CN108672852A - A kind of electric discharge machining method of pulse power single pulse energy non-uniform Distribution - Google Patents

Abstract

An electric discharge machining method in which a single pulse energy of a pulse power supply is non-uniformly distributed. The specific feature is that the pulse power supply can provide different pulse energies in different microscopic stages of spark discharge, so as to improve the energy utilization rate of the power supply, improve the processing efficiency, The purpose of reducing the loss of tool electrodes, improving the quality of the processed surface and accelerating the deionization between pulses. The invention has no special requirements on the magnitude of the pulse discharge energy and the type of the inter-electrode medium, and the processing effect can be improved only by changing the distribution form of the single pulse discharge energy. The method has many advantages such as simple method and easy realization.

Description

An electric discharge machining method with non-uniform distribution of single pulse energy of pulse power supply

technical field

The present invention relates to an electric discharge machining method, especially a machining method that can distribute single pulse discharge energy to achieve high efficiency, low loss and improve surface quality according to the needs of different machining processes. Specifically, it is a machining method based on The method of changing the energy distribution of a single pulse discharge due to the change of the microscopic process of the interelectrode discharge, in order to improve the utilization rate of pulse energy, improve the erosion rate and processing efficiency of materials, reduce the loss of tool electrodes, and improve the quality of processed surfaces.

Background technique

EDM is a processing method that uses pulsed spark discharge between tool electrodes and workpieces to erode materials in a medium. Because this method has many advantages, such as being suitable for processing difficult-to-machine materials, and can process parts with special and complex shapes, it has been widely used in many fields such as aviation, aerospace, automobiles, molds, and electronics, and has become an indispensable Lack of processing means.

Compared with cutting machining, the efficiency of EDM is generally lower. For this reason, many researchers have proposed many methods from the aspects of pulse power supply, composite machining technology, electrodes, and working fluid to improve machining efficiency. For the loss of electrodes, some researchers have proposed measures to reduce the energy of pulse discharge at the front of pulse discharge to reduce electrode loss. For the surface quality of processing, some researchers have also proposed to use such as triangular pulse wave or equal pulse energy processing to obtain better surface quality. However, most of the current pulse energy used in electric spark discharge is a rectangular wave pulse with uniform energy distribution. In the process of spark discharge, the microscopic process of inter-electrode discharge does not present a constant state. During the process of each state change, all The magnitude of the required pulse energy is also different. The current pulse discharge energy provided by the pulse power supply does not consider the actual and reasonable utilization of the pulse energy by various microscopic process changes in the discharge process.

At present, besides the most commonly used rectangular wave pulse form, different pulse discharge waveforms such as trapezoidal wave and triangular wave have been proposed for the pulse power supply used in EDM, but these methods are only aimed at reducing the loss of electrode wire in the initial stage of processing. Or it is simply proposed for improving the surface quality, and there is no scientific allocation of pulse energy for the energy needs of various changes in the microscopic process between electrodes during actual spark discharge.

In EDM, the microscopic process of each pulse discharge generally goes through the following four stages: ionization and breakdown of the inter-electrode medium to form a discharge channel; thermal decomposition of the medium, melting of electrode materials, thermal expansion of gasification; throwing of electrode materials ; Deionization of the interpolar medium. However, the single pulse energy provided by the pulse power supply currently used does not provide pulse energy according to the actual energy required for the above four microscopic discharge processes, resulting in the pulse discharge energy provided by the power supply not being used reasonably and effectively, resulting in the loss of power supply energy. At the same time, the potential for improving processing efficiency has not been further tapped, and the distribution of single pulse discharge energy cannot be reasonably allocated according to different requirements for processing effects.

The improvement of processing efficiency can generally be achieved by increasing the pulse discharge energy. Although the processing efficiency can be improved by increasing the discharge energy, when the processing efficiency exceeds a certain value, the increase of the discharge energy will be very slow, and the surface quality of the workpiece will also deteriorate with the increase of the pulse energy. , Correspondingly, it will also bring a series of problems such as increased tool electrode loss. Under the condition of high-energy processing, in order to obtain high processing efficiency, the energy output by the high-frequency pulse power supply must be improved and perfected, so as to optimize the single pulse discharge energy according to the processing effect requirements.

