Showing papers in "Precision Engineering-journal of The International Societies for Precision Engineering and Nanotechnology in 2012"

Improving anti-adhesion in aluminum alloy cutting by micro stripe texture

Abstract: Demand for aluminum alloy composites has rapidly increased, especially in the transport industry. This demand is due to such key advantages as a high strength to mass ratio and high corrosion resistance. However, aluminum alloy cutting has some serious problems. Aluminum chips readily and severely adhere to the surface of the cutting tool, often leading to tool failure, above all, in dry cutting. To address this problem, we have developed DLC-coated cutting tools with nano/micro-textured surfaces formed using femtosecond laser technology in our previous research. Face-milling experiments on aluminum alloys showed that the textured surface significantly improves the lubricity and the anti-adhesive properties at the tool-chip interface, but the problem associated with the tool-chip adhesion in dry cutting still remains. In this study, to overcome the problem, we designed new textures of cutting tool surface based on a mechanism for the formation of the chip adhesion and developed a cutting tool with micro stripe textured surface. As a result, it was revealed that the surface significantly improves cutting performances including the anti-adhesive properties both in wet and dry cutting without any coating technologies.

The effect of groove texture patterns on piston-ring pack friction

Abstract: A cylinder liner possesses fairly intricate surface requirements due to its complicated functions. It needs to provide adequate surface roughness to resist wear as well as to store and retain lubricants during high temperatures. The liner surface texture is anisotropic, produced by the honing process, with resultant deep visible scratches left on it [1] . The prominence of the honing grooves observed suggests that surface texture significantly affects ring-pack performance, although this effect is not clearly understood. In this paper, a numerical model was developed to investigate the effects of groove characteristics on the lubrication condition and friction at the interface between the piston ring and cylinder liner. This model aims to solve the average Reynolds equation, which depends on the real surface topographies of the cylinder liner, and describes the influence of surface irregularities on the lubricant flow under hydrodynamic lubrication conditions, considering lubricant film rupture and cavitations. Numerical results help to determine the optimum lateral groove characteristics to reduce friction and then noxious emissions.

Micro machining with continuous electrolytic free jet

Abstract: Electrochemical machining (ECM) is a potential procedure for high precision micro manufacturing. Especially the machining of metallic work pieces without any thermal or mechanical impact and the independence from the material's hardness are significant features. In this study, a special procedure for the fabrication of complex microgeometries and microstructured surfaces is investigated. This will be done by help of a continuous electrolytic free jet (Jet Electrochemical Machining—Jet-ECM). Characteristic for this technology is the restriction of the electric current to a limited area by the jet. Thereby, a high localization of the removal area is obtained which can easily be controlled by changing the electric current and the nozzle position. Applying continuous direct current, higher dissolution rates compared to pulsed EC processes are possible. The machining process is at first simulated by help of the finite elements method. Therefore, the commercial simulation software COMSOL Multiphysics was used applying time-dependent calculation rules. Experiments were performed to quantify the Jet-ECM process. By comparing the simulated and the experimental results, a good coincidence has been found. Furthermore, experiments were executed to show the capabilities of possible Jet-ECM applications regarding point erosions, cutting, drilling and milling.

A sub-nanometric three-axis surface encoder with short-period planar gratings for stage motion measurement

Abstract: A three-axis surface encoder was developed for stage motion measurement with sub-nanometric resolutions. The surface encoder was composed of a scale XY planar grating with X- and Y-directional periodic grating structures and an optical sensor head for reading the grating structures. A reference XY planar grating, which had the same periodic structures as those of the scale XY grating, was employed in the optical reading head. Four sets of interference signals, which were generated by superimposition of the X and Y-directional ±1 order diffracted beams from the two gratings, were employed for evaluation of the X-, Y- and Z-directional displacements of the optical sensor head with respect to the scale grating. The X- and Y-directional periodic structures of the gratings directly acted as the scale graduations for the X- and Y-directional displacement measurements, while the wavelength of the laser beam acted as the graduation period for the Z-directional displacement measurement. X- and Y-directional rectangular structures with a short period of 1 μm were designed and fabricated by the light lithography based on two beams interference for improvement of the resolutions of the surface encoder for X- and Y-directional position measurement. An optical sensor head was designed and constructed for reading the short period gratings. Experiments were carried out to confirm the basic performances of the three-axis surface encoder.

