Ceramic matrix composite ultrasonic vibration assisted grinding machining method

Abstract

The application belongs to the technical field of composite material processing, and particularly relates to a ceramic matrix composite ultrasonic vibration assisted grinding processing method, which comprises the following steps: carrying out single abrasive particle basic scratching test to obtain a micro-macro brittle fracture transition critical depth; obtaining ultrasonic vibration assisted grinding process parameters based on the micro-macro brittle fracture transition critical depth and a part processing surface quality; and carrying out ceramic matrix composite ultrasonic vibration assisted grinding processing based on the ultrasonic vibration assisted grinding process parameters. The technical scheme determines the micro-macro brittle fracture transition critical depth based on the part processing surface quality requirement and the basic scratching test, establishes a processing process parameter determination criterion, obtains the ultrasonic vibration assisted grinding process parameters, and carries out the ceramic matrix composite ultrasonic vibration assisted grinding processing with the parameters, so as to improve the grinding processing efficiency under the premise of ensuring the high-quality surface processing of the ceramic matrix composite.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of composite material processing, and particularly relates to a ceramic matrix composite ultrasonic vibration assisted grinding processing method. BACKGROUND

[0002] In the field of aerospace, with the development of equipment performance demand, it is necessary to use high-temperature-resistant, high-specific-strength and wear-resistant lightweight materials. Ceramic matrix composites have become a high-temperature-resistant material with great application prospect from among many materials. Ceramic matrix composites overcome the high brittleness of ceramic materials through exogenous toughening mechanism, and continuous fiber reinforced ceramic matrix composites achieve higher strength and fracture toughness through crack deflection and crack bridging.

[0003] Ceramic matrix composites are composed of components with significant performance differences, and the synergy of high-hardness ceramic matrix, anisotropic fiber reinforced phase and weak interface layer effectively improves the use performance of the material, but also leads to the poor processing performance of the ceramic matrix composite. Ceramic matrix composites are typical materials with both hard and brittle materials and composite materials, and are extremely prone to damage during processing. The reasons such as matrix collapse and fiber pull-out, peeling and random distribution of fracture during processing will reduce the quality of the processed surface. The material removal mechanism of ceramic matrix composites shows that high-quality surface processing can be achieved in the micro-brittle fracture domain, but the micro-macro brittle fracture transition critical cutting depth of ceramic matrix composites is generally small. Therefore, in order to achieve high surface quality processing of parts, the processing efficiency is usually sacrificed to ensure the surface quality.

[0004] In order to cope with the poor machinability of ceramic matrix composites, grinding is a relatively common processing technology, and ultrasonic vibration assisted processing is also a common processing method for hard and brittle materials. For ultrasonic vibration assisted grinding of ceramic matrix composites, it is extremely critical to scientifically and reasonably determine the processing parameters to achieve high-quality surface processing while improving processing efficiency. At present, the traditional method widely used to determine the processing parameters of ultrasonic vibration assisted grinding of ceramic matrix composites is to carry out orthogonal test or single factor test, and then to optimize the process parameters according to the responses such as force, surface roughness and material removal rate obtained by the test. The defects of this traditional method are that the process is complicated, time-consuming and labor-intensive, and the test parameter setting has a certain degree of randomness, making it difficult to balance the processing quality and processing efficiency at the same time. SUMMARY

[0005] The present application aims at the deficiencies in the prior art, and provides a ceramic matrix composite ultrasonic vibration assisted grinding processing method, which is based on a maximum undeformed chip thickness model established according to the three-dimensional motion trajectory of abrasive grains under the ultrasonic vibration assisted grinding condition, determines the processing in the micro-brittle domain according to the quality requirement of the processed surface, carries out a basic scratch test to determine the micro-macro brittle fracture transition critical depth of the ceramic matrix composite, establishes a processing parameter determination criterion based on the principle that the maximum undeformed chip thickness is not greater than the micro-macro brittle fracture transition critical depth, and obtains the ultrasonic vibration assisted grinding process parameters for processing, so as to improve the grinding processing efficiency while ensuring the high-quality surface processing of the ceramic matrix composite.

