Micro end milling is an important process in the manufacture of micro and meso scale products and has an advantage of creating more complex geometry in a wider variety of materials in comparison with other micro-machining methods. In this paper, a new methodology for predicting the cutting coefficients considering the edge radius and material strengthening effects is presented. Further a mechanistic model is developed to predict the cutting forces in micro end milling operation taking into account overlapping tooth engagements. The mechanistic model, derived from basics considering material property and principles of metal cutting, is valid for a wider range of cutting parameters. The model is validated with the results from micro slot end-milling of mild steel carried out on the basis of full factorial design. On comparing the amplitudes of cutting forces, it is seen that mechanistic model predicts the transverse force with an average absolute error of 12.29%, while a higher prediction error of 19.49% is obtained for feed force. Additionally the mechanistic model is able to predict the variations in the cutting forces with rotation of the cutter and average absolute deviations of 13% and 11% are obtained for feed and transverse forces, respectively. © 2012 Elsevier Ltd.

Shunmugam M S

Department of Mechanical Engineering

Y. G. Srinivasa

AVERAGE ABSOLUTE DEVIATION

Average absolute error

chip thickness

Complex geometries

Cutting coefficients

CUTTING EDGE RADIUS

Cutting forces

CUTTING PARAMETERS

END-MILLING

Experimental comparison

FEED FORCES

FULL FACTORIAL DESIGN

Material property

Mechanistic models

MESO SCALE

Micro End Milling

PREDICTION ERRORS

size effects

STRENGTHENING EFFECT

TRANSVERSE FORCE

Automobile manufacture

Carbon steel

Metal cutting

Milling (machining)

Forecasting

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

International Journal of Machine Tools and Manufacture

Free-form surfaces and micro features are finish machined by a micro ball end mill by removing steps left behind by flat end mill in the previous operation. For effective machining, off-centre ball end milling is employed in such a way that rubbing zone near ball tip is avoided. After confirming the limits of angular immersion from full-slot experimental results, both down and up off-centre milling experiments are conducted on edges of steps created on a test piece. The micro milling forces in off-centre mode are also investigated theoretically using a mechanistic model that considers the geometry of micro ball end mill and basic mechanics of cutting. The amplitudes of predicted forces match well with experimental values and the deviations in the experimental values arise out of micro level unevenness in the step edge. The up milling with lower transverse force is found to be more suitable for machining of thin features. © 2018 CIRP

CIRP Journal of Manufacturing Science and Technology

Experimental and theoretical investigation on cutting forces in off-centre micro ball end milling

Cutting edge radius plays an important role in conventional micro machining process, as it is of the same order as uncut chip thickness. Therefore it is important to measure the edge radius accurately. There is no recommended methodology, as of now, to measure edge radius of a ball end mill. An attempt is made in this paper to study edge radius of ball end mill at normal and transverse planes on a virtual ball end mill generated using kinematic relations in CAD environment. In the present study, non-destructive methods using confocal microscope and stereo microscope are used to measure edge radius. These measurements capture the edge radius on the transverse plane. For confirmation, the tool sectioned in the transverse plane by a low speed diamond saw is examined under scanning electron microscope and the radius is assessed using suitable software. Among the non-contact approaches proposed in this work, confocal method appeared to be more reliable considering the reproducibility aspect. © 2016 Elsevier Inc.

Precision Engineering

Study of micro ball end mill geometry and measurement of cutting edge radius

Metal cutting is an important machining operation in the manufacture of almost all engineering components. Cutting technology has undergone several changes with the development of machine tools and cutting tools to meet challenges posed by newer materials, complex shapes, product miniaturization and competitive environments. In this paper, challenges in macro and micro cutting are brought out. Conventional and micro end-milling are included as illustrative examples and details are presented along with discussion. Lengthy equations are avoided to the extent possible, as the emphasis is on the basic concepts. © 2015, The Institution of Engineers (India).

Journal of The Institution of Engineers (India): Series C

Machining Challenges: Macro to Micro Cutting

Mechanical micro-drilling process is often used in the manufacture of miniature components and molds. Frequent breakage of micro-drill is a major problem necessitating a thorough investigation into the process. One of the important responses measured during micro-drilling process is variation of thrust force and torque. Since the values of thrust force and torque are very low in micro-drilling, reliable measurements have to be carried out using high-resolution dynamometer. In the present work, micro-drilling is carried out using 0.5 mm diameter drill on Al 6061-T6 sheet of 3 mm thickness. The measurement results obtained from multi-component dynamometer are discussed first. Subsequently, a torque sensor mounted on the multi-component dynamometer is used to measure the torque, while the thrust force is acquired from latter. Since it is practically impossible to start acquiring the signals at a given time instant, the signals have to be synchronized in time domain using a novel signal processing technique. Different phases in micro-drilling, namely entry, full penetration and dwell are identified uniquely. © 2015 Elsevier Ltd. All rights reserved.

