Ultrasonic vibration assisted intermittent electrospark machining method

Abstract

The present invention relates to an ultrasonic vibration-assisted intermittent electrospark machining method, and belongs to the field of electromachining. The present invention proposes a machining method that couples the composite motion of a tool electrode with the application of a pulse power supply, and utilizes the composite motion of the low-frequency vibration of the tool electrode and the ultrasonic vibration, and applies a pulse power supply during the ultrasonic vibration stage to timely discharge the processed products in the machining area to avoid product accumulation; no pulse power supply is applied during the non-ultrasonic vibration stage, and at the same time, the low-frequency vibration of the tool electrode is utilized to force the working fluid in the machining area to circulate, which is beneficial to ensure the stable progress of the spark discharge. In addition, the present invention also makes full use of the reinforcing phase particles that fall off the surface of the workpiece during the machining process, and utilizes the strong hydraulic shock caused by the composite low-frequency vibration of the tool electrode and the ultrasonic vibration to drive the reinforcing phase particles to achieve micro-polishing of the workpiece surface, which is beneficial to improving the surface quality.

Description

Technical Field

[0001] The invention relates to a pulsed ultrasonic vibration assisted electric spark machining method, belonging to the field of ultrasonic electric spark composite machining. Background Art

[0002] Particle-reinforced metal matrix composites are a general term for composite materials with carbide, nitride, graphite and other particle reinforcement phases and metal or alloy as the matrix. Particle-reinforced metal matrix composites have low thermal expansion coefficient, high thermal conductivity, high specific stiffness, low density, good dimensional stability, and excellent mechanical and physical properties such as wear resistance and fatigue resistance. They have broad application prospects in the aerospace field. China's Mars rover "Zhurong" has dozens of parts such as the body load-bearing structure, mechanical movement mechanism, and probe structure using a variety of SiC with different silicon carbide contents. p / Al; SiC is also used in the key components of Chang'e 5 lunar sampling mechanism p / Al. The mechanical properties of particle-reinforced metal matrix composites are mainly related to the volume fraction of the reinforcement phase particles. It is generally believed that the higher the particle content, the better the wear resistance, dimensional stability and other properties of the material; however, the medium and high volume fraction of the particle reinforcement phase causes severe wear of the mechanical cutting tool, poor surface processing quality, low processing efficiency or even impossible processing, which limits the promotion and application of particle-reinforced metal matrix composites in the aerospace field.

[0003] The electrospark machining technology is based on the electro-corrosion phenomenon generated by spark discharge between the tool electrode and the workpiece to remove the workpiece material. It has the characteristics of high machining efficiency and no macro-cutting force during machining. Spark discharge will only occur between the tool electrode and the workpiece when the inter-electrode gap is reduced to tens of microns. Therefore, a large amount of machining products are easily accumulated in the machining area. At the same time, since metal matrix composites contain a large number of non-conductive reinforcing phase particles, it is difficult to erode them by gasification or melting during machining. They are very easy to accumulate in the machining gap, affecting the dielectric properties of the working fluid, affecting the efficiency and surface quality of electrospark machining. Researchers use chamfered or slotted electrodes to improve the product transport conditions in the machining area and process particle-reinforced metal matrix composites, but the actual effect is not ideal.

[0004] During ultrasonic machining, the end face of the tool vibrates at ultrasonic frequencies, and the free abrasive in the liquid between the tool and the workpiece is used to mechanically impact and polish the machined surface to remove the workpiece material. It has the advantages of low macro-cutting force and good surface quality, and is usually used for machining hard and brittle materials. Compared with hard and brittle materials, the metal matrix in particle-reinforced metal-based composites is prone to plastic deformation. Therefore, the abrasive is very easy to embed into the metal matrix during machining, which weakens the mechanical impact and polishing of the abrasive. It is difficult to obtain good machining results when machining particle-reinforced metal-based materials. At the same time, because the reinforcing phase particles are completely or partially wrapped by the metal matrix, the abrasive can only process the exposed part of the reinforcing phase particles under the action of ultrasound, and it is difficult to obtain high machining efficiency.

