ORDERLY-MICRO-GROOVED PCD GRINDING WHEEL AND METHOD FOR MAKING SAME

Abstract

An orderly-micro-grooved PCD grinding wheel includes a wheel hub, a polycrystalline diamond (PCD) film, a number of micro-grinding units and a number of microgrooves. The PCD film is deposited on an outer circumferential surface of the wheel hub. The PCD film is processed by a water-jet guided laser device to form the microgrooves with high depth-width ratio and micro-grinding units with positive rake angles on the entire outer circumferential surface of the PCD film. An axial length of each micro-grinding unit and an axial length of each microgroove are equal to a thickness of the grinding wheel, respectively. The microgrooves are spaced apart by the micro-grinding units.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No. 16/677,635, filed on Nov. 7, 2019, now pending, which is a continuation of International Patent Application PCT/CN2019/090698, filed on Jun. 11, 2019, and claims the benefit of priority from Chinese Patent Application No. 201810608183.3, filed on Jun. 13, 2018. The content of the aforementioned application, including any intervening amendments thereto, is incorporated herein by reference.

TECHNICAL FIELD

This application relates to a grinding wheel and preparation thereof, and more specifically to an orderly-micro-grooved PCD grinding wheel and a method for making the same.

BACKGROUND

Grinding has been widely applied in the precision machining due to the characteristics of high processing precision and good surface quality. However, in the traditional grinding process, abrasive grains are irregularly arranged on the working surface of the grinding wheel, and vary in geometrical shape and size, so that the abrasive grains often cut the surface of the workpiece in a large negative rake angle during grinding, which will increase the grinding force ratio, accelerate the conversion of grinding energy into heat and raise the grinding temperature, affecting the surface quality and grinding efficiency. In addition, the grinding wheel also has disadvantages of small chip space and low protrusion of abrasive grains, and the grains are easy to fall off, which may easily cause a blockage at the grinding wheel and produce a local high temperature to burn the workpiece surface, and reduce the service life of the grinding wheel.

Extensive researches have been performed to find a method for improving the grinding efficiency and service life of the grinding wheel. Chinese Publication No. 107962510A, titled “CVD diamond grinding wheel with ordered surface micro-structure” put forward a method in which a diamond film is deposited on the outer circumferential surface of a grinding wheel hub by chemical vapor deposition, and a large number of staggered and ordered microgrooves and grinding units with waist-type top surface are prepared on the outer circumferential surface of the whole diamond film by pulsed laser beam. This method improves the removal rate and grinding efficiency of the surface material and increases the holding force of the grinding wheel hub for the grinding units, improving the service life of the grinding wheel to a certain extent. However, the single grinding unit is still operated at a zero rake angle during the grinding process, so that the grinding efficiency and the surface quality cannot be further improved. Meanwhile, the circumferential spacing of the orderly arranged grinding units reaches 1 mm, which will result in a typical intermittent grinding, and the generated periodic vibrations by the grinding process may also affect the integrity of the ground surface.

Further, in order to improve the integrity of the ground surface and achieve the grinding in a positive rake angle, Chinese Publication No. 105728961A, titled “Method for manufacturing a new positive-rake angle diamond grinding tool based on pulse laser”, provides a method for preparing positive rake angles of diamond abrasive grains by laser. In the method, the large single-layer diamond abrasive grains orderly arranged on the working surface of the grinding wheel are ablated by laser to obtain a point angle less than 90°, which enables grinding with a positive rake angle. The method effectively solves the problem that abrasive grains of the conventional diamond grinding wheel cut the surface of the workpiece in a large negative rake angle, which improves the processing efficiency and reduces the damage to the ground surface, improving the integrity of the ground surface. However, in the process of preparing large-sized diamond abrasive grains by laser, the high laser ablation temperature will inevitably cause partial graphitization of the diamond abrasive grains, affecting the positive rake angle cutting of the abrasive grains for the workpiece surface and reducing the quality of the ground surface. At the same time, the single large-sized diamond abrasive grain may fall off if it is subjected to excessive or concentrated force, which may affect the grinding efficiency and even reduce the service life of the grinding wheel.

In order to further improve the quality of the ground surface and the grinding efficiency, Chinese Patent Application Publication No. 107243848A, titled “A spiral ordered fiber tool for positive rake angle processing and preparation method thereof”, discloses a method in which the matrix is prepared on the grinding wheel hub by pressing and sintering, and the ordered holes are processed on the matrix using a drilling bit. Then the fiber with positive rake angle is consolidated in the small holes by the epoxy resin. The method enables cutting with a positive rake angle, and further improves the surface quality and the processing precision. However, since the fiber has a cross-sectional size of 0.8 mm×0.8 mm and the number of fibers per square centimeter on the surface of the tool is only 14.26, the single fiber may have a large cutting depth, making it difficult to ensure the processing precision. Moreover, a rupture will occur if a single fiber is subjected to an excessive or concentrated force, which may affect the service life of the grinding wheel. There are also great difficulties in the process that all the fibers are inserted into the small holes one by one and consolidated.

