Real-time porosity reduction during metal directed energy deposition using a pulse laser

Abstract

Porosity is a challenging issue in additive manufacturing and is detrimental to the quality of the additively manufactured products. In this study, a real-time porosity reduction technique was developed by incorporating a pulse laser into a laser metal powder directed energy deposition (DED) system. The incorporated pulse laser can accelerate fluid flow within the melt pool and facilitate the escape of pores before complete solidification. It achieves this real-time porosity reduction by inducing accelerated and turbulent Marangoni flow, ultrasonic waves, and shock waves into the melt pool. The uniqueness and advantages of the proposed technique include the following: (1) For a laser metal powder DED process, this study proposed a noncontact, nondestructive, and real-time porosity reduction technique at the melt pool level. (2) It was experimentally and numerically validated that the developed technique did not alter the geometry and the grain structure of the manufactured Ti-6Al-4V samples. (3) Because the porosity reduction is accomplished at the melt pool level, its application is not limited by the size, shape, or complexity of the printing target. (4) The developed technique can be readily incorporated into the existing DED systems without any modification of the original tool-path design. The experimental results showed that the pore volume fraction decreased from 0.132% to 0.005%, no pores larger than 6 × 104 µm3 were observed, and a 91% reduction in the total pore number was achieved when the pulse laser energy reached 11.5 mJ.