Neuro-fuzzy Control of Laser Percussion Drilling

Abstract

Non-Conventional methods have recently been employed in the drilling of materials such as super alloys which are hard to machine using mechanical conventional methods. These materials are mainly used in turbines in the power generation and aerospace industries. One of the recently developed non-conventional methods for drilling is using pulsed lasers whereby a laser beam is focused to a spot equal in diameter to the hole to be drilled. Pulsed lasers such as Nd:YAG are mainly employed for this process. Laser percussion drilling is commonly employed to produce holes with small diameters, usually less than 1mm. With percussion drilling, the control of hole parameters such as taper, entrance and exit hole variation and roundness is difficult and these parameters are of utmost importance for small holes. Selection of machining parameter combinations for obtaining optimum circularity at entry and exit and minimum hole taper is a challenging task owing to the presence of a large number of process variables. There is therefore need to develop a control system that is able to adjust the various process parameters to the optimum values and hence control the drilling process. This paper discusses a neuro-fuzzy controller developed to control the hole diameters and taper through in-process adjustments of laser power and pulse duration. The controller is based on MATLAB and Lab VIEW platforms. The controllerwas implemented by simulating a laser drilling environment. It is seen that while using the controller, the diameters increase with increase in peak power and pulse duration upto an optimum level beyond which the peak power and pulse duration do not increase. The hole taper decreases with increase in peak power and pulse duration up to optimum level beyond which the peak power and pulse duration do not increase. Thus, the controller helps maintain the peak power and pulse duration at optimum levels.