Elastic grinding head for grinding ultrathin hard and brittle materials and grinding method

Abstract

The invention discloses an elastic grinding head for grinding ultrathin hard and brittle materials, which comprises a guide cylinder, a return spring, a T-shaped grinding head, a pressure spring and a plug which are coaxial, and the T-shaped grinding head is arranged in the guide cylinder and extends out of the bottom of the guide cylinder; the plug is mounted at the top of the guide cylinder; the pressure spring is mounted between the plug and the top of the T-shaped grinding head; the return spring is sleeved on the T-shaped grinding head; the pressure spring plays a role in conducting the pressure of a machine tool spindle on one hand, and plays a role in controlling the rigid contact pressure of a workpiece and the grinding head on the other hand, so that the elastic grinding head has elasticity, when encountering abnormal convex points on the surface of the workpiece, the elastic grinding head is lifted upwards by a certain distance, the load of a cutter at the abnormal convex points is effectively reduced, and the machining precision is improved. Concentration of machining stress at the abnormal salient points is reduced, cracks are reduced, and the rate of finished products is increased.

Description

Technical Field

[0001] The invention relates to the technical field of precision machining of hard and brittle materials, and in particular to an elastic grinding head and a grinding method for grinding ultra-thin hard and brittle materials. Background Art

[0002] In semiconductor manufacturing equipment, there are many ceramic and quartz precision parts such as silicon carbide, silicon nitride, aluminum oxide, and aluminum nitride. These parts are hard and brittle, but the processing requirements are very precise. They belong to a type of hard, brittle and difficult to process material. The traditional mechanical grinding process is equivalent to hard collision. The workpiece is very sensitive to external excitation. The vibration generated in the process will cause uneven removal of workpiece surface material, greatly affecting the grinding quality. On the other hand, the vibration often causes the workpiece to crack, collapse, and incomplete processing. To this end, improving the processing accuracy of the processing equipment to reduce the exciting force can reduce vibration, but excessive pursuit of equipment complexity and precision requirements will greatly increase manufacturing costs.

[0003] In recent years, high-frequency, low-amplitude ultrasonic-assisted processing technology has become increasingly mature. The principle of this technology is that the tool holder generates high-frequency and strong impact force under the action of the ultrasonic converter, driving the grinding rod to intermittently hit the surface of the part, causing the surface of the part to produce tiny vibrations. The local stress of the part far exceeds the brittle fracture stress of the material, thereby reducing the cutting force by 40% and the cutting heat by 30%, improving the processing efficiency and yield rate, and providing an excellent solution for processing hard and brittle materials.

[0004] However, for ultra-thin hard and brittle ceramic parts with a thickness of less than 0.5mm, such as ceramic mobile phone cases, ultra-thin ceramic heat sink substrates, SiC edge rings, special-shaped Al2O3 sealing sheets, SiC spray plates, etc., they have the characteristics of high clamping difficulty, small processing allowance, and low fracture load. Citing the three-point bending strength of typical hard and brittle ceramics of Kyocera of Japan, when the material thickness is 0.5mm, the span is 30mm, and the width is 3.0mm, the fracture load of the material is less than 10N, as shown in the following table.

[0005]

[0006]

[0007] The yield rate of such parts processed by ultrasonic-assisted machining is still very low. One reason may be that, although the impact load applied to the parts under ultrasonic-assisted machining can achieve the purpose of material removal under very small conditions, for ultra-thin hard and brittle materials, the impact load is very likely to exceed its fracture load limit, causing brittle fracture of the material; another possibility is that ultrasonic vibration-assisted machining only changes the traditional hard-to-hard machining method of constant load to intermittent hard-to-hard machining with impact load. This impact load can easily cause local stress concentration in the parts and produce more sub-surface microcracks. The cross-sectional size effect of ultra-thin hard and brittle materials makes the path for the steady-state development of microcracks extremely short, that is, the material will not fracture brittlely, but the crack expands under impact fatigue until the crack length exceeds the thickness of the ultra-thin material. This explains that in the initial stage of ultra-thin material processing, the material is intact, but as the material is further thinned, the crack gradually extends and increases and eventually breaks. Summary of the invention

