Determination of the maximum temperature and temperature distribution along the rake face of the cutting tool is of particular importance because of its controlling influence on tool life, as well as, the quality of the machined part. Numerous attempts have been made to approach the problem with different methods including experimental, analytical and numerical analysis. Although considerable research effort has been made on the thermal problem in metal cutting, there is hardly a consensus on the basics principles. The unique tribological contact phenomenon, which occur in metal cutting is highly localized and non-linear, and occurs at high temperatures, high pressures and high strains. This has made it extremely difficult to predict in a precise manner or even assess the performance of various models developed for modelling the machining process. Accurate and repeatable heat and temperature prediction remains challenging due to the complexity of the contact phenomena in the cutting process. In this paper, previous research on heat generation and heat dissipation in the orthogonal machining process is critically reviewed. In addition, temperature measurement techniques applied in metal cutting are briefly reviewed. The emphasis is on the comparability of test results, as well as, the relevance of temperature measurement method to high speed cutting. New temperature measurement results obtained by a thermal imaging camera in high speed cutting of high strength alloys are also presented. Finally, the latest work on estimation of heat generation, heat partition and temperature distribution in metal machining is reviewed. This includes an exploration of the different simplifying assumptions related to the geometry of the process components, material properties, boundary conditions and heat partition. The paper then proposes some modelling requirements for computer simulation of high speed machining processes.

Heat generation and temperature prediction in metal cutting: A review and implications for high speed machining

Nickel-based superalloy is widely employed in aircraft engines and the hot end components of various types of gas turbines with its high strength, strong corrosion resistance and excellent thermal fatigue properties and thermal stability. However, nickel-based superalloy is one of the extremely difficult-to-cut materials. During the machining process, the interaction between the tool and the workpiece causes the severe plastic deformation in the local area of workpiece, and the intense friction at the tool–workpiece interface. The resulting cutting heat coupled with the serious work hardening leads to a series of flaws, such as excessive tool wear, frequent tool change, short tool life, low productivity, and large amount of power consumption etc., in which the excessive tool wear has become one of the main bottlenecks that constraints the machinability of nickel-based superalloys and its wide range of applications. In this article, attention is mainly focused on the tool wear characteristics in the machining of nickel-based superalloys, and the state of the art in the fields of failure mechanism, monitoring and prediction, and control of tool wear are reviewed. The survey of existing works has revealed several gaps in the aspects of tool self-organizing process based on the non-equilibrium thermodynamics, tool wear considering the tool nose radius, thermal diffusion layer in coated tools, tool life prediction based on the thermal–mechanical coupling, and industrial application of tool wear online monitoring devices. The review aims at providing an insight into the tool wear characteristics in the machining of nickel-based superalloys and shows the great potential for further investigations and innovation in the field of tool wear.

Tool wear characteristics in machining of nickel-based superalloys

In the present contribution, numerical and experimental methodologies concerning orthogonal cutting are proposed in order to study the dry cutting of an aeronautic aluminium alloy (A2024-T351) The global aim concerns the comprehension of physical phenomena accompanying chip formation according to cutting velocity variation For the numerical model, material behaviour and its failure criterion are based on the Johnson–Cook law The model proposes a coupling between material damage evolution and its fracture energy A high-speed camera was used to capture the chip formation sequences The numerical results show that the chip–workpiece contact and the tool advancement induce bending loads on the chip Consequently, a fragmentation phenomenon takes place above the rake face when the chip begins to curl up The computed results corroborate with experimental ones The numerical results predict the residual stress distribution and show high values, along the cutting direction, on the machined workpiece surface

Numerical and experimental study of dry cutting for an aeronautic aluminium alloy (A2024-T351)

Experimental analysis and optimisation of tool wear in dry machining of aluminium alloys

Dynamic shear bands: an investigation using high speed optical and infrared diagnostics