Contents of the invention

The present invention provides a method for improving the energy utilization rate of the pulse power supply and optimizing the processing effect by changing the single pulse energy distribution of the pulse power supply. Tool electrode loss reduces the thickness of the solidified layer on the machined surface and improves the integrity of the machined surface.

Technical scheme of the present invention is as follows:

A method for improving the energy utilization rate of a pulse power supply and optimizing the processing effect by changing the single pulse energy distribution of a pulse power supply, which is characterized in that it includes the following content:

(1) The ionization and breakdown stage of the inter-electrode medium: After the pulse voltage is applied between the tool electrode and the workpiece, an electric field is immediately formed between the two electrodes. When the electric field strength exceeds the dielectric strength of the interpolar medium, the medium is ionized and broken down, and the generated electrons and ions move to the positive and negative electrodes respectively under the action of the electric field force, forming a discharge channel. At this stage, it is necessary to consume energy to ionize the working medium and form a discharge channel. The greater the energy applied between the electrodes, the larger the diameter of the generated discharge channel will be. In EDM, the medium used generally has a certain degree of conductivity, and the pulse voltage between the electrodes is generally fixed within a certain range. If a larger energy is used to break down, the energy consumption will inevitably cause more dielectric breakdown. Wearing it on will produce a larger diameter of the discharge channel. For the next spark discharge, the large diameter channel will reduce the predetermined pulse energy density, which will have adverse effects on the melting or gasification erosion, throwing and other processes of the material. impact; and if a smaller pulse energy is used to break down, the diameter of the generated discharge channel is also small, which is not only conducive to saving power supply energy in the stage of breaking down the ionized medium, but also beneficial to improving the energy density in the spark discharge stage, thus improving the material The process of melting or gasification erosion, throwing and other processes produces enhanced dynamics. Therefore, at the beginning of each single pulse, the present invention proposes that a smaller pulse energy should be used for dielectric breakdown.

(2) Electrode material melting and gasification stage: Once a discharge channel is formed between the electrodes, the electrons and positive ions in the channel rush to the positive and negative electrodes at high speed under the action of the electric field between the electrodes, converting electrical energy into kinetic energy. The high-speed collision of charged particles on the surface of the two poles converts the kinetic energy into heat energy, and the temperature of the materials on the two pole surfaces rises rapidly, causing the inter-electrode medium to gasify and thermally decompose, and also to melt and gasify the tool electrode and the workpiece material. At this stage, if the pulse energy is increased, a greater pulse energy density will be obtained in the formed discharge channel, and a higher temperature will be obtained on the surface of the workpiece, thereby increasing the proportion of material vaporization and erosion, and improving the quality of the material. erosion rate. Therefore, the present invention proposes to carry out the melting and gasification of the material at this stage with a higher energy than in the breakdown stage.

(3) The throwing stage of the electrode material: the vapor generated after the gasification of the inter-electrode medium and the gasification of the metal material expands instantaneously, and generates a high instantaneous pressure, so that the gas generated by the gasification continuously expands outwards and forms An expanding "bubble" that pushes, throws, and ejects molten or vaporized metallic material into the working fluid. At this stage, in order to make the molten and gasified metal material be thrown more thoroughly so that there are fewer metal droplets remaining on the surface of the electrode pit, a greater throwing power is required. For this reason, in addition to the need to provide higher pulse energy during the material melting and gasification stage to increase the proportion of material gasification erosion and thus increase the pressure of the gasification steam in the channel, it is also necessary to continue to maintain the gap between electrodes. The higher pulse energy density enables the material in the melting or gasification area to obtain greater throwing power.