[0008] In view of the above problems in the prior art, the present invention provides an elastic grinding head and a grinding method for grinding ultra-thin hard and brittle materials, which solves the problem of low yield of ultrasonic-assisted processing of ultra-thin hard and brittle ceramic parts.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0010] On the one hand, an elastic grinding head for grinding ultra-thin hard and brittle materials is provided, which includes a coaxial guide cylinder, a pull-back spring, a T-shaped grinding head, a pressure spring and a plug, wherein the T-shaped grinding head is arranged in the guide cylinder and extends from the bottom of the guide cylinder; the plug is installed on the top of the guide cylinder; the pressure spring is installed between the plug and the top of the T-shaped grinding head; and the pull-back spring is sleeved on the T-shaped grinding head.

[0011] The pressure spring of the present invention plays the role of transmitting the spindle pressure of the machine tool on the one hand, and plays the role of controlling the rigid contact pressure between the workpiece and the grinding head on the other hand, thereby making the elastic grinding head elastic. When encountering abnormal convex points on the surface of the workpiece, the elastic grinding head is lifted up a certain distance, effectively reducing the load of the tool at the abnormal convex points, reducing the concentration of machining stress at the abnormal convex points, reducing the occurrence of cracks, and improving the yield rate.

[0012] Further, the T-shaped grinding head comprises a connected T-table, a square-section long handle and a circular-section grinding end;

[0013] The pressure spring is installed between the plug and the upper surface of the T-stage; the pull-back spring is sleeved on the square-section long handle; the square-section long handle and the circular-section grinding end extend from the square hole preset at the bottom of the guide cylinder.

[0014] Furthermore, the stiffness of the pressure spring is 15N / mm to 35N / mm; the stiffness of the pull-back spring is one tenth of the stiffness of the pressure spring.

[0015] Furthermore, a pressure sensor is installed on the lower surface of the plug.

[0016] On the other hand, a grinding method according to an elastic grinding head for grinding ultra-thin hard and brittle materials comprises the following steps:

[0017] Step S1, clamping, clamping the surface to be ground of the workpiece horizontally upward on the grinding machine, collecting and recording the height value of the surface to be ground of the workpiece, and evaluating the clamping flatness of the workpiece;

[0018] Step S2, establishing a coordinate system, establishing a coordinate system at the center of the surface to be ground of the workpiece;

[0019] Step S3, measuring the back cutting amount, installing the elastic grinding head on the main shaft of the machine tool, slowly reducing the Z value, and recording the Z value when the pressure feedback from the pressure sensor in the elastic grinding head is 2 Newtons;

[0020] Step S4, programming and processing, programming is performed using the Z value recorded in step S3 as the back cutting amount, running the entire XY surface as a subroutine, and grinding the surface to be ground of the workpiece.

[0021] Furthermore, the method for establishing the coordinate system in S2 is: taking the lowest point of the height value collected in step S1 as the origin of the Z axis, and taking the center of the surface to be ground of the workpiece as the origin of the coordinate system.

[0022] Furthermore, in step S4, the method for grinding the surface to be ground of the workpiece is: feedback pressure information through a pressure sensor, if during the running process of the subroutine, the pressure feedback by the pressure sensor has a stage greater than 1 Newton, the Z-direction feed is zero, and the subroutine is repeatedly executed;

[0023] If the pressure feedback from the pressure sensor is less than 1 Newton during the execution of this subroutine, the program ends.

[0024] Furthermore, in step S4, the spindle speed is set to 800-18000 r / min, and the feed speed in a certain direction in the XY plane is 3-300 mm / min.

[0025] The present invention discloses an elastic grinding head and a grinding method for grinding ultra-thin hard and brittle materials, and the beneficial effects thereof are:

[0026] 1. The pressure spring of the present invention plays the role of transmitting the spindle pressure of the machine tool on the one hand, and plays the role of controlling the rigid contact pressure between the workpiece and the grinding head on the other hand, so that the elastic grinding head has elasticity. When encountering abnormal convex points on the surface of the workpiece, the elastic grinding head is lifted up a certain distance, which effectively reduces the load of the tool at the abnormal convex points, reduces the concentration of processing stress at the abnormal convex points, reduces the occurrence of cracks, and improves the yield rate.

