Showing papers in "Machining Science and Technology in 2012"

INVESTIGATING THE EFFECTS OF EDM PARAMETERS ON SURFACE INTEGRITY, MRR AND TWR IN MACHINING OF Ti–6Al–4V

Abstract: Ti–6Al–4V is a kind of difficult-to-cut material with poor machinability by traditional machining methods, while electrical discharge machining (EDM) is suitable for machining titanium alloys. In this paper, three input machining parameters including pulse current, pulse on time and open circuit voltage were changed during EDM tests. To investigate the output characteristics; material removal rate (MRR), tool wear ratio (TWR) and different aspects of surface integrity for Ti–6Al–4V samples such as topography of machined surface, crack formation, white layer (recast layer) thickness and microhardness were considered as performance criteria. The variations of MRR and TWR versus input machining parameters were investigated by means of main and interaction effect plots and also verified by ANOVA results. The effect of pulse energy based on pulse on time and pulse current variations against recast layer thickness and microhardness was studied. The possibility of forming different chemical elements and compound...

Rotary ultrasonic machining of carbon fiber-reinforced polymer: feasibility study

Abstract: Carbon fiber-reinforced polymer (CFRP) has been widely used in aircraft components, automotive parts, and sporting goods. Hole machining is the most frequently employed operation of secondary machining for fiber-reinforced composites. However, challenges (delamination, splintering, burr, short tool life, low machining precision, and low surface quality) still remain for their widespread applications. Rotary ultrasonic machining (RUM) is a non-conventional machining process that has been used to drill holes in composite materials. However, it has not been used to drill this type of CFRP. In this article, RUM is introduced into drilling holes in this type of CFRP for the first time. The feasibility to machine carbon fiber-reinforced epoxy using RUM is investigated experimentally. Chips, edge chipping, surface roughness, tool wear, and thrust force were measured. Effects of RUM process variables (rotation speed, vibration amplitude, and feedrate) on thrust force and surface roughness were studied. Results sh...

EXPERIMENTAL INVESTIGATION ON SURFACE MODIFICATION OF ALUMINUM BY ELECTRIC DISCHARGE COATING PROCESS USING TiC/Cu GREEN COMPACT TOOL-ELECTRODE

Abstract: This article presents the surface modification of aluminum workpiece by electric discharge coating (EDC) process using TiC/Cu green compact tool-electrode. Powder metallurgy (P/M) tool-electrodes were used to create hard layer(s) on the workpiece surface by a material transfer from this tool-electrode (produced with powder metallurgy) to the workpiece surface it was possible to create hard layer(s) there with high tribological properties and integrity. The present study has been carried out to investigate the effect of input parameters (peak current, pulse-on time, composition and compaction pressure of the tool-electrode) on process performance parameters (roughness and micro-hardness of workpiece surface and coating layer thickness). Regression models have been developed to define a mathematical correlation between input and process performance parameters. Analysis of variance has been conducted at the 95% confidence level, to test the significance of these models. The results of the experiments indicat...

Hole making using ball helical milling on titanium alloys

Abstract: In this article, results of helical ball milling for hole making on Ti-6Al-4V alloy are presented and compared with drilling. Two different machining strategies were tested with a ball end mill. In the first strategy only a helical milling path was used to achieve the nominal diameter. The second strategy has two stages; first, helical milling considering a diameter 50 µm below the nominal, and second, the tool flank of the ball end mill were used to remove the stock left with a single contouring operation. Experimental tests were performed taking into account the process time, final quality of holes, hole diameter, roughness and burr formation at tool entrance and exit. With helical milling two advantages were concluded: the process is versatile because one tool is suitable for a range of diameters and negligible burrs are produced. However hardness in the zones close to hole internal surfaces machined with the ball end mill tool decreases with respect to twist drilling. The information obtained from thi...

Penetration ability of abrasive waterjets in cutting of aluminum-silicon carbide particulate metal matrix composites

Abstract: This article presents a set of studies performed on aluminum-silicon carbide particulate metal matrix composites prepared by adding 5, 10, 15 and 20% of SiC in aluminum alloy and processed with abrasive water jets that are formed with garnet and silicon carbide abrasives of 80 mesh size. These studies are essentially meant to assess the penetration ability of abrasive water jets on different compositions of Al-SiC p MMCs produced by stir casting method. Abrasive waterjet cutting experiments were conducted on trapezoidal shaped specimens of different composites as well on the constituent materials i.e., 100% aluminum alloy and 100% SiC specimens by varying water pressure, jet traverse speed and abrasive mass flow rate, each at three different levels. The percentage contribution of individual and combined effects of process parameters on penetration ability was analyzed by means of analysis of variance. Contribution of waterjet pressure and traverse speed on jet penetration in these meaterials are found to ...

