Vincent Pina

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.

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.

Investigative method for radiative properties of water vapor in the 0.8 μM region by optical diagnostic of H 2 -Air combustion

To contribute to the development of more competitive combustors by the command of heat exchanges, the determination of temperature and concentration distributions of combustion products is required. Emission spectroscopy of gas species has been investigated for passive and nonintrusive measurements in combustion processes under severe conditions (T > 2000 K and P >10 bar). We have designed an experimental facility to study radiative properties of water vapor produced during combustion of a reactive H 2 -air mixture for different initial conditions. The enclosure is efficient and dynamic pressures up to 80 bar were recorded with a good reproducibility. Emission measurements of H 2 O were performed in the 0.8 w m band using a high resolution spectrometer and a CCD detector. These spectra are compared to simulations with the HITEMP database. In the measurement spectral range, extrapolations from the spectroscopic database gave similar results to our initial experimental ones.

Temperature Distributions in Adiabatic Shear Bands in Steel

Adiabatic shear bands appear on materials subjected to high strain rates. Up to now heat-exchange mechanisms have not been very well known. In order to determine the temperature distribution and the phase-change within the shear band we have developed a method of optical pyrometry using two wavelengths. Torsion tests have been carried out, and a temperature of 750°C has been measured within the shear band.