Linköping Studies in Science and Technology. Dissertations
No. 521

On constitutive modelling of the compaction
and sintering of cemented carbides

Jan Brandt

Akademisk avhandling

som för avläggande av teknisk doktorsexamen vid Linköpings Tekniska Högskola kommer att försvaras offentligt i sal Planck, Fysikhuset, Linköpings Universitet, torsdagen den 23:e april, kl 10.15. Fakultetsopponent är Professor Viggo Tveergard, Danmarks Tekniska Universitet, Lyngby.

Abstract

The common manufacturing procedure for components of cemented carbide is a closed die cold compaction of a powder and a subsequent sintering of the compact to full density and strength.

Major problems with the manufacturing process are the possible fracturing on ejection from the tooling and the distortion in the final shape. It is beneficial to perform the design iterations in the form of computer simulations, provided such simulations predict at least the final shape with good accuracy. This thesis concerns the development of computer simulation tools for both the compaction and the sintering.

A constitutive model for the compaction based on elasto-plasticity has been developed. The model has a compactness tensor that measures the directionality of the deformation history and a two-dimensional hardening parameter set. The model represents the deformation induced anisotropy in the form of a kinematic hardening combined with an isotropic hardening, and uses a flow rule that emanates from a non-associated flow potential.

Furthermore, a continuum model of the sintering with and without loading has been developed, based on a micromechanical model of the sintering without loading. The model is visco-elastic with the capillary forces represented by a sintering stress. The model parameters evolve with temperature, relative density and rate of temperature. The author presented a rationale for deciding, in which mechanism the rate of temperature influence belongs.

The models were implemented in the explicit FE-program LS-DYNA2D and verified against several experimental compaction and sintering tests. Finally, the models have been verified by the simulation of the complete compaction and sintering process of an industrial tool piece. The agreement between simulation and measurement in final shape is good. The convergence of the simulation concept is also demonstrated

Division of Solid Mechanics
Department of Mechanical Engineering
Linköping University, S-581 83 Linköping Sweden

Linköping 1998

ISBN 91-7219-174-0 ISSN 0345-7524