Ultra-precision grinding method for tungsten carbide or silicon carbide workpiece surfaces

Abstract

This invention provides an ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces. The method includes the following steps: semi-precision grinding of the workpiece using a water-soluble grinding fluid and a resin grinding wheel with preset grinding parameters and a grinding path; precision grinding of the workpiece using an oil-based grinding fluid and a fine ceramic grinding wheel with preset grinding parameters and a grinding path; and ultra-precision grinding of the workpiece after precision grinding. The workpiece surface profile accuracy (PV) is measured to be ≤0.2μm using a profilometer, and the surface roughness (Ra) is measured to be ≤5nm with a mid-frequency density (≤35nm) using an interferometer. Microscopic observation shows that the grinding marks on the workpiece surface exhibit a regular and uniform grid pattern. This invention employs a semi-precision grinding-precision grinding-ultra-precision grinding process, reducing grinding wheel wear during workpiece grinding, resulting in good workpiece surface uniformity and the absence of processing defects such as pits, protrusions, and microcracks. It can be widely applied in the field of ultra-precision grinding.

Description

Technical Field

[0001] This invention belongs to the field of ultra-precision grinding technology, and particularly relates to an ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces. Background Technology

[0002] Freeform lenses are characterized by their radius of curvature varying along their central axis, which improves optical quality, reduces the number of optical components, and lowers design costs. Optical systems designed using freeform surface technology can eliminate spherical aberration, coma, astigmatism, and field curvature, while reducing light energy loss, thereby achieving high-quality image effects and superior optical properties. They can be widely used in various military products, modern optoelectronic products, digital imaging products, security monitoring, automotive lenses, smartphones, laser displays, optical communications, and other industries. Meanwhile, the ultra-precision grinding technology used for mass production of aspherical lenses is a widely applicable and rapidly developing high-tech field in optics worldwide.

[0003] Because the temperature of glass molding environment reaches as high as 700℃, in order to ensure the precision of the product, only ultra-hard alloy molds such as tungsten carbide or silicon carbide with minimal high-temperature thermal deformation can be used. The difficulty of ultra-precision machining of such molds lies in the following: the material is hard alloy, the shape is aspherical, the scale is very small, ranging from tens of micrometers to a few millimeters, the precision requirements are very high, the surface shape accuracy requires PV to be below 200nm, and the surface roughness requires to reach the nanometer level; the equipment used is a grinding machine with nanometer-level resolution, and the processing environment requires constant temperature, humidity and purification; the processing space is very small and the heat dissipation conditions are poor; the diameter of the grinding wheel is very small and the rigidity is low, which can easily cause deformation and thus affect the processing accuracy. To achieve a certain linear speed requirement, the grinding wheel must rotate at a high speed, with a speed of 40,000-10,000 r / min. In terms of the development direction of grinding, precision has evolved from ordinary to high precision, then to ultra-precision, and finally to nanometer-level precision; efficiency has evolved from ordinary to high efficiency; shape has evolved from regular cylindrical and planar surfaces to spherical, aspherical, and free-form surfaces; size has evolved from conventional sizes to extremely small and large manufacturing directions; and materials have evolved from metallic materials to hard and brittle materials. Small-diameter aspherical mold grinding combines all the characteristics of these development directions: high precision, high speed, aspherical surface, extremely small manufacturing, and hard and brittle materials. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide an ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces.

[0005] The technical solution adopted by this invention to solve the technical problem is:

[0006] An ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces, comprising the following steps:

[0007] 1) Preparations before grinding: Sintered tungsten carbide or silicon carbide with mechanical properties meeting the requirements is machined to a blank shape, and the surface shape error (PV) is measured by a profilometer to be less than 20μm; the working characteristics of the ultra-precision grinding machine are ensured to be normal, and it is placed in an ultra-precision grinding laboratory with preset constant temperature, constant humidity, a Class 100,000 cleanroom, and a shockproof foundation. The machine is run idle until it reaches thermal stability; the tungsten carbide or silicon carbide workpiece is mounted on a tooling fixture with a flatness and parallelism requirement of 0.0005μm, and then the fixture is mounted on the vacuum chuck of the ultra-precision grinding machine spindle. The concentricity error of the tungsten carbide or silicon carbide workpiece is adjusted to be within 0.5μm; the grinding wheel is mounted on the grinding axis of the ultra-precision grinding machine, and the dynamic balance of the high-precision grinding axis is adjusted to be within 10nm. Tool setting is completed under the required processing conditions.

