An investigation of acoustic emission to monitoring flat lapping with non-replenished slurry

Lapping is a precision manufacturing process. However, the material removal rate and surface roughness show significant variation between trials for repeated experiments and, thus, the repeatability of the results depends on the machine operator’s skill. Acoustic emission (AE) seems to be capable of monitoring the process. Therefore, an understanding of AE generation during lapping is important to predict the performance of the grains and hence the lapping results. Based on a theoretical analysis and experimental results collected during flat lapping, the AE signal was investigated for the situation when slurry is supplied without replenishment. The experiments were carried out with a wireless rotating AE sensor mounted in the middle of the lapping plate. Three parameters related to the AE curve are proposed to monitor the process. The influence of process parameters (lapping pressure, velocity, average grain size, concentration of grains in lapping compound and the number of conditioning rings) on the characteristics of the AE curve was investigated.     

中等口径光学非球面的高效研抛技术

介绍了一种弹性模抛光与小磨头修正抛光相结合的两步研抛法实现中等口径光学非球面表面的快速抛光。利用弹性模预抛光来保证小工具抛光模型的准确稳定,并采用补偿的方法减小弹性模抛光对面形精度的破坏作用。然后利用优化的小磨头修正残留的表面误差来提高抛光精度。应用上述方法加工非球面,在较短的抛光周期中,获得的面形P-V精度达0.35μm。     

Experimental investigation of process parameters for roll-type linear chemical mechanical polishing (Roll-CMP) system

The fabrication processes for electronic components are now demanding a higher degree of planarity for integration and multistacking, with chemical mechanical polishing (CMP) processes replacing conventional etching or mechanical polishing owing to their ability to attain global planarization. As CMP has been applied to more and more fields, new types of CMP machines have been developed. This study introduces a novel roll-type linear CMP (Roll-CMP) process that uses a line-contact material removal mechanism to for the polish flexible substrates, and examines the effect of the process parameters on the material removal rate (MRR) and its nonuniformity (NU). The parameters affecting the Roll-CMP process include down force, roll speed, table feed rate, slurry flow rate, slurry temperature, and the table oscillation length. Increasing the down force, roll speed, slurry flow rate, and slurry temperature resulted in a high average MRR (MRR_avg). Further, the MRR_avg was found to decrease with an increase in the oscillation length because of the effect of the polishing area. A large down force, high roll speed, high table feed rate, and high slurry flow rate were effective for reducing the NU. These results will be helpful for understanding the newly developed Roll-CMP process.     

Effect of the components of Magnetic Compound Fluid (MCF) slurry on polishing characteristics in aspheric-surface finishing with the doughnut-shaped MCF tool

For the aspheric optical surface finished with a doughnut-shaped MCF (magnetic compound fluid) polishing tool, the performance of the polishing tool depends mainly on the properties of the MCF slurry. Therefore, understanding the effect of each MCF slurry component on the polishing characteristics is crucial to developing novel polishing techniques. In this paper, the polishing principle was depicted and the corresponding polishing jig was constructed with a six-degree-of-freedom manipulator. The conical surfaces, which were considered as special aspheric surfaces, were experimentally polished under proper polishing conditions to examine the effects of the carbonyl iron particles (CIPs) concentration and the sizes of the abrasive particles (APs) on the polishing ability to remove material/tool marks and improve work surface qualities. Theoretical analyses were also performed to gain a more comprehensive understanding of the behaviors of CIPs and APs in the magnetic field. The results were shown as follows: (1) The CIPs concentration affected positively the magnetization of the MCF slurry, leading to better performance in the removal rate of material/tool marks when a higher CIPs concentration of was applied. The best surface quality was attained with a CIPs concentration of 45 wt%. (2) Larger APs were beneficial for obtaining higher removal rates of material/tool marks. The APs with 1 μm in diameter were preferred for achieving a better surface quality. (3) Ferric clusters were formed along the magnetic line of force and their orientations changed periodically to stir the APs with the magnet revolution. (4) The Aps, at a given working gap, can squeeze the work-surface. The squeezing action was much more intense when larger APs and the MCF slurry with a higher magnetization were employed. (5) The material removal model suggested that the material was removed due to the APs and the relative motion between the work-surface and APs.     

An experimental study on the correlation of polishing force and material removal for bonnet polishing of cobalt chrome alloy

Cobalt chrome alloys are the most extensively used biomaterials for manufacturing artificial prostheses, which need nanometer scale surface roughness and micrometer scale form tolerance to extend their lifespan in the tough environment of the human body. In order to machine bearing surfaces to sufficiently high accuracy, the way in which material is removed by the final finishing, such as bonnet polishing, must be completely understood. This study has experimentally investigated the influence of process parameters (precess angle, head speed, tool offset, and tool pressure) on the polishing forces as well as the material removal in bonnet polishing of a medical grade cobalt chrome alloy. Experimental results indicate that normal force increases with the increase in the precess angle, head speed and tool offset, but varies only slightly with the variation of the tool pressure. Tangential force increases with the increase in the precess angle and tool offset while it shows little variation with the change of the head speed and tool pressure. It is concluded that both normal force and tangential force can contribute to the material removal rate, but tangential force is found to be more correlated with the width of the influence function while normal force has a stronger correlation with the maximal height of the influence function.     

