No abstract

Chip formation in machining plays an important role in the cutting process optimisation.Chip morphology often reflects the choice of cutting conditions, the tool wear and by consequences the integrity of the machined surface and tool life. In this study, photographs of the chip morphology during high speed machining of a middle hard steel (C20 similar to AISI1020} are taken by using a ballistic setup. From these recordings, the evolution of the chip morphology is presented and analysed in terms of cutting conditions. A simplified modeling is then proposed by considering the workpiece material as elastic perfectly plastic. The existence of a scaling taw governing the chip morphology in high speed machining is demonstrated. The cutting velocity is shown to have a weak effect at high speed machining as opposed to the well known strong influence of the velocity in the range of low cutting speeds.

The streamline method was used to investigate the plastic strain rate in machining. The streamline function presented in this paper is a general equation with three parameters controlling the complex variation of flow line shape. Velocity and deformation field were obtained by streamline analysis. The validation of this model was conducted by comparing with other experimental results published. It shows that the streamline model presented in the paper can be applied to the evaluation of strain rate in machining.

An experimental method using a specifically set-up is presented in order to investigate dry friction phenomena, which occurs in the cutting process at the tool chip contact, in a wide range of sliding speed. A ballistic set-up using an air gun launch is used to measure the friction coefficient for the steel/carbide contact between 15 m/s and 80 m/s. A series of tests are conducted according to the sliding velocity and the normal pressure. These measurements are also introduced in a finite element simulation. The focus of this work is to determine the relevance of the friction modeling in the finite element method of the high speed machining. Modeling results are compared with cutting forces measured on a similar experimental device, which can reproduce perfect orthogonal cutting conditions. Measurement of temperature fields during the cutting process complete the parameter required for modeling. The results show that in high cutting speed, the friction modeling usually used in the FE codes is limited and that novel formulations are needed.

Numerical and experimental approaches are mutually conducted to investigate the temperature rise in steel machining at high cutting speed. The process is modeled using a fully coupled thermo-mechanical finite element scheme. Cutting tests were carried out at 38 m/s on a ballistic orthogonal cutting set-up equipped with an intensified CCD camera. Analysis of experimental results leads to determine the variables which control heat transfer between the tool and chip. A discussion about the most important parameters controlling the temperature rise at the tool-chip interface is then proposed. The results also show that the temperature-dependence of the frictional stress modeling can improve the accuracy of the numerical simulations.

The tool-chip contact length, as an important parameter controlling the geometry of tool crater wear and understanding chip formation mechanism, is widely investigated in machining. The aim of this paper is to study the influence of chip curl on tool-chip contact length by means of experimental observations with high cutting speed. The relationship between tool-chip contact length, chip radius of curvature and uncut chip thickness was investigated. Experimental results show the effect of increasing spiral chip radius on tool-chip contact length with low uncut chip thickness in high speed machining.

Wear modeling makes it possible to predict the evolution of wear profile and explain wear mechanism from process variables, such as temperature, pressure and sliding velocity etc. A composite crater wear model considering adhesive and diffusion wear is established by means of experiment and modeling in conventional speed machining. A series of cutting tests are performed to obtain wear profiles and corresponding process variables. The constants in wear model are fitted by regression analysis with crater wear tests. This crater wear model shows a good predictive capability in conventional cutting speed.

Chip velocity is a crucial parameter in metal cutting. The continuous variation of chip velocity in primary shear zone can not be obtained from conventional shear plane model. Therefore a general streamline model was used to investigate the distribution of chip velocity field in metal cutting. This paper also verified the continuity of plastic flow in metal cutting by tracing the variation of particle area. The velocity of chip material was calculated from the mathematical expression of streamline model. The velocity results were compared with conventional shear plane model.