In Situ Pre-heating in Wire Arc Additive Manufacturing: Design, Development, and Experimental Investigation on Residual Stresses and Metallurgical and Mechanical Properties

Wire arc additive manufacturing (WAAM) employs an electric arc-based deposition process, but achieving the desired mechanical and metallurgical properties in WAAM is challenging. The pre-heating phase is critical for reducing residual stress and maintaining consistent heat input. This study introduces an automated induction-based pre-heating system integrated and made compatible with WAAM, evaluating its effectiveness on low carbon steel (ER 70S-6). The induction pre-heater is designed to meet application-specific needs, with dynamic power adjustments based on material composition and substrate size. It comprises a power source, cooling chiller, coil box, and pyrometer for temperature monitoring. Deposition is done using a CNC system utilizing a Cold Metal Transfer Metal Inert Gas (CMT-MIG) setup, comparing samples with and without pre-heating at maximum temperature. The study employs various techniques, including Electron Back-Scattered Diffraction analysis, x-ray diffraction, microhardness testing, and tensile tests, to assess the impact of pre-heating on dilution, grain size, residual stress, and mechanical properties. The results of this investigation illustrate that pre-heating markedly augments dilution by 15-20%, thereby fortifying interlayer bonding. Additionally, it refines the grain structure, diminishes residual stress by up to 50%, and elevates tensile strength by 10%, accompanied by an approximate 20% increase in hardness value for low carbon steel. The induction-based pre-heating system innovated in this research seamlessly integrates with Wire Arc Additive Manufacturing (WAAM), providing significant benefits in attaining the desired mechanical and metallurgical properties for additively manufactured components.