A new method for drilling holes in graphite workpieces

When processing through holes in graphite workpieces, a conventional machining method was initially adopted. That is, four contour blocks were placed on the workbench of the radial drilling machine to place the graphite workpieces on the contour block (to prevent the drill bit from damaging the work surface). ), After correcting the workpiece according to the scribe, press the workpiece with the pressure plate, and then perform the drilling process. We found that there are two disadvantages of using this processing method. First, the edge of the through hole on the back of the workpiece (ie, through the drilled hole) is prone to chipping at the edge, resulting in product failure; second, single-piece processing, and low production efficiency. . In view of this problem, we have conducted serious thinking. After analysis, the phenomenon of edge collapse after drilling is the result of the following three factors: 1 Graphite is a brittle material with low hardness; 2 When drilling, the axial force is too large. 3 As the workpiece is placed on the contour block, it is suspended when drilling. With the deepening of the drill bit, the rigidity of the workpiece at the drilling hole is gradually weakened, and thethe rigidity was worst when the hole is about to drill through.
After finding the cause of the disintegration, we used the following two measures: 1 When the hole is about to drill through, reduce the feed to achieve the purpose of reducing the axial force; 2 Place a plastic plate under the workpiece ( 20mm thick, that is to artificially increase the rigidity of the workpiece. When the hole in the workpiece is about to be drilled, the cutting edge at the top of the drill bit has entered the plastic plate, so the rigidity of the workpiece is increased, and at the same time, the cutting resistance on the workpiece does not suddenly disappear, which fundamentally eliminates the occurrence of chipping. External factors. Practice has proved that the use of the above measures can better solve the problem of easy disintegration when drilling through holes in graphite workpieces.
However, although the drilling quality of the workpiece is ensured by the above method, since it is a single-piece processing, the problem of low production efficiency has not yet been solved. Therefore, we have further improved the above processing methods:
1 According to the size of the drawings to make drilling dies, taking into account the quality of graphite and mold processing technology and mold material costs and many other factors, we decided to use easy processing and material prices Low PVC plastic plate, as the material for the production of drilling dies;
2 Turn the workpiece with the outer cylindrical surface in 5 pieces and place it directly on the working table of the radial drilling machine (The work surface should be clean and free of oil). The squares are placed 90° apart and close to the outer cylindrical surface of the workpiece to align the workpiece (the external cylindrical surface of the workpiece is formed by the lathe at one time);
3 After aligning the workpiece, carefully place the drilling dies. Above the first workpiece, then press the workpiece with the pressure plate;
4 use the drilling mold to produce holes, drilling depth of 90 mm (ie, the bottom of the workpiece is a blind hole, hole depth of 10 mm);
5 After the drilling is completed, remove the pressure plate and remove the drilling jig on the workpiece. The top 4 workpieces are the finished products, and the lowermost workpiece is used as the drilling jig for the second drilling. This cycle continues until the entire batch. Workpiece plus Completed. When drilling with this method, it is necessary to pay attention to the dimensional inspection of the workpiece which as a jig after processing a certain number of workpieces, so as to avoid the size of the drill hole beyond the drawing requirements due to error transmission.
With the improved new method, under the premise of guaranteeing drilling quality, there are the following 3 advantages: 1 Improved labor productivity, and the production efficiency is 4 times that of single-piece processing; 2 As the drilling does not require special preparation of plastic Pads, thus saving production costs; 3 reduce the use of drilling die, and thus extend the service life of the die. At the same time, this method can also be used for reference when it is used to drill holes in other similar brittle materials.
Author：Jiyong Liang