Method for machining hard and brittle material composite surface based on ultrasonic vibration assisted slow cutter servo

Abstract

The invention discloses a method for machining a hard and brittle material composite surface based on ultrasonic vibration assisted slow cutter servo. The method comprises the following steps that a prediction model is established, and the critical cutting depth is obtained; designing and inputting a processing track; installing a debugging auxiliary system and fixing the workpiece; rough surface machining; primary finish machining is conducted on the surface of the workpiece, an ultrasonic vibration auxiliary system is started, a slow tool servo control tool is assisted through ultrasonic vibration, and primary finish machining is conducted according to the designed machining track; second-time finish machining is conducted on the surface of the workpiece, an ultrasonic vibration auxiliary system is started, a slow tool servo control tool is assisted through ultrasonic vibration, and second-time finish machining is conducted under the condition that the cutting depth is lower than the critical cutting depth of the workpiece material; machining is completed, and the workpiece surface is cleaned; a processing machine tool used in processing is a five-axis ultra-precision machine tool. Pits and micro-cracks formed on the machined surface can be effectively inhibited, then tool abrasion is reduced, machining efficiency is improved, machining cost is reduced, and completeness of the composite surface can be improved.

Description

Technical Field

[0001] The invention relates to the technical field of ultra-precision machining, and in particular to a method for machining a composite surface of a hard and brittle material based on ultrasonic vibration-assisted slow-tool servo. Background Art

[0002] For hard and brittle materials, such as single crystal silicon, single crystal germanium, glass, phosphorus germanium zinc, magnesium aluminum spinel, silicon carbide and sapphire. For the flat products of this type of materials, they are widely used in military and national defense fields such as quantum computing, laser mirrors and infrared detection systems. For the microstructure array surface products of this type of materials, it is a type of surface with regularly distributed microscopic geometric topological shapes and specific functions. It is a key component in the fields of optoelectronics, information communication, precision engineering, etc. For example, microlens arrays for IC equipment light source systems, bionic compound eye structure arrays for target positioning, microprism arrays for spatial optical reflection, large-size diffraction gratings for laser-induced nuclear fusion, etc. Among the existing products with microstructure surfaces, the demand for such surface functions in hard and brittle material systems is increasing. In the traditional cutting process, the material is removed in the form of brittle fracture, which easily produces cracks and pits on the processed surface, seriously affecting the surface quality and performance of the product. Among the existing ultra-precision machining technologies, ultrasonic single-point diamond turning has been proven to be an effective micro-nano manufacturing method for continuous smooth free-form surfaces and continuous functional surfaces. It is widely used in high-tech fields such as national defense, aerospace, and microelectronics manufacturing. However, for hard and brittle materials, there are still problems such as difficult processing and unstable surface quality. Summary of the invention

[0003] The purpose of the present invention is to provide a method for ultrasonic vibration-assisted slow tool servo processing of composite surfaces of hard and brittle materials, which adopts ultrasonic vibration-assisted slow tool servo processing technology to achieve high-quality composite surface processing of hard and brittle materials, can effectively inhibit the formation of pits and microcracks on the processed surface, thereby reducing tool wear, improving processing efficiency and reducing processing costs, and can improve the integrity of the composite surface.

[0004] The present invention is achieved through the following technical solutions:

[0005] The method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo includes the following steps: step S1: establishing a prediction model and obtaining a critical cutting depth; step S2: designing and inputting a machining trajectory; step S3: installing and debugging an auxiliary system and fixing a workpiece; step S4: surface rough machining; step S5: turning on the ultrasonic vibration auxiliary system, using ultrasonic vibration-assisted slow tool servo to control the tool, and performing the first fine machining according to the designed machining trajectory; step S6: turning on the ultrasonic vibration auxiliary system, using ultrasonic vibration-assisted slow tool servo to control the tool, and performing the second fine machining at a depth lower than the critical cutting depth of the workpiece material; step S7: completing the machining and cleaning the workpiece surface; the machining machine tool used in steps S4, S5 and S6 is a five-axis ultra-precision machine tool. In order to solve the above technical problems and achieve corresponding technical effects, the present invention adopts ultrasonic vibration-assisted slow tool servo machining technology to realize high-quality composite surface machining of hard and brittle materials, which can effectively inhibit the formation of pits and microcracks on the machining surface, thereby reducing tool wear, improving machining efficiency and reducing machining costs, and improving the integrity of the composite surface.

