Fabrication of a resin-bonded ultra-fine diamond abrasive polishing tool by electrophoretic co-deposition for SiC processing

A resin-bonded ultra-fine diamond abrasive polishing tool is fabricated by electrophoretic co-deposition (EPcD), and the processing performance of the tool is evaluated in this study. The dispersion stability of suspensions is characterized by a laser particle size analyzer and settlement ratio. The cathodic EPcD of composite powder is realized by adding Al³⁺ into the suspension. The sintering temperature of composite coatings is determined by differential thermal analysis/thermogravimetry. The surface morphology of the composite coating is observed under a confocal microscope. Results show that uniform, dense, and smooth coatings with diamond and resin particles distributed homogeneously are obtained from the steel substrate. A large (Φ150 mm) polishing tool with a 20 μm-thick coating is successfully prepared using the above process. A smooth mirror surface of SiC wafer with a nanoscale roughness (4.3 nm) is achieved after processing with the ultra-fine diamond abrasive polishing tool.     

Electrogenerated chemical polishing of copper

Stress free polishing method is preferred for a damage free surface of copper with ultra-flatness and ultra-smoothness. Such a surface offers a perfect substrate for integrated circuits and micro-electromechanical systems fabrication. A new polishing method, called electrogenerated chemical polishing (EGCP), is proposed based on the principle of the scanning electrochemical microscope (SECM) and the diffusion controlled chemical reaction. Roughness of a Cu surface is reduced from 100.5 nm to 3.6 nm by the proposed method. To demonstrate the planarization capability of this new method, a patterned Cu surface with an array of micro-columns is planarized with a peak-valley (PV) value from 4.7 μm to 0.059 μm.     

Investigations on the effects of Nano-fluid in ECM of die steel

Formation of spikes in the electrochemically machined workpiece prevents to achieve the better performance of ElectroChemical Machining (ECM). Hence, this research work attempts to investigate the effects of Nano-fluid i.e. Nano Copper particles suspended NaCl electrolyte on the ECM of High carbon high chromium (HCHCr) die steel with a hardness of 63HRc. The influencing parameters are voltage, tool feed rate and electrolyte discharge rate with mixing levels. Seventy-two experiments have been conducted using Nano-fluid and plain NaCl electrolyte based on design of the experiment. The Nano Copper particles in the electrolyte break the gas layer at the inter electrode gap resulting in better MRR and surface roughness due to improved current density across the gap. A maximum MRR of 458.869 mm³/min and a minimum surface roughness of 1.39 μm Ra are obtained using Nano-fluid. The developed ANOVA models prove the significances of influencing factors in obtaining the better performance of ECM.     

Fundamental investigation on nano-precision surface finishing of electroless Ni–P-plated STAVAX steel using magnetic compound fluid slurry

Electroless nickel–phosphorus (Ni–P) plating used in a range of hot embossing metal molds/dies and injection metal molds/dies must be manufactured to nano-precision roughness for proper operation of the molds/dies. We therefore developed a novel polishing technique for mirror surface finishing of this kind of magnetic material using a magnetic compound fluid (MCF) slurry. The effects of the magnetic and gravitational forces acting on the carbonyl iron particles (CIPs) and abrasive particles (APs) within the MCF slurry were studied first, and the behaviors of the CIPs and APs in the presence of an external magnetic field were predicted. Then, experiments were performed to confirm the predictions by investigating the distribution of the CIPs and APs on the working surface of the MCF slurry. Finally, four MCF slurries containing CIPs and APs with different diameters were employed to finish the Ni–P-plated STAVAX steel specimen at different working gaps. The results revealed that for the magnetic workpiece, the resultant vertical force attracted CIPs towards the work surface, whereas APs were pushed away from the work surface. However, the CIPs and APs showed opposite behaviors with the non-magnetic workpiece. The percentage of APs distributed on the working surface increased and the distribution became more even as either the diameter of the CIPs or the working gap increased, whereas that of CIPs had the opposite tendency. The MCF slurry containing bigger CIPs and smaller APs should be employed and the working gap should be set at a smaller value in order to perform mirror surface finishing of a magnetic Ni–P-plated surface. Under the experimental conditions in this work, the Ni–P-plated surface quality improved significantly, and a mirror surface roughness (Ra) of 4 nm was successfully achieved without leaving scratches or particle adhesion when using an MCF slurry containing CIPs 7 μm in diameter and APs 1 μm in diameter, showing that MCF slurries containing commercial CIPs are applicable to the nano-precision finishing of magnetic materials.     