[0006] The technical scheme adopted to achieve the above object is as follows:

[0007] A ceramic matrix composite ultrasonic vibration assisted grinding processing method, comprising the following steps:

[0008] S1, a single abrasive grain basic scratch test is carried out on a ceramic matrix composite planar sample to determine the micro-macro brittle fracture transition critical depth thereof;

[0009] S2, based on the micro-macro brittle fracture transition critical depth, the ultrasonic vibration assisted grinding process parameters are obtained in combination with the quality requirement of the processed surface of the part;

[0010] S3, the ceramic matrix composite ultrasonic vibration assisted grinding processing is carried out based on the ultrasonic vibration assisted grinding process parameters.

[0011] Preferably, in the step S2, the quality requirement of the processed surface of the part includes the surface roughness and the surface damage condition after the processing of the part; wherein the surface roughness Sa is 2.0 μm, and the surface of the part after the processing is free of the pits formed by the fiber peeling and fiber pulling out.

[0012] Preferably, in the step S1, the single abrasive grain basic scratch test comprises the following steps:

[0013] S1-1, a steel disc with a single diamond abrasive grain welded on the circumferential surface is prepared, and the steel disc is installed on a numerical control machine tool;

[0014] S1-2, the numerical control machine tool is started, the steel disc is rotated under the driving of the numerical control machine tool, the diamond abrasive grain makes circumferential motion with the rotation of the steel disc, the ceramic matrix composite planar sample is scratched, and an arc-shaped depth scratch is formed on the ceramic matrix composite planar sample;

[0015] S1-3, observing the fiber fracture mode in the circular arc-shaped deep scratch by electron microscopy; wherein: the material removal caused by multiple brittle fractures in a single fiber is micro-brittle fracture, the material removal caused by one fracture in a single fiber is macro-brittle fracture, and the maximum scratch depth of the transition from micro-brittle fracture to macro-brittle fracture is the micro-macro brittle fracture transition critical depth.

[0016] Preferably, in step S3, the ultrasonic vibration assisted grinding machining of the ceramic matrix composite material includes the following steps:

[0017] S3-1, clamping the ceramic matrix composite workpiece on the numerical control machine tool;

[0018] S3-2, selecting a diamond grinding head and a longitudinal-torsional composite rotary ultrasonic tool holder to be installed on the machine tool;

[0019] S3-3, setting the ultrasonic vibration assisted grinding process parameters based on the numerical control machine tool;

[0020] S3-4, starting the numerical control machine tool, and the numerical control machine tool performs ultrasonic vibration assisted grinding machining of the ceramic matrix composite material according to the tool path trajectory specified by the numerical control program based on the ultrasonic vibration assisted grinding process parameters.

[0021] Preferably, in step S2, the ultrasonic vibration assisted grinding process parameters include spindle speed, feed speed, grinding depth, grinding width, longitudinal ultrasonic frequency, longitudinal ultrasonic amplitude, torsional ultrasonic frequency and torsional ultrasonic amplitude; wherein the spindle speed is selected according to the characteristics of the machine tool, the grinding depth and the grinding width are determined according to the machining allowance of the part, and the longitudinal ultrasonic frequency, the longitudinal ultrasonic amplitude, the torsional ultrasonic frequency and the torsional ultrasonic amplitude are determined according to the model of the longitudinal-torsional composite rotary ultrasonic tool holder.

[0022] Preferably, in step S2, when obtaining the ultrasonic vibration assisted grinding process parameters, the machining process parameter determination criterion is also established, and the feed speed is determined according to the machining process parameter determination criterion; the machining process parameter determination criterion is h max ≤h critical ; wherein h max is the maximum undeformed chip thickness; and h critical is the micro-macro brittle fracture transition critical depth.

