Process Mapping for Laser Metal Deposition of Wire using Thermal Simulations : A prediction of material transfer stability

University essay from Karlstads universitet/Fakulteten för hälsa, natur- och teknikvetenskap (from 2013)

Abstract: Additive manufacturing (AM) is a quickly rising method of manufacturing due to its ability to increase design freedom. This allows the manufacturing of components not possible by traditional subtractive manufacturing. AM can greatly reduce lead time and material waste, therefore decreasing the cost and environmental impact. The adoption of AM in the aerospace industry requires strict control and predictability of the material deposition to ensure safe flights.  The method of AM for this thesis is Laser Metal Deposition with wire (LMD-w). Using wire as a feedstock introduces a potential problem, the material transfer from the wire to the substrate. This requires all process parameters to be in balance to produce a stable deposition. The first sign of unbalanced process parameters are the material transfer stabilities; stubbing and dripping. Stubbing occurs when the energy to melt the wire is too low and the wire melts slower than required. Dripping occurs when too much energy is applied and the wire melts earlier than required.  These two reduce the predictability and stability that is required for robust manufacturing.  Therefore, the use of thermal simulations to predict the material transfer stability for LMD-w using Waspaloy as the deposition material has been studied.  It has been shown that it is possible to predict the material transfer stability using thermal simulations and criterions based on preexisting experimental data. The criterion for stubbing checks if the completed simulation result produces a wire that ends below the melt pool. For dripping two criterions shows good results, the dilution ratio is a good predictor if the tool elevation remains constant. If there is a change in tool elevation the dimensionless slenderness number is a better predictor.  Using these predictive criterions it is possible to qualitatively map the process window and better understand the influence of tool elevation and the cross-section of the deposited material.

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