Multi-axis direct metal deposition process with effective regrouping strategy

Abstract

Direct metal deposition (DMD) process has been regarded as a promising additive manufacturing technology. But this process is hard to fabricate structures with overhang features in a support-free manner because the machine equipped with a 3-axis platform could only fabricate structures in 2.5 dimensions instead of 3 dimensions. Therefore, the multi-axis DMD process has been developed to fabricate complicated metal structures without support combined with the motion of the platform. Decomposition operation of the input 3D model to generate several sub-volumes and the following regrouping operation of the sub-volumes are two key procedures in the multi-axis printing process. We adopt the decomposition strategy to obtain the horizontal deposition bases on the previous depth after rotation operations of the platform. However, the traditional regrouping strategy may result in excessively accumulated temperature fields at the connecting regions, especially for some hard-to-print materials like nickel-titanium alloy (NiTi). To solve these problems, the multi-axis DMD process with an improved regrouping strategy is developed in this paper. A novel sequence planning algorithm is proposed by minimizing the cost function to avoid excessively accumulated temperature fields. The cost function is directly related to the moving distance during the regrouping of sub-volumes at connecting regions. Numerical simulations with different interval time values are conducted to determine the cost function. Experiments are conducted to validate the effectiveness of our proposed multi-axis DMD algorithms. Three groups of “Y shape” samples are fabricated using different strategies for comparison and then various characterizations are carried out. Results show that compared with traditional decomposition and regrouping strategies, the samples fabricated with our proposed algorithms could obtain the pore-free morphology, higher microhardness value, and more homogeneous and fine microstructures. Therefore, our proposed strategies in this paper can significantly improve the characterization and microhardness of the fabricated structures during the multi-axis DMD process.