Lapping Process Research Articles

Ultra-fine grinding as a prerequisite for producing polishable free-form optics

In many conventional optical manufacturing processes, lapping is still a standard method to provide polishable surfaces. With the increasing use of CNC technology, efforts are being made to substitute the lapping process in the process chain. The paper presents studies that compare the lapping and fine grinding processes and provide an assessment of the subsequent polishing process. By using fine grinding with resin bond tools, polishing times can be significantly reduced and subsurface damage structures minimized. Ultra-fine grinding is also an important shaping process for the production of complex surface geometries, such as free-form optics.

Preface

The 2022 International Conference on Advanced Mechanical, Electronic and Electrical Engineering (ICAMEE 2022), an online conference, was successfully held on August 26-28, 2022 in Qingdao, China. ICAMEE 2022 provided experts, scholars, and engineering technicians in the fields of electrical engineering and mechatronics with shared scientific research results and cutting-edge technology, promoting cooperation in the industrialization of academic achievements.We were extremely honored to invite both Prof. Ziad Moumni from ENSTA Paris Tech, France and Prof. Shahid-Hussain from Jiangsu University, China to serve as our Conference General Chairs. There were 160 individuals and enterprises attending the conference. Divided into three parts, the conference agenda covered keynote speeches, oral presentations, and online Q&A discussion. Firstly, keynote speakers were each allocated 30-45 minutes to hold their speeches. Then in the oral presentations, the excellent papers we had selected were presented by their authors by turns.During the conference, four sophisticated professors were invited to address keynote speeches. Among them, Prof. Jiang Guo from Dalian University of Technology, China delivered a speech on the topic: Investigation on High Precision Double-Sided Lapping Process. The controlment of surface shape in double-sided lapping process was rarely investigated in previous researches. Therefore, this speech presented a double-sided lapping process with fixed abrasives, and analyzed the influence of residual stress on workpiece deformation. Additionally, Assoc. Prof. Anwar Ali from Zhejiang Sci-Tech University, China gave a report on the Attitude Control of a Small Spacecraft using Reconfigurable Embedded Magnetorquers. He showed that the nanosatellite market is rapidly growing for scientific and commercial applications, enabling many universities and small and medium-sized enterprises (SMEs) to develop their own satellites. To deal with the problem of small satellites’ space and weight constraints for housing a large number of required subsystems, attitude control system was proposed in this research and orientated the satellite in space to rotate solar panels towards Sun and antennas towards ground station. The wonderful and dramatic speeches of each keynote speaker had triggered heated discussion. Moreover, every participant praised this conference for disseminating useful and insightful knowledge.After months of well preparation and hard work, the proceedings of ICAMEE 2022 covering a bunch of papers are smoothly published. These papers feature but are not limited to the following areas: Mechatronics Control, 3D Printing Technologies, Electrical materials, Signal processing, etc. All the papers have been checked through rigorous review and processes to meet the requirements of publication.On behalf of the conference organizing committee, we would like to express our heartfelt appreciation to all the keynote speakers, peer reviewers, and all the participants. In particular, we would like to acknowledge the Journal of Physics: Conference Series, for the endeavor of all its colleagues in publishing this paper volume. We firmly believe that all the attendees have had fruitful discussions and gained valuable knowledge, and will enjoy the opportunity for future collaborations.Committee of ICAMEE 2022List of Committee member is available in this Pdf.

Lapping Quality Prediction of Ceramic Fiber Brush Based on Gaussian-Restricted Boltzmann Machine.

Although ceramic fiber brushes have been widely used for deburring and surface finishing, the associated relationship between process parameters and lapping quality is still unclear. In order to optimize the lapping process of ceramic fiber brushes, this paper proposes a multi-layer neural network based on the Gaussian-restricted Boltzmann machine (GRBM), and verified its prediction effectiveness. Compared with a traditional back-propagation neural network, its prediction error was reduced from 7.6% to 4.5%, and the determination coefficient was increased from 0.96 to 0.98, respectively. The comparison results showed that the proposed model can better grasp the relationship between process parameters and machining quality, which can be used as a decision-making foundation for lapping-process optimization.

