Analytical model development and experimental investigation of process model size effects in microforming.

摘要

With the emergence of micromanufacturing technologies, a critical need to develop process models that can accurately predict the required parameters, such as process forces, has arisen. As with the manufacturing processes themselves, macroscale process models can not effectively be used at the microscale due to size effects, i.e. changes in material and process parameters with miniaturization. Size effects with respect to material properties and frictional conditions have been demonstrated in past research. This dissertation demonstrates the existence of size effects due to process model assumptions and specimen deformation.; The two processes investigated in this research were microbending and microextrusion. For bending, the dissertation focuses on two macroscale process model assumptions that may not hold at the microscale. These are the assumptions of a logarithmic strain distribution through the sheet thickness and that of a curved wall profile for the deformed sheet. For extrusion the focus is on the increased shear due to deformation size effects. The term in the process model that is used to calculate the shear deformation force was altered to account for this increased shear. Using existing macroscale models, new models are proposed that include size effects for the two processes.; The new models were evaluated by comparing the predicted results to both experimental and finite element simulation results. These new models showed significantly improved predictions of the peak forces for the microscale processes investigated. This is significant because sheet metal forming processes such as bending and extrusion are ideal fabrication techniques for mass production of parts at very competitive unit costs.