Modeling and Analysis of the Shot Peening Process : a Study of the Residual Stresses in an Insert using the Finite Element Method

Abstract: Cutting tool inserts are often coated with thin layers either through chemical vapor deposition (CVD) or physical vapor deposition (PVD) processes. In order to have a better wear resistance cutting tools are mostly subjected to post-coating treatment processes. Shot peening is one of the processes that is used to improve the fatigue life of metallic components. In this study, the finite element (FE) method is employed to model the elastic-plastic deformation and development of residual stress distributions in a cutting tool after the impact of a shot medium. To carry out the work, CVD coated cemented carbide has been chosen to be the workpiece (insert), and the coatings of the chosen insert are Titanium Carbo Nitride (TiCN)  and Aluminum Oxide (Al2O3). Aim of the study is to model a single impact in the shot peening process on a surface of a coated cemented carbide insert while simulating the plastic deformation of the materials. In addition, the objective of the study is also to understand and explain the mechanics of shot peening process and find applicable mechanical properties of the materials for FE modeling. Conjugately, the influence of shot peening process parameters (e.g. velocity, diameter or shape of the peening media) on residual stress distribution has been investigated and the results obtained were compared to the one observed from experiment. The modeling in the study is carried out both with and without initial residual stresses in the materials. The initial residual stresses are estimated by applying a thermal load to the model. The results show that the compressive residual stresses achieved while shot peening by an edge-shaped medium are significantly higher at the surface (i.e. in a coated layer) than compared to a globular medium. In contrast, it is observed that the compressive residual stresses in the cemented carbide are significantly higher and deeper when shot peened with globular medium than the edge-shaped medium. Furthermore, the results of parameteric study demonstrate that the smaller medium induces higher residual stresses at the surface (i.e. in a coated layer) than in the cemented carbide. In contrast, it is observed that the bigger medium induces less residual stresses at the surface (i.e. in a coated layer) and higher residual stresses deeper in the cemented carbide. Whereas, it is observed that the higher residual stresses at the surface (i.e. in a coated layer) and in the cemeneted carbide can be achieved simultaneously by shot peens having a  higher velocity. Residual stress profiles modelled in this report correlate with data from previous studies.   This study has been carried out at Sandvik Coromant, Edge and Surfaces department in Stockholm, Sweden.