[0023] Preferably, in step S2, under the condition of the machining process parameter determination criterion, the relationship between the related ultrasonic vibration assisted grinding process parameters is as follows:

[0024] a p v f b=(2πrnCb)Vol c ;

[0025]

[0026] wherein a p is the grinding depth, v f is the feed speed, b is the grinding width, r is the radius of the grinding head; n is the spindle speed; C is the effective grain density of the diamond grinding head; Vol c is the material removal volume of a single grain of the diamond grinding head; l is the length of the three-dimensional motion trajectory of the grain; θ is the grain half-apex angle, which is 60°.

[0027] Preferably, the effective grain density of the diamond grinding head is obtained by the following formula:

[0028]

[0029] wherein f is the effective grain fraction, which is 0.5; d g is the average size of the grain; V g is the volume fraction of the grain, which is 0.25.

[0030] Preferably, the length of the three-dimensional motion trajectory of the grain is obtained by the following formula:

[0031]

[0032]

[0033] wherein t0 is the single contact time of the grain with the workpiece material; x' is the derivative of the X-direction component of the grain trajectory; y' is the derivative of the Y-direction component of the grain trajectory; z' is the derivative of the Z-direction component of the grain trajectory.

[0034] Preferably, the derivative of the X-direction component of the grain trajectory, the derivative of the Y-direction component of the grain trajectory, and the derivative of the Z-direction component of the grain trajectory are obtained by the following formula:

[0035]

[0036]

[0037]

[0038] wherein t is the time variable; θ r+t is the sum of the tool rotation angle and the angle change caused by the torsional ultrasonic vibration of the tool, i.e. f t is the frequency of the torsional ultrasonic vibration of the tool; A t is the amplitude of the torsional ultrasonic vibration of the tool; A l is the longitudinal ultrasonic amplitude of the tool; f l is the frequency of the longitudinal ultrasonic vibration of the tool.

[0039] The beneficial effects of the present application are:

[0040] 1) The technical solution is based on the support of single abrasive particle basic scratch test, and the micro-macro brittle fracture transition critical depth of the ceramic matrix composite material is obtained from the physical properties of the ceramic matrix composite material. The ultrasonic vibration assisted grinding process parameters obtained based on the combination of the micro-macro brittle fracture transition critical depth and the part machining surface quality requirements establish a unified and reasonable machining condition standard for the machining of the ceramic matrix composite workpiece, which has important significance for the high-quality and high-efficiency machining of the ceramic matrix composite material.

[0041] 2) The maximum undeformed chip thickness model is established based on the three-dimensional motion trajectory of the abrasive particles under the ultrasonic vibration assisted grinding condition. According to the machining surface quality requirements, the machining in the micro-brittle domain is determined, and the basic scratch test is carried out to determine the micro-macro brittle fracture transition critical depth of the ceramic matrix composite material. Based on the principle that the maximum undeformed chip thickness is not greater than the micro-macro brittle fracture transition critical depth, the machining process parameter determination criterion is established, and the ultrasonic vibration assisted grinding process parameters are obtained for machining, so as to realize the improvement of the grinding machining efficiency under the premise of ensuring the high-quality surface machining of the ceramic matrix composite material.

[0042] 3) The technical solution guides the scientific and reasonable selection of process parameters according to the machining process parameter determination criterion, avoiding the time-consuming and labor-consuming problem of optimizing and determining process parameters through complex tests in traditional methods, and can be applied to the selection of machining parameters under different conditions. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 It is a single diamond abrasive particle basic scratch test schematic diagram;

[0044] Figure 2 It is a ceramic matrix composite ultrasonic vibration assisted grinding machining schematic diagram;

[0045] Figure 3 It is an abrasive particle motion trajectory schematic diagram.

[0046] In the figure:

[0047] 1, steel disc; 2, single diamond abrasive particle; 3, spindle speed n; 4, ceramic matrix composite plane sample; 5, circular arc depth scratch; 6, longitudinal ultrasonic vibration; 7, torsional ultrasonic vibration; 8, ceramic matrix composite workpiece; 9, diamond grinding head; 10, grinding width b; 11, feed speed v f ; 12, grinding depth a p ; 13, maximum undeformed chip thickness h max ; 14, single abrasive particle material removal volume Vol c ; 15, abrasive particle three-dimensional motion trajectory length l. DETAILED DESCRIPTION

[0048] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below in conjunction with the accompanying drawings in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments.

