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Method to Reduce Final Part Deformation Using Thermal Control of the Directed Energy Deposition Process

Kyle Starr Odum

出版	University of California, Davis, 2019
ISBN	13926307119781392630716
URL	http://books.google.com.hk/books?id=qpv7zgEACAAJ&hl=&source=gbs_api

註釋

Directed energy deposition (DED) is an additive manufacturing (AM) technique where a high power, high intensity energy source is used to locally melt the surface of a metal part (the meltpool) while simultaneously delivering a metal feedstock into the meltpool. The feedstock completely melts and fuses to the substrate after cooling. Though DED parts are subject to essentially no mechanical loads during fabrication, final part distortion from heat is a common problem. The very large thermal loads create very large thermal gradients in DED parts during fabrication. Literature has shown that the thermal gradients contribute to the final part distortions in DED. Much of the literature regarding DED part distortion focuses on methods that minimize the energy input into the process to minimize the thermal gradients and heat affected zone sizes in DED parts. Minimization of input energy has been shown to be a somewhat effective method of distortion minimization, however the productivity and efficiency of the DED process suffers when input energy is decreased. In this thesis a methodology to reduce distortion in DED parts without reducing input energy is presented. Through experiments and numerical simulations of DED a dependency of the final part mean surface curvature distribution on the magnitude of the in-process thermal gradient near the meltpool is established. Also, observed was localized buckling of the substrate when excessive, non-uniform part heating occurred. Reducing the mean thermal gradient magnitude near the meltpool is shown to reduce final part curvature when substrate structural stability is maintained. A closed loop thermal control system and toolpath planning are used to manipulate the in-process thermal history of DED parts to flatten the thermal gradient near the meltpool and avoid overheating of the substrate. Numerical modeling, hardware and software development, and physical experiments were completed to develop and test the distortion optimization methodology in simple stainless-steel parts.