[0008] The temperature in the aforementioned ultra-precision grinding laboratory was controlled at 22±0.3℃, the water temperature at 22±0.1℃, the compressed air temperature at 22±0.1℃, and the oil content in the compressed air at 0.01mg / m³. 3 Humidity is controlled at 45±10%, and horizontal vibration acceleration is controlled at 0.005 m / s². 2 The vertical vibration acceleration is controlled at 0.01 m / s². 2 Vibration frequency below 10Hz and amplitude <1μm;

[0009] The aforementioned ultra-precision grinding machine is an ultra-precision machine tool with Z-axis, X-axis, B-axis, grinding axis, Y-axis and spindle;

[0010] The aforementioned tungsten carbide or silicon carbide workpieces are free-form surface molds with a diameter of less than 100 mm;

[0011] 2) Semi-precision grinding of tungsten carbide or silicon carbide workpieces: The grinding fluid is continuously turned on during the grinding process. Water-soluble grinding fluid is used, and cylindrical resin grinding wheels with a diameter of 1-20 mm and a grit size of 800# are used to perform semi-precision grinding of tungsten carbide or silicon carbide workpieces under preset grinding parameters and grinding paths. The preset grinding parameters include grinding depth, grinding wheel linear speed, workpiece feed speed, and grinding times. The grinding path is generated by comprehensively considering the profilometer measurement results, grinding parameters, and grinding wheel parameters. The semi-precision grinding process includes machining free-form surfaces, positioning the rotation center (positioning reference point), offline measurement by the profilometer, and surface shape compensation. After machining, the grinding axis and ultra-precision grinding machine are turned off, the tooling fixtures are removed, and the surface shape accuracy (PV) of the tungsten carbide or silicon carbide workpiece is measured by the profilometer to be below 1 μm. If it does not meet the requirement, step 2) is repeated.

[0012] The aforementioned semi-precision grinding process uses aspherical grinding, and the grinding trajectory is a near-helical trajectory;

[0013] The grinding parameters for the above semi-precision grinding process are set as follows: D = 2-10 μm, F = 1-5 mm / min, L = 5-20, where D is the grinding depth, F is the workpiece feed rate, and L is the number of cycles.

[0014] 3) Adjust the vibration of the grinding stone of the ultra-precision machining machine to control its dynamic balance within 10nm, adjust the spindle speed of the ultra-precision machining, and set the current speed of the grinding axis as a fixed value. Perform pre-machining by calculating the traces generated by the rotation of the spindle and the grinding axis, and then observe the grinding traces on the surface of the pre-machined workpiece. When the grinding traces show an intersecting shape, the requirements are met. This step mainly reduces the medium frequency of the workpiece surface.

[0015] 4) Precision grinding of tungsten carbide or silicon carbide workpieces: The grinding fluid is continuously turned on during the grinding process. Oil-based grinding fluid is used, and cylindrical fine ceramic grinding wheels with a diameter of 1-20mm and a grit size of 12000# are used. The contact point of the grinding wheel is dressed to an arc with a radius of R≈20μm. The vibration of the grinding axis is adjusted to within 10nm. Precision grinding is performed on the workpiece after semi-precision grinding with preset grinding parameters and grinding path. The tool marks on the workpiece after grinding are observed under a microscope. The linear velocity is calculated and the spindle speed is adjusted. The preset grinding parameters include grinding depth, grinding wheel linear velocity, workpiece feed rate, workpiece speed and grinding times. The grinding path takes into account the radius of the arc of the grinding wheel contact point, nonlinear wear data of the grinding wheel and the surface texture after grinding. The precision grinding process includes dressing the grinding wheel, grinding of free-form surfaces, offline accuracy detection, clamping concentricity (positioning accuracy) and surface compensation.

[0016] The grinding parameters for the above precision grinding process are set as follows: D = 1-5 μm, F = 0.5-2 mm / min, L = 1-10, where D is the grinding depth, F is the workpiece feed rate, and L is the number of cycles;

[0017] 5) After measurement, perform ultra-precision grinding: The grinding axis and ultra-precision grinding machine run continuously without load. Remove the tooling fixtures and test the workpiece surface accuracy PV using a profilometer. Measure the workpiece surface roughness Ra using an interferometer. Based on the surface accuracy PV, compensate and correct the grinding wheel in the machining program. Correct the feed rate and feed speed based on the surface roughness Ra. During the grinding process, keep the grinding fluid on continuously. Use oil-based grinding fluid and a cylindrical fine ceramic grinding wheel with a diameter of 1-20mm and a grit size of 12000#. Perform ultra-precision grinding on the workpiece after precision grinding. If, after ultra-precision grinding, the workpiece surface accuracy PV is ≤0.2μm as tested by a profilometer, the workpiece surface roughness Ra is ≤5nm as measured by an interferometer, and the intermediate frequency is ≤35nm, and the grinding pattern on the workpiece surface appears as a regular and uniform grid pattern when observed under a microscope, then it is qualified. If it does not meet the requirements, repeat the ultra-precision grinding process until the requirements are met.

