LASER AUGMENTED DIAMOND DRILLING APPARATUS AND METHOD
1. A method of machining a hard and/or brittle material, the method comprising:
- directing a laser beam through at least a portion of a light-transmitting cutting tool having at least one cutting edge whereby the laser beam exits the cutting tool adjacent the cutting edge;
bringing the cutting edge into moving contact with a surface of a hard and/or brittle material whereby the laser beam heats the surface and softens the material adjacent the surface.
A laser beam is transmitted through a drill bit comprising diamond or other suitable light-transmitting material having sufficient hardness. The laser beam exits a tip of the drill bit, thereby heating and softening the material being drilled at and/or near the interface of the drill with the material being drilled. The process may be utilized to drill hard and brittle materials such as ceramics and semiconductors, composites and ceramic matrix composites. The process may cause high pressure phase transformation, resulting in a more ductile and plastic material near the drill point/tip. The process provides more rapid drilling, improved surface quality in drilled holes, and less tool wear.
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Patent #US 10,449,644 B2
Current AssigneeMicro-LAM Inc.
Sponsoring EntityMicro-LAM Inc.
|Micro Laser Assisted Machining|
Patent #US 20100065536A1
Current AssigneeThe Board of Trustees of Western Michigan University
Sponsoring EntityWestern Michigan University
|Combination apparatus for machining material with a milling cutter and a laser|
Patent #US 7,257,879 B1
Current AssigneeJenoptik Automatisierungstechnik Gmbh
Sponsoring EntityJenoptik Automatisierungstechnik Gmbh
Patent #US 4,530,627 A
Current AssigneeCooper Industries
Sponsoring EntityCooper Industries
- 1. A method of machining a hard and/or brittle material, the method comprising:
directing a laser beam through at least a portion of a light-transmitting cutting tool having at least one cutting edge whereby the laser beam exits the cutting tool adjacent the cutting edge; bringing the cutting edge into moving contact with a surface of a hard and/or brittle material whereby the laser beam heats the surface and softens the material adjacent the surface.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
- 10. A laser augmented drilling system, comprising:
a laser source; a movable cutting tool having first and second opposite ends, the second end having at least one cutting edge, and wherein the cutting tool comprises a light-transmitting material; wherein the laser source is configured to direct a laser beam from the laser source into the first end of the cutting tool whereby the laser beam is transmitted through the light-transmitting material and exits the second end of the cutting tool and heats a material being drilled by the movable cutting tool.
- View Dependent Claims (11, 12, 13, 14)
- 15. A drill bit comprising:
a metal body portion having a passageway; a tip having at least one elongated light-transmitting cutting edge that is in optical communication with the passageway such that a laser beam can be directed through the passageway and through the tip to the at least one cutting edge.
- View Dependent Claims (16, 17, 18, 19)
- 20. A method of drilling a hole in a composite material, comprising:
bringing a rotating bit into contact with a composite material in a manner that produces a hole in the composite material having a surface that is substantially free of defects.
This application claims the benefit of U.S. Provisional Application No. 62/248,863 filed on Oct. 30, 2015, entitled, “LASER AUGMENTED DIAMOND DRILLING APPARATUS AND METHOD,” the entire contents of which are incorporated herein by reference.
Drilling technology may involve various techniques and processes depending upon the material being drilled, accuracy requirements, size of the hole being drilled etc. Existing micro drilling techniques may be utilized to form various types of holes, including micro-holes. Known techniques include conventional mechanical drilling, micro-electrical discharge machining (micro-EDM), laser, photo-etching, ultrasonic and micro-electrical chemical machining (micro-ECM), etc.
One aspect of the present invention is a method of drilling utilizing a laser which is focused through a hard light-transmitting material (e.g. diamond) to a tip (cutting edge) of a tool to thermally soften hard and brittle materials during a drilling process.
