Analysis on the concept of wire cutting in die processing.

The development of science and technology has promoted the development of industry and greatly promoted the processing of welded pipe molds, especially complicated welded pipe molds. In particular, EDM (wire cutting) machining method has been widely used in the processing of welded pipe dies because it can process complex straight-through and small taper cavities, with high cutting accuracy and good processing quality, and is not limited by the hardness of the workpiece. Foshan Yonghao found that reasonable process analysis, reasonable welded pipe mold structure design and reasonable processing technology analysis are related to the processing accuracy of welded pipe mold. It is an effective and important way to improve the cutting process by determining the wire piercing hole and optimizing the cutting route.

1.WEDM's machining principle: WEDM's principle is to use wire storage cylinder, upper frame and lower frame to make molybdenum wire reciprocate at high speed, in which bearings and guide wheels are arranged in the upper and lower frames to control the vertical accuracy and straightness of molybdenum wire, and the workpiece acts between the upper and lower frames and is supported by two pads. The pulse power supply charges 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 redundant part of the workpiece is cut off according to the predetermined trajectory. A processing method of welded pipe die structure that we need is obtained. WEDM is divided into fast WEDM and WEDM. High-speed WEDM has low machining accuracy and low cost, high cutting cost and high machining accuracy.

Second, the basic characteristics:

(1) With the improvement of WEDM technology, a CAD/CAM system from graphic input to machining process has been formed, and the automation of WEDM has been realized. In the manufacturing process, the plane geometric contour with complex shape can be cut.

(2) Due to the discharge of positive and negative electrodes, the temperature of the machining point can be as high as 10000℃, and various metal objects can be melted within this temperature range. Therefore, it can process various metals with high hardness, such as quenched tool steel, cemented carbide, polycrystalline diamond and so on.

(3) The sharp corners and clear corners that often appear in the mold cavities of many complicated welded pipes are difficult to realize in machining. If it is a through hole or a through hole with a small taper, this problem can be easily solved by wire cutting technology.

Third, the optimization of wiring.

Optimizing the electrode wire routing is beneficial to improve the cutting quality of welded pipe WEDM and shorten the die processing time. Therefore, in routing programming, the following factors 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 gap of the concave-convex die:

(1) In general, the layout of the parts shall be arranged as far as possible in the process of cutting, and the supporting frame of the clamping parts shall be kept in the same coordinate system to ensure the accuracy of positioning;

(2) The starting point of routing should be arranged to cut in the direction far away from the fixture of the parts, and finally cut in the direction of the fixture, and the separation cutting should be arranged at the end of routing;

(3) In the cutting process, some corners (or sharp corners) of welded pipe die are prone to collapse (or rounding), so the routing and process parameters should be adjusted appropriately according to the specific situation;

④ For some high-precision welded pipe dies, in order to reduce deformation, improve the deteriorated layer on the machined surface of welded pipe dies and prolong the service life of welded pipe dies.

⑤ Because of 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 welded pipe die. When cutting, according to the structure of welded pipe die, the cutting route should be selected reasonably to avoid bulging in the processing.

Fourth, the determination of discharge gap

In the actual production process, there are many factors that affect the discharge gap of WEDM, mainly including: the mechanical properties of welded pipe die material, the structural shape of welded pipe die, the technical requirements of welded pipe die, the wire feeding speed and tension of electrode wire, the running state of guide wheel, the type, concentration and dirt degree of working fluid, and the electrical specifications and parameters of pulse power supply.

In the actual operation process, in order to accurately determine the discharge gap, before each programming, according to the set processing conditions, take the specimen with the same material as the welded pipe mold and try to cut a square. Then, measure the discharge gap and calculate the reasonable offset as the adjustment basis of the center line (actual line path) of the electrode line. In addition, the size of discharge gap will be different with different welded pipe die materials. Generally speaking, the discharge gap of low melting point materials is larger than that of high melting point materials, and quenched steel is larger than that of non-quenched steel, and materials with small heat capacity and poor thermal conductivity are correspondingly larger.

Verb (abbreviation of verb) Selection of Fit Clearance of Welded Pipe Mould

The reasonable determination of the fit clearance between punch and die of blanking die is directly related to the precision and section quality of blanking parts, and affects the service life of welded pipe die. According to the mechanical properties and thickness of the machined parts, the gap of welded pipe mold is selected. As the blanking material changes from soft to hard, the gap between punch and die gradually increases. Generally speaking, the gap can be selected between 10% and 12% of the material thickness. Generally, for soft materials (such as soft aluminum, pure copper, etc. ), the gap is selected as 10% ~ 12% of the thickness of the punching sheet; For semi-hard materials (such as hard aluminum, brass and so on. ), selected as12%-15% of the punching thickness; For hard materials (such as thin steel sheet, silicon steel sheet, etc.). ), according to 15% ~ 20% of the thickness of stamping parts. In addition, some fine adjustments should be made according to the shape characteristics, accuracy requirements and technical conditions of stamping parts, as well as the structure and accuracy of welded pipe die. Due to the characteristics of WEDM, the gap between convex and concave die of WEDM should be slightly smaller than the conventional data, so as to prolong the service life of welded pipe die and obtain higher part quality.

