An increasing demand for flexibility and product integration, combined with reduced product development cycles, leads to continuous development of new manufacturing technologies such as additive ...manufacturing. Wire and arc additive manufacturing (WAAM) provides promising technology for the near net-shape production of large structures with complex geometry, using cost efficient production resources such as arc welding technology and wire materials. Compared to powder-based additive manufacturing processes, WAAM offers high deposition rates as well as enhanced material utilization. Because of the layer-by-layer built up approach, process conditions such as energy input, arc characteristics, and material composition result in a different processability during the additive manufacturing process. This experimental study aims to describe the effects of the welding process on buildup accuracy and material properties during wire arc additive manufacturing of aluminum structures. Following a process development using pulse cold metal transfer (CMT-P), linear wall samples were manufactured with variations of the filler metal. The samples were analyzed in terms of surface finishing, hardness, and residual stress. Furthermore, mechanical properties were determined in different building directions.
A reasonable material hardening model (MHM) should be determined for the accurate prediction of welding residual stresses (WRS) in numerical simulation. The present study methodically investigated ...the impact of material laws on the simulated residual stresses in ultra-high strength steel S960 weldments. Furthermore, mechanical tensile tests were performed to obtain the stress-strain curves and welding experiments were carried out to determine thermomechanical results for validation. The numerical and experimental results express that the amount of strain hardening for ultra-high strength steel S960 is very low at room temperature (RT) and high temperatures, while that is non-ignorable at medium temperatures such as from 200 to 500 °C here. The applied material plasticity model has almost no influence on the computed longitudinal residual stress in numerical simulation of S960 steel. Nevertheless, the predicted magnitude of transverse residual stress could be slightly affected by the employed MHM. For ultra-high strength steel S960, the perfect-plastic (non-hardening) model can accurately predict WRS, which is recommended to use in numerical simulation.
Preheating is generally required in the welding of ultra-high strength steels (UHSSs) for avoiding cold cracking. The present work systematically explores the influence of preheating on welding ...residual stresses (WRS) in components made of UHSS by means of both experiments and numerical simulations. The results reveal that, no matter what UHSS is with or without metallurgical phase transformation, preheating has a great influence on the magnitude of transverse residual stress (σT-RS). In general, the higher preheating temperature (TPH) the lower magnitude of σT-RS is. Preheating would change the longitudinal residual stress (σL-RS) sign in the weld area and σL-RS amount obviously diminishes with the increase of TPH for transforming UHSS, while that has nearly no influence on the maximum σL-RS but has an impact on the area of tensile σL-RS for non-transforming UHSS. The effect of entire preheating and partial preheating on WRS in UHSS welded components could be nearly the same. Nevertheless, TPH in the partial preheating case (about 300 °C here) should be higher than that in the entire preheating one (corresponding 100 °C here) for that same effect. The weld dimensions, especially the size of the heat-affected zone (HAZ), and cooling time Δt8/5 significantly increase with TPH. Preheating has almost no influence on the restraint degree of welded components.
Wire and arc additive manufacturing (WAAM) provides a promising alternative to conventional machining for the production of large structures with complex geometry, as well as individualized low ...quantity components, using cost-efficient production resources. Due to the layer-by-layer build-up approach, process conditions, such as energy input, deposition patterns and heat conduction during the additive manufacturing process result in a unique thermal history of the structure, affecting the build-up properties. This experimental study aims to describe the effects of thermal cycling on the geometrical and material properties of wire arc additive manufactured Al-5356 aluminum alloy. Under consideration, that Al-5356 is a non-heat treatable alloy, a significant effect on geometrical formation is expected. Linear wall samples were manufactured using pulsed cold metal transfer (CMT-P) under variation of wire-feed rate, travel speed and interpass temperatures. The samples were analyzed in terms of geometry; microstructural composition; hardness and residual stress. Furthermore, the mechanical properties were determined in different building directions.
Buckling distortion as a troublesome engineering issue is easily generated in thin-plate arc-welded components (generally less than 4 mm in thickness). This study aims to clarify the impact of ...welding sequence and external restraint on out-of-plane deformation in thin plates for finding out an effective and practical strategy for the prevention of welding-induced buckling distortion. The experimental method was utilized for investigation here. The experimental results reveal that the external restraint cannot prevent buckling distortion in the thin-walled weldments, while it can significantly mitigate the amount of transverse (about 4 mm here) but not longitudinal bending. The welding sequence method can prevent buckling distortion, but it cannot eliminate the transverse bending induced by the non-uniform temperature field in the thin-plate thickness direction. In the present work, the transverse bending in the symmetrical welding is the lowest (about 4 mm), while that in the back-step welding is the largest (around 7 mm). Furthermore, symmetrical welding and continuous welding introduce the lowest (about 1 mm) and highest (about 4 mm) longitudinal bending, respectively. Both external restraint and welding sequence could affect the buckling distortion mode. For the thin-plate arc-welded components, symmetrical welding combined with external restraint is a very effective strategy for the prevention of buckling distortion.
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•The relationship between deposition patterns and their characteristics is revealed.•Porosity and microstructure depend on local peak temperature and temperature gradient.•Residual ...stresses are related to the uniformity of global temperature distribution.•The S pattern produces smaller coarse-grain size, less porosity, and lower residual stress.
