ORDERLY-MICRO-GROOVED PCD GRINDING WHEEL FOR POSITIVE RAKE ANGLE PROCESSING AND METHOD FOR MAKING SAME

Abstract

Disclosed are an orderly-micro-grooved PCD grinding wheel for positive rake angle processing and a preparation method thereof. A PCD film is deposited on the outer circumferential surface of a wheel hub, and a plurality of microgrooves with high depth-width ratio and micro-grinding units with positive rake angles are orderly provided on the outer circumferential surface of the entire PCD film. The method includes: depositing the PCD film on the outer circumferential surface of the wheel hub by a HFCVD technique; and manufacturing a plurality of microgrooves with a high depth-width ratio (circumferential width: dozens of micrometers; depth: hundreds of micrometers) and an axial length that is equal to the thickness of the grinding wheel and a plurality of micro-grinding units with positive rake angles on the outer circumferential surface of the entire PCD film by water-jet guided laser technique, where the micro-grinding units and the microgrooves are orderly arranged.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent Application PCT/CN2019/090698, filed on Jun. 11, 2019, which 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 a preparation method thereof, and more specifically to an orderly-micro-grooved PCD grinding wheel for positive rake angle processing and a method for making the same.

BACKGROUND OF THE INVENTION

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 the grinding process, 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 damage 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 provided 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 in the grinding process 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 processed surface.

Further, in order to improve the integrity of the processed 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 processing 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 the positive-rake angle grinding. 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 processed surface, improving the integrity of the processed surface. However, in the process of processing large-sized diamond abrasive grains by laser, the high laser ablation temperature will inevitably cause partial graphitization on the diamond abrasive grains, affecting the positive-rake angle cutting of the abrasive grains for the workpiece surface and reducing the surface quality of the processed 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 processed surface and the grinding efficiency, Chinese 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 the positive-rake angle cutting, 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 OF THE INVENTION

This application provides an orderly-micro-grooved PCD grinding wheel for positive rake angle processing and a preparation method thereof to overcome the defects in the prior art.

The orderly-micro-grooved PCD grinding wheel produced herein comprises a polycrystalline diamond film (PCD film), a wheel hub, a plurality of microgrooves and a plurality of micro-grinding units, wherein the PCD film is deposited on an outer circumferential surface of the wheel hub; the microgrooves, which has an axial length that is equal to a thickness of the grinding wheel, a circumferential width of 20-50 μm, a depth of 500-800 μm and a depth-width ratio of 10-40:1, are provided on an outer circumferential surface of the PCD film; individual micro-grinding units with a positive rake angle is provided between two adjacent microgrooves; and the microgrooves and the micro-grinding units are respectively arranged in an ordered manner. In addition, the microgrooves and the micro-grinding units are connected as a whole by the PCD film, which can greatly improve the holding force of the grinding wheel on the micro-grinding units to prevent the micro-grinding units from singly falling off due to excessive or concentrated grinding force, extending the service life of the grinding wheel. At the same time, the ordered arrangement of the micro-grinding units with the positive rake angle and the microgrooves with a high depth-width ratio on the working surface of the grinding wheel can reduce the grinding force ratio, increase the chip-removing capacity and improve the chip-holding space, which effectively promotes the entering of the grinding fluid into the grinding zone to significantly improve the cooling effect for the grinding zone, reducing thermal damage to the grinding zone and effectively enhancing the grinding quality.

This application further provides a method for manufacturing the above PCD grinding wheel, comprising:

1) mechanically producing a wheel hub of a grinding wheel;

depositing a PCD film with a thickness of 1-2 mm on an outer circumferential surface of the wheel hub by a hot filament chemical vapor deposition technique (HFCVD);

2) polishing an outer circumferential surface of the diamond film by ion beam polishing to obtain a surface roughness of the PCD film of 0.15-0.2 μm;

3) processing the outer circumferential surface of the PCD film by water-jet guided laser preparation technique: focusing a laser beam emitted by a laser head in a nozzle through a glass window on a water chamber; pressurizing the water chamber to allow a water jet to be ejected from the nozzle and to guide the transmission of the laser beam to the outer circumferential surface of the PCD film; offsetting the grinding wheel by a certain angle, and producing a single microgroove with an axial length that is equal to the thickness of the grinding wheel, a circumferential width of 20-50 μm, a depth of 500-800 μm and a depth-width ratio of 10-40:1 according to a relative movement orbit of the water jet and the wheel hub; indexing the grinding wheel, and rotating an outer circumference of the PCD film through a circumferential width of one micro-grinding unit to carry out the processing of the next microgroove, wherein the micro-grinding unit with a positive rake angle is formed between the two adjacent microgrooves; and processing the micro-grinding unit to form a clearance angle;