[0018] The grinding parameters for the above-mentioned ultra-precision grinding process are set as follows: D = 0.1-1μm, F = 0.1-1mm / min, L = 1-5, where D is the grinding depth, F is the workpiece feed rate, and L is the number of cycles.

[0019] The beneficial effects of this invention are as follows: It employs a semi-precision grinding-precision grinding-ultra-precision grinding process, utilizing water-soluble grinding fluid and resin-based grinding wheels, as well as oil-based grinding fluid and fine ceramic grinding wheels. This reduces wheel wear, improves processing stability, and enhances workpiece accuracy during the grinding of tungsten carbide or silicon carbide workpieces. Furthermore, it produces workpieces with good surface uniformity, free from processing defects such as pits, protrusions, and microcracks. Offline detection using profilometers and microscopes achieves ultra-high precision processing. During processing, the workpiece surface exhibits excellent uniformity, yielding workpieces with a profile accuracy (PV) of less than 0.2 μm, a surface roughness (Ra) of less than 3 nm, and a surface mid-frequency (IF) of less than 35 nm. This invention can be widely applied in the field of ultra-precision grinding. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the structure of the ultra-precision grinding machine according to an embodiment of the present invention.

[0021] Figure 2 This is a surface profile data diagram after ultra-precision grinding according to an embodiment of the present invention.

[0022] Figure 3 This is a surface roughness diagram after ultra-precision grinding according to an embodiment of the present invention.

[0023] Figure 4 This is a surface texture diagram after ultra-precision grinding according to an embodiment of the present invention. Detailed Implementation

[0024] To make the objectives, technical methods, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present invention.

[0025] Example: Ultra-precision grinding of tungsten carbide freeform surface molds

[0026] 1) Preparations before grinding: The sintered tungsten carbide material with mechanical properties that meet the requirements of use is processed into a blank shape, and the surface shape error PV is less than 20μm as measured by a profilometer;

[0027] To ensure the ultra-precision grinding machine operates normally, it is placed in a pre-set ultra-precision machining laboratory with constant temperature, humidity, and air cleanliness for at least 48 hours, allowing it to warm up until it reaches thermal stability. In this embodiment, the ultra-precision machining laboratory is set with constant temperature control at 22±0.3℃, water temperature control at 22±0.1℃, compressed air temperature control at 22±0.1℃, and compressed air oil content control at 0.01mg / m³. 3 Humidity is controlled at 45±10%, and horizontal vibration acceleration is controlled at 0.005 m / s². 2 The vertical vibration acceleration is controlled at 0.01 m / s². 2 The vibration frequency should be below 10Hz and the amplitude should be <1μm; ensure that the working characteristics of each axis system of the ultra-precision grinding machine with X-axis 7, Y-axis 2, Z-axis 1, grinding axis 5, spindle 3, and B-axis 6 are normal, such as Figure 1 As shown;

[0028] The tungsten carbide workpiece is mounted on the corresponding tooling fixture, and then the fixture is mounted on the vacuum chuck of the spindle 3 in the ultra-precision grinding machine. The concentricity error of the tungsten carbide workpiece is adjusted to within 0.2μm. The 800# cylindrical resin grinding wheel 4 is mounted on the grinding axis 5 of the ultra-precision grinding machine, and the dynamic balance of the high-precision grinding axis is adjusted to within 10nm. Tool setting is completed under the processing conditions.

[0029] 2) Semi-precision grinding of tungsten carbide workpieces: The grinding fluid is continuously turned on during the grinding process. Water-soluble grinding fluid is used, and a cylindrical resin grinding wheel with a diameter of 10mm and a diameter of 800# is used to perform semi-precision grinding on the tungsten carbide workpiece under preset grinding parameters and grinding path. The grinding parameters for semi-precision grinding are set as follows: D = 2μm, F = 2mm / min, L = 6, where D is the grinding depth, F is the workpiece feed speed, and L is the number of cycles.