Detection of tool condition from the turned surface images using an accurate grey level co-occurrence technique

Abstract: With the advancement of digital image processing, tool condition monitoring using machine vision is gaining importance day by day. In this work, online acquisition of machined surface images has been done time to time and then those captured images were analysed using an improvised grey level co-occurrence matrix (GLCM) technique with appropriate pixel pair spacing ( pps ) or offset parameter. A novel technique has been used for choosing the appropriate pps for periodic texture images using power spectral density. Also the variation of texture descriptors, namely, contrast and homogeneity, obtained from GLCM of turned surface images have been studied with the variation of machining time along with surface roughness and tool wear at two different feed rates.

A study of micro-EDM and micro-ECM combined milling for 3D metallic micro-structures

Abstract: Micro-electrical discharge machining (EDM) and micro-electrochemical machining (ECM) combined milling for 3D micro-structure is investigated in this paper. These processes that consist of micro-EDM shaping and micro-ECM finishing are carried out in sequence on the same machine tool with the same electrode but different dielectric medium. The processing conditions are investigated experimentally by the cavity milling. The electrode which was used both in micro-EDM and micro-ECM processes is online fabricated by using an anti-copying block. The EDMed surface roughness of 0.707 μm Ra is lowered to 0.143 μm Ra by applying micro-ECM finishing. Meanwhile, the size and shape of the workpiece by combined milling is controlled precisely, which is much better than that machined merely by micro-ECM. As the large machining parameter values, the machining efficiency is also improved. In order to verify the combined machining performance, some 3D micro-structures were fabricated. The results show that the machining precision and shape accuracy is much better than that machined merely by micro-ECM milling, which can be exactly controlled. Since the EDMed recast layer and surface defects are removed completely, the surface quality and mechanical property of the workpiece is improved, which is better than that machined merely by micro-EDM. It proves that this combined milling method is possible and useful in the field of 3D metallic micro-structure milling.

Design and evaluation of a mechanical nanomanufacturing system for nanomilling

Abstract: This paper presents design and evaluation of a mechanical nanomanufacturing system for performing the nanomilling process. The nanomilling process uses a nanotool (an atomic force microscope probe tip) that is rotated at high speeds to fabricate three-dimensional (3D) nano-scale features on a sample surface. After explaining the kinematics of the two nanomilling process configurations, the nanomilling system, including the 3D piezoelectric actuator that rotates the nanotool, the nanopositioning stage that provides the feeding and depth motions, and the software program that controls the nanomilling motions are described. A measurement system is then constructed to measure the dynamic nanomilling motions. A compensation algorithm is developed to enable obtaining desired nanotool motions in the presence of frequency and amplitude-dependent nonlinearities of the 3D piezoelectric actuator. The nanomilling system is then evaluated directly by measuring the nanotool motions, and indirectly by assessing the accuracy of the fabricated nanoscale features. It was shown that the nanomilling system facilitates fabrication of complex nano-scale features with high accuracy through the high-stiffness nanotool assembly and high-frequency (compensated) nanotool motions.

