CUTTING TOOL HAVING SILICONIZED SILICON CARBIDE SHANK CONNECTED TO DIAMOND CUTTING HEAD VIA VACUUM-BRAZED THERMAL INTERFACE

Abstract

A rotating cutting tool having a shank composed of siliconized silicon carbide (SiSiC), and a diamond cutting head that is mechanically connected to and in thermal communication with the shank via a vacuum-brazed thermal interface.

Claims

1. A cutting tool for ultra-precision machining, comprising: a cutting tool head having a cutting edge to contact a workpiece during operation of the cutting tool, the cutting tool head being composed of a single-crystal diamond material; a shank having a shank body composed of siliconized silicon carbide; and a thermal interface composed of a metal material to form a vacuum-brazed connection between the cutting tool head and the shank body, the thermal interface being configured for thermal and physical contact between the cutting tool head to the shank body, wherein the thermal interface is configured to serve as a thermal conductor to transfer heat from the cutting tool head to the shank body, and the shank body is configured to act as a heat sink to transfer heat from the thermal interface in order that an operational temperature of the cutting edge is less than 482 C.

2. The cutting tool cutting tool of claim 1, wherein the cutting tool head is mechanically connected to and in thermal communication with the shank via a vacuum-brazed thermal interface.

3. The cutting tool cutting tool of claim 1, wherein the cutting tool head contacts the holder body at a single plane of contact interface where atomic bonds are shared.

4. The cutting tool cutting tool of claim 1, wherein the metal material has a thermal conductivity that is greater than the thermal conductivity of a holder material but less than the thermal conductivity of diamond.

5. The cutting tool cutting tool of claim 1, wherein the metal material comprises a silver alloy.

6. A cutting tool for ultra-precision machining, comprising: a cutting tool head having a cutting edge to contact a workpiece, the cutting tool head being composed of diamond; a cutting tool head holder upon which the cutting tool head is mounted, the cutting tool head holder being composed of a holder material having a thermal conductivity of at least 225 W/m.sup.2K and a modulus of elasticity of not less than 340 GPa; and a thermal interface configured for thermal and physical contact between the cutting tool head to the cutting tool head holder, the thermal interface being composed of a thermal conducting material to form a vacuum-brazed connection between the cutting tool head and the cutting tool head holder, and to also transfer heat from the cutting tool head to the cutting tool head holder in order to maintain an operational temperature of the cutting edge at less than a predetermined temperature.

7. The cutting tool of claim 6, wherein the holder material comprises siliconized silicon carbide.

8. The cutting tool of claim 6, wherein the predetermined temperature comprises 482 C.

9. The cutting tool of claim 6, wherein the cutting tool head contacts the cutting tool head holder at a single contact interface.

10. The cutting tool of claim 6, wherein the thermal conducting material comprises a metal material.

11. The cutting tool of claim 10, wherein the metal material has a thermal conductivity that is greater than the thermal conductivity of the cutting tool head holder and less than the thermal conductivity of diamond.

12. The cutting tool of claim 11, wherein the metal material comprises a silver alloy.

Description

DRAWINGS

[0032] Embodiments will be illustrated by way of example in the drawings and explained in the description hereinbelow.

[0033] FIG. 1 is a perspective view of an embodiment of a cutting tool.

[0034] FIG. 2 is a side sectional view of the cutting tool, in accordance with embodiments.

[0035] FIG. 3 is a block diagram of the cutting tool, in accordance with embodiments.

DESCRIPTION

[0036] Important terms:

[0037] Graphitization: The result of heating the exposed surface of a diamond, in the presence of oxygen, to 900 F. (482 C.) via rubbing or friction contact. This specific, hot, impinging, and/or sliding action causes the exposed diamond molecules, in the area of contact, to physically convert from diamond to the stable form of carbon, which is graphite. Once converted to graphite, it is swept away by the friction action, exposing fresh diamond molecules below it. Graphite does not re-convert to diamond.

[0038] Coefficient of Thermal Conductivity or Heat Transfer Coefficient: measured in Watts per square Meter Kelvin (W/m.sup.2K), and is a measure of how fast heat flows through a given material, from where heat is generated to where heat is extracted. Larger values equates to faster heat flow.

