Showing papers in "International Journal of Machine Tools & Manufacture in 2008"
TL;DR: The experimental and theoretical studies of LBM show that process performance can be improved considerably by proper selection of laser parameters, material parameters and operating parameters, and the trend for future research is outlined.
Abstract: Laser beam machining (LBM) is one of the most widely used thermal energy based non-contact type advance machining process which can be applied for almost whole range of materials. Laser beam is focussed for melting and vaporizing the unwanted material from the parent material. It is suitable for geometrically complex profile cutting and making miniature holes in sheetmetal. Among various type of lasers used for machining in industries, CO2 and Nd:YAG lasers are most established. In recent years, researchers have explored a number of ways to improve the LBM process performance by analysing the different factors that affect the quality characteristics. The experimental and theoretical studies show that process performance can be improved considerably by proper selection of laser parameters, material parameters and operating parameters. This paper reviews the research work carried out so far in the area of LBM of different materials and shapes. It reports about the experimental and theoretical studies of LBM to improve the process performance. Several modelling and optimization techniques for the determination of optimum laser beam cutting condition have been critically examined. The last part of this paper discusses the LBM developments and outlines the trend for future research.
754 citations
TL;DR: In this article, 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.
Abstract: 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.
533 citations
TL;DR: In this article, liquid nitrogen as a cryogenic coolant was investigated in detail in terms of application methods in material removal operations and its effects on cutting tool and workpiece material properties, cutting temperature, tool wear/life, surface roughness and dimensional deviation, friction and cutting forces.
Abstract: The cooling applications in machining operations play a very important role and many operations cannot be carried out efficiently without cooling. Application of a coolant in a cutting process can increase tool life and dimensional accuracy, decrease cutting temperatures, surface roughness and the amount of power consumed in a metal cutting process and thus improve the productivity. In this review, liquid nitrogen, as a cryogenic coolant, was investigated in detail in terms of application methods in material removal operations and its effects on cutting tool and workpiece material properties, cutting temperature, tool wear/life, surface roughness and dimensional deviation, friction and cutting forces. As a result, cryogenic cooling has been determined as one of the most favourable method for material cutting operations due to being capable of considerable improvement in tool life and surface finish through reduction in tool wear through control of machining temperature desirably at the cutting zone.
420 citations
TL;DR: In this article, a modified Johnson-Cook constitutive equation is formulated to model the material strengthening behaviors at micron level using strain gradient plasticity, and an analytical micro scale milling force model is developed based on the FE simulations using the cutting principles and the slip-line theory.
Abstract: This paper presents mechanisms studies of micro scale milling operation focusing on its characteristics, size effect, micro cutter edge radius and minimum chip thickness. Firstly, a modified Johnson–Cook constitutive equation is formulated to model the material strengthening behaviours at micron level using strain gradient plasticity. A finite element model for micro scale orthogonal machining process is developed considering the material strengthening behaviours, micro cutter edge radius and fracture behaviour of the work material. Then, an analytical micro scale milling force model is developed based on the FE simulations using the cutting principles and the slip-line theory. Extensive experiments of OFHC copper micro scale milling using 0.1 mm diameter micro tool were performed with miniaturized machine tool, and good agreements were achieved between the predicted and the experimental results. Finally, chip formation and size effect of micro scale milling are investigated using the proposed model, and the effects of material strengthening behaviours and minimum chip thickness are discussed as well. Some research findings can be drawn: (1) from the chip formation studies, minimum chip thickness is proposed to be 0.25 times of cutter edge radius for OFHC copper when rake angle is 10° and the cutting edge radius is 2 μm; (2) material strengthening behaviours are found to be the main cause of the size effect of micro scale machining, and the proposed constitutive equation can be used to explain it accurately. (3) That the specific shear energy increases greatly when the uncut chip thickness is smaller than minimum chip thickness is due to the ploughing phenomenon and the accumulation of the actual chip thickness.
341 citations
TL;DR: In this article, the authors extended the present trend prevailing in the literature on surface integrity analysis of superalloys by performing a comprehensive investigation to analyze the nature of deformation beneath the machined surface and arrive at the thickness of machining affected zone.