Measurement: Journal of the International Measurement Confederation

On reliable measurement of micro drilling forces and identification of different phases

Titanium alloy Ti-6Al-4V is commonly used in biomedical applications due to its superior properties such as biocompatibility, high strength-to-weight ratio and corrosion resistance. To understand the mechanics of the micro-turning process of these alloys, a mechanistic model has been developed for predicting the cutting forces. A modified Johnson-Cook material model with strain gradient plasticity is used to represent the flow stress of work material. The micro-turning experiments were conducted to verify the cutting forces predicted by mechanistic model. A finite element model is also developed with different shear friction factors and calibrated using experimental results to confirm and interpret the results of mechanistic model. It is inferred that strain rate increases by increasing cutting speed, whereas it decreases with increase in the feed rate due to increase in adiabatic shear band spacing. Since Ti-6Al-4V has low thermal conductivity, when cutting speed increases, there is an increase in the tool-chip interface temperature that leads to decrease in cutting forces. When cutting speed increases, chip morphology changes from discontinuous to continuous, and there is significant deterioration in the surface finish. It is observed that the average cutting force prediction errors for mechanistic and finite element models are 9.69% and 11.45% respectively. © Copyright 2015 Taylor & Francis Group, LLC.

Machining Science and Technology

Mechanistic and Finite Element Model for Prediction of Cutting Forces during Micro-Turning of Titanium Alloy

When a scale of metal cutting process reduces to micrometer range, mechanics of material removal are affected by various factors such as workpiece material, cutting tool geometry and cutting conditions. A suitable model of constitutive behaviour of the material is needed to represent properties of the work material at the conditions existing during chip formation. In this paper, a material model based on theory of strain gradient plasticity is proposed for material strengthening in micro cutting, taking into account size effect in micro cutting with a tool having an edge radius. The proposed model effectively combines strain gradient plasticity and basic mechanics of orthogonal cutting. The material model thus developed is validated using results obtained from micro-orthogonal cutting experiments on mild steel (AISI 1019). Micro-orthogonal experiments with varying uncut chip thickness are also carried out to fine-tune the material model and investigate the mechanics of micro cutting considering the minimum uncut chip thickness effect. The results are encouraging and shear strength is predicted with an average absolute error of 11.8%. FE simulations carried out with flow stress obtained from Johnson-Cook relation yield cutting forces that follow the trend in the experimentally obtained force signals, but they are unable to capture the strain gradient and ploughing effects. Copyright © 2013 Inderscience Enterprises Ltd.

International Journal of Manufacturing Research

Investigations into micro-orthogonal cutting and material strengthening

The study aims at developing a predictive analytical force model for the micro end-milling operation taking into account the material strengthening as well as the edge radius effects that come into play at the micro level. The mechanistic models for macro end-milling process have been extensively reported in literature and such models predominantly use milling force coefficients which are empirically determined from end-milling experiments. The proposed model for micro end-milling is based on determination of milling force coefficients from fundamental oblique cutting approach. The edge radius effect has been accounted by analyzing the rubbing action similar to the rolling of a cylinder over work surface. Johnson-Cook material model has been modified based on the strain gradient plasticity theory incorporating the increase in material strength with decreasing uncut chip thickness. From the micro orthogonal cutting experiments, a good agreement between the experimental and predicted shear strength values is observed. The force model is validated against measured forces in end-milling experiments carried out on the KERN Evo 5 axis micro machining center. The feed and lateral forces are predicted within 10% deviation on an average. © 2012 Copyright Taylor and Francis Group, LLC.

Analytical modeling of micro end-milling forces with edge radius and material strengthening effects

Netherlands International Law Review

Hague Case Law: Latest Developments

Analytical and experimental investigation of rake contact and friction behavior in metal cutting

Journal of Materials Processing Technology

Predictive modeling of transition undeformed chip thickness in ductile-regime micro-machining of single crystal brittle materials

Mechanistic model for prediction of cutting forces in micro end-milling and experimental comparison

Journal	International Journal of Machine Tools and Manufacture
ISSN	08906955
Open Access	No