G.L. Samuel

Evaluation of circularity from coordinate and form data using computational geometric techniques

Data for evaluating circularity error can be obtained from coordinate measuring machines or form measuring instruments. In this article, appropriate methods based on computational geometric techniques have been developed to deal with coordinate measurement data and form data. The computational geometric concepts of convex hulls are used, and a new heuristic algorithm is suggested to arrive at the inner hull. Equi-Distant (Voronoi) and newly proposed Equi-Angular diagrams are employed for establishing the assessment features under different conditions. The algorithms developed in this article are implemented and validated with the simulated data and the data available in the literature.

Evaluation of circularity and sphericity from coordinate measurement data

Abstract The coordinate measuring machines (CMMs) have proven to be reliable, flexible and very much suitable for determining the acceptability of manufactured parts. In this paper, techniques for evaluating circularity and sphericity error from CMM data are presented. The form error can be evaluated directly from CMM data by employing circle/sphere as assessment features and using normal deviations. The CMM data can also be transformed by applying appropriate methods that not only suppress the size but also introduce distortion. The form error is evaluated from the transformed data by employing limacon/limacoid as assessment features and using linear deviations. The methods for handling CMM and transformed data are given in this paper. The proposed methods are validated using the data available in literature.

Evaluation of sphericity error from form data using computational geometric techniques

The measurement data for evaluation of sphericity error can be obtained from inspection devices such as form measuring instruments/set-ups. Due to misalignment and size-suppression inherent in these measurements, sphericity data obtained will be distorted. Hence, the sphericity error is evaluated with reference to an assessment feature, referred to as a limacoid. Appropriate methods based on the computational geometry have been developed to establish Minimum Circumscribed, Maximum Inscribed and Minimum Zone Limacoids. The present methods start with the construction of 3-D hulls. A 3-D convex outer hull is established using computational geometric concepts presently available. A heuristic method is followed in this paper to establish a 3-D inner hull. Based on a new concept of 3-D equi-angular line, 3-D farthest or nearest equi-angular diagrams are constructed for establishing the assessment limacoids. Algorithms proposed in the present work are implemented and validated with the simulated data and the data available in the literature.

State-of-the-art research in machinability of hardened steels

The hardened steel materials have great demand for the manufacturing of automotive, aircraft and machine tool components due to their better strength, wear resistance and high thermal stability. The hard machining offers many potential benefits compared to grinding, which remains the standard finishing process for critical hardened surfaces. To enhance the implementation of this technology, questions about the ability of this process to produce surfaces that meet the surface finish and integrity requirements must be answered and it must be justified economically. With the development of harder work materials, the tool material technology is advancing at a faster rate so as to enable machining of these materials by higher material removal rate with reliability of performance. This review article presents an overview of the previous research on machining of hard steel materials. It mainly focuses on the influence of extrinsic factors on machinability of hardened steels, such as variation of cutting forces, chip morphology, tool wear and resulting surface integrity in the machined surface.

Evaluation of sphericity error from coordinate measurement data using computational geometric techniques

The measurement data of a spherical component can be obtained from inspection devices such as coordinate measuring machines (CMMs). The sphericity error is evaluated from such coordinate data based on the minimum circumscribed sphere, the maximum inscribed sphere and minimum zone spheres. Appropriate methods based on the computational geometry have been developed to establish these assessment spheres. The present methods start with construction of 3-D hulls. The 3-D convex outer hull is established using the computational geometric concept presently available. For establishing a 3-D inner hull, a new heuristic method is suggested in this paper. A new concept of 3-D equidistant (ED) line is introduced in the present method. Based on this concept, the authors have constructed 3-D farthest and nearest equidistant diagrams for establishing the assessment spheres. Algorithms proposed in the present work are implemented and validated with the simulated data and the data available in the literature.

Analysis on the effect of discharge energy on machining characteristics of wire electrical discharge turning process

Energy conservation is one of the most important aspects of electrical discharge machining process in which the material removal is by means of spark erosion. Metal removal in wire electrical discharge turning is a complex erosion mechanism which involves melting, vaporization and rapid cooling of molten material. In this work, the significance of discharge energy on the performance of wire electrical discharge turning process, namely, material removal rate, surface finish, thickness of recast layer and surface crack, is analyzed. New model to estimate material removal rate and surface finish in wire electrical discharge turning process have been proposed. Erosion energy and kinetic energy imparted by electrons and average physio-thermal properties of work material are utilized for the modeling. Proposed models are validated by conducting experiments on AISI 4340 steel material. The results obtained from the model are well in agreement with the experimental values. The influence of discharge energy on surface crack and recast layer thickness is analyzed using scanning electron microscope micrographs and energy-dispersive x-ray spectroscopy analysis. Surface crack is observed at higher discharge energy. The thickness of recast layer increases with the increase in discharge energy. Three-dimensional surface topography reveals the turbulent nature of machining process resulted from transient erosion phenomena of wire electrical discharge turning process. Higher material removal rates of the order of about 0.06 g/min with consistent average roughness in the range of 4.5–5.5 µm at the expense of 1.6–2.6 J of discharge energy are achieved in this work. The proposed models can be utilized for machining of difficult to machine material by effective utilization of energy that leads to energy conservation in wire electrical discharge turning process.

Harmonic-analysis-based method for separation of form error during evaluation of high-speed spindle radial errors

The measurement and evaluation of spindle errors is an important task in the assessment of the accuracy of machine tools. The commonly followed capacitive-sensor-based measurement technique requires a comprehensive error separation method for the identification of the unwanted contributions of centering error, the form error of the artifact and thermal drift. This paper presents a method for form error separation that is suitable for the evaluation of the radial error of high-speed spindles. In the present work, a fixed sensitive radial error motion test is conducted using a capacitive sensor and a cylindrical artifact at different spindle speeds. A mathematical model consisting of a second-order polynomial and Fourier series function is used to interpret the data measured in the time domain. The form profile of the artifact is measured separately in a roundness tester using a capacitive sensor. A harmonic analysis method is proposed to identify and separate the dominant harmonic components in the form profile of the artifact. A mathematical description of the proposed method is described and experimental results are presented. Application of the proposed method to the evaluation of the synchronous radial error of a high-spindle is provided for measured data. The proposed method analyzes the data measured in the time domain and is suitable for the identification of the spindle errors at high-speed conditions.

Least square curve fitting technique for processing time sampled high speed spindle data

Radial error measurement of a high speed spindle is commonly affected by speed variations, centring error, form error of master cylinder and thermal drift of the spindle. This paper presents a least square curve fitting technique for processing the high speed spindle data using a mathematical model consisting of a second-order polynomial and sum of sinusoidal functions. Re-sampling method is proposed for accounting the spindle speed variations. Performance of the proposed method is compared with Fourier transform based frequency domain filtering method. Simulation and experimental results confirm the accuracy of the proposed method for analysing the time sampled spindle data. [Received 18 March 2010; Revised 4 October 2010; Accepted 20 October 2010]

Investigation into energy consumption, surface roughness and material removal rate of cylindrical components machined using wire electrical discharge turning process

In this paper, the effect of input parameters such as pulse off time, servo feed and spindle rotation on energy consumption, surface roughness and material removal rate (MRR) of machined components are analysed during wire electrical discharge turning (WEDT) process. The parameters were varied at three levels and experiments were conducted using full factorial design. The energy consumption is measured using the power pulse train which is obtained from voltage and current pulse trains. It is observed that the pulse off time has significant effect on energy consumption and surface roughness is affected by the spindle rotation. It is also observed that material removal rate is affected by the energy dissipated during machining.

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

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.