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

Abstract: 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 i...

Optimal mql and cutting conditions determination for desired surface roughness in turning of brass using genetic algorithms

Abstract: The evolving concept of minimum quantity of lubrication (MQL) in machining is considered as one of the solutions to reduce the amount of lubricant to address the environmental, economical and ecological issues. This paper investigates the influence of cutting speed, feed rate and different amount of MQL on machining performance during turning of brass using K10 cemented carbide tool. The experiments have been planned as per Taguchi's orthogonal array and the second order surface roughness model in terms of machining parameters was developed using response surface methodology (RSM). The parametric analysis has been carried out to analyze the interaction effects of process parameters on surface roughness. The optimization is then carried out with genetic algorithms (GA) using surface roughness model for the selection of optimal MQL and cutting conditions. The GA program gives the minimum values of surface roughness and the corresponding optimal machining parameters.

Investigation into the characteristics of white layers produced in a nickel-based superalloy from drilling operations

Abstract: The nature of white layers generated during metal cutting operations have for some time been the object of scientific controversy in reference to their metallurgical nature/structure. This research aims to study the structure of the white layer from an abusive cutting operation (i.e., drilling) in a nickel-based superalloy at both macro and micro scale levels. This has been achieved by using (1) a Focus Ion Beam to mill a sample for Transmission Electron Microscopy to analyse the grain size within the white layer, (2) Scanning Electron Microscopy to see shape characteristics of the white layer generated, (3) X-ray diffraction to see any alterations to the crystallinity of the structure, and (4) nano-indentation within this layer to compare its hardness with that of the bulk material. The in-depth analysis of white layers generated from non-standard drilling parameters of alloy RR1000 has shown that the layer is of the same structure as the bulk material: face centre cubic (FCC). The analysis has also show...

Experimental investigations into the influence of major operating parameters during micro-electro discharge drilling of cemented carbide

Abstract: Present study investigates the influence of major operating parameters on the performance of micro-EDM drilling of cemented carbide (WC-10wt%Co) and identifies the ideal values for improved performance. The operating parameters studied were electrode polarity, gap voltage, resistance, peak current, pulse duration, pulse interval, duty ratio, electrode rotational speed and EDM speed. The performance of micro-EDM drilling process was evaluated by machining time, material removal rate (MRR), relative electrode wear ratio (RWR), spark gap, surface finish and dimensional accuracy of micro-holes. It has been found that there are two major conflicting issues in the micro-EDM of carbide. If the primary objective is to obtain better surface finish, it can be obtained by the sacrifice of high machining time, low MRR and high RWR. However, for faster micro-EDM, the surface roughness is higher and electrode wear is again much higher. It is concluded that negative electrode polarity, gap voltage of 120 V, resistance o...

Analytical modeling of the effect of the tool flank wear width on the residual stress distribution

Abstract: Tool flank wear has significant effects on the cutting process, as it affects cutting forces, temperature and residual stresses. In this article, analytical models are developed to predict the cutting temperature and residual stresses in the orthogonal machining of a worn tool. In these models, measured forces, cutting conditions, tool geometry, and material properties are used as inputs. Stresses resulting from thermal stresses, fresh tool stresses and stresses due to tool flank wear are used in this analytical elasto-plastic model, and the residual stresses are determined by a relaxation procedure. The analytical model is verified experimentally with X-ray diffraction measurements. With the analytical model presented here, accurate residual stress profiles in worn tools are shown, while the computational time is significantly reduced from days, typical for finite-element method (FEM) models, to seconds.

Machining of soda lime glass using abrasive hot air jet: an experimental study

Abstract: Abrasive Jet Machining is becoming one of the most prominent machining techniques for glass and other brittle materials. In this article, an attempt has been made to combine abrasive and hot air to form an abrasive hot air jet. Abrasive hot air jet machining can be applied to various operations such as drilling, surface etching, grooving and micro finishing on the glass and its composites. The effect of air temperature on the material removal rate applied to the process of glass etching and grooving is discussed in this article. The roughness of machined surface is also analyzed. It is found that the Material Removal Rate (MRR) increases as the temperature of carrier media (air) is increased. The results have revealed that the roughness of machined surface is reduced by increasing temperature of carrier media. The mechanism of material removal rate has been discussed with aid of SEM micrographs.