4) repeating step (3) to form a plurality of microgrooves with high depth-width ratio and a plurality of ordered micro-grinding units with the positive rake angle at the entire circumference of the PCD film; wherein respective micro-grinding units are the same in size; and

5) subjecting the product prepared in step (4) to pickling and then ultrasonic cleaning in deionized water to form the orderly-micro-grooved PCD grinding wheel for positive rake angle processing.

The wheel hub is made of titanium alloy, and has a diameter of 100-200 mm and a thickness of 6-20 mm.

Respective micro-grinding units have an axial length that is equal to the thickness of the grinding wheel, a circumferential width of 80-150 μm, a radial height of 500-800 μm and a circumferential spacing of 100-200 μm.

In step (3), the micro-grinding units formed by processing the PCD film with the laser beam have the positive rake angle of 10°-40° and the clearance angle of 20°-50°.

A laser device used in the water-jet guided laser technique is an Nd:YAG pulse laser which has a wavelength of 532 nm and a focused spot diameter of 30-100 μm.

A pressure of the water chamber used in the water-jet guided laser technique is 2-4 MPa, and a diameter of the water jet is 20-50 μm.

Compared to the prior art, this application has the following beneficial effects.

(1) This application significantly improves the grinding performance and efficiency.

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

(2) This application significantly increases the chip-holding space and the chip-removing.

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 the grinding process, 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 area, significantly improving the cooling effect for the grinding zone, reducing the thermal damage to the workpiece surface and further enhancing the grinding quality.

(3) This application effectively avoids the graphitization of the micro-grinding units and greatly extends the service life of the grinding wheel.

When the micro-grinding units are processed by the water-jet guided laser technique, a laser beam is focused in a nozzle through a glass window on a water chamber. Then the water chamber is pressurized to allow a water jet to be ejected from the nozzle and to guide the laser beam, where the laser beam propagates along the water jet in a total reflection in the water jet. 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.

(4) This application significantly extends the service life of the grinding wheel.

The PCD film on the outer circumferential surface of the grinding wheel prepared by a HFCVD technique is operated as a whole, and each micro-grinding unit is part thereof, which greatly improves the holding force of the grinding wheel on the micro-grinding units, preventing the micro-grinding units from singly falling off due to excessive or concentrated grinding force and significantly improving the service life of the grinding wheel.

(5) This application increases the number of effective cutting edges and alleviates the periodic vibration during the grinding.

The microgrooves obtained by the water-jet guided laser technique have a circumferential width of only 20 μm, and the micro-grinding units have a circumferential spacing of only 100 μm, so that the number of micro-grinding units involved in grinding per unit area is significantly increased, greatly alleviating the periodic vibration during the grinding. The micro-grinding units prepared by the method have the characteristics of high protrusion and good consistency, so that the cutting edge of each micro-grinding unit can participate in the grinding, which greatly increases the number of effective cutting edges in the grinding process and reduces the cutting depth of the single cutting edge, effectively improving the grinding precision and efficiency.

(6) This application has simple preparation process and low cost.

The size and shape 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-Microjet device and the grinding wheel can be controlled by the numerical control technology, which greatly reduces the difficulty in preparation of the grinding wheel and lowers the cost.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a three-dimensional view showing a grinding wheel hub after deposited with a polycrystalline diamond film on the outer circumferential surface.

FIG. 2 schematically shows the processing of a microgroove by water-jet guided laser technique.

FIG. 3 is a schematic diagram showing the grinding wheel provided with microgrooves on the outer circumference and a partially enlarged view thereof.

FIG. 4 is a schematic diagram showing the processing of a workpiece with a grinding wheel and a partially enlarged view showing a contact zone between the grinding wheel and the workpiece.

In the drawings:

1—wheel hub; 2—PCD film; 3—laser head; 4—glass window; 5—water chamber; 6—nozzle; 7—laser beam; 8—water jet; 9—micro-grinding unit; 10—microgroove; 11—positive rake angle; 12—workpiece; and 13—clearance angle.

