically illustrates an embodiment of the tool according to the invention in which the channel 13 and the cutting member 11 have a shape so as to substantially reduce the tensile forces induced in the cutting member 11 during a brazing or fusing process. As shown in Fig. 4, the channel 13 is tapering from the opening of the channel towards the bottom wall 14 of the channel . In the embodiment shown in Fig. 4 the opposite channel side walls are slightly concavely curved. When the cutting member 11 is to be mounted in the channel 13 one or more spacing wires 16, for example copper wires may be positioned in the channel 13. Each wire is positioned as shown in Fig. 4 so as to extend along the inner walls of the channel 13 in a plane substantially at right angles to the longitudinal axis of the channel. The inner part 17 of the cutting member 11 may now be pressed into frictional engagement with the wire 16 whereby it may be retained in the correct position during a subsequent brazing or fusing process. A part 18 of the cutting member 11 pro- trudes in the axial direction of the drill body 10 outwardly from the channel 13 and defines a cutting edge 19 which is spaced from the axis 20 of the drill body 10.

Fig. 5 illustrates an embodiment in which each of the channel side walls 15 is formed by an outer, convexly curved wall part 21 and an inner, plane wall part 22 extending tangen- tially in relation to the curved, cylindrical wall part 21.

EXAMPLES

Drills having an outer diameter of 5.6 mm and with channel and cutting member designs as shown in Figs. 5 and 6, respec- tively, are made.

Fig. 5 shows a drill with dimensions as indicated in Fig. 5. The angle defined between the opposite plane side wall parts 22 may be varied so as to obtain a friction between the cutting member 11 and the spacing wire 16 sufficient to retain the cutting member 11 in position. Also the radius r and the angle v indicated in Fig. 5 may be chosen as desired. The embodiment shown in Fig. 6 corresponds to the embodiment shown in Fig. 4 and is made with the dimensions indicated in Fig. 6.

The cutting members 11 of the embodiment shown in Figs. 5 and 6 are made from cemented carbide in which the cobalt content is reduces from 8 to 6 percent whereby the wear resistance is considerably increased. The useful life of the hammer drills produced is considerably increased compared to conventional hammer drills of the type shown in Figs. 1 and 2.

It should be understood that various amendments and modifications of the embodiments shown in the drawings could be made within the scope of the present invention. Thus, the side walls 15 of the channel 13 may have any suitable shape provided that the channel tapers continuously from its opening towards its bottom wall 14. It should also be understood that the invention could also be utilized in connection with other types of cutting tools than percussive drills.

Claims

1. A method of mounting a cutting member (11) made from cemented carbide in a tool body (10) made from metal, such as steel, said method comprising: forming in the tool body an open channel (13) which at least along a substantial part of the depth of the channel has a width decreasing continuously from the opening of the channel towards the bottom thereof, positioning an inner part (17) of the cutting member (11) in the channel, an outer part (18) of the cutting member (11) extending outwardly from the channel opening, and fusing the inner part of the cutting member together with metal defining adjacent wall parts of the channel by heating to a fusing temperature and subsequently cooling said inner part (17) of the cutting member and said adjacent wall parts.

2. A method according to claim 1, wherein braze metal is introduced in the space defined between the inner part (17) of the cutting member (11) and the adjacent channel wall parts prior to heating and fusing.

3. A method according to claim 2, further comprising arranging spacing means (16) between the inner part (17) of the cutting member (11) and the channel wall parts prior to heating so as to facilitate positioning of the cutting member in relation to the tool body (10) .

4. A method according to claim 3, wherein the spacing means (16) is made from a metal with a melting point exceeding the fusing temperature to which the inner part of the cutting member and the adjacent channel wall parts are heated.

5. A method according to claim 3, wherein the spacing means are made from braze metal.

6. A method according to any of the claims 1-5, wherein the cross-sectional shape of the inner part (17) of the cutting member (11) is substantially complementary to the cross- sectional shape of the channel (13) so as to define a sub- stantially uniform spacing between the inner part of the cutting member and the adjacent channel wall parts.

7. A method according to any of the claims 4-6, wherein the spacing means comprises at least one metal wire (16) extending transversely to the longitudinal direction of the chan- nel.

8. A method according to any of the claims 1-7, wherein the channel (13) is shaped so as to minimize the maximum tensile stresses to which the cutting member (11) is exposed due to fusing and subsequent cooling.

9. A method according to any of the claims 1-8, wherein the cross-sectional shapes of the channel (13) and of the inner part (17) of the cutting member (11) received therein are substantially unchanged along the length of the channel.

