Study Of Criterion Of Material Removal Mode Of Single Crystal Silicon In Micro USM

Monocrystalline silicon, piezoelectric quartz and engineering ceramincs are widely used in the fields of aerospace, medical and automotive because of their excellent physical properties such as high hardness, high temperature resistance and corrosion resistance. With the progress of micromachining technology, the demands for the dimensional accuracy and surface integrity is increasingly improved. Therefore, Micro ultrasonic machining (MUSM) becomes the most suitable processing method for hard-and-brittle materials because the material removal by MUSM is not limited by the electrical conductivity and thermal conductivity.Many scholars have also observed the ductile machining characteristics in hard and brittle materials in turning, milling and grinding and other processing methods. Conventionally, the removal mode of hard-and-brittle materials in MUSM is dominated by the brittle mode in which the machined surfaces are usually covered with many collapse pits and cracks. The material mechanical properties with such surface are reduced significantly. It is reported that the ratio of ductile removal increase by adjusting machining parameters properly in MUSM and the surface integrity can be improved. However, the current method to identify brittle or ductile removal mode in MUSM generally depends on the personal observation other than an unbiased method to avoid human factor involving in the evaluation. In this study, extensive experiments of MUSM without tool rotation are conducted to find the criterion of material removal mode in MUSM. After the image observation, data analysis and verification tests, the range of brittle-ductile transition critical force of monocrystalline silicon<100> in MUSM was found. When the impact force of single abrasive particle in MUSM is less than0.065g, the ductile removal is achieved. When the impact force of single abrasive particle is larger than0.15g, the machined surface shows the brittle material removal characteristic.Between these two values of impact force, the material is removed in ductile-brittle transaction mode in MUSM. The machined surfaces under various conditions of MUSM were analyzed by an interferometer. It was found that the surface roughness, Rpk, is suitable to identify the material removal mode in MUSM. When Rpk is larger than500nm, the surface is machined in brittle mode. When Rpk is less than450nm, the surface is generated in ductile mode. The ductile-brittle transaction mode in MUSM can be identified when the Rpk is between450nm and500nm.In addition, experiments of MUSM with tool rotation are carried out. It was found that the surface roughness Rpk is also applicable to identify the material removal mode of MUSM. To study the influence of machining conditions on the machined surface roughness by changing the input variables such as tool rotation, particle size and vibration amplitude, it was found that the tool rotation in MUSM has little effect on the roughness of machined surface, compared with that of without tool rotation MUSM. Under the same impact force of single particle, the surface roughness by large abrasive grains larger than that by small abrasive grains. Vibration amplitude has little influence on the surface integrity.