Investigating and eliminating powder separation in pre-mixed powder supply for laser metal deposition process

摘要

Laser Metal Deposition (LMD) is an effective process to fabricate customized material compositions using pre-mixed powders. The deposited material composition is expected to be similar or same as supplied powder mixture. The current investigation is aimed at optimizing and setting up powder feed capable of producing consistent composition ratio in the output material using LMD process. Through experimental investigation the authors identified an important phenomenon: separation in powder mixture during flow from feeder to melt pool. Such separation can cause severe composition deviation in deposited material. This paper introduces a novel particle size optimization method as the solution to eliminate the powder separation. Two types of experiments were done in this study. First, pure Cu and 4047 Al powders were mixed with equal volume percentages (50%-50%), and were transported from the powder feeder to the deposition site. The flow out of the feed tube was captured and preserved in an epoxy resin coating. The volume percentage of each type of powder was plotted by quantifying the distribution of different particles in the pattern. Clear powder separation and consequently composition deviation was found in the first experiment result. During the second experiment, powder mixtures with the same volume percentage composition was transported and captured. However, the particle size distributions of Al4047 and Cu were optimized to equalize the particle acceleration during transportation in the feed tube. By optimizing powder size to equalize acceleration the powder separation was observed to be effectively eliminated. The composition deviation was also significantly reduced. The results from this study are pathbreaking contributions in the research of customized material fabrication with pre-mixed powder in LMD process.