[0049] Therefore, the following detailed description of the present application provided in the accompanying drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art without creative labor based on the embodiments in the present application are within the scope of protection of the present application.

[0050] Embodiment 1

[0051] The embodiment discloses a ceramic matrix composite ultrasonic vibration assisted grinding processing method, as a preferred embodiment of the technical solution, comprising the following steps:

[0052] S1, a single abrasive particle based scratching test is carried out on a ceramic matrix composite plane pattern to determine the micro-macro brittle fracture transition critical depth;

[0053] S2, based on the micro-macro brittle fracture transition critical depth, combined with the part processing surface quality requirement, the ultrasonic vibration assisted grinding process parameters are obtained;

[0054] S3, based on the ultrasonic vibration assisted grinding process parameters, the ceramic matrix composite ultrasonic vibration assisted grinding processing is carried out.

[0055] Embodiment 2

[0056] The embodiment discloses a ceramic matrix composite ultrasonic vibration assisted grinding processing method, as a preferred embodiment of the technical solution, comprising the following steps:

[0057] S1, a single abrasive particle based scratching test is carried out on a ceramic matrix composite plane pattern to determine the micro-macro brittle fracture transition critical depth. The single abrasive particle based scratching test comprises the following steps:

[0058] S1-1, a steel disc with a single diamond abrasive particle welded on the circumferential surface is prepared, and the steel disc is installed on a numerical control machine tool;

[0059] S1-2, the numerical control machine tool is started, the steel disc is rotated under the driving of the numerical control machine tool, the diamond abrasive particle makes circumferential motion with the rotation of the steel disc, and the ceramic matrix composite plane sample is scratched to form a circular arc shaped depth scratch on the ceramic matrix composite plane sample;

[0060] S1-3, observing the fiber fracture mode in the circular arc variable-depth scratch by electron microscopy; wherein: the material removal caused by multiple (microscale) brittle fractures within a single fiber is micro-brittle fracture, the material removal caused by a single fracture of a single fiber is macro-brittle fracture, and the maximum scratch depth at which the micro-brittle fracture turns into macro-brittle fracture is the micro-macro brittle fracture transition critical depth.

[0061] S2, obtaining the ultrasonic vibration assisted grinding process parameters based on the micro-macro brittle fracture transition critical depth and in combination with the part machining surface quality requirements. The part machining surface quality requirements include the surface roughness and surface damage after part machining; the surface roughness Sa is 2.0 μm, and the surface after part machining is free of pits caused by fiber peeling and fiber pull-out, and the processing can be performed in the micro-brittle fracture domain according to the material removal mechanism.

[0062] S3, performing the ceramic matrix composite ultrasonic vibration assisted grinding machining based on the ultrasonic vibration assisted grinding process parameters.

[0063] Embodiment 3

[0064] The embodiment discloses a ceramic matrix composite ultrasonic vibration assisted grinding machining method, as a preferred embodiment of the technical solution, comprising the following steps:

[0065] S1, performing single-grain basic scratching test on a ceramic matrix composite planar sample to determine the micro-macro brittle fracture transition critical depth. The single-grain basic scratching test comprises the following steps:

[0066] S1-1, preparing a steel disc with a single diamond grain welded on the circumferential surface, and installing the steel disc on a numerical control machine tool;

[0067] S1-2, starting the numerical control machine tool to rotate the steel disc under the driving of the numerical control machine tool, and the diamond grain performs circumferential motion with the rotation of the steel disc to scratch the ceramic matrix composite planar sample, thereby forming a circular arc variable-depth scratch on the ceramic matrix composite planar sample;

[0068] S1-3, observing the fiber fracture mode in the circular arc variable-depth scratch by electron microscopy; wherein: the material removal caused by multiple (microscale) brittle fractures within a single fiber is micro-brittle fracture, the material removal caused by a single fracture of a single fiber is macro-brittle fracture, and the maximum scratch depth at which the micro-brittle fracture turns into macro-brittle fracture is the micro-macro brittle fracture transition critical depth.