DETAILED DESCRIPTION OF EMBODIMENTS

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

Referring to FIGS. 1-4, an orderly-micro-grooved PCD grinding wheel for positive rake angle processing includes a wheel hub 1, a PCD film 2, a plurality of micro-grinding units 9 with a positive rake angle 11 and a plurality of microgrooves 10 with a high depth-width ratio. The PCD film 2 with a thickness of 1-2 mm is deposited on an outer circumferential surface of the wheel hub 1. The microgrooves 10 which have an axial length that is equal to a thickness of the grinding wheel, a circumferential width of 20-50 μm, a depth of 500-800 μm and a depth-width ratio of 10-40:1 are provided on the outer circumferential surface of the PCD film 2. The micro-grinding unit 9 with the positive rake angle 11 is provided between two adjacent microgrooves 10, and the microgrooves 10 and the micro-grinding units 9 are both orderly arranged. When the grinding wheel is configured to grind a workpiece 12, the micro-grinding unit 9 is in contact with the workpiece 12 in the positive rake angle 11, which ensures that the micro-grinding unit 9 can be used to process the workpiece in a positive rake angle 11. The microgrooves 10 are mainly configured to hold chip and store grinding liquid. The micro-grinding units 9 with a positive rake angle 11 can process the workpiece in a positive rake angle, which reduces the grinding force ratio and the grinding temperature, effectively reducing the surface damage and greatly improving the grinding performance and efficiency.

The orderly-micro-grooved PCD grinding wheel for positive rake angle processing is manufactured as follows.

Step (1)

A wheel hub 1 was mechanically prepared from titanium alloy, and had a diameter of 100 mm and a thickness of 12 mm. A PCD film 2 with a thickness of 2 mm was deposited on an outer circumferential surface of the wheel hub 1 made of titanium alloy by a HFCVD technique, then the outer circumferential surface of the PCD film 2 was polished by ion beam polishing to obtain a surface roughness of the PCD film of 0.2 μm. The prepared PCD film 2 was used as a whole, which facilitated the combination with the wheel hub 1, so that the prepared PCD film 2 can bear greater grinding force, and was less prone to falling off, improving the service life of the grinding wheel.

Step (2)

The outer circumferential surface of the PCD film 2 was processed by water-jet guided laser technique, where a laser beam 7 emitted by a laser head 3 was focused in a nozzle 6 through a glass window 4 on a water chamber 5. The water chamber 5 was 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 grinding wheel was offset by a certain angle, and a single microgroove 10 with an axial length (12 mm) that is equal to the thickness of the grinding wheel, a circumferential width of 20 μm, a depth of 500 μm and a depth-width ratio of 25 was manufactured by changing the relative movement orbit of the water jet 8 and the wheel hub 1. Then the grinding wheel was indexed, and the outer circumference of the PCD film 2 was rotated over 100 μm, i.e., the circumferential width of a micro-grinding unit 9, to carry out the processing for the next microgroove 10. The micro-grinding unit 9 with a positive rake angle of 30° was formed between the two microgrooves 10. Then the micro-grinding unit 9 was processed to form a clearance angle 13 of 40°. The micro-grinding unit 9 was configured to cut a workpiece in a positive rake angle during the grinding process, which reduced the grinding force ratio and the grinding temperature, effectively reducing the occurrence of surface micro-crack and greatly improving the grinding performance and efficiency. Meanwhile, the water-jet guided laser technique can effectively prevent the micro-grinding unit 9 from being graphitized, so that the micro-grinding unit 9 can provide better surface-cutting effect, greatly extending the service life of the grinding wheel and improving the surface quality.

Step (3)

Step (2) was repeated to form a plurality of microgrooves 10 with high depth-width ratio and a plurality of ordered micro-grinding units 9 with a positive rake angle 11 at the entire circumference of the PCD film 2, and respective micro-grinding units 9 were the same in size. The ordered arrangement of the microgrooves 10 and the micro-grinding units 9 greatly improved the chip-holding space and facilitated the formation of ordered chip-removing channels during the grinding process, so that the chip-removing capacity was improved, which made the grinding wheel less prone to blockage. Moreover, the grinding fluid was promoted to enter into the grinding zone to provide an improved cooling effect, reducing surface thermal damage and effectively improving the grinding quality and surface-processing precision. Meanwhile, respective micro-grinding units were identical in geometry and size, so that the number of micro-grinding units involved in grinding per unit area was significantly increased during the grinding process, and the cutting edge of each micro-grinding unit can participate in the grinding, which greatly increased the effective number of cutting edges and reduced the cutting depth of the single cutting edge, effectively improving the grinding precision and efficiency.

