Showing papers in "Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology in 2016"

Surface texture metrology for metal additive manufacturing: a review

Abstract: A comprehensive analysis of literature pertaining to surface texture metrology for metal additive manufacturing has been performed. This review paper structures the results of this analysis into sections that address specific areas of interest: industrial domain; additive manufacturing processes and materials; types of surface investigated; surface measurement technology and surface texture characterisation. Each section reports on how frequently specific techniques, processes or materials have been utilised and discusses how and why they are employed. Based on these results, possible optimisation of methods and reporting is suggested and the areas that may have significant potential for future research are highlighted.

Laser trackers for large-scale dimensional metrology: A review

Abstract: Thirty years since their invention, laser trackers are now recognized as the measurement tool of choice in the manufacture and assembly of large components. The general design of laser trackers, i.e., a ranging unit on a two-axis gimbal, has not changed significantly over the years. However, innovations in ranging technology, for example, the emergence of increasingly accurate absolute distance meters (ADMs), are providing users with an alternative to interferometers (IFMs). Hand-held accessories such as touch probes and line scanners are expanding the scope and applicability of laser trackers. In this paper, we survey the literature in all areas of laser trackers as applied to large-scale dimensional metrology (LSDM), with emphasis on error modeling, measurement uncertainty, performance evaluation and standardization.

Wire sawing technology: A state-of-the-art review

Abstract: Wire sawing technology has been widely adopted for slicing of brittle-and-hard materials including crystalline silicon, SiC and sapphire. This paper presents a literature review on the research efforts on wire sawing related topics. First, the system and process level investigations of wire sawing technology, including both multi-wire slurry sawing and diamond wire sawing, are summarized. Ingot materials used in wire sawing technology, as well as their properties and behavior during sawing operation are discussed. As modeling and analysis of single grit indentation and scribing of brittle materials provide fundamental insight on material removal and these can be leveraged for wire sawing analysis at system level, a review of those models and modified models proposed particularly for wire sawing process are also presented. After the survey of current state-of-the-art, this contribution proposes important research aspects to be further worked on to gain more complete scientific understanding of wire sawing technology.

Dissimilar metal deposition with a stainless steel and nickel-based alloy using wire and arc-based additive manufacturing

Abstract: The wire and arc-based additive manufacturing process applies arc welding technology; the wire material is melted by the arc discharge, and is then accumulated successively in this process. The wire and arc-based additive manufacturing process directly and locally adds material to the molten pool. By changing the material locally during the process, more than one kind of material can be used simultaneously in a single manufactured component. In this study, two kinds of dissimilar metal deposition were conducted. A combination used was a stainless steel and Ni-based alloy. Mechanical properties near the interface such as hardness and bond strength were investigated. As a result, it was found that the mechanical properties of the manufactured alloy were comparable to those of a bulk material. In addition, an additive manufacturing system and a torch path planning method for using more than two kinds of material were proposed. By using this method, highly functional shapes whose surfaces and inner structures are made of different material could be made.

A review on material removal mechanism in electrochemical discharge machining (ECDM) and possibilities to enhance the material removal rate

Abstract: The concept of electrochemical discharge machining (ECDM), also known as electrochemical spark machining (ECSM), was presented for the first time in 1968. Since then, this technology remains as research topic and was never explained seriously for industrial applications. The ECDM is a non-traditional machining technology used for machining of electrically non-conducting materials like glass, ceramics, quartz, etc. The literature reveals that the concept of mechanism of material removal in this machining process is not yet understood well. However, phenomena involved in the material removal needs to be investigated well in order to improve the process. In this paper, the concept of mechanism of material removal in ECDM is reviewed till date; scopes for further research have been identified. Possible future efforts to enhance the material removal rate in ECDM are also discussed.

