Prediction method of critical depth in ultrasonic ELID composite grinding considering online electrolysis

Abstract

The present application relates to precision machining technical field, especially for the critical depth prediction method of ultrasonic ELID compound grinding considering on-line electrolysis, including the following steps: S1: according to the process that single abrasive grain of grinding wheel in ultrasonic ELID compound grinding is exposed to the increasing radius of falling off, change curve is established, and single abrasive grain radius change model in ultrasonic ELID compound grinding is established;S2: selecting diamond abrasive grain of any radius on the above curve carries out ultrasonic ELID variable depth scratch test, and the brittle plastic transition critical depth of material is obtained;S3: repeating S2, using different radius abrasive grain carries out test, and the change curve of brittle plastic transition critical depth with the radius of abrasive grain is established and formula is fitted;S4: the model in S1, S3 and relationship are integrated, and the critical depth prediction model is established.The present application finally obtains the critical depth prediction method of ultrasonic ELID compound grinding considering on-line electrolysis, can adjust the grinding depth in grinding in real time, realizes the ductile region grinding of maximum depth of cut.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of precision machining, and particularly relates to a method for predicting the critical depth of ultrasonic ELID compound grinding considering the online electrolysis effect. BACKGROUND

[0002] In recent years, with the development of manufacturing technology and material science, high hardness, high wear resistance and temperature resistance materials (such as titanium alloy, high-temperature alloy, metal / ceramic / polymer-based composite materials, etc.) have been widely used in aerospace and biomedical industries. At present, the machining of high-hardness and high-brittle materials mainly relies on diamond tool grinding, and the precision grinding and polishing of super-hard fine abrasive are used to realize ultra-precision machining. This processing method not only has low production efficiency, but also is easy to produce subsurface damage, which makes the processing cost higher.

[0003] Non-traditional energy (vibration, laser, electricity, etc.) is used to improve the machinability of local materials and reduce the burden of mechanical processing. This provides a feasible and promising method to improve material removal rate and surface quality, reduce processing force and prolong tool life. Ultrasonic vibration assisted grinding technology combines ultrasonic machining technology and traditional grinding technology, and has the advantages of high processing efficiency, good processing surface quality and effective reduction of grinding heat. ELID mirror grinding technology is a new type of grinding technology, and the ELID grinding wheel has good sharpening effect, which can significantly reduce the grinding force and the roughness of the ground surface. Ultrasonic ELID compound grinding technology combines ultrasonic vibration assisted grinding and online electrolytic dressing technology, further reduces the grinding force and the roughness of the ground surface, and is suitable for ultra-precision machining of hard and brittle materials.

[0004] The brittle-plastic transition critical depth refers to the critical grinding depth of hard and brittle materials in grinding process from plastic deformation state to brittle fracture state. When the grinding depth is less than the critical value, the material removal is realized by plastic deformation, and when the grinding depth is greater than the critical value, the material removal process appears brittle failure. It is an important reference index for hard and brittle materials to realize plastic domain cutting. The variable depth scratching test is a common means to obtain the brittle-plastic transition critical depth, but the diamond variable depth scratching test directly on the material is easy to have problems such as serious tool wear and easy surface crack propagation.

[0005] In order to solve the above problems, the present application proposes a method for predicting the critical depth of ultrasonic ELID compound grinding considering the online electrolysis effect. Ultrasonic ELID compound grinding has the effects of sharpening abrasive particles and changing the material removal mode, which can solve the problems of serious tool wear and easy surface crack propagation, and can better reflect the continuous transition process of material brittle-plastic transition. SUMMARY

[0006] The purpose of the present application is to propose an ultrasonic ELID compound grinding critical depth prediction method considering online electrolysis to solve the problems proposed in the background art:

[0007] The existing variable depth scratching test directly uses diamond variable depth scratching test on the material, which is prone to problems such as serious tool wear and easy expansion of surface cracks.