[0005] Therefore, in order to meet the rapidly growing manufacturing needs of particle-reinforced metal matrix materials in the aerospace field, innovative processing methods that take into account both processing efficiency and surface quality are urgently needed. Summary of the invention

[0006] The present invention provides an ultrasonic vibration assisted discontinuous electric spark machining method to solve the problems existing in the prior art and can effectively improve the machining efficiency and surface quality of particle-reinforced metal-based composite materials.

[0007] An ultrasonic vibration-assisted intermittent electrospark machining method, characterized in that it includes the following steps: Step 1: The workpiece is connected to the positive electrode of a pulse power supply, and the tool electrode is connected to the negative electrode of the pulse power supply. At the same time, the tool electrode (9) rotates at a high speed around its axis according to a preset speed, and the working fluid is ejected from the inner hole of the tool electrode and enters the machining area. When the pulse power supply is turned on, the tool electrode is fed along the tool electrode feeding direction toward the workpiece. The tool electrode moves along its axis with a period of T2 and an amplitude of I. mThe composite motion is a coupling motion of ultrasonic vibration and low-frequency vibration with a period of T1 along the feed direction, and the period of the composite motion is T1; a composite motion period T1 includes three stages, namely, the low-frequency vibration feeding stage (AB segment), the coupled motion discharge stage (BD segment), and the low-frequency vibration retreat stage (DE segment); Step 2: In the low-frequency vibration feeding stage (AB segment), the tool electrode is gradually fed from the maximum side gap H2 (point A) to the maximum speed (point B), the pulse power supply remains in the off state, the tool electrode is fed at a constant speed along the feed direction, and the tool electrode is vibrated and fed along the low-frequency vibration direction, the side machining gap gradually decreases from the maximum gap H2, and at the same time a large amount of fresh working fluid is brought into the machining area, so that the working fluid in the machining area is restored to the dielectric state, and the shedding increase The strong phase particles enter the working fluid and act as abrasives; Step three: In the coupled motion discharge stage (BD segment), the tool electrode continues to feed at a low frequency from the maximum speed (point B) toward the workpiece to the minimum side gap (point C), and then retreats at a low frequency away from the workpiece to the maximum speed (point D). At the same time, the tool electrode begins to perform ultrasonic vibration movement along the axial direction. The side gap between the tool electrode and the workpiece gradually decreases and then increases. The pulse power supply is turned on, and multiple spark discharges occur in the processing area. At the same time, the tool electrode begins to perform ultrasonic vibration along the axial direction, and a large number of micro cavities are formed in the working fluid. Under the action of ultrasound, a large number of spark discharge products are taken away from the processing area, and the free strengthening phase particles produce mechanical impact and polishing effects on the workpiece, thereby improving the surface quality of EDM. Step 4: In the low-frequency vibration retreat stage (DE segment), the tool electrode retreats from the maximum speed point (D point) along the low-frequency vibration direction, and the side machining gap gradually increases to H2. The tool electrode has a great acceleration when vibrating and retreating, and a large amount of spark discharge products in the machining area are taken away from the machining area. Fresh working fluid flows back into the machining area, so that the working fluid in the machining area is restored to the dielectric state; Step 5: The machining area continuously repeats the above three stages from step 2 to step 4. Under the intermittent machining action of the tool electrode low-frequency vibration and ultrasonic vibration composite motion and the pulse power supply, high-quality machining of the workpiece is achieved; wherein the period T1 of the tool electrode low-frequency vibration and ultrasonic vibration coupling motion is equal to the low-frequency vibration feeding stage time t a , coupled motion discharge stage t b The low-frequency vibration retreat phase time t c sum.

[0008] During the machining process, the tool electrode vibrates rapidly along its axis with a large acceleration, so that the working fluid in the machining area produces a very strong hydraulic shock, compresses the plasma discharge channel in the machining area, avoids the ineffective expansion of the plasma channel, reduces energy consumption, and uses more energy to remove materials, which is beneficial to improving machining efficiency; at the same time, since the workpiece contains a large number of reinforcing phase particles, the present invention utilizes the reinforcing phase particles that fall off and are free from the working fluid during the machining process. Under the action of the ultrasonic vibration of the tool electrode, the detached reinforcing phase particles act as abrasives, produce mechanical impact and polishing effects on the surface of the workpiece, which is beneficial to improving the surface quality of electrospark machining.