Abstract: Stringent control on the quality of machined surface and sub-surface during high-speed machining of Inconel 718 is necessary so as to achieve components with greater reliability and longevity. This paper extends the present trend prevailing in the literature on surface integrity analysis of superalloys by performing a comprehensive investigation to analyze the nature of deformation beneath the machined surface and arrive at the thickness of machining affected zone (MAZ). The residual stress analysis, microhardness measurements and degree of work hardening in the machined sub-surfaces were used as criteria to obtain the optimum machining conditions that give machined surfaces with high integrity. It is observed that the highest cutting speed, the lowest feedrate, and the moderate depth of cut coupled with the use of honed cutting edge can ensure induction of compressive residual stresses in the machined surfaces, which in turn were found to be free of smeared areas and adhered chip particles.
329 citations
TL;DR: In this paper, the UVC mechanism is influenced by three important parameters: tool vibration frequency, tool vibration amplitude and workpiece cutting speed that determine the cutting force, which in turn reduces both cutting force and tool wear, improves surface quality and prolongs tool life.
Abstract: The ultrasonic vibration cutting (UVC) method is an efficient cutting technique for difficult-to-machine materials. It is found that the UVC mechanism is influenced by three important parameters: tool vibration frequency, tool vibration amplitude and workpiece cutting speed that determine the cutting force. However, the relation between the cutting force and these three parameters in the UVC is not clearly established. This paper presents firstly the mechanism how these parameters effect the UVC. With theoretical studies, it is established that the tool–workpiece contact ratio (TWCR) plays a key role in the UVC process where the increase in both the tool vibration parameters and the decrease in the cutting speed reduce the TWCR, which in turn reduces both cutting force and tool wear, improves surface quality and prolongs tool life. This paper also experimentally investigates the effect of cutting parameters on cutting performances in the cutting of Inconel 718 by applying both the UVC and the conventional turning (CT) methods. It is observed that the UVC method promises better surface finish and improves tool life in hard cutting at low cutting speed as compared to the CT method. The experiments also show that the TWCR, when investigating the effect of cutting speed, has a significant effect on both the cutting force and the tool wear in the UVC method, which substantiates the theoretical findings.
276 citations
TL;DR: In this article, a comparison between the conventional (Fd) and adjusted (Fda) delamination factor is presented, and the experimental results indicate that the use of HSM is suitable for drilling GFRP ensuring low damage levels.
Abstract: High speed machining (HSM) is an outstanding technology capable of improving productivity and lowering production costs in manufacturing companies. Drilling is probably the machining process most widely applied to composite materials; nevertheless, the damage induced by this operation may reduce drastically the component performance. This work employs HSM to realize high performance drilling of glass fibre reinforced plastics (GFRP) with reduced damage. In order to establish the damage level, digital analysis is used to assess delamination. A comparison between the conventional (Fd) and adjusted (Fda) delamination factor is presented. The experimental results indicate that the use of HSM is suitable for drilling GFRP ensuring low damage levels.
263 citations
TL;DR: In this paper, numerical and experimental methodologies concerning orthogonal cutting are proposed in order to study the dry cutting of an aeronautic aluminium alloy (A2024-T351).
Abstract: In the present contribution, numerical and experimental methodologies concerning orthogonal cutting are proposed in order to study the dry cutting of an aeronautic aluminium alloy (A2024-T351) The global aim concerns the comprehension of physical phenomena accompanying chip formation according to cutting velocity variation For the numerical model, material behaviour and its failure criterion are based on the Johnson–Cook law The model proposes a coupling between material damage evolution and its fracture energy A high-speed camera was used to capture the chip formation sequences The numerical results show that the chip–workpiece contact and the tool advancement induce bending loads on the chip Consequently, a fragmentation phenomenon takes place above the rake face when the chip begins to curl up The computed results corroborate with experimental ones The numerical results predict the residual stress distribution and show high values, along the cutting direction, on the machined workpiece surface
261 citations
TL;DR: In this paper, the surface and subsurface damages have been studied with scanning electron microscope (SEM) and the effects of grinding conditions on surface/subsurface damage have been discussed.
