Improvement in Geometrical Accuracy and Mechanical Property for Arc-Based Additive Manufacturing Using Metamorphic Rolling Mechanism

Background: Additive manufacturing (AM), or 3D printing, is drawing considerable contemporary interest due to characteristic of high material utilization, great flexibility in product design and inherent mouldless process. Arc-based additive manufacturing (AAM) is a promising AM method with high deposition rate and favorable build-up quality. Components made by AAM are fabricated through superimposed weld beads deposited from metal wire. Unlike laser-based additive manufacturing (LAM), AAM is more difficult to control. Because of the large energy input of the energy source and the liquidity of the melting metal material, bottleneck problems like shrinkage porosity, cracking, residual stresses and deformation occur. Resultant poor geometrical accuracy and mechanical property keep AAM from industrial application. Especially in the aerospace industry, structural and mechanical property specifications are stringent and critical. Method of approach: This paper presents a novel hybrid manufacturing method by using hot-rolling process to assist the arc welding to solve above problems. Initially, a miniature metamorphic rolling mechanism (MRM) was developed using metamorphic mechanism theory. Configuration and topology of the MRM can change according to the feature of the components to roll the top and lateral surfaces of the bead. Subsequently, three single-pass multi-layer walls were built respectively for comparison. Results: For top surface rolling, accumulated maximum height absolute error was reduced from 2.4 mm to 0.2 mm. For lateral surface rolling, maximum width absolute error was reduced from 0.45 mm to 0.12 mm. The thickness of each layer is 1.55 mm, controlled accurately under hybrid manufacturing method. The mechanical properties were improved by 4.0% for yield strength, 6.6% for ultimate tensile strength and 7.4% for elongation in travel direction compared with AAM specimens. The improved mechanical properties were superior to wrought material. In vertical direction, the improvement is 9.3% for yield strength, 1.8% for ultimate tensile strength and 10.4% for elongation. Conclusions: The rolled results show significant improvement in geometrical accuracy of the built features. Tensile test results demonstrate improvement in mechanical properties. The improved mechanical properties of rolled specimens are superior to wrought material in travel direction. Microstructure comparisons indicate columnar grains observed in vertical direction and fusion zones were suppressed. Eventually, fabrication of a large-scale aerospace component validates the feasibility of industry application for the hybrid manufacturing technology. Keywords: Arc-based additive manufacturing, hot rolling, metamorphic mechanism