Determination of actual size of cutting edge of intransitive verb blanking die

The determination of the size of blanking parts by cutting edge wear is directly related to the dimensional accuracy of punch and die blanking parts, and the size of blanking parts becomes larger after cutting edge wear. For the blanking die, the size of the part is close to that of the female die, and the actual machining size of the female die cutting edge is required to be close to or equal to the minimum limit size of the blanking part during wire cutting. In the stamping die, the size of the part is close to that of the punch, and the actual machining size of the punch cutting edge is required to be close to or equal to the maximum size of stamping. In this way, on the premise of ensuring the dimensional accuracy of blanking parts, it is beneficial to prolong the service life of welded pipe die and improve economic benefits. In the production process, reasonable processing methods should be adopted according to the processing situation of welded pipe mold to meet the processing requirements of welded pipe mold, and the processing accuracy of welded pipe mold should be selected according to the accuracy of parts. On the premise of meeting the accuracy requirements of parts, the manufacturing accuracy of welded pipe mold should be reduced as much as possible to reduce the cost. According to the processing situation of welded pipe die, the manufacturing accuracy of male die should be one level higher than that of female die.

Seven. Application of WEDM in Welded Pipe Mould

In production, some quality problems will appear after the welded pipe mould is used for a period of time, and some measures should be taken to solve them according to the actual situation. If the cutting edge of the main parts of the welded pipe die (convex-concave die) has cracks, it is conventional to re-blank and re-process the welded pipe die. But now, we can use wire cutting technology and "cutting insert method" to repair welded pipe mold. In order to adapt to the NC wire cutting technology to process welded pipe die.

Improvement of die structure design for welded pipe. The traditional punch is usually designed into 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 to prevent the punch from being pulled out of the fixed plate. These three steps are indispensable and each has its own function. CNC WEDM punch is processed after quenching, and can only be processed into a straight punch with the same top and bottom. According to this feature, if the punch is designed as a straight table, the traditional method of fixing the punch and the fixing plate is bonding and riveting, and the practice proves that the bonding is not reliable. It's easy to fall off at work. Although 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 hardness in air, and the working part of the punch should have a high hardness, but the back part cannot have hardness, which brings great difficulties to the heat treatment of the punch. Obviously, these two methods are not simple, economical and unreliable. Through a lot of experiments, I summed up a set of punch structure which is completely suitable for NC wire cutting. If it is a short and narrow punch, it can be designed as a straight table according to the working position of the punch, and the same step is also used for positioning and fixing the punch. The axial fixation is fixed by inserting the pin into the lateral cylindrical hole. This cylinder is cut from the outside to the inside by the punch, so there is a cutting seam of about 0. 1mm behind the punch. After the pin is inserted into the axial fixing pin and pressed against the fixing plate, the strength of the punch is not affected. Cut a cylindrical hole on the punch, correspondingly mill a semicircular groove on the fixing plate, install a pin, and completely position and fix the punch. If it is a narrow and long punch, more cylindrical holes can be added, and the specific diameter and number of cylindrical holes are determined by the discharging force.

The rear end face of the punch is designed with a threaded hole, the backing plate is correspondingly thickened, and bolts are installed to position and fix the punch. If the cross-sectional area of the punch is large enough, a threaded hole can be designed at the rear end face of the punch and fastened with bolts to prevent the punch from falling off. Through the improvement of this example, the punch has been completely adapted to the CNC wire cutting process, and the structure is simple, which is convenient for CNC wire cutting. In the production process, there will be some quality problems when the welded pipe die is used for a long time. According to the actual structure of welded pipe mould, the welded pipe mould is maintained. When designing the structure of welded pipe mold, we should adopt some reasonable structures to design and process according to the processing situation, structure and material properties of welded pipe mold, so as to make the processing of welded pipe mold easier, reduce the cost, shorten the manufacturing cycle and meet the needs of production and processing.

Eight, the development trend of CNC wire cutting technology

The development space of numerical control WEDM technology in the future is very broad. Due to the complexity of the WEDM process itself, the mechanism of WEDM is still immature, and most of the research results are based on a large number of systematic process experiments. Therefore, the in-depth study of WEDM principle and its direct guidance and application to actual machining are the basis for the development of numerical control WEDM technology. WEDM has the phenomenon of high cost, and high-speed WEDM has the problem of relatively low machining accuracy. On the basis of the existing technical level, it will be the development direction of numerical control WEDM technology to continuously develop new technologies. Numerical control WEDM will develop in a more reasonable and advantageous direction in the structural design and development of pulse power supply. Numerical control WEDM will develop to a higher level of automation and intelligence in control technology. The network management technology of numerical control WEDM has been initially applied in machine tools, and will be gradually popularized to obtain better system management effect. In a word, the numerical control WEDM technology is developing continuously in the welded pipe mold industry with the goal of improving processing quality, improving processing efficiency, expanding processing scope and reducing processing cost.