Formation mechanism of concave and convex surface shapes in double-sided lapping

Double-sided lapping process is a key technology for obtaining high efficiency and flatness in fabricating plane-parallel workpiece surfaces, such as wafers, optical windows, seal rings, etc. However, the formation of the concave and convex surface shapes of workpieces was rarely investigated in the previous research, and the mechanism was unknown. This paper establishes a new kinematic model to clarify the formation mechanism of concave and convex surface shapes, in which the workpiece eccentricity and rotation in the planetary wheel are considered for the first time. The measurement and control method of workpiece rotational speed in the planetary wheel is proposed. The formation of the concave and convex surface shapes is validated experimentally by adjusting the rotational speed of the workpiece, and the results show a good consistency with the calculation results. A flatness error convergency method is proposed based on the surface shape formation mechanism, and flatness superior to 5 µm is achieved on Φ200 × 2 mm thin copper substrates.

Processing performance of vitrified bonded fixed-abrasive lapping plates for sapphire wafers

To enhance the lapping effects of sapphire wafers, two vitrified bonded fixed-abrasive lapping plates with different mechanical properties were developed and used to lap sapphire wafers to evaluate the effects of lapping time and dressing cycle on the lapping process effect and the stability of the lapping plates. The results indicate that the lapping material removal rate (MRR) and surface roughness (Ra) of the workpiece decrease with increasing lapping time; the higher the hardness of the lapping plate, the larger the MRR and Ra. There are differences in the primary wear forms between the two types of plates, with the high-hardness plate being mainly abrasive wear and abrasive breakage, while the low-hardness plate being mainly abrasive peeling off and abrasive wear. The two plates have the same trend in material removal for sapphire wafers - increasing the lapping time, the MRR is found to be gradually decreased and plateaued after 30 min, which is only about 20% of that of the initial lapping time, resulting in the plates needing to be dressed. After dressing the lapping plates, the plate processing performance returns to its initial state; the MRR deviation is less than 10% within the same period of use after several dressings.

Au–Au Bonding-Associated Lapping and Polishing Technique for Sapphire-Based Fabry–Perot Acoustic Sensor Applied for Harsh Environment

This article presents a sapphire-based Fabry–Perot acoustic sensor with potential for application in harsh environment acoustic sensing. The key component of the sensor is a thin sapphire diaphragm with a diameter of 20 mm and thickness down to 10 proposed Au–Au bonding-associated lapping and polishing technique. Microfabrication characterizations have corroborated the availability of realizing wafer-class thin sapphire diaphragm fabrication by employing the Au–Au bonding-associated lapping and polishing technique, and the diaphragm can be then easily transferred and assembled as a sensor. The strategy for optimizing the stripping phenomenon during lapping is also proposed. Acoustic calibration experiment through a plane wave tube indicates the sensitivity of 13.58 mV/Pa at 10 kHz and the frequency response range of 100250 kHz. The temperature tolerance experiment through the muffle furnace shows that no structural damage or optical spectrum invalidity occurs even if the environmental temperature reaches 800°, which indicates a high working temperature of the sensor up to 80°. Major findings and future application directions of this article are concluded as: 1) realization of an innovative sapphire-based Fabry–Perot acoustic sensor that shows significant potential in applications of numerous key industrial domains, such as aerospace engineering, and 2) a novel approach for achieving wafer-class sapphire ultrathin diaphragm fabrication, which might offer innovative methods for the optimization of sapphire-based harsh environment sensors and give reference to the sapphire lapping process as demanded in the gallium nitride (GaN)-based light-emitting diodes (LED) industry.

