Geometry modeling and control by infrared and laser sensing in thermal manufacturing with material deposition

A lumped-parameter, analytical model of material and thermal transfer is established in this paper for metal deposition by a moving, concentrated source. This is a dynamic description of the distinct width, height, length, and temperature of the ellipsoidal molten puddle, expressed with respect to the torch power, material feed and angle, and the source motion. This is established through scalar mass, momentum and energy balances of the puddle control volume, and thermal conduction in the substrate. The model is validated by GMA welding experiments, through measurements by an infrared camera and a laser profilometry scanner. These sensors are next employed for real-time identification of the model efficiency parameters, and for output feedback in a closed-loop geometry control system. Because of sensor delays, the model is run in-process to provide substitute estimates to the controller in a Smith predictor scheme. Closed-loop testing was conducted for control of the bead cross section profile through the torch velocity, and the applicability of such geometry regulation to solid freeform fabrication is discussed.