Fem analysis of micro/meso-scale tooling of a precision unit

Abstract

Machining vibrations or chatter is an unwanted phenomenon during machining processes due to unwanted machining marks left on the workpiece. To identify feasible machining speed for chatter-free machining, frequency response functions (FRF) of the machine-tool structure is required. However, due to almost infinite number of combinations between machine-spindle-toolholder-tool, it is impractical to obtain FRF of each combination by modal testing. Thus receptance coupling substructure analysis (RCSA) is used to reduce the number of modal testing required to be carried out when same machine-spindle-toolholder substructure is reused with other tool configurations. This project derived various RCSA algorithms and verified them using finite element method and experimental testing. RCSA is carried out using the derived algorithms and the process is simplified by using beam theories to substitute finite element analysis (FEA) to obtain free-free FRFs of tools and blanks. Besides that, the complex tool dimensions are also simplified using different analytical models. The prediction from RCSA is then compared to the experiment results obtained from modal testing on similar structure. The assumption of rigid connections between toolholder and tool is also investigated and compared to non-rigid connection assumption, which arises due to the elastic clamping of tool to the toolholders. This assumption states that the two substructures do not have same displacement at the joint location, and the displacement mismatch is compensated by means of springs and dampers between them. The value of the spring stiffness and damping coefficient is unknown, and varies according to different tool or blank configurations. Thus, their relationship with various tool/blank configurations are observed and the relationships are then used to predict values of these coefficients for other tool/blank configurations. The values are then used together with RCSA method to predict the tool point FRFs, and iss compared to the experimental results from modal testing.