SUMMARY

The present disclosure provides a grinding wheel, comprising a wheel hub, a polycrystalline diamond (PCD) film, a plurality of micro-grinding units and a plurality of microgrooves;

wherein an outer circumferential surface of the wheel hub is deposited with the PCD film; the plurality of micro-grinding units and the plurality of microgrooves are orderly distributed on a whole outer circumferential surface of the PCD film; the plurality of micro-grinding units form a part of the PCD film; and the plurality of microgrooves are spaced apart by the plurality of micro-grinding units;

each of the plurality of microgrooves and each of the plurality of micro-grinding units both have an axial length equal to a thickness of the grinding wheel; the micro-grinding units each comprise two side surfaces and an outer surface; the microgrooves each comprise two side walls that form one of the two side surfaces of two adjacent micro-grinding units, respectively; and

the micro-grinding units each have an positive rake angle.

In some embodiments, the positive rake angle of each micro-grinding unit is 10°-40°, and the micro-grinding units each have a clearance angle of 20°-50°.

In some embodiments, the micro-grinding units have substantially the same geometric shapes and dimensions.

In some embodiments, a thickness of the PCD film is 1-2 mm.

In some embodiments, each micro-grinding unit has a circumferential width of 80-150 μm and a radial height of 500-800 μm.

In some embodiments, each microgroove has a circumferential width of 20-50 μm, a depth of 500-800 μm and a depth-width ratio of 10-40:1.

In some embodiments, the wheel hub is made of titanium alloy; and the wheel hub has a diameter of 100-200 mm and a thickness of 6-20 mm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view and a partial enlarged view showing a PCD grinding wheel having a number of microgrooves and a number of micro-grinding units on its entire surface in accordance with an embodiment of the present invention;

FIG. 2 is a front view and a partial enlarged view showing the grinding wheel in contact with a surface of a workpiece in accordance with an embodiment of the present invention;

FIG. 3 is a perspective view showing a grinding wheel having a wheel hub on which a PCD film is deposited in accordance with an embodiment of the present invention; and

FIG. 4 is a schematic diagram showing the processing of the PCD film on the wheel hub of the grinding wheel by a water-jet guided laser device in accordance with an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

Definitions

Term “reference plane” is a plane which is perpendicular to cutting velocity vector at a selected point on a cutting tool. Herein, the cutting tool may refer to abrasives, or particularly grinding units.

Term “cutting plane” is a plane which is tangent to the selected point of the cutting tool where it is in contact with the surface of the workpiece. The cutting plane is perpendicular to the reference plane.

Term “rake angle” is an angle between a rake face of the cutting tool and the reference plane. The rake angle may be categorized into three types: positive, zero or neutral, and negative. Herein, the cutting tool has a positive rake angle.

Term “clearance angle” is an angle between a flank face of the cutting tool and the cutting plane.

Term “substantially” herein refers to two or more elements are identical to a great extent or degree, almost, but not absolutely the same.

Term “pickling” is a metal surface treatment used to remove impurities, such as stains, inorganic contaminants, rust or scale from ferrous metals, copper, precious metals and aluminum alloys, and a solution called pickle liquor, which usually contains acid, is used to remove the surface impurities.

This application will be further illustrated with reference to the embodiments and drawings.

Referring to FIG. 1, a grinding wheel includes a wheel hub 1, a polycrystalline diamond (PCD) film 2, a plurality of micro-grinding units 9 and a plurality of microgrooves 10. An outer circumferential surface of the wheel hub 1 is deposited with a PCD film 2. The micro-grinding units 9 and the microgrooves 10 are orderly distributed on a whole outer circumferential surface of the PCD film. The microgrooves 10 are configured to hold chip and store grinding liquid.

Each microgroove 10 and each micro-grinding unit 9 both have an axial length equal to a thickness of the grinding wheel. The microgrooves 10 each have a circumferential width of 20-50 μm, a depth of 500-800 μm, and a depth-width ratio of 10-40:1. Since the arrangement of the micro-grinding units 9 and the microgrooves 10 are formed by subtractive manufacturing or processing of the PCD film, the micro-grinding units 9 are a part of the PCD film. The microgrooves 10 are spaced apart by the micro-grinding units 9 to create an ordered arrangement.

