Gautier List

High speed turning for hard material with PCBN inserts : tool wear analysis

Because of tool wear, High Speed Machining (HSM) is rarely used for hard turning process and the cutting speeds are generally selected around 100 or 200 m/min. In this work, HSM is performed for hard turning of a 50 HRC hardened steel (AISI 4140/42CrMo4) with a PCBN tool by using high cutting speeds (300 and 400 m/min). The results show that HSM for hard turning can be acceptable for industrial application by providing very good surface roughness and keeping significant tool life. A qualitative correlation is also presented between the crater wear and the temperature distribution at the tool-chip interface, predicted by a thermomechanical model. Flank wear, crater wear and surface roughness are examined in order to choose an appropriate wear criterion. Investigations by SEM/EDS and white light interferometry highlight the importance of crater wear and help us to better understand the role of chemical/diffusion phenomena in wear mechanisms.

Calculation of Material Flow in Orthogonal Cutting by Using Streamline Model

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.

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.

Experimental study and synthesis of the dynamic behaviour in high speed drilling

This paper concerns an experimental approach of vibration phenomena in High Speed Drilling (HSD) of aluminium alloys. In order to study these phenomena, different results have been chosen to illustrate that these vibrations are generated by different deformations of the drill and the machining system. The relevant parameters at the origin of these vibrations in HSD are pointed out and their influence on the quality of drilling is analysed. The effect of the drill geometry on surface quality is reported and in particular the role of the chisel edge, the helix angle which controls the sharpness of tool corner, the thickness and the number of margins which allow the drill to be held in the hole and the rigidity of the drill materialised by its overhang. Depending on its length, the drill can deform differently. The influence of the drilling conditions on surface quality has also been evaluated: the feed rate per tooth and the cutting speed as well as the rotation frequency and the feed speed. The effect of lubrication and machine rigidity (in our case an industrial robot) has been analysed. Finally, we pointed out the apparition of vibration when two aluminium plates are drilled together. The behaviour is very variable and different steps of the drilling have to be considered: the drill entry in the aluminium part, the drilling, the drill exit from the plate and the drill backward movement. This allows for a particular value of drill diameter and drill overhang to determine the optimised feed rate and rotation frequency in order to achieve the best quality of the hole surface.