Material removal with constant depth in CNC laser milling based on adaptive control of laser fluence

Computer numerical control CNC laser milling is an innovative technology to produce precision parts in micron and even nanometer scale. However, due to the restriction of dynamic performance of the machine tool, the preset feed rate cannot be reached immediately, and the actual feed rate is unpredictable when the part with rapidly varied geometric feature is machined. At this moment, the incident laser energy is still the default value, so the feed rate below the target value will cause excessive accumulation of laser fluence into the workpiece surface, eventually leading to an inhomogeneous milling depth and developing the excessive heat affect zone (HAZ). Aiming at the problem in CNC laser milling of the parts with rapidly varied geometric feature in this study, a method of real-time adaptive control of laser fluence according to actual feed rate was proposed. Firstly, a prediction model of laser milling depth was established. Then, based on the model and small amount of preliminary trials, laser fluence required at arbitrary feed rate was obtained to realize the material removal with constant depth. Furthermore, the adaptive control technology of laser fluence on the basis of actual feed rate was investigated. By monitoring the actual feed rate of the machine tool and regulating the laser fluence with it, the machining depth of the parts with rapidly varied geometric feature by CNC laser milling can remain constant. CNC laser milling experiments conducted in this paper demonstrate the feasibility and veracity of the adaptive control strategy.