Particularly, referring to a partial enlarged view on the right side in FIG. 1, the micro-grinding units 9 each comprise two side surfaces 11, 13 and an outer surface 14. The microgrooves 10 each comprise two side walls 11, 13 which form one of the two side surfaces 11, 13 of two adjacent micro-grinding units, respectively. In other words, every two adjacent micro-grinding units and the microgroove 10 between them share the side walls/surfaces 11, 13.

Referring to FIG. 2, particularly a partial enlarged view on the right side, each micro-grinding unit 9 has a rake angle β, which is the angle between a rake face (i.e. side surface 13) of the micro-grinding unit 9 and a reference plane π_R. The rake angle β is positive, ranging from 10° to 40°. In an embodiment, the rake angle β is 10°, 15°, 20°, 25°, 30°, 35° or 40°, for the purpose of illustration.

Continuing to refer to FIG. 2, each micro-grinding unit 9 has a clearance angle α, which is the angle between a flank face (i.e. outer surface 14) of the micro-grinding unit 9 and a cutting plane π_C. The cutting plane is tangent to a selected point of the micro-grinding unit 9 on a surface of a workpiece 12, as shown in FIG. 2. Here, the selected point refers to the intersection of the rake face (i.e. side surface 13) and the flank face (i.e. outer surface 14), as seen from a front view of the grinding wheel. The reference plane π_R is perpendicular to the cutting plane π_C. The clearance angle α of the micro-grinding unit 9 is 20°-50°. In an embodiment, the clearance angle a is 20°, 25°, 30°, 35°, 40°, 45° or 50°.

FIGS. 3-4 illustrate main procedures for the manufacturing of the grinding wheel as shown in FIGS. 1-2.

Referring to FIG. 3, a layer of a PCD film 2 having a thickness of 1-2 mm is deposited on a wheel hub 1 by a hot filament chemical vapor deposition (HFCVD) technique. Hot filament CVD is a method that has been applied to the deposition of diamond films and is available to persons skilled in the art. The thickness of the PCD film 2 may be 2 mm. The wheel hub 1 may be made of titanium alloy, with a diameter of 100-200 mm and a thickness of 6-12 mm. Preferably, the diameter of the wheel hub is 100 mm, and the thickness of the wheel hub is 12 mm. The outer circumferential surface of the PCD film 2 is polished by ion beam polishing to reach a surface roughness of 0.15-0.2 preferably 0.2 The outer circumferential surface of the PCD film 2 is processed by a water-jet guided laser device, for example Laser MicroJet® Integration Package (LMJ-iP) to form a number of microgrooves and micro-grinding units on the entire surface of the PCD film 2. The process is a reduction of material, that is subtractive manufacturing, so the micro-grinding units formed is a part of the PCD film. In an embodiment, the laser device is an Nd: YAG pulse laser with a wavelength of 532 nm and a focused spot diameter of 30-100 μm.

Referring to FIG. 4, the water-jet guided laser device comprises a laser head 3, a glass window 4, a water chamber 5 and a nozzle 6. Laser beam 7 emitted by the laser head 3 is focused in the nozzle 6 through the glass window 4 on the water chamber 5. The water chamber 5 is pressurized to allow a water jet 8 to be ejected from the nozzle 6 and to guide the transmission of the laser beam 7 to the outer circumferential surface of the PCD film 2. The pressure of the water chamber is 2-4 MPa, and the diameter of the water jet is 20-50 μm. The grinding wheel is offset by a certain angle that is equal to a desired rake angle (for example 30°) of the micro-grinding unit 9, to form the first single microgroove 10. The microgroove 10 has an axial length, for example 12 mm, that is equal to the thickness of the grinding wheel. In an embodiment, the microgroove 10 has a circumferential width of 20 μm, a depth of 500 μm and a depth-width ratio of 25. During the processing, relative movement between the water jet 8 and the wheel hub 1 is changed to create the microgroove 10. The grinding wheel is indexed. When the processing of the first single microgroove 10 is finished, the outer circumference of the PCD film 2 is rotated over, for example 100 μm, i.e., a circumferential width of a micro-grinding unit 9, to carry out the processing for the next microgroove 10. Upon the completion of the second microgroove 10, the micro-grinding unit 9 is formed between the first and the second microgrooves 10. Then the micro-grinding unit 9 is processed to form a clearance angle 13, for example 40°. These procedures are repeated to continue to process the PCD film so as to form a number of microgrooves 10 with high depth-width ratio and a number of micro-grinding units 9 on the entire circumferential surface of the PCD film 2. The formed micro-grinding units 9 have substantially the same shapes and dimensions. The details about a water-jet guided laser device may refer to Yaowen W U et al. (Overview on the development and critical issues of water jet guided laser machining technology, Optics and Laser Technology, 137 (2021), 106820), Yi S H I et al. (Texturing of metallic surfaces for superhydrophobicity by water jet guided laser micro-machining, Applied Surface Science, 500 (2020) 144286) which are incorporated herein by reference.