[0008] In order to achieve the above purpose, the present application adopts the following technical solutions:

[0009] The ultrasonic ELID compound grinding critical depth prediction method considering online electrolysis is realized based on an ultrasonic ELID compound cutting depth scratching test device, the device includes an ultrasonic auxiliary machining tool and a workbench for fixing a workpiece, the ultrasonic auxiliary machining tool is fixedly installed below the main shaft of the grinding machine, and is used for adding ultrasonic vibration in the scratch test; the workbench is arranged below the ultrasonic auxiliary machining tool and is used for fixing the workpiece.

[0010] The ultrasonic auxiliary machining tool includes an ultrasonic tool holder, an ultrasonic generator, a transducer and an amplitude transformer; the ultrasonic tool holder is fixed below the main shaft of the grinding machine, the transducer is fixed below the ultrasonic tool holder, the transducer is connected with the ultrasonic generator through a connecting line, the amplitude transformer is fixed below the transducer, and a diamond abrasive grain connected with an ELID power supply through a lead wire is further fixed below the amplitude transformer through a thread; the diamond abrasive grain acts on the workpiece to perform ultrasonic ELID variable depth scratching test.

[0011] The workbench includes a vacuum chuck and a platform, and the workpiece is fixed on the platform through the vacuum chuck.

[0012] The method includes the following steps:

[0013] S1: According to the process that the radius of the single abrasive grain of the grinding wheel in ultrasonic ELID compound grinding is constantly increased from exposure to falling, a change curve is established, and a single abrasive grain radius change model in ultrasonic ELID compound grinding is established;

[0014] S2: The diamond abrasive grain with any radius on the curve obtained in S1 is selected to perform ultrasonic ELID variable depth scratching test, the characteristics when the material is removed in brittleness are analyzed, and the critical depth of brittle-plastic transition of the material is obtained;

[0015] S3: S2 is repeated, ultrasonic ELID variable depth scratching test is performed using abrasive grains with different radii, and corresponding critical depths are obtained, a change curve of the critical depth of brittle-plastic transition with the radius of the abrasive grain is established, and a formula is fitted;

[0016] S4: The models and the relationship in S1 and S3 are integrated to establish a critical depth prediction model.

[0017] Preferably, in the S1, the ELID power supply and ultrasonic generator are started, and in the process of using the conductive grinding wheel to grind the workpiece, the metal bond in the conductive grinding wheel is electrolyzed, while the single abrasive grains in the grinding wheel are not affected by electrolysis and are exposed, and as the clamping force of the grinding wheel on the abrasive grains decreases, the passivated abrasive grains fall off under the action of the grinding force.

[0018] Preferably, in the S1, the radius of the abrasive grain continuously increases from the exposure to the falling of the diamond abrasive grain, and the change model of the abrasive grain radius in the process of ultrasonic ELID grinding is as follows:

[0019]

[0020] wherein dR e represents the change of the radius of the abrasive grain; dt represents the change of time; v represents the relative sliding speed of the abrasive grain and the chip; t represents the scratching time; a and b represent the constants of the reaction abrasive wear; p represents the normal pressure of the contact between the abrasive grain and the workpiece surface; c represents the comprehensive coefficient; a represents the factor related to ultrasonic vibration; I represents the electrolysis current; and T represents the scratching temperature.

[0021] Preferably, in the S2, the ultrasonic ELID compound cutting and scratching test device is assembled, the diamond abrasive grains with any radius on the curve obtained in the S1 are selected, the main shaft of the grinding machine is controlled to feed along a straight line, and the cutting depth increases linearly with the increase of the scratch length during the scratching process, so that continuous variable-depth scratches are obtained on the workpiece surface, the workpiece is removed after the test is completed; the three-dimensional morphology and the scratch depth of the single abrasive grain scratch of the workpiece are observed by the ultra-depth three-dimensional microscope, the characteristics of the brittle removal of the material are analyzed, cracks and small peeling pits begin to appear on the groove walls on both sides of the groove, while other parts of the groove wall remain smooth, the micro-morphology graph under the different material removal mechanisms of the scratches is compared, and the critical depth of the brittle-plastic transition of the material is obtained.

