A fundamental investigation on ultrasonic vibration-assisted laser engineered net shaping of stainless steel

Laser engineered net shaping (LENS), a laser beam deposition additive manufacturing method, has been utilized as a key technology in the direct manufacturing or repairing of metal parts. However, deposition defects such as pores, cavity, micro-cracks, residual stress, and uncertain microstructures always exist in the LENS fabricated parts, which will greatly affect the qualities and mechanical properties. In this paper, a novel ultrasonic vibration-assisted (UV-A) LENS process is proposed to reduce or eliminate the common defects due to the nonlinear actions and influences of ultrasonic vibration in molten materials. An experimental investigation is conducted on the effects of ultrasonic vibration on fabricated part geometry, powder utilization efficiency, surface roughness, geometry of molten pool and dilution zone, pores and micro-cracks, and grain size of the LENS-deposited AISI 630 stainless steel. The mechanical properties including tensile properties and hardness of the fabricated parts are evaluated and compared between UV-A LENS and LENS without ultrasonic vibration. The results show that process with ultrasonic vibration led to higher powder utilization efficiency, smaller flatness and surface roughness, and larger molten pool dimensions. Pores and micro-cracks were successfully reduced and crystal grains were significantly refined in UV-A LENS process. The improvement of these geometrical and microstructural characteristics induced by ultrasonic vibration further led to the increase in both tensile properties and hardness of LENS fabricated parts. The fundamental investigation in this work will help to establish an efficient and effective process for additive manufacturing and remanufacturing of metal parts with significantly improved qualities.