Previous research has demonstrated that ductile mode machining of semiconductors and ceramics is possible due to the occurrence of high pressure phase transformation (HPPT) in the material. A laser augmented drilling system according to the present invention may be used to preferentially heat and thermally soften a workpiece material in contact with a diamond cutting tool. This heating and softening may include HPPT in materials such as semiconductors and ceramics. However, in the case of composites and other materials, HPPT may not occur. Laser augmented drilling according to the present disclosure may nevertheless be utilized in various non-HPPT materials. In materials that do not experience HPPT during laser augmented drilling, the material (in its natural or native, atmospheric state), needs only to absorb the incident laser radiation wavelength. In the case of composites, the materials are typically not transparent to the laser wavelength, like ceramics or semiconductors. Thus, the composite materials may absorb all or most of the laser energy. In a laser augmented drilling system/method according to the present invention, a laser and diamond cutting tool may be integrated into a single package. In this system/method, the laser energy is delivered by a fiber to and through a diamond cutting tool. A lens system may be utilized to focus/shape the laser beam so that the laser beam has a non-circular cross sectional shape corresponding to the cutting edge (or edges) of the diamond cutting tool. A system/method according to the present invention may increase the critical depth of cut (DoC) to provide a larger ductile-to-brittle transition (DBT) depth in ductile regime machining to thereby provide a higher material removal rate.
During laser augmented drilling operations as disclosed herein, the diamond contact and resultant pressure on the material being machined (e.g. drilled) may create a high pressure phase transformation (HPPT) (at room pressure and temperature), which lowers the hardness by converting the material from a covalent bond to a metallic bond. A ductile and plastic (softer) material results from the phase transformation. The present invention utilizes laser heating to lower the HPPT pressure to thereby create more HPPT at the same conditions (force, pressure).
However, as discussed above, it will be understood that laser augmented diamond drilling processes according to the present invention do not necessarily require HPPT, and the drilling processes of the present invention will work even if HPPT does not occur (e.g. in composite materials), or if HPPT occurs only partially. The tool/process of the present invention causes more softened and ductile material to form compared to conventional processes that do not utilize laser heating, or that utilize laser heating before or after drilling. Alternatively, utilizing laser heating permits use of a lower force on the tool to create a corresponding amount of HPPT material (compared to room/atmospheric temperature), leading to a reduced propensity for fracture, or an apparent decrease in brittleness and an increase in fracture toughness. Also, the laser heats and softens the HPPT material in situ, thereby providing enhanced ductility and plastic deformation. While the HPPT makes the material “softer” at room temperature (by rearrangement of the atomic structure into a new material and softer structure), the laser heating initially reduces the force/pressure needed to create this softened HPPT material. The laser then heats the HPPT material and provides thermal softening. This added “thermal” softening due to the laser heating is in addition to the original HPPT softening effect (due to force and pressure and atomic structure changer from covalent to metallic bonding).
As discussed in more detail below, the present invention utilizes a laser that is focused to transmit through a diamond drill bit that may have 1 or 2 cutting edges or more. A laser is focused to illuminate at least a portion (preferably the entirety) of the edge or edges of the diamond bit to thereby transmit laser energy to the work piece. The laser beam may be focused and/or directed so that it exits the diamond bit at the cutting edge and/or the rake face and/or the flank or clearance face. For example, the diamond bit may be configured such that the laser beam exits the bit simultaneously at the cutting edge, rake face, and flank faces. Also, the laser beam can be shaped/directed using suitable optical components (e.g. collimator and/or lenses) whereby the laser beam is (for example) elliptical or rectangular in cross section. The elliptical or rectangular laser beam can be directed onto/through a linear cutting edge of the diamond bit to heat material adjacent the cutting edge immediately prior to removal of the material. In general, the rake angle of a diamond bit according to the present invention may vary from positive to extremely negative, depending on the requirements of a particular application. The bit can also be tilted as required for a particular application.
The test set up described below demonstrates the technology with a single diamond crystal bit having only one edge. This single crystal/single edge drill bit of the test was formed using conventional grinding methods. A double-edged drill bit may be formed from a single diamond crystal or a poly crystal diamond (PCD). An ion-beam machining tool/process is preferably utilized to fabricate single and double edge diamond drill bits. Although conventional grinding processes may be utilized to form PCD drill bits, an ion-beam process is preferred if the drill bit comprises a single crystal diamond. An ion-beam process is also preferred if a diamond bit has a complicated geometry that cannot be formed utilizing conventional grinding processes or the like.