During the machining of metals, plastic deformation and friction lead to the generation of heat in the workpiece, which results in thermomechanically coupled deformation. Recently, several numerical models of this highly coupled process have been produced in response to increased interest in high speed machining. It is important to characterize the thermal field in the cutting zone in order to completely verify these models of high speed machining and to direct further advancement in this area. In this work, HgCdTe infrared detectors are used to experimentally measure the temperature distribution at the surface of a workpiece during orthogonal cutting. From these temperature measurements, the heat generated in the primary shear zone and the friction zone can be examined and characterized. A modified Hopkinson bar technique has been developed to perform orthogonal machining at speeds ranging from 10 to 100 m/s. In the present work, a cutting velocity of 15 m/s is employed in all the tests in order to demonstrate the capability of the apparatus and characterize thermal fields during low speed machining. Temperature fields are obtained during the orthogonal cutting of aluminum as a function of depth of cut. It is seen that depth of cut can vary both the maximum temperature as well as the distribution of the temperature field in the aluminum workpiece. the maximum temperature increased with depth of cut (238°C for 1.5 mm cut, 207°C for 1.0 mm cut and 138°C for 0.5 mm cut) and the temperature field extended further beneath the cut surface with decreasing depth of cut.

Experimental Study of the Temperature Field Generated During Orthogonal Machining of an Aluminum Alloy

Impact experiments are performed on edgenotched specimens in the two-dimensional punch geometry. Materials tested include 18Ni(350) maraging steel; S7 tool steel; 4340, 300M, HP 9-4-20 and D-6ac ultra high-strength steels; and Ti6Al4V alloy. These materials have shown a high susceptibility to dynamic shear failure in previous studies. Impact velocity ranged from 25 m/s to 45 m/s, and shear bands were found to form at the notch tip and at the die corner on the back side of the specimen for all materials tested. Metallurgical analysis confirms the existence of adiabatic shear bands followed by a crack propagating through the fully developed shear band. High-speed photography was used to observe the initiation of adiabatic shear bands shortly after impact. Laser-etched lines on the specimen surfaces allowed the determination of the time of impact and the initiation time of shear failure. The elapsed time between the two was used to estimate the stress intensity factor at the time of shear band initiation. Comparisons of shear band initiation stress intensity factors at the notch tip and die corner are made. It is seen that the shear bands initiate at approximately the same stress intensity factor at both the notch tip and die corner. Finite element simulations support the use of a square root singularity for the stress in the plate near the corners of a deformable punch or die.

Adiabatic shear localization in the impact of edge-notched specimens

This study focuses on experimental modeling of dry high-speed machining at 30 m/s cutting velocity using 6061-T6 aluminum alloy. A modified Hopkinson bar apparatus is employed to simulate orthogonal machining, a focused array of mercury–cadmium–tellurium infrared detectors is used to measure the temperature distribution around the tool tip, and a three-component quartz force transducer is utilized in measuring the cutting and feed forces. The resulting measurements confirm the assumption of steady-state cutting and allow for estimation of the partition of cutting work into heating, shear, and momentum changes in the chip. In an earlier study, measurements of temperature distributions showed little heating of the finished surface. Therefore, a study of the temperature fields generated during machining with a cutting tool that has a wear-land was performed. The wear-land contributes significantly to the heating of the workpiece and, at this speed, is the most likely mechanism for the generation of residual stresses and a temperature rise on the finished surface.

Measurements of Forces and Temperature Fields in High-Speed Machining of 6061-T6 Aluminum Alloy

An experimental investigation is conducted on the two-dimensional punch problem for isotropic materials and unidirectional fiber-reinforced composite materials under quasi-static and impact loading. Singular stresses are generated in the specimen near the punch corners, and the stress intensity factorKIis introduced to describe the singular stress field. Laser interferometry is used to measure in-plane stresses (transmission mode) and out-of-plane displacements (reflection mode) and then estimate the stress intensity factor. In the dynamic case, a high-speed photography technique was employed to capture the transient response of the specimen and measureK(t) just after the impact. In all the cases, a good agreement between the measurements ofK and theoretical predictions was found.

J. J. Mason

Papers

Experimental Study of the Temperature Field Generated During Orthogonal Machining of an Aluminum Alloy

Adiabatic shear localization in the impact of edge-notched specimens

Measurements of Forces and Temperature Fields in High-Speed Machining of 6061-T6 Aluminum Alloy

Experimental investigation of dynamic punch tests on isotropic and composite materials