Material piling up and spreading effects in the cutting processes with small feed rates

Abstract

Previous studies only reported that the material piling up effect will occur in the cutting processes with relatively small feed rates, and even in this case, there is no further theoretical report to touch its generation mechanism. In this work, it is the first time to experimentally report that obvious material spreading phenomenon together with the material piling up effect appears in the cutting process, whose uncut chip thickness is less than the minimum uncut chip thickness (MUCT). It is found that one part of the material to be cut will be piled up in front of the cutter’s rake face. Meanwhile, the remained part flows into the cutter’s clearance face, followed by further compression. As a result, the cutting tooth actually does not remove the material, but rolls the material by its rounded edge. Just because of this rolling effect, the flowed material is deformed and spread along the width direction of the workpiece surface, and this spreading behaviour leads to that the width of the machined workpiece is larger than its initial value. The spread width of the workpiece is quantitatively characterized by using Tselikov’s theory, which is widely used to capture the rolling behaviour. The volume of the material piled up in front of the cutter’s rake surface is calculated by subtracting the volume of the spread material, which is calculated based on the spread width, from the volume of the initial material to be cut according to the volume invariance principle. Subsequently, the height of the piled up material is calculated by geometrically modelling the piling up area as a triangle region. Based on the above analyses, the material spreading and piling up mechanisms in cutting are theoretically explored. The validity of the theoretically calculated spread width and piling up height is verified by the numerical results obtained from finite element simulations. Finally, a cutting force model that can characterize the influences of spreading and piling up effects is established. Several cutting experiments, including both the micro and conventional milling tests, confirm that the proposed methods can give better prediction accuracy of the cutting forces, especially when the ratio of feed rate to the radius of the rounded cutting edge is small.