Development of a microstructure-level finite element model for the prediction of tool failure by chipping in tungsten carbide-cobalt systems.

摘要

A microstructure-level finite element machining process simulation model has been developed to predict failure of WC-Co tool grades due to chipping during continuous and intermittent cutting. The model is capable of simulating orthogonal machining process with varying compositions of WC-Co materials and machining conditions to predict tool failure.; A methodology was developed to simulate arbitrary WC-Co microstructures. Material properties of pure WC and Co samples were individually characterized by uniaxial compression tests over a range of temperatures. A model was developed to predict tool failure for uncoated tool systems based on the mixed mode fracture criterion. A finite element based simulation methodology was developed for orthogonal machining. Continuous turning experiments were conducted to validate the model and the results showed that the model predictions agree well with the observation from the experiments. The model was then employed to investigate the effects of microstructural parameters and machining conditions on fracture toughness.; The model has been extended to tool failure prediction with coated WC-Co grades in continuous cutting. Microstructures of coating layers were characterized and criteria of the subsurface fracture and coating delamination were included. The model was then validated by continuous turning experiments with both monolayer and multilayer coated tools. The model successfully predicted tool failure in coated WC-Co systems for continuous cutting.; The methodology has further been extended to tool failure prediction in intermittent cutting. In order to simulate cyclic loading conditions during intermittent cutting, mechanical and thermal boundary conditions were applied during cutting phases and removed during non-cutting phases. The changing mechanical and thermal boundary conditions enable cracks to continue to grow during non-cutting phases and during the subsequent cutting cycles. The failure prediction model was validated by interrupted turning experiments. Tool failure was successfully predicted within 20% error between the predictions and experiments.; The model has also been applied to a problem of WC-Co grade design for the improved performance. Validation experiments demonstrated the efficacy of model predictions. The simulation results agreed well with the observation found in the past literature that fatigue strength increases in a non-linear fashion with increase of Co amount.