Nondestructive evaluation and real-time monitoring of laser surface hardening

An infrared process monitor was used to monitor in real-time the infrared emissions during laser surface hardening of ferrous alloys. The signals from the monitor were correlated with the hardness and case depth of the laser-treated tracks. Test data show that a linear relationship exists between the monitor output DC level voltage and hardness up to the maximum hardness possible and also between the monitor output DC level voltage and case depth. This simple relationship makes it easy to monitor process hardness, case depth and quality of laser heat-treated workpiece. A calibration test on a prototypic material can be used to determine the upper and lower bounds of the voltage signals for a sound quality treatment. In-process monitoring or real-time nondestructive measurement of the hardness and depth of the laser transformation hardened case can then be achieved. The monitor is also capable of tracking changes in surface quality or flatness of the part that is being treated.