Modelling the Effects of Friction on Tool-Chip Interface Temperature During Orthogonal Cutting of Al6061-T6 Aluminium Alloy

© IEOM Society International - IEOM 2019In this work, finite element simulations based on the analytical model derived with the MATLAB software were used to establish the temperature fields within the cutting tool and tool-chip interface. The average tool-chip interface temperature model was simulated and the simulation results were compared with experimental results for validation. At a maximum cutting speed of 90 m/min, the maximum temperature obtained from the experiment was 410 oC, at same rake angle of 0o. However, the developed model predicted 490 oC under the same conditions. The higher value obtained by the model can be attributed to the negligence of heat losses to the surrounding by both convection and radiation modes, as an assumption in the formulated model. A similar trend of these results was also recorded for the case of rake angle and feed rate of 30o and 0.0635 mm/rev, respectively. It was observed that the simulation results and experimental measurements for the average tool-chip interface temperature agreed significantly.Final Published versio

A simulated investigation on the machining instability and dynamic surface generation

In this paper, the authors propose the generic concept of machining instability based on the analysis of all kinds of machining instable behaviors and their features. The investigation covers all aspects of the machining process, including the machine tool structural response, cutting process variables, tooling geometry and workpiece material property in a full dynamic scenario. The paper presents a novel approach for coping with the sophisticated machining instability and enabling better understanding of its effect on the surface generation through a combination of the numerical method with the characteristic equations and using block diagrams/functions to represent implicit equations and nonlinear factors. It therefore avoids the lengthy algebraic manipulations in deriving the outcome and the solution scheme is thus simple, robust and intuitive. Several machining case studies and their simulation results demonstrate the proposed approach is feasible for shop floor CNC machining optimisation in particular. The results also indicate the proposed approach is useful to monitor the machining instability and surface topography and to be potentially applied in adaptive control of the instability in real time

A dynamics-driven approach to precision machines design for micro-manufacturing and its implementation perspectives

Precision machines are essential elements in fabricating high quality micro products or micro features and directly affect the machining accuracy, repeatability and efficiency. There are a number of literatures on the design of industrial machine elements and a couple of precision machines commercially available. However, few researchers have systematically addressed the design of precision machines from the dynamics point of view. In this paper, the design issues of precision machines are presented with particular emphasis on the dynamics aspects as the major factors affecting the performance of the precision machines and machining processes. This paper begins with a brief review of the design principles of precision machines with emphasis on machining dynamics. Then design processes of precision machines are discussed, and followed by a practical modelling and simulation approaches. Two case studies are provided including the design and analysis of a fast tool servo system and a 5-axis bench-top micro-milling machine respectively. The design and analysis used in the two case studies are formulated based on the design methodology and guidelines

An investigation on the mechanics of nanometric cutting and the development of its test-bed

The mechanics of machining at a very small depth of cut (100 nm or less) is not well understood. The chip formation physics, cutting forces generation, resulting temperatures and the size effects significantly affect the efficiency of the process and the surface quality of the workpiece. In this paper, the cutting mechanics at nanometric scale are investigated in comparison with conventional cutting principles. Molecular Dynamics (MD) is used to model and simulate the nanometric cutting processes. The models and simulated results are evaluated and validated by the cutting trials on an atomic force microscope (AFM). Furthermore, the conceptual design of a bench-type ultraprecision machine tool is presented and the machine aims to be a facility for nanometric cutting of threedimensional MEMS devices. The paper concludes with a discussion on the potential and applications of nanometric cutting techniques/equipment for the predictabilty, producibility and productivity of manufacturing at the nanoscale

Thermal error modelling of machine tools based on ANFIS with fuzzy c-means clustering using a thermal imaging camera

Thermal errors are often quoted as being the largest contributor to CNC machine tool errors, but they can be effectively reduced using error compensation. The performance of a thermal error compensation system depends on the accuracy and robustness of the thermal error model and the quality of the inputs to the model. The location of temperature measurement must provide a representative measurement of the change in temperature that will affect the machine structure. The number of sensors and their locations are not always intuitive and the time required to identify the optimal locations is often prohibitive, resulting in compromise and poor results. In this paper, a new intelligent compensation system for reducing thermal errors of machine tools using data obtained from a thermal imaging camera is introduced. Different groups of key temperature points were identified from thermal images using a novel schema based on a Grey model GM (0, N) and Fuzzy c-means (FCM) clustering method. An Adaptive Neuro-Fuzzy Inference System with Fuzzy c-means clustering (FCM-ANFIS) was employed to design the thermal prediction model. In order to optimise the approach, a parametric study was carried out by changing the number of inputs and number of membership functions to the FCM-ANFIS model, and comparing the relative robustness of the designs. According to the results, the FCM-ANFIS model with four inputs and six membership functions achieves the best performance in terms of the accuracy of its predictive ability. The residual value of the model is smaller than ± 2 μm, which represents a 95% reduction in the thermally-induced error on the machine. Finally, the proposed method is shown to compare favourably against an Artificial Neural Network (ANN) model