[0027] 2. The stiffness of the pressure spring in the present invention is 15N / mm to 35N / mm, which effectively controls the load applied by the elastic grinding head on the ultra-thin hard and brittle material workpiece. The load is less than the ultimate bending load of the ultra-thin hard and brittle material workpiece and will not cause bending and fracture of the material.

[0028] 3. In the grinding method for grinding ultra-thin hard and brittle materials of the present invention, the method for measuring the back cutting amount and the determination of the program termination greatly improve the grinding accuracy of ultra-thin hard and brittle materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 The schematic diagram of the structure of an elastic grinding head for grinding ultra-thin hard and brittle materials according to the present invention.

[0030] Figure 2 It is a schematic cross-sectional view of an elastic grinding head for grinding ultra-thin hard and brittle materials according to the present invention.

[0031] Figure 3 It is a structural schematic diagram of the guide tube of the present invention.

[0032] Figure 4 It is a schematic structural diagram of the T-shaped grinding head of the present invention.

[0033] Among them, 1. guide cylinder; 11. square hole; 2. pull-back spring; 3. T-shaped grinding head; 31. T-table; 32. square section long handle; 33. circular section grinding end; 4. pressure spring; 5. plug; 51. pressure sensor. DETAILED DESCRIPTION

[0034] The specific embodiments of the present invention are described to facilitate those skilled in the art to understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0035] Example 1

[0036] This embodiment provides an elastic grinding head for grinding ultra-thin hard and brittle materials, the purpose of which is to solve the problem of low yield rate of ultra-thin hard and brittle ceramic parts assisted by ultrasonic wave. Figure 1-Figure 4 , the specific structure of this embodiment will be described in detail below.

[0037] An elastic grinding head for grinding ultra-thin hard and brittle materials comprises a coaxial guide cylinder 1, a pull-back spring 2, a T-shaped grinding head 3, a pressure spring 4 and a plug 5.

[0038] Among them, the T-shaped grinding head 3 is arranged in the guide cylinder 1 and extends from the bottom of the guide cylinder 1; the plug 5 is installed on the top of the guide cylinder 1; the pressure spring 4 is installed between the plug 5 and the top of the T-shaped grinding head 3; the pull-back spring 2 is sleeved on the T-shaped grinding head 3.

[0039] In this embodiment, the T-shaped grinding head 3 is embedded from the top of the guide cylinder 1, and the grinding head end of the T-shaped grinding head 3 is extended from the bottom of the guide cylinder 1, and then the plug 5 is installed on the top of the guide cylinder 1 through a thread, so that the pressure spring 4 is installed between the plug 5 and the top of the T-shaped grinding head 3, and acts between the T-shaped grinding head 3 and the top of the guide cylinder 1, and the return spring 2 is sleeved on the T-shaped grinding head 3, and acts between the T-shaped grinding head 3 and the bottom of the guide cylinder 1, so that the pressure spring 4 is used to transmit the spindle pressure of the machine tool on the one hand, and to control the rigid contact pressure between the workpiece and the grinding head on the other hand, so that the elastic grinding head has elasticity. When encountering abnormal convex points on the surface of the workpiece, the elastic grinding head is lifted up a certain distance, which effectively reduces the load of the tool at the abnormal convex points, reduces the concentration of machining stress at the abnormal convex points, reduces the occurrence of cracks, and improves the yield rate.

[0040] Specifically, the T-shaped grinding head 3 includes a connected T-stage 31, a square-section long handle 32 and a circular-section grinding end 33; the pressure spring 4 is installed between the plug 5 and the upper surface of the T-stage 31; the return spring 2 is sleeved on the square-section long handle 32; the square-section long handle 32 and the circular-section grinding end 33 extend from the square hole 11 preset at the bottom of the guide cylinder 1.

