Controlled-fracture of prescored alumina ceramics using simultaneous CO ₂ lasers

While brittle materials such as ceramics will clearly be at the forefront of improved energy efficiency, manufacturing problems related to shaping have proven to be troublesome. Fortunately, the usage of laser machining to shape structural ceramics is increasingly gaining acceptance as an alternative to traditional grinding and cutting methods. Despite the great promise of lasers for a variety of cutting and drilling procedures, premature fractures, poor surface quality, microscale damage, and prohibitively low cutting-speeds are still among the greatest obstacles, especially as the thickness is increased. While many factors contribute to the fractures encountered during laser machining, it is the inevitable and localized increase in temperature and the ensuing thermal stresses that usually cause the damage. As such, the minimization of heat buildup and the resulting thermal stresses often requires the slow and expensive practice of multiple pass or interrupted cutting or drilling. To help control fractures and allow faster machining, a unique method of simultaneously scoring and cutting known as "prescoring" was explored using alumina plates. This concept has now been used to refine the "controlled fracture" approach, where thermal stresses are used to drive a propagating crack along a preordained path using simultaneous CO ₂ lasers. Using this technique and a systematic design of experiment approach to investigate the effects of various parameters, the use of the dual-beam technique was shown to be capable of predictably controlling fractures in relatively thick alumina plates. In addition to providing a clean fracture surface, this method was also shown to be capable of machining these specimens faster and with less energy input than other laser machining procedures will allow.