1 Two main methods for precision EDM grinding of shaft parts Block electrode Radial feed EDM grinding Block electrode Radial feed EDM grinding method also known as forming block reverse copying or inverse copying method . It uses a block electrode with the same surface shape as that of the micro-axis busbar, so that the forming surface is radially servo-fed against the axis of the rotating fine axis (Fig. 1). The electric discharge grinding of the wire electrode by electric wire spark grinding was invented in 1984 by Prof. Masawachi Takahisa of Tokyo University. It is particularly suitable for precision EDM grinding of fine shaft parts. The basic principle is shown in Figure 2. The wire electrode EDM method uses a wire electrode that moves along the guide surface of a guide (not a turning guide) fixed on a numerical control table as a processing tool, and a numerical control system controls the relative motion path of the fixed guide tangent point. The wire electrode is servo-fed in the radial and axial directions of the rotating fine axis. Comparison of two processing methods
3 Characteristics of block electrode tangential feed precision EDM method Automatic tool compensation for tool electrode loss The loss compensation of the electrode and the servo feed are combined, which overcomes the electrode electrode of the block electrode radial feed method. The disadvantage of loss compensation is that it does not require special tool electrode compensation (wire removal) mechanisms such as the wire electrode method. Particularly suitable for batch processing. One electrode can be used to process multiple workpieces at a time, and the consistency of the shape and size of the machined workpiece is good. The number of workpieces processed per batch and the wear rate of the tool electrode are related to the length of the tool electrode. For example, a Ø5 mm elastic alloy bar is machined to Ø0.6 mm using a tangential feed method. Using a block-like copper electrode and adopting the electrical parameters of a medium gauge, the measured electrode wear rate is 1.75%. After eight consecutive workpieces are machined, the length of the significant loss zone on the top surface of the electrode front end is approximately 4 mm, the loss depth at the front end is approximately 2 mm, and the shape of the depletion zone is a right-angled triangle with a hypotenuse. If the electrode length is 80mm, an electrode can process 160 workpieces at a minimum. If the radial feed method is used, to achieve the same processing quality, only 10 pieces of the same length electrode surface can be machined. The tangential feed method works like a “out of a moldâ€. Its shape depends mainly on the shape of the surface of the tool electrode. Its size depends mainly on the offset position of the tool electrode relative to the axis of the workpiece, and the tool and the workpiece. The gap between the discharges, so that the controllability of the process is strong, in theory can achieve a very high shape and size consistency. As for the control of dimensional accuracy, it mainly depends on the manufacturing precision and adjustment level of the tool electrode. It is possible to test the adjustment condition by trial grinding a workpiece. If the dimensional requirements are reached, batch production can be started. The material utilization rate of the tool electrode is different from that of the wire electrode method. The tool electrode of the tangential feed method automatically compensates the feed after sufficient wear and tear, without excessive movement: When a plurality of workpieces are processed, the surface on which the tool electrode has been lost naturally Participate in the processing of the next workpiece to make full use of the tool electrode: The tool electrode completely worn out on the upper surface can be used after being reprocessed. Therefore, the tool electrode utilization ratio of the tangential feed method is higher than the radial feed method and the wire electrode method. Can increase the degree of automation of the processing After the tool electrode is adjusted once, the workpiece is automatically machined to the size: In addition to loading and unloading the workpiece, multiple manual interventions are reduced. With reasonable programming, coarse, medium, and fine machining can be achieved at one feed. Continuously completed during the process. The pulse equivalent tangential feed method that phasing out the feed in a similar way is similar to the feed of the slant feed for small angles in the machining process, and the actually generated single pulse feed amount is greatly reduced. The tiny feed pulse equivalent is conducive to the stability of servo feed, especially for subtle EDM. The small feed pulse equivalent also results in a significant decrease in the speed of the retreat, and there may be difficulties in getting out of the arc. Although electric discharge grinding is not prone to arcing, measures should be taken to prevent it from occurring. Elimination speed is high. Because of the tangential feed method, the feed effect of small-angle bevels makes the EDM more continuous and stable, and the erosion rate is also greatly improved. Compared with the radial feed method, it can increase by 20%-30. %. More importantly, the tangential feed method eliminates a large amount of manual intervention assistance time, so the productivity is much higher than radial feed method. Tool electrode manufacturing, positioning and adjustment require a higher level. We conducted a preliminary experimental study on the tangential feed EDM method of block electrodes. The experimental results show that the tangential feed electric discharge grinding method of block electrode is feasible, and the processed workpiece has a good consistency of shape and size.
