-The aim of this study was to investigate the tribological behaviour of laser cladded aluminum bronze tool surfaces for dry metal forming. In a first part of this work a process window for cladding aluminum bronze on steel substrate was investigated to ensure a low dilution. Therefore, the cladding speed, the powder feed rate, the laser power and the distance between the process head and the substrate were varied. The target of the second part was to investigate the influence of different process parameters on the tribological behaviour of the cladded tracks. The laser claddings were carried out on both aluminum bronze and cold work tool steel as substrate materials. Two different particle sizes of the cladding powder material were used. The cladding speed was varied and a post-processing laser remelting treatment was applied. It is shown that the tribological behaviour of the surface in a dry oscillating ball-on-plate test is highly dependent on the substrate material. In the third part a deep drawing tool was additively manufactured by direct laser deposition. Furthermore, the tool was applied to form circular cups with and without lubrication.
A manifold variety of additive manufacturing techniques has a significant positive impact on many industry sectors. Large components are often manufactured via directed energy deposition (DED) instead of using powder bed fusion processes (PBF). The advantages of the DED process are a high build-up rate with values up to 300 cm3/h and a nearly limitless build-up volume. In combination with the lightweight material aluminum it is possible to manufacture large lightweight components with geometries adapted to customer requirements in small batches. This contributes the pursuit of higher efficiency of machines through lightweight materials as well as lightweight design. A low-defect additive manufacturing of high strength aluminum EN AW-7075 powder via DED is an important challenge. The laser power has a significant influence on the remaining porosity. By increasing the laser power from 2 kW to 4 kW the porosity in single welding tracks can be lowered from 2.1% to only (0.09 ± 0.07)% (n = 3). However, when manufacturing larger specimens; the remaining porosity is higher than in single tracks; which can be attributed to the oxide skin on the preceding welding tracks. Further investigations regarding the mechanical properties were carried out. In tensile tests an ultimate tensile strength of (222 ± 17) MPa (n = 6) was measured. The DED processed EN AW-7075 shows comparable mechanical properties to PBF processed EN AW-7075.
As a widely used additive manufacturing technique, the laser metal deposition process (LMD) also known as direct energy deposition (DED) is often used to manufacture large-scale parts. Advantages of the LMD process are the high build-up rate as well as its nearly limitless build-up volume. To manufacture large-scale parts in lightweight design with high strength aluminium alloy EN AW-7075, the LMD process has a disadvantage that must be considered. During the process, the aluminium alloy is melted and has therefore a high solubility for hydrogen. As soon as the melt pool solidifies again, the hydrogen cannot escape the melt and hydrogen pores are formed which weakens the mechanical properties of the manufactured part. To counter this disadvantage, the hydrogen must be successfully kept away from the process zone. Therefore, the covering of the process zone with shielding gas can be improved by an additional shielding gas shroud. Furthermore, the process parameters energy input per unit length as well as the horizontal overlapping between two single tracks can be varied to minimize the pore volume. Best results can be achieved in single tracks with an elevated energy input per unit length from 3000 to 6000 J/cm. To manufacture layers, a minimal horizontal overlapping will lead to lowest pore volume, although this results in a very wavy surface, as a compromise of low pore volume and a nearly even surface a horizontal overlapping of 30 to 37% leads to a pore volume of 0.95% ± 0.50%.
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