(4) Medium deionization stage: After the pulse voltage is turned off, the pulse current also quickly drops to zero, the charged particles in the channel recombine to be neutral, and the medium restores its dielectric strength, which provides for the next breakdown discharge at other positions on the electrode surface condition. At this stage, in order to speed up the deionization of the inter-electrode medium and reduce the time between pulses, the polarity of the pulse power supply is changed and a smaller pulse energy is provided between the two poles.

In the above four microscopic processes, small energy is used in the stage of medium ionization and breakdown, and high energy is used in the stage of material melting and gasification. The loss of the tool electrode wire used repeatedly for reciprocating wire feeding will not cause greater loss. Because in positive polarity machining, when the inter-electrode dielectric is just broken down to generate discharge, a small energy breakdown is used, and the positive ions in the channel have a relatively weak bombardment effect on the tool electrode. At this time, it is mainly the bombardment effect of electrons on the surface of the anode workpiece strong. When the pulse energy is increased during the melting and gasification stages of the material, the wire electrode also runs for a certain distance at a higher wire speed, causing the discharge pit on its surface to elongate along the direction of wire running, so that due to the wire electrode High-speed operation reduces the depth of the surface erosion pit, and will not seriously increase the radial loss of the wire, especially in high-energy EDM cutting, using the above pulse energy distribution method, compared with a single pulse energy uniformly distributed , It is also beneficial to reduce the loss of electrode wire.

Therefore, the innovation of the patent of the present invention lies in: proposing a method of rationally distributing and utilizing pulse discharge energy according to various changes in the microscopic state between electrodes, that is, according to the needs of pulse energy for different microscopic processes of spark discharge and the individual pulse energy The size is reasonably distributed, rather than applying a uniformly distributed pulse energy to the different microscopic stages of the spark discharge. This method can rationally distribute the energy of a single pulse according to the needs of the processing effect, which can not only improve the effective utilization rate of the pulse energy, but also improve the erosion rate of the workpiece material, reduce the loss of the tool electrode, and improve the quality of the processed surface. The method is suitable for electric discharge machining with any energy, especially for high-efficiency machining under high energy.

Beneficial effects of the present invention:

The present invention proposes a method for non-uniform distribution of single pulse energy of a pulse power supply, which can solve the problem of different requirements for energy in different inter-electrode microscopic change processes during spark discharge, not only can fully utilize the power supply energy, but also can use different pulse energies Distribution form to optimize the processing effect. Such as increasing the erosion rate of materials, reducing the loss of electrodes, improving the quality of processed surfaces, etc. This method changes the single pulse energy of the power supply according to the microscopic process of the inter-electrode discharge, which is different from the uniform distribution of pulse discharge energy currently used, and has important theoretical and practical significance for rational use of power supply energy and improving processing effects.

The invention is suitable for EDM under any pulse discharge energy, especially suitable for EDM under large pulse discharge energy. At this time, the power supply energy is more fully utilized, and the material erosion rate is greater, and the surface of the workpiece is melted The reduction of the thickness of the metal solidified layer can solve a series of problems in the current high-energy processing, such as serious electrode loss, slow deionization of the medium and increased short-circuit probability, large thickness of the material surface metamorphic layer, and poor surface integrity.

The present invention is applicable to different electric discharge machining types, and has no special requirements on the machining medium, and can achieve the purpose of optimizing the machining effect only by changing the single pulse energy distribution form output by the pulse power supply.

The invention adopts a pulse power supply whose single pulse discharge energy can be changed, and has the characteristics of simple method, easy realization and the like.

Description of drawings

Figure 1 is a waveform in which the pulse energy is non-uniformly distributed by changing the peak current in different microscopic stages of a single pulse.

The schematic diagrams of (1), (2), (3), and (4) in Figure 2 are schematic diagrams of the microscopic process of inter-electrode discharge corresponding to the waveform segments a, b, c, d, and e in Figure 1.

Fig. 3 is a comparison chart of cutting efficiency obtained by using different energy distribution forms of a single pulse in high-speed reciprocating wire electric discharge machining.

Fig. 4 is a photo of pits etched by single pulse discharge obtained by using different forms of energy distribution of a single pulse.