Compensation of machine tool thermal deformation in spindle axis direction based on decomposition method

Abstract: One of the fundamental areas in high precision cutting is represented by the machine's thermal state monitoring. Understanding of this state gives significant information about the overall machine condition such as proper performance of cooling system as well as software compensation of machine's thermal deformation during manufacturing. This paper presents a method focused on compensation of machine's thermal deformation in spindle axis direction based on decomposition analysis. The machine decomposition is performed with the help of specially developed measuring frame, which is able to measure deformation of machine column, headstock, spindle and tool simultaneously. Compensation is than calculated as a sum of multinomial regression equations using temperature measurement. New placements of temperature measurement like spindle cooling liquid or workspace are used to improve the accuracy of this calculation. Decomposition process allows describing each machine part's thermal dynamic more precisely than the usual deformation curve usually used one deformation curve for the complete machine. The residual thermal deformation of the machine is considerably reduced with this cheap and effective strategy. The advantage is also in the simplicity of presented method which is clear and can be used also on older machines with slower control systems without strong computing power.

Modeling of geometric errors of linear guideway and their influence on joint kinematic error in machine tools

Abstract: This paper presents the problems of the geometric accuracy of machine tools. The analytical and experimental examinations were carried out for a table in which guideway geometric errors may result in significant deformations. The main aim was to propose a method of analytical examination of the influence of geometric errors in linear guideway on joint kinematic errors. The proposed method served to isolate and simulate geometric errors, one of the causes of volumetric errors in machine tools. This approach helped to understand and interpret the results of experimental examinations of angular kinematic errors (pitch, yaw, roll) obtained for a real machine tool. The results helped to verify the hypothesis that the deformation of a table may be a significant source of errors in volumetric error models. One of the final conclusions indicated that off-line compensation of some characteristics of angular kinematic errors in machine tools may be unjustified.

Ductile mode material removal and high-pressure phase transformation in silicon during micro-laser assisted machining

Abstract: Micro-laser assisted machining is a novel micro/nano machining technique developed for ductile mode machining of ceramics and semiconductors. Ductile mode material removal is possible in a nominally brittle material due to the high-pressure phase transformation (HPPT) phenomenon during the machining process. This paper investigates the mechanism of machining by analyzing the HPPTs under different scratch conditions, with and without laser heating. Micro-Raman (μ-Raman) spectroscopy studies of the nano-scratched regions provided evidence for HPPT in single crystal Silicon (Si). Annealing of the high-pressure phases into a recrystallized diamond structure (Si-I) at higher laser powers and its effect on machining characteristics is also discussed. This has been the first time that HPPT is reported in the material removed region where the material's phase transformation and laser heating occur simultaneously and instantaneously (the annealing process occurs instantaneously and is not time dependent in this case).

In situ non-contact measurements of surface roughness

Abstract: Surface roughness measurements are often required to validate a machining process. However, when using a 3D surface roughness measuring instruments it is usually necessary to remove the part from the machine tool between two operations, potentially introducing systematic errors. Furthermore, surface roughness measuring instruments are not suited for measuring heavy and large parts such as stamping dies. This paper presents a method to measure the surface topography of a part in situ, i.e. directly on the machine tool without removing the part. After introducing the sensor technology and the data acquisition chain, the effects of geometric imperfections of the machine tool and compensation for thermal effects on the measurement results are discussed. An application of the method is then presented to assess a finishing process on a five-axis machining centre including milling and polishing operations.

Diamond Micro Chiseling of large-scale retroreflective arrays

Abstract: Triple mirror retroreflectors are essential components for safety applications, communications and measurement equipment. While downscaling of characteristic dimension is possible for triangular retroreflectors, this is a challenging task for full-cube retroreflectors, due to the absence of continuous tool paths. Thus, the Diamond Micro Chiseling (DMC) process has been developed which allows the machining of full-cube retroreflectors by overlapping a series of sharp-edged pyramidal microcavities. In the past, this has been successfully demonstrated on a small-scale up to 3 mm × 3 mm with a structure size of 150 μm. Industrial applications, however, require the structuring of areas which are significantly larger than 10 mm × 10 mm. This paper will introduce the technology for machining such pattern with the help of the DMC process. Particular attention will be given to the measurement procedures and required tolerances for performing an in situ tool change as well as the optimization strategies for reducing the required process time.

