Device and process for assisting in grinding hard and brittle materials through controllable damage induced by laser ablation

Abstract

The invention discloses a device and a process for assisting in grinding hard and brittle materials through controllable damage induced by laser ablation, according to the method, laser is irradiated on the surface of the materials, a laser focus is focused on the to-be-machined surface of the materials, and the materials are subjected to ablation removal and specific-depth damage induction. By controlling the laser power, the scanning speed and the ablation track, the thermally induced damage degree and the damage type of the laser ablation induced material are effectively controlled. And a grinding wheel grinding path and a laser ablation path are controlled on the same axis, the distance between laser ablation and grinding wheel grinding is set, and the ablated surface of the workpiece is ground under the optimal grinding parameters. According to the method, a quantitative control strategy for the surface damage degree of the laser ablation material is systematically provided, the laser-induced damage layer is removed through precise control over the surface damage of the material and precise grinding, and high-efficiency and high-quality machining of the hard and brittle material is achieved.

Description

Technical Field

[0001] The invention belongs to the field of laser-assisted processing, and in particular relates to a device and a process for laser ablation-induced controllable damage-assisted grinding of hard and brittle materials in the field of hard and brittle materials difficult to process. Background Art

[0002] Hard and brittle materials such as reaction-sintered silicon carbide, WC / Co cemented carbide and ceramic-based composites have excellent mechanical properties, including high hardness, high strength, high temperature resistance and oxidation resistance. However, the high brittleness and high hardness of the materials bring difficulties to processing. The tool wear will be serious during the processing, and it is difficult to ensure the surface quality of the material after processing. Single grinding has problems such as easy surface cracks, low efficiency, and easy tool wear. Brittle fracture and subsurface cracks on the surface of hard and brittle materials seriously affect the mechanical properties and service life of the processed parts. Therefore, how to improve the processing quality and efficiency of hard and brittle materials has become a problem to be solved.

[0003] At present, laser-assisted grinding, laser-assisted turning, and laser-assisted milling technologies are gradually becoming research hotspots in recent years. However, the thermal softening effect is not obvious on high-temperature resistant materials. The energy density of high-energy laser beams is relatively concentrated, and the surface of the material obtained by ablation processing has the advantages of controllable ablation area, ablation depth, and ablation damage. While laser ablation removes materials, the degree of damage to the surface of the ablated material is accurately controlled, and the surface of the modified material is removed by grinding. High-quality, efficient and precise processing of difficult-to-process materials is achieved. Materials include hard and brittle materials such as reaction-sintered silicon carbide, WC / Co cemented carbide, and ceramic-based composites to improve the processing surface quality of difficult-to-process materials and increase the service life of tools.

[0004] In order to eliminate and control the surface damage of hard and brittle materials after grinding, the advantages of laser processing and grinding are combined, and the laser ablation material surface damage control assisted grinding hard and brittle material process provides an effective measure to solve the problem of difficult processing of such materials.

[0005] Existing laser-assisted grinding processes have mainly carried out some research work on the optimization of processing parameters, including: laser parameter optimization and scanning trajectory optimization, and no relevant research has been carried out on the internal damage problem. Zheng Dihao and others from Shanghai University of Technology optimized the influence of laser scanning patterns on the processing quality of silicon nitride, and obtained that the circular regular pattern is the best laser-induced microgroove trajectory. No in-depth research has been carried out on the influence of precise control of ablation damage on surface quality. Liu Wei and others from Hunan University of Science and Technology carried out laser modified grinding of silicon carbide ceramics. The surface hardness of the material is reduced by laser irradiation of the material surface. The precise control of laser power on the degree of crack propagation on the material surface has not yet been explored. At the same time, laser ablation has not been achieved to remove materials, resulting in limitations on grinding depth and material removal.

[0006] Currently, there is no literature published on methods for precise control of internal damage in laser ablation of hard and brittle materials. Summary of the invention

[0007] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a device and process for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials. Laser ablation of the material surface is used to accurately control the surface damage and assist grinding with a grinding wheel, thereby solving the problem of difficult processing of hard and brittle materials, improving material processing efficiency and processing quality, and reducing grinding wheel wear.

