High throughput hybrid laser assisted machining of sintered reaction bonded silicon nitride

Silicon nitride is a high-performance ceramic reserved for the most demanding high-temperature structural applications due to its elevated strength, fracture toughness, corrosion resistance and hardness. These aspects also make it extremely difficult to machine, leading to component costs that are prohibitive in many fields where its physical properties could nonetheless provide improvements in performance, efficiency and lifespan. In the present work, precision two-step laser assisted machining of sintered reaction bonded silicon nitride is performed to reduce grinding forces and improve tool service life. Laser surface treatment is first undertaken at 15 mm/s with a 980 nm wavelength 3.3 kW diode laser focused to a 32 mm × 2 mm rectangular spot, inducing thermal cracks to a depth of approximately 615 μm with 2.5-3 kW laser power, corresponding to an energy dose of 4.7-5.6 J/mm2. Grinding tests are then performed on the treated areas, confirming a reduction in peak and average machining forces of approximately 26-27% where thermal cracks are present. A numerical simulation is developed to provide insight into the failure mechanisms leading to thermal cracking and afford a relatively simple method of selecting laser parameters for real mechanical components.