Abstract
In machining processes, a decreasing undeformed chip thickness leads to an increase in the specific machining forces. This effect is commonly known as the scaling effect in chip formation. In the literature, several reasons for this effect are discussed. One approach focuses on the increase in the strain rate due to a decrease in the undeformed chip thickness. The increase in the strain rate leads to a hardening effect of the machined material which results in higher specific cutting forces. However, it has not been definitely proven that this is the cause of the scaling effect in chip formation. This paper describes an approach for examining the influence of the strain rate on the scaling effect. Firstly, FE-simulations have been carried out to gain knowledge about the strain rates in the center of the shear zone. By means of these simulations, cutting speeds which lead to constant strain rates in the center of the shear zone have been determined for a broad range of chip thickness. In a second step, experimental investigations have been carried out using the simulated cutting speeds and chip thicknesses. The chip formation processes and the machining forces have been analyzed with constant strain rates and different chip thicknesses as well as with a constant cutting speed. The main result of these investigations is that the strain rate has only a minor influence on the specific cutting forces. It is shown that the temperature in the shear zone decreases with a decrease in the chip thickness. This leads to lower thermal softening of the material and thus to higher specific cutting forces.
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Acknowledgments
The authors thank the German Research Foundation (DFG) for funding this work within the project “Influence of the chip cross section shape on the chip formation mechanism” as part of the special research program SPP 1138 “Process Scaling”.
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Denkena, B., de Leon, L. & Köhler, J. Influence of scaled undeformed sections of cut on strain rate, cutting force and temperature. Prod. Eng. Res. Devel. 4, 457–464 (2010). https://doi.org/10.1007/s11740-010-0230-9
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DOI: https://doi.org/10.1007/s11740-010-0230-9