Binder jetting of aluminum alloys: Design for Additive Manufacturing and Material Characterization

Examensarbete för masterexamen
Master's Thesis
Product development (MPPDE), MSc
Alam, Didarul
Dessai, Omkar Rajan
Binder jetting technology (BJT) is an additive manufacturing (AM) process wherein a liquid binder is deposited on the power bed to join the particles together layer by layer, thus creating the desired geometry. This process can print various metals and polymers with higher productivity. Even so, among other metals, aluminum alloys are not commercially available to be produced by BJT. However, due to aluminum’s intrinsic characteristics and properties, the passenger and commercial vehicle industries extensively utilize this metal. For this reason, it is a highly desired material for BJT/M in the automotive industry due to the possibility of printing complex shapes and having higher productivity than other metal additive manufacturing technologies. A Japanese company, RICOH Company Ltd, is currently working on developing technology for printing aluminum alloys in BJT. In this master thesis, design for AM and material characterization studies were conducted in collaboration with Volvo Car Corporation (VCC) and RICOH to study a heat sink for the headlamp for the XC90 production series car against two different aluminum alloys. As-produced aluminum alloy was 4000 series aluminum alloy, which had a Si content of less than 10 wt.%, and high pressure die casted aluminum alloy had a Si content of 12 wt.%. A study of design guidelines was carried out by printing design artefacts, and the geometry evaluation was done using scanning and superimposing CAD data. This provided knowledge about critical design features that can be produced using the technology and the limit. 10mm3 produced cubes were analyzed for porosity using Light Optical Microscopy (LOM). Density verification on the cubes using LOM, Geometrical, and Archimedes showed a relatively high density of 98% with a standard deviation of 0.91. The primary function of the heatsink studied here is dissipating heat away from other components. Thus, thermal conductivity and convection performance were measured. Thermal conductivity for as-sintered material was found to be 154.41 W/mK at room temperature (20 °C), and it was increased to 166.68 W/mK after Hot Isostatic pressing (HIP), compared to 97.94 W/mK for as-casted aluminum alloy which is currently being used. To improve the thermal convection, the new design features, namely Gyroid with varying wall thicknesses, were produced as test pieces and tested in the experimental setup to determine the design with the best performance. Heat dissipation increased by 99% in free convection and 82% in forced convection compared to the as-casted heatsink; this was demonstrated during the experiment. A new heatsink design produced using BJT Al alloys also resulted in a weight reduction of 42% to the existing design. Regarding the mechanical properties, HV5 was found to be 51.91% less for as-sintered aluminum alloy compared to as-casted aluminum alloy and 48.98% less for as-sintered aluminum alloy when HK1 was considered. The microstructure analysis showed that the reason for the thermal conductivity increase and hardness decrease in the aluminum alloy produced by BJT/M is connected to the lower Si content. Hence, the lower fraction of AlSi-precipitates was produced.
Additive manufacturing , Binder Jetting for Metals , Gyroid Structures , Material Characterisation , Hardness , Thermal conductivity , Thermal convection , Hot Isostatic Pressing
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