[0022] Preferably, in the S3, the abrasive grains with five different radii in the S1 curve are extracted and used to perform the ultrasonic ELID variable-cutting-depth scratching test in sequence, so that the critical depths of the brittle-plastic transition of the material corresponding to the abrasive grains with different radii are obtained; the curve of the critical depth of the brittle-plastic transition with the change of the radius of the abrasive grain is obtained, and the formula is as follows:

[0023]

[0024] wherein a c represents the critical cutting thickness; β represents a dimensionless constant; A represents a factor related to the on-line electrolysis action; E represents the elastic modulus; k ic represents the static fracture toughness; K d represents the dynamic change coefficient considering the ultrasonic; and H represents the Vickers hardness.

[0025] Preferably, in S4, the relationship between the abrasive radius and time in S1 and the relationship between the critical depth and the abrasive radius in S3 are integrated to establish a critical depth prediction model as follows:

[0026]

[0027] The above model is used to adjust the grinding depth in real time to achieve ductile region grinding with maximum cutting depth.

[0028] Compared with the prior art, the present invention provides a method for predicting the critical depth of ultrasonic ELID composite grinding taking into account online electrolysis, which has the following beneficial effects:

[0029] This paper designs an ultrasonic ELID variable cutting depth scratching test protocol, leveraging the effects of ultrasonic ELID to better reflect the continuous transition process between the brittle and ductile transitions. By changing the abrasive grains and the radius of the diamond abrasive particles, the radius variation of a single abrasive particle under ultrasonic ELID composite grinding conditions is simulated, enhancing the applicability of the present method. The brittle-ductile transition critical depth prediction model obtained through this invention provides greater guidance for achieving maximum efficiency in the ductile region grinding of brittle and hard materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of the method mentioned in Example 1 of the present invention;

[0031] Figure 2 This is a graph showing the change in radius of the abrasive grains mentioned in Example 1 of the present invention;

[0032] Figure 3 This is a model diagram of the change in particle size of diamond abrasive grains mentioned in Example 1 of the present invention;

[0033] Figure 4 This is a diagram of the ultrasonic ELID composite variable cutting depth scratching test device mentioned in Example 1 of the present invention;

[0034] Figure 5 This is a simplified diagram of the diamond abrasive grains mentioned in Example 1 of the present invention;

[0035] Figure 6 This is a schematic diagram of the diamond abrasive scratching process mentioned in Example 1 of the present invention;

[0036] Figure 7 This is a graph showing the change in scratch morphology of the SiC ceramic mentioned in Example 1 of the present invention with respect to scratch depth;

[0037] Figure 8 This is a graph showing the variation of the critical depth of the brittle-ductile transition with the abrasive particle radius mentioned in Example 1 of the present invention;

[0038] Figure 9This is the effect diagram of the ultrasonic ELID composite ductile domain grinding of SiC ceramic mirror mentioned in Example 1 of the present invention.

[0039] The meaning of the marks in the figure:

[0040] 1. Grinding machine spindle; 2. Ultrasonic generator; 3. Transducer; 4. Diamond abrasive; 5. Workpiece; 6. Vacuum suction cup; 7. Platform; 8. ELID power supply; 9. Amplitude transformer; 10. Ultrasonic tool holder. DETAILED DESCRIPTION

[0041] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0042] This invention designs an ultrasonic ELID variable cutting depth scratching test protocol, leveraging the effects of ultrasonic ELID to better reflect the continuous transition process between the brittle and ductile transitions. By changing the abrasive grains and varying the radius of the diamond abrasive particles, the radius variation of a single abrasive particle under ultrasonic ELID composite grinding conditions is simulated, enhancing the applicability of the invented method. The resulting prediction model for the critical depth of the brittle-ductile transition provides enhanced guidance for achieving maximum efficiency in the ductile region grinding of brittle and hard materials. Specifically, this includes the following:

[0043] Example 1:

[0044] See also Figure 1-9 The ultrasonic ELID composite grinding critical depth prediction method considering the online electrolysis effect of the present invention is used to further compare and illustrate the implementation process and beneficial effects of the present invention in combination with the following examples. In this example, the material tested is SiC ceramic with a size of 12mm×10mm×5mm.