[0008] To achieve the above object, the present invention is implemented through the following technical solutions:

[0009] A device for laser ablation-induced controllable damage-assisted grinding of hard and brittle materials, comprising: a drive motor (1), a fastening flange (2), a laser system, a mobile platform, a workpiece (5), and a grinding wheel (3); the drive motor (1) is mounted on a device body (4), and the grinding wheel (3) is mounted on a main shaft of the drive motor via a fastening flange 2); the laser system is mounted on a guide rail (11) of the mobile platform; (5) is fixed on a workbench (6) of the mobile platform of the device;

[0010] The laser system adjusts the laser beam to act on the surface of the workpiece (5) and the front end of the grinding wheel in the grinding direction;

[0011] By precisely controlling the motion trajectory of the laser system within the laser defocus range, microstructure types with different degrees of damage are obtained on the surface of the workpiece to be processed. The workpiece (5) is driven to perform feed motion by the worktable (6), and the grinding wheel rotates while the grinding process of the laser ablated microstructure area is achieved.

[0012] The laser system comprises: a laser controller (10), a transmission optical fiber (9), an optical path, and a laser galvanometer (7); the laser galvanometer is connected to the laser controller (10) via the transmission optical fiber (9); the laser controller (10) controls laser parameters of the output light beam including but not limited to incident frequency, laser power and pulse time; the laser acts on the surface of the workpiece (5) via the laser galvanometer (7); the incident angle, optical path, and distance from the workpiece surface of the laser beam are adjustable; the light spot position is at the front end of the grinding wheel grinding direction, and the distance is adjusted according to the processing characteristics of different materials.

[0013] The laser controller (10) controls the laser output power, frequency and pulse width, thereby controlling the energy introduced into the material surface, thereby controlling the degree of damage, and obtaining different texture types on the surface of the workpiece to be processed, including but not limited to: arc line texture, square texture, parallel line texture, zigzag texture, diamond texture and vertical line texture.

[0014] A process for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials, characterized in that it comprises the following steps:

[0015] Step 1: Install the workpiece to be processed on the workbench of the grinding device, and install the grinding tool on the rotating spindle through the fastening flange;

[0016] Step 2: Adjust the grinding wheel and the laser head of the laser system to the area where the hard and brittle material is to be ground. The laser galvanometer adjusts the position and angle between the laser and the workpiece by rotation to ensure that the laser is irradiated on the surface of the material. Adjust the distance between the laser spot and the surface of the material to ensure that it is within the defocus range of the laser beam to ensure that the surface of the material is ablated and removed;

[0017] Step 3: Control the ablation damage on the material surface by precisely controlling the motion trajectory of the laser system within the laser defocus range. While laser ablation removes the surface material, the material melts, oxidizes, and recondenses, causing changes in the surface properties of the material; at the same time, high temperature causes thermal crack damage inside the material; in order to effectively control the damage on the surface of the laser ablated material, the laser pulse energy, scanning speed, and scanning trajectory are precisely controlled to achieve the purpose of controlling the damage distribution and damage depth. The laser used is a Gaussian beam, and the laser heat flux on the material surface is regarded as a surface heat source. The laser heat flux can be expressed as:

[0018]

[0019] in,

[0020]

[0021] Where H(τ-t) is a step function, A=1-R is the absorptivity of the material under infrared laser, R is the reflectivity, ω0 is the laser waist radius, Q0 is the laser peak energy density, and P is the laser power.

[0022] Under the condition of a fixed laser scanning speed, the energy of the laser acting on the material surface is controlled by controlling the input power P, thereby controlling the degree of ablation and damage on the material surface.