Shape modulation due to sub-surface damage difference on N-type 4H–SiC wafer during lapping and polishing

The technology enhancement of obtaining 4H–SiC wafers with a concave Si face shape has improved the performance of GaN-on-SiC. For manufacturers, the wafer shape has a tremendous impact on the deposited films quality by increasing defects generation or causing undesirable strain. Therefore, it is crucial to control the wafer shape and explore the mechanism. This study recorded the wafer shape evolution by flatness tester during the machining process of lapping, mechanical polishing (MP), and chemical mechanical polishing (CMP). The varying shapes of SiC wafers are due to surface damage and intrinsic stress caused by the early lapping process, but the intrinsic stress is dominant. The measurement results show that double side MP and single side CMP make the wafer more convex and concave. It indicates that the residual surface stress is involved in shape formation. Perfect symmetrical shape between (0001) Si face and (000 1‾) C face suggests that there is indeed bending stress within the wafer. In this study, atomic force microscopy (AFM), high-resolution X-ray diffractometry (HRXRD), and scanning electron microscopy (SEM) was used to investigate the surface damage between SiC polar faces. According to the results, the damage to the Si face is more severe than that to the C face after double-sided mechanical polishing, leading to the wafer becoming more convex.

Fractal Characteristic-Induced Optimization of the Fixed Abrasive Lapping Plate in Fabricating Bipolar Plate of Proton-Exchange Membrane Fuel Cells

Purpose: A bipolar plate with fractal-characterized microstructures can realize intelligent energy transmission and obtain a high efficiency of proton-exchange membrane fuel cells. In this paper, fixed abrasive lapping technology is proposed to fabricate a surface microstructure on a bipolar plate with fractal characteristics. Methodology: The kinematics of the fixed abrasive lapping process was developed and employed to numerically investigate the particle trajectories moving on the target surface by considering the different arraying forms of diamonds on the lapping plate. Findings: It was found from an analysis of both the uniformity and the fractal characteristics that the arraying form of diamonds on the lapping plate, with the distribution of latitude and longitude with an angle of 30° and a gap of concentric circles of 40 mm with a minimum radius of 70 mm and maximum radius of 190 mm, can be used to obtain the best uniformity and fractal characteristics in the fixed abrasive lapping of a bipolar plate. Conclusions: The distribution of the latitude and longitude of 40° and 30° considered in this study is expected to realize the best machining performance in the bipolar plate and present good cell performance.

Surface quality prediction and lapping process optimisation on the fixed-abrasive lapping plate of sapphire wafers

PurposeLapping is a vital flattening process to improve the quality of processed semiconductor wafers such as single-crystal sapphire wafers. This study aims to optimise the lapping process of the fixed-abrasive lapping plate of sapphire wafers with good overall performance [i.e. high material removal rate (MRR), small surface roughness (Ra) of the wafers after lapping and small lapping plate wear ratio (η)].Design/methodology/approachThe influence of process parameters such as lapping time, abrasive size, abrasive concentration, lapping pressure and lapping speed on MRR, Ra and η of lapping-processed sapphire wafers was studied, and the results were combined with experimental data to establish a regression model. The multi-evaluation index optimisation problem was transformed into a single-index optimisation problem via an entropy method and the grey relational analysis (GRA) to comprehensively evaluate the performance of each parameter.FindingsThe results revealed that lapping time, abrasive size, abrasive concentration, lapping pressure and lapping speed had different influence degrees on MRR, Ra and η. Among these parameters, lapping time, lapping speed and abrasive size had the most significant effects on MRR, Ra and η, and the established regression equations predicted the response values of MRR, Ra and η to be 99.56%, 99.51% and 93.88% and the relative errors between the predicted and actual measured values were <12%, respectively. With increased lapping time, MRR, Ra and η gradually decreased. With increased abrasive size, MRR increased nearly linearly, whereas Ra and η initially decreased but subsequently increased. With an increase in abrasive concentration, MRR, Ra and η initially increased but subsequently decreased. With increased lapping pressure, MRR and η increased nearly linearly and continuously, whereas Ra decreased nearly linearly and continuously. With increased lapping speed, Ra initially decreased sharply but subsequently increased gradually, whereas η initially increased sharply but subsequently decreased gradually; however, the change in MRR was not significant. Comparing the optimised results obtained via the analysis of influence law, the parameters optimised via the entropy method and GRA were used to obtain sapphire wafers lapping with an MRR of 4.26 µm/min, Ra of 0.141 µm and η of 25.08, and the lapping effect was significantly improved.Originality/valueTherefore, GRA can provide new ideas for ultra-precision processing and process optimisation of semiconductor materials such as sapphire wafers.

Effect of Abrasive Grain Concession on Micromechanical Behavior of Lapping Sapphire by FAP.