An investigation into superficial embedment in mirror-like machining using abrasive jet polishing

This study performs experimental investigation into the application of abrasive jet polishing (AJP) to the surface finishing of electrical-discharge-machined SKD61 mold steel workpieces. The results indicate that the AJP processing conditions which optimize the surface quality of the SKD61 workpiece when polishing using #2000SiC abrasives are as follows: an abrasive material to additive ratio of 1:2, an impact angle of 30°, a gas pressure of 4 kg/cm² (0.4 MPa), a nozzle-to-workpiece height of 10 mm, a platform rotational velocity of 200 rpm, and a platform travel speed of 150 mm/s. Under these processing conditions, a polishing time of 20 min is sufficient to reduce the surface roughness from an initial value of Ra?=?1.7 μm to a final value of Ra?=?0.27 μm, corresponding to an improvement of 84.12%. The experimental results demonstrate that the maximum attainable improvement in the surface quality of the polished workpiece is limited by a surface-hardening effect caused by the ball-impact phenomenon and the embedment of #2000SiC fragments in the workpiece surface.     

An experimental investigation of oblique cutting mechanics

In this study, an experimental investigation of oblique cutting process is presented for titanium alloy Ti-6Al-4V, AISI 4340, and Al 7075. Important process parameters such as shear angle, friction angle, shear stress, and chip flow angle are analyzed. Transformation of the data from the orthogonal cutting test results to oblique cutting process is applied, and the results are compared with actual oblique cutting tests. Effects of hone radius on cutting forces and flank contact length are also investigated. It is observed that the shear angle, friction angle, and shear stress in oblique cutting have the same trend with the ones obtained from the orthogonal cutting tests. The transformed oblique force coefficients from orthogonal tests have about 10% discrepancy in the feed and tangential directions. For the chip flow angle, the predictions based on kinematic and force balance results yield better results than Stabler's chip flow law. Finally, it is shown that the method of oblique transformation applied on the orthogonal cutting data yields more accurate results using the predicted chip flow angles compared to the ones obtained by the Stabler's rule.     

An experimental study on roughness noise of dry rough flat surfaces

This paper presents an experimental study of the friction noise, between two rough and dry flat surfaces. The domain of interest is the dry contact under light pressure where the roughness is the dominant cause of noise. The results show that, for sliding rough surfaces under light load, the fundamental mechanism of radiated noise is the presence of shocks occurring between antagonist asperities of sliding surfaces. The radiated roughness noise is controlled simultaneously by the detailed topography of the surfaces in contact, the sliding speed and the dynamics of the surfaces. In terms of topography and sliding speed, it was shown that the roughness noise is simultaneously an increasing linear function of the logarithm of the surface roughness and the sliding speed. In terms of dynamics, the roughness noise is generated for light dynamical coupling. Hence, the natural modes of samples are stiffer than the contact and therefore the resulting vibrations are not affected by the additional rigidity. The deformation of surfaces during contact is very light and its magnitude is negligible compared to the surface roughness.     

An experimental investigation on composite fretting mode

An apparatus for composite fretting tests on a steel ball opposite to the inclined steel flat with different inclined angles (60° and 45°) have been carried out. During the tests, the maximum imposed loads were varied from 200 N to 400 N and 800 N at a constant loading speed of 12 mm/min. Dynamic analysis in combination with microscopic examinations through optical microscopy, profilometery, and SEM have been performed. Composite fretting behaviour has been analyzed and compared with the conventional fretting.     

An experimental investigation into load relaxation in aluminium (HE30TB) and mild steel (EN1A)

Short-time room-temperature tensile load relaxation tests were conducted on aluminium alloy (HE30TB) and mild steel (EN1A) specimens using a closed-loop, electrohydraulic servo-controlled testing machine under strain control by means of an extensometer mounted directly on the parallel section of the tested specimens. The relaxation periods (usually 60 sec.) were interruptions at chosen points in constant strain rate tensile loadings. The loading strain rates in the different tests varied from 5 × 10⁻⁴ to 10⁻² sec. The transient relaxation behaviour was investigated for the purpose of testing the applicability of the most widely assumed viscoplastic constitutive models. This was achieved by comparing the plastic strain rate just after the beginning of load relaxation at constant total strain to the plastic strain rate during the tensile loading just before the start of the relaxation interval. All common viscoplastic theories predict that the plastic strain rate ratio should be unity. The experimental results for both materials indicate, however, that the plastic strain rate ratio varies from almost zero for relaxation periods early in the loading, to a maximum of around 0·2 for some relaxation periods beginning at relatively high loads and strains. This agrees with previously reported results on pure aluminium, which is not very rate sensitive, but the results for the more rate-sensitive mild steel may be surprising. Only if the actual relaxation rate drops by a factor of about 100 in 0.2 sec, could the findings of this experimental programme be reconciled with predictions of the usual viscoplastic theories. The experimental programme also included constant strain-rate tests at several rates and jump tests, in which the rate was switched back and forth between 10⁻⁴ and 10⁻²/sec.     

