Process Modeling, Monitoring and Control of Laser Metal Forming

Laser Metal Forming (LMF) process is one of the prominent Rapid Prototyping (RP) process that can be used to develop functional and fully dense metal parts. This paper addresses process modeling, monitoring and control of a laser metal forming system currently under development at Laser Aided Manufacturing Processes (LAMP) laboratory at University of Missouri–Rolla. This LMF system is based on a 2.5kW Nd:YAG laser as energy source and integrates five axis metal deposition and five axis machining. The current paper is aimed at characterization of effects of operating parameters such as traverse speed, mass flow-rate and laser power on the LMF process. A low cost monitoring system is being developed using off the shelf sensors like infrared temperature sensor, near infrared CCD camera and laser displacement sensor to measure the process index parameters. A closed loop control structure has been simulated for online control of the LMF process. Introduction In today’s competitive world, the critical factors for success are product quality, time to market and cost. A faster development cycle requires the production of a highly accurate model directly from the CAD data. Rapid prototyping (RP) technologies offer a viable solution for this purpose. RP technology was commercially introduced in 1987 with stereolithography apparatus (SLA). Currently many commercial RP systems such as selective laser sintering (SLS), laminated object manufacturing (LOM), fused deposition modelling (FDM), solid ground curing (SGC) are available. However all these systems can only fabricate geometrically identical parts and not functional parts. Some progress has been made to use these RP techniques for the rapid manufacture of functional parts such as mold cavities and investment and vacuum-castings. Along with these commercial efforts, lot of research has been going on to design and develop rapid manufacturing processes to directly fabricate functional metal parts. One of the techniques that’s been widely developed by several of these research groups is the direct metal layered manufacturing. In Layered Manufacturing, solid model of the part is built layer-by-layer using material delivery or a curing system capable of tracing out the layer. Yevko et al. [1] classified these methods into two groups, depending on the techniques as conventional welding-based processes and laser-based powder spraying processes. Dickens et al. [2] introduced 3D welding based on the technology of MIG welding process. In this method, a robot-mounted MIG torch is used to build the part via layer-by-layer welding. The accuracy of this process has been reported in the literature at about ± 0.5 mm. Hartmann et al [3] introduced this layer-by-layer fabrication method where the part is built by deposoiting layers composed of primary and a support structure material. Deposition of layers is carried out using variety of techniques such as thermal spraying, welding and microcasting. Five axis machining is used to shape the layers and shot-peened to control the residual stresses. The support structure is removed by etching when the building process is completed.