In search of machining solutions for the micro-world
Requirements for miniature components are continuously increasing for manufacturers that continue to chase efficient machining solutions. The biomedical industry, for example, thrives on developing the least-invasive devices for surgical applications. On the other hand, industries as diverse as micro-electronics and aerospace demand complex, smaller components made from exotic and difficult-to-machine materials. As manufacturers strive to meet the increasingly tight tolerances of components that are becoming smaller, the use of conventional forming processes leads to damaging miniature materials. Within the MACHMINI project, new definitions of plastic deformation characteristics of miniature materials were formulated to support modelling of forming processes. Considering both grain size and surface effects that are more pronounced than in bulk materials, a microstructural model of a single crystal was used to predict the behaviour of elementary volumes. The model was developed by project partners at the Société Lorraine de Services Informatiques and implemented in the finite element code ABAQUS®. More specifically, mechanisms of plastic gliding observed in the laboratory on slip systems of well-defined geometry formed the basis of the User Material (UMAT) subroutine formulating the model. Among the model's internal variables, the dislocation densities were calculated for each slip system. On the other hand, simulations of simple tensile tests performed on thin metal sheets offered a better understanding of observed dislocation. As metal sheets were pulled, their response to the forces applied revealed the role of the grains' relative dimension and position with respect to the free surface. These theoretical results allowed the MACHMINI project research to be oriented towards an improved design of forming equipment incorporating piezo-activation to effect controlled deformation of miniature materials.