[0069] S2, obtaining the ultrasonic vibration assisted grinding process parameters based on the micro-macro brittle fracture transition critical depth and the part machining surface quality requirements. The part machining surface quality requirements include the surface roughness and surface damage after part machining; the surface roughness Sa is 2.0 μm, and the surface after part machining is free of pits formed by fiber peeling and fiber pulling out, so the machining can be performed in the micro-brittle fracture domain according to the material removal mechanism. In addition, the ultrasonic vibration assisted grinding process parameters include spindle speed, feed speed, grinding depth, grinding width, longitudinal ultrasonic frequency, longitudinal ultrasonic amplitude, torsional ultrasonic frequency and torsional ultrasonic amplitude; the spindle speed is selected according to the characteristics of the machine tool, the grinding depth and the grinding width are determined according to the part machining allowance, and the longitudinal ultrasonic frequency, the longitudinal ultrasonic amplitude, the torsional ultrasonic frequency and the torsional ultrasonic amplitude are determined according to the model of the longitudinal-torsional composite rotary ultrasonic tool holder.

[0070] S3, performing the ultrasonic vibration assisted grinding machining of the ceramic matrix composite material based on the ultrasonic vibration assisted grinding process parameters. The ultrasonic vibration assisted grinding machining of the ceramic matrix composite material includes the following steps:

[0071] S3-1, clamping the ceramic matrix composite workpiece on the numerical control machine tool;

[0072] S3-2, selecting the diamond grinding head and the longitudinal-torsional composite rotary ultrasonic tool holder to be installed on the machine tool;

[0073] S3-3, setting the ultrasonic vibration assisted grinding process parameters based on the numerical control machine tool;

[0074] S3-4, starting the numerical control machine tool, and the numerical control machine tool performs the ultrasonic vibration assisted grinding machining of the ceramic matrix composite material according to the tool path trajectory specified by the numerical control program based on the ultrasonic vibration assisted grinding process parameters.

[0075] Further, the longitudinal-torsional composite rotary ultrasonic tool holder can simultaneously apply longitudinal ultrasonic vibration and torsional ultrasonic vibration to the tool (i.e. the diamond grinding head) during the machining process.

[0076] Example 4

[0077] The embodiment discloses a ceramic matrix composite ultrasonic vibration assisted grinding machining method, as a preferred embodiment of the technical solution, including the following steps:

[0078] S1, performing single abrasive particle based scratching test on the ceramic matrix composite material plane pattern to determine the micro-macro brittle fracture transition critical depth. The single abrasive particle based scratching test includes the following steps:

[0079] S1-1, preparing a steel disc with a single diamond abrasive particle welded on the circumferential surface, and installing the steel disc on the numerical control machine tool;

[0080] S1-2, start the numerical control machine tool, and make the steel disc rotate under the driving of the numerical control machine tool, and the diamond abrasive grains make a circular motion with the rotation of the steel disc to scratch the ceramic matrix composite material plane sample to form a circular arc variable-depth scratch on the ceramic matrix composite material plane sample;

[0081] S1-3, observe the fiber fracture mode in the circular arc variable-depth scratch by an electron microscope; wherein: the micro-brittle fracture that occurs multiple times (in a small scale) in a single fiber to cause material removal is micro-brittle fracture, the macro-brittle fracture that occurs once in a single fiber to cause material removal is macro-brittle fracture, and the maximum scratch depth that changes from micro-brittle fracture to macro-brittle fracture is the micro-macro brittle fracture transition critical depth.

