Cold Metal Transfer-Gas Metal Arc Welding (CMT-GMAW) Wire + Arc Additive Manufacturing (WAAM) Process Control Implementation
Type of DegreePhD Dissertation
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While additive manufacturing is comprised of metal and polymer fabrication, current additively manufactured polymer-based products are much further from being put into industrial applications. Metal-based additive manufacturing is comprised into wire- and powder-based processes. While the powder processes have the advantage of fine detailed resolution, they are limited by the production rate it takes to produce these fine details. Wire processes have much higher deposition rates, while at the same time having lower start-up, production, and consumable costs. Due to these reasons, a wire-based system was chosen for this research. A Fronius Cold Metal Transfer (CMT) welder has been modified to a CNC 3-Axis gantry system for the purposes of a Wire + Arc Additive Manufacturing (WAAM) system. One of the biggest issues currently with additive manufacturing is the lack of control over the process. Issues such as scale error, thermal management, and variable control plague the technology. Many work-arounds have been developed to increase productivity, repeatability, and reliability (such as scaling, pausing, or trail-and-error); however, no real-time process control has been implemented successively on a broad basis. This research attempts to close the gap on control over the WAAM process via multiple control schemes. The three biggest issues noted in literature are issues with scale error, thermal management, and process variable control. Closed-loop feedback control systems have been developed, analyzed, and quantified to address these specific issues. The control schemes have been successfully evaluated and have indeed improved the WAAM process. Mechanical properties such as ultimate tensile strength, yield strength, and hardness have been characterized at multiple temperatures and via different welding control lines. Support material such as wiring diagrams, operating manuals, and operational machine codes have also been developed for replication of this research and to further the research started here. Using the results found in this research, future users can easily produce quality additive metal parts quickly, efficiently, and easily thanks to the controls developed to aid in the ease of using WAAM. The use of all the control schemes in conjunction with each other is highly recommended for all future users for all occasions. This not only benefits the user and the ‘printed’ part, but also the machine. In additive manufacturing the need for optimal mechanical properties is not always necessary. Often a simple working prototype for proof of concept is all that is necessary. In this case the fastest method, without compromising the machine, is best. If material strength is to be optimized, maintaining a low temperature set point, without sacrificing time, is recommended for both materials (steel, stainless). Isotropic tendencies were found in steel, and near-isotropic properties were found in stainless with the combined control schemes.