Thermal Generation of Residual Stress Fields for Purpose of Distortion Minimization

Abstract

Thermal treatments of steel components with the goal of hardening often result in distortion by releasing the residual stresses which were brought into the specimen during the preceding processing steps. The goal of the presented work is the minimization of this distortion. By generating definite residual stress fields and investigating the resulting distortion, the distortion mechanism can be observed in detail. A flexible and reproducible way to generate such residual stress fields inside a specimen is by means of local thermal treatment with a laser beam. Computer simulations as well as experiments were carried out using an idealized tooth of a gearwheel (finger sample) as a model system. The deformation of the samples due to the laser heat treatment and the stress fields generated inside the samples were determined with respect to different process parameters.

Monitoring a laser beam heat treatment process by means of digital speckle photography

“…With a primary objective of correcting and/or eliminating unwanted distortions in various steel production processes, an additional process step in the production chain (thermal induced pre-stressing) has been proposed and designed in the framework of SFB 570 Distortion Engineering [1,2]. Thereby, local laser based heat treatment is employed to manipulate residual stresses in the work piece.…”

“…Undergoing work aimed at the development and optimisation of this additional process essentially comprises in employment of both experimental and simulational tools to help determine key process parameters and their magnitude. To investigate which thermal forming mechanisms are involved in this process, hardening and stress relief heat treatment was investigated numerically [3,4]. Moreover, since changes in residual stresses are always accompanied by geometrical changes, experiments were undertaken to determine the magnitude of deformation.…”

“…Moreover, since changes in residual stresses are always accompanied by geometrical changes, experiments were undertaken to determine the magnitude of deformation. For this purpose, geometrical measurements were carried out before and after heat treatment using a coordinate measurement machine [1]. This pre and post process measurements, however, only give very limited insight into the in-process changes.…”

In Situ Digital Image Correlation Observations of Laser Forming

“…This phase transformation always needs to be taken into account when laser processing of Ti or its alloys is studied [13][14][15]. It is shown in [16] that changes in the deformation bending angles of up to 0.1 • can occur in steel when the phase changes from ferrite to austenite. This phase transformation and all other microstructural changes developed during the LF process can be characterized with the aid of electron back-scatter diffraction (EBSD) when considering crystallographic properties of the laser heat-affected zone (LHAZ) within the specimen.…”

Simulation of the distortion manipulation of gear wheel teeth by thermal pre‐stressing

“…A flexible and reproducible way to generate such residual stress inside a specimen is thermal treatment with a laser beam. The component is deformed due the activation of different thermal forming mechanisms: temperature gradient mechanism, residual stress relaxation mechanism [3] and martensite expansion mechanism [4]. A prediction of the final distortion of the component in dependence on the process parameters of the thermal pre-stressing can be done, by calculation of the time dependent development of the temperature field, the stress field and the deformation of the component using a simulation model, which accounts for thermomechanical effects as well as phase transformations.…”