Application of mashan EDM technology in mold manufacturing (2)
Second, the main factors affecting the quality of mold EDM Previous page next page
The processing quality of the mold mainly includes the processing precision and the quality of the etched surface. Since the input and output parameters in the EDM process are many and complicated, the process factors affecting the machining accuracy of the mold involve the manufacturing precision of the machine itself, the clamping accuracy of the workpiece, the manufacturing and clamping precision of the electrode, the electrode loss, and the discharge gap. , processing slope and many other aspects, which have a large impact on electrode loss and discharge gap.
1. Influence of electrode loss on machining accuracy
In the process of die electric discharge machining, the pulse discharge will cause the tool electrode to be corroded and damaged, so that the electrode loss law can be understood and mastered, and various measures are taken to minimize the loss of the tool electrode, which can ensure the higher processing of the mold. Precision. In EDM, the loss of the different parts of the tool electrode is different. Generally, the electric field strength of the convex part such as the sharp corner and the edge is high, and the tip discharge is easy to form, so the loss is faster than the flat part, and the unevenness is uneven. Loss will inevitably lead to a decrease in machining accuracy.
At the same time, the loss of the electrode is also affected by the thermal physical constant of the electrode material. The melting point, boiling point, specific heat capacity, melting and vaporization latent heat of the electrode material are higher, and the higher the thermal conductivity, the better the corrosion resistance and the stronger the heat transfer capability, thereby reducing the loss of the electrode.
2. Influence of discharge gap on machining accuracy
In the EDM mold, the pulse discharge between the tool electrode and the workpiece needs to maintain a certain discharge gap, so that the processed workpiece hole size is different from the electrode size, and a discharge gap is different along the machining contour. The discharge gap mainly determines the processing stability, and generally increasing the pulse discharge gap time can improve the processing stability. Increasing the peak current will increase productivity, but the electrode loss will increase.
The surface metamorphic layer is deepened and the roughness becomes large. In order to keep the discharge gap stable, it is necessary to keep the electrical parameters of the pulse power supply stable. In addition, the accuracy and rigidity of the machine tool should be kept stable, and special attention should be paid to the influence of the secondary discharge caused by the electrolytic corrosion product on the discharge gap.
3. Influence on the surface roughness of the machined surface
The roughness evaluation parameter Ra of the etched surface increases as the pulse width and current peak increase. Under certain processing conditions, the increase of pulse width and current peak will increase the energy of a single pulse and increase the cross-sectional size of the etch pit. Therefore, the surface roughness mainly depends on the energy of a single pulse. To reduce the value of the surface roughness Ra, the energy of a single pulse must be reduced.
4. Effect of surface change layer on mold surface quality
The surface of the mold after EDM processing will produce a surface change layer comprising a solidified layer and a heat affected layer. The solidified layer is a metal layer that melts under the action of the instantaneous high temperature of the pulse discharge and cannot be thrown. The metal layer is rapidly cooled and solidified after the end of the pulse discharge. The metal grain of the layer is very small and has a strong Corrosion resistance.
The heat-affected layer is located between the solidified layer and the workpiece matrix material, and the metallographic structure of the material changes due to the high temperature transmitted from the discharge point. In the process of processing, due to the selected electrical parameters, cooling conditions and the original heat treatment conditions of the workpiece material, the hardness of the changing layer will change differently. The thickness of the surface change layer is related to the electrical properties of the workpiece material and the pulse power source, and is thickened as the pulse energy increases, and the hardness of the solidified layer is generally high. Therefore, the surface wear resistance of the mold after EDM is better than that of ordinary machining.