A study on material removal mechanism of ultramicro-grinding (UMG) considering tool parallel run-out and deflection

Abstract

Micro-grinding is capable of machining complex structures in a wide variety of hard and brittle materials when compared to other micro-machining processes. In recent years, more attentions have been paid to micro-grinding field, but not much even little has been paid to ultramicro-grinding (UMG). What usually be called UMG is a kind of micro-grinding process, during which grinding tool is extremely small, usually less than 50 μm. In this scale, tool parallel run-out and tool deflection have a big effect on grinding results. In view of the abovementioned facts, the exact prediction of grinding force in UMG is still not fully developed, especially when considering tool parallel run-out and tool deflection. In order to better explain the grinding process and the material removal mechanism in UMG, this paper proposes an analytical grinding force prediction model considering the related cutting parameters, tool parallel run-out, tool deflection, size effect, and the exact trochoidal trajectory of single grain. In this prediction model, final undeformed chip thickness is computed by considering tool parallel run-out and tool deflection, then forces are calculated based on the final undeformed chip thickness. In order to study the special characteristics of UMG, a series of UMG single-factor experiments have been conducted, and the parameters of tool parallel run-out and tool deflection were measured during the experiment. The proposed grinding force model is validated through UMG orthogonal experiment with grinding tool about 40 μm diameter, and the workpiece is single-crystal silicon. During the experiment, the total indicated run-out (TIR) and grinding forces in both x and y directions are measured and analyzed, and the relationship between grinding forces and cutting parameters, between TIR value and cutting parameters, and between grinding forces and TIR value are investigated. Relative to the general cutting condition, a sliding situation (cutting depth is extremely low) is found and analyzed. Based on the experiment results, an empirical formula for cutting parameters and TIR is obtained. To verify the model, comparisons among experimental result, the proposed model and the previous three force models are made, and the final comparison result shows that the proposed model agrees better with the experimental results than other three previous models, only a few mismatched points (E > 10%) are found, and the biggest error for Fx is 18.12% and for Fy is 20.91%, indicating the effectiveness and accuracy of the proposed model. The proposed grinding force model is not only expected to be meaningful to optimize grinding parameters but also anticipated to be powerful to provide the basis for the more accurate grinding force prediction.