[0006] Further technical solutions:

[0007] In step S1, the prediction model established is as follows:

[0008]

[0009] Among them, E pd-x is the specific cutting energy dissipation value of plastic cutting, E cd-x is the specific cutting energy dissipation value of brittle cutting, E p is the energy consumed in a single cycle of plastic processing, E g is the energy dissipated in the plowing area of ​​the rear blade, E w is the energy dissipated by plastic flow, E sp Energy dissipated in a single cycle of plastic deformation, E stp is the energy dissipated by elastic deformation, E c is the energy consumed in single cycle brittle machining, A c is the undeformed cutting area, v c is the cutting speed, f is the cutting frequency, V b is the cutting volume, E cf is the energy dissipated by crack propagation, C l is the crack depth;

[0010] Get E pd-x and E cd-x The value corresponding to the intersection of the two curves is the conventional predicted critical depth value h. kl ;

[0011] After obtaining the conventional predicted critical depth value hkl Finally, the critical cutting depth d under ultrasonic vibration assisted slow tool servo machining is obtained by combining vibration parameters and cutting parameters. c .

[0012] Further: step S2 comprises:

[0013] Step S21: starting the ultrasonic vibration auxiliary system;

[0014] Step S22: slow tool processing route design;

[0015] Step S23: Ultrasonic vibration assisted processing route design;

[0016] Step S24: route input control system;

[0017] Further: Step S22: Design of the first finishing route, completing the design of the slow tool processing route according to the workpiece processing surface morphology requirements;

[0018] Step S23: Based on the slow tool processing route and in combination with the vibration condition of the ultrasonic vibration assisted system, the ultrasonic vibration assisted processing route is designed.

[0019] Furthermore: the axial vibration amplitude of the ultrasonic vibration auxiliary system parallel to the tool tip is 2 μm, the longitudinal vibration amplitude perpendicular to the tool tip is 2 μm, and the vibration frequency of the ultrasonic vibration auxiliary system is 45 KHz.

[0020] Further: Step S3 comprises the following steps:

[0021] Step S31: Start the hydraulic station and wait for the axis coordinate error of the machine tool to stabilize within ±0.005 μm;

[0022] Step S32: installing the ultrasonic vibration auxiliary system on the C-axis tool holder of the machining machine, and adjusting the tool position so that the tool tip is perpendicular to the workpiece plane;

[0023] Step S33: installing the visual monitoring system on the C-axis tool post of the processing machine tool, and adjusting the tool tip to the center of the shooting screen of the visual monitoring system;

[0024] Step S34: mounting the workpiece on the vacuum chuck of the B-axis of the processing machine tool, and performing dynamic balance adjustment on the B-axis;

[0025] Environmental factors including temperature, humidity and cleanliness also need to be adjusted, and the temperature of the working environment is adjusted to 21±0.1℃, the humidity is adjusted to 30±5%, the cleanliness is not less than Class 10000, and other machine tools and equipment in the working environment need to be shut down.

[0026] Further: in step S4, the workpiece surface is rough-machined using a tool, during which the tool rotates at a speed of 1000 r / min and feeds forward at a feed rate of 10 μm / min;

[0027] The front angle of the tool is -25°, the back angle of the tool is 15°, the edge radius of the tool is 1.004 mm, and the cutting depth of the tool is 6 to 10 μm.

[0028] Further: Step S5: the tool performs a first fine machining on the workpiece surface according to the ultrasonic vibration assisted machining route, during which the tool rotates at a speed of 1000 r / min and feeds forward at a feed rate of 4 μm / min;

[0029] The front angle of the tool is -25°, the back angle of the tool is 15°, the edge radius of the tool is 1.004 mm, and the cutting depth of the tool is 2 to 4 μm.