State of the art in powder mixed dielectric for EDM applications

Abstract: Electrical discharge machining (EDM) is a non-conventional machining technique for removing material based on the thermal impact of a series of repetitive sparks occurring between the tool and workpiece in the presence of dielectric fluid. Since the machining characteristics are highly dependent on the dielectric’s performance, significant attention has been directed to modifying the hydrocarbon oil properties or introducing alternative dielectrics to achieve higher productivity. This article provides a review of dielectric modifications through adding powder to dielectric. Utilizing powder mixed dielectric in the process is called powder mixed EDM (PMEDM). In order to select an appropriate host dielectric for enhancing machining characteristics by adding powder, a brief background is initially provided on the performance of pure dielectrics and their selection criteria for PMEDM application follow by powder mixed dielectric thoroughly review. Research shows that PMEDM facilitates producing parts with predominantly high surface quality. Additionally, some studies indicate that appropriate powder selection increases machining efficiency in terms of material removal rate. Therefore, the role of powder addition in the discharge characteristics and its influence on machining output parameters are explained in detail. Furthermore, by considering the influence of the main thermo-physical properties and concentration of powder particles, the performance of various powder materials is discussed extensively. Since suitable powder selection depends on many factors, such as variations in EDM, machining scale and electrical and non-electrical parameter settings, a thorough comparative review of powder materials is presented to facilitate a deeper insight into powder selection parameters for future studies. Finally, PMEDM research trends, findings, gaps and industrialization difficulties are discussed extensively.

A piezoelectric motor for precision positioning applications

Abstract: This study presents a novel precise piezoelectric motor capable of operating in either an AC drive mode or DC drive mode. In the AC drive mode, the motor acts as an ultrasonic motor which is driven by two orthogonal mechanical vibration modes to generate elliptical motion at the stator to push the slider into motion. In the DC drive mode, stick-slip friction between the stator and slider is used to drive the motor step-by-step. The experimental results show that the AC drive mode can drive the motor at a high moving speed, while the DC drive mode can simply drive the motor with a nanoscale resolution. In our experiments, a prototype motor is fabricated and its actions are measured. The results demonstrate that in the AC drive mode, the piezoelectric motor can achieve a 106 mm/s speed without a mechanical load and a 34 mm/s speed with 340 g of mechanical load when applying two sine waves with a drive of 11.3 V at 38.5 kHz. Meanwhile, in a DC driving mode, the motor is capable of performing precision positioning with a displacement resolution of 6 nm when driving at 100 Hz.

On-machine tool prediction of flank wear from machined surface images using texture analyses and support vector regression

Abstract: In this paper, a method for on-machine tool condition monitoring by processing the turned surface images has been proposed. Progressive monitoring of cutting tool condition is inevitable to maintain product quality. Thus, image texture analyses using gray level co-occurrence matrix, Voronoi tessellation and discrete wavelet transform based methods have been applied on turned surface images for extracting eight useful features to describe progressive tool flank wear. Prediction of cutting tool flank wear has also been performed using these eight features as predictors by utilizing linear support vector machine based regression technique with a maximum 4.9% prediction error.

Hysteresis modeling and displacement control of piezoelectric actuators with the frequency-dependent behavior using a generalized Bouc–Wen model

Abstract: Piezoelectric actuators (PAs) are widely used in precision positioning control and active vibration control. However, positioning accuracy can be compromised by the hysteresis of PAs. We can put forward a model to accurately describe the hysteresis and then compensate the hysteretic effect to solve the above problem based on the proposed model. In order to model the hysteresis of a PA which possesses the asymmetrical characteristics and the frequency-dependent behavior, a generalized Bouc–Wen model is developed for the PA. A model-based control using the proposed generalized Bouc–Wen model is applied to force the output displacement of the PA to track the desired displacement accurately thereafter. Experiments are conducted to validate this new approach. The results highlight significantly improved accuracy in the displacement control of the PA.

Cutting performance of nano-crystalline diamond (NCD) coating in micro-milling of Ti6Al4V alloy

Abstract: Hard coatings are an important factor affecting the cutting performance of tools. In particular, they directly affect tool life, cutting forces, surface quality and burr formation in the micro-milling process. In this study, the performance of nano-crystalline diamond (NCD) coated tools was evaluated by comparing it with TiN-coated, AlCrN-coated and uncoated carbide tools in micro-milling of Ti 6 Al 4 V alloy. A series of micro-milling tests was carried out to determine the effects of coating type and machining conditions on tool wear, cutting force, surface roughness and burr size. Flat end-mill tools with two flutes and a diameter of 0.5 mm were used in the micro-milling process. The minimum chip thickness depending on both the cutting force and the surface roughness were determined. The results showed that the minimum chip thickness is about 0.3 times that of the cutter corner radius for Ti 6 Al 4 V alloy and changes very little with coating type. It was observed from wear tests that the dominant wear mechanism was abrasion. Maximum wear occurred on NCD-coated and uncoated tools. In addition, maximum burr size was obtained in the cutting process with the uncoated tool.