The system/process of the present invention may be utilized for drilling brittle materials such as ceramics, semiconductors, rocks, composites and ceramic matrix composites. As discussed above, high pressure phase transformation (HPPT) of the drilled material may occur when a material is drilled using a laser augmented diamond drilling process according to the present invention. Utilizing sufficient pressure, laser heating, etc. to cause HPPT may be advantageous in some applications because the phase transformation results in greater absorbance of laser energy by the material after the phase transformation. However, HPPT is not required, and laser heating and tool pressures resulting in thermal softening (without HPPT) may also be utilized. It will be understood that laser heating reduces the pressure needed to cause HPPT. Thus, the present invention may be utilized to provide HPPT in drilling processes at a lower pressure than would be required if no laser heating is used. Holes (bores) formed using a laser augmented system/process according to the present invention are of the expected size, and the sidewalls of the holes are smooth such that additional buffing (which could increase the diameter of the bore) is not required.
The present invention may utilize a relatively low power laser that only heats the material where the bit edge is pressing on the material to produce a localized thermal softening and/or phase transformation. The laser may comprise a green laser, or the laser may comprise an ultraviolet or infrared laser, or other suitable laser wavelengths. In contrast to known laser assisted machining (LAM) devices/processes, the present disclosure provides a laser beam that is pointed in a direction that is parallel (or approximately parallel) to the axis of rotation of the diamond drill bit. The co-axial alignment of the laser beam, drill bit and cutting (drilling) direction provides increased efficiency for the drilling process and reduced pressure required on the drill bit. Due to the alignment of the laser beam, the heat generated from the laser source (location and concentration) is of greater benefit (beneficial) for the drilling operation. Also, the alignment of the laser and drilling direction applies the heat where it is most beneficial (along the axis of the drill direction). Less laser power is needed compared to known LAM processes because the laser heating is at the same spot (co-axial) during the process. The laser decreases the pressure needed to cause a phase transformation and/or cause thermal softening of the material to provide ductile mode drilling. The laser augmented drilling system/process of the present invention also reduces wear on the drill bit due to the reduced pressure. Cutting fluids can be utilized in the system/process of the present invention. In general, cutting fluids do not interfere with the effectiveness of the laser beam. The invention may be utilized to drill materials such as tooth, bone, and gem stones. The invention may also be utilized for drilling bedrock in connection with oil and gas drilling operations and the like.
These and other features, advantages, and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification, claims, and appended drawings.
For purposes of description herein, the terms “upper,” “lower,” “right,” “left,” “rear,” “front,” “vertical,” “horizontal,” and derivatives thereof shall relate to the invention as oriented in
This application is related to U.S. Pat. No. 8,933,366, the entire contents of which are incorporated herein by reference.
Some micro drilling applications involve high quality materials that are mechanically harder. However, such materials may need to be manufactured with a high level precision and accuracy. Drilling brittle and hard materials such as ceramics and semiconductors to produce holes that are free of fractures, surface and subsurface damage and cracks and micro-cracks, with good edges and high surface quality, may be a challenge due to the low fracture toughness of these materials. Severe fracture may occur during drilling operations due to the low fracture toughness of these materials. For example silicon has a fracture toughness of 0.83 to 0.95 MPa·m0.5, depending on the crystal orientation.
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An infrared (IR) continuous wave (CW) fiber laser 6 (
It will be understood that other lasers may be utilized according to other aspects of the present invention. For example, a green laser having a wavelength of about 532 nm and a power of about 200 W may also be utilized. In general, the wavelength of the laser may be selected based, at least in part, on the type of material being machined. Some materials absorb more laser energy (i.e. higher percentage of the energy incident on the material) if the wavelength of the laser beam falls within a specific frequency range. For example, the HPPT phase of silicon absorbs more energy at around 532 nm (green) than around 1070 nm (IR laser). Thus, although an IR laser is utilized in the following example, it will be understood that this is not necessarily the preferred wavelength for all applications/materials. Also, a continuous wave (CW) laser is presently preferred to provide constant heating of the material being machined. In general, a CW laser provides constant heating that thermally softens the material being drilled to permit plastic/ductile deformation of the material without spalling. However, pulsed lasers may also be utilized if required for a particular application.