[0030] Further: Step S6: the tool performs a second finishing process on the workpiece surface according to the ultrasonic vibration assisted processing route, during which the tool rotates at a speed of 1000 r / min and feeds forward at a feed rate of 1 μm / min;

[0031] The front angle of the tool is -25°, the back angle of the tool is 15°, the edge radius of the tool is 1.004 mm, and the cutting depth of the tool is 0 to 1.5 μm.

[0032] Further: Step S7: Complete the processing and clean the workpiece surface. The specific method is as follows: stop the processing machine tool, turn off the visual monitoring system and the ultrasonic vibration auxiliary system, remove the workpiece, clean the workpiece surface with anhydrous ethanol, and dry and store the workpiece.

[0033] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0034] 1. The present invention is based on a method for ultrasonic vibration-assisted slow tool servo processing of composite surfaces of hard and brittle materials. The ultrasonic vibration-assisted slow tool servo processing technology is used to achieve high-quality composite surface processing of hard and brittle materials. It can effectively suppress the formation of pits and microcracks on the processed surface, thereby reducing tool wear, improving processing efficiency and reducing processing costs, and can improve the integrity of the composite surface. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0036] Figure 1 is a flow chart of the method of the present invention;

[0037] Figure 2 It is a schematic diagram of the slow tool servo machining trajectory and the ultrasonic vibration assisted machining trajectory;

[0038] Figure 3 This is the surface white light interferometer result diagram of the finished flat product;

[0039] Figure 4 This is the surface micro-morphology detection map of the micro-structured finished product;

[0040] Figure 5 It is a structural schematic diagram of the processing machine tool in the processing state;

[0041] Figure 6 This is a schematic diagram of the structure of the ultrasonic vibration-assisted slow-tool servo machining device.

[0042] Marks and corresponding parts names in the attached drawings: DETAILED DESCRIPTION

[0043] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0044] In the following description, a large number of specific details are set forth in order to provide a thorough understanding of the present invention. However, it is apparent to one of ordinary skill in the art that these specific details are not necessarily employed to practice the present invention. In other embodiments, in order to avoid obscuring the present invention, well-known structures, circuits, materials, or methods are not specifically described.

[0045] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment," "an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. In addition, it will be appreciated by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0046] In the description of the present invention, the directions or positional relationships indicated by terms such as “front”, “rear”, “left”, “right”, “up”, “down”, “vertical”, “horizontal”, “high”, “low”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the scope of protection of the present invention.

[0047] Embodiment 1:

[0048] like Figure 1 , Figure 2 As shown, the method of ultrasonic vibration-assisted slow tool servo processing of the composite surface of hard and brittle materials includes the following steps: step S1: establishing a prediction model and obtaining a critical cutting depth; step S2: designing and inputting a processing trajectory; step S3: installing and debugging the auxiliary system and fixing the workpiece; step S4: surface rough processing; step S5: first fine processing of the workpiece surface, turning on the ultrasonic vibration auxiliary system, using ultrasonic vibration to assist the slow tool servo to control the tool, and performing the first fine processing according to the designed processing trajectory; step S6: second fine processing of the workpiece surface, turning on the ultrasonic vibration auxiliary system, using ultrasonic vibration to assist the slow tool servo to control the tool, and performing the second fine processing at a depth lower than the critical cutting depth of the workpiece material; step S7: completing the processing and cleaning the workpiece surface; the processing machine tool used in steps S4, S5 and S6 is a five-axis ultra-precision machine tool.

[0049] The specific processing methods are as follows:

[0050] First, in step S1, the prediction model established is as follows:

[0051]

[0052] Among them, E pd-x is the specific cutting energy dissipation value of plastic cutting, E cd-x is the specific cutting energy dissipation value of brittle cutting, E p is the energy consumed in a single cycle of plastic processing, E g is the energy dissipated in the plowing area of ​​the rear blade, E w is the energy dissipated by plastic flow, E sp Energy dissipated in a single cycle of plastic deformation, E stp is the energy dissipated by elastic deformation, E c is the energy consumed in single cycle brittle machining, A c is the undeformed cutting area, v c is the cutting speed, f is the cutting frequency, V b is the cutting volume, E cf is the energy dissipated by crack propagation, Cl is the crack depth;

