Application of wire cutting in mold processing

A reasonable process analysis, a reasonable design of the mold structure, and a reasonable analysis of the processing technology are related to the processing accuracy of the mold. Through the determination of the threading hole and the optimization of the cutting route, the cutting process is improved, which is an effective and important way to improve the cutting quality and production efficiency.

1. The processing principle of wire cutting:

The principle of wire cutting is to use the wire storage tube, upper and lower frames to make the molybdenum wire reciprocate at high speed. Among them, there are bearings and guide wheels in the upper and lower wire frames to control the vertical precision and linearity of the molybdenum wire, and the workpiece acts on the upper and lower wire frames. It is supported by two backing plates. The pulse power supply carries the positive and negative electrodes of the molybdenum wire and the workpiece respectively, and the metal is melted and vaporized by the high temperature generated by the discharge, so that the excess part of the workpiece is cut off according to the predetermined trajectory to obtain what we need. A processing method of the mold structure, wire cutting processing is divided into fast wire and slow wire. The fast wire has low processing precision and low cost, and the fast wire has high cost and high processing accuracy.

2. Basic characteristics:

(1) As the wire cutting technology is becoming more and more perfect, a CAD/CAM system from graphics input to the machining process has been formed, and the automation of wire EDM machining has been realized. In the production process, complex shapes and plane geometric contours can be cut out.
(2) Because of the positive and negative discharges, the processing point can generate temperatures as high as 10 000 ℃. Within this temperature range, various metal objects can be melted. Therefore, it can process a variety of high-hardness metals, such as quenched tool steel, cemented carbide, polycrystalline diamond and so on.
(3) The sharp corners and clear corners that often appear in many complex mold cavities are difficult to achieve in machining. If it is a through hole and a through hole with a small taper, the wire cutting process can easily solve this problem. problem.
  three. Optimization of the silk route
In the wire cutting mold, optimizing the wire routing of the electrode wire is beneficial to improve the cutting quality and shorten the processing time. Therefore, in the programming of the wire routing, it should be based on the size, shape and accuracy requirements of the workpiece, the size of the electrode wire discharge gap and the size of the gap between the concave and convex molds and other factors, combined with the following points to comprehensively analyze: ① In general, Try to arrange the wire route in the cutting process of the part and keep the support frame of the clamping part in the same coordinate system to ensure the accuracy of positioning; ②The starting point of the wire route should be arranged in the direction away from the part fixture for cutting , Finally turn to the direction of the fixture to cut, and arrange the separation and cutting at the end of the wire line; ③In the cutting process, corners (or sharp corners) of some molds are prone to collapse (or rounding), which should be appropriate according to the specific situation Trim the wire routing and process parameters; ④ For some molds with high precision requirements, in order to reduce deformation, improve the metamorphic layer of the mold processing surface, and increase the service life of the mold. ⑤ Due to the diameter of the electrode wire and the discharge gap, a high line protruding from the cutting surface may sometimes appear at the junction of the cutting surface of the mold. When cutting, it is necessary to select a reasonable cutting route according to the structure of the mold, and try to avoid the phenomenon of protrusions in the processing process.
Four. Determination of discharge gap
In the actual production process, there are many factors that affect the discharge gap of wire cutting, mainly including: the mechanical properties of the material of the mold, the structure and shape of the mold, the technical requirements of the mold, the speed of the electrode wire, the size of the tension, and the operation of the guide wheel. Status, type of working fluid, concentration and degree of contamination, as well as electrical regulation parameters of pulse power supply, etc.
In the actual operation process, in order to accurately determine the discharge gap, before each programming, according to the set processing conditions, take a test piece of the same material as the mold and try to cut a square. Then, the discharge gap is actually measured, and a reasonable offset is calculated as the basis for adjusting the center line of the electrode wire (the actual wire trajectory). In addition, the size of the discharge gap will vary depending on the mold material. Generally speaking, the material with low melting point has a larger discharge gap than the material with high melting point. The discharge gap of quenched steel is larger than that of unquenched steel, and the discharge gap of materials with small heat capacity and poor thermal conductivity is correspondingly larger.
  Fives. Selection of mold fit clearance
The reasonable determination of the matching gap between the convex and concave dies of the blanking die is directly related to the accuracy of the blanking part and the quality of the cross-section of the blanking part, and affects the service life of the die. According to the thickness of the mechanical properties of the parts to be processed, the gap of the mold is selected. As the material of the blanking parts changes from soft to hard, the gap between the convex and concave dies gradually increases. The gap can generally be selected at 10% to 12% of the thickness of the material. Generally, for soft materials (such as soft aluminum, pure copper, etc.), the gap is selected based on 10% to 12% of the thickness of the blanking part; for semi-hard materials (such as hard aluminum, brass, etc.), the gap is selected according to the thickness of the blanking part Select 12%-15% of the thickness; for hard materials (such as thin steel plates, silicon steel sheets, etc.), select 15%-20% of the thickness of the punched part. In addition, appropriate micro adjustments should be made according to the shape features, accuracy requirements and technical conditions of the blanking parts, as well as the structure and accuracy of the mold. Due to the characteristics of wire cutting, the gap between the convex and concave molds of the wire cutting mold should be slightly smaller than the conventional data, so as to extend the service life of the mold and obtain higher part quality.
Six. Determination of the actual size of the cutting edge of the blanking die
