Injection mold EDM is widely used in precision cavity mold manufacturing.
The so-called “mirror EDM” generally refers to the EDM with a surface roughness value of Ra<0.2μm and a mirror reflection effect on the surface. Mirror EDM for some precision machining can replace the manual polishing process, improve the quality of parts, has practical significance.
1. Type of processing
The mirror effect of electric discharge machining is directly related to the carbon black layer produced in electric discharge machining. If the processing part can quickly form a uniform carbon black layer, it means that it is easy to process a mirror effect.
2. Mold steel
The mirror effect can be quickly achieved in some die steel EDM, while in any case, it cannot be achieved in some other die steel. Additionally, the hardness of the mold steel is higher, resulting in a superior EDM mirror effect.
3. Some requirements for electrodes in mirror EDM
The electrode materials commonly used for mirror EDM are copper and chromium copper, with the latter exhibiting less electrode loss. When selecting copper material, it is crucial to ensure uniform texture and minimal impurities as poor quality copper can result in abnormal phenomena such as significant electrode loss and surface wrinkling during mirror processing. Although copper alloy electrodes may achieve low levels of electrode loss, they do not produce satisfactory mirror effects.
Notes for mirror EDM
a. Control the machining allowance of mirror EDM
The process of EDM is a process from roughing to finishing. First of all, the roughing electrode is used to corrode a large amount of metal under the condition of ensuring a certain processing quality (dimensional accuracy, shape accuracy, position accuracy, surface roughness), so as to shorten the processing time and improve the processing efficiency. Then replace the finishing electrode and use a smaller discharge energy to finish the finishing. Whether it is roughing or finishing, multiple discharge conditions will be used, and the current is also from large to small, through the depth feed to repair the light bottom, through the translational repair of the light side.
b. Reasonable use of discharge parameters and machining control of mirror machining
In processing using negative polarity processing, the selection of some non-main electrical parameters is also very important, and the choice of conventional processing, there are also some differences, such as the discharge time to set longer, the lifting tool height is shorter, the lifting tool speed can not be too fast, the purpose of this setting is to maintain a stable small energy electrical corrosion process, because in mirror processing, itself will not produce a lot of electrical corrosion products, Too often the knife lifting action will interfere with the continuous and stable discharge.
The electrical corrosion ability of mirror machining is very weak, and the processing takes a long time. Because the dimensional change of mirror processing has been very small, only the role of polishing, in fact, as long as the processing to the required surface roughness can be finished, therefore, the timing processing function of CNC EDM machine tool can be used, according to experience to determine how long the processing time.
c. Large area processing using powder mixing technology to achieve mirror processing effect
Mixed powder EDM is a technology to improve the surface roughness of EDM.
The so-called mixed powder EDM refers to the addition of micro powder, such as silicon powder, aluminum powder, chromium powder, and related additives, in the working fluid in order to obtain a mirror effect on the processed surface. The use of mixed powder processing technology can obtain faster processing speed (reducing finishing time by 20%-30%) and better surface roughness than that without mixed powder processing technology under the same electrical parameter conditions. For the large area of EDM, it has a significant improvement effect.