Micromilling in minimum quantity lubrication

Abstract: This study investigates micromilling of 316 L stainless steel under minimum quantity lubrication. A laser-based technique was developed to measure spindle runout and assist tool setting for fragile micro cutting tools. Thresholds were established to help select cutting parameters and avoid catastrophic tool failure. Computational fluid dynamics was used to simulate flow of lubricant microdroplets around a rotating tool. When properly applied to wet the tool and workpiece, minimum quality lubrication reduces the build up edge on a cutting tool and increases the tool life up to 100 times compared to dry micromilling of 316L and stainless steel.

A study of micro-channeling on glasses using an abrasive slurry jet

Abstract: A study of micro-channeling on glasses using an abrasive slurry jet is presented. The mechanism of channel formation is discussed. It is found that the cross section of the channel is characterized by a V-shape, where the maximum channel width is larger than the nozzle inner diameter. The surface morphology features with two types of major and minor wave patterns. The major wave patterns with large wavelength developed along the channel are caused by the jet deflection during nozzle traverse motion. The minor wave patterns are a result of the secondary viscous flow that is induced by the impact of jet on the target. Material was eroded predominantly by the ductile mode, resulting in a smooth surface. The depth of the channel is mainly affected by the jet kinetic energy transferring to material via abrasive particles. In contrast, the viscous flow plays a main role in the formation of the channel width. The turbulent flow that drives the moving particles accumulated at the bottom of the channel contributes...

Modeling workpiece dynamics using sets of decoupled oscillator models

Abstract: During the machining of thin-walled components, the dynamic behavior of the workpiece has a significant influence on the machining process and on the quality of the machined surfaces. In this article, a hybrid simulation concept for modeling regenerative workpiece vibrations is presented, which couples a geometric workpiece model with sets of decoupled harmonic oscillators to take the workpiece dynamics into account.

Microstructural alteration and microhardness at near-surface of aisi h13 steel by hard milling

Abstract: In the present research, the microstructural alteration and microhardness at near-surface of AISI H13 steel by hard milling under different cutting parameters with coated cutting tools have been investigated. Very thin white layer forms or even no obvious microstructural alteration layer appears at the near-surface. It is reasonable that the formation of the very thin white layer is primarily due to mechanical effect (severe plastic deformation) rather than thermal effect (rapid heating and quenching). The ‘hook’ shape of the microhardness profile indicates that the highest microhardness appears on the very top surface; while the smallest microhardness occurs at the depth of 25 µm below the machined surface. Moreover, the microhardness profiles below the machined surfaces well correlate with the microstructural change of the machined near-surface. It is expected that the experimental results will provide a useful guide to control or minimize the white layer formation and, more significantly, to promote th...

Response surface analysis of slicing of silicon ingots with focus on photovoltaic application

Abstract: Polycrystalline silicon wafers are widely used in Photovoltaic (PV) industry as a base material for the solar cells. The existing silicon ingot slicing methods typically provide minimum wafer thickness of 300–350 μm and a surface finish of 3–5 μm Ra while incurring considerable kerf loss of 35–40%. Consequently, efficient dicing methods need to be developed, and in the quest for developing new processes for silicon ingot slicing, the wire-EDM (electric discharge machining) is emerging as a potential process. Slicing of a 3′′ square silicon ingot into wafers of 500 μm in thickness has been performed to study the process capability. This article analyzes the effect of processing parameters on the cutting process. The objective of the experimental study is improvement in slicing speed, minimization of kerf loss and surface roughness. A central composite design-based response surface methodology (RSM) has been used to study the slicing of polycrystalline silicon ingot via wire-EDM. A zinc-coated brass wire, 1...

Tool condition monitoring using acoustic emission, surface roughness and growing cell structures neural network

Abstract: The monitoring of tool wear is a most difficult task in the case of various metal-cutting processes. Artificial Neural Networks (ANN) has been used to estimate or classify certain wear parameters, using continuous acquisition of signals from multi-sensor systems. Most of the research has been concentrated on the use of supervised neural network types like multi-layer perceptron (MLP), using back-propagation algorithm and Radial Basis Function (RBF) network. In this article, a new constructive learning algorithm proposed by Fritzke, namely Growing Cell Structures (GCS) has been used for tool wear estimation in face milling operations, thereby monitoring the condition of the tool. GCS generates compact network architecture in less training time and performs well on new untrained data. The performance of this network has been compared with that of another constructive learning algorithm-based neural network, namely the Resource Allocation Network (RAN). For the sake of establishing the effectiveness of GCS, ...

