Alloy design or three-dimensional printing of hardenable tool materials

Abstract

Three-dimensional printing (3DP) is a state-of-the-art manufacturing technology, One of its many important applications is to fabricate the metal tooling for plastic injection molding. In order to achieve a fully dense 3DP metal tool, the current 3DP process involves five steps: printing, debinding, sintering, liquid metal infiltration and heat treatment. Due to the infiltration requirement, all 3DP tools made to date are composed of a high-strength skeleton material and a low-strength infiltrant. The search for a hardenable/hard 3DP system is the mission of this dissertation. Five major accomplishments can be found in the dissertation: (1) development of the 420/bronze material system for 3DP tooling; (2) development and optimization of the post-processing of the system; (3) development of a computer model simulating the interaction of powder/liquid infiltrant; (4) computer-aided material system design and (5) methodology exploration of the material system development.The 420/bronze material system with a minimum reaction was developed experimentally, by screening 30 potential material systems. Compared to the initial 3DP and reactive system, the system strength was significantly improved. More than 50 3DP injection tools have been fabricated using this material system. A 3DP tool made of the 420/bronze system has been used to mold more than one hundred thousand plastic products without major repairing of the tool. It was the first time that an injection mold was made of 60 vol% 420 and 40 vol% bronze. The system was a milestone in the 3DP material system development. In addition, the post-processing of the system was well established and defined in terms of the procedures and parameters. Four problems associated with the processing were identified. The porosity, erosion, and reaction have been minimized. The dimensional accuracy has been substantially improved. The dimensional error is approaching to an average of ±0.1% in linear dimension. A 3DP tool made of the 420/bronze has achieved the second best in dimensional accuracy among many current rapid prototyping technologies. The procedures and parameters that have been developed serve as a good benchmark for future 3DP system. A thermodynamic database for steels, refractory metals and copper-based infiltrants for use with Thermo-Calc was developed with assessments of fifteen binary systems.

(cont.) Among the fifteen assessments, five were modified from published data; and ten were self-assessed. These data were combined with those in a commercial database to make a customized user database for 3DP materials system design/assessment. The user database has been successfully used for the simulation of a multi-component infiltration reaction. The computer predictions have excellent agreement with the experimental results. The model can be used for the development of a wide range of infiltrated composite materials. The most straightforward approach for materials... selection using this database is to search for a powder/infiltrant combination in which there is very limited tendency for interdiffusion of alloying elements between the powder and infiltrant alloys. Thermodynamic calculations that reveal solubilities of infiltrant elements in the powder alloy, and vice versa, provide an excellent predictive tool for minimizing powder/infiltrant reactions ...