Theoretical study on brittle–ductile transition behavior in elliptical ultrasonic assisted grinding of hard brittle materials

Abstract: The elliptical ultrasonic assisted vibration can lead to a higher comprehensive performance with better machined quality and lower grinding force during brittle materials machining. The undeformed chip thickness in grinding can be defined as the distance between two consecutive grinding surfaces formed by the adjacent abrasive grain trajectories. The ductile–brittle transition point of chip formation in brittle materials machining is believed to be represented by the threshold value of undeformed chip thickness (critical undeformed chip thickness). In this paper, an energy based method is proposed to predict the critical undeformed chip thickness in elliptical ultrasonic assisted grinding (EUAG). The effects of vibration parameters on grinding force and specific grinding energy are analyzed in detail. Results show that the axial vibration amplitude leads to a slight reduction in grinding force, whereas the vertical vibration amplitude results in a significant reduction of grinding force. The increase of wheel speed and ultrasonic vibration frequency can reduce the grinding force as well. Nevertheless, the grinding force ratio remains relatively steady fluctuating from 1.37 to 1.56. Additionally, the critical undeformed chip thickness increases with the increasing grinding speed, axial vibration amplitude and ultrasonic vibration frequency, while firstly increases and then decreases with the increasing vertical vibration amplitude. Especially, a ductile-mode grinding in micron-level can be achieved when the axial vibration amplitude is above 3 μm and a totally brittle fracture occurs when the axial vibration does not exist. Thus, a reasonable selection of vibration parameters in EUAG process is required. The above theoretical evaluations coincide well with the variable experimental results.

Micro-drilling of Ti–6Al–4V alloy: The effects of cooling/lubricating

Abstract: This paper presents a series of experimental investigations of the effects of various machining conditions [dry, flooded, minimum quantity lubrication (MQL), and cryogenic] and cutting parameters (cutting speed and feed rate) on thrust force, torque, tool wear, burr formation, and surface roughness in micro-drilling of Ti–6Al–4V alloy. A set of uncoated carbide twist drills with a diameter of 700 μm were used for making holes in the workpiece material. Both machining conditions and cutting parameters were found to influence the thrust force and torque. The thrust force and torque are higher in cryogenic cooling. It was found that the MQL condition produced the highest engagement torque amplitude in comparison to the other coolant–lubrication conditions. The maximum average torque value was obtained in the dry drilling process. There was no substantial effect of various coolant–lubrication conditions on burr height. However, it was observed that the burr height was at a minimum level in cryogenic drilling. Increasing feed rate and decreasing spindle speed increased the entry and exit burr height. The minimum surface roughness values were obtained in the flood cooling condition. In the dry drilling process, increased cutting speed resulted in reduced hardness on the subsurface of the drilled hole. This indicates that the surface and subsurface of the drilled hole were subject to softening in the dry micro-drilling process. The softening at the subsurface of drilled holes under different cooling and lubrication conditions is much smaller compared to the dry micro-drilling process.

Precision surface characterization for finish cylindrical milling with dynamic tool displacements model

Abstract: In this work a new approach to surface roughness parameters estimation during finish cylindrical end milling is presented. The proposed model includes the influence of cutting parameters, the tool’s static run out and dynamic phenomena related to instantaneous tool deflections. The modeling procedure consists of two parts. In the first stage, tool working part instantaneous displacements are estimated using an analytical model which considers tool dynamic deflections and static errors of the machine – tool-holder – tool system. The obtained height of the tool’s displacement envelope is then applied in the second stage to the calculation of surface roughness parameters. These calculations assume that in the cylindrical milling process, two different mechanisms of surface profile formation exist. Which mechanism is present is dependent on the feed per tooth and the maximum height of the tool’s displacement envelope. The developed model is validated during cylindrical milling of hardened hot-work tool steel 55NiCrMoV6 using a stylus profiler and scanning laser vibrometer over a range of cutting parameters. The surface roughness values predicted by the developed model are in good agreement with measured values. It is found that the employment of a model which includes only the effect of static displacements gives an inferior estimation of surface roughness compared to the model incorporating dynamic tool deflections.