[0023] It is found that under the condition of rated laser power P, the mapping relationship between the energy Q required for material crack extension and the ablation damage length L is:

[0024]

[0025] Different power percentage is i%, and the corresponding damage length is L i , calculated as follows:

[0026]

[0027] Based on the above theoretical calculation, the corresponding relationship between laser power control and ablation damage was obtained, so as to achieve precise control of the damage degree of laser ablation and guide the grinding process.

[0028] Similarly, under the condition of fixed laser power, the scanning speed can be controlled to control the amount of energy of the laser acting on the material surface, thereby controlling the degree of ablation and damage on the material surface.

[0029] Laser ablation removes part of the material, plans the laser scanning trajectory to achieve the preparation of surface microstructure, and controls the distribution of material surface damage. Ablation microstructures include: arc line texture, square texture, parallel line texture, zigzag texture, diamond texture and vertical line texture.

[0030] Step 4: In order to process the entire workpiece surface, the laser performs surface damage control scanning according to the set ablation trajectory.

[0031] Step 5: In order to completely remove the laser ablation area on the material surface, the grinding depth of the grinding wheel should be greater than the depth of the laser ablation microstructure;

[0032] Step 6. Turn off the laser system and grinding equipment after processing is completed.

[0033] Compared with the prior art, the present invention can bring the following beneficial effects:

[0034] (1) The present invention is based on the material properties of hard and brittle material workpieces. The laser beam is irradiated on the material surface, and the spot defocus is adjusted to control it within the focal length of laser ablation to ensure that the material is removed by laser ablation. (2) The laser beam is irradiated at the front end of the grinding area of ​​the grinding wheel to prevent interference with the beam when ablating different microstructures. (3) The incident angle of the laser beam can be adjusted according to the processing conditions to control the shape of the groove on the surface of the laser ablated material. (4) Precise control of the laser output energy and motion trajectory can control the degree and direction of ablation damage on the material surface. (5) The laser galvanometer is installed in front of the grinding wheel and its position is adjustable. The ablation area is consistent with the grinding area. By precisely controlling the damage on the material surface, the laser ablation and grinding processes are coordinated to achieve efficient and precise grinding of hard and brittle materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 This is a schematic diagram of a device for laser ablation-induced controllable damage-assisted grinding of hard and brittle materials according to the present invention.

[0036] Figure 2 The effect of laser power on ablation damage of hard and brittle materials in the present invention. Among them: (a) material ablation characteristics when the laser power is 30W, (b) material ablation characteristics when the laser power is 60W, (c) material ablation characteristics when the laser power is 90W.

[0037] Figure 3 This is the effect of the laser scanning trajectory on the ablation damage of hard and brittle materials in the present invention.

[0038] Figure 4 This is an example of laser scanning processing of the present invention.

[0039] Figure 5 This is an example of laser ablation-induced controllable damage-assisted grinding of hard and brittle materials according to the present invention; wherein: (a) laser ablation-assisted grinding is not added; (b) laser ablation-assisted grinding is added (the damage type is parallel line texture).

[0040] In the figure: 1-driving motor; 2-fastening flange; 3-grinding wheel; 4-device body; 5-workpiece; 6-working table; 7-laser galvanometer; 8-light beam; 9-optical fiber; 10-laser controller; 11-guide rail; 12-grinding chips; 13-laser ablation microstructure; 14-diamond. DETAILED DESCRIPTION

[0041] The present invention will be described in detail below in conjunction with the accompanying drawings, but it should be noted that the implementation of the present invention is not limited to the following embodiments.

[0042] Figure 1 Schematic diagram of the device used in the present invention, see Figure 1 As shown, a laser ablation-induced controllable damage-assisted grinding device for hard and brittle materials comprises: a driving motor 1, a fastening flange 2, a laser system, a mobile platform, a workpiece 5, and a grinding wheel 3. The driving motor 1 is mounted on the device body 4, and the grinding wheel 3 is mounted on the main shaft of the driving motor through the fastening flange 2; the laser system is mounted on the guide rail 11 of the mobile platform; and the workpiece 5 is fixed on the workbench 6 of the mobile platform of the device.