[0053] Get E pd-x and E cd-x The value corresponding to the intersection of the two curves is the conventional predicted critical depth value h. kl ; After obtaining the conventional predicted critical depth value h kl Finally, the critical cutting depth d under ultrasonic vibration assisted slow tool servo machining is obtained by combining vibration parameters and cutting parameters. c . In determining the lower critical cutting depth d c Then, proceed to step S2, specifically, step S2 comprises the following steps: step S21: start the ultrasonic vibration auxiliary system; step S22: slow tool processing route design; step S23: ultrasonic vibration auxiliary processing route design; step S24: route input control system; specifically, Figure 2As shown, step S22: the first finishing route design, the slow tool processing route design is completed according to the workpiece processing surface morphology requirements; step S23: on the basis of the slow tool processing route, combined with the vibration condition of the ultrasonic vibration auxiliary system, the ultrasonic vibration auxiliary system completes the design of the ultrasonic vibration auxiliary system. The axial vibration amplitude of the parallel tool tip and the longitudinal vibration amplitude of the perpendicular tool tip are 2μm, and the vibration frequency of the ultrasonic vibration auxiliary system is 45KHz. After the route design is completed and input, step S3 is performed, and step S3 includes the following steps: step S31: turn on the hydraulic station and wait for the coordinate error of the machine tool axis system to stably jump to ±0.005μm; step S32: install the ultrasonic vibration auxiliary system on the C-axis (axis rotating around the Y-axis) tool holder of the processing machine tool, and adjust the tool position so that the tool tip is perpendicular to the workpiece plane; step S33: install the visual monitoring system on the C-axis tool holder of the processing machine tool, and adjust the tool tip to the center of the visual monitoring system shooting screen; step S34: install the workpiece on the vacuum suction cup of the B-axis 9 (axis rotating around the X-axis) of the processing machine tool, and perform dynamic balance adjustment of the B-axis; before adjustment, environmental factors including temperature, humidity and cleanliness need to be adjusted, and the temperature of the working environment is adjusted to 21±0.1℃, the humidity is adjusted to 30±5%, the cleanliness is not less than Class 10000, and other machine tool equipment in the working environment needs to be turned off. Then, in step S4, the tool is used to perform rough machining on the workpiece surface. During the machining process, the tool rotates at a speed of 1000r / min and feeds forward at a feed rate of 10μm / min; the front angle of the tool is -25°, the back foot of the tool is 15°, the tool edge radius is 1.004mm, and the tool cutting depth is 6-10μm. Then, in step S5, the tool performs the first fine machining on the workpiece surface according to the ultrasonic vibration assisted machining route. During the machining process, the tool rotates at a speed of 1000r / min and feeds forward at a feed rate of 4μm / min; the front angle of the tool is -25°, the back foot of the tool is 15°, the tool edge radius is 1.004mm, and the tool cutting depth is 2-4μm. In step S6, the tool performs a second finishing process on the workpiece surface according to the ultrasonic vibration assisted processing route. During the processing, the tool rotates at a speed of 1000r / min and feeds forward at a feed rate of 1μm / min; the front angle of the tool is -25°, the back foot of the tool is 15°, the tool edge radius is 1.004mm, and the cutting depth of the tool is 0-1.5μm. After the workpiece surface processing is completed, step S7 is implemented: complete the processing and clean the workpiece surface. The specific method is as follows: the processing machine tool is stopped, the visual monitoring system and the ultrasonic vibration assisted system are turned off, and the workpiece is removed, the workpiece surface is cleaned with anhydrous ethanol, and the workpiece is dried and stored.

[0054] Embodiment 2:

[0055] This embodiment uses the method in Embodiment 1 to perform plane processing. This embodiment takes the processing of zinc germanium phosphorus (ZGP) crystal material as an example.

