金属AMにおける相変態を用いた応力解放技術に関する研究

<p>For the manufacture of plastic molds and die casting molds, metal optical modeling of the PBF system capable of creating a cooling pipe inside is effective, and effects of shortening of the production cycle and improvement of the accuracy are obtained. However, the metal optical modeling of the PBF system has problems of warpage and cracking, and it is difficult to manufacture a shape object in which stress concentration occurs or a large modeled.</p><p> In this paper, it was investigated that how to suppress warpage and cracking using martensitic stainless-steel SUS420J2 powder, which is commonly used as a mold material for plastics molding.</p><p>The main cause of the generation of the residual stress in the metal optical modeling of the PDF system was considered to be shrinkage generated in melting and re-solidification, and the method of expanding and restoring the contracted part was considered to be effective, and the utilization of the martensitic transformation was examined. Firstly, it was confirmed by on-machine experiments that the Ms point was 95℃ / the Mf point was 24℃ or less for the shaped object made of SUS420J2 powder. From these results, a modeling experiment was conducted at a thickness of 10mm at a table temperature of 24℃, 50℃, 70℃, 90℃, and 120℃ during modeling. As a result, at 70℃, shrinkage during modeling and expansion due to martensitic transformation were balanced and stress was released, and warpage was suppressed to -20μm. Also, an experiment of stress release by cooling at every constant lamination thickness was carried out, and it was confirmed that the appropriate combination of "lamination thickness/table temperature at the time of molding" was "1 mm/96℃", "2 mm/85℃", "3 mm/82℃", "5 mm/80℃" and "10 mm/77℃". As a result of the crack test under this condition, it was confirmed that all cracks occurred in the method of fixing the table temperature at the time of molding up to now, but no cracks occurred at the appropriate "stacking thickness/table temperature at the time of molding" (10 mm/77℃.) obtained by the experiment.</p><p> Finally, comparable results were obtained by comparing the mechanical strengths of the present method and the conventional method.</p>