State of the art of Deep Rolling

Abstract: It is vital to control fatigue life in different industrial sectors, and to improve this, surface treatments are usually used. Some of the most important surface treatments are Shot Peening (SP), Laser Shock Peening (LSP) or Deep Rolling (DR), which are used to improve the surface properties and resistance to cyclic loading of the components. The idea of this article is to focus on Deep Rolling and revise the state of its development at the present time, with a particular emphasis on implementation and changes in materials. A comparison of Deep Rolling versus other surface has been made, and different processes that can improve the effects of Deep Rolling, such as heat treatments, are shown. It can be concluded that the pressure of the tool during the process is the most important control parameter for Deep Rolling and that the residual stresses and strain hardening have the greatest influence in terms of fatigue life. Moreover, selecting the correct values of the other control parameters for DR, depending on the material on which DR is to be done, allows increased compressive residual stresses, a hardened layer near the surface and lower surface roughness, all of which produce an improvement in fatigue life.

Surface roughness prediction by extreme learning machine constructed with abrasive water jet

Abstract: In this study, the novel method based on extreme learning machine (ELM) is adapted to estimate roughness of surface machined with abrasive water jet. Roughness of surface is one of the main attributes of quality of products derived from water jet processing, and directly depends on the cutting parameters, such as thickness of the workpiece, abrasive flow rate, cutting speed and others. In this study, in order to provide data on influence of parameters on surface roughness, extensive experiments were carried out for different cutting regimes. Measured data were used to model the process by using ELM model. Estimation and prediction results of ELM model were compared with genetic programming (GP) and artificial neural networks (ANNs) models. The experimental results show that an improvement in predictive accuracy and capability of generalization can be achieved by the ELM approach in comparison with GP and ANN. Moreover, achieved results indicate that developed ELM models can be used with confidence for further work on formulating novel model predictive strategy for roughness of the surface machined with abrasive water jet. In conclusion, it is conclusively found that application of ELM is particularly promising as an alternative method to estimate the roughness of the surface machined with abrasive water jet.

An experimental study on the effect of magnetic field orientations and electrolyte concentrations on ECDM milling performance of glass

Abstract: In this work, effects of magnetic field orientation, machining voltage and electrolyte concentration on electrochemical discharge machining (ECDM) performance have been studied. The microchannels have been machined on the glass substrate; microchannel's depth and surface quality have been taken as indexes of machining characteristic. Experimental results show that the Lorenz force of magnetic field affects a direction of bubble's motion, consequently, changes the electrochemical discharge behavior of electrolyte. The presence of magnetic field causes magnetohydrodynamic (MHD) convection which, by its turn, accelerates the repulsion of the bubbles from the cathodic surface. However, it should mention that the direction of bubble movement depends on the magnetic field orientation. If the magnetic field orientation induces upward Lorenz force (downward Lorenz force), the gas bubbles will repel from (will attract to) inter-electrode area. The obtained results demonstrate that when the magnetic field applies, the machined surface will be smoother for the lower concentration values of electrolyte and higher machining voltages. Enhancements of both the machining voltage and electrolyte concentration increase the machining depth. For the same values of applied voltages, application of magnetic field will also increase the machining depth in a certain machining process duration; this will be intensified for the lower values of electrolyte concentration. The results of this study explain how the combination of the magnetic field orientation and the values of machining voltage and electrolyte concentration should be defined in order to increase both the channel depth and surface quality.

Effects of molding conditions on injection molded direct joining using a metal with nano-structured surface

Abstract: Injection molded direct joining (IMDJ) is one of the metal-plastic direct joining processes and is based on a combination of a special surface treatment of a metal piece and an insert molding. This study employed a chemical processing as the special surface treatment to form nano-structures on the metal piece. We investigated relationship between joining strengths and molding conditions; we focused on pressure of a mold cavity and injection speed as molding conditions in this work. To evaluate the IMDJ samples processed under various molding conditions, we carried out tensile-shear tests. Then we compared the results of the tests to discuss how much each condition variation affected the joining strength. From the discussion, we found an interesting effect of the injection speed, which is unique to the IMDJ using a metal piece with nano-structures. The findings of this study will promote a better understanding of the IMDJ.