Abstract: The difficulty and cost involved in the abrasive machining of hard and brittle ceramics are among the major impediments to the widespread use of advanced ceramics in industries these days. It is often desired to increase the machining rate while maintaining the desired surface integrity. The success of this approach, however, relies in the understanding of mechanism of material removal on the microstructural scale and the relationship between the grinding characteristics and formation of surface/subsurface machining-induced damage. In this paper, grinding characteristics, surface integrity and material removal mechanisms of SiC ground with diamond wheel on surface grinding machine have been investigated. The surface and subsurface damages have been studied with scanning electron microscope (SEM). The effects of grinding conditions on surface/subsurface damage have been discussed. This research links the surface roughness, surface and subsurface damages to grinding parameters and provides valuable insights into the material removal mechanism and the dependence of grinding-induced damage on grinding conditions.
261 citations
TL;DR: In this paper, a feed scheduling algorithm for CNC systems is presented to minimize the machining time for five-axis contour machining of sculptured surfaces, where the variation of the feed along the tool-path is expressed in a cubic B-spline form.
Abstract: Real time control of five-axis machine tools requires smooth generation of feed, acceleration and jerk in CNC systems without violating the physical limits of the drives. This paper presents a feed scheduling algorithm for CNC systems to minimize the machining time for five-axis contour machining of sculptured surfaces. The variation of the feed along the five-axis tool-path is expressed in a cubic B-spline form. The velocity, acceleration and jerk limits of the five axes are considered in finding the most optimal feed along the tool-path in order to ensure smooth and linear operation of the servo drives with minimal tracking error. The time optimal feed motion is obtained by iteratively modulating the feed control points of the B-spline to maximize the feed along the tool-path without violating the programmed feed and the drives’ physical limits. Long tool-paths are handled efficiently by applying a moving window technique. The improvement in the productivity and linear operation of the five drives is demonstrated with five-axis simulations and experiments on a CNC machine tool.
217 citations
TL;DR: In this article, the influence of laser cutting on the static strength of a carbon fiber-reinforced plastics (CFRP) laminate was investigated using three different high-power laser sources: a pulsed Nd:YAG laser, a disk laser and a CO2 laser.
Abstract: To increase production volume and efficiency in the area of CFRP (carbon fiber-reinforced plastics) component production, fast, flexible and cost-efficient technologies are needed. One process that is necessary during CFRP component production is trimming and cutting. Although laser cutting in principle meets these requirements, it is often not used for component trimming and contour cutting, due to insufficient knowledge about the influences of thermal machining on the material behavior. It is a common argument that lasers, as a thermally acting tool, may damage the CFRP, thus reducing its strength properties. This, however, has never been proven or disproven. Therefore, this paper presents investigations on the influence of laser cutting on the static strength of a CFRP laminate. The material is cut using three different high-power laser sources: a pulsed Nd:YAG laser, a disk laser and a CO2 laser. Appropriate cutting parameters have been found, and the results in cut quality and heat-affected zone are discussed. With these parameter sets, specimens for tensile strength and bending tests have been prepared. These specimens have been tested under static tensile and bending conditions, and the results have been compared to conventional milling as well as abrasive water-jet cut samples. Though a clear dependency of the static strength values on the heat-affected zone was detected, all strengths were found to be far above the material values given by the producer of the laminate.
TL;DR: The experimental result shows that GPR models have the advantage over other regressive models in terms of model accuracy and feature scaling and probabilistic variance, and the effectiveness of controlling optimization process to acquire more reliable optimum predictive solutions.
Abstract: The paper discusses the development of reliable multi-objective optimization based on Gaussian process regression (GPR) to optimize the high-speed wire-cut electrical discharge machining (WEDM-HS) process, considering mean current, on-time and off-time as input features and material remove rate (MRR) and Surface Roughness (SR) as output responses. In order to achieve an accurate estimation for the nonlinear electrical discharging and thermal erosion process, the multiple GPR models due to its simplicity and flexibility identify WEDM-HS process with measurement noise. Objective functions of predictive reliability multi-objectives optimization are built by probabilistic variance of predictive response used as empirical reliability measurement and responses of GPR models. Finally, the cluster class centers of Pareto front are the optional solutions to be chosen. Experiments on WEDM-HS (DK7732C2) are conducted to evaluate the proposed intelligent approach in terms of optimization process accuracy and reliability. The experimental result shows that GPR models have the advantage over other regressive models in terms of model accuracy and feature scaling and probabilistic variance. Given the regulable coefficient parameters, the experimental optimization and optional solutions show the effectiveness of controlling optimization process to acquire more reliable optimum predictive solutions.
