This paper is focused on optimizing the cutting conditions for the surface roughness, inner-diameter error and roundness obtained in hard turning of an inner ring bore. The hard-turning experiments were conducted on hardened and tempered AISI 52100 bearing rings using the L9 orthogonal array on a CNC lathe. The cutting speed, feed rate and number of the machined part were selected as control factors. The optimum cutting conditions were determined using the signal-to-noise (S/N) ratio. S/N ratios were calculated using the lower-the-better approach. An analysis of variance (ANOVA) was also employed to determine the level of the effect of the control factors for the surface roughness, inner-diameter error and roundness. The statistical analysis showed that the feed rate was the most significant factor for the surface roughness while the cutting speed was the most significant factor for the roundness and inner-diameter error. Finally, the optimum cutting conditions were further confirmed with confirmation tests. Keywords: diameter error, hard turning, roundness, surface roughness, Taguchi method lanek je osredinjen na optimiranje razmer pri rezanju glede na hrapavost povr{ine, napake notranjega premera in okroglosti pri trdem stru`enju notranjega roba izvrtine. Preizkusi trdega stru`enja so bili izvr{eni pri kaljenem in popu{~enem AISI 52100 obro~u le`aja z uporabo L9 ortogonalne matrike na CNC-stru`nici. Hitrost rezanja, hitrost podajanja in {tevilo obdelanih kosov so bili izbrani kot kontrolni faktorji. Optimalne razmere rezanja so bile izbrane z uporabo razmerja signal-hrup (S/N). S/N-razmerja so bila izra~unana s pribli`kom~im manj tem bolj{e. Analiza variance (ANOVA) je bila tudi uporabljena za dolo~itev vpliva kontrolnih faktorjev na hrapavost povr{ine, napak notranjega premera in okroglosti. Kon~no so bili optimalni parametri potrjeni s potrditvenimi preizkusi.

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Experimental investigation of residual stresses after heat treatment and grinding processes in the production of ball bearing rings has been carried out. The residual stresses were measured by X-ray diffraction method utilizing chromium radiation, which has an average penetration depth of 5 μm incident on 100Cr6 (AISI-E52100) ball bearing steel. The process parameters of heat treatment and grinding processes were varied so as to represent the extreme values that can be applied in the respective processes. Hardness and percent retained austenite limit the heat treatment process parameters; while roundness, surface roughness and form the grinding process. Tensile surface residual stresses on the raceway of ball bearing rings changes to compression after grinding in both circumferential and axial directions. In grinding relatively higher compressive stresses were measured in axial direction compared to the circumferential direction. This experimental investigation also showed that the influence of heat treatment process parameters on the magnitude and distribution of residual stresses survived even after grinding process; i.e. heat treatment and grinding processes cannot be evaluated independently in process design for favourable residual stresses.

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The aim of this study is to investigate surface residual stresses after heat treatment and grinding processes in the production of rollers. The residual stresses were measured using the X-ray diffraction method utilizing chromium radiation, which has an average penetration depth of 5 μm incident on AISI-E52100 (100Cr6) ball bearing steel. Taguchi design of experiments (DOE) is applied to define the set of experiments for grinding, which facilitates evaluation of the individual influences of process parameters on residual stresses and also eliminates unnecessary experiments. Response of residual stresses to each parameter is evaluated with the help of the results of residual stress measurements by X-ray diffraction. In grinding with aluminum oxide wheels, it was concluded that the lower the cutting speed and the higher the workpiece speed the higher the magnitude of surface compressive residual stresses. Higher compressive stresses were measured in axial direction compared to the circumferential direction after the grinding process.