G. Sutter

An experimental technique for the measurement of temperature fields for the orthogonal cutting in high speed machining

Cutting temperature and heat generated at the tool-chip interface during high speed machining operations have been recognized as major factors that influence tool performance and workpiece geometry or properties. This paper presents an experimental setup able to determine the temperature field in the cutting zone, during an orthogonal machining operation with 42 CrMo 4 steel. The machining was performed with a gas gun, using standard carbide tools TiCN coated and for cutting speeds up to 50 ms-1. The technique of temperature measurement was developed on the principle of pyrometry in the visible spectral range by using an intensified CCD camera with very short exposure time and interference filter at 0.8 μm. Temperature gradients were obtained in an area close to the cutting edge of the tool, along the secondary shear zone. Effects of the cutting speed and the chip thickness on the temperature profile in the chip were determined. Maximum chip temperature of about 825 °C was found, for cutting speed close to 20 ms-1, located at a distance of 300 μm of the tool tip. It was established that this experimental arrangement is quite efficient and can provide fundamental data on the temperature field in materials during orthogonal high speed machining.

An Experimental Study of High Speed Orthogonal Cutting

A new high speed machining experiment is designed to obtain orthogonal cutting in a wide range of cutting speeds from 7 m/s to 100 m/s. Quasi-stationary cutting conditions are obtained. The measurement of the longitudinal cutting force reveals the existence of an optimal cutting speed for which the energy consumption is minimum. The genuine tool-workpiece material interaction can be analyzed with that experimental device.

Temperature Measurement by Visible Pyrometry: Orthogonal Cutting Application

The working processes of metallic materials at high strain rate like forging, stamping and machining often induce high temperatures that are difficult to quantify precisely. In this work we, developed a high-speed broad band visible pyrometer using an intensified CCD camera (spectral range: 0.4 μm-0.9 μm). The advantage of the visible pyrometry technique is to limit the temperature error due to the uncertainties on the emissivity value and to have a good spatial resolution (3.6 μm) and a large observation area. This pyrometer was validated in the case of high speed machining and more precisely in the orthogonal cutting of a low carbon steel XC18. The cutting speed varies between 22 ms -1 and 60 ms -1 . The experimental device allows one to visualize the evolution of the temperature field in the chip according to the cutting speed. The maximum temperature in the chip can reach 730°C and minimal temperature which can be detected is around 550°C.

Experimental measurement of temperature distribution in the chip generated during high speed orthogonal cutting process

Temperature field measurements in the chip are performed during high speed machining of a low carbon steel (XC18) and a medium carbon steel (42CrMo4). An original mechanical device based on the propelling of a projectile by decompression of air allows to investigate a wide range of cutting speeds from 10 to 120 m/s. The technique of temperature measurement using the principle of pyrometry in the visible spectral range is realised with an intensified CCD camera with a very short exposure time. Temperature maps presented for the two steels confirm that the heating in the chip is not uniform and the presence of a maximal temperature area. The effects of cutting parameters such as chip thickness and cutting velocity are presented.

Temperature Rise and Heat Transfer in High Speed Machining: FEM Modeling and Experimental Validation

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.

Experimental Measurement of Friction Coefficient Applied to HSM Modeling

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.

Raman characterization of Ti–6Al–4V oxides and thermal history after kinetic friction

Raman spectroscopy is applied to study the surfaces of a pair of tantalum and titanium alloy samples after high-speed dry friction. The surface of titanium alloy (Ti–6Al–4V) shows titanium oxides on the rubbing surfaces. Raman spectra enable to differentiate the allotropic phases of anatase or rutile. The presence of these phases is the signature of the local thermal history during the friction tests. Moreover, Raman mapping allows localizing area the flash temperatures that may have been produced by the friction between sample asperities.

Crater Wear Modeling in Conventional 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.

Influence of Chip Curl on Tool-Chip Contact Length in High Speed Machining

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.

Determination of Chip Velocity Field in Metal Cutting

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.