TL;DR: In this article, the effects of reinforcement particles on the machinability of metal matrix composites were investigated experimentally and it was shown that the surface residual stresses on a machined MMC are compressive, the surface roughness is controlled by feed and particle pull-out influences the roughness when feed is low.
Abstract: Machining forces, chip formation, surface integrity and shear and friction angles are important factors to understand the machinability of metal matrix composites (MMCs). However, because of the complexity of the reinforcement mechanisms of the ceramic particles, a fair assessment of the machinability of MMCs is still a difficult issue. This paper investigates experimentally the effects of reinforcement particles on the machining of MMCs. The major findings are: (1) the surface residual stresses on the machined MMC are compressive; (2) the surface roughness is controlled by feed; (3) particle pull-out influences the roughness when feed is low; (4) particles facilitate chip breaking and affect the generation of residual stresses; and (5) the shear and friction angles depend significantly on feed but are almost independent of speed. These results reveal the roles of the reinforcement particles on the machinability of MMCs and provide a useful guide for a better control of their machining processes.
TL;DR: In this article, a finite element model for white layer formation in orthogonal machining of hardened AISI 52100 steel under thermally dominant cutting conditions that promote martensitic phase transformations is presented.
Abstract: This paper presents a finite element model for white layer formation in orthogonal machining of hardened AISI 52100 steel under thermally dominant cutting conditions that promote martensitic phase transformations. The model explicitly accounts for the effects of stress and strain, transformation plasticity and the effect of volume expansion accompanying phase transformation on the transformation temperature. Model predictions of white layer depth are found to be in agreement with experimental values. The paper also analyzes the effect of white layer formation on residual stress evolution in orthogonal cutting of AISI 52100 hardened steel. Model simulations show that white layer formation does have a significant impact on the magnitude of surface residual stress and on the location of the peak compressive residual stress.
TL;DR: In this article, a thermal model of friction stir welding was developed that utilizes a new slip factor based on the energy per unit length of weld, which is derived from an empirical linear relationship observed between the ratio of the maximum welding temperature to the solidus temperature and the welding energy.
Abstract: A thermal model of friction stir welding was developed that utilizes a new slip factor based on the energy per unit length of weld. The slip factor is derived from an empirical, linear relationship observed between the ratio of the maximum welding temperature to the solidus temperature and the welding energy. The thermal model successfully predicts the maximum welding temperature over a wide range of energy levels but under predicts the temperature for low energy levels for which heat from plastic deformation dominates. The thermal model supports the hypothesis that the relationship between the temperature ratio and energy level is characteristic of aluminum alloys that share similar thermal diffusivities. The thermal model can be used to generate characteristic temperature curves from which the maximum welding temperature in an alloy may be estimated if the thermal diffusivity, welding parameters and tool geometry are known.
TL;DR: In this article, a new method is proposed for hot incremental forming, which makes use of electric current for heating hard-to-form sheet metals at the tool-sheet interface in order to fully utilize the formability of these materials.
Abstract: In the current work, a new method is proposed for hot incremental forming. The method is based on simple tooling and is easy to employ. It makes use of electric current for heating hard-to-form sheet metals at the tool–sheet interface in order to fully utilize the formability of these materials. The potential effect of processing parameters, namely current, tool size, feed rate and step size, on the formability are investigated using AZ31 magnesium. In addition to this, the shape distortion of TiAl2Mn1.5 titanium workpiece after hot forming has also been addressed herein. Experimental results demonstrate that this technique is feasible and easy to control.
TL;DR: In this article, a finite element method (FEM) based milling process verification model and associated tools are presented, which by considering the effects of fixturing, operation sequence, tool path and cutting parameters simulates the milling processes in a transient 3D virtual environment and predicts the part thin wall deflections and elastic-plastic deformations during machining.