[0030] 3) Adjust the vibration of the whetstone of the ultra-precision machining tool to control its dynamic balance within 10nm, adjust the spindle speed of the ultra-precision machining, and pre-process the workpiece by calculating the traces generated by the rotation of the spindle and the workpiece axis based on the current speed of the cutting axis. Then observe the grinding traces on the surface of the pre-processed workpiece. The grinding traces show an intersecting shape, and the surface roughness after processing is ≈3nm, which is suitable for precision machining.

[0031] 4) Precision grinding of tungsten carbide workpieces: Grinding fluid is continuously turned on during the grinding process. Oil-based grinding fluid is used, and a 10mm diameter, 12000# cylindrical fine ceramic grinding wheel is employed. The wheel contact point is dressed to an arc radius of approximately 20μm. The grinding axis vibration is adjusted to 9nm. Precision grinding is then performed on the semi-precision ground workpiece using preset grinding parameters and a grinding path. Tool marks on the ground workpiece are observed under a microscope. The linear velocity is calculated, and the spindle speed is adjusted accordingly. The grinding path takes into account the circularity of the wheel contact point. The parameters for ultra-precision grinding include: arc radius, nonlinear wear data of grinding wheel, and surface texture after grinding. The preset grinding parameters include grinding depth, grinding wheel linear speed, workpiece feed speed, workpiece rotation speed, and number of grinding cycles. The ultra-precision grinding process includes dressing the grinding wheel, grinding free-form surface, offline accuracy detection, clamping concentricity, and surface compensation. The grinding parameters for precision grinding are set as follows: D = 1 μm, F = 0.5 mm / min, L = 3, where D is the grinding depth, F is the workpiece feed speed, and L is the number of cycles.

[0032] 5) Ultra-precision grinding of tungsten carbide workpieces: The grinding spindle and ultra-precision grinding machine are continuously idled. The tooling fixtures are removed, and the surface accuracy PV of the workpiece is tested by a profilometer. The surface roughness Ra of the workpiece is measured by an interferometer. The grinding program is compensated and corrected based on the actual measurement results of the profilometer. The feed rate and feed speed are corrected based on the measurement results of the interferometer. The grinding fluid is continuously turned on during the grinding process. Oil-based grinding fluid is used, and a cylindrical fine ceramic grinding wheel with a diameter of 10 mm and a grit size of 12000# is used for ultra-precision grinding. The grinding parameters for ultra-precision grinding are set as follows: D = 0.5 μm, F = 0.3 mm / min, L = 3, where D is the grinding depth, F is the workpiece feed rate, and L is the number of cycles.

[0033] The workpiece was removed and measured offline using a profilometer and white light interferometer. The surface profile accuracy PV = 0.1 μm, surface roughness Ra = 2.85 nm, and intermediate frequency = 32 nm. Microscopic observation revealed a regular and uniform grid pattern in the grinding marks, with no pits or microcracks or other machining defects. Figure 2-4 As shown.

Claims

1. A method for ultra-precision grinding of the surface of tungsten carbide or silicon carbide workpieces, characterized in that, The method includes the following steps: 1) Use water-soluble grinding fluid and resin grinding wheel to perform semi-precision grinding on tungsten carbide or silicon carbide workpieces under preset grinding parameters and grinding path; turn off the grinding axis and ultra-precision grinding machine, remove the tooling fixture and measure the surface accuracy PV of tungsten carbide or silicon carbide workpieces with a profiler to reach below 1μm. If it does not meet the requirement, repeat step 1). The grinding parameters for the semi-precision grinding process are set as follows: D = 2-10 μm, F = 1-5 mm / min, L = 5-20, where D is the grinding depth, F is the workpiece feed rate, and L is the number of cycles. 2) Use oil-based grinding fluid and fine ceramic grinding wheels to perform precision grinding on the workpiece after semi-precision grinding with preset grinding parameters and grinding paths; The grinding parameters for the precision grinding process are set as follows: D = 1-5 μm, F = 0.5-2 mm / min, L = 1-10, where D is the grinding depth, F is the workpiece feed rate, and L is the number of cycles. 3) Test the workpiece surface profile accuracy (PV) using a profilometer and measure the workpiece surface roughness (Ra) using an interferometer. Based on the surface profile accuracy (PV), perform grinding wheel compensation correction on the machining program. Based on the surface roughness (Ra), correct the feed rate and feed speed. Use oil-based grinding fluid and a fine ceramic grinding wheel to perform ultra-precision grinding on the workpiece after precision grinding. If, after ultra-precision grinding, the workpiece surface profile accuracy (PV) is ≤0.2μm as measured by a profilometer, the workpiece surface roughness (Ra) is ≤5nm as measured by an interferometer, and the intermediate frequency is ≤35nm, and the grinding pattern on the workpiece surface appears as a regular and uniform grid pattern when observed under a microscope, then it is qualified. If it does not meet the requirements, repeat step 3) until the requirements are met.