Step (4)

The prepared grinding wheel was subjected to pickling and then ultrasonic cleaning in deionized water for 15 min to form the orderly-micro-grooved PCD grinding wheel for positive rake angle processing.

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 defined by the appended claims.

Claims

1. An orderly-micro-grooved PCD grinding wheel for positive rake angle processing, comprising:

a wheel hub;

a PCD film;

a plurality of micro-grinding units with a positive rake angle; and

a plurality of microgrooves;

wherein the PCD film with a thickness of 1-2 mm is deposited on an outer circumferential surface of the wheel hub; the microgrooves are provided on an outer circumferential surface of the PCD film, wherein each of the microgrooves has an axial length that is equal to a thickness of the grinding wheel, a circumferential width of 20-50 μm, a depth of 500-800 μm and a depth-width ratio of 10-40:1; respective micro-grinding units with the positive rake angle are provided between two adjacent microgrooves, and the microgrooves and the micro-grinding units are respectively arranged in an ordered manner;

when the grinding wheel is configured to grind a workpiece, respective micro-grinding units are in contact with the workpiece in the positive rake angle to achieve positive rake angle processing; and the microgrooves are mainly configured to hold chips and store a liquid.

2. The PCD grinding wheel of claim 1, wherein the wheel hub is made of titanium alloy, and has a diameter of 100-200 mm and a thickness of 6-20 mm.

3. The PCD grinding wheel of claim 1, wherein respective micro-grinding units have an axial length that is equal to the thickness of the grinding wheel, a circumferential width of 80-150 μm, a radial height of 500-800 μm and a circumferential spacing of 100-200 μm.

4. A method of manufacturing the PCD grinding wheel of claim 1, comprising:

1) depositing the PCD film with a thickness of 1-2 mm on the outer circumferential surface of the wheel hub by a HFCVD technique;

2) polishing the outer circumferential surface of the PCD film by ion beam polishing to obtain a surface roughness of the PCD film of 0.15-0.2 μm;

3) processing the outer circumferential surface of the PCD film by water-jet guided laser preparation technology: and focusing a laser beam emitted by a laser head in a nozzle through a glass window on a water chamber; pressurizing the water chamber to allow a water jet to be ejected from the nozzle and to guide the transmission of the laser beam to the outer circumferential surface of the PCD film; offsetting the grinding wheel by a certain angle, and producing one microgroove with an axial length that is equal to the thickness of the grinding wheel, a circumferential width of 20-50 μm, a depth of 500-800 μm and a depth-width ratio of 10-40:1 according to a relative movement orbit of the water jet and the wheel hub; indexing the grinding wheel, and rotating an outer circumference of the PCD film through a circumferential width of one micro-grinding unit to carry out the processing of the next microgroove, wherein the micro-grinding unit with a positive rake angle is formed between the two microgrooves; and processing the micro-grinding unit to form a clearance angle;

4) repeating step (3) to form a plurality of microgrooves with high depth-width ratio and a plurality of ordered micro-grinding units with the positive rake angle at the entire circumference of the PCD film; wherein respective micro-grinding units are the same in size; and

5) subjecting the product prepared in step (4) to pickling and then ultrasonic cleaning in deionized water to produce the orderly-micro-grooved PCD grinding wheel for positive rake angle processing.

5. The method of claim 4, wherein the wheel hub is made of titanium alloy, and has a diameter of 100-200 mm and a thickness of 6-20 mm.

6. The method of claim 4, wherein respective micro-grinding units have an axial length that is equal to the thickness of the grinding wheel, a circumferential width of 80-150 μm, a radial height of 500-800 μm and a circumferential spacing of 100-200 μm.

7. The method of claim 4, wherein in step (3), the micro-grinding units formed by processing the PCD film with the laser beam have the positive rake angle of 10°-40° and the clearance angle of 20°-50°.

8. The method of claim 4, wherein in step (3), a laser device used in the water-jet guided laser technique is an Nd:YAG pulse laser, and the Nd:YAG pulse laser has a wavelength of 532 nm and a focused spot diameter of 30-100 μm.

9. The method of claim 4, wherein in step (3), a pressure of the water chamber used in the water-jet guided laser technique is 2-4 MPa, and a diameter of the water jet is 20-50 μm.