Spindle dynamics identification for Receptance Coupling Substructure Analysis

Abstract: In this paper, two techniques are described for experimentally identifying the spindle-machine receptances required for tool point frequency response prediction using Receptance Coupling Substructure Analysis (RCSA). In the RCSA approach, the tool–holder–spindle-machine assembly is separated into three components: the tool, holder, and spindle-machine. The spindle-machine receptances are measured and archived. These receptances are then analytically coupled to beam models that represent the tool–holder. The spindle-machine dynamics are determined using: (1) a synthesis approach where a direct frequency response measurement of a standard artifact inserted in the test spindle is combined with a cross frequency response measurement to calculate the required rotational receptances; and (2) a new Euler–Bernoulli beam approach where the direct frequency response measurement is fit using an assumed (fixed-free) form of each mode within the measurement bandwidth. Experimental results are included for two spindles and four tool–holder combinations. The veracity of the new Euler–Bernoulli beam approach, which requires only a single measurement, reduces noise, and improves tool point dynamics prediction accuracy, is demonstrated.

A Technique for measuring radial error motions of ultra-high-speed miniature spindles used for micromachining

Abstract: Ultra-high-speed (UHS) miniature spindles are widely used for mechanical micromachining processes, such as micromilling and microdrilling, as well as for precision machining processes. The accuracy of features created in those processes depends on the trajectory of the tool tip as the spindle rotates. The tool-tip trajectory can be obtained by measuring the speed-dependent radial motions (which are sometimes referred to as the dynamic runout ) at the tool tip. The main contributors to the tool-tip speed-dependent radial motions are the error motions of the spindle, the form accuracy of the cutting tool, the alignment of the tool with respect to the axis of rotation, and the vibrations resulting from the rotating eccentricity. This paper describes a methodology that uses two laser Doppler vibrometer (LDV) systems to measure the radial motions at two axial locations of a precision cylindrical artifact attached to the spindle, while the spindle is rotated at its operational speeds. Measured radial motions are then processed to obtain radial and tilt error motions of the UHS spindle in the rotating sensitive direction. An alignment procedure is developed to ensure the mutual perpendicularity of the two ( X and Y ) laser beams. The methodology is demonstrated on an UHS air-turbine driven spindle with aerostatic-bearings. Subsequently, an analysis is performed to determine the measurement uncertainty associated with the presented methodology. It is concluded that the presented methodology can be used to effectively measure radial and tilt error motions of UHS spindles. Furthermore, it is shown that the average radial motion, synchronous radial error motion value and the standard deviation of the asynchronous radial error motion vary significantly with the spindle speed due to dynamic effects.

Multi-scale Alignment and Positioning System – MAPS

Abstract: In this article we describe the design of a universal ultra-precision positioning platform to be used in the development of many different nano-manufacturing processes. The system incorporates the concept of employing different interchangeable manufacturing and characterization tools with one ultra-precision positioning system. A multi-linear-motor-driven XY planar stage floating on a thin film of air is used to traverse a substrate through a 10 mm × 10 mm travel range with an XY linear position resolution of less than 1 nm and an angular resolution about the Z axis of 0.05 μrad over a range of about a degree (determined by plane mirror interferometer optics). A piezoelectric transducer (PZT) driven tripod positioning system is used to align each manufacturing and characterization tool with the substrate through a travel range of 40 μm along the Z axis and 245 μrad of rotation about the X and Y axes. The mechanical design, an overview of the system error analysis, preliminary component performance results, and the results of the first micro-imprint fabricated with the machine are presented.

Dynamics modeling and quantitative analysis of multibody systems including revolute clearance joint

Abstract: The dynamics characteristics of multibody mechanical systems including revolute joints with clearance are investigated using a computational methodology and a quantitative analysis method is proposed in this work. The contact force model in revolute joint clearance is performed using a nonlinear continuous contact force model and the friction effect is considered using a modified Coulomb friction model. The planar four-bar mechanism is used as demonstrative application example to validate the quantitative analysis method. Numerical results for four-bar mechanism with revolute clearance joint are presented and discussed. Further, two kinds of dimensionless indicator are defined for quantitative analysis of mechanical system with joint clearance. And the clearance size, friction effects and crank driving speed are analyzed separately.

