Investigations into the use of ball-burnishing of hardened steel components as a finishing process.

摘要

Burnishing is a chipless surface plastic deformation process. Its results are: smoothness is improved, and compressive stresses are induced in the surface layer. The contact pressure generated by the indenter must exceed the yield point of the material. When the material has a high hardness (up to 65 HRC), the most effective possibility to reach such high pressures is given by a ball-type tool.; The research presented in this dissertation is focused on burnishing of hardened steels as a finishing process. Stages accomplished: (1) Background research. (2) Screening experimental stage, to determine the basic trends. (3) Extended experimental stage, narrowing the range of the input variables. Influences in the process were determined, and prediction equations were derived. (4) Changes of the surface profile and dimensional changes were analyzed. (5) Fatigue strength improvement was proven. (6) Modeling of the component and ball and using a calibration methodology based on geometrical comparison with experimental indentation. (7) Simulation of the process using a specialized software and analysis of results. (8) A new simulation methodology was created, by considering surface with initial asperities.; The simulation focused on stress evolution in the subsurface, while real process parameters are used. The stages of simulation were: (1) Develop the burnishing model, with appropriate geometry and mesh. (2) Calibrate the model according to real indentation. (3) Selection of the main simulation features and parameters. (4) Simulation with and without initial asperities. (5) Analysis of the simulation output data.; The originality in this work consists of: (1) Proved the possibility to achieve the surface roughness in the range of grinding. (2) A unique link of the burnishing process with the previous hard turning has been offered. (3) Proved the capability of burnishing to improve fatigue strength. (4) A FE instrument of stress analysis was created, for surfaces with initial asperities.; The outputs obtained from simulation recommends them for further use in the following directions: (1) Use the methodology for predicting displacements and calculate the roughness after burnishing. (2) Use the simulation to predict surface strengthening. (3) Use the methodology for extended burnishing conditions and optimize the process.