Application of wire cutting in mould processing

1. The processing principle of wire cutting processing:

The principle of wire cutting processing is to use the wire storage drum, the upper and lower frames to make the molybdenum wire reciprocate at high speed. 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, and the pulse power supply brings the positive and negative electrodes to the molybdenum wire and the workpiece respectively, and the high temperature generated by the discharge melts and vaporizes the metal, so that the excess part of the workpiece is cut off according to the predetermined trajectory, and we need. A processing method of mold structure, wire cutting processing is divided into fast wire feeding and slow wire feeding, fast wire feeding has low processing precision and low cost, and fast wire feeding has high cost and high processing accuracy.

2. Basic features:

(1) As the technology of wire EDM becomes more and more perfect, a CAD/CAM system from graphic input to machining process has been formed, which realizes the automation of EDM machining. In the production process, complex shapes and plane geometric contours can be cut out.
(2) Due to the discharge of the positive and negative electrodes, the temperature of the processing point can be as high as 10,000 °C, and within this temperature range, various metal objects can be melted. Therefore, it can process all kinds of high hardness metals, such as hardened tool steel, cemented carbide, polycrystalline diamond, etc.
(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.

3. Optimisation of the wire route

In the wire cutting die, optimizing the wire routingof 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 comprehensively analyzed according to the size, shape and accuracy requirements of the workpiece, the size of the discharge gap of the electrode wire and the size of the gap of the concave and convex die, and combined with the following points: ① In general, Try to arrange the wire routing during the cutting process of the part and keep the support frame for clamping the part in the same coordinate system to ensure the accuracy of positioning; ② The starting point of the wire routing should be arranged in the direction away from the part fixture for cutting , and finally turn to the direction of the fixture to cut, and arrange the separation cutting at the end of the wire line; ③ During the cutting process, the corners (or sharp corners) of some molds are prone to collapse (or rounding), which should be appropriate according to the specific situation. Trimming the wire route and process parameters; ④ For some molds with high precision requirements, in order to reduce deformation, improve the metamorphic layer on the surface of the mold, and increase the service life of the mold. ⑤Due to the diameter of the electrode wire and the discharge gap, sometimes a high line protruding from the cutting surface will appear at the junction of the cutting surface of the die. When cutting, according to the structure of the mold, the cutting route should be selected reasonably, and the phenomenon of bulge during the processing should be avoided as much as possible.

4. Determination of the discharge gap

In the actual production process, there are many factors that affect the discharge gap of the wire cutting process, mainly including: the mechanical properties of the mold material, the structure and shape of the mold, the technical requirements of the mold, the speed of the wire electrode wire, the tension force, and the operation of the guide wheel. Status, type of working fluid, concentration and degree of contamination, as well as electrical standard 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 the same test piece as the mold material, and try to cut a square. Then, measure the discharge gap, and then calculate a reasonable offset, which is used as the adjustment basis for the center line of the electrode wire (the actual wire trajectory). In addition, the size of the discharge gap will also vary depending on the mold material. In general, materials with a low melting point have a larger discharge gap than materials with a high melting point, quenched steel has a larger discharge gap than unquenched steel, and materials with small heat capacity and poor thermal conductivity have a correspondingly larger discharge gap.

5.The choice of mold matching 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 cross-sectional quality of the blanking part, and affects the service life of the die. The gap of the mold is selected according to the thickness of the mechanical properties of the part to be processed. As the blanking material changes from soft to hard, the gap between the convex and concave dies gradually increases. The gap can generally be selected according to 10% to 12% of the material thickness. Usually, for soft materials (such as soft aluminum, pure copper, etc.), the gap is selected according to 10% to 12% of the thickness of the blanking part; for semi-hard materials (such as hard aluminum, brass, etc.), the thickness of the blanking part is selected according to the thickness of the blanking part. For hard materials (such as thin steel plates, silicon steel sheets, etc.), it is selected according to 15% to 20% of the thickness of the blanking part. In addition, appropriate micro-adjustments should be made according to the shape characteristics, precision requirements and technical conditions of the blanking parts, as well as the structure and precision of the mold. Due to the characteristics of wire cutting processing, the selection of the gap between the convex and concave molds of the wire cutting processing mold should be slightly smaller than the conventional data, so as to prolong the service life of the mold and obtain higher quality parts.

