Comparison of density measurement techniques for additive manufactured metallic parts

Abstract

Purpose -In the optimisation of processing parameters for additive manufactured parts using, e.g. selective laser melting (SLM) or electron beam melting, the measurement of the part densities is essential and of high interest. However, there is no common standard. Different institutes and system providers are using their own principles and guidelines. This study investigates the accuracies of the three measurement principles: Archimedes method, microscopic analysis of cross sections and X-ray scanning. Design/methodology/approach -A total of 15 test samples on five density levels (densities between 90 and 99.5 per cent) were produced using the SLM process. The samples are analysed regarding the accuracy of the measurement principles and their reproducibility taking into account influencing parameters like the buoyancy of a sample in air (Archimedes method) or different magnifications of a cross section. Findings -The Archimedes method shows a very high accuracy (^0.08 per cent for high densities) and repeatability (^, 0.1 per cent) on all density levels. In contrast to the Archimedes method, taking a micrograph of a specific cross section allows to influence the resulting density and the coefficient of variation reaches values . 4 per cent. However, for low porosities, mean densities are comparable to the results of the Archimedes method even though calculated densities are typically somewhat too high. The advantage of the image guided analysis (2D and 3D) is getting more information about the distribution, size and form of pores in the part. Originality/value -The findings do not only refer to metallic parts but generally to all parts having a specific porosity. The study is a contribution to the American Society for Testing and Materials initiative F42 "Additive Manufacturing Technology" and especially to the subcommittee "test methods".

Influence of the particle size distribution on surface quality and mechanical properties in AM steel parts

“…A comparison of different density measurement methods [8] showed that the repeatability of this method is < 0.1% for high part densities. The minimal scan energy density for high density parts depends on the powder characteristics and the layer thickness [5,6], as shown in Figure 2.…”

Optimization of selective laser sintering process parameters to achieve the maximum density and hardness in polyamide parts

“…Density determinations are frequently performed using Mettler Toledo AL204 balance by means of Archimedes' principle (buoyancy method) [18,19] at room temperature with the use of n-Butyl acetate (0.88) as a liquid medium, which is also the method used by the density determination kit for balances. Hardness testing of different polyamide samples on top of surface is performed on Rockwell hardness tester, and the specification and other parameters are listed in Table 2.…”

Direct Metal Laser Sintering

“…Part quality, quality assurance Part quality [3][4][5][6] is influenced by the powder material, exposure parameters as well as inert gas flow and temperature at the building platform. Defects like porosity, lack of fusion and rough surfaces can arise if wrong parameters are used.…”