1. Micro shaft 2. Block electrode
Figure 1 block electrode radial feed method
1. Micro shaft 2. Fixed guide 3. Wire electrode
Figure 2 wire electrode grinding method
1. Micro shaft 2. Block electrode
Figure 3 Block electrode tangential feeding method
Due to the large difference in size of the discharge processing area, the bulk electrode method has a significantly faster erasure rate than the line electrode method (about 5 times or more). Because the loss of the tool electrode of the block electrode method cannot be compensated in time, resulting in frequent interruption of processing, it is necessary to constantly measure the processing size, observe the loss of the tool, and update the discharge working surface of the tool. Due to the interruption of the machining process, only a limited number of manual interventions are generally performed. Therefore, it is difficult to control the wear and tear on the surface of the tool electrode when machining ends, which affects the shape and dimensional accuracy of the workpiece. Especially in the multi-piece machining, the consistency of the shape and size of the workpiece is poor. The energy consumption of the wire electrode is continuously compensated by the movement of the wire electrode, and the loss of the tool can be ignored. The shape and dimensional accuracy of the workpiece are ensured by the numerical control motion accuracy. In block electrode method processing, manual intervention is more difficult to achieve processing automation: In the online electrode method processing, because there is no such problem, it can continuously achieve rough, fine processing. Block electrode wear surface can be reused after being repaired. The wire electrode is a one-time use, the processing time is long, the wire electrode is consumed, and a set of precise wire moving mechanism is also needed, so the wire electrode method has high processing cost. Block electrode manufacturing, positioning and adjustment levels require higher levels. The shape and dimensional accuracy of the wire electrode and the smoothness of the wire movement also affect the machining accuracy. 2 Block electrode tangential feeding EDM grinding method In order to overcome the deficiencies of the above two methods, we proposed a new block electrode EDM method that can automatically perform electrode loss compensation—tool electrode tangential feed the way. The basic principle of the block electrode tangential feed EDM method is shown in Figure 3. The tangential feeding method is that the upper surface of the horizontally placed tool electrode is used as the main working surface, and the distance between the upper surface and the workpiece axis is e. This distance is the processing radius pre-achieved by the workpiece. The upper surface of the tool is along Servo feed in the horizontal direction. In the process of machining, after the loss of the tool electrode surface in the processing area, the loss is automatically compensated by the tangential servo feed until the predetermined machining radius of the workpiece is reached and the machining is ended. The upper surface of the tool electrode should be long enough to allow the workpiece to eventually be withdrawn from the surface of the tool that has not been lost or lost so that a predetermined shape and dimensional accuracy can be achieved.3 Characteristics of block electrode tangential feed precision EDM method Automatic tool compensation for tool electrode loss The loss compensation of the electrode and the servo feed are combined, which overcomes the electrode electrode of the block electrode radial feed method. The disadvantage of loss compensation is that it does not require special tool electrode compensation (wire removal) mechanisms such as the wire electrode method. Particularly suitable for batch processing. One electrode can be used to process multiple workpieces at a time, and the consistency of the shape and size of the machined workpiece is good. The number of workpieces processed per batch and the wear rate of the tool electrode are related to the length of the tool electrode. For example, a Ø5 mm elastic alloy bar is machined to Ø0.6 mm using a tangential feed method. Using a block-like copper electrode and adopting the electrical parameters of a medium gauge, the measured electrode wear rate is 1.75%. After eight consecutive workpieces are machined, the length of the significant loss zone on the top surface of the electrode front end is approximately 4 mm, the loss depth at the front end is approximately 2 mm, and the shape of the depletion zone is a right-angled triangle with a hypotenuse. If the electrode length is 80mm, an electrode can process 160 workpieces at a minimum. If the radial feed method is used, to achieve the same processing quality, only 10 pieces of the same length electrode surface can be machined. The tangential feed method works like a “out of a moldâ€. Its shape depends mainly on the shape of the surface of the tool electrode. Its size depends mainly on the offset position of the tool electrode relative to the axis of the workpiece, and the tool and the workpiece. The gap between the discharges, so that the controllability of the process is strong, in theory can achieve a very high shape and size consistency. As for the control of dimensional accuracy, it mainly depends on the manufacturing precision and adjustment level of the tool electrode. It is possible to test the adjustment condition by trial grinding a workpiece. If the dimensional requirements are reached, batch production can be started. The material utilization rate of the tool electrode is different from that of the wire electrode method. The tool electrode of the tangential feed method automatically compensates the feed after sufficient wear and tear, without excessive movement: When a plurality of workpieces are processed, the surface on which the tool electrode has been lost naturally Participate in the processing of the next workpiece to make full use of the tool electrode: The tool electrode completely worn out on the upper surface can be used after being reprocessed. Therefore, the tool electrode utilization ratio of the tangential feed method is higher than the radial feed method and the wire electrode method. Can increase the degree of automation of the processing After the tool electrode is adjusted once, the workpiece is automatically machined to the size: In addition to loading and unloading the workpiece, multiple manual interventions are reduced. With reasonable programming, coarse, medium, and fine machining can be achieved at one feed. Continuously completed during the process. The pulse equivalent tangential feed method that phasing out the feed in a similar way is similar to the feed of the slant feed for small angles in the machining process, and the actually generated single pulse feed amount is greatly reduced. The tiny feed pulse equivalent is conducive to the stability of servo feed, especially for subtle EDM. The small feed pulse equivalent also results in a significant decrease in the speed of the retreat, and there may be difficulties in getting out of the arc. Although electric discharge grinding is not prone to arcing, measures should be taken to prevent it from occurring. Elimination speed is high. Because of the tangential feed method, the feed effect of small-angle bevels makes the EDM more continuous and stable, and the erosion rate is also greatly improved. Compared with the radial feed method, it can increase by 20%-30. %. More importantly, the tangential feed method eliminates a large amount of manual intervention assistance time, so the productivity is much higher than radial feed method. Tool electrode manufacturing, positioning and adjustment require a higher level. We conducted a preliminary experimental study on the tangential feed EDM method of block electrodes. The experimental results show that the tangential feed electric discharge grinding method of block electrode is feasible, and the processed workpiece has a good consistency of shape and size.
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