Processing technology and key points of lower-speed wire cutting punch

Lower speed wire-cutting machine tools are widely used and of great significance. In the production and processing of plastic molds and precision multi-position progressive die, it can not only ensure good dimensional accuracy, but also directly affect the assembly accuracy of the mold, the accuracy of parts, and the service life of the mold.

Punch Processing Technology

　　The punch plays a very important role in the mold. Its design shape, dimensional accuracy and material hardness directly affect the punching quality, service life and accuracy of the stamping parts. In actual production and processing, in order to reduce the residual stress deformation inside the workpiece blank and the thermal stress deformation caused by discharge, it is necessary first to use an electric spark drilling machine (brass electrode tubes , copper electrode tubes ) to make threading holes, and then make a closed cut to avoid distortion from an open cut as much as possible. If the closed cutting cannot be performed due to the size of the workpiece blank, for the square blank, it should be taken care to select the cutting route (or cutting direction) during programming. The cutting route should be conducive to ensuring that the workpiece is always kept in the same coordinate system with the EDM JIG (EDM Plain Vice ,Wire EDM Extensions Clamp, Wire EDM Clamp, etc.) during processing, avoiding the influence of stress deformation. The EDM JIGs are fixed at the left end, and the workpiece is cut in a counterclockwise direction from the left side of the workpiece. The entire blank is divided into left and right parts according to the cutting route. Because the material connecting the left and right sides of the blank is cut smaller and smaller, the right side of the blank is gradually separated from the fixture, which cannot resist the internal residual stress and deforms, and the workpiece is also deformed. If cutting in a clockwise direction, the workpiece is left on the left side of the blank, close to the clamping part. Most of the cutting process keeps the workpiece and the fixture in the same coordinate system, which has better rigidity and avoids stress deformation. In general, a reasonable cutting route should arrange the cutting section where the workpiece and the clamping part are separated at the end of the overall cutting program, that is, leave the bridge close to the clamping end of the blank.

The following focuses on analyzing the cutting process of cemented carbide tooth punch.Usually, the reserved connection part (Bridge, that is, a small section of cutting track line reserved so that the workpiece is not completely separated from the blank after the first rough cutting) is often left in the plane position for lower speed processing. After most of the fine cutting is completed, only one cut is made on the reserved connection part, and then the fitter will grind and smooth it, which can reduce the processing cost of the punch in the slow wire cutting.

Due to the high hardness and narrow shape of the carbide punch materials, we recommend the use of zinc coated wire. Compared with the brass electrode wire, the zinc coated wire can increase the cutting speed by 25% and reduce the deformation, but in the case of irregular shape, the grinding of the reserved connection part will bring great difficulty to the fitter. Therefore, the process can be properly adjusted in the process of lower speed wire cutting, so that the dimensional accuracy of the shape can meet the requirements, and the grinding process of the bridge before assembly by the fitter is eliminated.

Due to the high hardness of cemented carbide and large cutting thickness, the processing speed is slow and the torsional deformation is serious. Most of the shape processing and the processing of the reserved connection part (Bridge) are cut in 4 times, and the cutting parameters and offsets of the two parts are the same. The offset of the first cutting electrode wire is increased to 0.5-0.8mm, so that the workpiece can fully release the internal stress and completely torsional deformation. In the next three times, there can be enough margin for fine cutting processing, so that the final size of the workpiece can be guaranteed.

The specific process analysis is as follows:

• Threading holes of Φ0—Φ1.5mm are machined in advance at the appropriate position of the workpiece blank with a drilling machine, and the length of the lead-in cutting line between the center of the threading hole and the punch contour line is selected to be 5—10mm.
• The width of the contour line of the punch and the edge of the blank should be at least 1/5 of the thickness of the blank.
• The connection part (Bridge) reserved for subsequent cutting should be near the center of gravity of the workpiece blank, with a width of 3-4mm.
• In order to compensate the torsional deformation, most of the residual deformation is left in the first rough cutting stage, and the offset is increased to 0.5-0.8mm. The next 3 times adopt the fine cutting method, and because the cutting allowance is small, so the deformation amount is also smaller.
• After 4 times of cutting and processing most of the shape, the workpiece is blown dry with compressed air, and then the end face of the workpiece blank is washed with alcohol solution, dried, and then the metal with a thickness of about 1.5mm that has been ground by the grinder is ground with a binder. Stick the sheet firmly on the blank, and then cut the reserved connection part of the workpiece according to the  4 offsets as before(Note: Do not drip glue into the lower nozzle, wire guide, conductive block or the reserved connection part of the workpiece , so as not to cause non-conductivity and cannot be processed).

WEDM has high processing precision and strong function, but the processing cost is also expensive. In order to give full play to the role of the machine tool and create good economic benefits, it is necessary to carry out a reasonable processing technology analysis of the workpiece to maximize its effectiveness.