Machine vision micro-milling tool wear inspection by image reconstruction and light reflectance

Abstract: The paper presents a method for micro-milling tool wear inspection using machine vision. An original Wavelet-based Extended Depth of Field image reconstruction is proposed. The method enables geometrical measurements required to locate the cutting edges of the micro-tool. In the proposed method, variable light intensity is used during image acquisition to detect regions of different reflective properties. Geometrical information and reflective properties are then used to evaluate the tool wear. The proposed method is introduced to a prototype inspection machine. The results were compared to SEM images creating interesting conclusions.

A planar 3-DOF nanopositioning platform with large magnification

Abstract: Piezo-actuated flexure-based precision positioning platforms have been widely used in micro/nano manipulation. A conventional major challenge is the trade-off between high rigidity, large magnification, high-precision tracking, and high-accuracy positioning. A compact planar three-degrees-of-freedom (3-DOF) nanopositioning platform is described in which three two-level lever amplifiers are arranged symmetrically to achieve large magnification. The parallel-kinematic configuration with optimised sizes increases the rigidity. Displacement loss models (DLM) are proposed for the external preload port of the actuator, the input port of the platform and the flexible lever mechanism. The kinematic and dynamic modelling accuracies are improved by the compensation afforded by the three DLMs. Experimental results validate the proposed design and modelling methods. The proposed platform possesses high rigidity, large magnification, high-precision circle tracking and high-accuracy positioning.

Kinematic calibration of a 5-DoF parallel kinematic machine

Abstract: Kinematic calibration of a 5 degree-of-freedom parallel kinematic machine (T5 PKM) resorting to a step-by-step strategy is carried out, which conducts the identification modeling, measurement planning, parameter identification and modification of substructure I and then substructure II. On the basis of geometrical error model, a ridge estimation method based on L-curve selection is applied to the ill-conditioning inverse problem of the identification modeling of both substructures. Sensitivity analysis of substructure I and parameter analysis of substructure II are then employed to select the geometrical error parameters to be identified. Measurement planning is conducted by four principles to minimize the number of measuring configurations. Parameter identification and modification is implemented by SolidWorks simulation, which is able to check the correctness of identification modeling and measuring planning and to virtually manipulate the experimental procedure. Finally, kinematic calibration experiments are performed, which effectively validates that the proposed kinematic calibration is highly accurate and efficient.

Measurement accuracy in X-ray computed tomography metrology: Toward a systematic analysis of interference effects in tomographic imaging

Abstract: In this paper an investigation of interference effects leading to limitations of metrological performance of X-ray computed tomography (CT) used as a coordinate measuring technique is presented. Using reconstruction data, image quality metrics, and calculations of artifact formation, a deeper understanding and explanation of the physical and technical limitations of CT used in dimensional metrology is given. This is demonstrated in a case study using a simple hollow cylinder made of steel as a test object and calibration measurements from a tactile coordinate measuring machine (CMM). Two different threshold determination strategies for surface computation are applied. Within the study it is also shown that CT image properties, threshold determination strategies, and systematic and random measurement errors must have a definite correlation. As a conclusion it is recommended to focus more strongly on the correlation of local CT image quality and data evaluation operations in order to reduce systematic errors in surface computation and to increase repeatability of dimensional CT measurements.

Mechanistic force model coefficients: A comparison of linear regression and nonlinear optimization

Abstract: This paper describes a comparative study devised to examine the dependence of specific force coefficients, which are used in mechanistic cutting force models, on various milling process parameters such as feed per tooth, spindle speed, milling configuration, and radial immersion. Two methods are described for determining the specific force coefficients: (1) the average force, linear regression method; and (2) the instantaneous force, nonlinear optimization method. A series of test cuts were performed and the specific force coefficients calculated using the two methods were compared. Additionally, a technique for extending the bandwidth over which the cutting forces were measured using a commercially available cutting force dynamometer is presented. Finally, a series of milling stability experiments were conducted to validate the calculated specific force coefficients. It was found that milling process parameters such as feed per tooth, spindle speed, and radial immersion exhibit a nonlinear relationship with the specific force coefficients.