Effect on crystalline structure of AISI M2 steel using tungsten–thorium electrode through MRR,EWR, and surface finish

To investigate on the crystalline structure of AISI M2 steel by using tungsten–thorium electrode in electrical discharge machining (EDM) process was studied. Furthermore, the investigation were carried out for finding the value of material removal rate (MRR), electrode wear rate (EWR) and surface roughness (SR) of tool steel material depending upon three variable input process parameters. On the basis of weight loss, the value of MRR and EWR were calculated at optimized process parameter. Subsequently, surface topography of the processed material were examined through different characterization techniques like scanning electron microscopy (SEM), Optical surface profiler (OSP) and Atomic force microscopy (AFM), respectively. In XRD study, broadening of the peak was observed which confirmed the change in material properties due to the homogeneous dispersion of the particles inside the matrix. Lowest surface roughness and MRR of 0.001208 mg/min was obtained. Minimum surface roughness was obtained 1.12 μm and 2.18427 nm by OSP and AFM study, respectively. Also, minimum EWR was found as 0.013986 mg/min.     

Nanofinishing of freeform surfaces (knee joint implant) by rotational-magnetorheological abrasive flow finishing (R-MRAFF) process

Freeform complex surfaces have become an inevitable part of many devices to perform specific functions. Some of these components require nanolevel surface roughness value to meet the desired requirements in their applications. Finishing of freeform surfaces to nanometer surface roughness value is always difficult for any process. Rotational-magnetorheological abrasive flow finishing (R-MRAFF) process has been applied so far for finishing internal surfaces of relatively simple geometry. In this work, an attempt has been made to improve external topography of freeform surfaces using this process. Large hydrodynamic pressure coupled with magnetic fluid is the principal idea behind these experiments. A smooth mirror like finished surface is achieved with improved finishing rate (nanometer/min) by controlling two motions (axial and rotational) simultaneously on stainless steel workpiece similar to knee joint implant. Magnetorheological polishing fluid with different mesh sizes of abrasive particles and at different extrusion pressures is used to reduce final surface roughness value, to increase uniformity of surface finish on the freeform surface and to enhance finishing rate. Surface roughness ranging from 35 to 78 nm is achieved at various locations as compared to larger variation in Ra value obtained in the earlier research work.     

Investigating material removal rate and surface roughness using multi-objective optimization for focused ion beam (FIB) micro-milling of cemented carbide

Cemented carbide has been investigated as a useful material for the fabrication of micro devices. Focused ion beam (FIB) micro-milling has been found to be one of the most appropriate methods for the fabrication of micro devices. The experimental FIB micro-milling on cemented carbide have been conducted according to the L₁₆ orthogonal array of Taguchi technique. Beam current, extraction voltage, angle of beam incidence, dwell time and percentage overlap between beam diameters have been considered as process variables of FIB micro-milling in experimental design. Material removal rate (MRR) and surface roughness have been determined experimentally for FIB micro-milling of cemented carbide and beam current has been identified as the most significant parameter. The minimum surface roughness of 5.6 nm has been reported on cemented carbide, which is not a usual practice to achieve on such polycrystalline material, and hence it may be considered as a significant research contribution. Maximum MRR of 0.4836 μm³/s has been reported. Moreover, genetic algorithm toolbox of MATLAB has been utilized for multi-objective optimization between MRR and surface roughness. The corresponding optimum values of MRR and surface roughness for multi-objective optimization have been represented by pareto optimum solution generated by genetic algorithm. The research work presented in this paper determines the setting of process parameters of FIB micro-milling for achieving a specific combination of MRR and surface roughness on cemented carbide.     

