Tensile properties of aluminium 4047A built in droplet-based metal printing

Abstract

Purpose Directly printing molten metal droplets on a build platform to create full dense metal parts is a promising additive manufacturing process. This study aims of to analyse the effects of the thermal conditions on the resulting tensile properties of parts made from aluminium 4047A built in droplet-based metal printing. Design/methodology/approach A drop-on-demand print head with pneumatic actuation is used to eject droplets on a nickel sheet mounted on the heated build platform. Tensile specimens are machined from cuboid blocks built by successive droplet deposition and tested in a universal testing machine. The ultimate tensile strength, uniform elongation and yield strength are evaluated and presented. Micro-sections are taken from the printed blocks to examine the internal pores and the metal’s microstructure. Findings With an increase in the interface temperature the uniform elongation increases from 0.5 to 12%, while the yield strength decreases from 130 to 90 MPa. The ultimate tensile strength increases from 130 MPa to a maximum of 190 MPa at an interface temperature of 530º C and slightly falls for higher interface temperatures. Those values are in the same range as conventionally casted parts of the same alloy. The authors’ hypothesis is that the main effect responsible for the mechanical properties is the wetting of solid material by the liquid droplet and not remelting, as has been reported in literature. Originality/value To the best of the authors’ knowledge, this is the first time that mechanical properties of aluminium 4047A built by a droplet-based additive manufacturing process are published for different interface temperatures. It is also the first time that the main effect on mechanical properties is attributed to wetting instead of remelting.

Influence of Salt Support Structures on Material Jetted Aluminum Parts

“…All samples for this investigation are printed on a pneumatically actuated drop on-demand MJT test stand with interchangeable print heads, that was originally developed for printing aluminum. The test stand is described in detail by Himmel et al [ 16 ]. For salt printing, a print head was designed with materials that were selected in a previous work [ 3 ].…”

“…Our investigation is focused on the aluminum silicon alloy AlSi12(a) as build material and a eutectic mixture of potassium chloride (KCl) and sodium chloride (NaCl) as support material. Printing AlSi12(a) in an MJT process has already been demonstrated [ 16 ]. KCl-NaCl has been selected in previous work from a wide variety of salts and salt mixtures because of its comparatively good processability in a prototype MJT test stand [ 3 ].…”

Analysis of salts for use as support structure in metal material jetting

“…The test stand, developed for the printing of aluminium, has been previously described in detail by Himmel et al [2] and Rumschoettel et al [19]. Figure 6 shows a schematic view of the test stand.…”

“…Molten droplets of metal are ejected onto a heated build platform and bond. This results in dense metal parts with mechanical properties that can be better than those of the cast reference due to high cooling rates [2]. The inexpensive raw materials in the form of metal wire combined with the low equipment cost and potentially high printing speed are the main attractions of this technology.…”

“…However, there has already been research conducted on expanding the printable materials into the field of aluminium alloys. Liu et al [3] presented a piezo actuated continuous jet print head, Karampelas et al [4] developed a magnetohydrodynamic drop-on-demand print head and Himmel et al examined the tensile properties of specimens printed from an aluminium silicon alloy [2].…”