[0009] The ultrasonic vibration-assisted intermittent electrospark machining method is characterized in that the amplitude of the low-frequency vibration of the tool electrode is several 100 microns to 4 mm, the amplitude of the ultrasonic vibration of the tool electrode is 1-20 microns, and the period T2 of the ultrasonic vibration is several 5-100 microseconds.

[0010] The low-frequency vibration amplitude of the tool is much greater than the ultrasonic vibration amplitude, which can completely renew the working fluid in the processing area, discharge a large amount of products generated in the processing area, and improve processing stability. The ultrasonic vibration amplitude of the tool electrode is small and the vibration frequency is extremely high, which can quickly renew the working fluid in a small area and promote the transportation of processed products in the micro area.

[0011] The ultrasonic vibration assisted intermittent EDM method is characterized in that: the low frequency vibration feeding time t a , low frequency vibration retreat time t c and ultrasonic vibration time t b Both can be adjusted to increase the ultrasonic vibration time t b To increase energy input and obtain higher processing efficiency; increase the low-frequency vibration feed time t a , low frequency vibration retreat time t c This is beneficial to accelerate the transportation of processed products in the processing area and obtain better surface quality. By adjusting the time of the above three stages, different processing effects can be obtained by using one type of tool electrode, reducing the electrode design time.

[0012] The ultrasonic vibration-assisted intermittent electrospark machining method is characterized in that the tool electrode material is copper-tungsten alloy, graphite, copper, and copper.

[0013] The ultrasonic vibration-assisted intermittent electrospark machining method is characterized in that the workpiece is a particle-reinforced metal matrix composite material with a medium to high volume fraction. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A schematic diagram of the low-frequency vibration feeding stage of the tool electrode in an ultrasonic vibration-assisted intermittent electrospark machining method proposed by the present invention;

[0015] Figure 2 A schematic diagram of the ultrasonic vibration stage of the tool electrode in an ultrasonic vibration-assisted intermittent electrospark machining method proposed by the present invention;

[0016] Figure 3 A schematic diagram of the low-frequency vibration retreat stage of the tool electrode in an ultrasonic vibration-assisted intermittent electrospark machining method proposed by the present invention;

[0017] Figure 4 A schematic diagram of the coupling application mode of the tool electrode composite motion and the pulse power supply in an ultrasonic vibration-assisted intermittent electrospark machining method proposed by the present invention;

[0018] The numbers in the figure are: 1. low-frequency vibration direction; 2. working fluid; 3. spark discharge product; 4. pulse power supply; 5. microcavity; 6. workpiece; 7. spark discharge; 8. reinforcing phase particles; 9. tool electrode; 10. tool electrode feeding direction. DETAILED DESCRIPTION

[0019] The present invention will be further described in detail below in conjunction with the specific drawings.

[0020] Figure 1 This is a schematic diagram of the low-frequency vibration feeding stage of the tool electrode in the ultrasonic vibration-assisted intermittent EDM method. The pulse power supply 4 remains in an off state, the workpiece 6 is fed at a constant speed along the feeding direction 10, and the tool electrode 9 is fed at a low frequency vibration along the low frequency vibration direction 1. The low frequency vibration feeding time in a tool electrode 9 composite motion cycle T2 is t a , and the side machining gap gradually decreases from the maximum gap H2, while the bottom machining gap H0 remains unchanged. Since the tool electrode 9 has a large acceleration in the process of moving toward the workpiece, a large amount of fresh working fluid 2 is brought into the machining area at high speed, so that the working fluid 2 in the machining area is restored to a dielectric state, and under the high-speed flushing of the working fluid 2, the detached reinforcing phase particles 8 enter the working fluid 2 and act as abrasives;