[0082] S2, obtain the ultrasonic vibration assisted grinding process parameters based on the micro-macro brittle fracture transition critical depth and in combination with the part machining surface quality requirements; wherein, the part machining surface quality requirements include the surface roughness and the surface damage condition after part machining; wherein, the surface roughness Sa is 2.0 μm, and the surface after part machining is free of pits caused by fiber peeling and fiber pull-out, and the machining can be performed in the micro-brittle fracture domain according to the material removal mechanism. In addition, the ultrasonic vibration assisted grinding process parameters include the spindle speed, the feed speed, the grinding depth, the grinding width, the longitudinal ultrasonic frequency, the longitudinal ultrasonic amplitude, the torsional ultrasonic frequency and the torsional ultrasonic amplitude; wherein, the spindle speed is selected according to the machine tool characteristics, the grinding depth and the grinding width are determined according to the part machining allowance, and the longitudinal ultrasonic frequency, the longitudinal ultrasonic amplitude, the torsional ultrasonic frequency and the torsional ultrasonic amplitude are determined according to the longitudinal-torsional composite rotary ultrasonic tool holder model.

[0083] Further, in step S2, when obtaining the ultrasonic vibration assisted grinding process parameters, the machining process parameter determination criterion is also established, and the feed speed is determined according to the machining process parameter determination criterion; the machining process parameter determination criterion is h max ≤h critical ; wherein, h max is the maximum undeformed chip thickness, and h critical is the micro-macro brittle fracture transition critical depth. Specifically, under the condition of the machining process parameter determination criterion, the relationships of the related ultrasonic vibration assisted grinding process parameters are as follows:

[0084] a p v f b=(2πrnCb)Vol c ;

[0085]

[0086] wherein, a p is the grinding depth, v fis the feed speed, b is the grinding width, r is the radius of the grinding head; n is the spindle speed; C is the effective grain density of the diamond grinding head; Vol c is the material removal volume of a single grain of the diamond grinding head; l is the length of the three-dimensional motion trajectory of the grain; θ is the half-apex angle of the grain, and is 60°.

[0087] S3, based on the ultrasonic vibration assisted grinding process parameters, the ceramic matrix composite ultrasonic vibration assisted grinding is carried out. The ceramic matrix composite ultrasonic vibration assisted grinding includes the following steps:

[0088] S3-1, the ceramic matrix composite workpiece is clamped on the numerical control machine tool;

[0089] S3-2, the diamond grinding head and the longitudinal torsional composite rotary ultrasonic tool holder are installed on the machine tool;

[0090] S3-3, based on the numerical control machine tool, the ultrasonic vibration assisted grinding process parameters are set;

[0091] S3-4, the numerical control machine tool is started, and the numerical control machine tool carries out the ceramic matrix composite ultrasonic vibration assisted grinding according to the tool path trajectory specified by the numerical control program based on the ultrasonic vibration assisted grinding process parameters.

[0092] Embodiment 5

[0093] The embodiment discloses a ceramic matrix composite ultrasonic vibration assisted grinding processing method, which is a preferred embodiment of the technical scheme, that is, in combination with embodiment 4, the acquisition mode of the related parameters is determined, in particular:

[0094] The effective grain density of the diamond grinding head is obtained by the following formula:

[0095]

[0096] Wherein, f is the effective grain fraction, and the value is 0.5; d g is the average size of the grain; V g is the volume fraction of the grain, and the value is 0.25.

[0097] The length of the three-dimensional motion trajectory of the grain is obtained by the following formula:

[0098]

[0099]

[0100] Wherein, t0 is the single contact time of the grain and the workpiece material; x' is the derivative of the X direction component of the grain trajectory; y' is the derivative of the Y direction component of the grain trajectory; z' is the derivative of the Z direction component of the grain trajectory.

[0101] Derivatives of the X-direction component of the abrasive particle trajectory, the Y-direction component of the abrasive particle trajectory, and the Z-direction component of the abrasive particle trajectory are obtained by the following formulas:

[0102]

[0103]

[0104]

[0105] where t is a time variable; θ r+t is the sum of the tool rotation angle and the angle change caused by the tool torsional ultrasonic vibration, i.e. f t is the tool torsional ultrasonic vibration frequency; A t is the tool torsional ultrasonic amplitude; A l is the tool longitudinal ultrasonic amplitude; f l is the tool longitudinal ultrasonic vibration frequency.