An investigation on the mechanics of nanometric cutting and the development of its test-bed

The mechanics of machining at a very small depth of cut (100 nm or less) is not well understood. The chip formation physics, cutting forces generation, resulting temperatures and the size effects significantly affect the efficiency of the process and the surface quality of the workpiece. In this paper, the cutting mechanics at nanometric scale are investigated in comparison with conventional cutting principles. Molecular Dynamics (MD) is used to model and simulate the nanometric cutting processes. The models and simulated results are evaluated and validated by the cutting trials on an atomic force microscope (AFM). Furthermore, the conceptual design of a bench-type ultraprecision machine tool is presented and the machine aims to be a facility for nanometric cutting of threedimensional MEMS devices. The paper concludes with a discussion on the potential and applications of nanometric cutting techniques/equipment for the predictabilty, producibility and productivity of manufacturing at the nanoscale

Aluminium extrusion analysis by the finite volume method

Present work proposes a novel numerical scheme to calculate stress and velocity fields of metal flow in axisymmetric extrusion process in steady state. Extrusion of aluminium is one main metal forming process largely applied in manufacturing bars and products with complex cross section shape. The upper-bound, slab, slip-line methods and more recently the numerical methods such as the Finite Element Method have been commonly applied in aluminium extrusion analysis. However, recently in the academy, the Finite Volume Method has been developed for metal flow analysis: literature suggests that extrusion of metals can be modelled by the flow formulation. Hence, metal flow can be mathematically modelled such us an incompressible non linear viscous fluid, owing to volume constancy and varying viscosity in metal forming. The governing equations were discretized by the Finite Volume Method, using the Explicit MacCormack Method in structured and collocated mesh. The MacCormack Method is commonly used to simulate compressible fluid flow by the finite volume method. However, metal plastic flow and incompressible fluid flow do not present state equations for the evolution of pressure, and therefore, a velocity-pressure coupling method is necessary to obtain a consistent velocity and pressure fields. The SIMPLE Method was applied to attain pressure-velocity coupling. This new numerical scheme was applied to forward hot extrusion process of an aluminium alloy. The metal extrusion velocity fields achieved fast convergence and a good agreement with experimental results. The MacCormack Method applied to metal extrusion produced consistent results without the need of artificial viscosity as employed by the compressible flow simulation approaches. Therefore, present numerical results also suggest that MacCormack method together with SIMPLE method can be applied in the solution of metal forming processes in addition to the traditional application for compressible fluid flow

A new material model for 2D numerical simulation of serrated chip formation when machining titanium alloy Ti-6Al-4V

A new material constitutive law is implemented in a 2D finite element model to analyse the chip formation and shear localisation when machining titanium alloys. The numerical simulations use a commercial finite element software (FORGE 2005) able to solve complex thermo-mechanical problems. One of the main machining characteristics of titanium alloys is to produce segmented chips for a wide range of cutting speeds and feeds. The present study assumes that the chip segmentation is only induced by adiabatic shear banding, without material failure in the primary shear zone. The new developed model takes into account the influence of strain, strain rate and temperature on the flow stress and also introduces a strain softening effect. The tool chip friction is managed by a combined Coulomb–Tresca friction law. The influence of two different strain softening levels and machining parameters on the cutting forces and chip morphology has been studied. Chip morphology, cutting and feed forces predicted by numerical simulations are compared with experimental results

A novel haptic model and environment for maxillofacial surgical operation planning and manipulation

This paper presents a practical method and a new haptic model to support manipulations of bones and their segments during the planning of a surgical operation in a virtual environment using a haptic interface. To perform an effective dental surgery it is important to have all the operation related information of the patient available beforehand in order to plan the operation and avoid any complications. A haptic interface with a virtual and accurate patient model to support the planning of bone cuts is therefore critical, useful and necessary for the surgeons. The system proposed uses DICOM images taken from a digital tomography scanner and creates a mesh model of the filtered skull, from which the jaw bone can be isolated for further use. A novel solution for cutting the bones has been developed and it uses the haptic tool to determine and define the bone-cutting plane in the bone, and this new approach creates three new meshes of the original model. Using this approach the computational power is optimized and a real time feedback can be achieved during all bone manipulations. During the movement of the mesh cutting, a novel friction profile is predefined in the haptical system to simulate the force feedback feel of different densities in the bone