[0043] The grinding wheel 3 is a diamond wheel or a CBN wheel, and in the following embodiment, it is a resin-based diamond wheel, and the abrasive grain diameter is 76 μm. The hard and brittle material is reaction sintered SiC, single crystal silicon, WC / Co hard alloy and ceramic matrix composite material, and in the following embodiment, it is WC / Co hard alloy.

[0044] The laser system includes: a laser controller 10, a transmission optical fiber 9, an optical path, and a laser galvanometer 7. The laser galvanometer is connected to the laser controller 10 through the transmission optical fiber 9. The laser controller 10 can control the incident frequency, laser power, pulse time and other parameters of the output light beam. The laser acts on the surface of the workpiece 5 through the laser galvanometer 7, and the incident angle of the laser beam is adjustable; the spot position is at the front end of the grinding direction of the grinding wheel, and its distance is adjusted according to the processing characteristics of different materials.

[0045] Specifically, when in use, the laser galvanometer 7 adjusts the position between the laser galvanometer 7 and the workpiece 5 through the fine adjustment device, thereby ensuring that the laser beam 8 can be controlled to ablate within the laser defocus range. The output beam of the laser galvanometer 7 can be changed by designing the optical path to achieve accurate and controllable scanning trajectory of the laser on the workpiece surface.

[0046] Different damage types are obtained by precisely controlling the motion trajectory of the laser galvanometer 7, and then the workpiece 5 is driven to perform feeding motion by the workbench 6, and the grinding process of the laser ablation microstructure area is realized while the grinding wheel rotates.

[0047] Example 1

[0048] Investigate the influence of different laser powers on the ablation depth and damage degree of the ablation material surface, such as Figure 2 When the laser power is 10W, the material ablation characteristics are as follows. Figure 2 As shown in (a), lower laser power results in less material removal and less damage caused by thermal effects. At a laser power of 30W, higher power increases the degree of material ablation and higher laser energy leads to increased ablation crack damage, as shown in Figure 2 (b) When the laser power is further increased to 50W, the ablation damage further increases. Different ablation degrees and damage degrees are obtained according to different laser powers.

[0049] The laser controller 10 controls the laser output power, scanning speed and scanning trajectory to control the energy introduced into the material surface, thereby controlling the degree of damage. In this embodiment, the laser used is an ideal Gaussian beam, and the laser heat flux on the material surface is regarded as a surface heat source, which can be expressed as:

[0050]

[0051] in,

[0052]

[0053] Where H(τ-t) is a step function, A=1-R is the absorptivity of the material under infrared laser, R is the reflectivity, ω0 is the laser waist radius, Q0 is the laser peak energy density, and P is the laser power.

[0054] Under the condition of fixed laser scanning speed, by controlling the input power P, the energy of the laser acting on the material surface is controlled, thereby controlling the degree of ablation and damage on the material surface;

[0055] It is found that under the condition of rated laser power P, the mapping relationship between the energy Q required for material crack extension and the ablation damage length L is:

[0056]

[0057] The different power ratios are i%, and the corresponding damage length is L i , and the calculation is as follows:

[0058]

[0059] The feeding motion of the workbench 6 enables the diamond 14 on the surface of the grinding wheel 3 to grind the material surface. The grinding process of the grinding wheel is controlled according to the actual laser ablation damage degree, so as to obtain the optimal machining surface quality.

[0060] For example, when the laser power is 50W, the scanning speed is 40mm / s, and the pulse frequency is 50kHz, the surface trajectory characteristics and damage obtained by scanning once are as Figure 4 (f) shows.

