Neck growth kinetics during ultrasonic-assisted sintering of copper powder

The present paper presents an investigation of the neck growth kinetics during ultrasonic-assisted sintering of the loose spherical copper particles. The study was performed to identify the sintering mechanism during the initial stage sintering of the copper powder. The classical sphere-to-sphere approach was used to determine the neck growth between the particles at four different sintering temperatures 700, 800, 900 and 950 ℃ at different soaking time of 60, 180, 300, 600, and 900 s. The neck growth exponent was found to be 6.21, 4.92, 5.26 and 5.13 for different sintering temperatures, respectively, which signified the involvement of surface and volume diffusion mechanism during the initial stage sintering of copper particles with ultrasonic vibration assistance. The neck growth calculation was attempted to compare with conventional sintering. The evidence of the local heating between the particles was evolved from the activation energy calculations, which was found to be lower than the conventional sintering. An attempt was made to develop a numerical model for the prediction of neck growth by considering the rise in temperature due to friction between the particles owing to ultrasonic vibrations at different sintering temperature and soaking time. The model was obtained to be in-line with the trend of the experimental results.

The role of heating and cooling in viscous sintering of pairs of spheres and pairs of cylinders

Purpose This study aims to develop mathematical models for the determination of the effects of heating or cooling on neck growth in Selective Laser Sintering (SLS) and Fused Filament Fabrication (FFF). Two particle shapes are studied: spherical and cylindrical. Design/methodology/approach The time required for the coalescence (sintering) process is determined by balancing the work of surface tension forces and viscous dissipation. Heating and cooling effects are studied by incorporating temperature dependence of viscosity in an exponential form. Heating by a laser, convective and/or radiative heat transfer is assumed. It is also assumed that there are no temperature gradients within the coalescing molten polymers (lumped parameter heat transfer analysis). Findings The models predict faster sintering with heating and slower with cooling, as expected because of the effect of temperature on viscosity. For the isothermal case of pairs of cylinders, the present model predicts significantly longer time for completion of sintering than a previously developed and frequently cited model by Hopper. Originality/value An isothermal sintering model for two spheres was reworked for two long cylinders, and for the first time it has been compared to other models available in the literature. The mathematical models are capable of predicting neck growth under non-isothermal conditions for both spheres and cylinders. They are useful in assessment of bonding in selective laser sintering and fused deposition fabrication.

Modelling the Sintering Neck Growth Process of Metal Fibers under the Surface Diffusion Mechanism Using the Lattice Boltzmann Method

In this paper, the sintering neck growth process of metal fibers under the surface diffusion mechanism is simulated by using the Lattice Boltzmann method (LBM). The surface diffusion model is developed considering the geometrical characteristic of metal fibers. Then, the LBM scheme is constructed for solving the developed surface diffusion model. The sintering neck growth process of two metal fibers with different fiber angles is simulated by LBM. The simulated morphologies of sintering metal fibers well agree with ones obtained by experiments. Moreover, the numerical simulation results show that the sintering neck radius of two metal fibers is increased with the increase of fiber angle, which implies that the initial geometrical characteristic plays an important role in the sintering neck formation and growth of metal fibers.