According to the linear speed of processing electrode wire, the electric discharge wire cutting machine can be divided into three types: slow walking, middle walking and fast walking. Quick walking and middle walking are summarized here as high speed walking. The surface roughness and processing accuracy of the workpiece processed by the low speed wire cutting machine are slightly better than the high speed wire cutting machine. However, the machine cost and the use cost of the low speed wire cutting machine are relatively high, and the original high speed wire cutting machine in China With simple structure, low machine tool cost and use cost, it is easy to process large-thickness workpieces. After nearly 40 years of development, it has become one of the largest output and most widely used types of machine tools in China. It has been acquired in mold manufacturing, new product trial production and parts processing. widely used.
Since the high-speed wire cutting machine adopts a wire electrode high-speed reciprocating wire feeding method, the loss of the wire electrode is evenly distributed on the electrode wire of nearly 300 meters. Although the loss of the wire electrode is extremely small, the processing of the wire electric discharge machine affects its processing. There are many factors in the surface quality of the workpiece, and it is necessary to make reasonable selection of the relevant processing parameters in order to ensure the surface quality of the processed workpiece.
The factors directly affecting the quality of wire-cutting processes mainly involve personnel, equipment, and materials. In order to improve the surface quality of the machined workpiece, the control method and improvement method of the processing quality can be considered from the three aspects of human factors, machine tool factors, and material factors that have the greatest impact. In the teaching, scientific research and production practice, the author has made some explorations and studies on the factors affecting the surface quality of wire-cutting workpieces, and has accumulated a few effective working experiences. The following is introduced.
The control and improvement of human factors that affect the surface quality of wire-cutting workpieces The control and improvement of human factors mainly include the determination of processing technology and the selection of processing methods. This can be achieved by the following points:
(1) Reasonably arrange cutting routes. The guiding ideology of this measure is to avoid destroying the original internal stress balance of the workpiece material as much as possible, and to prevent the workpiece material from being significantly deformed due to the unreasonable arrangement of the cutting line during the cutting process due to the action of the jig and the like, so that the quality of the cutting surface is reduced. For example: The separation of the workpiece and its holding part should be arranged at the end to make the processing more rigid.
(2) The correct choice of cutting parameters. For different coarse and fine processing, the wire speed and wire tension should be appropriately adjusted based on the parameter table. To ensure that the machined workpiece has higher accuracy and surface quality, the wire tension of the wire cutting machine can be appropriately increased. Manufacturers of wire-cutting machine tools have provided parameters that can be adapted to different cutting conditions. However, due to the influence of the material of the workpiece, the required machining accuracy, and other factors, people cannot completely copy the cutting conditions described in the book, but should use these conditions. Based on actual needs, make corresponding adjustments. For example, if you want to process a workpiece with a thickness of 27mm, you can't find a comparable situation in the processing condition table. Under this condition, you must make adjustments according to the cutting conditions with a thickness of between 20mm and 30mm. The main method is: machining the workpiece. Which standard thickness the thickness is close to is selected as the processing thickness that should be set.
(3) Adopt close-range processing. In order to achieve high precision and high surface quality of the workpiece, the height of the wire frame is adjusted in time according to the thickness of the workpiece so that the distance between the upper nozzle and the workpiece is as close as possible, thus avoiding excessive amplitude of the wire electrode due to the distance between the upper nozzle and the workpiece. The surface quality of the workpiece.
(4) Pay attention to the fixing of the workpiece. When the machining workpiece is about to be cut, its connection strength to the parent material is bound to decrease. At this time, it is necessary to prevent the machining workpiece from being deflected due to the impact of the machining fluid, because once the deflection occurs, the cutting clearance will be changed, and the light affects the workpiece. The surface quality, in severe cases, causes the workpiece to be scrapped and scrapped, so it is necessary to fix the workpiece to be machined.
The control and improvement of machine tool factors that affect the surface quality of wire-cutting workpieces High-speed wire-cut electric discharge wire-cutting machines belong to high-precision machine tools. The maintenance of the machine tools is very important because the high precision and high quality of the machined workpieces are directly established on the machine tool. On the basis of accuracy, it is necessary to check the working status of the machine before each machining in order to provide the conditions for obtaining high-quality machined parts. The links to be noted and the measures to be taken are as follows:
(1)Before processing, the electrode wire must be inspected. The tension of the electrode wire also has a great influence on the surface quality of the workpiece. When the workpiece with high surface quality is required, the wire tension should be increased as much as possible under the premise of continuous wire. .
