Meanwhile laser-based Additive Manufacturing (AM) technologies such as Laser Metal Deposition (LMD) have been introduced in various fields of applications. The latter is not only used for the fabrication of complete new parts, but also for the purpose of repair and redesign. Therefore, weld beads with dimensions above 1 mm were mostly used in the past. In some cases, bead widths can even exceed 10 mm or more. However, the build-up of filigree parts by means of sub-millimeter structures has gained interest during the several last years. Fabrication of structures with small dimensions requires different process modifications along the process chain. This includes general process strategies but also adjusted system components. The changed process yields material deposition of varying geometries possibly used in aerospace, space, medical technology as well as micro tooling. Additionally, it can be also used for the repair of worn or damaged micro parts.Within this paper, the aforementioned process modifications are shown and demonstrated. In addition, high-speed process observations are discussed and, finally, fabricated parts are analyzed. The latter includes non-destructive and also destructive methods. Based on the combination of changed process elements, a stable laser-based AM procedure is presented which is already in production.
In the last few years, coaxial laser heads have been developed with centric wire feeding equipment, which enables the laser processing of complex-shaped objects in various applications. These newly developed laser heads are being used particularly in laser brazing experiments in the automotive industry. This study presents experimental results of using a coaxial laser head for cold- and hot-wire cladding application. The coaxial wire cladding method has significant improvements compared with the off-axis wire cladding method such as independence of the travel direction, alignment of the wire to the laser beam, and a reduced number of controlling parameters. These features are important to achieve high quality coatings. Cladding tests were conducted on mild steel with a coaxial laser wire welding head using Ni-based Inconel 625 and Thermanit 2509 super duplex stainless steel solid wires in order to determine the properties of the cladding process and the coatings deposited. The corrosion resistance of the obtained coatings was examined by long-term acetic acid salt spray (AASS) and electrochemical critical pitting temperature tests. The test results showed that by using the coaxial wire cladding method, defect-free high quality and corrosion resistant Inconel 625 and super duplex stainless steel coatings with low dilution were achieved. The average pitting temperature for Thermanit 2509 duplex coating was 75 °C in 1M NaCl solution, which was comparable to wrought 2507 duplex stainless steel. Low diluted Inconel 625 coating survived the AASS test for 2000 h without signs of corrosion.
In the field of laser additive manufacturing, modern hybrid technologies offer advantageous solutions for combining the high quality level of laser surface claddings with the industry's economical requirements regarding productivity and energy efficiency. The technical approach is to supply energy sources in two fundamentally different ways. First, welding material in the form of wire is directly heated, i.e., by electrical resistance, almost to its melting point and is fed to the process region simultaneously with the laser beam. A newly developed coaxial wire head allows for omni-directional welding operation and, thus, the use of wire even for complex surface claddings as well as layer-by-layer fabrication of metallic parts. Second, an additional energy source is used to heat the substrate in order to compensate for the heat conduction losses. This technical variant is suitable for use with both wire and powder as deposition materials. Additionally, heating and cooling gradients can be precisely adjusted, thus improving the build-up of structures of hard and brittle metallic super-alloys. Currently, deposition rates up to 18 kg/h of metal alloys and metal matrix composites have been demonstrated using these laser hybrid techniques. Industrial applications are, among others, large hydraulic cylinders and tools of the oil and mining industries. V C 2014 Laser Institute of America.
Abstract. In the field of Laser Additive Manufacturing, modern wire-based laser deposition techniques offer advantageous solutions for combining the high quality level of layer-by-layer fabrication of high value parts with the industry's economical requirements regarding productivity and energy efficiency. A newly developed coaxial wire head allows for omni-directional welding operation and, thus, the use of wire even for complex surface claddings as well as the generation of three-dimensional structures. Currently, several metallic alloys as steel, titanium, aluminium, and nickel are available for the generation of defect-free structures. Even cored wires containing carbide hardmetals can be used for the production of extra wear-resistant parts. Simultaneous heating of the wire using efficient electric energy increases significantly the deposition rate and energy efficiency. Examples of application are light-weight automotive parts, turbine blades of Nickel super alloys, and complex inserts of injection moulds. IntroductionLaser buildup welding is a well-established technique in industrial applications of surface cladding and direct fabrication of metallic parts. As construction materials, powders are widely used because of the large number of available alloys and the simple matching with the shaped laser beam. However, the powder utilization is always less than 90 %, characteristic values are in the range of 60 %, and so a serious part of the material is lost. Additionally, there is a risk for machine, operators and environment due to dangerous metal dust. The alternative use of wires as buildup material offers a number of advantages: The material utilization is always 100 %, and rightly independent from the part's shape and size. The process is clean and safe, and so the effort for protecting personnel and environment is much less. Also the wire feed is completely independent from the gravity which is of great advantage especially in applications of three-dimensional material deposition.The main challenge compared to powder is the realization of an omni-directional welding operation with stable conditions of the wire supply. The only possible solution therefore is to feed the wire coaxially in the centre axis of the laser beam. This technology requires a complex optical system which permits the integration of the
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