[0039] Siliconized Silicon Carbide (SiSiC): a solid material based on silicon carbide (SiC), and is enhanced with 15% pure silicon to produce a significantly greater thermal conductivity (225 W/m.sup.2K) than just pure silicon carbide.

[0040] Modulus of elasticity: the measure of a materials' elasticity, lower numbers indicate very elastic (bendable), higher numbers indicate a lack of elasticity (rigidity or stiffness), measured in Giga-Pascals (GPa).

[0041] Diamond: the solid, single piece having a cutting edge skillfully sculpted, and includes a flat surface specifically produced to provide a mating interface to the shank. The diamond must be skillfully selected for exceptional quality and crystalographically oriented for optimum cutting edge performance. Internal flaws and one specific orientation {111} must be avoided.

[0042] Tungsten Carbide (non-enhanced): a man-made material (thermal conductivity of 83 W/m.sup.2K) used extensively where high rigidity is desired (Modulus of elasticity=500 GPa). The industrial nickname for this material is Carbide.

[0043] Silicon Carbide (non-enhanced): SiC is a man-made powdered material that when formed into a solid is used as a heat sink (thermal conductivity of 100 W/m.sup.2K).

[0044] Thermal expansion and contraction: measured in microinches per F., per inch of material thickness. Most materials expand when warmed and contract when cooled. Each material has a known amount of expansion/contraction. This is stated as the materials coefficient of thermal expansion or CTE. For example, Steel shrinks or expands 7 millionths of an inch per F. per inch of thickness. Aluminum's CTE is 13 millionths of an inch per F. per inch of thickness.

[0045] Surface Figure Accuracy: The deviation from the perfect, exact, mathematical model, and the actual surface profile produced. Measured in fractions of a wavelength of red laser light.

[0046] Surface Roughness (Rq): The microscopic RMS surface texture, with its peaks and valleys, averaged over an area of about of a square millimeter, measured in Angstroms because that is how smooth the customer needs it to be.

[0047] Special units of measure:

[0048] 1 Microinch equals 1 millionth of 1 inch.

[0049] 1 Micron (one one-thousandths of a millimeter) approximately equals 40 millionths of 1 inch.

[0050] 1 Angstrom=110.sup.10 meter (or one ten billionth of a meter). 254 Angstroms equal 1 microinch.

[0051] 1 wavelength or Wave of red laser light approximately equals 25 microinches.

[0052] Temperatures measured in either Kelvin or the Celsius scale are interchangeable in mathematical calculations.

[0053] As illustrated in FIGS. 1 to 3, embodiments relate to a cutting tool 10 to perform ultra-precision machining of a workpiece. The cutting tool 10 includes a cutting tool head 11 having a cutting edge 11a to contact the workpiece during a machining operation. In accordance with embodiments, the cutting tool head 11 comprises a single-crystal diamond material. Embodiments are intended to cover diamond-machining processes performed at or near room temperature and atmospheric pressure, and in the presence of oxygen.

[0054] A shank 12 is specifically configured to serve as a heat sink which transfers heat H generated by frictional contact between the cutting edge 11a and the workpiece. The shank 12 comprises a shank body connected at one end to a tool post 13 and another end to the cutting tool head 11. In accordance with embodiments, the shank is composed of a material having a predetermined thermal conductivity that permits the transfer of heat from the cutting tool head 11 at a rate sufficient to prevent the operational temperature of the cutting tool edge 11a to exceed 482 C. This advantageously prevents undesirable graphitization, reduces or otherwise eliminates operational wear of the cutting edge 11a caused by graphitization, thereby extending the operating life of the cutting tool head 11. In accordance with embodiments, the predetermined thermal conductivity of such a material is 225 W/m.sup.2K. The material may, for example, comprise siliconized silicon carbide (SiSiC). The chemical composition of the shank 12 may be, for example, approximately 85% pure silicon carbide, and approximately 15% pure silicon (with less than approximately 0.05% other materials). The modulus of elasticity the shank 12 should not be less than 340 GPa and its thermal conductivity should not be less than 225 W/m.sup.2K. This is in opposition to use of an enhanced tungsten shank that has a maximum thermal conductivity of 113 W/m.sup.2K.

