Anisotropy Effect on Cutting Monocrystal Sapphire by Micro-Laser Assisted Machining Technique

Machining of hard and brittle materials such as ceramics and semiconductors has been a challenge for many years. They have many applications in optics, MEMS and electronic industries due to their many desirable properties, such as being light weight, strong, and hard. Achieving good surface finish, avoiding surface and subsurface damage and at the same time achieving a high material removal rate are extremely challenging for these materials. Materials such as single crystal silicon and sapphire have a crystal orientation or anisotropy effect which makes their machining even more difficult. Because of this characteristic, their behavior is directional and they have different fracture toughness for each direction. In past works in our research group, it has been demonstrated that machining of brittle materials in ductile regime is possible due to the high pressure phase transformation (HPPT) occurring in the material caused by the high compressive and shear stresses induced by a single point diamond tool tip. In the current study scratch tests were performed on the monocrystal sapphire in four different perpendicular directions and to further augment the process, traditional cutting is coupled with a laser to heat and soften the material to either enhance the ductility, resulting in a deeper cut, or reducing brittleness leading to decreased fracture damage. Results of scratch tests, with and without laser heating, for different cutting loads have been compared. The effect of laser heating was studied by analyzing the image of cuts and verifying the depth of cuts which were made using varying laser power during the process. Microscopic images and three-dimensional profiles of the cuts taken by using a white light interferometer were investigated.