(2) High-speed wire cutting machines generally use special working fluids. The spark discharge must be carried out in a liquid medium with certain insulating properties. The insulating properties of the working fluid can compress the discharge channel after breakdown, thus confining the spark discharge within a small channel radius, forming instantaneous and local high temperatures to melt gas. After the metal is discharged, the discharge gap is quickly restored to the insulating state. If the insulation performance is too low, the working fluid becomes an electrical conductor and spark discharge cannot be formed. If the insulating performance is too high, the discharge gap is small, the chip removal is difficult, and the cutting speed is reduced. Before processing, different types of emulsions are selected according to different process conditions. In addition, the conditions related to the coolant must be checked to check the fluid volume and the degree of contamination of the fluid to ensure that the fluid's insulation performance, cleaning performance, and cooling performance meet the requirements.
(3) The wear of the conductive block must be checked. High-speed wire cutting machines generally consider changing the cutting position of the conductive block or replacing the conductive block after processing for 50 to 80 hours. Cleaning is required when there is dirt. It must be noted that when the position of the conductive block is changed or the conductive block is replaced, the perpendicularity of the electrode wire must be re-calibrated to ensure the precision and surface quality of the machined workpiece.
(4) Check the rotation of the guide wheel. If the rotation is not good, it should be replaced. The damage of the upper and lower nozzles and the degree of contamination must be carefully checked. Dirty matters should be removed with the cleaning fluid. When there is damage, it must be replaced in time. The condition of the inner wire of the wire storage drum should also be inspected frequently. If the wire loss is too large, it will affect the machining accuracy and surface quality, and it needs to be replaced in time. In addition, the poor condition of the conductive block, the guide roller, and the upper and lower nozzles also causes the vibration of the wire electrode. Even if the machined surface can perform good discharge at this time, due to the vibration of the wire electrode, the processed surface is likely to produce peaks or stripes. Eventually cause the surface roughness of the workpiece to deteriorate.
(5) Maintain a stable power supply voltage. Unstable power supply voltage will cause the electrode and the workpiece to be unstable at both ends, which will cause instability of the breakdown discharge process and affect the surface quality of the workpiece.
Control and improvement of material factors that affect the surface quality of wire-cutting workpieces In order to machine wire-cut products with high dimensional accuracy and good surface quality, careful consideration must be given to the used workpiece materials:
(1) Because of different workpiece materials, the melting point, gasification point, and thermal conductivity are not the same. Therefore, even if processed in the same manner, the quality of the obtained workpiece surface is not the same. Therefore, the workpiece material must be made according to the actual required surface quality. The corresponding choice. For example, to achieve high accuracy, carbide-based materials must be selected instead of stainless steel or unhardened high-carbon steel, otherwise it is difficult to meet the required requirements.
(2) As the internal residual stress of the workpiece material has a great influence on the machining, when the heat-treated material is processed, the relative balance of the internal residual stress of the material is destroyed due to the large-area metal removal and cutting processing, which may affect the parts. The machining accuracy and surface quality. To avoid these conditions, materials with good forgeability, good hardenability, and low heat-treatment distortion should be selected.
(3) The parameters should be adjusted to the best state during the processing to reduce the broken wire. If the broken wire is bound to return to the starting point, the wire will be re-processed again, and the surface quality and processing accuracy of the machined workpiece will be reduced. In the process of processing should also pay attention to listening to the sound of the machine tool, the normal processing of the sound should be a very smooth "squeak and bang" sound. At the same time, during normal machining, the pointer of the current meter and voltmeter of the machine tool should have a small amplitude and be in a stable state. At this time, the feed speed is uniform and stable.
There are many factors that affect the surface quality of WEDM workpieces, but as long as they are systematically analyzed and scientifically classified, such complex and messy factors can be controlled and deployed to improve and improve the surface quality of workpieces.