线性液动压抛光加工的流体动压特性研究

基于流体动压润滑原理提出了线性液动压抛光加工方法。借助计算流体力学数值模拟，研究了抛光辊子结构和加工工艺参数对液动压力大小及分布均匀性的作用规律。结果表明：具有矩形微结构的抛光辊子可以在工件表面产生均匀的液动压力；更大直径的抛光辊子、更高的转速和更小的抛光间隙都可以获得更大的流体动压力，但同时也会使液动压力分布均匀性变差。搭建实验平台并进行抛光实验，线性液动压抛光加工后，K9玻璃表面粗糙度Ra值从45.41 nm降低到0.91 nm。     

介电泳效应磨粒流抛光中的电极形态

针对薄壁陶瓷工件内表面抛光，提出一种基于介电泳效应的磨粒流抛光方法。将非均匀电场布置于陶瓷工件外表面，极化磨粒，实现陶瓷工件内表面高效抛光。仿真分析发现:电极间隙比为2时，SiC磨粒具有最好的介电泳效应，参与抛光的磨粒最多。陶瓷工件初始内表面粗糙度值Ra为(208±5)nm时，抛光10 h后，无介电泳效应的磨粒流抛光工件内表面粗糙度值Ra为51 nm，有介电泳效应的磨粒流抛光工件内表面粗糙度值Ra为23 nm。     

Parameters optimization on surface roughness improvement of Zerodur optical glass using an innovative rotary abrasive fluid multi-jet polishing process

With the advance of contemporary technology, high precision surface finishing techniques for optical glasses are of great concern and developing to meet the requirements of the effective industrialized processes. Not only the used tools but also process parameters have great influence on the surface roughness improvements. In this paper, surface roughness improvement of Zerodur optical glass using an innovative rotary abrasive fluid multi-jet polishing process has been presented. For the same purpose, a tool for executing ultra precision polishing was designed and manufactured. Taguchi's experimental approach, an L₁₈ orthogonal array was employed to obtain the optimal process parameters. ANOVA analysis has also been carried out to determine the significant factors. It was observed that about a 98.33% improvement on surface roughness from (R_a) 0.360 μm to (R_a) 0.006 μm has been achieved. The experimental results show that a surface finished achieved can satisfy the requirements for optical-quality surface (R_a < 12 nm). In addition, the influence of significant factors on surface roughness improvement has been discussed in this study.     

基于响应曲面法的YG8硬质合金刀片化学机械抛光工艺参数优化

为了快速确定YG8前刀面抛光的最佳工艺参数,提高加工效率和精度,利用响应曲面法对YG8硬质合金刀片抛光工艺进行优化试验研究。通过单因素试验确定抛光转速、抛光压力、磨粒粒径和磨粒浓度的水平,并对4个工艺参数进行中心复合设计试验。建立了材料去除率RMR和表面粗糙度Ra的预测模型,基于响应曲面法优化工艺参数获得最佳工艺参数为抛光转速65.5 r/min、抛光压力156.7 kPa、磨粒粒径1.1 μm、磨粒浓度14%,此时得到了最小表面粗糙度预测值Ra=0.019 μm,材料去除率RMR=56.6 nm/min。试验结果表明,基于响应曲面法的材料去除率与表面粗糙度预测模型准确有效。     

Nano–level finishing of single crystal silicon blank using magnetorheological finishing process

Magnetorheological finishing (MRF) utilizes magnetorheological (MR) fluid, which consists of magnetic particles, nonmagnetic abrasives, and some additives in water or other carrier to polish the materials. An experimental study is conducted to predict the effect of process parameters (concentration of magnetic particles and abrasive particles, carrier wheel speed, and initial surface roughness) on surface finish and material removal rate in MRF of single crystal silicon blank. The final surface roughness value in terms of arithmetical mean roughness (Ra) obtained is as low as 8 nm from the initial value of 1300 nm. An optimization study is also carried out to find optimum values of process parameters from the selected range.     

Ultrasonic vibration assisted grinding of hard and brittle linear micro-structured surfaces