[0056] The specific processing method is as follows: According to the established critical cutting depth prediction model, h is obtained through software analysis. t =230nm, according to the subsequent vibration parameters and cutting parameters, the critical cutting depth d of ZGP material under ultrasonic vibration assisted slow tool servo machining is obtained c =351nm. The initial plane cutting trajectory based on slow tool servo machining is designed, the tool micro radius is used as the compensation parameter, and the ultrasonic vibration auxiliary parameters are combined to convert the cutting trajectory into an ultrasonic vibration assisted machining trajectory. Adjust the temperature of the ultra-precision machining laboratory to 21±0.1℃, the humidity to 25~335%, and the cleanliness level to above Class 10000; turn off the machine tools and equipment in the laboratory that are not related to this machining; turn on the machine tool, turn on the hydraulic station, wait for the machine tool axis coordinate error to stabilize at ±0.005μm, debug and install the ultrasonic vibration auxiliary system, debug and install the visual monitoring system, and install the workpiece sample and fixture; wait for the machine tool axis coordinate error to stabilize at ±0.005μm; start the ultrasonic vibration assisted cutting system, and use the ultrasonic vibration assisted slow tool servo machining method to perform semi-precision machining on the rough machining surface of the ZGP crystal workpiece according to the converted plane machining trajectory; set the machining parameters as follows: ultrasonic vibration assisted parallel tool tip axial vibration of 2μm, vertical tool tip longitudinal vibration of 2μm, vibration frequency of 45kHz, spindle speed of 10r / min, feed rate of 4μm / min, and cutting depth of 2-4μm. The phase difference between the two phases is 90°, the tool rake angle is -25°, the tool back angle is 15°, and the tool edge radius is 1.004mm. The ultrasonic vibration assisted cutting system is started, and the ultrasonic vibration assisted slow tool servo processing method is used to perform ultra-dense processing on the semi-precision machining surface of the ZGP crystal workpiece according to the converted plane machining trajectory. Unlike semi-precision machining, its cutting depth d c = 351nm or less, the feed rate is 1μm / min, and the ultra-precision machining is completed. Turn off the ultrasonic vibration assisted cutting system, turn off the visual monitoring system, and process the machine tool; remove the ZGP crystal workpiece for processing Yangping, clean it with sewage ethanol and save it, and obtain a high-quality surface of ultrasonic vibration assisted slow tool servo machining. The roughness of the ultra-precision machined pure iron surface prepared in the present invention is detected by white light interferometer, and the surface roughness Ra = 0.5039nm, Sa = 2.368nm, Figure 3 shown.

[0057] In order to facilitate understanding, the present embodiment provides a processing state structure of a processing machine tool, such as Figure 5 , Figure 6 As shown, specifically, Figure 5In the middle, number 1 is the vacuum suction cup, number 2 is the workpiece and its fixture, number 3 is the visual monitoring system, number 4 is the ultrasonic vibration auxiliary system, number 5 is the support frame, number 6 is the ultrasonic vibration auxiliary system controller, number 7 is the rotating tool holder, number 8 is the tool, number 9 is the machine tool control center, number 10 is the B-axis / spindle; number 11 is the Y-axis, number 12 is the X-axis, number 13 is the Z-axis, and number 14 is the C-spindle. Figure 6 The reference numeral 15 is a vacuum suction cup fixture, the reference numeral 16 is a workpiece to be processed, the reference numeral 17 is a vertical vibration displacement sensor, and the reference numeral 18 is a horizontal vibration displacement sensor.

[0058] Embodiment 3:

[0059] This embodiment uses the method in Embodiment 1 to process the microstructure surface. This embodiment takes the processing of zinc germanium phosphorus (ZGP) crystal material as an example.

[0060] The specific processing methods are as follows:

