A Novel Study of Applying Indentation Plastometry on the WAAM Deposit

Abstract

This study explores the potential of using Profilometry Indentation Plastometry (PIP) to develop a methodology for guiding the process parameters optimisation in large-scale Wire Arc Additive Manufacturing (WAAM) deposits. The reliability of PIP measurements in evaluating the mechanical properties of WAAM deposits is assessed in comparison to traditional mechanical testing methods, while also examining how process parameters influence the microstructure and mechanical properties (material responses). The focus is more on the mechanical properties including the hardness, yield strength and tensile strength as the material (Mn Si alloyed steel solid wire, ER70S-6) investigated is well developed and studied in the literature.
The research focused on depositing sample using two deposition modes for investigating the material responses to the process. The two deposition methods are pulsed welding and Super Active Wire Process (SAWP) using a Gas Metal Arc Welding (GMAW) system from Panasonic. SAWP is a short circuit welding process working together with its mechanical push pull motor to manage heat input. A total of 119 samples were produced from single bead ramping tests, along with three larger blocks (250 mm × 90 mm × 250mm) deposited using heat inputs of low, medium and high levels, respectively. The mechanical behaviour of the ramping samples was measured using a PIP device and then the measurements were analysed through curve fitting to find any potential physical trends. An exponential relation was found between the material response and the heat input. Additional single beads were also deposited on the substrate with different starting temperatures using a selected condition. This to simulate the bead deposition when depositing 3D block. Subsequently, the cross sections of these samples were prepared and measured using the PIP device. The trend curves then plotted with different exponential power index to find the correlation between the PIP measurements and the substrate starting temperature. These curve plotted together with PIP measurements of the samples extracted from the block deposited using different heat inputs, in which a good agreement was found. These results shown that it is promising to develop a systematic procedure that can correlate the single bead depositions with the large scale component to be deposited. The PIP measurements can help to reduce the R&D lead time and to guide the parametric optimisation when using WAAM for 3Dmetallic printing. The power index value may have correlation with the cooling rate, as the resulting material properties are determined by the resulting microstructure, which depending on its chemical composition, grain size and orientation. These are interested aspects to be further investigated but cannot be included in this thesis.
Additionally, the obtained results also shown that the methodology of combining the single bead ramping together with the PIP measurement can effectively guide the selection of processing conditions and inter pass temperature for larger WAAM deposits, which are important conditions to define the 3D printing procedure. Process parameters, particularly heat input, had a significant impact on the resulting mechanical properties of WAAM deposits, with a too high heat inputs, it can lead to reduced hardness. PIP hardness measurements shown a good agreement with the Vickers hardness measurements, and PIP strength measured shown reasonable agreement with the uniaxial tensile test results. It was noticed that yield strength measured using the PIP device shown the values systemically lower than the uniaxial measurements. This is likely due to limitations in the device’s fitting model inputs that has been predefined within the PIP device as a Blackbox towards the normal user. Further researches are expected to enable a better utilization of the PIP device to measure the WAAM deposits. Meanwhile it also expected that the device manufacturer (in collaboration with us in this thesis work) can further improve the device stability, accuracy and user friendliness based on our feedback that has been communicates. Nonetheless, the main research question of using PIP for assisting speed up of the process optimization was successfully answered.