Detailed ways

The present invention will be further described below in conjunction with drawings and embodiments.

As shown in Figure 1 and 2.

A method to improve the energy utilization rate and processing effect of a pulse power supply by changing the energy distribution in a single pulse, aiming at the following purposes in the EDM process to reasonably distribute the energy of a single pulse: further excavate the energy utilization rate of the power supply pulse and improve the processing efficiency , speed up the deionization speed between the electrodes after the discharge, reduce the thickness of the solidified layer on the processed surface, and improve the integrity of the processed surface. Including the following energy distribution content:

(1) The ionization and breakdown stages of the interpolar medium

After the pulse voltage is applied between the tool electrode and the workpiece, an electric field is formed between the two electrodes immediately. When the electric field strength exceeds the dielectric strength of the interpolar medium, the medium is ionized and broken down, and the generated electrons and ions move to the positive and negative electrodes respectively under the action of the electric field force, forming a discharge channel. The waveforms of sections a and b in Figure 1 and the microscopic state between electrodes in Figure 2 (1). At this stage, it is necessary to consume energy to ionize the working medium and form a discharge channel. The greater the energy applied, the larger the diameter of the generated discharge channel will be. In EDM, the medium used generally has a certain conductivity, and the pulse voltage between the electrodes is generally fixed within a certain range. If a larger energy is used to break down, the energy will inevitably be consumed to make more medium On the breakdown, a discharge channel with a larger diameter is generated. For the subsequent spark discharge, the large-diameter channel will reduce the energy density of the given pulse energy, thereby affecting the melting or gasification of the material. Erosion, throwing and other processes produce adverse effects. For this reason, a smaller pulse energy is used to break down at this stage, and the diameter of the generated pulse channel is also small, which not only helps to save energy in the stage of breaking down the ionized medium, but also improves the energy density in the spark discharge stage. The process of melting or gasification erosion, throwing and other processes of materials in the inter-electrode micro-process change stage produces enhanced dynamics. Therefore, at the initial stage of each single pulse, the present invention proposes that smaller pulse energy should be used for ionization and breakdown of the medium.

(2) Electrode material melting and gasification stage

Once the discharge channel is formed between the electrodes, the electrons and positive ions in the channel rush to the positive and negative electrodes at high speed under the action of the electric field between the electrodes, so that the electrical energy is converted into kinetic energy. The high-speed collision of charged particles on the surface of the two poles converts the kinetic energy into heat energy, and the temperature of the material on the two poles rises rapidly, causing the inter-electrode medium to gasify and thermally decompose, and at the same time to melt and gasify the tool electrode and the workpiece material. At this stage, if the pulse energy is increased, a greater pulse energy density will be obtained in the formed discharge channel, and a higher temperature will be obtained on the surface of the workpiece, thereby increasing the proportion of material vaporization and erosion, and improving the quality of the material. erosion rate. Therefore, the present invention proposes to carry out the melting and gasification of the material at this stage with a higher energy than in the breakdown stage. For the high-speed reciprocating wire EDM that uses the electrode wire repeatedly, in order to reduce the radial loss of the electrode wire after the dielectric breakdown, the pulse discharge energy is kept constant for a short time after the dielectric breakdown, so that The erosion pit generated on the surface of the wire electrode is stretched for a certain length with the operation of the wire electrode, and then the pulse discharge energy is increased, so that the depth of the erosion pit on the surface of the electrode wire is reduced, and the loss of the electrode wire is reduced. As shown in the c and d sections of the waveform in Figure 1 and the microscopic state between the electrodes in Figures 2 (2) and 2 (3).

(3) Throwing stage of electrode material

The vapor produced after the gasification of the interpolar medium and metal materials expands instantaneously and generates a high instantaneous pressure, which makes the gas generated by the gasification continuously expand outwards and form an expanding "bubble", thus melting Or gasified metal material pushes, throws and enters the working fluid. At this stage, in order to make the molten and gasified metal material be thrown more thoroughly so that there are fewer metal droplets remaining on the surface of the electrode pit, a greater throwing power is required. For this reason, in addition to the need to provide higher pulse energy during the material melting and gasification stage to increase the proportion of material gasification erosion and thus increase the pressure of the gasification steam in the channel, it is also necessary to continue to maintain the gap between electrodes. The higher pulse energy density enables the material in the melting or gasification area to obtain greater throwing power. As shown in Figure 2(3), the microscopic state between the poles.