[0061] According to the established critical cutting depth prediction model, h is obtained through software analysis. t =230nm, according to the subsequent vibration parameters and cutting parameters, the critical cutting depth d of ZGP material under ultrasonic vibration assisted slow tool servo machining is obtained c =351nm. The initial plane cutting trajectory based on slow tool servo machining is designed, the tool micro radius is used as the compensation parameter, and the ultrasonic vibration auxiliary parameters are combined to convert the cutting trajectory into an ultrasonic vibration assisted machining trajectory. Adjust the temperature of the ultra-precision machining laboratory to 21±0.1℃, the humidity to 25~335%, and the cleanliness level to above Class 10000; turn off the machine tools and equipment in the laboratory that are not related to this machining; turn on the machine tool, turn on the hydraulic station, wait for the machine tool axis coordinate error to stabilize at ±0.005μm, debug and install the ultrasonic vibration auxiliary system, debug and install the visual monitoring system, and install the workpiece sample and fixture; wait for the machine tool axis coordinate error to stabilize at ±0.005μm; start the ultrasonic vibration assisted cutting system, and use the ultrasonic vibration assisted slow tool servo machining method to perform semi-precision machining on the rough machining surface of the ZGP crystal workpiece according to the converted plane machining trajectory; set the machining parameters as follows: ultrasonic vibration assisted parallel tool tip axial vibration of 2μm, vertical tool tip longitudinal vibration of 2μm, vibration frequency of 45kHz, spindle speed of 10r / min, feed rate of 4μm / min, and cutting depth of 2-4μm. The phase difference between the two phases is 90°, the tool rake angle is -25°, the tool back angle is 15°, and the tool edge radius is 1.004mm. The ultrasonic vibration assisted cutting system is started, and the ultrasonic vibration assisted slow tool servo processing method is used to perform ultra-dense processing on the semi-precision machining surface of the ZGP crystal workpiece according to the converted plane machining trajectory. Unlike semi-precision machining, its cutting depth d c= 351nm or less, feed rate is 1μm / min, and ultra-precision machining is completed. Turn off the ultrasonic vibration assisted cutting system, turn off the visual monitoring system, and process the machine tool; remove the ZGP crystal workpiece processing sample, clean and preserve it with sewage ethanol, and obtain a high-quality surface of ultrasonic vibration assisted slow tool servo machining.

[0062] The surface morphology of the prepared ultra-precision machined ZGP crystal microstructure can be detected by white light interferometry, and the surface microstructure can be obtained as follows: Figure 4 As shown, the height is about 40μm and the structure is complete and has no defects.

[0063] In order to facilitate understanding, the present embodiment provides a processing state structure of a processing machine tool, such as Figure 5 , Figure 6 As shown, specifically, Figure 5 In the middle, number 1 is the vacuum suction cup, number 2 is the workpiece and its fixture, number 3 is the visual monitoring system, number 4 is the ultrasonic vibration auxiliary system, number 5 is the support frame, number 6 is the ultrasonic vibration auxiliary system controller, number 7 is the rotating tool holder, number 8 is the tool, number 9 is the machine tool control center, number 10 is the B-axis / spindle; number 11 is the Y-axis, number 12 is the X-axis, number 13 is the Z-axis, and number 14 is the C-spindle. Figure 6 The reference numeral 15 is a vacuum suction cup fixture, the reference numeral 16 is a workpiece to be processed, the reference numeral 17 is a vertical vibration displacement sensor, and the reference numeral 18 is a horizontal vibration displacement sensor.

[0064] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo, characterized in that: The steps include: Step S1: Establish a prediction model and obtain the critical cutting depth; Step S2: Design and input of processing trajectory; Step S3: Install the debugging auxiliary system and fix the workpiece; Step S4: surface rough machining; Step S5: Turn on the ultrasonic vibration auxiliary system, use ultrasonic vibration to assist the slow tool servo to control the tool, and perform the first finishing according to the designed machining trajectory; Step S6: turning on the ultrasonic vibration auxiliary system, using ultrasonic vibration to assist the slow tool servo to control the tool, and performing a second finishing operation at a depth lower than the critical cutting depth of the workpiece material; Step S7: finishing the processing and cleaning the workpiece surface; The processing machine tool used in steps S4, S5 and S6 is a five-axis ultra-precision machine tool.

