An Experimental Study on Edge-Breakage of Explosive Parts in Machining Using Micro-Photographic Observation Method

Crack on the sharp edge remains a major concern and a key problem cries for solution in the course of explosive cutting currently. The adoption of the idea that enlarges the cutting zone and records the cutting behaviors again has founded the micro-photographic system for the cutting process. Tests have found that this system can be applied to research the nucleation and expansion of deep rock crack and the formation and dropping of the chips. The extension direction that controls the cracks is the key to resolve the cracks on the sharp edge. As for the initial stage of cutting, the cracks usually expand from the relatively weak surface of the work piece, while the final stage of the cutting, the cracks point to the weak end face through the inner part of the work piece. The latter is easier to have the cracks on the sharp edge comparing to the former. Working orthogonal rake of tool is an important factor that affects the extension direction of the cracks. At the final stage of the cutting, if the working orthogonal rake is -6°, the angel from the crack extension direction to the main cutting direction is -35°. When the working orthogonal rake is 9°, the angel turns to be -54°. This has shown that enlarging the working orthogonal rake to a certain extend can lower the degree of crack on the sharp edge. In addition, tests have found out that the relatively small working orthogonal rake is likely to bring out potential cracks. However, enlarging the rake angle excessively will lower the rigidity of the tool and thus add risks of shocking.