Numerical investigation on the formation mechanism of residual stress in metal cutting

Abstract

Residual stress can be introduced unintentionally into the workpiece with various magnitudes and distributions through all manufacturing processes. These stresses have a significant effect upon the performance of the final component. Understanding the residual stress imparted by machining is an essential aspect of understanding the machining process and overall part quality. Although many investigations have been conducted over the past few decades in measurement, modelling and mechanisms of residual stresses induced by the different manufacturing processes, the insights of residual stresses induced during the machining are still far from being completely understood. Several crucial issues still have to be investigated. In particular, the residual stress generation under different circumstances (segmented chip, the variation of tool geometries, multiple cuts, and curved surface turning) still has to be fully assessed. In this dissertation, finite element method (FEM) was employed to simulate and analysis the residual stress induced by the metal cutting process aiming to contribute to further understanding of the machining-induced residual stress.
The dissertation covers four aspects of research. First, the cyclic residual stress distribution in machined workpiece with a segmented chip was simulated and investigated. It is shown that the feed force increase firstly and then decrease during one segment genesis. It is the increased feed force that cause an increase in the local normal/tangential stress acting on the machined surface, leading to a less tensile residual stress in the lower stress zone.
Second, the effect of tool geometry on residual stresses induced in an orthogonal cutting process was investigated. The thermal and mechanical contribution to the formation of residual stress was also distinguished. The local normal/tangential stress was used to determine the degree of the tensile plastic deformation induced by the tool, providing a reasonable explanation for the variation of subsurface compressive residual stress with the changing of tool geometry.
Third, the influences of multiple cuts and correspondent cutting parameters and tool geometry on residual stresses evolution were explored. For the first time, material loading cycles were developed in multiple cutting operations based on the quantified stress/strain that is obtained numerically. The results indicate that the existence of the previous cut tends to generate more compressive residual stress in the finished workpiece, and this effect is more evident when the previous cut is implemented at the cutting conditions producing a larger compressive stress/tensile strain in the subsurface.
Finally, the residual stress evolution when turning a fillet surface was simulated and analysed. The variation of the size and shape of uncut chip cross-section in outer/end surfaces turning was analyzed. It is shown that the residual stress becomes more compressive when the tool position changes from outer face to end face, although the difference is not significant.
All four aspects of research present new and novel contributions to the field of metal cutting simulations and numerical analysis. The key physical quantities (i.e., stresses, plastic strains, shear angle, material degradations, forces, and temperatures) generated in the cutting processes are thoroughly evaluated and analyzed to significantly increase the interpretation and understanding of residual stresses formation under different aspects.

• author: Liu, Yang
• supervisor: Jinming Zhou; Aylin Ahadi; Rachid M'saoubi
• opponent: Prof. Beno, Tomas, University West, Sweden.
• organization: Production and Materials Engineering; SPI: Sustainable Production Initiative
• publishing date: 2021-12-18
• type: Thesis
• publication status: published
• subject: Mechanical Engineering
• keywords: Residual stress, FEM,, Metal cutting, Thermal-mechanical load, Plastic deformation
• defense location: Lecture hall KC:A, Kemicentrum, Naturvetarvägen 14, Faculty of Engineering LTH, Lund University, Lund.
• defense date: 2021-12-17 09:00:00
• ISBN: 978-91-8039-077-4
• ISBN: 978-91-8039-078-1
• language: English
• LU publication?: yes
• id: 58dd1f2b-5d3f-42cd-b221-de243fb1ad81
• date added to LUP: 2021-11-17 11:52:35
• date last changed: 2022-04-07 09:30:58