[0045] Reference Figure 4 First, an ultrasonic ELID composite deep cutting and scratching test device for the test is built. The device includes an ultrasonic assisted processing tool and a workbench for fixing the workpiece 5. The ultrasonic assisted processing tool is fixedly installed under the grinder spindle 1, and is used to add ultrasonic vibration in the scratch test to provide physical conditions for ultrasonic ELID grinding of the workpiece 5; the workbench is set under the ultrasonic assisted processing tool for fixing the workpiece 5; the ultrasonic assisted processing tool includes an ultrasonic tool holder 10, an ultrasonic generator 2, a transducer 3 and an amplitude transformer 9 from top to bottom; the ultrasonic tool holder 10 is fixed under the grinder spindle 1, and a transducer 3 is fixed under the ultrasonic tool holder 10, and the transducer 3 is connected to the ultrasonic generator 2 through a connecting line. A amplitude transformer 9 is fixed under the transducer 3, and diamond abrasive grains 4 connected to the ELID power supply 8 through a wire are also fixed under the amplitude transformer 9 by threads. The bottom end of the diamond abrasive grains 4 can be specifically referred to. Figure 5The diamond abrasive 4 acts on the workpiece 5 to perform the ultrasonic ELID variable cutting depth scratch test. The specific test effect of the diamond abrasive 4 on the workpiece 5 can be referred to Figure 6 The workbench includes a vacuum suction cup 6 and a platform 7 from top to bottom, and the workpiece 5 is fixed on the platform 7 by the vacuum suction cup 6.

[0046] The specific test method includes the following steps:

[0047] S1: Based on the process of increasing radius of a single abrasive grain from exposure to shedding during ultrasonic ELID composite grinding, a change curve is established, and a radius change model of a single abrasive grain during ultrasonic ELID composite grinding is established; the details are as follows:

[0048] During ultrasonic ELID grinding, the metal binder in the conductive grinding wheel is electrolyzed, and the abrasive grains are exposed without being affected by the electrolysis. The abrasive holding force decreases, and the passivated abrasive grains fall off under the action of the grinding force. When grinding SiC ceramics under ultrasonic ELID composite conditions, a certain abrasive grain on the grinding wheel is marked and its particle size change is observed every one minute to obtain the following Figure 2 The curve of the abrasive particle radius changing with time shows that the abrasive particle radius increases continuously from the exposure to the shedding of the diamond abrasive particle 4. Figure 3 As shown in Figure 4, the radius variation model of diamond abrasive grains during ultrasonic ELID grinding of SiC ceramics was obtained.

[0049]

[0050] Among them, dR e represents the change of abrasive radius; dt represents the change of time; v represents the relative sliding velocity between abrasive and chip; t represents the scratching time; a and b represent constants reflecting abrasive wear; p represents the positive pressure between the abrasive and the surface of the workpiece 5; c represents the comprehensive coefficient; α represents the factor related to ultrasonic vibration; I represents the electrolysis current; and T represents the scratching temperature.

[0051] S2: Select diamond abrasive grains 4 of arbitrary radius on the curve obtained in S1 to conduct ultrasonic ELID variable cutting depth scratch test, analyze the characteristics of material brittle removal, and obtain the critical depth of brittle-ductile transition of the material; the details are as follows:

[0052] Finish Figure 4The ultrasonic ELID composite deep cutting test device shown is assembled, using an ultrasonic assisted processing tool, including an ultrasonic tool holder 10, an amplitude variable rod 9, a transducer 3, and an ultrasonic generator 2. The transducer 3 is connected to the ultrasonic generator 2 via a connecting line, and the ultrasonic assisted processing tool is fixed on the grinder spindle 1, and is used to add ultrasonic vibrations to the scratch test. The ultrasonic assisted processing tool includes an ultrasonic tool holder 10, an ultrasonic generator 2, a transducer 3 and an amplitude variable rod 9; the ultrasonic tool holder 10 is fixed under the grinder spindle 1, the transducer 3 is fixed under the ultrasonic tool holder 10, and the amplitude variable rod 9 is fixed under the transducer 3, wherein the transducer 3 converts the energy form to meet the device requirements, and the amplitude variable rod 9 adjusts the vibration amplitude of the diamond abrasive 4 by the different lengths of the rods, thereby controlling the effect of ultrasonic processing. The transducer 3 is connected to the ultrasonic generator 2 via a connecting line, and the diamond abrasive 4 is fixed to the bottom of the ultrasonic assisted processing tool with a thread. The diamond abrasive 4 is also connected to the ELID power supply 8 through a wire to achieve online electrolysis. Figure 2 Select the following Figure 5 The conical diamond abrasive grains 4 shown have a tip angle of 100° and an arc radius of 5.3 μm. During the test, the ultrasonic amplitude A = 1 μm, the grinding machine spindle 1 feeds in a straight line, and the SiC ceramic workpiece 5 remains stationary on the worktable. The feed rate is 100 mm / min.

[0053] The SiC ceramic workpiece 5 is fixed on the platform 7 by the vacuum chuck 6. The diamond abrasive 4 is controlled to approach the SiC ceramic workpiece 5 and start to scratch continuously in the x direction. During the scratching process, the cutting depth increases linearly from 0 to the maximum cutting depth as the scratch length increases. Continuous scratches of varying depths are obtained on the surface of the SiC ceramic workpiece 5. The scratching process is as follows: Figure 6 After the test is completed, the SiC ceramic workpiece 5 is removed;

[0054] The three-dimensional morphology and scratch depth of a single abrasive grain scratch on SiC ceramic workpiece 5 were observed by ultra-depth three-dimensional microscope. Figure 7 , compared with the micromorphology images under different material removal mechanisms, it is found that the critical ductility grinding depth of SiC ceramic workpiece 5 under ultrasonic ELID composite grinding is about 3.73μm.

[0055] S3: Repeat S2, use different radius abrasives to conduct ultrasonic ELID variable cutting depth test and obtain the corresponding critical depth, establish the curve of the critical depth of brittle-ductile transition with the abrasive radius and fit the formula; the details are as follows:

[0056] exist Figure 2 In the curve, abrasive particles with radii of 5.4μm, 5.6μm, 5.7μm and 5.9μm were selected to carry out ultrasonic ELID variable cutting depth test on SiC ceramic workpiece 5, and the critical depth of brittle-ductile transition of SiC ceramic workpiece 5 corresponding to abrasive particles with different radii was obtained. Figure 8 The curve of the critical depth of brittle-ductile transition of SiC ceramic workpiece 5 changing with the abrasive radius and the fitting formula are shown.

[0057]

[0058] Among them, a c represents the critical cutting thickness; β represents a dimensionless constant; A represents a factor related to online electrolysis; E represents the elastic modulus; k ic Represents static fracture toughness; K d represents the dynamic change coefficient considering ultrasound; H represents the Vickers hardness.

[0059] In detail, the SiC ceramic of this embodiment has a Vickers hardness of H=22.2 GPa and a fracture toughness k ic =3.2MPa / m 2 , elastic modulus E = 370GPa.

[0060] S4: Integrate the models and relationships in S1 and S3 to establish a critical depth prediction model. The details are as follows:

[0061] The models in S1 and S3 are reorganized to obtain the relationship between the critical depth of brittle-ductile transition of materials and time under ultrasonic ELID composite grinding considering online electrolysis:

[0062]

[0063] Using the above model to adjust the grinding depth in real time and achieve ductile region grinding with maximum cutting depth, the following can be obtained: Figure 9 The shown figure shows the effect of ultrasonic ELID composite ductile domain grinding of SiC ceramic mirror.

[0064] The above description is only a preferred specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field, within the technical scope disclosed by the present invention, who makes equivalent replacements or changes based on the technical solution and inventive concept of the present invention, should be covered by the scope of protection of the present invention.