High frequency measurements of cutting forces in milling by inverse filtering

Abstract: Accurate estimates of cutting forces are important in the evaluation of different cutting tool geometries and concepts. However, dynamic influences from the measurement system affect the result, which can make the obtained cutting force data erroneous and misleading. This article presents a method to obtain an inverse filter which compensates for the dynamic influences of the measurement system. Using this approach, unwanted dynamic effects of the measurement system can be counteracted, making it possible to retain information related to the cutting forces contained in the high frequency region. The advantage of the proposed method is illustrated by comparing simulated, inverse- and low-pass filtered forces to unfiltered forces under different cutting conditions. The results show that inverse filtering increases the usable frequency range of the force dynamometer and thereby provide more reliable results compared to both low-pass and unfiltered forces.

GREEN MACHINING ORIENTED TO DIMINISH DENSITY GRADIENT FOR MINIMIZATION of DISTORTION IN ADVANCED CERAMICS

Abstract: After sintering advanced ceramics, there are invariably distortions, caused in large part by the heterogeneous distribution of density gradients along the compacted piece. To correct distortions, machining is generally used to manufacture pieces within dimensional and geometric tolerances. Hence, narrow material removal limit conditions are applied, which minimize the generation of damage. Another alternative is machining the compacted piece before sintering, called the green ceramic stage, which allows machining without damage to mechanical strength. Since the greatest concentration of density gradients is located in the outer-most layers of the compacted piece, this study investigated the removal of different allowance values by means of green machining. The output variables are distortion after sintering, tool wear, cutting force, and the surface roughness of the green ceramics and the sintered ones. The following results have been noted: less distortion is verified in the sintered piece after 1 mm all...

Simulations and experiments on machining carbon and low alloy steels at rake face temperatures up to 1200°c

Abstract: Finite element simulations are reported of the machining of carbon and low alloy steels at speeds from 50 to 300 m/min and feeds from 0.125 to 0.3 mm/rev. Their mechanical models include yield delay (resulting in an upper yield point followed by a yield drop). Predictions are compared with experimentally measured cutting and thrust forces, shear plane angles and rake face temperatures (from tool-work thermocouple measurements) in these conditions. Agreements are generally within 10% for all quantities, except that some uncertainty arises from comparing the semi-orthogonal experimental with the plane strain simulation data.

Finite element modeling of burr formation in orthogonal cutting

Abstract: A finite element model for orthogonal cutting is developed and applied to simulate burr formation. Three typical workpiece materials were investigated. The simulation results reveal the entire burr formation process. The simulation produces either positive or negative burrs depending on the material properties, which is in agreement with experimental observations from literature. Both shear and normal stress failures are presented for negative burr formation while only shear stress failure leads to positive burr formation. The FE modeling results confirm that material property is the dominant factor in controlling burr formation.

An examination of abrasive waterjet peening with elastic pre-stress and the effects of boundary conditions

Abstract: & Abrasive Waterjet Peening (AWJP) has emerged as a potentially viable method of surface treatment for components requiring compressive residual stress and a rough surface texture. In the present investigation the residual stress distributions resulting from AWJP of Ti6Al4V with load and displacement control flexure pre-stress were compared. An experimental evaluation was conducted to quantify the variations in the residual stress characteristics (magnitude and depth) as a function of boundary conditions over a pre-stress ranging from 0 to 75% of the material’s yield strength. In addition, a finite element model for indentation-based surface treatments was developed to investigate the mechanisms contributing to the observed trends in experimental results. Overall, AWJP of the Ti6Al4V resulted in a surface residual stress ranging from approximately 800 to 1600MPa. Load control pre-stress resulted in a larger surface residual stress (up to 50% greater) than that achieved under displacement control treatments. Although the maximum surface residual stress was obtained at the largest applied pre-stress, the difference between load and displacement control treatments decreased with pre-stress magnitude. Boundary conditions had limited influence on the depth of residual stress achieved, but were important to the depth of plasticized zone beneath the treated surface.

Model-based assistant tool for the setting-up and optimization of centerless grinding process

Abstract: Recent advances in process modeling allow for more accurate prediction of complex phenomena. A combination of different modeling approaches makes it possible to develop new products to set up, control and optimize machining operations. In the near future, a continuous improvement strategy should be adopted, as improvements to advanced models open up new opportunities for industrial applications. In particular, the efforts made by different research groups on grinding have given rise to significant developments in this area, some of which have recently been made into applied software. As an example of the necessity for process modeling and the viability of industrialized tools based on it, this article presents the work carried out on the development of an assistant tool for the setting up and optimization of the centerless grinding process, focusing on avoiding the main limitations of this process and optimizing productivity.