(4) Medium deionization stage

After the pulse voltage is turned off, the pulse current also drops to zero rapidly, the charged particles in the channel recombine to be neutral, and the dielectric recovers its dielectric strength, which provides conditions for the next breakdown discharge at other positions on the electrode surface. At this stage, in order to speed up the deionization of the inter-electrode medium, reduce the time between pulses, and improve the processing efficiency, the polarity of the pulse power supply is changed and a smaller pulse energy is provided between the two poles. As shown in Figure 2(4), the microscopic state between the poles.

As shown in Figure 3 and 4.

In the high-speed reciprocating WEDM processing, three groups of parameters with different total pulse discharge energy are selected. Under each pulse discharge energy parameter, three different single pulse energy non-uniform distribution forms are used, which have a great impact on the processing efficiency. comparing. The experimental results show that when the total pulse energy provided by the pulse power supply remains unchanged, the cutting efficiency can be improved by optimizing the energy distribution of a single pulse discharge, as shown in Figure 3. Form 1, nearly 20% more efficient. In addition, the cutting efficiency of the non-uniform distribution of pulse energy and the uniform distribution of pulse energy were compared, and it was found that the non-uniform distribution of pulse energy has a higher utilization rate of power supply energy and higher cutting efficiency. Therefore, according to the microscopic process between electrodes during spark discharge The corresponding pulse energy is provided according to the actual change of the machine, which is more in line with the objective law and is conducive to optimizing the processing effect.

In Fig. 4, the single-pulse test was carried out using non-uniform pulse energy distribution form 1, non-uniform pulse energy distribution form 2, and non-uniform pulse energy distribution form 3. It was found that the size of the erosion pit was different and the melting form of the material was also different. Therefore, reasonable Distributing the energy distribution of the pulse discharge is beneficial to improve the quality of the machined surface.

Claims (5)

1. An electric discharge machining method in which the single pulse discharge energy of a pulse power supply is non-uniformly distributed. According to the different energy required for the change of the microscopic physical process between electrodes in each stage of spark discharge, the distribution of single pulse energy is reasonably distributed to make full use of the pulse energy, improve the processing efficiency and optimize the processing effect. It is characterized in that it includes the following principles of power pulse energy distribution : (1) In the stage of ionization, breakdown, and formation of discharge channel breakdown in the medium between the tool electrode and the workpiece, a small pulse energy is provided between the electrodes; (2) Increase the pulse energy output by the pulse power supply during the thermal decomposition of the inter-electrode medium, the melting of the electrode material, and the thermal expansion of gasification. (3) During the throwing stage of the electrode material, continuously provide large pulse discharge energy between the electrodes; (4) In the deionization stage of the interpolar medium, reduce the pulse energy and change the processing polarity. 2. The method according to claim 1, characterized in that the single pulse discharge energy output by the pulse power supply can be allocated according to needs, and it is a high-frequency pulse power supply with non-uniform distribution of single pulse discharge energy. 3. The method according to claim 1, characterized in that there is no special limit to the size of the pulse energy used in EDM, as long as it can break through the inter-electrode medium to generate spark discharge, this method can be used to perform single pulse discharge energy Discharge machining after non-uniform distribution. 4. The method according to claim 1 can be aimed at various process requirements, by rationally adjusting the distribution of single pulse discharge energy, respectively achieving mainly to improve processing efficiency; mainly to improve surface integrity; to reduce electrode Loss is the main goal. 5. The method according to claim 1, which can carry out the energy deployment of a single pulse discharge energy in different stages according to different EDM forms such as wire electric discharge cutting, electric discharge forming processing, and electric discharge perforation processing.