Investigation On Laser Crack-free Cutting Of Ceramics

Structural ceramic is one of the most used engineering materials for a variety ofindustrial applications. Unfortunately, conventional machining techniques areunsuitable to machine ceramics due to their high hardness and brittleness. Lasermachining has offered an alternative for rapid processing of brittle and hardengineering ceramics. However, the material properties, especially the high thermalexpansion coefficient, would cause ceramic workpiece fracture due to thermal crackformation. It is a barrier of ceramics to be applied in industries. The major challengesto laser cutting of ceramics are crack formation, low process efficiency, low finishsurface quality, and low processing precision. In order to face these challenges, theprocess in laser cutting of ceramics was theoretically and experimentally studied inthis work.Crack-free drilling is the first step for crack-free laser cutting. The crackformation in laser drilling is attributed to the thermal-stress development. Based onthe theoretical study, experimental investigation and numerical simulation, the processparameters of laser peak power, pulse duty cycle and pulse repetition rate wereoptimized, by which crack-free, low-taper and low-spatter-deposition through-holedrilling was achieved.In laser cutting of thick-section ceramics, the high laser peak power, short pulseduration, low pulse repetition rate and high feed rate contribute to significantly reducethermal stress distribution and hence resist crack formation. The laser close-piercinglapping （CPL） cutting technique was therefore presented, by which crack-free cuttingof10-mm-thick alumina ceramics can be achieved. Based on the CPL technique, alow pulse rate cutting strategy was proposed. Crack-free cutting of6-mm-thickalumina ceramics was achieved by a CO₂laser and a fiber laser, respectively. Thecutting speeds were both increased to90mm/min.The laser controlled fracture peeling technique was developed for damage-freeremoval of recast layer on laser cut surface. The formed subsurface roughness is2.18μm. The microstructure of the formed subsurface is same as the base material. A paraxial positioning device based on “twice positioning” method was also proposed inorder to meet the requirement of the high absolute positioning precision in laserfine-cutting of electronic ceramics. This technique increases the absolute positioningprecision up to the stage precision and makes the laser cutting stage suitable to cuttingof ceramic substrate with pre-printed circuit. A new approach of opticalsuper-resolution imaging: scanning particle-lens imaging （SPI） was also demonstratedin this work. The imaging resolution is <50nm （λ/8）, which would open newopportunities to direct imaging of nano-structures on electrical insulating ceramics.