Aiming at exploring the material removal mechanism for sapphire using diamond abrasive grains at the microscopic level, this paper modeled and analyzed the microscopic yield behavior of diamond abrasive grains in the FAP grinding process of sapphire. Molecular dynamics were used to simulate the effects of abrasive particle size on the cutting force, potential energy, and temperature in the Newtonian zone during micro-cutting. The effect of different abrasive particle sizes on material removal was analyzed through experiments. The simulation results show that the abrasive particle radius was 12 Å, the micro-cutting force reached more than 3500 nN, while the cutting force with an abrasive particle radius of 8 Å only reached 1000 nN. Moreover, the potential energy, cutting force, and temperature in the Newtonian zone between the sapphire crystal atoms also increased. The results showed that the material removal rate saw a nonlinear increasing trend with the increase in particle sizes, while the surface roughness showed an approximately linear increase. Both of them showed a similar trend. The experimental results lay a theoretical basis for the selection of the lapping process parameters in sapphire.

Improvement of the Carrying Capacity of Cast Iron Pipes Due to the Coating Lapping Process

Improvement of the Carrying Capacity of Cast Iron Pipes Due to the Coating Lapping Process

Machining Stability Research of Soft-Brittle Crystals Lapping by Fixed-Abrasive Pad

Fixed-abrasive (FA) lapping and polishing process is the main approach to realize the residual-free and low damage processing of soft-brittle crystals. The hardness of matrix and the abrasive micro-fragmentation are the key parameters impacting the stability of the continuous batch machining. The FA pads were prepared with hard and soft matrix, respectively, and the single diamond (SD) and the aggregated diamond (AD) were mixed in the FA pads, respectively. The FA lapping tests were carried out with LN wafers under the applied load of 10.5 kPa. The continuous batch machining stability of four pads tests were evaluated by the evaluation indexes of the material removal rate (MRR), surface roughness Ra and the material removal rate variation (MRRV). The workpiece surface morphology and abrasive wear pattern were analyzed. The results indicate that: hard matrix is not conducive to the shedding and replacement of abrasive grains because of the high holding force, causing a MRRV of 50%. The MRR of the hard matrix pad tests signally decrease from 3.71 μm/min to 1.9 μm/min. By contrast, the low hardness matrix pad can be applied to improve the machining efficiency owing to its MRRV only about 30%. The MRR of the AD pad is over 600 nm/min, which is far more than that of the SD pad, and the MRRV of the AD pad is just about 20%. While MRRV of the SD pad is as high as 75% with the remarkably decline of MRR. At the view of Ra values, the SD pad and the AD pad both attain nanoscale. The Ra values of the SD pad tests are smaller and the workpiece are superior in surface quality. In the rough lapping and fine lapping stage, the SD can be used to prepare FA pad to improve lapping stability.

Surface Morphology Evaluation and Material Removal Mechanism Analysis by Single Abrasive Scratching of RB-SiC Ceramics

Reaction-Bonded Silicon Carbide (RB-SiC) ceramics possessing excellent mechanical and chemical properties, whose surface integrities have an essential effect on their performance and service life, have been widely used as substrates in the core parts of aerospace, optics and semiconductors industries. The single abrasive scratching test is considered as the effective way to provide the fundamental material removal mechanisms in the abrasive lapping and polishing of RB-SiC ceramics for the best surface finish. In this study, a novel single abrasive scratching test with an increasing scratching depth has been properly designed to represent the real abrasive lapping and polishing process and employed to experimentally investigate the surface integrity regarding different scratching speeds. Three typical and different material removal stages, including the ductile mode, ductile–brittle transition mode and brittle mode, can be clearly distinguished and it is found that in the ductile material removal stage by increasing the scratching speed would inhibit the plastic deformation and improve its surface integrity. It is also found that in the ductile–brittle transition and brittle material removal stages, to increase the scratching speed would inhibit the plastic deformation due to the fast scratching speed that limits the time of plastic deformation on the target, but it also results in the increased length of lateral cracks with the increased scratching speed which can reflect that the size of brittle chips, like brittle fractures and large grain fragmentations, increases as the scratching speed increases. It can provide the references for the optimization of the abrasive lapping and polishing of RB-SiC ceramics with high efficiency and surface quality.