In this paper, a novel ultrasonic vibration assisted grinding (UVAG) technique was presented for machining hard and brittle linear micro-structured surfaces. The kinematics of the UVAG for micro-structures was first analyzed by considering both the vibration trace and the topological features on the machined surface. Then, the influences of the ultrasonic vibration parameters and the tilt angle on the ground quality of micro-structured surfaces were investigated. The experimental results indicate that the introduction of ultrasonic vibration is able to improve the surface quality (The roughness SR_a was reduced to 78 nm from 136 nm), especially in guaranteeing the edge sharpness of micro-structures. By increasing the tilt angle, the surface roughness can be further reduced to 56 nm for a 59% improvement in total. By using the preferred UVAG parameters realized by orthogonal experiments, a micro cylinder array with surface roughness of less than 50 nm and edge radius of less than 1 μm was fabricated. The primary and secondary sequence of the grinding parameters obtained by the orthogonal experiments are as follows: feed rate, tilt angle of workpiece, depth of grinding, vibration frequency and amplitude. The spindle speed in the range of 1000 rpm–3000 rpm does not significantly affect the machined micro-structured surface roughness. Finally, more micro-structures including a micro V-groove array and a micro pyramid array were machined on binderless WC as well as SiC ceramic by means of the UVAG technique. The edge radius on the V-grooves and pyramids are both less than 1 μm, indicating the feasibility of UVAG in machining hard and brittle micro-structured surfaces for an improved surface quality.     

Impact of die wear and punch surface textures on aluminium can wall

Aluminium can manufacturing uses a wide range of punch sleeve surface roughness and textures. The ironing die and the punch tooling both can vary in the roughness from 0.04 μm to 0.4 μm Ra during the can forming process. This, together with the roughness of the incoming can body sheet (from 0.3 μm to 0.6 μm Ra) creates a wide range of tool/metal interface coefficients of friction. Ironing dies become rougher and have to be replaced frequently once they lose their shape. Punches maintain a consistent roughness for periods of a week to a month and any surface wear is compensated for with die changes. The initial die and punch surface finish adopted by a manufacturing unit determines the long time plant productivity and punch life. A higher friction on the punch side, compared to the die side, is the preferred manufacturing operating condition. Departures from the preferred condition with ground, polished, cross-hatch and media textured punches are examined. Plants that prefer polished carbide punches over cross-hatched must have their lubrication and coolant parameters controlled within a very narrow operating window. A larger operating window and better performance is achieved with the cross-hatch and micro-textured punches having a Ra less than half that of the can body sheet. Above all, a random isotropic texture is identified as the ideal punch sleeve surface texture and the best performer for aluminium can manufacture.     

Surface roughness measurement based on fiber optic sensor

The multi-wavelength fiber sensor for measuring surface roughness and surface scattering characteristics were investigated. In this paper, specimens with different surface roughness were analyzed by using 650 nm, 1310 nm and 1550 nm laser as the light source, respectively. The working distance of 2 mm was chosen as the optimum measurement distance. The experimental results indicate that multi-wavelength fiber sensor can accurately measure surface roughness, and can effectively reduce the unsystematic error. The light scattering intensity ratio has a good linear relationship with the surface roughness. The minimum relative error of the surface roughness is 2.92%, the maximum relative error is 13.4%, and the average relative error is about 7.48%. The accuracy for measuring surface roughness by multi-wavelength fiber sensor is about twice as large as that by single-wavelength fiber sensor.     

Multi-objective optimization of circular magnetic abrasive polishing of SUS304 and Cu materials

In this paper, a Multi-objective particle swarm optimization algorithm (MOPSOA) is applied to optimize surface roughness of workpiece after circular magnetic abrasive polishing. The most important parameters of polishing model, namely current, gap between pole and workpiece, spindle speed and polishing time, were considered in this approach. The objective functions of the MOPSOA depend on the quality of surface roughness of polishing materials with both simultaneous surfaces (Ra1, Ra2), which are determined by means of experimental approach with the aid of circular magnetic field. Finally, the effectiveness of the approach is compared between the optimal results with the experimental data. The results show that the new proposed polishing optimization method is more feasible.

     

Polishing tool with phyllotactic distributed through-holes for photochemically combined mechanical polishing of N-type gallium nitride wafers