[0061] In this embodiment, the workpiece to be ground is WC / Co cemented carbide. Design a laser scanning trajectory as Figure 3 shown (including but not limited to: horizontal straight line, vertical straight line, broken line, arc, "field" shape, diamond). According to the designed laser trajectory, workpieces with modified material surfaces of different damage depths and degrees are processed, such as Figure 4 shown (including but not limited to: arc line texture, square texture, parallel line texture, zigzag texture, diamond texture and vertical line texture). Compare the surface of the material after grinding without introducing laser and the surface of the material after grinding with laser ablation controlled damage. The results show that when the material without laser ablation is ground, there is plowing and rubbing of some materials on the surface. At the same time, due to the brittle removal of the material after laser ablation damage, continuous fragmentation and micro-pits are generated on the surface after grinding. However, the difference in the exposed height of the abrasive grains on the surface of the diamond grinding wheel is relatively large, making it difficult to unify the cutting thickness of a single abrasive grain during grinding, which in turn affects the different material removal mechanisms. When the cutting thickness of a single abrasive grain is greater than the critical cutting thickness of the material, the material is mainly removed in the brittle domain; when the cutting thickness of a single abrasive grain is less than the critical cutting thickness of the material, the material mainly undergoes plastic domain removal, as Figure 5 (a) shows. During grinding with the grinding wheel, the high brittleness of the WC grains leads to severe fragmentation in the grinding area. Using the same grinding parameters, when grinding the surface of the material with laser ablation damage, the proportion of plastic removal on the grinding surface of laser-assisted machining increases significantly, a large number of plowing grooves are generated, and obvious plastic bulges appear on both sides of the scratches under the extrusion of the abrasive grains, indicating that obvious plastic flow occurs in the material and the surface quality is significantly improved, as Figure 5 (b) shows.

[0062] The above embodiments of the invention should be understood that these embodiments are only used to more clearly illustrate the present invention. They are not used to limit the scope of the present invention. After reading the present invention, the modifications of various equivalent forms of the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

Claims

1. A device for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials, characterized in that: include: A driving motor (1), a fastening flange (2), a laser system, a mobile platform, a workpiece (5), and a grinding wheel (3); the driving motor (1) is mounted on a device body (4), and the grinding wheel (3) is mounted on a main shaft of the driving motor via a fastening flange 2); the laser system is mounted on a guide rail (11) of the mobile platform; (5) is fixed on a workbench (6) of the mobile platform of the device; The laser system adjusts the laser beam to act on the surface of the workpiece (5) and the front end of the grinding wheel in the grinding direction; By precisely controlling the motion trajectory of the laser system within the laser defocus range, microstructure types with different degrees of damage are obtained on the surface of the workpiece to be processed. The workpiece (5) is driven to perform feed motion by the worktable (6), and the grinding wheel rotates while the grinding process of the laser ablated microstructure area is achieved.

2. The device for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials according to claim 1, characterized in that: The laser system comprises: a laser controller (10), a transmission optical fiber (9), an optical path, and a laser galvanometer (7); the laser galvanometer is connected to the laser controller (10) via the transmission optical fiber (9); the laser controller (10) controls laser parameters of the output light beam including but not limited to incident frequency, laser power and pulse time; the laser acts on the surface of the workpiece (5) via the laser galvanometer (7); the incident angle, optical path, and distance from the workpiece surface of the laser beam are adjustable; the light spot position is at the front end of the grinding wheel grinding direction, and the distance is adjusted according to the processing characteristics of different materials.

3. The device for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials according to claim 1, characterized in that: The laser controller (10) controls the laser output power, frequency and pulse width, thereby controlling the energy introduced into the material surface, thereby controlling the degree of damage, and obtaining different texture types on the surface of the workpiece to be processed, including but not limited to: arc line texture, square texture, parallel line texture, zigzag texture, diamond texture and vertical line texture.

