Experimental Study On Drilling C/C-SiC Composites

C/C-SiC is a kind of advanced composite material. Featuring in high hardness, low density, corrosion resistance, anti-oxidant performance, preferable mechanical property at high temperature and thermal physical property excellent, this kind of composite material has been increasingly and widely applied as a new high-temperature structural material and functional material in fields including aerospace and automobile. Nonetheless, C/C-SiC has the characteristic of anisotropy in terms of its mechanical property; what’s worse, with the mal condition for machining and its low interlaminar strength, the delamination, dilaceration and edge collapse may easily appear during the process of C/C-SiC cutting under the effect of cutting force. On the other hand, with the characteristics of high intensity and high hardness of C/C-SiC due to the existence of SiC, the cutting tools would easily be worn and even lose efficacy; besides, the drilling process would be more difficult. Therefore, C/C-SiC is a kind of typical difficult-to-machine material. Focusing on the C/C-SiC composites, this thesis studies its mechanical property and microstructure and performs experimental study on the axial force produced during the cutting process, the quality of the draw bore and tool wear condition.Through determining the properties of C/C-SiC and the observation and analysis to its microstructure, the thesis draws the conclusion that C/C-SiC with a relatively high content of SiC presents the characteristics of relatively low bending strength and quite poor breaking toughness. Under the same sample material, the property of C/C-SiC presented on the condition that pressure direction goes perpendicular with carbon fiber placement direction would significantly outperformed that of C/C-SiC presented on the condition that pressure direction goes parallel with carbon fiber placement direction. The fracture mode of C/C-SiC is mainly brittle fracture with the manifestation of neat brittle fracture, fiber pull-out and fiber separation in terms of carbon fiber.With brazed diamond bit and electroplated diamond bit, the drilling experiment on C/C-SiC is performed to study the effects of tool material and machining parameter on cutting force. The result indicates that under the same machining parameter, cutting force caused by brazed diamond bit is smaller than caused by electroplated diamond bit, cutting force is significantly affected by feed, which means that under that same rotate speed, axial force would be on increase with the increase of feed and that under the same feed, axial force shows the tendency of decrease as rotate speed increases; in addition, with the increase of hole machining, drilling force presents the tendency of gradual increase. With a relatively high content of SiC, the drilling force produced during the drilling process would accordingly become greater, at the same time, the drilling axial force on the condition that carbon fiber placement direction goes perpendicular with drilling feed direction would be significantly smaller than the drilling force on the condition that carbon fiber placement direction goes parallel with drilling feed direction.Observe the processing quality of hole thorough scanning electron microscopy and compare the processing quality of holes based on different parameters. Then after analysis, we concluded that the main processing defects are edge collapse, tear and delamination. Along with the increase of feed, the processing quality is getting poor. As the speed increases, the processing quality of the hole is getting better and the quality of entrance is much better than that of the exit. The quality of holes processed by brazed diamond bit is better than that by electroplated diamond bit. The quality of holes made from materials whose content of SiC is low is much better. The quality of holes is best when the drilling parameters are n=5500r/min and f=20mm/min. The edge collapse defects are not only related to processing defects of materials themselves but also related to carbon fiber direction and cutting direction. Tear and delamination often occur at the exit of the hole. To gain better processing quality, we can set graphite plate to the exit and reduce input.Observe the wearing conditions of diamond particles through scanning electron microscopy and study about them with different parameters. The results show that the wearing conditions of diamond particles mainly include crushing, fracture and shedding. The wearing degree caused by brazed diamond bit is lower than that caused by electroplated diamond bit. The wearing degree caused by electroplated diamond bit of those C/C-SiC composite materials which contains much more SiC is higher. The wearing degree caused by brazed diamond bit when the feed direction and carbon fiber ply direction are vertical is lower than that when the two directions are parallel. Besides, the wearing mechanism is analyzed in this paper. Due to the various distribution of diamond particles, the wearing forms of diamond particles are also different. Unlike the bonding strength of binders, the wearing forms and degree are also different.