Study On High Speed Drilling Of Brittle Thin-wall Graphite

As the traditional fossil energy is non-renewable and pollutional, solar photovoltaic industry is developing rapidly and this caused the solar photovoltaic industrial graphite boat pieces are demanded heavily, as well as the accuracy of graphite boat slice is constantly increasing. Graphite has heterogeneity structure of the brittle material, uneven, porous structure. It can be easily cracked during the machining process,which affects the hole quality in graphite boat piece drilling. Research on high speed drilling of thin-walled brittle graphite piece helps to improve manufacturing efficiency and quality. It's valuable and important to develop solar photovoltaic industry.Lots of drilling experiments on brittle thin-wall graphite boat piece have been done in this paper. A detailed analysis has been made on drill thrust and torque, drilling process,hole formation process, hole quality,through theoretical analysis, experimental analysis and optimization design.On drilling process and the quality of the hole, orthogonal cutting and drilling process, hole entrance and cross section shape were observed through the axial stepping into methods by high speed camera and digital microscope. It's found that the chip shape is spurious ribbon or flocculent under small depth of cut in 0-0.06mm;with moderate depth of cut in 0.06-0.12mm,several small collapse chips appear; with large depth of cut in 0.12-0.24mm, the chips mostly are break-up. The formation of the hole has close relation on drill structure. There are crack, avulsion and scrape on the outside of the hole. The diameter of hole is very important for assembling. The main detects in the machining process are cracks in the entrance of the hole, hole wall surface coarse and fine crack, crush in the outside of the hole, roundness and size error. Suggestions were purposed on how to improve the quality of the hole, such as raising drilling speed, the rational choice of drilling parameters and cutter, jig optimization and so on.On drilling thrust and torque in high speed drilling of brittle thin-wall graphite boat piece, drill bit structure, the effect of drilling parameters on drilling thrust and torque, and the influence significantly of various factors, by single factor experiment and the orthogonal experiment. In experimental parameters range, the drilling thrust and torque have declined along with the increase of drilling speed gradually; with the feed increase, the drilling thrust increase, however, the torque decreased, but volatile. The bit of drill structure is another main factor to the drilling characteristics. The drilling thrust and torque of manual twist drill is smaller than that of three blade drill. It is helpful to reduce the drilling thrust and torque and to improve the quality of the hole.WC twist drill and TiAlN coating twist drill wear process can be divided into three stages:initial wear stage, stable wear stage and sharp wear stage. The wear of drill happened mainly on drill blade, cutting edge sword, and flank, the flank was especially significant. The main wear form is abrasive attrition. "Micro cutting" is the major wear mechanism in the steady stage of WC twist drill, TiAlN coating twist drill is "polishing" abrasive attrition and "micro cutting" abrasive attrition both.