Theoretical and experimental investigation of surface generation in swing precess bonnet polishing of complex three-dimensional structured surfaces

Three-dimensional structured surfaces (3D-structured surfaces) possessing specially designed functional textures are widely used in the development of advanced products. This paper presents a novel swing precess bonnet polishing (SPBP) method for generating complex 3D-structured surfaces which is accomplished by the combination of specific polishing tool orientation and tool path. The SPBP method is a sub-aperture finishing process in which the polishing spindle is swung around the normal direction of the target surface within the scope of swing angle while moving around the center of the bonnet. This is quite different from the ‘single precess’ and ‘continuous precessing’ polishing regime, in which the precess angle is constant. The technological merits of the SPBP were realized through a series of polishing experiments. The results show that the generation of complex 3D-structured surfaces is affected by many factors which include point spacing, track spacing, swing speed, swing angle, head speed, tool pressure, tool radius, feed rate, polishing depth, polishing cloth, polishing strategies, polishing slurry, etc. To better understand and determine the surface generation of complex 3D-structured surfaces by the SPBP method, a multi-scale material removal model and hence a surface generation model have been built for characterizing the tool influence function and predicting the 3D-structured surface generation in SPBP based on the study of contact mechanics, kinematics theory, abrasive wear mechanism, and the convolution of the tool influence function and dwell time map along the swing precess polishing tool path. The predicted results agree reasonably well with the experimental results.     

An experimental investigation on micro machining of fine-grained graphite

Industrial applications of the micro milling process require sufficient experimental data from various micro tools. Research has been carried out on micro milling of various engineering materials in the past two decades. However, there is no report in the literature on micro milling of graphite. This paper presents an experimental investigation on micro machinability of micro milling of moulded fine-grained graphite. Full immersion slot milling was conducted using diamond-coated, TiAlN-coated and uncoated tungsten carbide micro end mills with a uniform tool diameter of 0.5 mm. The experiments were carried out on a standard industrial precision machining centre with a high-speed micro machining spindle. Design of experiments (DoE) techniques were applied to design and analysis of the machining process. Surface roughness, surface topography and burrs formation under varying machining conditions were characterized using white light interferometry, SEM and a precision surface profiler. Influence of variation of cutting parameters including cutting speeds, feedrate and axial depth of cut on surface roughness and surface damage was analysed using ANOVA method. The experimental results show that feedrate has the most significant influence on surface roughness for all types of tools, and diamond tools are not sensitive to cutting speed and depth of cut. Surface damage and burrs analysis show that the primary material removal mode is still brittle fracture or partial ductile in the experimental cutting conditions. 3D intricate micro EDM electrodes were fabricated with good dimensional accuracy and surface finishes using optimized machining conditions to demonstrate that micro milling is an ideal process for graphite machining.     

An experimental investigation of incompressible flow in conical diffusers

Experiments have been performed in clear-plastic diffusers, using water flow discharging into a plenum tank, to obtain performance and flow-régime information for a wide range of conical diffuser geometries.A line of first appreciable stall has been located with sufficient precision that it is useful in conical diffuser design. Performance data obtained allow solution of the four common optimum problems encountered in diffuser design.At present these results can be extrapolated only with caution to diffuser geometries other than those tested.     

An experimental investigation on the effect of subsonic inlet mach number on the performance of conical diffusers

Experiments have been performed to determine the effect of subsonic inlet Mach number on diffuser performance and flow régimes for a wide range of conical diffuser geometries.

For incompressible flow the line of first appreciable stall, line a-a, is essentially that found by McDonald and Fox. As the Mach number is increased, the flow tends more toward separation in all cases.

Diffuser performance maps are presented for three different inlet Mach numbers (M₁ = 0·25, 0·55, 0·70). There is no significant variation in the location of the line of maximum performance at constant length to inlet radius ratio, line -, with inlet Mach number.     

Elastohydrodynamic films in mixed lubrication: An experimental investigation

Experimental investigations were carried out with a Roxana rolling four-ball tester in the mixed lubrication regime. The electrical resistance technique was used in conjunction with ball profiles taken with a stylus apparatus to gain information about the formation of elastohydrodynamic films between rough surfaces and their evolution during running-in. The results show that rough surfaces in general make thinner films than smooth ones, but if $\text{h}{}_0\text{σ}{}_{\mathrm{h}}\text{> 2}$ roughness has a negligible effect.     

磁力研磨法去毛刺的实验研究

研制了去毛刺实验装置,用有限元法分析了加工间隙磁场分布,实验结果表明利用磁力研磨法能够去除棱边毛刺,并保持适宜的棱边圆角半径。