[0106] Example 6

[0107] This embodiment discloses an ultrasonic vibration assisted grinding machining method of ceramic matrix composite material, as a preferred embodiment of the technical solution, taking C f / SiC ceramic matrix composite material machining as an example for illustration, based on an embodiment as described in Example 5, the specific steps are as follows:

[0108] (1) A single abrasive particle basic scratch test is carried out to determine the micro-macro brittle fracture transition critical depth:

[0109] A single diamond abrasive particle is brazed on the circumferential surface of a (high-speed) steel disc, and the steel disc is installed on a numerical control machine tool. The spindle speed is set to 3000 r / min. The numerical control machine tool is started, and the diamond abrasive particle is used to perform a single abrasive particle scratch test on the ceramic matrix composite material plane sample under the driving of the steel disc numerical control machine tool. An electron microscope is used to observe the fiber micro-morphology of the circular arc scratch area, and the micro-macro brittle fracture transition critical depth is obtained as 5.1 μm.

[0110] (2) Determine the ultrasonic vibration assisted grinding machining condition:

[0111] A diamond grinding head with a diameter of Φ10 mm and a granularity of 120 mesh is selected. The diamond grinding head is installed on the numerical control machine tool by using a longitudinal-torsional composite rotary ultrasonic tool holder.

[0112] The longitudinal ultrasonic vibration frequency is set to 20.06 kHz, the torsional ultrasonic vibration frequency is set to 20.06 kHz, the longitudinal-torsional ratio is set to 14:5, the longitudinal ultrasonic amplitude is set to 11 μm, and the torsional ultrasonic amplitude is set to 3.9 μm.

[0113] According to the machine tool performance, the spindle speed during machining is set to 3000 rpm, the grinding depth is 0.3 mm, and the grinding width is 6 mm.

[0114] In addition, the conventional grinding process is set as a control group, and the grinding parameters of the control group are consistent with the above grinding parameters. No ultrasonic vibration is applied during the machining process.

[0115] (3) Calculate the feed speed:

[0116] Satisfy the machining process parameter determination criterion h max ≤h critical When, based on the formula a p v f b=(2πrnCb)Vol c The feed speed under the condition of ultrasonic vibration assisted grinding is calculated to be 192 mm / min, and the measured roughness Sa of the machined surface after machining is 1.73±0.21 μm. Without applying ultrasonic vibration, the conventional grinding process is used, the feed speed is 163 mm / min, and the measured roughness Sa of the machined surface after machining is 1.76±0.19 μm.

[0117] In summary, compared with conventional machining, the use of ultrasonic vibration assisted grinding machining can improve the machining efficiency by 17.8% under the working condition set in this embodiment while ensuring the quality of the machined surface.

Claims

1. A method for ultrasonic vibration-assisted grinding of ceramic matrix composite materials, characterized in that, Includes the following steps: S1. Single-grain abrasive-based scratch tests are conducted on planar samples of ceramic matrix composites to determine their critical depth for the micro-to-macro brittle fracture transition. The single-grain abrasive-based scratch test includes the following steps: S1-1, Prepare a steel disc with a single diamond abrasive grain welded to its circumference, and install the steel disc on a CNC machine tool; S1-2, Start the CNC machine tool, and make the steel disc rotate under the drive of the CNC machine tool. The diamond abrasive grains move in a circular motion with the rotation of the steel disc to scratch the ceramic matrix composite planar sample, forming an arc-shaped variable depth scratch on the ceramic matrix composite planar sample. S1-3, the fracture mode of fibers in arc-shaped variable depth scratches was observed by electron microscopy; among them: multiple brittle fractures inside a single fiber leading to material removal are micro brittle fractures, and a single fracture of a single fiber leading to material removal is a macro brittle fracture. The maximum scratch depth from micro brittle fracture to macro brittle fracture is the critical depth of the micro-macro brittle fracture transition. S2, based on the critical depth of the micro-to-macro brittle fracture transition and combined with the surface quality requirements of the part, obtain the ultrasonic vibration-assisted grinding process parameters, including determining the spindle speed, feed rate, grinding depth, grinding width, longitudinal ultrasonic frequency, longitudinal ultrasonic amplitude, torsional ultrasonic frequency, and torsional ultrasonic amplitude; wherein, the spindle speed is selected according to the machine tool characteristics, the grinding depth and grinding width are determined according to the part machining allowance, and the longitudinal ultrasonic frequency, longitudinal ultrasonic amplitude, torsional ultrasonic frequency, and torsional ultrasonic amplitude are determined according to the model of the longitudinal-torsional composite rotary ultrasonic tool holder; S3, ultrasonic vibration-assisted grinding of ceramic matrix composites based on ultrasonic vibration-assisted grinding process parameters, including the following steps: S3-1, clamping the ceramic matrix composite workpiece onto a CNC machine tool; S3-2, Select a diamond grinding head and a longitudinal torsion composite rotary ultrasonic tool holder to install on the machine tool; S3-3, setting ultrasonic vibration-assisted grinding process parameters based on CNC machine tools; S3-4, Start the CNC machine tool. The CNC machine tool performs ultrasonic vibration-assisted grinding of ceramic matrix composite materials based on the ultrasonic vibration-assisted grinding process parameters and according to the tool path trajectory specified in the CNC program.