10. A method according to any of the claims 1-9, wherein the inner part (17) of the cutting member (11) is symmetrical about a longitudinal symmetry plane .

11. A method according to claim 10, wherein the outer part (18) of the cutting member (11) defines a cutting edge (19) extending substantially parallel with and spaced from the symmetry plane.

12. A method according to any of the claims 1-11, wherein the channel (13) is defined by a pair of opposite side walls (15) and a bottom wall (14) , each side wall comprising an outer wall part (21) being shaped substantially as a convex section of a circular cylinder surface and an inner, plane wall part (22) extending tangentially in relation to the cylindrical outer wall part.

13. A method according to any of the claims 1-12, wherein the channel (13) is defined by a pair of opposite side walls (15) and a bottom wall (14) , each side wall being shaped substantially as a concave section of a circular cylinder surface.

14. A method according to any of the claims 1-13, wherein the height of the outer part (18) of the cutting member (11) extending outwardly from the channel opening of the tool body

(10) is 1/5 - 2/5, preferably 1/3, of the total height of the cutting member.

15. A method according to any of the claims 1-14, wherein the tool is a drill of the percussive type, such a hammer drill.

16. A tool comprising: a tool body (10) being made from metal, such as steel, and defining an open channel (13) , which at least along a substantial part of the depth of the channel has a width decreasing continuously from the opening of the channel towards the bottom (14) thereof, and a cutting member (11) made from cemented carbide and having an inner part (17) , which is received in the channel and fused together with metal defining adjacent wall parts of the channel, and an outer part (18) extending outwardly through the channel opening.

17. A tool according to claim 16, wherein the inner part (17) of the cutting member (11) is fused to the adjacent wall parts of the channel (13) by means of braze metal.

18. A tool according to claim 16 or 17, wherein the cross- sectional shape of the inner part (17) of the cutting member

(11) is substantially complementary to the cross-sectional shape of the channel (13) .

19. A tool according to any of the claims 16-18, wherein the channel (13) and the cutting member (11) are shaped so as to minimize the maximum tensile stress to which the cutting member is exposed due to fusing of the cutting member to the adjacent channel wall parts (14, 15) .

20. A tool according to any of the claims 16-19, wherein the cross-sectional shapes of the channel (13) and of the inner part (17) of the cutting member (11) received therein are substantially unchanged along the length of the channel (13) .

21. A tool according to any of the claims 16-20, wherein the inner part (17) of the cutting member (11) is symmetrical about a longitudinal symmetry plane .

22. A tool according to any of the claims 16-21, wherein the channel (13) is defined by a pair of opposite side walls (15) and a bottom wall (14) , each side wall comprising an outer wall part (21) being shaped substantially as a convex section of a circular cylinder surface and an inner, plane wall part (22) extending tangentially in relation to the cylindrical outer wall part.

23. A tool according to any of the claims 16-22, wherein the channel (13) is defined by a pair of opposite side walls (15) and a bottom wall (14) , each side wall being shaped substan- tially as a concave section of a circular cylinder surface.

24. A tool according to any of the claims 16-23, wherein the height of the outer part (18) of the cutting member (11) extending outwardly from the channel opening of the tool body

(10) is 1/5 - 2/5 of the total height of the cutting member (11) .

25. A tool according to claim 24, wherein the height of the outer part (18) of the cutting member (11) is about 1/3 of the total height of the cutting member.

26. A tool according to claim 21 and any of the claims 22-25, wherein the outer part (18) of the cutting member (11) defines a cutting edge (19) extending substantially parallel with and spaced from the symmetry plane .

27. A tool according to any of the claims 16-26 being a drill of the percussive type, such as a hammer drill.

AMENDED CLAIMS

[received by the International Bureau on 22 July 1998 (22.07.98), original claims 1-27 replaced by amended claims 1-25 (5 pages)]

1. A method of mounting a cutting member (11) made from cemented carbide in a tool body (10) made from metal, such as steel, said method comprising: forming in the tool body an open channel (13) defined by a pair of opposite side walls (15) and a bottom wall (14) at least along a substantial part of the depth of the channel the width of the channel or the mutual spacing of its opposite side walls (15) decreasing continuously from the opening of the channel towards the bottom wall (14) , positioning an inner part (17) of the cutting member (11) in the channel, an outer part (18) of the cutting member (11) extending outwardly from the channel opening, and fusing the inner part of the cutting member together with metal defining adjacent wall parts of the channel by heating to a fusing temperature and subsequently cooling said inner part (17) of the cutting member and said adjacent wall parts, at least part of at least one of the channel side walls being formed with a concavely or convexly curved cross-sectional shape so as to minimize the maximum tensile stresses to which the cutting member is exposed due to fusing and subsequent cooling.