Abstract: The rigid body motion of the workpieces and their elastic-plastic deformations induced during high speed milling of thin-walled parts are the main root causes of part geometrical and dimensional variabilities; these are governed mainly from the choice of process plan parameters such as fixture layout design, operation sequence, selected tool path strategies and the values of cutting variables. Therefore, it becomes necessary to judge the validity of a given process plan before going into actual machining. This paper presents an overview of a comprehensive finite element method (FEM) based milling process plan verification model and associated tools, which by considering the effects of fixturing, operation sequence, tool path and cutting parameters simulates the milling process in a transient 3D virtual environment and predicts the part thin wall deflections and elastic-plastic deformations during machining. The advantages of the proposed model over previous works are: (i) Performs a computationally efficient transient thermo-mechanical coupled field milling simulation of complex prismatic parts comprising any combination of machining features like steps, slots, pockets, nested features, etc., using a feature based milling simulation approach; (ii) Predicts the workpiece non-linear behavior during machining due to its changing geometry, inelastic material properties and fixture-workpiece flexible contacts; (iii) Allows the modelling of the effects of initial residual stresses (residing inside the raw stock) on part deformations; (iv) Incorporates an integrated analytical machining load (cutting force components and average shear plane temperature) model; and (v) Provides a seamless interface to import an automatic programming tool file (APT file) generated by CAM packages like CATIA V5. The prediction accuracy of the model was validated experimentally and the obtained numerical and experimental results were found in good agreement. (C) 2007 Elsevier Ltd. All rights reserved.
TL;DR: In this paper, a new theoretical model for rotational symmetric single point incremental forming (SPIF) was developed under membrane analysis with bi-directional in-plane contact friction forces.
Abstract: Knowledge of the physics behind the fracture of material at the transition between the inclined wall and the corner radius of the sheet is of great importance for understanding the fundamentals of single point incremental forming (SPIF). How the material fractures, what is the state of strain and stress in the small localized deformation zone and how these two subjects are brought together in order to explain the overall formability of SPIF in terms of ductile damage are still not well understood. However, they are of great importance for improving the robustness and enhancing the predictability of currently existing numerical models and for extending the scope of industrial applications of the process. This paper attempts to provide answers to these questions by means of a new theoretical model for rotational symmetric SPIF that was developed under membrane analysis with bi-directional in-plane contact friction forces.
TL;DR: In this paper, the design of an ultrasonically vibrated workpiece holder and the experimental investigation of ultrasonic assisted dry grinding of 100Cr6 were presented. And the surface roughness and grinding forces of the ultrasonic and conventionally ground workpieces were measured and compared.
Abstract: Dry machining has been increasingly investigated in order to decrease the negative environmental impact of the cutting fluids, diminishing problems concerning waste disposal demand and also due to interest in decreasing manufacturing costs. However, generally in dry grinding, as there are no cutting fluids to transfer the heat from the contact zone, problems frequently occur in terms of high heat generation on grinding wheel surface and workpiece surface, increasing the grinding energy, wear of grinding wheel, low material removal rate (regarding relatively low depth of cuts) as well as poor surface roughness compared to conventional grinding. A recent and promising method to overcome these technological constraints is the use of ultrasonic assistance, where high-frequency and low amplitude vibrations are superimposed on the movement of the workpiece. The design of an ultrasonically vibrated workpiece holder and the experimental investigation of ultrasonically assisted dry grinding of 100Cr6 are presented. The surface roughness and grinding forces of the ultrasonically and conventionally ground workpieces were measured and compared. The obtained results show that the application of ultrasonic vibration can eliminate the thermal damage on the workpiece, increase the G-ratio and decrease the grinding forces considerably. A decrease of up to 60–70% of normal grinding forces and up to 30–50% of tangential grinding forces has been achieved.
TL;DR: In this article, a Taylor speed-based dry machining equation was used to predict tool-wear/tool-life performance in NDM by extending the Taylor speed equation to NDM.
Abstract: Traditionally, metal working fluids (MWF) are known to improve machining performance despite poor ecological and health side effects. A new sustainable process that has minimized the use and application of MWFs is NDM (near dry machining). Although there is much controversy on the effectiveness of NDM, it is agreed that a lack of science-based modeling prevents its widespread use. This paper presents a new method to predict tool-wear/tool-life performance in NDM by extending a Taylor speed-based dry machining equation. Experimental work and validation of the model was performed in an automotive production environment in the machining of steel wheel rims. Machining experiments and validation of the new equation reveal that tool-wear can be predicted within 10% when the effect of NDM is statistically different than dry machining. Tool-wear measurements obtained during the validation of the model showed that NDM can improve tool-wear/tool-life over four times compared to dry machining which underlines the need to develop sustainable models to match current practices.