2. The ultrasonic vibration-assisted grinding method for ceramic matrix composite materials as described in claim 1, characterized in that: In step S2, the surface quality requirements for the part include the surface roughness and surface damage after the part is processed; wherein, the surface roughness Sa is 2.0 μm, and the surface of the part after processing is free from fiber peeling and pits formed by fiber pull-out.

3. The ultrasonic vibration-assisted grinding method for ceramic matrix composites as described in claim 1, characterized in that: In step S2, obtaining the ultrasonic vibration-assisted grinding process parameters also includes establishing a process parameter determination criterion, and the feed rate is determined according to the process parameter determination criterion; the process parameter determination criterion is as follows: ;in, h max The maximum thickness of undeformed wear debris; h critical It is the critical depth for the transition from micro to macroscopic brittle fracture.

4. The ultrasonic vibration-assisted grinding method for ceramic matrix composite materials as described in claim 3, characterized in that: In step S2, under the conditions of determining the machining process parameters, the relationship between the relevant ultrasonic vibration-assisted grinding process parameters is as follows: ； ； in, a p For grinding depth, v f For feed rate, b For grinding width, r The radius of the grinding head; n Main spindle speed; C The effective abrasive density of a diamond grinding head; Vol c To remove material volume per abrasive grain of a diamond grinding head; l The length of the three-dimensional motion trajectory of the abrasive particles; θ The value is 60°, which is the half-apex angle of the abrasive grain.

5. The ultrasonic vibration-assisted grinding method for ceramic matrix composite materials as described in claim 4, characterized in that: The effective abrasive density of the diamond grinding head is obtained by the following formula: ；(3) in, f The effective abrasive fraction is set to 0.

5. d g This represents the average size of the abrasive grains. V g This represents the volume fraction of abrasive particles, with a value of 0.

25.

6. The ultrasonic vibration-assisted grinding method for ceramic matrix composite materials as described in claim 4, characterized in that: The length of the three-dimensional motion trajectory of the abrasive grains is obtained by the following formula: ； ； in, t 0 represents the single contact time between the abrasive grain and the workpiece material; x ' is the derivative of the X-direction component of the abrasive grain trajectory; y ' is the derivative of the Y-direction component of the abrasive grain trajectory; z ' is the derivative of the Z-direction component of the abrasive grain trajectory.

7. The ultrasonic vibration-assisted grinding method for ceramic matrix composite materials as described in claim 6, characterized in that: The derivatives of the X-axis component, Y-axis component, and Z-axis component of the abrasive grain trajectory are obtained using the following formulas: ； ； ； in, t It is a time variable; θ r+t This is the sum of the tool rotation angle and the angle change caused by the tool torsional ultrasonic vibration, i.e. ; f t The frequency of ultrasonic vibration during tool torsion; A t The amplitude of the ultrasonic torsion of the cutting tool; A l The longitudinal ultrasonic amplitude of the cutting tool; f l The longitudinal ultrasonic vibration frequency of the cutting tool.

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