Identification of transfer function by inverse analysis of self-excited chatter vibration in milling operations

Abstract: Analysis of the stability limits in self-excited chatter vibration requires the transfer function of the mechanical structure, and thus the accuracy of the analytical prediction strongly depends upon the accuracy of the transfer function, which is generally measured by the impulse response method. However, it is often difficult to measure the transfer function accurately, especially in a case where a small-diameter tool or a workpiece is flexible, or when the transfer function changes as a result of spindle rotation. This paper presents a novel method of identifying the transfer function by utilizing inverse analysis of the self-excited chatter vibration measured during an end milling experiment. In the proposed method, the transfer function can be identified to minimize errors between chatter analysis and experimental results. A basic end milling test verified that the transfer function identified by the developed method is similar to that measured by the impulse response method, and that it yields a more accurate prediction of the stability limits. Further applications using a small-diameter end mill were conducted, and the feasibility of identifying the transfer function by using the proposed method was investigated.

Algorithms for Morphological Profile Filters and their Comparison

Abstract: Morphological filters, regarded as the complement of mean-line based filters, are useful in the analysis of surface texture and the prediction of functional performance. The paper first recalls two existing algorithms, the naive algorithm and the motif combination algorithm, originally developed for the traditional envelope filter. With minor extension, they could be used to compute morphological filters. A recent novel approach based on the relationship between the alpha shape and morphological closing and opening operations is presented as well. Afterwards two novel algorithms are developed. By correlating the convex hull and morphological operations, the Graham scan algorithm, original developed for the convex hull is modified to compute the morphological envelopes. The alpha shape method depending on the Delaunay triangulation is costly and redundant for the computation for the alpha shape for a given radius. A recursive algorithm is proposed to solve this problem. A series of observations are presented for searching the contact points. Based on the proposed observations, the algorithm partitions the profile data into small segments and searches the contact points in a recursive manner. The paper proceeds to compare the five distinct algorithms in five aspects: algorithm verification, algorithm analysis, performance evaluation, end effects correction, and areal extension. By looking into these aspects, the merits and shortcomings of these algorithms are evaluated and compared.

Research on error averaging effect of hydrostatic guideways

Abstract: Hydrostatic guideways can obtain high motion accuracy due to their error averaging ability. In order to optimize the structural and accuracy design of hydrostatic guideways, the mechanism and affecting factors of the error averaging effect are investigated in detail in this paper. A new method is proposed to quantitatively analyze the motion errors of a typical closed hydrostatic guideway with four pads, and the restrictor is also taken into consideration. A hydrostatic guideway in an ultra-precision grinding machine LGF750 is analyzed with the method. The results show that the wavelength of each profile error component is a main affecting factor on the error averaging effect. Fluid films usually show obvious error averaging effect on each profile error component when the wavelength λ is shorter than twice of the pad length 2 l u . However, for each component with the wavelength λ over 2 l u , the error averaging effect becomes obvious only when the ratio of the pad length to the evaluation length of motion straightness l u / l e is greater than 0.5. Furthermore, the instability of the oil supply system is taken into consideration, and possible influences on the error averaging effect due to the supply pressure fluctuation are investigated preliminarily.

A study of the cutting performance of poly-crystalline oxygen free copper with single crystalline diamond micro-tools

Abstract: A study was carried out to investigate the crystallographic effects on the performance of cutting poly-crystalline oxygen free copper C10200 (OFC) with single crystalline diamond (SCD) micro-tools. At both large cutting depth and cross-feed rate, as the micro-tool traversed a grain with a crystallographic orientation less favorable for a stable machining process, the work material in front of the rake face was found to be severely deformed. This may lead to a reduced shear angle, thick chip, striation at the back of the chip, high cutting forces, degraded machined surface and the possibility of burr formation. The results showed minimal variations in the machined surface integrity and cutting forces compared to cut amorphous NiP plating with micro-tools. For a high cutting depth, burrs were also observed due to material deformation and pile-up occurring at the groove edges since the localized stress probably built up in front of the rake face. Cutting strategies were demonstrated to improve the performance of cutting OFC with micro-tools and to generate high aspect ratio micro-pillar arrays.