[0021] Figure 2 The tool electrode 9 continues to vibrate at a low frequency along the low frequency vibration direction 1, and the side machining gap gradually decreases to the minimum gap H1, and then gradually increases, and the tool electrode 9 begins to vibrate ultrasonically along the axial direction, with a period of ultrasonic vibration of T2 and an amplitude of ultrasonic vibration of I. m The bottom machining gap varies between H3 and H4. The ultrasonic vibration stage time of the tool electrode 9 in a tool electrode 9 composite motion cycle T1 is t b At the same time, the pulse power supply 4 is turned on, and the pulse power supply emits multiple pulses with a width of T during the ultrasonic vibration stage. on , the pulse interval is Toff The pulse voltage is 1000V. During this process, multiple spark discharges 7 occur in the machining area. Under the action of ultrasound, a large number of micro-cavities 5 are formed in the working fluid 2. The micro-cavities 5 are continuously closed, causing a strong hydraulic shock, which takes a large number of spark discharge products 3 away from the machining area. The free reinforcing phase particles 8 have a mechanical impact and polishing effect on the workpiece 6, thereby improving the surface quality of the EDM.

[0022] Figure 3 This is a schematic diagram of the low-frequency vibration retreat stage of the tool electrode in the ultrasonic vibration-assisted intermittent EDM method. The tool electrode 9 stops ultrasonic vibration, and the tool electrode 9 starts to retreat in the low-frequency vibration direction 1. The side machining gap gradually increases to H2. In a tool electrode 9 composite motion cycle T2, the low-frequency vibration retreat time of the tool electrode 9 is t c , since the tool electrode 9 has a large acceleration when retreating with low-frequency vibration, a large amount of spark discharge products 3 in the processing area are taken away from the processing area, and fresh working fluid 2 flows back into the processing area, so that the working fluid 2 in the processing area is restored to a dielectric state;

[0023] Figure 4 The schematic diagram of the ultrasonic vibration-assisted intermittent EDM method is a schematic diagram of the combined motion of the tool electrode and the pulse power supply coupling application method. The period T1 of the combined motion of the tool electrode 9 low-frequency vibration and ultrasonic vibration is equal to the low-frequency vibration feeding time t a , low frequency vibration retreat period t c The ultrasonic vibration stage time t b The sum of the ultrasonic vibration stage time t b The inner tool electrode 9 generates multiple vibrations with an amplitude of I m , ultrasonic vibration with a period of T2, and at the same time in this stage the pulse power supply 4 sends out multiple pulses with a width of T on , the pulse interval is T off pulse voltage; in the low-frequency vibration feeding stage, the side machining gap gradually decreases from H2, and the bottom machining gap H0 remains unchanged; in the low-frequency vibration retreat stage, the side machining gap gradually increases to H2, and the bottom machining gap H0 remains unchanged; by increasing the ultrasonic vibration stage time t within a tool electrode 9 composite motion cycle T1 b It is beneficial to obtain higher processing efficiency and increase the low-frequency vibration feeding time t a , low frequency vibration retreat period t c It is conducive to obtaining better surface quality.

[0024] The present invention proposes an ultrasonic vibration-assisted intermittent EDM method, which proposes a method of promoting the transport of processed products by ultrasonic vibration, and combines the characteristics of particle-reinforced metal matrix composites to expand the application scope of EDM technology, greatly improving the processing efficiency and surface quality of particle-reinforced metal matrix composites. However, the above description cannot be understood as a limitation on the patent of the present invention. It should be noted that several improvements can be made without departing from the concept of the present invention, and these should all fall under the protection of the patent of the present invention.