[0041] In this embodiment, the square hole 11 matches the cross-sectional shape of the square-section long handle 32, so that the square-section long handle 32 and the circular-section grinding end 33 of the T-shaped grinding head 3 axially pass through the return spring 2 and the square hole 11 preset at the bottom of the guide cylinder 1, and extend out. The cross-sectional area of ​​the T-stage 31 is larger than the area of ​​the square hole 11, so that a pressure spring 4 is arranged between the upper surface of the T-stage 31 and the plug 5, and a return spring 2 is arranged between the lower surface of the T-stage 31 and the bottom end of the guide cylinder 1, thereby controlling the rigid contact pressure between the workpiece and the grinding head.

[0042] Specifically, the stiffness of the pressure spring 4 is 15 N / mm to 35 N / mm; the stiffness of the pull-back spring 2 is one tenth of the stiffness of the pressure spring 4 .

[0043] In this embodiment, the material to be ground is an ultra-thin hard and brittle material, which is brittle ceramic or glass, etc., and its thickness is less than 0.5 mm. The flatness or concave-convex point difference of the surface to be ground is less than 0.08 mm. The fracture strength safety factor of the brittle material is generally 2 to 3.5. According to Hooke's law, the following formula (1) can be obtained:

[0044]

[0045] in:

[0046] F 断 ——Material breaking strength, value is 10N;

[0047] F 预压 ——Pre-pressure of grinding material, value is 2N;

[0048] α——Safety factor of brittle material (α1=3.5, α2=2.0);

[0049] λ——The flatness or concave-convex point difference of the surface to be ground is less than 0.08mm, and the value is 0.08

[0050] C——is the design stiffness of the pressure spring, calculated to be 10.625N / mm≤C≤37.5N / mm.

[0051] In this embodiment, the design stiffness of the pressure spring 4 is 15N / mm~35N / mm, which effectively controls the load applied by the elastic grinding head on the ultra-thin hard and brittle material workpiece. The load is smaller than the limit bending load of the ultra-thin hard and brittle material workpiece and will not cause bending and fracture of the material.

[0052] In order to reduce the risk of brittle fracture of ultra-thin materials during processing and improve the stability of the elastic grinding head, the stiffness of the pressure spring 4 of the elastic grinding head is 35N / mm, the number of support turns is 2.5, and the number of effective turns is 4 to 8; the stiffness of the pull-back spring 2 is 3.5N / mm.

[0053] Specifically, a pressure sensor 51 is installed on the lower surface of the plug 5 .

[0054] In this embodiment, the plug 5 is blocked at the top of the guide cylinder 1 through a threaded structure, and a pressure sensor 51 is installed on the lower surface of the plug 5. The pressure sensor 51 adopts a strain gauge pressure sensor to feedback the pressure information of the pressure spring 4. In addition, when the elastic grinding head in this embodiment is not in working state, the return spring 2 is in a compressed state, and the pressure spring 4 is in a free state.

[0055] Example 2

[0056] Based on Example 1, this embodiment provides a grinding method based on an elastic grinding head for grinding ultra-thin hard and brittle materials. Its purpose is to solve the problem of low yield of ultrasonic-assisted processing of ultra-thin hard and brittle ceramic parts. The specific steps in this embodiment will be described in detail below.

[0057] A grinding method according to an elastic grinding head for grinding ultra-thin hard and brittle materials, wherein the workpiece is a silicon nitride ceramic blank with a thickness of 0.44±0.04 mm and a flatness of 0.083, and the grinding flatness thereof is less than 0.03;

[0058] Select elastic grinding head, the stiffness of pressure spring is 35N / mm, the number of supporting circles is 2.5, the number of effective circles is 4; the stiffness of pull-back spring 2 is 3.5N / mm;

[0059] The following steps are involved:

[0060] Step S1, clamping, clamp the workpiece surface to be ground horizontally upward on the grinding machine, collect and record the height value of the workpiece surface to be ground, and evaluate the clamping flatness of the workpiece. The clamping flatness of the workpiece is required to be ≤0.08mm, otherwise re-clamp. In this embodiment, the clamping flatness of the workpiece is 0.05mm.