Influence of the cutting edge radius and the material grain size on the cutting force in micro cutting

Abstract: In micro cutting, both the cutting edge radius and the material grain size have a great influence on the cutting force. The study of the influence of the material grain size on the cutting force is unavoidably affected by the dual effect of the cutting edge radius. In this paper, a method for estimating the shearing force is proposed. In addition, micro turning experiments were performed to investigate the influence of the cutting edge radius and the material grain size on the cutting force. The results showed that a smaller material grain size leads to a larger cutting force and a higher specific cutting energy. Furthermore, the difference in cutting force observed for different material grain sizes increased with the cutting edge radius. By separating the shearing force, this dual effect was found to be caused by the ploughing force. The influence of the material grain size on the cutting force and the specific cutting energy is much lower than the influence of the cutting edge radius.

On the mechanism of edge chipping reduction in rotary ultrasonic drilling: A novel experimental method

Abstract: Edge chipping induced by the mechanical machining of holes in brittle materials restricts the applications of the brittle materials. Rotary ultrasonic drilling is a suitable approach for the machining of holes in brittle materials with a smaller size of edge chipping. A good understanding of the mechanism of edge chipping reduction when employing rotary ultrasonic drilling is helpful to the application and optimization of the drilling technique. In this study, a novel edge chipping mechanism for the machining of holes considering machining-induced cracks was proposed and verified by experiments on quartz glass. The size of the machining-induced crack was evaluated experimentally. Experimental results indicate that the initiation of edge chipping is determined by both the magnitude of the driving force and the size of the machining-induced crack. However, the size of edge chipping strongly depends on the undrilled thickness following a directly proportional relation. Moreover, the geometric similarity of edge chipping is evidence for the consistency of the crack propagation direction when edge chipping begins. Finally, experiments conducted under various machining conditions demonstrate that the reduction of the size of machining-induced cracks in rotary ultrasonic drilling is another important factor contributing to the reduction of the size of edge chipping in rotary ultrasonic drilling, comparing with conventional diamond drilling.

A long-stroke 3D contact scanning probe for micro/nano coordinate measuring machine

Abstract: This paper presents a long-stroke contact scanning probe with high precision and low stiffness for micro/nano coordinate measuring machines (micro/nano CMMs). The displacements of the probe tip in 3D are detected by two plane mirrors supported by an elastic mechanism, which is comprised of a tungsten stylus, a floating plate and two orthogonal Z-shaped leaf springs fixed to the outer case. A Michelson interferometer is used to detect the vertical displacement of the mirror mounted on the center of the floating plate. An autocollimator based two dimensional angle sensor is used to detect the tilt of the other plane mirror located at the end of the arm of the floating plate. The stiffness and the dynamic properties are investigated by simulation. The optimal structural parameters of the probe are obtained based on the force-motion model and the constrained conditions of stiffness, measurement range and horizontal size. The results of the performance tests show that the probe has a contact force gradient within 0.5 mN/μm, a measuring range of (±20 μm), (±20 μm), and 20 μm, respectively, in X, Y and Z directions, and a measurement standard deviation of 30 nm. The feasibility of the probe has preliminarily been verified by testing the curved surface of a convex lens.

Electrical discharge machining of the AISI D6 tool steel: Prediction and modeling of the material removal rate and tool wear ratio

Abstract: In this investigation, response surface method was used to predict and optimize the material removal rate and tool wear ratio during electrical discharge machining of AISI D6 tool steel. Pulse on time, pulse current, and voltage were considered as input process parameters. Furthermore, the analysis of variance was employed for checking the developed model results. The results revealed that higher values of pulse on time resulted in higher values of material removal rate and lower amounts of tool wear ratio. In addition, increasing the pulse current caused to higher amounts of both material removal rate and tool wear ratio. Moreover, the higher the input voltage, the lower the both material removal rate and tool wear ratio. The optimal condition to obtain a maximum of material removal rate and a minimum of tool wear rate was 40 μs, 14 A and 150 V, respectively for the pulse on time, pulse current and input voltage.

