Flow regime analyses during the filling stage in powder metallurgy processes: experimental study and numerical modelling

Abstract

Experimental and numerical studies of powder\ud flow during the die filling stage in powder metallurgy cold\ud compaction processes are presented. An experimental setting\ud consisting of a horizontal pneumatically activated shoe,\ud a vertical die and high-speed video system has been designed.\ud The experiments show the existence of three flow regimes:\ud continuous, transitory and discrete, which are identified in\ud terms of the particle size, the morphology and the speed of\ud the shoe. In the continuous regime the powder flows in a progressive\ud manner but in the discrete one some perturbations\ud appear as a consequence of a shear band formation that forms\ud discrete avalanches. A numerical model, based on a ratedependent\ud constitutive model, via a flow formulation, and in\ud the framework of the particle finite element method (PFEM)\ud is also proposed. For the purpose of this study, the use of the\ud PFEM assumes that the powder can be modelled as a continuous\ud medium. The model, provided with the corresponding\ud characterisation of the parameters, is able to capture the two\ud fundamental phenomena observed during the filling process:\ud (1) the irreversibility of most of the deformation experienced\ud by the material and (2) the quick dissipation of the potential\ud gravitatory energy of the granular system through the inter-particle friction processes, modelled by the plastic dissipation\ud associated with the material model. Experimental and\ud numerical results have been compared in order to study the\ud viability of the proposed model.Peer ReviewedPreprin

The particle finite element method for transient granular material flow: modelling and validation

“…The first constitutive model is based on a constitutive relation for the flow of plastic and visco-plastic solids. It was originally outlined in [87] and was specialized in [8] to a Drucker-Prager yield surface [19], with a non-associated flow rule.…”

“…(8) reduces to rate independent plasticity theory when μ p → 0. Cante et al [8] specialized the Perzyna relationship to the Drucker-Prager yield surface ( Fig. 4), which has the following functional form…”

“…In the present study, the flow rule assigned to the Drucker-Prager yield surface is non-associated and consists of a purely deviatoric strain rate, and it can be expressed as The material flows at F ≥ 0 and from Eqs. (8) to (10) the following expression can be obtained…”

Meshless methods for the simulation of material forming

“…If free-surface flows are considered, it is again of utmost importance to employ any technique for the reconstruction of the geometry of the evolving domain. While most meshless approaches do not employ any particular technique, thus provoking results depending on the shape functions' support, shape constructors have been employed in a number of works [84,59,72,71,19,68]. α-shapes [43,44,31] are perhaps the most widely used shape constructors in this context.…”

Estudo de variáveis no processo de compactação de pós a base de alumina

“…Se a densidade solta estiver abaixo da adequada pode haver elevada quantidade de ar aprisionada entre os grânulos, podendo provocar a geração de um tipo característico de defeito, a chamada delaminação; além disso, nos processos automatizados, a densidade a verde do compactado está diretamente relacionada à densidade solta e, portanto esta deve ser reprodutível [24] .…”