4. A method according to claim 3 , wherein the spacing means (16) is made from a metal with a melting point exceeding the fusing temperature to which the inner part of the cutting member and the adjacent channel wall parts are heated.

6. A method according to any of the claims 1-5, wherein the cross-sectional shape of the inner part (17) of the cutting member (11) is substantially complementary to the cross- sectional shape of the channel (13) so as to define a substantially uniform spacing between the inner part of the cutting member and the adjacent channel wall parts.

7. A method according to any of the claims 4-6, wherein the spacing means comprises at least one metal wire (16) extending transversely to the longitudinal direction of the channel .

8. A method according to any of the claims 1-7, wherein the cross-sectional shapes of the channel (13) and of the inner part (17) of the cutting member (11) received therein are substantially unchanged along the length of the channel.

9. A method according to any of the claims 1-8, wherein the inner part (17) of the cutting member (11) is symmetrical about a longitudinal symmetry plane.

10. A method according to claim 9, wherein the outer part (18) of the cutting member (11) defines a cutting edge (19) extending substantially parallel with and spaced from the symmetry plane.

11. A method according to any of the claims 1-10, wherein each channel side wall (15) comprises an outer wall part (21) being shaped substantially as a convex section of a circular cylinder surface and an inner, plane wall part (22) extending tangentially in relation to the cylindrical outer wall part.

12. A method according to any of the claims 1-10, wherein each channel side wall (15) is shaped substantially as a concave section of a circular cylinder surface.

13. A method according to any of the claims 1-12, wherein the height of the outer part (18) of the cutting member (11) extending outwardly from the channel opening of the tool body (10) is 1/5 - 2/5, preferably 1/3, of the total height of the cutting member.

14. A method according to any of the claims 1-13, wherein the tool is a drill of the percussive type, such a hammer drill.

15. A tool comprising: a tool body (10) being made from metal, such as steel, and defining an open channel (13) defined by a pair of opposite side walls (15) and a bottom wall (14) at least along a substantial part of the depth of the channel the width of the channels or the mutual spacing of its opposite side walls decreasing continuously from the opening of the channel towards the bottom wall (14) thereof, and a cutting member (11) made from cemented carbide and having an inner part (17) , which is received in the channel and fused together with metal defining adjacent wall parts of the channel, and an outer part (18) extending outwardly through the channel opening, at least part of at least one of the channel side walls (15) being formed with a concavely or convexly curved cross-sectional shape so as to minimize the maximum tensile stresses to which the cutting member is exposed due to fusing and subsequent cooling.

16. A tool according to claim 15, wherein the inner part (17) of the cutting member (11) is fused to the adjacent wall parts of the channel (13) by means of braze metal.

17. A tool according to claim 15 or 16, wherein the cross- sectional shape of the inner part (17) of the cutting member (11) is substantially complementary to the cross-sectional shape of the channel (13) .

18. A tool according to any of the claims 15-17, wherein the cross-sectional shapes of the channel (13) and of the inner part (17) of the cutting member (11) received therein are substantially unchanged along the length of the channel (13) .

19. A tool according to any of the claims 15-18, wherein the inner part (17) of the cutting member (11) is symmetrical about a longitudinal symmetry plane.

20. A tool according to any of the claims 15-19, wherein each side wall (15) comprises an outer wall part (21) being shaped substantially as a convex section of a circular cylinder surface and an inner, plane wall part (22) extending tangentially in relation to the cylindrical outer wall part.

21. A tool according to any of the claims 15-20, wherein each side wall is shaped substantially as a concave section of a circular cylinder surface.

22. A tool according to any of the claims 15-21, wherein the height of the outer part (18) of the cutting member (11) extending outwardly from the channel opening of the tool body

(10) is 1/5 - 2/5 of the total height of the cutting member

(11) .

23. A tool according to claim 22, wherein the height of the outer part (18) of the cutting member (11) is about 1/3 of the total height of the cutting member.

24. A tool according to claim 19 and any of the claims 20-23, wherein the outer part (18) of the cutting member (11) defines a cutting edge (19) extending substantially parallel with and spaced from the symmetry plane.

25. A tool according to any of the claims 15-24 being a drill of the percussive type, such as a hammer drill.