Claims

1. A method for predicting the critical depth of ultrasonic ELID composite grinding considering online electrolysis, characterized in that: The method is implemented based on an ultrasonic ELID composite variable cutting depth scratching test device, the device comprising an ultrasonic assisted processing tool and a workbench for fixing a workpiece (5), the ultrasonic assisted processing tool being fixedly mounted below a grinding machine spindle (1) and being used to add ultrasonic vibration to a scratching test; the workbench being arranged below the ultrasonic assisted processing tool and being used to fix the workpiece (5); The ultrasonic assisted machining tool comprises an ultrasonic tool holder (10), an ultrasonic generator (2), a transducer (3) and an amplitude variable rod (9); the ultrasonic tool holder (10) is fixed below the grinding machine spindle (1); the transducer (3) is fixed below the ultrasonic tool holder (10); the transducer (3) is connected to the ultrasonic generator (2) via a connecting line; the amplitude variable rod (9) is fixed below the transducer (3); diamond abrasive grains (4) connected to an ELID power supply (8) via a wire are also fixed below the amplitude variable rod (9) via a thread; the diamond abrasive grains (4) act on a workpiece (5) to perform an ultrasonic ELID variable cutting depth scratching test; The workbench comprises a vacuum suction cup (6) and a platform (7), and the workpiece (5) is fixed on the platform (7) via the vacuum suction cup (6); The method comprises the following steps: S1: Based on the process of increasing radius of a single diamond abrasive grain from exposure to shedding in ultrasonic ELID composite grinding, a change curve is established, and a radius change model of a single diamond abrasive grain in ultrasonic ELID composite grinding is established. The formula is as follows: ， in, dR e Indicates the change of abrasive particle radius; dt Indicates time changes; v Indicates the relative sliding speed between abrasive particles and chips; t Indicates the marking of time; a , b A constant representing the reaction abrasive wear; p It represents the normal pressure of the abrasive grain in contact with the workpiece (5) surface; c represents the comprehensive coefficient; α Indicates factors related to ultrasonic vibration; I represents the electrolysis current; T Indicates the scratch temperature; S2: Select diamond abrasive grains (4) of arbitrary radius on the curve obtained in S1 to conduct ultrasonic ELID variable cutting depth scratching test, analyze the characteristics of material brittle removal, and obtain the critical depth of brittle-ductile transition of the material; S3: Repeat S2, use different radius abrasives to perform ultrasonic ELID variable cutting depth scratching test and obtain the corresponding critical depth, establish the curve of the critical depth of brittle-ductile transition with the abrasive radius and fit the formula; S4: Integrate the model in S1 and the formula in S3 to establish a critical depth prediction model.

2. The method for predicting the critical depth of ultrasonic ELID composite grinding considering online electrolysis according to claim 1 is characterized in that: In the step S1, the ELID power supply (8) and the ultrasonic generator (2) are started. During the ultrasonic ELID grinding of the workpiece (5) using the conductive grinding wheel, the metal adhesive in the conductive grinding wheel is electrolyzed, while the single abrasive grains in the grinding wheel are not affected by the electrolysis and are exposed. As the clamping force of the grinding wheel on the abrasive grains decreases, the passivated abrasive grains fall off under the action of the grinding force.

3. The method for predicting the critical depth of ultrasonic ELID composite grinding considering online electrolysis according to claim 1, characterized in that: In the S2, the ultrasonic ELID composite variable cutting depth scratching test device is assembled, and diamond abrasive grains (4) of arbitrary radius on the curve obtained in S1 are selected. The grinding machine spindle (1) is controlled to feed along a straight line, and the cutting depth increases linearly with the increase of the scratch length during the scratching process. Continuous variable depth scratches are obtained on the surface of the workpiece (5). After the test is completed, the workpiece (5) is removed; the three-dimensional morphology and scratch depth of the single abrasive grain scratch on the workpiece (5) are observed by an ultra-depth three-dimensional microscope, and the characteristics of the material when brittleness is removed are analyzed to obtain the critical depth of the brittle-ductile transition of the material.

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