Quality assurance is one of the largest challenges to the widespread adoption of metal additive manufacturing technology. Deposition pattern can significantly impact the temperature distribution during manufacturing process and thus the overall quality and residual stress formation of the manufactured components. In order to explore the intricate relationship, three different deposition patterns in DED-Arc additive manufacturing, the meander pattern, the spiral pattern and the newly developed S pattern, were experimentally and numerically scrutinized in terms of the resulting temperature distribution, grain size, porosity as well as residual stress formation. The study reveals that the variation of the deposition paths results in characteristic temperature fields and gradients with distinct local peak temperatures that determine the deposition quality, and simultaneously offers great degrees of freedom for optimal pattern design. Comparing the results with different deposition patterns, the S pattern leads to a more homogeneous temperature distribution, showing beneficial effects on the microstructure, porosity and residual stress formation in the deposited Al-4046 material, and is thus regarded as a promising alternative for improving additively manufactured parts quality.
The temperature- and phase-dependent yield strength plays a decisive role in the precise prediction of residual stresses in structural steel weldments. Since it is very expensive and time-consuming ...to directly measure the yield strength of a given steel by experimental method, numerical simulation has commonly been performed using the available yield strength of the same steel grades in scientific literature and material database or using the evaluated data based on the empirical formulations in standards/codes for the given steel. Nevertheless, the yield strengths of the same steel grades are usually different mainly due to the disparity in chemical composition and grain size. Furthermore, there are considerable differences in the yield strength at elevated temperatures obtained from the predictive functions for the given steel. Therefore, it is necessary to clarify the influence of the variation in temperature- and phase-dependent yield strength obtained from different methods on the predicted welding residual stresses in numerical simulation. In this study, numerical sensitivity analyses have been conducted to clarify the effect of yield strength on the predicted residual stresses in ultra-high strength steel S960 weldments. Furthermore, tensile tests and welding experiments were carried out for comparison and validation. Based on the current work, the effect of temperature- and phase-dependent yield strength on the calculated welding residual stresses is clarified. Besides, the reliability of the proposed functions to evaluate yield strength based on the tensile test results mainly from mild steels and conventional high strength steels is assessed for the recently developed ultra-high strength steel S960. Finally, guidance on how to economically determine the reliable temperature- and phase-dependent yield strength for S960 steel in numerical welding simulation is provided.
Additive manufacturing (AM) in industrial applications benefits from increasing interest due to its automation potential and its flexibility in manufacturing complex structures. The construction and ...architecture sector sees the potential of AM especially in the free form design of steel components, such as force flow optimized nodes or bionic-inspired spaceframes. Robot-guided wire and arc additive manufacturing (WAAM) is capable of combining a high degree of automation and geometric freedom with high process efficiency. The build-up strategy (layer by layer) and the corresponding heat input influence the mechanical properties of the WAAM products. This study investigates the WAAM process by welding a bar regarding the build-up geometry, surface topography, and material properties. For tensile testing, an advanced testing procedure is applied to determine the strain fields and mechanical properties of the bars on the component and material scale.
Welding-induced residual stresses (WIRS) can have influence on the performance and service life of the welded structures. The present study experimentally and numerically investigates the reason and ...mechanism behind the generation and distribution of WIRS concretely. The results show that the thermal shrinkage process and phase transformation process are the main sources generating welding-induced longitudinal residual stress (σLRS). Nevertheless, except for these two processes, the quenching process would be another source producing transverse residual stress (σTRS). In the current work, it is found that the maximum σLRS generally reaches the yield strength (σy) of base metal (BM) at ambient temperature (TRT) for both transforming and non-transforming materials but located at different areas. In the single-pass weldments without external restraint, σTRS profile on the top surface is usually always M-shaped for the non-transforming materials but W-shaped instead for the transforming materials. The distribution mechanism behind the M-shaped or W-shaped σTRS profile is systematically clarified here.
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•Interlayer boundaries and local minima and maxima of the surface profile do not generally coincide.•The waviness profile contains representative features of the surface ...topography.•Surface parameters describe the waviness resulting from different manufacturing parameters.
Additive manufacturing of structural metallic components is an emerging technology. The DED-arc (direct energy deposition) process combines efficiency with high degrees of freedom and predictable quality. Compared to powder-based processes, the surface is relatively coarse as a result of high heat input and larger molten zones. In industrial applications, the post-treatment of surfaces of DED-arc components cannot be guaranteed for economic reasons or due to geometric constraints. Hence, the surface topography must be evaluated and quality levels need to be defined. Unfortunately, established surface parameters and their determination cannot be directly transferred to DED-arc components and further research on this topic is needed. This article demonstrates surface topography features of representative DED-arc components. Furthermore, waviness profiles were established by applying an alternative cutoff wavelength to better represent the DED-arc surface characteristics. Based on these waviness profiles, 2-dimensional height parameters were calculated. The waviness parameters were determined for four DED-arc specimens made from high strength wire electrodes. The manufacturing parameters were varied in terms of different energy input and interpass temperature, resulting in varying deposition rates and surface qualities. The waviness parameters correlated with manufacturing parameters. A mixed deterministic and random nature of the surface topography was verified.
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