TL;DR: In this article, a wide range of PVD coatings were evaluated based on multiple criteria of tool wear, surface finish and burr size, and the results clearly show that compared to other coatings or uncoated fine grain carbide tools, TiN coatings offer the best performance in terms of tools wear reduction and improvement in quality of machined surface.
Abstract: In conventional or macroscale milling, appropriate physical vapour deposition (PVD) coatings can be used to improve machining performance, promote the use of higher cutting speeds and facilitate dry machining or the use of minimum quantity lubrication (MQL). When micro tools (1–999 μm in diameter) are used in milling, the undeformed chip thickness is usually very small and comparable to the cutting edge radius. This condition determines the effective rake angle and hence plays a significant role in the mechanics of micro machining. The differences between macro and microscale machining influence process factors such as cutting interface temperatures, forces, strains and strain rates. The mechanisms through which coatings protect cutting tools are influenced by such process conditions. Additionally, due to the size of micro tools applying coatings evenly around the cutting edges is a technological challenge. Despite these new challenges, there is hardly any work reported in literature dedicated to the selection of hard coatings for micro machining of tool steels. The work reported in this paper identified coating wear mechanisms in micro milling of hardened tool steels. A wide range of PVD coatings were evaluated based on multiple criteria of tool wear, surface finish and burr size. The results clearly show that compared to other coatings or uncoated fine grain carbide tools, TiN coatings offer the best performance in terms of tool wear reduction and improvement in quality of machined surface.
TL;DR: In this paper, historical perspectives on grinding of silicon wafers, impacts of wafer size progression on applications of grinding in silicon wafer manufacturing, and interrelationships between grinding and two other silicon machining processes (slicing and polishing) are discussed.
Abstract: The majority of semiconductor devices are built on silicon wafers. Manufacturing of high-quality silicon wafers involves several machining processes including grinding. This review paper discusses historical perspectives on grinding of silicon wafers, impacts of wafer size progression on applications of grinding in silicon wafer manufacturing, and interrelationships between grinding and two other silicon machining processes (slicing and polishing). It is intended to help readers to gain a more comprehensive view on grinding of silicon wafers, and to be instrumental for research and development in grinding of wafers made from other materials (such as gallium arsenide, germanium, lithium niobate, sapphire, and silicon carbide).
TL;DR: In this paper, the thermal histories and temperature distributions in a workpiece during a friction stir welding (FSW) process involving the butt joining of aluminum 6061-T6 were explored.
Abstract: This study aims to experimentally explore the thermal histories and temperature distributions in a workpiece during a friction stir welding (FSW) process involving the butt joining of aluminum 6061-T6. Different types of thermocouple layout are devised to measure the temperature histories during FSW at different locations on the workpiece in the welding direction. Successful welding processes are achieved by appropriately controlling the maximum temperatures during the welding process. Regression analyses by the least squares method are used to predict the temperatures at the joint line. A second-order polynomial curve is found to best fit the experimental temperature values in the width direction of the workpiece. The Vickers hardness test is conducted on the welds to evaluate the hardness distribution in the thermal-mechanical affected zone, the heat affected zone, and the base metal zone. Tensile tests are also carried out, and the tensile strength of the welded product is compared with that of the base metal.
TL;DR: In this article, acoustic emission (AE) has been employed for tool condition monitoring of continuous machining operations (e.g. turning, drilling), but relatively little attention has been paid to monitor interrupted processes such as milling and especially to detect the occurrence of possible surface anomalies.
Abstract: The industrial demands for automated machining systems to increase process productivity and quality in milling of aerospace critical safety components requires advanced investigations of the monitoring techniques. This is focussed on the detection and prediction of the occurrence of process malfunctions at both of tool (e.g. wear/chipping of cutting edges) and workpiece surface integrity (e.g. material drags, laps, pluckings) levels. Acoustic emission (AE) has been employed predominantly for tool condition monitoring of continuous machining operations (e.g. turning, drilling), but relatively little attention has been paid to monitor interrupted processes such as milling and especially to detect the occurrence of possible surface anomalies. This paper reports for the first time on the possibility of using AE sensory measures for monitoring both tool and workpiece surface integrity to enable milling of “damage-free” surfaces. The research focussed on identifying advanced monitoring techniques to enable the calculation of comprehensive AE sensory measures that can be applied independently and/or in conjunction with other sensory signals (e.g. force) to respond to the following technical requirements: (i) to identify time domain patterns that are independent from the tool path; (ii) ability to “calibrate” AE sensory measures against the gradual increase of tool wear/force signals; (iii) capability to detect workpiece surface defects (anomalies) as result of high energy transfer to the machined surfaces when abusive milling is applied. Although some drawbacks exist due to the amount of data manipulation, the results show good evidence that the proposed AE sensory measures have a great potential to be used in flexible and easily implementable solutions for monitoring tool and/or workpiece surface anomalies in milling operations.
