Search

Coaxial laser metal deposition with wire (LMD-w) is an innovative additive manufacturing technology in which a wire is coaxially fed through the center of a hollow laser beam into a laser-induced melt pool. This special configuration results in a direction-independent process, which facilitates the manufacturing of thin-walled metal components at high deposition rates. However, laborious experimental test series must be conducted to adjust the process parameters so that the substrate and the part do not overheat. Therefore, models are needed to predict the resulting temperature field and melt pool dimensions efficiently. This paper proposes a finite element simulation model using an innovative heat source, which considers the unique intensity distribution of the annular laser spot. The heat source parameters were calibrated experimentally based on fusion lines obtained from metallographic cross sections of aluminum alloy samples (AA5078 wire and AA6082 substrate). Subsequently, the temperature distribution in the substrate plate was measured by means of thermocouples to validate the developed model. It was shown that the proposed heat source replicates the heat input accurately. With the presented model, essential features for process development, such as the temperature field and the melt pool dimensions, can be reliably predicted. The model contributes to a better understanding of the LMD-w process and facilitates an efficient process development in future research work as well as for industrial applications. Key words: thermal simulation, annular laser spot, heat source, laser metal deposition, coaxial wire feeding, directed energy deposition

Laser metal deposition (LMD) is an additive manufacturing process in which a metal powder or wire is added to a laser-induced molten pool. This localized deposition of material is used for the manufacturing, modification, and repair of a wide range of metal components. The use of wire as feedstock offers various advantages over the use of powder in terms of the contamination of the process environment, the material utilization rate, the ease of handling, and the material price. However, to achieve a stable process as well as defined geometrical and microstructural properties over many layers, precise knowledge on the effects of the input variables of the process on the resulting deposition characteristics is required. In this work, the melt pool temperature was used as an input parameter in LMD with coaxial wire feeding of stainless steel, which was made possible through the use of a dedicated closed-loop control system based on pyrometry. Initially, a temperature range was determined for different process conditions in which a stable deposition was obtained. Within this range, the cause-effect relationships between the melt pool temperature and the resulting geometry as well as the material properties were investigated for individual weld beads. It was found that the melt pool temperature is positively correlated with the width of the weld bead as well as the dilution. In addition, a dependence of the microhardness distribution over the cross section of a weld bead on the melt pool temperature was demonstrated, with an increased temperature negatively affecting the hardness.

Welding of sheet metal structures in the automotive industry involves inflexible and expensive clamping devices to properly position and fasten the parts. The approach of feature-based fixturing can reduce fixtures in the joining process. It is based on part-inherent fastening features that realize the fixture functions. The proper design of these features requires knowledge of forces that result from the joining process and thus need to be compensated. For this paper, process forces were investigated during remote laser beam welding. This was achieved by using a thermomechanical simulation model. The aspects described in this paper are model build-up and validation, application of the approach to a real structure, and affiliated parameter studies. The studies show that required clamping forces depend, among other things, on the clamping condition and on the weld strategy. Finally, the simulation model allows for the design of fastening features to reduce joining fixtures in the automotive body shop.Welding of sheet metal structures in the automotive industry involves inflexible and expensive clamping devices to properly position and fasten the parts. The approach of feature-based fixturing can reduce fixtures in the joining process. It is based on part-inherent fastening features that realize the fixture functions. The proper design of these features requires knowledge of forces that result from the joining process and thus need to be compensated. For this paper, process forces were investigated during remote laser beam welding. This was achieved by using a thermomechanical simulation model. The aspects described in this paper are model build-up and validation, application of the approach to a real structure, and affiliated parameter studies. The studies show that required clamping forces depend, among other things, on the clamping condition and on the weld strategy. Finally, the simulation model allo...