Samuel G L

High-aspect-ratio high-quality microholes are required in turbine blades to improve cooling performance. These cooling holes are drilled by pulsed laser and hence dimensional as well as geometrical tolerances like circularity and cylindricity are important. The measurement of geometrical features of the microholes is a very challenging task without destroying the components. In the present work, the microholes are produced on Ti6Al4V alloy by ultra-short pulse laser. The geometrical features of microholes are then captured using a non-destructive technique, namely computed tomography. CT-scanned 3D data is directly used for geometrical analysis using open-source software, GOM Inspect. Since algorithms used in the GOM Inspect are proprietary in nature, the extracted coordinate data are also analyzed using the computational methods developed by the authors based on least squares technique. The dimension, circularity, and cylindricity of microholes are compared with the results obtained from GOM Inspect software and a close match is found.

The hard turning process with advanced cutting tool materials has several advantages over grinding such as short cycle time, process flexibility, compatible surface roughness, higher material removal rate and less environment problems without the use of cutting fluid. However, the main concerns of hard turning are the cost of expensive tool materials and the effect of the process on machinability characteristics. The poor selection of the process parameters may cause excessive tool wear and increased work surface roughness. Hence, there is a need to study the machinability aspects in high-hardened components. In this work, an attempt has been made to analyze the influence of cutting speed, feed rate, depth of cut and machining time on machinability characteristics such as machining force, surface roughness and tool wear using response surface methodology (RSM) based second order mathematical models during turning of AISI 4340 high strength low alloy steel using coated carbide inserts. The experiments were planned as per full factorial design (FFD). From the parametric analysis, it is revealed that, the combination of low feed rate, low depth of cut and low machining time with high cutting speed is beneficial for minimizing the machining force and surface roughness. On the other hand, the interaction plots suggest that employing lower cutting speed with lower feed rate can reduce tool wear. Chip morphology study indicates the formation of various types of chips operating under several cutting conditions. © 2012 Elsevier Ltd.

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. © 2013 IMechE.

Wire electrical discharge turning (WEDT) process is one of the emerging non-traditional machining processes for manufacture of micro- and axi-symmetric components. In WEDT process, material is removed by successive sparks that form craters. The material removal by crater formation is associated with energy supplied in the gap referred as discharge energy. This energy must be controlled for effective machining. In this paper, a model is proposed for predicting the crater diameter based on anode erosion. Finite element method (FEM) is used to simulate the crater for different plasma flushing efficiency. Effect of discharge energy developed in the gap, physio-thermal properties of the material are considered for modeling. The erosion energy required to form a crater is also evaluated using anode erosion model. The proposed models are validated by conducting WEDT experiments on high-tensile steel [AISI 4340]. The crater morphology is investigated by using images obtained from scanning electron microscope (SEM) and energy-dispersive X-ray analysis. The crater diameter predicted by anode erosion and FEM models are compared with diameter obtained from SEM micrograph. The results obtained from the proposed models are well in agreement with the experimental results. The anode erosion model predicts the crater diameter and erosion energy with an average absolute error of 5.65 and 17.86 %, respectively. By estimating the energy required to erode a material and by setting appropriate process settings, the discharge energy can be effectively utilized for material removal.

Surface roughness parameter prediction and evaluation are important factors in determining the satisfactory performance of machined surfaces in many fields. The recent trend towards the measurement and evaluation of surface roughness has led to renewed interest in the use of newly developed non-contact sensors. In the present work, an attempt has been made to measure the surface roughness parameter of different machined surfaces using a high sensitivity capacitive sensor. A capacitive response model is proposed to predict theoretical average capacitive surface roughness and compare it with the capacitive sensor measurement results. The measurements were carried out for 18 specimens using the proposed capacitive-sensor-based non-contact measurement setup. The results show that surface roughness values measured using a sensor well agree with the model output. For ground and milled surfaces, the correlation coefficients obtained are high, while for the surfaces generated by shaping, the correlation coefficient is low. It is observed that the sensor can effectively assess the fine and moderate rough-machined surfaces compared to rough surfaces generated by a shaping process. Furthermore, a linear regression model is proposed to predict the surface roughness from the measured average capacitive roughness. It can be further used in on-machine measurement, on-line monitoring and control of surface roughne ss in the machine tool environment. © 2011 Polish Academy of Sciences. All rights reserved.

