Design of a model based feedforward controller for additive manufacturing by laser metal deposition

Abstract

Laser metal deposition, also known as laser cladding or direct metal deposition, is an emerging additive manufacturing technology for the creation of solid 3D-parts. We propose a feedforward controller for the melt pool width that is derived from a first principle model based on the heat conduction equation. Essentially, it adjusts the laser power to the path taken by the machine, thus using another input that is usually kept constant during a production process. The controller is constructed for compatibility with existing computerized numerical control (CNC) for laser metal deposition. This is accomplished by designing the feedforward controller for compatibility with G-code, the standard programming language for CNC machines. Since G-code is not based on time steps or a sampling frequency but, roughly speaking, on velocity and position signals, special care must be taken to ensure compatibility of the proposed model-based discrete-time feedforward controller and the existing CNC machine control. The presented controller is evaluated with a benchmark scenario, where it shows good performance without the need for any additional sensors.