TL;DR: In this article, the authors examined the link between chatter instability and surface roughness evolution for thin wall milling and developed an explicit numerical model to solve the nonlinear system of delay differential equations.
Abstract: High-speed milling operations of thin walls are often limited by the so-called regenerative effect that causes poor surface finish. The aim of this paper is to examine the link between chatter instability and surface roughness evolution for thin wall milling. Firstly, the linear stability lobes theory for the thin wall milling optimisation was used. Then, in order to consider the modal interactions, an explicit numerical model was developed. The resulting nonlinear system of delay differential equations is solved by numerical integration. The model takes into account the coupling mode, the modal shape, the fact that the tool may leave the cut and the ploughing effect. Dedicated experiments are carried out in order to confirm this modelling. This paper presents surface roughness and chatter frequency measurements. The stability lobes are validated by thin wall milling. Finally, the modal behaviour and the mode coupling give a new interpretation of the complex surface finish deterioration often observed during thin wall milling.
TL;DR: In this paper, the authors focus on the current state and recent developments in different stages of product design: springback prediction, springback compensation and optimization by finite element (FE) analysis.
Abstract: Numerical simulations are being deployed widely for product design. However, the accuracy of the numerical tools is not yet always sufficiently accurate and reliable. This article focuses on the current state and recent developments in different stages of product design: springback prediction, springback compensation and optimization by finite element (FE) analysis. To improve the springback prediction by FE analysis, guidelines regarding the mesh discretization are provided and a new through-thickness integration scheme for shell elements is launched. In the next stage of virtual product design the product is compensated for springback. Currently, deformations due to springback are manually compensated in the industry. Here, a procedure to automatically compensate the tool geometry, including the CAD description, is presented and it is successfully applied to an industrial automotive part. The last stage in virtual product design comprises optimization. This article presents an optimization scheme which is capable of designing optimal and robust metal forming processes efficiently.
TL;DR: In this paper, an experimental investigation is carried out to minimize or eliminate the kerf taper in abrasive waterjet (AWJ) cutting of alumina ceramics by using a kerf-taper compensation technique.
Abstract: Kerf taper is a special and undesirable geometrical feature inherent to abrasive waterjet (AWJ) machining. In this study, an experimental investigation is carried out to minimise or eliminate the kerf taper in AWJ cutting of alumina ceramics by using a kerf-taper compensation technique. Among the cutting parameters studied, kerf-taper compensation angle is found to have the most significant effect on the kerf taper and the kerf taper angle varies almost linearly with this compensation angle. It shows that with this technique, it is possible to achieve a zero kerf taper angle without compromising the nozzle traverse speed or cutting rate. Depending on the other cutting parameters considered in this study, it is found that a kerf-taper compensation angle in the range of 4–5° can minimise the kerf taper angle to around zero. Using a dimensional analysis technique, a predictive model for the kerf taper angle is then developed and verified. An assessment of the model shows that the model can give adequate predictions with an average percentage deviation of 6.2% and the standard deviation of 13.4% from the corresponding experimental data.
TL;DR: In this paper, the authors investigated the size effects on the material flow curve of thin sheet metals under hydraulic bulge testing conditions, where the ratio of the sheet thickness to the material grain size (N=t0/d) was used as a parameter to characterize the interactive effects between the specimen and the grain sizes at the micro-scales.
