Observation, Prediction, and Correlation of Geometric Shape Evolution Induced by Non-Isothermal Sintering of Polymer Powder

Abstract

Sintering of powders occurs in a wide array of manufacturing technologies and geophysical phenomena. Despite the prevalence of powder sintering, little attention has been paid to sintering of macroscopic shapes under non-isothermal conditions. In this paper (1) features of a representative, experimentally grown solid shape produced by non-isothermal sintering are discussed, (2) prediction of the solid shape evolution is achieved using a hybrid heat transfer, sintering, and consolidation model, (3) comparison of the actual and predicted solid shapes is made, (4) parametric simulation of solid part growth in conjunction with void expansion is attained, and (5) analytical predictions of the void space evolution are developed and discussed.

Physical Aspects of Process Control in Selective Laser Sintering of Metals

“…Equation 9 shows that for heterogeneous nucleation to proceed, the critical radius of the nucleus r* depends on the solid-liquid interfacial free energy c SL . In SLS, the solid and liquid are of nearly the same composition (assuming negligible contamination or segregation).…”

A pragmatic model for selective laser melting with evaporation

“…Their work was extended to three-dimensional parts and two-component metal powders by Zhang and co-workers [8][9][10][11][12][13], taking into account fluid flow caused by capillary and gravity forces through Darcy's law [8] or through the NavierStokes equations [13], investigating the effect of the powder layer thickness [9] and of the substrate [12], studying partial shrinkage [11]. The group of Childs developed a finite-element model for SLS/SLM using a similar viscous sintering law as Kandis and Bergman [6] to study the behavior of amorphous polymer powders [14], crystalline and glassfilled crystalline polymer powders [15], and stainless and tool steel powders [16]. Gusarov and co-workers studied in detail the phenomena related to the radiative heat transfer in powders and the interaction with the substrate.…”

“…In what follows, we briefly discuss an illustrative selection. Kandis, Bergman and co-workers [6,7] used a constitutive relation based on experimental measurements to account for the density change caused by sintering in SLS, and compared their simulations on polymer powders with experimentally produced parts. Their work was extended to three-dimensional parts and two-component metal powders by Zhang and co-workers [8][9][10][11][12][13], taking into account fluid flow caused by capillary and gravity forces through Darcy's law [8] or through the NavierStokes equations [13], investigating the effect of the powder layer thickness [9] and of the substrate [12], studying partial shrinkage [11].…”

Analysis of Non‐Isothermal Viscous Flow Coalescence at Micro Scale

“…Despite all of these improvements, there are still very few modelling or experimental studies on micro‐scale coalescence that consider non‐isothermal conditions . This is because the spatial temperature distribution inside the particles/droplets was always neglected during the bridge formation due to their small size and, consequently, small Bi numbers ( Bi = hL/k ; where h is convection heat transfer coefficient of the surroundings, k is the conduction heat transfer coefficient of the body, and L is a characteristic length in the system, e.g., radius of the spheres) …”

“…However, several numerical and experimental studies demonstrated the importance of the influence of temperature on the coalescence rate in larger scales . By combining the micro‐scale model of Pokluda with the macro‐scale heat conduction equation, Tarafdar and Bergman investigated the non‐isothermal sintering of a series of amorphous polycarbonate particles under a temperature gradient.…”