6. Determination of the actual size of the cutting edge of the blanking die

Cutting edge wear determines the size of the blanking piece. The cutting edge size of the punch and the concave die is directly related to the dimensional accuracy of the blanking piece. After the cutting edge is worn, the size of the blanking piece becomes larger. For the blanking die, the size of the part is close to the size of the die, and the actual processing size of the die edge should be close to or equal to the minimum limit size of the blanking part during wire cutting; for the punching die, the size of the part is close to the punch. Wire cutting requires that the actual processing size of the punch edge should be close to or equal to the maximum size of the punching hole. In this way, on the premise of ensuring the dimensional accuracy of the blanking parts, it is beneficial to prolong the service life of the mold and improve the economic benefit.
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 machining accuracy of the mold should be selected according to the accuracy of the parts. In order to reduce the cost, according to the processing conditions of the mold, the manufacturing accuracy of the punch should be one level higher than that of the concave.

7.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 should be taken according to the actual situation to solve it. If the main part of the mold (convex and concave mold) has cracks on the cutting edge, it is normal to re-cut the material and re-process 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 the CNC wire cutting technology to process the mold. Improvements to mold structure design.
The traditional punch is usually designed with three steps, the smallest step is the working edge, the middle platform is the fixed positioning step, and the largest step is the axial positioning step to prevent the punch from being pulled out of the fixed plate, and one of these three steps is missing. No, each has its own function. The CNC wire cutting punch is processed after quenching, and can only be processed into a straight punch that is consistent up and down. According to this feature, if the punch is designed as a straight table, how to fix the punch and the fixing plate? The 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 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 should have high hardness, but the rear part should not have hardness, which brings great difficulty to the heat treatment of the punch. Obviously, these two This method is not a simple, economical and reliable method. Through a lot of experiments, I have concluded a set of punch structures that are fully adapted to the CNC wire cutting process. If it is a short and narrow 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 done by inserting the pin into the side cylindrical hole. After the punch is cut, the cylindrical hole is cut from the outside to the inside on the wire 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 inserted into the axial fixing pin and pressed against 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 out on the fixing plate accordingly, and a pin can be 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 threaded holes are designed on the rear face of the punch, the backing plate is thickened accordingly, and bolts are installed, the punch can be positioned and fixed. If the cross-sectional area of the punch is large enough, threaded holes can be designed on the rear face of the punch and fastened with bolts to prevent the punch from falling off. Through this series of improved punches, it has been fully adapted to the numerical control wire cutting process, and the structure is simple, which is convenient for numerical control wire cutting processing.
In the production process, if the mold is used for a long time, there will be some quality problems. The mold should be repaired according to the actual structure of the mold. When designing the mold structure, some reasonable structures should be designed and processed according to the mold processing situation, mold structure, and mold material performance, so as to make the mold processing easier, reduce costs, shorten the manufacturing cycle, and meet the production and processing requirements. needs.

8. The development trend of CNC wire cutting technology

The future development space of CNC wire cutting processing technology is very broad. Due to the complexity of the wire cutting process itself, the mechanism of the wire cutting process is still immature so far, and most of the research results are based on a large number of systematic process experiments. Guidance and application in practical machining are the foundation of the development of CNC wire cutting machining technology. The slow-moving wire cutting has the phenomenon of high 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 supply development; CNC wire cutting processing will develop towards a higher level of automation and intelligence in control technology; CNC wire cutting The network management technology of cutting processing has been initially applied in high-end machine tools, and will be gradually promoted and applied to obtain better system management effects. In a word, CNC wire cutting processing technology is developing continuously in the mold industry with the goal of improving processing quality, improving processing efficiency, expanding processing scope and reducing processing costs.