[0055] Taking into account a 200 C. input, the shank 12, which is composed of SiSiC, is configured to distribute the frictional heat to the tool post, through 1.125 square inches of contact surface, thereby heating the junction surfaces to 30 C. The SiSiC shank dissipates approximately 27.76 W of heat. 2251.125170/1550 (1550 square inches to a square meter)=27.76 W dissipated.

[0056] Accordingly, use of a shank material having a thermal conductivity that prevents the cutting edge 11a from reaching a predetermined threshold temperature of 482 C. 225 W/m.sup.2K will serve to prolong the operational life of a diamond head used for a precision cutting tool. There is a breakpoint somewhere between 113 W/m.sup.2K and 150 W/m.sup.2K, where heat finally travels fast enough so that the diamond head is not heated to the point where the diamonds' cutting edge 11a attains a temperature of 482 C.

[0057] As illustrated in FIGS. 2 and 3, a thermal interface 14 is arranged between the cutting tool head 11 and the shank 12. The thermal interface 14 is configured to form a thermal and physical connection between the cutting tool head 11 and the shank 12. In accordance with embodiments, the thermal interface 14 is configured to serve as a thermal conductor which transfers the frictional heat from the cutting tool head 11 to the shank 12 via heat conduction.

[0058] In accordance with embodiments, the thermal interface 14 is composed of a thermal conducting material, such as, for example, a metal material. Such a metal material may comprise, for example, a silver-based alloy which is vacuumed brazed to form a vacuum-brazed connection between the cutting tool head 11 and the shank 12. The metal material should have a thermal conductivity that is greater than the thermal conductivity of the shank 12 but less that the thermal conductivity of the diamond cutting tool head 11. In that way, the thermal interface 14 is configured to quickly transfer heat H from the cutting tool head 11 so that an operational temperature of the cutting edge 11a does not reach or go above the threshold temperature of 482 C. when contacting the workpiece. In accordance with embodiments, a heat-conductive paste is to be applied at any boundary(ies) between the shank 12 and the lathe where heat transfer can be enhanced. The cutting tool head 11 is configured to contact the shank 12 at a single plane of contact interface where atomic bonds are shared.

[0059] In operation, the cutting tool 10 is to perform such that heat H is transferred from the diamond cutting tool head 11 to the thermal interface 14, then to the shank 12, and then to the tool-holder/tool post 13.

[0060] Practice of embodiments provide for numerous technical advantages. For instance, use of an enhanced SiSiC shank 12 results in quick removal of heat H generated by the diamond cutting tool edge 11a during operation of the cutting tool 10. In that way, the temperature of the cutting edge 11a does not reach or exceed the threshold temperature of 482 C. when contacting the workpiece. Consequently, operational wear caused by graphitization is significantly limited or otherwise eliminated. This thereby extends the operating life of the cutting tool 11, and reduces overall maintenance costs connected to the replacement of cutting tools due to the fact that the entire tool 10 must be removed and sent to the sharpening service. The head is not removed from the shank to facilitate sharpening.

[0061] The shank 12, due to it comprising a SiSiC material, limits graphitization of all single-crystal diamonds, natural mined stones, or synthetically grown diamonds. Polycrystalline (PCD) and Chemical Vapor Deposition (CVD) diamond tooling will also be benefitted. It bears noting that PCD diamond heads (and so the cutting edge) cannot be sharpened to much better than chip free at 250 power magnification due to of the diamond powder being oriented in the {111} cleave plane.

[0062] The cutting tool 10 advantageously has a design in which the diamond head 11 and the shank 12 are connected at a single contact surface by a vacuum-brazed connection that also serves as a thermal interface 14. This serves to quickly transfer heat H from the cutting edge 11a of the diamond cutting tool head 11 to the heat sink (i.e., shank 12). The shank 12 may then transfer the heat H to the tool-holder/tool post 13.