2. The ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces as described in claim 1, characterized in that, Before step 1), there are the following steps: sintered tungsten carbide or silicon carbide with mechanical properties that meet the requirements of use are processed into a blank shape, and the surface shape error PV is measured by a contour instrument and is required to be less than 20μm; the ultra-precision grinding machine is placed in an ultra-precision grinding laboratory with preset constant temperature, constant humidity, 100,000-level clean room and anti-vibration foundation requirements, and the machine is started and run idle until the machine reaches thermal stability; the tungsten carbide or silicon carbide workpiece is installed on the tooling fixture, and then the fixture is installed on the vacuum chuck of the ultra-precision grinding machine spindle (3), and the concentricity error of the tungsten carbide or silicon carbide workpiece is adjusted to be within 0.5μm; the grinding wheel is installed on the grinding axis (5) of the ultra-precision grinding machine, and the dynamic balance of the high-precision grinding axis is adjusted to be within 10nm, and the tool setting is completed under the processing conditions.

3. The ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces as described in claim 2, characterized in that, The temperature in the ultra-precision grinding laboratory is controlled at 22±0.3℃, the water temperature at 22±0.1℃, the compressed air temperature at 22±0.1℃, and the oil content of the compressed air at 0.01mg / m³. 3 Humidity is controlled at 45±10%, and horizontal vibration acceleration is controlled at 0.005 m / s². 2 The vertical vibration acceleration is controlled at 0.01 m / s². 2 The vibration frequency is below 10Hz and the amplitude is <1μm; the ultra-precision machining grinding machine has a Z-axis (1), X-axis (7), B-axis (6), grinding axis (5), Y-axis (2) and spindle (3).

4. The ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces as described in claim 2, characterized in that, The tungsten carbide or silicon carbide workpiece is a free-form surface mold with a diameter of less than 100 mm.

5. The ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces as described in claim 1, characterized in that, Step 1) The semi-precision grinding process adopts aspherical grinding, and the grinding trajectory is a near-helical trajectory; the resin grinding wheel adopts a cylindrical resin grinding wheel with a diameter of 1-20mm and a grit size of 800#.

6. The ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces as described in claim 1, characterized in that, Step 1) The preset grinding parameters include grinding depth, grinding wheel linear speed, workpiece feed speed and grinding times. The grinding path is generated by the profilometer measurement results, grinding parameters and grinding wheel parameters. The semi-precision grinding process includes machining free-form surfaces, positioning the rotation center, offline profilometer measurement and surface compensation.

7. The ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces as described in claim 1, characterized in that, After step 1), there are further steps: adjust the vibration of the grinding stone of the ultra-precision machining grinding machine to control its dynamic balance to within 10nm, adjust the spindle speed, and set the current speed of the grinding axis as a fixed value. Perform pre-processing by calculating the traces generated by the rotation of the spindle and the grinding axis, and then observe the grinding traces on the surface of the workpiece. When the grinding traces show an intersecting shape, the requirements are met.

8. The ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces as described in claim 1, characterized in that, In step 2), the grinding wheel contact point is dressed to an arc with a radius of approximately 20 μm (R≈20 μm), the grinding axis vibration is adjusted to within 10 nm, the tool marks on the workpiece are observed under a microscope, the linear velocity is calculated, and the spindle speed is adjusted. The preset grinding parameters include grinding depth, grinding wheel linear velocity, workpiece feed rate, workpiece speed, and number of grinding passes. The grinding path considers the radius of the grinding wheel contact point arc, nonlinear wear data of the grinding wheel, and the surface texture after grinding. The precision grinding process includes dressing the grinding wheel, grinding free-form surfaces, offline precision detection, clamping concentricity, and surface compensation.

9. The ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces as described in claim 1, characterized in that, The fine ceramic grinding wheel mentioned in steps 2) and 3) is a cylindrical fine ceramic grinding wheel with a diameter of 1-20 mm and a grit size of 12000#.

10. The ultra-precision grinding method for the surface of tungsten carbide or silicon carbide workpieces as described in claim 1, characterized in that, Step 3) The grinding parameters for the ultra-precision grinding process are set as follows: D = 0.1-1 μm, F = 0.1-1 mm / min, L = 1-5, where D is the grinding depth, F is the workpiece feed rate, and L is the number of cycles.

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