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PublicationAssessing the Environmental and Economic Impact of Wire-Arc Additive Manufacturing( 2024-05)
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PublicationInfluence on the Bead Geometry in Laser Metal Deposition with Wire( 2023-09-28)Laser metal deposition with wire (LMD-w) is a promising additive manufacturing technology, which attracts interest due to the low waste of material, the flexible application possibilities along the production chain and the improved metallurgical properties compared to powder-based processes. However, the complex handling of the technology and the resulting low process stability inhibit the broad industrial application. In particular, the varying bead geometry prevents automation and series production. To improve the geometric accuracy, it is necessary to understand influencing parameters. For this purpose, a parameter study is carried out in the present work. Different combinations of laser power, wire feed rate, traverse speed and welding angle are set, and the deposited beads are evaluated in terms of height and width. A factorial design experiment with the Box-Behnken was used to analyse and understand the interaction of these parameters on the deposited beads.
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PublicationBenchmark of Abrasives for Different Applications( 2022)The industrial use of abrasive waterjet (AWJ) technology has its strength in the machining of conventionally difficult-to-machine materials where the use of abrasives is obligatory. Since the use of AWJ technology, garnet abrasive has become the standard due to its performance and availability. Facing the impending shortage of natural raw materials, rising prices, and increasing environmental requirements, users of waterjet technology must optimize their processes. A wide range of individual machining tasks and materials to be processed holds great potential for tailoring the consumption of valuable resources and costs in the future. A fundamental comparison of different abrasive grit is made to contribute to the efficient use of solids for dedicated applications and to identify resource-efficient alternatives. For this purpose, an overview is given of the abrasive performance in AWJ machining. The experiments will be examined for both AWJ cutting through (CT) and controlled-depth machining (CDM) or AWJ milling techniques on two heat-treated modifications of a 42CrMo4 steel alloy. Finally, a fundamental discussion of grit properties on the systematic change of size distribution serves as a basis to meet the requirements of reusability and their attractiveness for future waterjet production.
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PublicationProcess stabilization through pulsed laser-induced melt pool shaping in dual-beam LMD( 2022)Laser Metal Deposition (LMD) is an additive manufacturing process that reaches high deposition rates. Its applications are mainly found in repair, cladding and manufacturing. The two commonly used LMD processes are powder-based (LMD-p) and wire-based (LMD-w). Despite the fact that wire-based LMD uses material more efficiently, its process stability is a major concern. One approach to increase the process stability is superposing a pulsed laser (pw) beam with the conventionally used continuous laser (cw). Previous studies have shown that the metal vapor caused by pulsed laser-induced evaporation in the process zone significantly improves energy absorption. Furthermore, a direct relation between vapor pressure and melt pool form has been demonstrated. In this contribution, we correlate the pw-controlled melt pool geometry to process stability. High-speed camera imaging is employed to evaluate the dynamic melt pool behavior as a function of pw frequency and power. It is shown that irregular melt pool oscillations impairing process stability in conventional LMD-w are reduced if the pulsed laser is added. The melt front is shaped depending on the acting pw-induced pressure. This leads to a more stable interaction between wire and melt pool. Furthermore, the pw pressure changes the welding bead height and width. This cross-sectional geometry has an impact on the resulting waviness in 3D build-up. We also investigate how the waviness influences process stability during multilayer LMD-w. The results demonstrate that the dual beam technology is a promising way to develop more reliable and resource-efficient AM processes.
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PublicationImproving position accuracy in large-scale laser structuring processes using surface feature detection algorithms( 2022)
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PublicationExpress Wire Coil Cladding (EW2C) as an Advanced Technology to Accelerate Additive Manufacturing and Coating( 2021)Metal shafts are indispensable components in mobility, energy and mechanical engineering. In such applications, the shafts need to withstand severe mechanical loads, friction, high temperature or corrosive media. This is why shafts are often completely made of high-performance alloys. From a technical point of view, coating an inexpensive base shaft with a thin layer of high-performance material is mostly sufficient to ensure its functionality. Adding functional parts such as shoulders or bearing seats by Additive Manufacturing (AM) instead of creating them by subtractive manufacturing is an advantageous approach to increase flexibility and material efficiency. Reliable and economic AM and coating processes need to be developed further, and laser-based processes such as wire-based Laser Metal Deposition (LMD-w) offer high potential to accomplish this. They can generate a stable metallurgical bond between the base material and the cladding or the added feature without excessively heating the work piece. Due to their low build-up rate, however, LMD processes are not economically competitive with high-speed subtractive technologies such as drilling or turning, which are predominately used for shaft production. Motivated by this challenge, we present an alternative approach that increases the deposition rate for laser-based shaft cladding. Instead of adding the filler wire continuously, wire coils are wound and preplaced on the shaft. In a second step, laser processing while rotating the part generates a metallurgical bond between the wire and the substrate. In this study, several solid and flux-cored wires were analyzed regarding their suitability for this two-step coil winding and LMD process. The results from LMD experiments give an overview of the resulting surface state and of the welded joint quality after deposition. Metallographic cross sections show low porosity of the deposited layers and small heat-affected zones in the base shaft. Thanks to its good scalability, this innovative two-step process can help strongly increase the build-up rate compared to classic LMD-w.
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PublicationReflectometry-based investigation of temperature fields during dual-beam Laser Metal Deposition( 2021)Laser Metal Deposition (LMD) is a high deposition rate metal Additive Manufacturing process. Its applications are basically repair, cladding and manufacturing. The two most commonly used LMD processes are powder-based (LMD-p) and wire-based (LMD-w). Despite the fact that wire-based LMD is more material efficient, process stability is a major concern. By adding a modulated laser beam to the continuous process beam, a change of the melt pool geometry and increased energy absorption are observed. This relation shows great potential to increase process stability. In this contribution, the positive effect of the dual laser-beam use on LMD-w processes is demonstrated. To understand the cause-effect relation, the workpiece temperature field was investigated by optical backscatter reflectometry ( OBR). The results were then correlated to simultaneously performed IR camera measurements of the workpieces upper surface. By better understanding the thermal phenomena in dual-beam LMD, research can improve process temperature control. This leads to a new perspective for the LMD-w manufacturing process in many industry sectors such as mobility, energy and engineering.