CHARACTERIZATION OF FRICTION COEFFICIENT AND HEAT PARTITION COEFFICIENT BETWEEN AN AUSTENITIC STEEL AISI304L AND A TiN-COATED CARBIDE CUTTING TOOL

Abstract: This work aims at characterizing the tribological behavior of an AISI304L austenitic steel and a TiN-coated carbide tool under extreme conditions corresponding to the one occurring at the cutting tool-work material in dry machining. A specially designed open tribometer has been used to characterize the friction coefficient, heat partition coefficient and adhesion in the contact versus sliding velocity and contact pressure. It has been shown that sliding velocity is the most influential parameter. An increase of sliding velocity induces a great decrease of friction coefficient, whereas contact pressure seems to play a secondary role on the friction coefficient. Adhesion is minimized when sliding speed increases. Heat partition coefficient decreases with sliding velocity, which tends to decrease the ratio of heat transmitted to cutting tools when sliding velocity increases. Finally, this work provides quantitative data of friction and heat partition coefficients versus sliding velocity and contact pressure ...

On the characteristics of high-performance internal peel grinding using electroplated cbn wheels

Abstract: The enhancement of material removal rates in hard machining is one major aspect of the applied cutting technologies; to increase the production rates. With respect to the required part quality, emphasis is put on the finishing process as a key element of the process chain. Especially internal finish operations constitute a challenging task because of the complex contact situation. This article presents a recent study on internal peel grinding, using the combined roughing-finishing procedure in combination with the excellent cutting performance of electroplated CBN wheels, to achieve highest removal rates with high surface finish.

Stability lobes prediction for corner radius end mill using nonlinear cutting force coefficients

Abstract: There are a vast number of different types of end mill tools used in the manufacturing industry, each type with a unique shape. These tool shapes have a direct influence on the cutting force it generates during machining. This article presents a more accurate approach to predicting the stability margin in machining by considering the cutting force coefficients and axial immersion angle as variables along the axial depth of cut. A numerical approach to obtaining a converged solution to the stability model is presented. The results obtained are validated using experimental results and a very good agreement is seen.

Relationship between machining forces and diamond tool wear during ductile regime machining of silicon nitride

Abstract: Silicon nitride by nature is hard and brittle. In previous works, it has been demonstrated that silicon nitride can be machined by single-edge diamond tool as an alternative to the traditional finishing process. But commercial viability of such diamond turning processes is limited by tool wear. In this paper, an attempt has been made to edge machine silicon nitride disks with diamond tools of different geometries and operating conditions. Amount of tool wear under these operating conditions is studied and characterized. Our studies show that radius tools perform better than straight-edged tools but with a cost trade-off.

Geometrical approach for reduction of tool shape degeneration in electric discharge machining (edm)

Abstract: In this study, the geometric wear characteristics of tool electrodes were obtained for various pulse time, discharge current and machining depth settings in electric discharge machining. Different forms of protrusions were machined on the front surface of the tool to reduce the geometric wear. Significant reductions in original tool geometric wear characteristics (front wear, side wear and edge wear) were obtained with the use of square cross-section protrusions. The dimensions of the square cross-section protrusions were modeled mathematically in terms of machining parameters used in the experiments.

Dynamic analysis of the lengthened shrink-fit holder and cutting tool system in high-speed milling

Abstract: A finite element model of the matching of lengthened shrink-fit holder (LSFH) and cutting tool is established and the Rayleigh viscous damping model is used to calculate the reasonable structural damping of this model. A milling force model is developed to predict the transient milling force using back propagation neural network (BPNN). The dynamic characteristic of matching of LSFH and cutting tool is analyzed by means of the universal commercial software ANSYS10.0. The results of numerical simulation are obtained and verified against the practical measurements that show that they are consistent. This study is important to optimum design of LSFH, and to rationally choose the matching of LSFH and cutting tool, deformation analysis, error compensation and parameters optimization in high-speed milling.

Correlation-based estimation of cutting force coefficients for ball-end milling

Abstract: This article presents a methodology to estimate cutting force coefficients based on the least squares approximation using correlation factor between the estimated and measured cutting forces in order to determine the corresponding tool angular position. This method can be applied on measured cutting force data over any small interval of time that need not contain information of the time instant when the cutting tool enters the workpiece, which has been the main requirement in the conventional method. This allows a quick estimation of the cutting force coefficients regardless of the chosen cutting conditions and tool-workpiece material, which is often the case in industrial machining processes. This proposed method has been validated by comparison of cutting force coefficients obtained using conventional estimation technique for a slot ball-end milling test. Besides being useful for predictive evaluation of forces, such estimation of cutting force coefficients of the cutting force model can be useful for u...