[0061] Step S2, establishing a coordinate system, establishing a coordinate system at the center of the surface to be ground of the workpiece;

[0062] Specifically, the method for establishing the coordinate system in step S2 is: taking the lowest point of the height value collected in step S1 as the origin of the Z axis, and taking the center of the surface to be ground of the workpiece as the origin of the coordinate system.

[0063] Step S3, measuring the back cutting amount, installing the elastic grinding head on the main shaft of the machine tool, slowly reducing the Z value, and recording the Z value when the pressure feedback from the pressure sensor 51 in the elastic grinding head is 2 Newtons;

[0064] Step S4, programming and processing, programming is performed using the Z value recorded in step S3 as the back cutting amount, running the entire XY surface as a subroutine, and grinding the surface to be ground of the workpiece.

[0065] The method for grinding the surface to be ground of the workpiece in step S4 is: feedback pressure information through the pressure sensor 51, if during the running process of the subroutine, the pressure feedback from the pressure sensor 51 has a stage greater than 1 Newton, the Z-direction feed is zero, and the subroutine is repeatedly executed;

[0066] If the pressure fed back by the pressure sensor 51 is less than 1 Newton during the execution of the subroutine, the execution of the program ends.

[0067] In step S4, the spindle speed is set to 800-18000 r / min, and the feed speed in a certain direction in the XY plane is 3-300 mm / min. In this embodiment, the spindle speed is set to 18000 r / min, and the feed speed in a certain direction in the XY plane is 300 mm / min.

[0068] Three-coordinate measurement: The flatness of the processed silicon nitride wafer is 0.02mm.

[0069] Example 2

[0070] Based on Example 1, this embodiment provides a grinding method based on an elastic grinding head for grinding ultra-thin hard and brittle materials. Its purpose is to solve the problem of low yield of ultrasonic-assisted processing of ultra-thin hard and brittle ceramic parts. The specific steps in this embodiment will be described in detail below.

[0071] A grinding method based on an elastic grinding head for grinding ultra-thin hard and brittle materials, wherein the workpiece is a silicon nitride ceramic blank with a thickness of 0.3+0.1 mm and a flatness of 0.092, and the grinding flatness thereof is less than 0.015;

[0072] Select elastic grinding head, the stiffness of pressure spring is 40N / mm, the number of supporting circles is 2.5, the number of effective circles is 8; the stiffness of pull-back spring 2 is 4N / mm;

[0073] The following steps are involved:

[0074] Step S1, clamping, clamp the workpiece surface to be ground horizontally upward on the grinding machine, collect and record the height value of the workpiece surface to be ground, and evaluate the clamping flatness of the workpiece. The clamping flatness of the workpiece is required to be ≤0.08mm, otherwise re-clamp. In this embodiment, the clamping flatness of the workpiece is 0.05mm.

[0075] Step S2, establishing a coordinate system, establishing a coordinate system at the center of the surface to be ground of the workpiece;

[0076] Specifically, the method for establishing the coordinate system in step S2 is: taking the lowest point of the height value collected in step S1 as the origin of the Z axis, and taking the center of the surface to be ground of the workpiece as the origin of the coordinate system.

[0077] Step S3, measuring the back cutting amount, installing the elastic grinding head on the main shaft of the machine tool, slowly reducing the Z value, and recording the Z value when the pressure feedback from the pressure sensor 51 in the elastic grinding head is 2 Newtons;

[0078] Step S4, programming and processing, programming is performed using the Z value recorded in step S3 as the back cutting amount, running the entire XY surface as a subroutine, and grinding the surface to be ground of the workpiece.

[0079] The method for grinding the surface to be ground of the workpiece in step S4 is: feedback pressure information through the pressure sensor 51, if during the running process of the subroutine, the pressure feedback from the pressure sensor 51 has a stage greater than 1 Newton, the Z-direction feed is zero, and the subroutine is repeatedly executed;

[0080] If the pressure fed back by the pressure sensor 51 is less than 1 Newton during the execution of the subroutine, the execution of the program ends.

