Basic Study on Remelting Process to Enhance Density of Inconel 625 in Direct Energy Deposition

Abstract

Although the applicability of additive manufacturing (AM) to the production of complex shapes has attracted attention from the automobile and aerospace industries, companies hesitate to introduce AM processes because of their low reliability, which is due to pores inside the produced parts. Consequently, many researchers have experimentally evaluated the relation between the pore evolution and production conditions in AM processes. On the other hand, several studies have focused on finishing processes in order to enhance the quality of AM production, considering that production quality cannot be improved enough only by modifying the production conditions in AM processes. To reduce pores in a metal product, hot isostatic pressing (HIP), which applies high pressure and heat energy to metal AM products and enhances production density, has proven to be an efficient approach. However, special equipment is required to produce a high-temperature and high-pressure environment, leading to high cost and low productivity. From the view point of practicability, a simple finishing process would be a fundamental solution to make metal AM processes highly reliable. This paper therefore proposes a method of reducing pores through a remelting process in the direct energy deposition of Inconel 625. Furthermore, a method of doing a graphical analysis to evaluate the bias of pore distribution in the deposited object is proposed. The pore reduction effect in remelting is experimentally evaluated by irradiating the low density area with a laser beam, and a graphical evaluation clarifies that the concentration of residual pores occurs in the top layer of a deposited object. As a result, residual pores are eliminated with certainty through the remelting process. The density of the deposit can be enhanced easily and without any complicated finishing systems with just the laser system originally introduced in a DED machine.