Abstract
The fatigue behavior of components made of quenched and tempered steel alloys is of elementary importance, especially in the automotive industry. To a great extent, the components’ fatigue strength is influenced by the surface integrity properties. For machined components, the generated surface is often exposed to the highest thermomechanical loads, potentially resulting in transformations of the subsurface microstructure and hardness as well as the residual stress state. While the measurement of the mechanical load using dynamometers is well established, in-process temperature measurements are challenging, especially for drilling processes due to the process kinematics and the difficult to access cutting zone. To access the impact of the thermomechanical load during the single-lip drilling process on the produced surface integrity, an in-process measurement was developed and applied for different cutting parameters. By using a two-color pyrometer for temperature measurements at the tool’s cutting edge in combination with a dynamometer for measuring the occurring force and torque, the influence of different cutting parameter variations on the thermomechanical impact on the bore surface are evaluated. By correlating force and temperature values with the resultant surface integrity, a range of process parameters can be determined in which the highest dynamic strength of the samples is expected. Thermally induced defects, such as the formation of white etching layers (WEL), can be avoided by the exact identification of critical parameter combinations whereas a mechanically induced microstructure refinement and the induction of residual compressive stresses in the subsurface zone is targeted. Further, eddy-current analysis as a non-destructive method for surface integrity evaluation is used for the characterization of the surface integrity properties.
Highlights
Quenched and tempered steels such as AISI 4140 (42CrMo4 + QT, 1.7225) are widely used in industrial applications where components are subjected to high static or dynamic loads
The superposition of thermomechanical loads acting on the bore As wall during the drilling process are decisiveoffor the resulting surface previously mentioned, the superposition thermomechanical loadsintegrity
Allow the tool assumption the measurement in the boreinvestigations wall as well aspublished in the contact area between and borethat surface correlation is caused by changes in the subsurface microstructure of the bores wall
Summary
Quenched and tempered steels such as AISI 4140 (42CrMo4 + QT, 1.7225) are widely used in industrial applications where components are subjected to high static or dynamic loads. The main characteristics, that are used to describe the surface integrity are the surfaces’ topography, and the microstructure, hardness, and residual stresses of the surface layers [2] For hydraulic components, such as fuel injectors or fuel distribution systems in the automotive industry, or components such as valves in high-pressure hydraulic applications in mechanical engineering, the inner surface is critical for fatigue strength. Since these surfaces of the components are often subjected to high dynamic loads, it is highly important to specify and apply a manufacturing process to avoid any damage in the surface and rather specify a process that will even enhance a parts fatigue performance [1]. These areas appear as white etching layers (WEL)
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