Improved finite element modelingfor chip morphology prediction inmachining of C45E steel

Sammanfattning: Within the manufacturing of metallic components, machining plays an important role and is of vital significance to ensure process reliability. From a cutting tool design perspective, physics-based numerical modeling that can predict chip morphology is highly necessary to design tool macro geometry. The chip morphology describes the chip shape geometry and the chip curl geometry. Improved chip morphology prediction increases process reliability by improved chip breakability and effective chip evacuation.To this end, in this work, a platform is developed to compare a numerical model'schip morphology prediction with experimental results. The investigated cuttingprocesses are orthogonal cutting process and nose turning process. Numerical models that simulate the chip formation process are used to predict the chip morphology accompanied by machining experiments. Computed tomography isused to scan the chips obtained from machining experiments evaluating its ability to capture the chip morphology variation. For the nose turning process, chip curl parameters need to be calculated during the cutting process. Kharkevich model is utilized in this regard for calculating the 'chip in process' chip curl parameters. High-speed videography is used to measure the chip side-flow angle during thecutting process experiments enabling comparison with physics-based model predictions.With regards to chip shape predictability, the numerical models that simulate the chip formation process are improved by improving the flow stress models and evaluating advanced damage models. The workpiece material, C45E steel, arecharacterized using Gleeble thermo-mechanical simulator. The obtained flow stress is modeled using phenomenological flow stress models. Existing phenomenological flow stress models are modified to improve their accuracy. The fracture initiation strain component of damage models' influence on the prediction of transition from continuous chip to segmented chip is studied. The flow stress models and the damage models are implemented in the numerical models through FORTRAN subroutines. The prediction of continuous to segmented chip transitions are evaluated for varying rake angles and feed rate ata constant cutting velocity.The results from the numerical model evaluation platform show that the methodology provides the framework where an advance in numerical models is evaluated reliably from a 'chip morphology prediction capability' viewpoint forthe nose turning process. The numerical modeling results show that the chip curl variation for varying cutting conditions is predicted qualitatively. The flow stress curves obtained through Gleeble thermo-mechanical simulator show dynamic strain aging presence in specific temperature -strain rate ranges. The results of the phenomenological model modification show their ability to incorporate the dynamic strain aging influence. The modified phenomenological model improvesthe accuracy of the numerical models' prediction accuracy. The flow stress models combined with advanced damage model can predict the transition from continuous to segmented chip. Within damage model, the fracture initiation strain component is observed to influence the continuous chip to segmented chip transition and chip segmentation intensity for varying rake angle and feed rate and at a constant cutting velocity.