[0063] In accordance with embodiments, the diamond cutting tool head 11 must be vacuum-brazed to the shank 12, and not sintered. Sintering is a mechanical capture method which does not permit the sharing of atomic bonds, and thus, allows the diamond cutting tool head 11 to become loose in its mount at a microscopic level, significantly impairing its ability to produce minimized roughness and accurate surface figure. In accordance with embodiments, therefore, the diamond cutting tool head 11 is configured to contact the shank 12 only through the braze media of the thermal interface 14 therebetween, where atomic bonds are shared between the diamond cutting tool head 11 and the shank 12. The thermal conductivity of the silver-braze media is greater than that of the shank 12, but less than that of the diamond cutting tool head 11.

[0064] In accordance with embodiments, diamond-machining processes where air, coolants, and/or lubricants are directed into the machining interface may be used in conjunction with the cutting tool 10 to further enhance the transfer of heat (about 20 Watts/m.sup.2K).

ADDITIONAL NOTES AND EXAMPLES

[0065] Example One may include a cutting tool for ultra-precision machining, comprising: a cutting tool head having a cutting edge to contact a workpiece during operation of the cutting tool, the cutting tool head being composed of a single-crystal diamond material; a shank having a shank body composed of siliconized silicon carbide; and a thermal interface composed of a metal material to form a vacuum-brazed connection between the cutting tool head and the shank body, the thermal interface being configured for thermal and physical contact between the cutting tool head to the shank body, wherein the thermal interface is configured to act as a thermal conductor to transfer heat from the cutting tool head to the shank body, and the shank body is configured to act as a heat sink to transfer or conduct heat from the thermal interface in order that an operational temperature of the cutting edge is less than 482 C.

[0066] Example Two may include the cutting tool of Example One, wherein the cutting tool head is mechanically connected to and in thermal communication with the shank via a vacuum-brazed thermal interface.

[0067] Example Three may include the cutting tool of Example One, wherein the cutting tool head contacts the holder body at a single plane of contact interface where atomic bonds are shared.

[0068] Example Four may include the cutting tool of Example One, wherein the metal material has a thermal conductivity that is greater than the thermal conductivity of a holder material but less than the thermal conductivity of diamond.

[0069] Example Five may include the cutting tool of Example One, wherein the metal material comprises a silver alloy.

[0070] Example Six may include a cutting tool for ultra-precision machining, comprising: a cutting tool head having a cutting edge to contact a workpiece, the cutting tool head being composed of diamond; a cutting tool head holder upon which the cutting tool head is mounted, the cutting tool head holder being composed of a holder material having a thermal conductivity of at least 225 W/m.sup.2K and a modulus of elasticity of not less than 340 GPa; and a thermal interface configured for thermal and physical contact between the cutting tool head to the cutting tool head holder, the thermal interface being composed of a thermal conducting material to form a vacuum-brazed connection between the cutting tool head and the cutting tool head holder, and to also transfer heat from the cutting tool head to the cutting tool head holder in order to maintain an operational temperature of the cutting edge at less than a predetermined temperature.

[0071] Example Seven may include the cutting tool of Example Six, wherein the holder material comprises siliconized silicon carbide.

[0072] Example Eight may include the cutting tool of Example Six, wherein the predetermined temperature comprises 482 C.

[0073] Example Nine may include the cutting tool of Example Six, wherein the cutting tool head contacts the cutting tool head holder at a single contact interface.

[0074] Example Ten may include the cutting tool of Example Six, wherein the thermal conducting material comprises a metal material.

[0075] Example Eleven may include the cutting tool of Example Ten, wherein the metal material has a thermal conductivity that is greater than the thermal conductivity of the cutting tool tip holder and less than the thermal conductivity of diamond.

[0076] Example Twelve may include the cutting tool of Example Eleven, wherein the metal material comprises silver or a silver alloy.

[0077] The terms coupled, attached, or connected may be used herein to refer to any type of relationship, direct or indirect, between the components in question, and may apply to electrical, mechanical, fluid, optical, electromagnetic, electromechanical or other connections. In addition, the terms first, second, etc. are used herein only to facilitate discussion, and carry no particular temporal or chronological significance unless otherwise indicated.

[0078] Those skilled in the art will appreciate from the foregoing description that the broad techniques of the embodiments can be implemented in a variety of forms. Therefore, while the embodiments have been described in connection with particular examples thereof, the true scope of the embodiments should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, specification, and following claims.