Claims

1. An ultrasonic vibration-assisted intermittent electrospark machining method, characterized in that The following steps are involved: Step 1: The workpiece (6) is connected to the positive electrode of the pulse power supply (4), and the tool electrode (9) is connected to the negative electrode of the pulse power supply (4). At the same time, the tool electrode (9) rotates at a high speed around its axis according to a preset speed, and the working fluid (2) is ejected from the inner hole of the tool electrode (9) and enters the processing area. When the pulse power supply (4) is turned on, the tool electrode (9) is fed along the tool electrode feeding direction (10) toward the workpiece. The tool electrode (9) makes an oscillation along its axis with a period of T2 and an amplitude of I m The composite motion is a coupling motion of ultrasonic vibration and low-frequency vibration with a period of T1 along the feeding direction (10), and the period of the composite motion is T1; a composite motion period T1 includes three stages, namely, a low-frequency vibration feeding stage (AB segment), a coupled motion discharge stage (BD segment), and a low-frequency vibration retreat stage (DE segment); Step 2: In the low-frequency vibration feeding stage (AB section), the tool electrode (9) is gradually fed from the maximum side gap H2 (point A) to the maximum speed (point B), the pulse power supply (4) remains in the off state, the tool electrode (9) is fed at a constant speed along the feeding direction (10), and the tool electrode (9) is vibrated and fed along the low-frequency vibration direction (1), the side machining gap is gradually reduced from the maximum gap H2, and at the same time a large amount of fresh working fluid (2) is brought into the machining area, so that the working fluid (2) in the machining area is restored to a dielectric state, and the detached reinforcing phase particles (8) enter the working fluid (2) and act as abrasives; Step 3: In the coupled motion discharge stage (BD segment), the tool electrode (9) continues to be fed at a low frequency from the maximum speed (point B) in the direction close to the workpiece (6) to the minimum side gap (point C), and then retreats at a low frequency in the direction away from the workpiece (6) to the maximum speed (point D). At the same time, the tool electrode (9) begins to perform ultrasonic vibration movement along the axial direction. The side gap between the tool electrode (9) and the workpiece (6) first gradually decreases and then gradually increases. The pulse power supply (4) is turned on, and multiple spark discharges (7) occur in the processing area. At the same time, the tool electrode (9) begins to perform ultrasonic vibration along the axial direction. A large number of micro cavities (5) are formed in the working fluid (2). Under the action of ultrasound, a large number of spark discharge products (3) are taken away from the processing area, and the free reinforcing phase particles (8) produce mechanical impact and polishing effects on the workpiece (6), thereby improving the surface quality of the EDM. Step 4: In the low-frequency vibration retreat stage (segment DE), the tool electrode (9) retreats from the maximum speed point (point D) along the low-frequency vibration direction (1), and the side machining gap gradually increases to H2. The tool electrode (9) has a great acceleration when vibrating and retreating, and a large amount of spark discharge products (3) in the machining area are taken away from the machining area, and fresh working fluid (2) flows back into the machining area, so that the working fluid (2) in the machining area is restored to a dielectric state; Step 5: The processing area continuously repeats the above three stages of step 2 to step 4, and high-quality processing of the workpiece (6) is achieved under the intermittent processing action of the low-frequency vibration and ultrasonic vibration combined motion of the tool electrode (9) and the pulse power supply (4); wherein the period T1 of the coupled motion of the low-frequency vibration and ultrasonic vibration of the tool electrode (9) is equal to the time t of the low-frequency vibration feeding stage a , coupled motion discharge stage t b The low-frequency vibration retreat phase time t c sum.

2. The ultrasonic vibration-assisted intermittent electrospark machining method according to claim 1, characterized in that: The amplitude of the low-frequency vibration of the tool electrode (9) is several 100 micrometers to 4 millimeters, the amplitude of the ultrasonic vibration of the tool electrode (9) is 1-20 micrometers, and the period T2 of the ultrasonic vibration is several 5-100 microseconds.

3. The ultrasonic vibration-assisted intermittent electrospark machining method according to claim 1, characterized in that: Low frequency vibration feeding time t a , low frequency vibration retreat time t c and ultrasonic vibration time t b Both can be adjusted to increase the ultrasonic vibration time t b To increase energy input and obtain higher processing efficiency; increase the low-frequency vibration feed time t a , low frequency vibration retreat time t c It is helpful to speed up the transportation of processed products in the processing area and obtain better surface quality.

4. The ultrasonic vibration-assisted intermittent electrospark machining method according to claim 1, characterized in that: The material of the tool electrode (9) is copper-tungsten alloy, graphite, red copper, or red copper.

5. The ultrasonic vibration-assisted intermittent electrospark machining method according to claim 1, characterized in that: The workpiece (6) is a medium to high volume fraction particle reinforced metal matrix composite material.

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