A. Moufki

A review of developments towards dry and high speed machining of Inconel 718 alloy

Abstract The increasing attention to the environmental and health impacts of industry activities by governmental regulation and by the growing awareness in society is forcing manufacturers to reduce the use of lubricants. In the machining of aeronautical materials, classified as difficult-to-machine materials, the consumption of cooling lubricant during the machining operations is very important. The associated costs of coolant acquisition, use, disposal and washing the machined components are significant, up to four times the cost of consumable tooling used in the cutting operations. To reduce the costs of production and to make the processes environmentally safe, the goal of the aeronautical manufacturers is to move toward dry cutting by eliminating or minimising cutting fluids. This goal can be achieved by a clear understanding of the cutting fluid function in machining operations, in particular in high speed cutting, and by the development and the use of new materials for tools and coatings. High speed cutting is another important aspect of advanced manufacturing technology introduced to achieve high productivity and to save machining cost. The combination of high speed cutting and dry cutting for difficult-to-cut aerospace materials is the growing challenge to deal with the economic, environmental and health aspects of machining. In this paper, attention is focussed on Inconel 718 and recent work and advances concerning machining of this material are presented. In addition, some solutions to reduce the use of coolants are explored, and different coating techniques to enable a move towards dry machining are examined.

Modelling of orthogonal cutting with a temperature dependent friction law

Abstract In this paper the process of orthogonal cutting is studied by analytical means. A thermomechanical model of the primary shear zone is combined with a modelling of the contact problem at the tool-chip interface. A friction law is introduced that accounts for temperature effects. The effects of cutting conditions and material behaviour on the temperature distribution along the contact zone, on the mean friction and on the global cutting forces are evaluated. The experimental trends are shown to be well described by the proposed model.

Thermoviscoplastic modelling of oblique cutting: forces and chip flow predictions

Abstract A modelling of oblique cutting for viscoplastic materials is presented. The thermomechanical properties and the inertia effects are accounted for to describe the material flow in the primary shear zone. At the tool–chip interface, a temperature-dependent friction law is introduced to take account of the extreme conditions of pressure, velocities and temperature encountered during machining. The chip flow angle is calculated by assuming that the friction force is collinear to the chip flow direction on the tool rake face. Due to the temperature dependence of the friction law at the tool–chip interface, the chip flow angle predicted by the model, is affected by the cutting speed, the undeformed chip thickness, the normal rake angle, the edge inclination angle and the thermomechanical behavior of the work material. This dependence and the trends predicted by the present approach are confirmed by experimental observations. Effects of cutting conditions on the cutting forces are also presented and compared to experiments.

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.

Mechanistic approach applied to the gear hobbing process

Abstract This paper proposes a new approach to simulate 3D cutting force components generated during the finishing hobbing process of larger spur gear parts. This new approach combines three modelling steps. In the first step, the profile of the undeformed chip created for every hob’s tooth is calculated using the geometrical simulation of the gear hobbing process. In the second step, the calibration of the specific force coefficients (cutting and edge effects) is obtained from a 2D numerical model. In the final step, a mechanistic model is applied to the hobbing process. The results of this investigation are presented in terms of the analysis of the undeformed chip characteristics and the evolution of the hobbing cutting forces.

An Analytical Thermomechanical Modelling of Peripheral Milling Process Using a Predictive Machining Theory

In this work, a predictive machining theory, based on an analytical thermomechanical approach of oblique cutting [17,18], has been applied to the peripheral milling process. That leads to a three dimensional cutting force model for end milling operations which is an alternative approach in comparison with the mechanistic one. In this model, the material characteristics such as strain rate sensitivity, strain hardening and thermal softening are considered and thermomechanical coupling and inertia effects are accounted for. Calculated and experimental results are compared for up-milling.

Some cases of machining large-scale parts: Characterization and modelling of heavy turning, deep drilling and broaching

Machining large-scale parts involves extreme loading at the cutting zone. This paper presents an overview of some cases of machining large-scale parts: heavy turning, deep drilling and broaching processes. It focuses on experimental characterization and modelling methods of these processes. Observed phenomena and/or measured cutting forces are reported. The paper also discusses the predictive ability of the proposed models to reproduce experimental data.

A thermomechanical analysis of sticking-sliding zones at the tool-chip interface in dry high-speed machining of aluminium alloy A2024–T351: A hybrid Analytical-Fe model

In high speed dry machining of aluminium alloy (A2024-T351), the tribological conditions at the tool-chip interface strongly affect the thermomechanical process of chip formation, the tool wear and the surface integrity. In order to contribute to the understanding of the effect of friction conditions, a hybrid Analytical-FE model is presented. The transient nonlinear thermal problem in the tool-chip-workpiece system is solved by using a Petrov-Galerkin finite element model. To illustrate the model results, the relationship between the local friction coefficient, in the sliding zone, and the apparent friction coefficient, which takes into account the whole tool-chip contact, is presented.