Evaluation of Residual Stresses Induced by High Speed Milling Using an Indentation Method

Abstract

In this work, a recently developed method based on the change of distance between collinear indents is used to evaluate different states of residual stress, which were generated in samples of AA 6082-T6 and AA 7075-T6 aluminium alloys milled at high speed. One of the advantages of this method, which needs a universal measuring machine, is not requiring neither the use of specific equipment nor highly skilled operators. Also, by integrating an indentation device to the mentioned machine, the absolute error of measurement can be reduced. In results obtained in samples subjected to different cutting conditions it is observed a correlation between the stress values and the depth of cut, showing the AA 6082-T6 alloy higher susceptibility to be stressed. Furthermore, the high sensitivity of the method allowed detecting very small differences in the values reached by different normal components in the zones corresponding to climb and conventional cutting. It is important to note that these differences were similar for both evaluated alloys. Finally, the directions associated with the principal components of residual stress, where maximum local plastic stretching occurs, were found to be strongly dependent on the rolling direction prior to machining.

Study of Residual Stresses from Two Machining Protocols Using an Indentation Method

“…The details of the indentation technique used in this work for determining different components of the residual stress can be found in previous studies [10][11][12]. In general terms, this technique consists of two stages.…”

“…Then, the micro-indent coordinates are measured, before and after a thermal distension treatment, using a universal measuring machine (UMM) of high accuracy. It is noteworthy that these machines are very versatile, allowing to carry out different types of measurements in mechanical components, including the determination of orthogonal coordinates (x, y, z) at any point through the incorporation of a high precision microscope in the main header of the machine [12]. Moreover, to carry out the aforementioned machining tests, we used a face mill of 63 mm in diameter.…”

“…Then, as mentioned previously, the micro-indent coordinates are measured, before and after a distension treatment, using a precision microscope incorporated to the measuring machine (GSIP MU-314). Afterwards, by processing all micro-indent coordinates associated to the evaluated point, it is possible to obtain the normal components of the residual strain (εx, εy), which correspond to the centroid of the square [12]. Finally, through these strain components and assuming that the new surface is under plane stress conditions [13], the normal components of the residual stress, in the case of a homogeneous, isotropic and linear elastic material, may be expressed as…”

“…Recently, Wyatt and Berry [9] developed a technique based on the change that occurs in the distance between micro-indents when the machined component is subjected to a distension treatment. More recently, through an optimized version of this technique, it was possible to conduct different studies in order to analyze the influence of high-speed machining process parameters on the generation of residual stresses in samples of different aluminum alloys [10][11][12].…”

Modeling and Parameter Optimization for Surface Roughness and Residual Stress in Dry Turning Process

“…Thus, the residual stress in a machined layer has been studied by many researchers. The majority of research work on residual stresses in metal cutting has been limited to experimental study [9][10][11][12][13]. Despite these efforts, the quantitative relationship between cutting conditions and residual stresses is still unknown due to the inherent complexity nature of the formation of residual stresses in metal cutting.…”