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Process control in Binder Jetting
Euro PM2020 technical review: Advances in process control for metal Binder Jetting (BJT) Within the programme of the well-received Euro PM2020 Virtual Congress, held October 5–7, 2020, and organised by the European Powder Metallurgy Association (EPMA), a technical session was held on process control in metal Binder Jetting. In this article, Dr David Whittaker provides a summary of two of the papers presented, which look at applying the Master Sintering Curve for 316L parts, and process parameter optimisation for 17-4 PH parts.
The Master Sintering Curve and its application on 316L steel produced by Binder Jetting This paper was presented by Markus Schneider, Philipp Gabriel, Simon Hoeges and Christopher Schaak (GKN Sinter Metals Engineering GmbH, Germany) and addressed the benefits of using the Master Sintering Curve (MSC) approach in optimising the sintering of 316L stainless steel in Binder Jetting [1]. The main hurdles in BJT are the achievement of the required final sintered density ρs and a proper control over the sintering process. The Master Sintering Curve approach is a helpful tool to understand the sintering kinetics and to predict the resulting final sintered density ρs from simple dilatometry experiments. In the reported study, different industrial sintering profiles T(t) were numerically integrated to obtain the MSC. The MSC approach assumes a sigmoidal evolution of the densification parameter Ψ as a
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function of the logarithmic sintering work ϴ(t, T), which incorporates the whole sintering profile T(t). In most cases, the sintering profile T(t) is too complex for an analytical integration, because the corresponding antiderivative cannot be found. Only for isothermal conditions, T(t)=const, can the integral be solved. However, the integral can be solved numerically by the summation of the sintering work increments if the sintering profile T(t) is partitioned into time increments of width Δt. Several applications of the MSC approach are focused on the estimation of the apparent activation energy QMSC (an average of all
contributing transport mechanisms) by minimising the perpendicular distance (error) to the average residual squares R by varying of the apparent activation energy QMSC. A simple estimation for the activation energy for self-diffusion/sintering Qs is based on the Engel-Brewer theory, in which the activation energy is related to the crystal type and the absolute melting temperature Tm. In the study, gas (argon) atomised austenitic 316L stainless steel powder was used for all tests. Typical values of the skewed powder particle size distribution Q3(d) were in the range of d10=4.85 µm, d50=12.74 µm and d90=24.24 µm.
“The Master Sintering Curve approach is a helpful tool to understand the sintering kinetics and to predict the resulting final sintered density ρs from simple dilatometry experiments.”
Metal Additive Manufacturing | Spring 2021
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