[0081] In step S4, the spindle speed is set to 800-18000 r / min, and the feed speed in a certain direction in the XY plane is 3-300 mm / min. In this embodiment, the spindle speed is set to 8000 r / min, and the feed speed in a certain direction in the XY plane is 3 mm / min.

[0082] Three-coordinate measurement: The flatness of the processed silicon nitride wafer is 0.01mm.

[0083] Although the specific implementation of the invention is described in detail in conjunction with the drawings, it should not be understood as limiting the scope of protection of this patent. Within the scope described in the claims, various modifications and variations that can be made by those skilled in the art without creative work still fall within the scope of protection of this patent.

Claims

1. An elastic grinding head for grinding ultra-thin hard and brittle materials, characterized in that: It comprises a coaxial guide cylinder (1), a pull-back spring (2), a T-shaped grinding head (3), a pressure spring (4) and a plug (5); The T-shaped grinding head (3) is arranged in the guide cylinder (1) and extends out from the bottom of the guide cylinder (1); the plug (5) is installed on the top of the guide cylinder (1); the pressure spring (4) is installed between the plug (5) and the top of the T-shaped grinding head (3); and the return spring (2) is sleeved on the T-shaped grinding head (3).

2. The elastic grinding head for grinding ultra-thin hard and brittle materials according to claim 1, characterized in that: The T-shaped grinding head (3) comprises a connected T-table (31), a long handle with a square cross section (32) and a grinding end with a circular cross section (33); The pressure spring (4) is installed between the plug (5) and the upper surface of the T-stage (31); the pull-back spring (2) is sleeved on the square-section long handle (32); the square-section long handle (32) and the circular-section grinding end (33) extend from a square hole (11) preset at the bottom of the guide cylinder (1).

3. The elastic grinding head for grinding ultra-thin hard and brittle materials according to claim 1, characterized in that: The stiffness of the pressure spring (4) is 15 N / mm to 35 N / mm; the stiffness of the pull-back spring (2) is one tenth of the stiffness of the pressure spring (4).

4. The elastic grinding head for grinding ultra-thin hard and brittle materials according to claim 1, characterized in that: A pressure sensor (51) is installed on the lower surface of the plug (5).

5. A grinding method for grinding ultra-thin hard and brittle materials with an elastic grinding head according to any one of claims 1 to 4, characterized in that: The following steps are involved: Step S1, clamping, clamping the surface to be ground of the workpiece horizontally upward on the grinding machine, collecting and recording the height value of the surface to be ground of the workpiece, and evaluating the clamping flatness of the workpiece; Step S2, establishing a coordinate system, establishing a coordinate system at the center of the surface to be ground of the workpiece; Step S3, measuring the back cutting amount, installing the elastic grinding head on the main shaft of the machine tool, slowly reducing the Z value, and recording the Z value when the pressure feedback from the pressure sensor (51) in the elastic grinding head is 2 Newtons; Step S4, programming and processing, programming is performed using the Z value recorded in step S3 as the back cutting amount, running the entire XY surface as a subroutine, and grinding the surface to be ground of the workpiece.

6. The grinding method of the elastic grinding head for grinding ultra-thin hard and brittle materials according to claim 5, characterized in that: The method for establishing the coordinate system in step S2 is: taking the lowest point of the height value collected in step S1 as the origin of the Z axis, and taking the center of the surface to be ground of the workpiece as the origin of the coordinate system.

7. The grinding method of the elastic grinding head for grinding ultra-thin hard and brittle materials according to claim 5, characterized in that: The method for grinding the surface to be ground of the workpiece in step S4 is as follows: feedback pressure information through a pressure sensor (51); if during the operation of the subroutine, the pressure feedback from the pressure sensor (51) has a stage greater than 1 Newton, the Z-direction feed is zero, and the subroutine is repeatedly executed; If during the execution of the subroutine, the pressure fed back by the pressure sensor (51) is less than 1 Newton, the execution of the subroutine ends.

8. The grinding method of the elastic grinding head for grinding ultra-thin hard and brittle materials according to claim 7, characterized in that: In step S4, the spindle speed is set to 800-18000 r / min, and the feed speed in a certain direction in the XY plane is 3-300 mm / min.

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