In-situ manifestation of lapping mechanisms by rapid intelligent pattern recognition analysis (RIPRA) of acoustic emission via a point density fuzzy C-means (PD-FCM) method

Rapid pattern-recognition capabilities are very challenging tasks to fulfill while essential steps for the ultimate mission of achieving in-time security response, hazardous disaster prevention, structural failure prediction, and intelligent manufacturing applications. Mechanistic manifestation of a machining process through pattern recognition is even more daunting since one has to gain full understanding at the very fundamental level of the manufacturing processes, but it would be the most beneficial should it be accomplished. We designed and built an in-situ Acoustic Emission (AE) monitoring system, and successfully applied this newly developed AE system to manifest the lapping removal mechanisms of a novel fixed abrasive pad embedded with agglomerated diamond (AD) abrasives. To successfully extract valuable mechanistic information, the time-frequency spectrum of collected AE signals in a sapphire lapping process was decomposed by Wavelet Packet Transform (WPT) into three characteristically patterned bands, each representing rubbing, ploughing and cutting action in the lapping process correspondingly. We creatively applied Point Density Fuzzy C-Means (PD-FCM) algorithm for self-identifying clustering centers to classify contributions from rubbing, ploughing and cutting actions in the lapping process. By rapid intelligent pattern recognition analysis (RIPRA) of AE signals, the lapping removal mechanisms using fixed abrasive pads were clearly identified and quantitatively monitored in-situ throughout the whole lapping processes. Such a capable approach implicates a great potential in a wide range of ultra-precision manufacturing applications.

Optimization of Lapping and Polishing of Steel Samples for Nanoindentation Based on SVM-GA

The nanoindentation test is extensively used to obtain the mechanics performance of different kinds of materials. In this study, the general process in the lapping and polishing of Q235 steel samples for nanoindentation has been analyzed by considering the pressure (P), rotation speed of the lapping and polishing plate (rp), flow rate of abrasive slurry (Qa), and the processing time (t). It is found from the lapping experiments with a full factorial design that the optimized processing parameters are rp of 200 r/min, P of 30 N, and t of 4 min considered in this study by considering the material removal rate and subsurface damage. The central composite design method has been used to design the polishing experiments, and the support vector machine (SVM) method has been used to deal with these experimental results, and it is found that the developed SVM model can accurately predict the surface roughness under different processing parameters. Then, based on the SVM model, the genetic algorithm (GA) method is used to obtain the optimized processing parameters in the polishing process, and it is found from the SVM-GA study that the optimized processing parameters in the lapping process are rp of 108 r/min, P of 33 N, Qa of 20 ml/min, and t of 3 min. Finally, a set of nanoindentation tests have been conducted to evaluate the lapping and polishing performance, and it is found that the surface integrity has been significantly improved after the optimization of the lapping and polishing parameters by using the SVM-GA method considered in this study.

Surface Form Accuracy Evaluation in Abrasive Lapping of Single-Crystal Silicon Wafers

Silicon-based materials still dominate the current semiconductor industry for the foreseeable years such that it is needed in continuously developing the related advanced manufacturing technologies. For the abrasive precision lapping of single-crystal silicon wafers, the surface form accuracy is very important which can significantly improve its efficiency and reduce the cost in the following ultra-precision polishing process. In this study, a novel driving system is proposed in the single-side planetary lapping process that could realize the irrational rotation speed ratio of the lapping plate to the workpiece, and it is found from the numerical qualitative and quantitative analysis that the uniformity of the particle trajectories moving on the target surface has been significantly improved using the irrational rotation speed ratio and hence resulting in the higher surface form accuracy than that driven by the rational rotation speed ratio. Moreover, an in-house developed irrational rotation speed ratio driving system has been designed for the experimental study, and it is found that the effect of the rational and irrational rotation speed ratios on surface roughness is not significant, while all the five essential values related to the surface form accuracy are better under the rotation speed ratio of i = 1.0772… than that under the rotation speed ratio of i = 1, which demonstrates that the irrational rotation speed ratio driving system has the advantage of being able to obtain a good surface form accuracy and agrees well with the numerical simulation results.