Testing of micro drilling silicon by a diamond coated drill bit utilizing the test setup of
Due to low fracture toughness of brittle materials, fracture may occur when such materials are under tensile stress. Therefore entrance and especially exit of a through hole are very important as tensile stresses are much higher than compressive stresses in these zones, particularly the latter. The testing described herein is focused on the benefits of using a laser drilling process, and the wall surface roughness and edge quality of the hole entrance produced by this process. A dimple-shaped hole 20 (
The spindle RPM for this testing was 350. For each cut, both with a laser and with no laser, load was kept at about 80 g, and the tool (drill bit 10) was fed continuously to reach a 150 micron depth. For the first test, the sample 14 was drilled with no laser to establish a baseline.
Surface roughness parameters (Ra and Rz) of the hole inner surface were measured with a white light interferometer (WYKO). Due to brittle mode cut and the fractures that occurred during the process (
For the next test a new silicon sample 14 was drilled with the aid of a laser. 10 W laser power was used for the laser-assisted testing. However, due to reflection, absorption, error of the laser, and scattering, the actual laser output was less than 4 W. In order to retain the same conditions for both tests, the same setup (
In order to help visualize the obtained surfaces, a three dimensional (3D) profile of the inner surface of the hole was generated by the WYKO profiler for each test. A 3D drilled whole wall produced by drilling without laser assist is shown in
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Laser beam location and laser beam shaping may be utilized in connection with the diamond drill bits disclosed herein. In particular, the beam can be shaped to heat the diameter (surface) of the drilled hole (OD) to impact the resultant process. Shaping the laser beam to favor heating the OD (compared to other configurations) results in additional concentration of the heating effect at the finished surface of the hole. The beam can also be shaped (focused and lengthened with an ellipse or a rectangular shape) along the length of the drill bit cutting edge as described above. Laser heating can be different along the cutting edge depending on its function. For example, increased laser heating can be utilized at the center of the tip of the drill bit to make the material being drilled as soft as possible to thereby improve the drilling efficiency and/or speed. Additional heating at the edge improves the hole quality by reducing cracking and chipping.
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A laser augmented diamond drilling (LADD) process according to the present disclosure may be used for drilling different materials such as ceramics, carbon fiber reinforced composites, ceramic matrix composites, rocks, or gems. Parameters such as RPM, laser power and feed rate may be adjusted as required for particular materials as required. LADD has been demonstrated to be beneficial for composite materials (carbon fiber composites, CFRP) and can be used on ceramic matrix composites (CMCs) as well. LADD reduces the cutting forces, thus decreasing tool bit wear. The LADD process/device described herein improves hole quality and reduces damage to the material when used to drill CFRP and CMC materials.
Cutting fluid may also be utilized in laser augmented drilling processes according to other aspects of the present disclosure. Cutting fluid does not interfere with the laser action because the laser is directed through the drill bit and not outside the drill bit, through the cutting fluid. A laser augmented diamond drilling system/process according to the present invention may be utilized to form precise holes in silicon (and other materials) in a ductile regime with higher edge quality compared to drilling without laser assist. The laser augmented diamond drilling system/process of the present invention can achieve enhanced ductility due to reduced hardness and reduced brittleness resulting from laser assisted heating and thermal softening. The present invention may also provide higher material removal rate, lower electrical power and torque needed, better surface finishes, less damage, higher quality, less tool wear, and less down time for equipment. The present invention thereby provides a more efficient and less costly drilling/machining process.
In addition to diamond, other materials that are optically transparent (to a laser beam) can be utilized to form drill bits according to other aspects of the present disclosure. Examples include sapphire, ruby, emeralds, and garnet. In general, the tool must be harder than the workpiece material. Thus, tools made from other optically transparent materials that are easier to shape can be used effectively with the LADD technology. It will be understood that the term laser augmented diamond drilling (LADD), as used herein, is not limited to processes and devices that utilize diamond drill bits.