ALUMINUM DIAMOND CUTTING TOOL

Abstract

A novel diamond cutting tool and its use in cutting and grinding applications. The cutting surface of the tool is composed of an aluminum/diamond metal matrix composite comprising diamond particles dispersed in a matrix of aluminum or an aluminum alloy, and wherein the diamond particles have thin layers of beta-SiC chemically bonded to the surfaces thereof.

Claims

1. In a method for machining a workpiece comprising cutting or grinding said workpiece with a rotating cylindrical diamond cutting tool comprising an outer diamond-containing cutting surface bonded to an inner metal core, the improvement wherein said cutting surface is composed of an aluminum/diamond metal matrix composite comprising diamond particles dispersed in a matrix of aluminum or an aluminum alloy, said diamond particles having thin layers of beta-SiC chemically bonded to the surfaces thereof.

2. The method of claim 1, wherein said aluminum/diamond metal matrix composite has a thermal conductivity of greater than about 500 W/mK.

3. The method of claim 1, wherein said cutting surface has a thickness of from about 0.020 inch to about 1.00 inch.

4. The method of claim 1, wherein the beta-SiC layers chemically bonded to the surfaces of the diamond particles are comprised of a conversion coating formed by a chemical vapor reaction of SiO with the diamond particles.

5. The method of claim 1, wherein said matrix is an alloy of aluminum containing silicon as the second major component.

6. The method of claim 1, wherein the concentration of diamond particles in said aluminum/diamond metal matrix composite is within the range of from about 20 to about 80 volume percent.

7. The method of claim 6, wherein said diamond particles concentration is within the range of from about 55 to about 70 volume percent.

8. The method of claim 1, wherein said diamond particles are coarse diamond particles having an average particle size of about 150 micron.

9. The method of claim 1, wherein said diamond particles are fine diamond particles having an average particle size of about 15 micron.

10. The method of claim 1, wherein said inner metal core is formed of titanium, stainless steel, zirconium or molybdenum.

11. The method of claim 1, wherein said outer cutting surface and said inner metal core are each provided with interlocking grooves or protrusions for improved bonding between them.

12. The method of claim 1, wherein said diamond cutting tool also includes a cylindrical metal shank member secured at one end thereof to said inner metal core and coupled at its other end to an apparatus for rotating said tool.

13. The method of claim 12, wherein said shank member is formed as an integral unit with said inner metal core.

14. A diamond cutting tool comprising a cylindrical outer diamond-containing cutting surface bonded to an inner metal core, said cutting surface being composed of an aluminum/diamond metal matrix composite comprising diamond particles dispersed in a matrix of aluminum or an aluminum alloy, said diamond particles having thin layers of beta-SiC chemically bonded to the surfaces thereof.

15. The diamond cutting tool of claim 14, wherein said aluminum/diamond metal matrix composite has a thermal conductivity of greater than about 500 W/mK.

16. The diamond cutting tool of claim 14, wherein said cutting surface has a thickness of from about 0.020 inch to about 1.00 inch.

17. The diamond cutting tool of claim 14, wherein the beta-SiC layers chemically bonded to the surfaces of the diamond particles are comprised of a conversion coating formed by a chemical vapor reaction of SiO with the diamond particles.

18. The diamond cutting tool of claim 14, wherein said matrix is an alloy of aluminum containing silicon as the second major component.

19. The diamond cutting tool of claim 14, wherein the concentration of diamond particles in said aluminum/diamond metal matrix composite is within the range of from about 20 to about 80 volume percent.

20. The diamond cutting tool of claim 19, wherein said diamond particles concentration is within the range of from about 55 to about 70 volume percent.

21. The diamond cutting tool of claim 14, wherein said diamond particles are coarse diamond particles having an average particle size of about 150 micron.

22. The diamond cutting tool of claim 14, wherein said diamond particles are fine diamond particles having an average particle size of about 15 micron.

23. The diamond cutting tool of claim 14, wherein said inner metal core is formed of titanium, stainless steel, zirconium or molybdenum.

24. The diamond cutting tool of claim 14, wherein said outer cutting surface and said inner metal core are each provided with interlocking grooves or protrusions for improved bonding between them.

25. The diamond cutting tool of claim 14, further including a cylindrical metal shank member secured at one end thereof to said inner metal core.

26. The diamond cutting tool of claim 25, wherein said shank member is formed as an integral unit with said inner metal core.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a perspective view of a typical diamond cutting tool in accordance with the present invention.

[0011] FIG. 2 is an enlarged schematic view of a portion of the diamond cutting tool of FIG. 1.

[0012] FIG. 3 is a transverse sectional view of the diamond cutting tool of FIG. 2 taken along section line 3-3 of FIG. 2.

DESCRIPTION OF DEPICTED EMBODIMENTS

[0013] A typical diamond cutting tool 10 in accordance with the present invention is illustrated in FIG. 1. As shown in detail in FIGS. 2 and 3, the cutting tool 10 comprises a cylindrical outer diamond-containing cutting surface 12 bonded to an inner metal core 14. A cylindrical metal shank member 16 is secured at one end thereof to the core 14. In the depicted embodiment, as best shown in FIG. 2, the shank member 16 is formed as an integral unit with the core 14, but may be a separate piece otherwise secured to the core 14, for example, by means of a threaded connection. As shown in FIG. 3, the cutting surface 12 and core 14 are each provided with interlocking grooves 18 and protrusions 20 for improved bonding between them. Although it should be appreciated that alternative manners for improving the bonding between the cutting surface 12 and the core 14 are contemplated, the surface of core 14 can also be roughened by a knurling process or an alternative interlocking shape such as threading to improve bonding with surface 12.

