Fatigue Design Curves for Laser-Metal-Deposited Type 420 Stainless Steel and Effect of an Interval during Deposition Process

Fully-reversed axial loading fatigue tests were conducted using type 420J1 martensitic stainless steel. The specimens were additively manufactured by a laser metal deposition (LMD) process. The results were compared with conventionally-manufactured (CMed) type 420J2 stainless steel. According to the axial loading fatigue test results, the fatigue strengths of the laser-metal-deposited (LMDed) specimens were nearly comparable to those of the CMed specimens. Fractographic analyses revealed that process-induced defects were hardly seen at the fatigue crack initiation sites of the LMDed specimens. It indicates that defect-free deposition was possible by the LMD process. On the other hand, when the LMD specimens experienced intervals during deposition processes, local softening occurred due to the tempering of the building plate. Fatigue tests revealed that the interval during LMD process had detrimental effect on the fatigue strengths due to the local softening. The upper and lower bounds of S-N curves were proposed as fatigue design curves for the samples with and without the interval during LMD process.

Numerical and experimental investigations for distortion-reduced laser heat treatment of aluminum

In the field of mobility, increased safety and emission requirements lead to steadily rising demands on materials used and their performance. Over the last decades, 5000 and 6000 series aluminum alloys have become more and more attractive as lightweight material due to their beneficial weight to strength ratio. The 7000 series offers extended lightweight potential due to its high strength. Until now, this class of alloys has not been widely used in mass production due to its limited corrosion resistance and poor forming behavior. By using so-called Tailor Heat Treated Blanks, it is possible to set increased forming limits of previously locally heat treated components. The reason for the enhanced formability is the local softening, with the resulting improved material flow and the reduced critical forming stresses of the sheet metal before the forming operation. Despite these advantages, the use of previously heat treated materials has been very limited so far. For example, the distortion that occurs during local heat treatment reduces geometrical accuracy and thus automated handling. Therefore, the focus of this thesis is the investigation of tailored heat treatment strategies, permitting a distortion-reduced local short-term heat treatment. For this purpose, the distortion behavior is represented and quantified both numerically and experimentally. The generated knowledge is then transferred to a large volume component and characterized.

Recent Advances in the Laser Forming Process: A Review

Laser forming is an emerging manufacturing process capable of producing either uncomplicated and complicated shapes by employing a concentrated heating source. The heat source movement creates local softening, and a plastic strain will be induced during the rise of temperature and the subsequent cooling. This contactless forming process may be used for the simple bending of sheets and tubes or fabrication of doubly-curved parts. Different studies have been carried out over recent years to understand the mechanism of forming and predicting the bending angle. The analysis of process parameters and search for optimized manufacturing conditions are among the most discussed topics. This review describes the main recent findings in the laser forming of single and multilayer sheets, composite and fiber-metal laminate plates, force assisted laser bending, tube bending by laser beam, the optimization technique implemented for process parameters selection and control, doubly-curved parts, and the analytical solutions in laser bending. The main focus is set to the researches published since 2015.