Prediction of machining accuracy degradation of machine tools

Abstract: Machine tool has to maintain its accuracy for quality control of products. After a long period of cutting operations, obvious wear will occur on the contact surfaces of the slide and the guideway. Such a wear will degrade the accuracy of machine tool due to the increase of Abbe errors. This research proposes a mathematical model so that, at given cutting forces and parameters of the slide-guideway, it is able to calculate the geometric errors of the slide due to contact deformation caused by the wear of the guideway and then predict the positioning errors after a long-term operation. Cutting forces applied to the worktable will cause reaction forces on contact surfaces between the slide and the guideway. Such reaction forces can be solved by static equilibrium equations of deformed free-body diagram of the slide. The induced abrasive wear can then be estimated. A simulation study on a heavy duty machine tool with slide-guideway will show the magnitude of wear on the sliding surface and the consequently caused geometric errors of the moving axis. Experimental tests show that, if modifying the wear coefficient to a function of sliding distance, the analytical result is in good agreement with the experimental result.

Rapid optical surface figuring using reactive atom plasma

Abstract: In the context of large optics figure correction, the reactive atom plasma (RAP) process constitutes a fast and unique solution for ultra-precise surface figuring. The RAP process combines high material removal rates with the advantages of non-contact machining methods. The RAP technology is based on an inductively coupled plasma torch that produces a sub-aperture near-Gaussian etching footprint, with material removal repeatability at nanometre level. A large-scale RAP figuring facility, Helios 1200, has been developed in the Precision Engineering Centre at Cranfield University to optimize and apply the RAP technology on metre-sized optical surfaces. In this paper, the first examples of figure correction carried out with Helios 1200 are reported. These experimental results were achieved over 100 and 140 mm diameter areas by means of in-house developed timedwell figuring techniques and a dedicated tool motion path. In particular, classical de-convolution techniques were adapted to the non-linear nature of the etching rate in order to derive velocity maps, while the tool-path algorithm was designed to induce a homogeneous temperature distribution on the process surface. Still, surface temperature raises are known to increase the rate of material chemical etching. Therefore, as a form of heat effects compensation, the adapted tool-path algorithm was combined with an iterative figuring procedure in order to assure faster process convergence. This promptly enabled the realization of figure error corrections down to λ/40 rms. High overall rates of convergence between 78 and 89% were attained within a maximum of three iterations. The mean processing times per iterative step were 6.6 minutes over the 140 mm diameter areas, thus confirming the potentiality of RAP as large surface figuring technique. Applied to metre-class optics, the method should then deliver comparable levels of form accuracy within less than ten hours processing time. The scope of the work presented included both investigation and verification of the effects of tool-path parameters, as well as of the modified de-convolution method. The validated figuring procedure can be progressively scaled up to medium and large optical surfaces. The surface texture after plasma machining was characterized. Some deterioration of surface roughness was observed.