In this work, we further developed the photochemically combined mechanical polishing (PCMP) method for finishing N-type gallium nitride (GaN) wafers. A core improvement is to design a novel polishing tool with phyllotactic distributed through-holes, through which the wafer surface underneath through-holes can receive ultraviolet (UV)-light for the photochemical oxidation, while the rest parts undergo mechanical polishing. During PCMP, the co-rotation of the wafer and polishing tool allows the wafer surface to undergo the uniform and high-frequency conversion of oxidation and polishing. Based on the designed PCMP system and apparatus, the fundamental issues arising from such an alternate processing mode, which is different from the parallel mode of conventional chemical mechanical polishing (CMP), were investigated. Results show that the technical features of PCMP depend on the nature of the photochemical oxidation of wafers themselves if the mechanical polishing procedure can sufficiently remove oxides in time. The material removal rate (MRR) is inversely proportional to the dislocation density of wafers. Under acidic conditions, the oxidation proceeds by the GaN monocrystal step orientation, allowing PCMP to clear surface/subsurface damages (SSDs) and to prepare step-terrace structures on the wafer surface. When the polishing solution (pH = 1.5) includes 0.1 M K₂S₂O₈ oxidants and 10 wt% SiO₂ abrasives, the surface roughness Sa attains 0.21 nm in 10 × 10 μm², and the MRR reaches 275.3 nm/h. The present study shows that the phyllotactic distributed through-hole array structure designed for polishing tools offers rich possibilities for the innovation of polishing technologies combining with various oxidation approaches.     

Experimental investigation and mechanism of material removal in nano finishing of MMCs using abrasive flow finishing (AFF) process

Aluminum alloy and its composites appear to have a good future as a candidate material for engineering and structural components. Finishing of these materials is a big challenge as they are heterogeneous in nature having abrasive particles randomly distributed and oriented in the matrix material. Metal matrix composite (MMC-aluminum alloy and its reinforcement with SiC) workpieces were initially ground to a surface roughness value in the range of 0.6 ± 0.1 μm, and later were finished to the R_a value of 0.25 ± 0.05 μm by using Abrasive Flow Finishing (AFF) process. The effects of different process parameters, such as extrusion pressure, number of cycles and viscosity of the medium were studied on a change in average surface roughness (ΔR_a) and material removal. The relationship between extrusion pressure and ΔR_a shows an optimum at about 6 MPa. In the same way, the relationship between weight percentage of processing oil (plasticizer) and ΔR_a also shows an optimum at 10 wt%. Further, an increase in workpiece hardness requires more number of cycles to achieve the same level of improvement in ΔR_a. Material removal also increases with an increase in extrusion pressure and number of cycles while it decreases with an increase in processing oil content in the medium. It is also concluded that the mechanism of finishing and material removal in case of alloys is different from that in case of MMC.     

Lubricating property of MQL grinding of Al2O3/SiC mixed nanofluid with different particle sizes and microtopography analysis by cross-correlation

With the increased requirements for environmental protection, energy conservation, and low consumption, nanofluid minimal quantity lubrication (MQL) grinding, which is an environment-friendly machining method, has been paid increasing attention. Improving the lubricating property of nanofluids effectively is currently a main research trend. Meanwhile, optimizing mixed nanoparticle (NP) size ratio is an effective way for enhancing the lubricating property of MQL grinding. In the experiment, different sizes (30, 50, and 70 nm) of Al₂O₃ and SiC NPs were mixed, and nanofluids were prepared at 2% (volume fraction) mixed NPs and base oil. The prepared nanofluids were then used in MQL grinding on a hard Ni-based alloy (inconel 718). The experiment was then evaluated by specific grinding force, removal rate of workpiece, surface roughness, morphology of grinding debris, and contact angle. The effect of the sizes of the Al₂O₃/SiC mixed NPs on MQL grinding performance was discussed in accordance with the period and amplitude, as well as cross-correlation coefficient, of the workpiece surface cross-correlation function curve profile. Experimental results suggest that different Al₂O₃/SiC mixed NP sizes affect the nanofluid MQL grinding performance variably. The highest removal rate of the workpiece [189.05 mm³/(s N)] and the lowest RSm (0.0381 mm) were achieved when the Al₂O₃/SiC mixed NP size ratio was 70:30. The lowest Ra (0.298 μm) was obtained at 50:30. Meanwhile, the highest length ratio of the profile support (90%), the best morphology of abrasive dusts, and the largest wetting area of liquid drops were acquired at 30:70. Furthermore, a cross-correlation analysis of the workpiece surface profile curve under three size ratios (30:70, 50:30, and 70:30) was carried out. The cross-correlation function curve of the workpiece surface profile under 30:70 attained the shortest period, the largest amplitude, and the largest cross-correlation coefficient (0.67), thereby indicating good workpiece surface quality. Therefore, 30:70 was the best size ratio of the Al₂O₃/SiC mixed nanofluid.