Cutting edge wear is used to determine the size of the blanking part. For punches and dies, the cutting edge size is directly related to the dimensional accuracy of the blanking part. After the cutting edge is worn, the size of the blanking part becomes larger. For the blanking die, the size of the part is close to the size of the die. When wire cutting, the actual machining size of the die edge is required to be close to or equal to the minimum limit size of the punching part; for the punching die, the size of the part is close to the punching die. When wire cutting, the actual processing size of the punch edge should be close to or equal to the most extreme size of punching. In this way, under the premise of ensuring the dimensional accuracy of the blanking parts, it is beneficial to extend the service life of the mold and improve economic benefits.
In the production process, reasonable processing methods should be adopted according to the processing conditions of the mold to meet the processing requirements of the mold. The processing accuracy of the mold should be selected according to the accuracy of the parts. On the premise of meeting the accuracy requirements of the parts, the manufacturing of the mold should be reduced as much as possible. Accuracy, in order to reduce costs, according to the processing conditions of the mold, the manufacturing accuracy of the convex mold should be one level higher than that of the concave mold.
Seven, the application of wire cutting in the mold
In production, some quality problems will occur after the mold is used for a period of time, and some measures must be taken to solve it according to the actual situation. If the main part of the mold (convex and concave mold) has cracks in the cutting edge, it is usual to re-cut the material and reprocess the mold, but now using the wire cutting process, the "cutting insert method" can be used to repair the mold.
In order to adapt to CNC wire cutting technology for processing molds. Improvement of mold structure design.
Traditional punches are usually designed with three steps, the smallest step is the working edge, the middle table is the fixed positioning step, and the largest step is the axial positioning step that prevents the punch from being pulled out of the fixed plate. One of these three steps is missing. No, each has its own function. The CNC wire cutting punch is processed after quenching, and it can only be processed into a straight table punch with the same upper and lower sides. According to this feature, if the punch is designed as a straight platform, how to fix the punch and the fixed plate? Traditional methods include bonding and riveting. Practice has proved that the bonding is unreliable. It is easy to fall off during work. Although the riveting is firm and reliable, the rear part of the punch cannot be quenched during quenching. We know that high-carbon alloy steel can be quenched to a certain degree of hardness in the air. The working part of the punch must have high hardness, but the rear part cannot have hardness. This brings great difficulty to the heat treatment of the punch. Obviously these two This method is not simple, economical, and reliable. Through a lot of experiments, I have concluded a set of punch structure that is fully adapted to the CNC wire cutting process. If it is a shorter and narrower punch, it can be designed as a straight table type according to the working part of the punch, and the same step is used for the positioning and fixing of the punch. Axial fixation is fixed by inserting a pin into the side cylindrical hole. After the punch is cut, the cylindrical hole is cut from the outside to the inside on the online cutting, so there is a 0.1 mm left and right at the rear of the punch. Cutting seam, this gap has no effect on the strength of the punch after the pin is installed in the axial fixing pin to press the fixing plate. It can be seen from Figure 1 that a cylindrical hole is cut out on the punch, and a semicircular groove is milled on the fixing plate correspondingly, and the pin is installed to completely position and fix the punch. If it is a narrower and longer punch, several more cylindrical holes can be added. The specific diameter and number of cylindrical holes are determined by the discharge force. It can be seen from Figure 2 that a threaded hole is designed on the rear surface of the punch, and the backing plate is thickened accordingly, and bolts are installed, and the punch can be positioned and fixed. If the cross-sectional area of the punch is large enough, a threaded hole can be designed on the rear face of the punch and fastened with bolts to prevent the punch from falling off. Through the improvement of this series of examples, the punch has fully adapted to the CNC wire cutting process, and the structure is simple, which is convenient for the CNC wire cutting process.
In the production process, if the mold is used for a long time, some quality problems will occur. The mold must be repaired according to the actual structure of the mold. When designing the mold structure, some reasonable structure should be adopted for design and processing according to the mold processing situation, the structure of the mold, and the performance of the mold material to make the processing of the mold easier, reduce the cost, shorten the manufacturing cycle, and meet the production and processing requirements. Needs.
Eight, the development trend of CNC wire cutting technology
The development space of CNC wire cutting technology in the future is very broad. Due to the complexity of the wire cutting process itself, the mechanism of wire cutting is still immature. Most of the research results are based on a large number of systematic process experiments. Therefore, the in-depth research on the principle of wire cutting is directly used. Guidance and application in practical processing are the fundamentals of the development of CNC wire cutting processing technology. The slow-moving wire cutting has the phenomenon of higher cost, and the fast-moving wire cutting has the problem of relatively low processing accuracy. On the basis of the existing technical level, the continuous development of new processes will be the development direction of CNC wire cutting technology. CNC wire-cutting machine tools will develop in a more reasonable and advantageous direction in terms of structural design and pulse power development; CNC wire-cutting processing will develop toward a higher level of automation and intelligence in terms of control technology; CNC wire The network management technology of cutting processing has been initially applied on high-end machine tools, and will be gradually promoted and applied to obtain better system management effects. In short, CNC wire cutting processing technology aims to improve processing quality, improve processing efficiency, expand processing scope and reduce processing costs, etc., and it is continuously developing in the mold industry.