Abstract: Reliable material models are necessary for accurate analysis of micro-forming and micro-manufacturing processes. The grain-to-feature size ratio (d/Dc) in micro-forming processes is predicted to have a critical impact on the material behavior in addition to the well-known effect of the grain size (d) itself as manifested by the Hall–Petch relation. In this study, we investigated the “size effects” on the material flow curve of thin sheet metals under hydraulic bulge testing conditions. The ratio of the sheet thickness to the material grain size (N=t0/d) was used as a parameter to characterize the interactive effects between the specimen and the grain sizes at the micro-scales, while the ratio of the bulge die diameter to the sheet thickness (M=Dc/t0) was used to represent the effect of the feature size in the bulge test. Thin sheets of stainless steel 304 (SS304) with an initial thickness (t0) of 51 μm and three different grain sizes (d) of 9.3, 10.6, and 17 μm were tested using five bulge diameters (Dc) of 2.5, 5, 10, 20, and 100 mm. A systematic approach for determining the flow curve of thin sheet metals in bulge testing was discussed and presented. The results of the bulge tests at different scales showed a decrease in the material flow curve with decreasing N value from 5.5 to 3.0, and with decreasing M value from 1961 to 191. However, as M value was decreased further from 191 to 49, an inversed relation between the flow curve and M value was observed; that is, the flow curve was found to increase with decreasing M value from 191 to 49, a new observed phenomenon that has never been reported in any open literature. New material models, both qualitatively and quantitatively, were developed to explain the size effects on the material flow curve by using the N and M as the characteristic parameters of relative size between the grain, the specimen (i.e., sheet thickness), and the part feature (i.e., bulge diameter). The explanation and prediction of the flow curve behavior based on these models were shown to be in good agreement with the bulge test results in this study and in the literature.
TL;DR: In this paper, a new tribometer has been designed in order to reach relevant values of pressures, temperatures and sliding velocities at the tool-chip-workpiece interface for dry cutting of an AISI316L austenitic stainless steel with TiN coated carbide tools.
Abstract: The characterization of frictional phenomena at the tool–chip-workpiece interface remains an issue. This paper aims to identify a friction model able to describe the friction coefficient at this interface during the dry cutting of an AISI316L austenitic stainless steel with TiN coated carbide tools. A new tribometer has been designed in order to reach relevant values of pressures, temperatures and sliding velocities. This set-up is based on a modified pin-on-ring system. Additionally, a numerical model simulating the frictional test has been associated in order to identify local phenomena around the spherical pin, from the standard macroscopic data provided by the experimental system. A range of cutting speeds and pressures have been investigated. It has been shown that the friction coefficient is mainly dependant on the sliding velocity, whereas the pressure has a secondary importance. Moreover, a new key parameter has been revealed, i.e. the average local sliding velocity at the contact. Finally, a new friction model has been identified based on this local sliding velocity.
TL;DR: In this article, the impact of diamond-like carbon (DLC) coatings on dry drilling of high-speed steel (HSS) alloys was investigated. And the results showed that using non-hydrogenated and hydrogenated DLC was preferred to hydrogenated DLC because it resulted in smaller built-up edge (BUE) formation and also less amount of drill flute aluminium adhesion.
Abstract: The dry drilling of aluminium alloys (without using cutting fluids) is an environmentally friendly machining process but also an exceedingly difficult task due to aluminium's tendency to adhere to the drills made of conventional materials such as the high-speed steel (HSS). Diamond-like carbon (DLC) coatings improve the dry drilling performance due to their adhesion mitigating properties. In this work, improvements that are possible when DLC coated tools are used under minimum quantity lubrication (MQL) condition in drilling of an Al–6%Si (319 Al) alloy were examined. Results were compared with drilling using conventional flooded coolant. The experimental approach consisted of the evaluation of the cutting performance of DLC coated HSS drills in a distilled water spray (30 ml/h) used as the MQL agent. Two types of DLCs (non-hydrogenated and hydrogenated) with different tribological responses in H2O testing environment were considered. The H2O-MQL cutting of 319 Al using either type of DLC coated drills reduced the drilling torque compared to dry drilling to a level similar to the performance under the flooded condition. An added advantage of the H2O-MQL over dry drilling was that the process was more stable; a smaller percentage of drilled holes exhibited “torque spikes”, i.e., an abrupt increase in torque, indicative of adhesion. H2O-MQL cutting using non-hydrogenated DLC was preferred to hydrogenated DLC because it resulted in smaller built-up edge (BUE) formation and also less amount of drill flute aluminium adhesion resulting in less torque and thrust force being required during drilling.