2. The method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo according to claim 1 is characterized in that: In step S1, the prediction model established is as follows: Among them, E pd-x is the specific cutting energy dissipation value of plastic cutting, E cd-x is the specific cutting energy dissipation value of brittle cutting, E p is the energy consumed in a single cycle of plastic processing, E g is the energy dissipated in the plowing area of ​​the rear blade, E w is the energy dissipated by plastic flow, E sp Energy dissipated in a single cycle of plastic deformation, E stp is the energy dissipated by elastic deformation, E c is the energy consumed in single cycle brittle machining, A c is the undeformed cutting area, v c is the cutting speed, f is the cutting frequency, V b is the cutting volume, E cf is the energy dissipated by crack propagation, C l is the crack depth; Get E pd-x and E cd-x The value corresponding to the intersection of the two curves is the conventional predicted critical depth value h. kl ; After obtaining the conventional predicted critical depth value h kl Finally, the critical cutting depth d under ultrasonic vibration assisted slow tool servo machining is obtained by combining vibration parameters and cutting parameters. c .

3. The method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo according to claim 1 is characterized in that: Step S2 includes: Step S21: starting the ultrasonic vibration auxiliary system; Step S22: slow tool processing route design; Step S23: Ultrasonic vibration assisted processing route design; Step S24: Route input into the control system.

4. The method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo according to claim 3 is characterized in that: Step S22: Design of the first finishing route, completing the design of the slow tool processing route according to the workpiece processing surface morphology requirements; Step S23: Based on the slow tool processing route and in combination with the vibration condition of the ultrasonic vibration assisted system, the ultrasonic vibration assisted processing route is designed.

5. The method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo according to claim 4 is characterized in that: The axial vibration amplitude of the ultrasonic vibration auxiliary system parallel to the tool tip is 2 μm, the longitudinal vibration amplitude perpendicular to the tool tip is 2 μm, and the vibration frequency of the ultrasonic vibration auxiliary system is 45 KHz.

6. The method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo according to claim 1, characterized in that: The step S3 comprises the following steps: Step S31: Start the hydraulic station and wait for the axis coordinate error of the machine tool to stabilize within ±0.005 μm; Step S32: installing the ultrasonic vibration auxiliary system on the C-axis tool holder of the machining machine, and adjusting the tool position so that the tool tip is perpendicular to the workpiece plane; Step S33: installing the visual monitoring system on the C-axis tool post of the processing machine tool, and adjusting the tool tip to the center of the shooting screen of the visual monitoring system; Step S34: mounting the workpiece on the vacuum chuck of the B-axis of the processing machine tool, and performing dynamic balance adjustment on the B-axis; Environmental factors including temperature, humidity and cleanliness also need to be adjusted, and the temperature of the working environment is adjusted to 21±0.1℃, the humidity is adjusted to 30±5%, the cleanliness is not less than Class 10000, and other machine tools and equipment in the working environment need to be shut down.

7. The method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo according to claim 5, characterized in that: In step S4, the workpiece surface is rough-machined using a tool, during which the tool rotates at a speed of 1000 r / min and feeds forward at a feed rate of 10 μm / min; The front angle of the tool is -25°, the back angle of the tool is 15°, the edge radius of the tool is 1.004 mm, and the cutting depth of the tool is 6 to 10 μm.

8. The method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo according to claim 5, characterized in that: Step S5: the tool performs the first finishing of the workpiece surface according to the ultrasonic vibration assisted machining route. During the machining process, the tool rotates at a speed of 1000 r / min and feeds forward at a feed rate of 4 μm / min; The front angle of the tool is -25°, the back angle of the tool is 15°, the edge radius of the tool is 1.004 mm, and the cutting depth of the tool is 2 to 4 μm.

9. The method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo according to claim 5, characterized in that: Step S6: the tool performs a second finishing process on the workpiece surface according to the ultrasonic vibration assisted processing route. During the processing, the tool rotates at a speed of 1000 r / min and feeds forward at a feed rate of 1 μm / min; The front angle of the tool is -25°, the back angle of the tool is 15°, the edge radius of the tool is 1.004 mm, and the cutting depth of the tool is 0 to 1.5 μm.

10. The method for machining the composite surface of hard and brittle materials based on ultrasonic vibration-assisted slow tool servo according to claim 6, characterized in that: Step S7: Complete the processing and clean the workpiece surface. The specific method is as follows: stop the processing machine tool, turn off the visual monitoring system and the ultrasonic vibration auxiliary system, remove the workpiece, clean the workpiece surface with anhydrous ethanol, and dry and store the workpiece.

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