4. The device for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials according to claim 3, characterized in that: The control of the damage degree is achieved by: The laser used is an ideal Gaussian beam, and the laser heat flux on the material surface is regarded as a surface heat source, which can be expressed as: in, Where H(τ-t) is a step function, A=1-R is the absorptivity of the material under infrared laser, R is the reflectivity, ω0 is the laser waist radius, Q0 is the laser peak energy density, and P is the laser power; Under the condition of fixed laser scanning speed, by controlling the input power P, the energy of the laser acting on the material surface is controlled, thereby controlling the degree of ablation and damage on the material surface; It is found that under the condition of rated laser power P, the mapping relationship between the energy Q required for material crack extension and the ablation damage length L is: Different power percentage is i%, and the corresponding damage length is L i , calculated as follows: According to the above formula, the corresponding relationship between laser power control and ablation damage is obtained, so that the degree of damage can be accurately controlled by laser ablation. Similarly, under the condition of fixed laser power, the energy accumulation of the laser on the material surface can be controlled by controlling the scanning speed, thereby controlling the degree of ablation and damage on the material surface.

5. The device for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials according to claim 1, characterized in that: The grinding wheel (3) is a diamond grinding wheel or a CBN grinding wheel; the hard and brittle material includes but is not limited to reaction sintered SiC, single crystal silicon, WC / Co hard alloy and ceramic-based composite material.

6. A process for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials based on the device for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials according to claim 1, characterized in that: The following steps are involved: 1) Install the workpiece to be processed on the workbench of the grinding device, and install the grinding wheel on the rotating spindle through the fastening flange; 2) Adjust the grinding wheel and the laser head of the laser system to the area where the hard and brittle material is to be ground, and adjust the position and angle between the laser galvanometer and the workpiece by rotating it to ensure that the laser is irradiated on the surface of the material; adjust the distance between the laser spot and the surface of the material to ensure that it is within the defocus range of the laser beam and that the surface of the material is ablated and removed; 3) Control the ablation damage on the material surface by precisely controlling the motion trajectory of the laser system within the laser defocus range; while laser ablation removes the surface material, the material melts, oxidizes and recondenses, causing changes in the surface properties of the material; at the same time, high temperature causes thermal crack damage inside the material; in order to effectively control the damage on the surface of the laser ablated material, the laser pulse energy, scanning speed and scanning trajectory are precisely controlled to achieve the purpose of controlling the damage distribution and damage depth; 4) The laser used is a typical Gaussian beam. The laser heat flux on the material surface is regarded as a surface heat source. The laser heat flux can be expressed as: in, Where H(τ-t) is a step function, A=1-R is the absorptivity of the material under infrared laser, R is the reflectivity, ω0 is the laser waist radius, Q0 is the laser peak energy density, and P is the laser power; Under the condition of fixed laser scanning speed, by controlling the input power P, the energy of the laser acting on the material surface is controlled, thereby controlling the degree of ablation and damage on the material surface; under the condition of rated laser power P, the mapping relationship between the energy Q required for material crack extension and the ablation damage length L is: Different power percentage is i%, and the corresponding damage length is L i , calculated as follows: According to the above formula, the corresponding relationship between laser power control and ablation damage is calculated, so as to achieve accurate control of the damage degree of laser ablation and guide the selection of grinding process parameters. Similarly, under the condition of fixed laser power, the amount of accumulated energy of the laser acting on the material surface can be controlled by controlling the scanning speed, thereby controlling the ablation degree and damage degree of the material surface. 5) Laser ablation removes part of the material, plans the laser scanning trajectory to achieve the preparation of surface microstructure, and controls the distribution of material surface damage; in order to completely remove the laser ablation area on the material surface, the grinding depth of the grinding wheel should be greater than the depth of the laser ablation microstructure; 6) After processing is completed, turn off the laser system and grinding wheel grinding system.

7. The process for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials according to claim 6, characterized in that: In step 1), the material of the workpiece to be processed is a hard and brittle material type, including but not limited to reaction sintered SiC, single crystal silicon, WC / Co cemented carbide and ceramic-based composite materials; the grinding wheel used is a diamond grinding wheel or a CBN grinding wheel.

8. The process for laser ablation-induced controlled damage-assisted grinding of hard and brittle materials according to claim 6, characterized in that: In step 2), a microstructure is ablated, including but not limited to arc line texture, square texture, parallel line texture, zigzag texture, diamond texture and vertical line texture.

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