The PCD film 2 on the wheel hub 1 is finally processed with ordered arrangement of the microgrooves 10 and the micro-grinding units 9, as shown in FIGS. 1 and 2. A pickling treatment and ultrasonic cleaning in deionized water for 15 min may be further performed on the grinding wheel.

The outer circumferential working surface of the grinding wheel is provided with a large number of micro-grinding units with positive rake angle, which ensures that the micro-grinding units are worked in a positive rake angle during grinding, lowering the grinding force ratio and temperature, effectively reducing the damage to the surface and greatly improving the grinding performance and efficiency.

A large number of microgrooves with high depth-width ratio are provided on the outer circumferential working surface of the grinding wheel, which greatly improves the chip-holding space. Meanwhile the micro-grinding units are orderly arranged so that ordered chip-removing channels are formed during grinding, which greatly improves the chip-removing capacity and makes the grinding wheel less prone to blockage, effectively promoting the entering of the grinding fluid into the grinding zone, significantly improving the cooling effect for the grinding zone, reducing the thermal damage to the workpiece surface and further enhancing the grinding quality.

When the micro-grinding units are processed by the water-jet guided laser technique, the laser beam propagates along the water jet in a total reflection. During the processing, the laser is guided by the water jet to the surface of the PCD film to ablate the PCD film, and the ablated PCD film is carried away by the water jet. Additionally, the water jet also cools the surface of the PCD film, which effectively prevents the graphitization of the micro-grinding units, providing better grinding performance and greatly enhancing the surface quality.

The service life of the grinding wheel is extended. The PCD film on the outer circumferential surface of the grinding wheel is deposited by the HFCVD technique. The micro-grinding units are a part of the PCD film, which prevents the micro-grinding units from singly falling off due to excessive or concentrated grinding force and significantly improves the service life of the grinding wheel.

The number of effective cutting edges per unit area is increased and alleviates the periodic vibration during grinding. The micro-grinding units have the characteristics of high protrusion and good consistency, so that the cutting edge of each micro-grinding unit can participate in the grinding.

The shape and dimension of the micro-grinding units on the outer circumferential surface of the grinding wheel both have a good periodicity. Therefore, in the preparation process, the relative motion relationship between the Laser-Micro jet device and the grinding wheel can be controlled by the numerical control technology, which greatly reduces the difficulty in the preparation of the grinding wheel and lowers the cost.

It should be understood that the above embodiments are only illustrative of the invention and are not intended to limit the invention. In addition, various equivalent modifications and changes made by those skilled in the art without departing from the spirit of the invention fall within the scope of the invention as defined by the appended claims

Claims

1. A grinding wheel, comprising:

a wheel hub;

a polycrystalline diamond (PCD) film;

a plurality of micro-grinding units; and

a plurality of microgrooves;

wherein an outer circumferential surface of the wheel hub is deposited with the PCD film; the plurality of micro-grinding units and the plurality of microgrooves are orderly distributed on a whole outer circumferential surface of the PCD film; the plurality of micro-grinding units form a part of the PCD film; and the plurality of microgrooves are spaced apart by the plurality of micro-grinding units;

each of the plurality of microgrooves and each of the plurality of micro-grinding units both have an axial length equal to a thickness of the grinding wheel;

the micro-grinding units each comprise two side surfaces and an outer surface; the microgrooves each comprise two side walls that form one of the two side surfaces of two adjacent micro-grinding units, respectively; and

the micro-grinding units each have a rake angle that is positive.

2. The grinding wheel of claim 1, wherein the rake angle is 10°-40°.

3. The grinding wheel of claim 1, wherein the micro-grinding units each have a clearance angle of 20°-50°.

4. The grinding wheel of claim 1, wherein the micro-grinding units have substantially the same geometric shapes and dimensions.

5. The grinding wheel of claim 1, wherein a thickness of the PCD film is 1-2 mm.

6. The grinding wheel of claim 1, wherein each of the micro-grinding units has a circumferential width of 80-150 μm and a radial height of 500-800 μm

7. The grinding wheel of claim 1, wherein each of the microgrooves has a circumferential width of 20-50 μm, a depth of 500-800 μm and a depth-width ratio of 10-40:1.

8. The grinding wheel of claim 1, wherein the wheel hub is made of titanium alloy.

9. The grinding wheel of claim 8, wherein the wheel hub has a diameter of 100-200 mm and a thickness of 6-20 mm.