[0014] The heart of the present invention resides in utilizing, as the diamond-containing material of the cutting surface 12, an aluminum/diamond metal matrix composite comprising diamond particles dispersed in a matrix of aluminum or an aluminum alloy, and wherein the diamond particles have thin layers of beta-SiC chemically bonded to the surfaces thereof. This is an entirely new use for these Al/Diamond MMCs, whose previously known use was primarily as a heat-dissipating substrate in electronic applications. It has now been surprisingly discovered that the extremely high thermal conductivity and enhanced bond mechanical strength attributed to the SiC layers on the diamond particles help to render these Al/Diamond MMCs equally attractive as a diamond cutting tool cutting surface.

[0015] The core 14/shank member 16 combination is formed of a material that is easily machinable, has a coefficient of thermal expansion (CTE) similar to that of the Al/Diamond MMC so as to form a firm bond therewith and not impart undue thermally induced stresses so as to prevent premature failure and minimize dimensional change during heating or cooling, and has a dimensionally true cylindrical region for attaching the tool to the apparatus rotating the tool. Preferred materials are titanium, stainless steel, zirconium and molybdenum.

[0016] Fabrication of the diamond cutting tool of the present invention is carried out in a two-piece tooling designed to hold in place the core or core/shank member combination and create a pocket around the core in which the SiC-coated diamond particles can be packed for infiltration with molten aluminum. The tooling needs to have porosity or gates to allow the flow of molten aluminum to enter, encompass and coat the diamond particles. The tooling also needs to be dimensionally stable and be compatible with the temperature used in aluminum casting (800° C.) and also the CTE of the Al/Diamond MMC to ensure that undue break-inducing stresses are not placed on the MMC or tooling during the heating and cooling process of production, the casting does not get stuck due to being rigidly constrained by the tooling, and the tooling is re-usable in subsequent castings. For these reasons, the tooling is typically made from graphite, graphite/AI which has a CTE between 5-8 ppm/K, and/or titanium which has a CTE between 8.5-10.0 ppm/K.

[0017] The SiC-coated diamond particles employed in fabricating the diamond cutting tool of the present invention are those formed by a chemical vapor reaction of SiO with the diamond particles, as described in detail in the above-referenced Pickard et al. U.S. patents incorporated herein by reference. The particle size of the diamond particles will vary based on the cutting requirements of the tool being fabricated. For example, for coarse grinding, coarse diamond particles having an average particle size of about 150 micron can be used, whereas fine diamond particles having an average particle size of about 15 micron can be used for fine grinding. A wide range of diamond particle sizes in between, smaller, or larger than these example sizes can be used based on the application need such as between 5 micron to 300 micron.

[0018] Aluminum is infiltrated into the tooling containing the SiC-coated diamond particles and the core or core/shank member combination, by a pressure infiltration process which may be either squeeze casting or gas pressure infiltration. Both processes involve the melting of aluminum around the tooling, a die or can that contains the tooling, and the application of high pressure (>800 psi) to force the molten aluminum through the tooling porosity and/or gates to encompass the diamond particles and provide the finished cast part geometry. The aluminum used can be pure aluminum or an aluminum alloy, preferably an alloy of aluminum containing silicon as the second major component.

[0019] The relative proportions of aluminum and diamond particles employed in the tool fabrication should be such as to provide a diamond particle concentration in the formed Al/Diamond MMC within the range of from about 20 to about 80 volume percent, preferably from about 55 to about 70 volume percent.

[0020] The above-described fabrication process can be used to produce diamond cutting tools with Al/Diamond MMC cutting surfaces of varying thickness ranging from about 0.020 inch to about 1.00 inch and exhibiting strong bond mechanical strength and extremely high thermal conductivity of greater than about 500 W/mK. When coupled through its shank member to an apparatus for rotating the tool, such as a grinder, mill, or drill press, the rotating tool may be used in the machining of various types of workpieces for various applications as listed above. Certain of these applications may, however, require some fine tuning of the tool to achieve the necessary tolerance level not achievable by the casting fabrication process described above.

[0021] Castings inherently have tolerances that can be in the range of 0.005″ to 0.010″. These casting tolerances, when present on a rotating tool, can cause run-out that is too much for certain cutting/grinding applications. Precision optical grinding applications, for example, require a run-out of approximately 10 micron (393 micro inch, 0.00039″). Furthermore, some features, such as grooves, can be difficult to cast, as they might prevent the cast cutting tool from coming out of the tooling used in fabrication. For these types of situations, rotary wire EDM machining of the tool would be the remedy and would also leave a surface with exposed diamond, necessary for cutting tool application. When the diamond becomes worn from cutting, the tool can be redressed by dissolving the aluminum and thus exposing fresh diamond surfaces. This can be done by simply dipping the cutting surface of the tool in acidic or basic solutions that are known to dissolve aluminum, such as dilute solutions of hydrochloric acid, sulfuric acid, potassium hydroxide, or sodium hydroxide.

[0022] It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.