Experimental investigation, prediction and optimization of cylindricity and perpendicularity during drilling of WCB material using grey relational analysis

Abstract: Manufacturing is always the heart of majority of industries. Drilling is an extremely important and an essential machining process which requires a lot of attention as in most of the cases it is required for assembly purposes. Majority of the holes produced during drilling are made with the help of Vertical Machining Centre (VMC) meant for pin- hole assembly. Though the tolerance is within limit, assembly problems arise due to the improper geometry of these holes. Various geometrical tolerances like cylindricity, circularity, perpendicularity and position errors are responsible for such assembly problems. This investigation is focussed on cylindricity and perpendicularity in the drilling of Wrought Cast Steel Grade B (WCB) material using SOMX 050204 DT insert. In this work, effect of machining variables like cutting speed, feed rate and depth of cut (canned cycle) are investigated and optimized using grey relational analysis (GRA). Reliable experiments are conducted based on a 33 full factorial, replicated twice. Second order regression models are developed for predicting cylindricity and perpendicularity. The models’ adequacy has been checked by calculating correlation coefficient. It shows that the developed models are well fitted for the prediction of responses within the specific range of input variables.

Rotary spatial vibration-assisted diamond cutting of brittle materials

Abstract: In the present study, a novel process, namely rotary spatial vibration (RSV) assisted diamond cutting, is introduced to overcome cutting velocity induced cutting parameter inconsistencies as well as the cutting direction induced insufficient utilization of vibration assistance in vibration-assisted turning and milling of brittle materials. In RSV-assisted diamond cutting, a rotary motion component, generated by the rotation of the machine's spindle, is superimposed onto the three-degrees-of-freedom translational vibrations of the diamond tool. The resulting complex motions of the diamond tool assure the possibility of consistent cutting performance that is always guaranteed even when processing arbitrarily large areas. In practice, the feasibility and superiority of this technique for processing brittle materials is well demonstrated by fabricating a set of circular micro-grooves on monocrystalline silicon wafers with gradually varying depth-of-cut.

An accurate method for five-axis flute grinding in cylindrical end-mills using standard 1V1/1A1 grinding wheels

Abstract: Flute grinding is a critical process in end-mill manufacturing. The wheel geometry and position during the grinding process govern the flute profile and determine the flute parameters (i.e. rake angle, core radius, and flute width). Accuracy of these parameters should be ensured to obtain optimal cutting performance. For a given wheel geometry, the current technologies can only determine the wheel position for the desired rake angle and core radius without consideration of the flute width. This disadvantage seriously restricts the improvement of machining quality and the flexibility of flute grinding. To cope with this problem, this paper presents a novel method of five-axis flute grinding using standard 1V1/1A1 wheels to ensure the accuracy of the three flute parameters. Based on the theories of analytic geometry and envelope, equations for calculating the flute parameters are first derived. Afterwards, a system of nonlinear equations is created to calculate the wheel position for flute grinding. The validity of the proposed method is verified by 3D simulations and machining experiments. Lastly, the sensitivity of the valid flute width with respect to the wheel geometric parameters is further investigated in this work.

Surface contact stress-based nonlinear virtual material method for dynamic analysis of bolted joint of machine tool

Abstract: The components of machine tools are mainly fixed and connected by bolts. The performance of the assembly can be affected by the dynamic characteristics of the bolted joints. This paper presents a nonlinear virtual material method based on surface contact stress to describe the bolted joint for accurate dynamic performance analysis of the bolted assembly. Fractal geometry theory is used to describe the surface topography. The elastic modulus and shear modulus of one micro-contact are derived based on fractal contact theory. The equivalent elastic modulus, Poisson ratio, and density of the bolted joint can be obtained through the weighted mean method. In order to obtain the stress distribution, the contact surface is assumed flat in the macro-scale, and the uneven distribution of contact stress can be obtained by the finite element method (FEM). The contact surface can be divided into several sections, and the parameters of a virtual material layer can be determined based on the mean contact stress. Both theoretical and experimental results for a bolted joint are obtained for a box-shaped specimen under equal pre-tightening force and bending moment effect. The results show that the theoretical mode shapes are in good agreement with the experimental mode shapes. The relative errors between the theoretical and experimental natural frequencies are less than 4.41%, which indicates that the present nonlinear virtual material method is appropriate for the bolted joint in modeling CNC machine tools.