Research on Critical Load of Lithium Niobate Crystal Lapping

The elastic modulus and hardness of lithium niobate crystals were obtained by nanoindentation technology, and critical load and critical indentation depth range were determined by AFM by indentation morphology under different loads. According to the normal distribution characteristics of abrasive grains, the critical load model of lapping was deduced, and the critical load of lithium niobate during lapping process under different grain sizes was obtained. It was verified using a single-factor experiment in which experimental results were consistent with theoretical research.

Investigation of Technological and Load Intensity Parameters of the Finishing Process of Materials on Equipment with Tools Translational Kinematics.

The regularities of the formation of the resulting raster tool trajectories based on Lissajous figures for the lapping process of planes are established. This makes it possible to maximize the cutting ability of the tool, which contributes to its more uniform wear and increased productivity and processing quality. Optimal parameters of productivity and roughness of the treated surface during lapping of zirconium ceramics are achieved through the use of ASM paste 28/20 µm. Based on Preston’s hypothesis, an exponential dependence of the change in the contact area during the lapping of planes of different initial shape of the macrorelief is obtained. The obtained theoretical and practical results of the study of the process of flat lapping with constant and variable clamping force of the treated surface to the surface of the tool. The influence of the force factor on the formation of the surface in the process of abrasive lapping has been established. Studies have been carried out and the main technological recommendations of precision surface treatment of workpieces based on hard, brittle ceramic material and bronze samples on equipment with a raster trajectory of the tool movement are presented. The optimal pressure value when processing ceramics should be considered 203–270 kPa (2.1–2.8 kg/cm2).

Lapping performance of diamond cone array tool prepared by double bias assisted HFCVD

In this paper, the free-standing diamond (FSD) and microcrystalline diamond (MCD) film were etched by double-bias assisted hot filament chemical vapor deposition (HFCVD) to prepare two kinds of diamond cone array tools (DCATs) for precision processing. It is the first time to use free-standing diamond cone array tool (FSD-CAT) and microcrystalline diamond cone array tool (MCD-CAT) to perform the lapping processing experiment for monocrystalline silicon and to carry out the performance evaluation of DCAT. The surface roughness of the silicon lapped by FSD-CAT is 28.9 nm, and the surface roughness of the silicon lapped by MCD-CAT is 18 nm. By using the combination of both DCATs to lapped silicon, a smooth surface with a surface roughness of 5 nm is obtained. By comparing the surface roughness of monocrystalline silicon which lapped by diamond tools with and without etching, because of the smaller cross-section of the cones cut into the surface of monocrystalline silicon, DCAT can effectively reduce the Surface roughness of the silicon.

Effect of Fiber Type and Content on Mechanical Property and Lapping Machinability of Fiber-Reinforced Polyetheretherketone.

Polyetheretherketone (PEEK) is a novel polymer material with excellent material properties. The hardness and strength of PEEK can be further improved by introducing fiber reinforcements to meet the high-performance index of the aerospace industry. The machinability will be influenced when the material properties change. Therefore, it is crucial to investigate the influence of material properties of the fiber-reinforced PEEK on machinability. In this paper, the main materials include pure PEEK, short carbon-fiber-reinforced PEEK (CF/PEEK), and short glass-fiber-reinforced PEEK (GF/PEEK). The effects of the fiber type and mass fraction on the tensile strength, hardness, and elastic modulus of materials were discussed using the tensile test and nanoindentation experiments. Furthermore, the fiber-reinforced PEEK lapping machinability was investigated using lapping experiments with abrasive papers of different mesh sizes. The results showed that the hardness and elastic modulus of PEEK could be improved with fiber mass fraction, and the tensile strength of CF/PEEK can be improved compared with that of GF/PEEK. In terms of lapping ability, the material removal rates of the fiber-reinforced materials were found to be lower than the pure PEEK due to the higher hardness of the fiber. During the lapping process, the material removal methods mainly included the ductile deformation or desquamation of reinforcing fiber and ductile removal of the PEEK matrix. The lapped surface roughness of PEEK material can be improved by fiber reinforcement.