Electrical discharge machining (EDM) is a non-contact machining process in which rapid electric discharges are used to remove material from a workpiece by melting and vaporisation. The need for components with intricate and difficult to manufacture features have increased drastically over the past few years in different fields of application. The objective of this work was to carry out experimental investigations on the machining of EN31 steel alloy by varying input parameters like peak current and pulse-on-time, with different tool electrodes using the injection flushing configuration, to compare the effect of electrodes on material removal rate, tool wear rate and surface roughness in drilling annular holes on the workpiece. Finite element modelling of the process was done using COMSOL Multiphysics to calculate the temperature distribution and the volume of the craters formed during sparking. The results obtained from the model are then compared with the experimental data and were found that they are complementing each other. Copper is a better electrode material for machining EN31 alloy steel to obtain better material removal rate with least tool wear rate.

The unique feature of wire electrical discharge machining (EDM) is using thermal energy to machine electrically conductive parts; this distinctive advantage has been utilised in the manufacture of moulds and dies, automotive, aerospace and surgical components. In this paper, the application of wire EDM for machining axisymmetric form and helical profiles on cylindrical workpieces with different diameters is presented. The required rotary and linear motions of the workpiece are obtained by using a special rotary attachment and a motorised linear stage. The rotary motion of the spindle, linear motion of the motorised linear set-up and the wire EDM table movement were controlled to obtain a desired form of the workpiece. The workpieces after machining were measured and evaluated for dimensional accuracies. The dimensional accuracy of the axisymmetric components machined in the present work is found to be about 3.3%. The accuracy of the helical profiles is found to be high, with a maximum error 0.031 mm in average and a standard deviation of 0.028 mm. The present work can be extended to optimise machining parameters for further improving the quality of the machined parts. Copyright © 2012 Inderscience Enterprises Ltd.

In metal cutting processes, reduction in sliding friction at the cutting regime can improve the machining performances in terms of cutting force reduction, built-up edge stabilization and improved surface integrity. However in drilling, as the cutting action occurs inside the hole, minimization of frictional effect at the contact interfaces is always a challenging task, as the reachability of cutting fluids at the machining zone is obstructed by the upward motion of chips sliding along the flute surface. This challenge can be addressed by functionalizing the drill tool surfaces with microtextures. Hence, in the present work, a novel drill tool having microtextures at the flute and margin side is used to reduce the sliding friction. The performance evaluation of microtextured drill tool was done based on the variation in thrust and torque. Margin textured tool was found to be more efficient than flute textured and non-textured tool recording a net thrust force reduction of 10–12% in dry, 15–20% in wet and 15–19% in MQL condition. Reduction in contact length, wear debris entrapment and formation of micropool lubrication effect at the cutting regime are found to be the underlying mechanisms responsible for the improved performance of microtextured drill tools.

Imperfections in the miniaturised machine tool will affect dimensional accuracy of micro components. It is necessary to measure these errors and apply compensation to improve their performance. In the present work, parametric errors of a miniaturised vertical milling machine were measured using capacitance sensors and the data is analysed using computational geometric techniques. Kinematic model of micro machine is developed and the error compensation is applied. To investigate the effect of error compensation on the dimensional accuracy of components, experiments were conducted while the machine tool is operating under point to point (PTP) control and continuous control. Machined profiles before and after compensation were inspected using a CMM and found that the profiles machined after applying compensation had better dimensional accuracy. This is due to the improvement of tool positioning accuracy after compensation. The details of measurement, modelling, error compensation, experiments and the results are presented in this paper. Copyright © 2010 Inderscience Enterprises Ltd.

Verification of engineering components having freeform profiles on a coordinate measuring machine (CMM) requires accurate measurement of sufficient number of sample points. While the measurement accuracy increases with increased sample size, it is often limited by cost and time considerations. Thus, for a given sample size, the locations of the measurement points are to be determined such that the actual shape may be effectively characterized. Several attempts are reported in the literature. A simple algorithm based on dominant points is proposed in this paper. Simulation studies have been carried out on a freeform profile. Comparison of the results with those obtained from uniform spacing and equi-parameter sampling methods reveals that the proposed method performs effectively.