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Abstract
AISI 52100 steel is often used as material for highly loaded rolling bearings in machine tools. An improved surface integrity, which can be achieved by means of mechanical surface layer finishing, can avoid premature failure. One of these finishing processes is machine hammer peening (MHP) which is a high-frequency incremental forming process and mostly used on machining centers. However, the influence of robot-guided MHP processing on the surface integrity of AISI 52100 steel is still unknown. Therefore, the objective of this work is to investigate experimentally the robot-based influences during MHP processing and the resulting surface integrity of unhardened AISI 52100 steel. The results show that the axial and lateral deviations of the robot due to process vibrations are in the lower µm range, thus enabling stable and reproducible MHP processing. By selecting suitable MHP process parameters and thus defined contact energies, even ground surfaces can be further smoothed and a hardness increase of 75% in the energy range considered can be achieved. In addition, compressive residual stress maxima of 950 MPa below the surface and a grain size reduction to a surface layer depth of 150 µm can be realized.
Highlights
Because of the lower stiffness of an industrial robot compared to a machining center, the robot dynamics and its influence on the hammering result were investigated before the machine hammer peening (MHP) experiments
The topic of different velocity profiles in robot-based MHP processing and the resulting uneven energy input due to different numbers of individual impacts has already been addressed by Krall [21]
By a targeted coupling of the MHP system via a serial interface expected that those lower feed rates in the case of surface machining will lead to a further increase in the range of the constant robot velocity
Summary
Rolling bearings are technical elements that are used in a variety of machines to enable rotational movements. The components of rolling bearings (bearing rings and rolling elements) must withstand high cyclic loads because of over rolling [1], which consist of high contact pressures (up to 3000 MPa) [2], high speeds, and occasionally elevated temperatures [3] and occur with relatively small sliding movements [4]. The material requirements can be derived from the technical requirements for rolling bearings: high hardness, rolling strength and wear resistance, no structural changes and sufficient ductility [5]. When the bearing is properly lubricated, the phenomenon of rolling contact fatigue begins as a micro-crack beneath the surface, which spreads as a macro-crack toward the surface, and when subjected to further loading leads to shell-shaped pittings [10]
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