(1) Ultra-Precision Manufacturing based on femtosecond laser
Chemically-strengthened glass is exclusively used for the display panel of today’s smartphones and tablet PCs, but due to its deeply stress-compressed surface, cutting the strengthened glass into desired shapes is not an easy task. Several cutting methods mostly relying on mechanical tools or lasers are currently being employed in industry; examples are sand blast, water jet, laser ablation and crack propagation. Conventional glass cutting leaves behind surface cracks and heat-affected zones that have to be removed by adopting post-treatments based on grinding, etching and cleaning, which are hazardous to environment. In order to realize the concept of green manufacturing and also improve the production throughput, it is demanded to develop ideal processes that are capable of slicing the strengthened glass without post-treatments using toxic chemicals.
In this research, femtosecond laser pulses are used to examine the possibility of establishing an ideal cutting process for the strengthened glass. The intension is to optimize the input heat flux so that the strengthened glass is cut by means of crack propagation along not only straight lines but also curved contours of complex patterns, preferably in a single path. For the purpose, a fiber-based femtosecond laser source has specially been built, which permits controlling the pulse energy and repetition rate over an extensive range. At the same time, the focusing depth location of laser pulses within the glass substrate is precisely adjusted with aid of a high resolution auto-focusing technique.
Experimental results show that the process parameters can be combined to effectively induce seed-crack which is created from side and immediately stretched vertically over the cross-section. The crack propagation across the glass substrate is then carefully steered to follow curved paths by controlling the feed rate of the laser beam. A remarkable feature is that the crack propagation can be regulated to maintain a ~100 μm lateral offset from the laser beam path. Consequently, contoured cutting is realized with a mirror-like profile free from heat-induced damages. We are trying to understand the fundamental phenomena of this cutting event, and to enhance the cutting speed and accuracy.