Events
Seminar on "Constitutive models for die compaction of powder materials"
| Date: | Thursday 23 February 2006 16:00 - 17:00 |
| Location: | IRC seminar room |
By Dr. Csaba Sinka, Merck Sharp and Dohme Ltd. Hoddesdon, UK
abstract
Powder compaction is a manufacturing operation used in powder metallurgy, ceramics, hard metals, pharmaceuticals, detergents and other industries. Compression represents one of the most important unit operations because the shape, strength and other important mechanical properties of the compacts are determined during this process. These properties are dictated not only by the characteristics of the powder constituents, but also by the selection of the process parameters, which are imposed by the production machinery. Numerical modelling of the compaction process is used in industry as means of optimizing the formulation of the powders blends, selection of process parameters and tool design. We present the current state of constitutive model development for the compaction behaviour of metal, ceramic and pharmaceutical powders. Finite element modelling involves solving of equilibrium, compatibility and constitutive equations and requires knowledge of the following four factors:
constitutive behaviour of powder under compaction, which relates the strains and stresses during the compaction process, that is the deformation of a volume of powder under a given set of external loads. The details of the contact interaction between neighbouring powder particles i.e. the cohesion and interparticulate friction are incorporated in a macroscopic continuum constitutive model. friction behaviour between powder and tooling (die and
punches) geometry of die and punches (including initial conditions resulting from die
filling)
loading schedule (sequence of punch motions)
initial condition of powder which result from die fill
Finite element simulations of the density distribution in powder compacts are presented together with experimental validation. Density variations within compacts are important because they induce local variation of compact properties. The effect of density distribution on post-compaction behaviour is examined. Applications of the analysis to product and tool design are presented in the context of an overall process model covering all stages from powder formulation and granule design, powder handling and die fill, compaction and post-compaction operations, to packaging, transport, storage and use.