Internal finishing of capillary tubes by magnetic abrasive finishing using a multiple pole-tip system

Abstract: Due to difficulties in controlling magnetic abrasive in the finishing area during internal magnetic abrasive finishing (MAF) of capillary tubes, the finished length is limited in practice to just a few times the pole-tip width The accumulation of multiple short finishing passes is necessary for long-tube finishing, which results in excessive finishing times The use of a multiple pole-tip system with a tool, a solid rod consisting of alternating magnetic and nonmagnetic regions, was proposed to overcome this issue The tool enables multiple finishing regions to be engaged simultaneously This paper clarifies the finishing characteristics and mechanism and shows the effects of the tool's magnetic properties (including the intervals between magnetic and non-magnetic regions) on the tool and abrasive motion and the interior finishing characteristics of capillary tubes This paper also proposes a simple method to determine the pole-tip feed length, which allows the MAF process to achieve a uniformly finished surface in half the time of the existing single pole-tip system

Nonrigid geometric metrology using generalized numerical inspection fixtures

Abstract: Freeform surfaces have become an integral part of the automobile and aerospace industries. The parts with a very thin wall in proportion to their size are referred to as nonrigid (or flexible) parts. Generally, for the geometric inspection of such flexible parts, special inspection fixtures , in combination with coordinate measuring systems (CMM), are used because these parts may have different shapes in a free state from the design model due to dimensional and geometric variations, gravity loads and residual strains. A general procedure to eliminate the use of inspection fixtures will be developed. Presented methodology is based on the fact that the interpoint geodesic distance between any two points of a shape remains unchangeable during isometric deformation. This study elaborates on the theory and general methods for the metrology of nonrigid parts. We will merge existing technologies in metric and computational geometry, statistics, and finite element method to develop a general approach to the geometrical inspection of nonrigid parts.

Performance of inherently compensated flat pad aerostatic bearings subject to dynamic perturbation forces

Abstract: The importance of air bearing design is growing in engineering. As the trend to precision and ultra precision manufacture gains pace and the drive to higher quality and more reliable products continues, the advantages which can be gained from applying aerostatic bearings to machine tools, instrumentation and test rigs is becoming more apparent. The inlet restrictor design is significant for air bearings because it affects the static and dynamic performance of the air bearing. For instance pocketed orifice bearings give higher load capacity as compared to inherently compensated orifice type bearings, however inherently compensated orifices, also known as laminar flow restrictors are known to give highly stable air bearing systems (less prone to pneumatic hammer) as compared to pocketed orifice air bearing systems. However, they are not commonly used because of the difficulties encountered in manufacturing and assembly of the orifice designs. This paper aims to analyse the static and dynamic characteristics of inherently compensated orifice based flat pad air bearing system. Based on Reynolds equation and mass conservation equation for incompressible flow, the steady state characteristics are studied while the dynamic state characteristics are performed in a similar manner however, using the above equations for compressible flow. Steady state experiments were also performed for a single orifice air bearing and the results are compared to that obtained from theoretical studies. A technique to ease the assembly of orifices with the air bearing plate has also been discussed so as to make the manufacturing of the inherently compensated bearings more commercially viable. (c) 2012 Elsevier Inc. All rights reserved.

Effect of side edge angle and effective rake angle on top burrs in micro-milling

Abstract: Experimental investigations on the effect of side wall edge strengthening, to reduce top burr formation, in micro-milling slots in Al-6061 alloy using a carbide tool are reported here. The side edge is strengthened by increasing the edge angle to a value higher than the usual 90°. Side edge angle is varied in two ways: one, by changing the work geometry and two, by introducing a taper into the milling tool. The burrs formed are examined qualitatively in a scanning electron microscope and quantitatively using a surface profiler. The analysis of the results shows that top burrs are reduced both by strengthening the side edge and also by the effect of the taper angle in the micro-milling tool. The effect of the side edge angle in the tool can be attributed to the edge strengthening. On the other hand, an analysis of the tapered tool geometry indicates that the velocity rake, normal rake and effective rake angles increase with the taper angle and can hence explain the observed burr reductions.

Planarization of C-face 4H-SiC substrate using Fe particles and hydrogen peroxide solution

Abstract: We have proposed a surface planarization method for silicon carbide (SiC) substrates using Fe abrasive particles and hydrogen peroxide (H2O2) solution. In this proposed method, the SiC surface is first oxidized by hydroxyl radicals generated by the decomposition of H2O2 on the surface of Fe abrasive particles, and then an oxide layer is formed on the SiC substrate. This layer is then mechanically and/or chemically removed by Fe abrasive particles and H2O2 solution, resulting in a smooth and damage-free SiC surface. In this study, the chemical mechanical planarization of a 4H-SiC ( 0 0 0 1 ¯ ) C-face substrate by our proposed method was examined. The morphology was observed by phase-shift interferometric microscopy, Nomarski differential interference contrast microscopy and atomic force microscopy. The subsurface damage on the processed surface was evaluated by high-resolution transmission electron microscopy. These observations showed that the surface roughness of the SiC substrate was markedly improved and that a damage-free and scratch-free SiC surface was obtained. These results provide useful information for preparing high-integrity SiC substrates with high efficiency.

Flatness error evaluation and verification based on new generation geometrical product specification (GPS)

Abstract: New generation geometrical product specification (GPS) links the whole course of a geometrical product from the research, development, design, manufacturing and verification to its release, utilization, and maintenance. Measurement process is one of the most important part of verification/inspection in the new generation GPS. With the knowledge-intensive and globalization trend of the economy, unifying the evaluation and verification of form errors will play a vital role in international trade and technical communication. Considering the plane feature is one of the most basic geometric primitives which contribute significantly to fundamental mechanical products such as guide way of machine tool to achieve intended functionalities, the mathematical model of flatness error minimum zone solution is formulated and an improved genetic algorithm (IGA) is proposed to implement flatness error minimum zone evaluation. Then, two evaluation methods of flatness error uncertainty are proposed, which are based on the Guide to the Expression of Uncertainty in Measurement (GUM) and a Monte Carlo Method (MCM). The calculating formula and the propagation coefficients of each element and correlation coefficients based on GUM and the procedures based on MCM are developed. Finally, two examples are listed to prove the effectiveness of the proposed method. An investigation into the source and effects of different uncertainty contributors for practical measurement on CMM is carried out and the uncertainty contributors significant are analyzed for flatness error verification. Compared with conventional methods, the proposed method not only has the advantages of simple algorithm, good flexibility, more efficiency and accuracy, but also guarantees the minimum zone solution specified in the ISO/1101 standard. Furthermore, it accords with the requirement of the new generation GPS standard which the measurement uncertainty characterizing the reliability of the results is given together. And it is also extended to other form errors evaluation and verification.

Application of Virtual Spheres Plate for AACMMs evaluation

Abstract: This work presents the development, calibration and application of an alternative gauge to check the performance of Articulated Arm Coordinate Measuring Machines (AACMMs). The gauge was developed having 16 groups of four conic holes placed on an aluminum plate to determine 16 virtual spheres named Virtual Spheres Plate. The gauge was placed at 3 positions on an AACMM work volume to take coordinates’ points at each hole with a spherical rigid probe, having next computed the diameters and the distances center-to-center of spheres. The results were compared with the ASME B89 performance test applied with a calibrated ball bar. The gauge may be applied to carry out interlaboratorial comparison of AACMMs.

Novel micro deep drilling using micro long flat drill with ultrasonic vibration

Abstract: This paper highlights the development of micro long flat drills with nominal diameter and flute length of 20 μm and 200 μm, respectively, by precision grinding. Furthermore, it also covers the evaluation of the developed micro long flat drill in micro deep drilling. Micro long flat drills were made of ultra-fine grained cemented carbide containing WC particles with an average particle diameter of 90 nm. First, the study focused on establishing the optimal web thickness of micro long flat drill showing the best performance in micro deep drilling. In drilling experiment, observation was conducted with the aim of finding the best conditions and method of micro deep drilling into both duralumin and stainless steel workpieces. This observation included the applications of ultrasonic vibration (USV) and step feeding method. The study proved that there was an optimum web thickness resulting in the best drilling performance. Furthermore, the application of USV during drilling could lead to a longer tool life significantly. However, there was no improvement of drilling performance in drilling with step feeding.