Lapping Tool Research Articles

Enhanced precision lapping techniques for fused quartz optical elements: Synergistic integration of mechanical and mechanochemical processes

Fused silica is a material of great importance in the field of precision optical equipment due to its excellent optical properties, e.g. photolithography, laser fusion devices, etc. However, the material's inherent hardness and brittleness render it a challenging material to process. Therefore, an enhanced precision lapping technique was proposed, i.e., a synergistic integration of mechanical and mechanochemical lapping processes. Firstly, a synergistic lapping tool with an outer layer of porous diamond abrasive and an inner layer of CeO2 abrasive was fabricated by hot press forming method. The reduction of layer thickness due to abrasion and detachment of the porous diamond abrasive layer was analyzed, and the lapping mechanism of porous diamond on fused silica materials was revealed. The surface creation mechanism of the CeO2 abrasive layer on fused silica material was analyzed by molecular dynamics simulation and the results were validated by enhanced precision lapping experiment. The results demonstrated that the surface atoms of fused silica are removed in a ‘remote disordered’ manner by conventional diamond abrasive grains, whereas the surface atoms of fused silica are removed in a ‘proximally ordered’ manner by the fine porous diamond abrasive grains through the micro-multi-flute cutting. Consequently, the grinding of a porous diamond abrasive layer can significantly reduce the processing damage, with the surface roughness of the lapping Ra reaching 199 nm. The lapping of CeO2 induces the formation of an oxygen bridge on the surface of fused silica, which then produces bending vibration. This is followed by the adsorption and diffusion of oxygen atoms, which form the -Ce-O-Si intermediate with the oxygen atoms shared with the fused silica. This process results in the formation of CeSiO3 and CaSiO3 compounds. The final surface quality with a surface roughness of Ra 21 nm was obtained by mechanochemical lapping of the cerium oxide abrasive layer. The single mechanical-mechanochemical composite ultra-precision lapping process provides technical support for the efficient and low-damage processing of hard and brittle components.

Study on the wear characteristics of a 3D printed tool in flat lapping of Al2O3 ceramic materials

Widespread and popular use of ceramic products in various industry sectors necessitates the search for methods of their efficient processing. Lapping technology, which enables obtaining high dimensional and shape accuracy and high surface flatness, is one of the basic methods of finishing hard and brittle technical ceramics with a porous structure. This study analyzed the characteristics and wear value of an SLS-printed abrasive tool intended for single-sided lapping of Al2O3 technical ceramics. As earlier research demonstrated, introduction of a 3D printed lapping plate by selective laser sintering (SLS), leads to a significant development in the field of precision machining technology. This method showed not only efficient machining performance on oxide technical materials, but was also characterized by relatively low abrasive wear. Straightness errors were evaluated with the use of a least-squares method (LSQ) and minimum zone method based on control line rotation scheme (CLRS). The proposed model proved the experimental results by identifying a similar location of a higher contact density on the lapping tool, where this location is expected to be the one for bigger wear. Surface topography of the lapping tool depends on the tool wear intensity and as a consequence on its shape error. An SLS-printed lapping plate, by obtaining good technological effects, revealed its potential ability in machining hard and brittle technical ceramics.

A Study on the Material Removal Characteristics and Damage Mechanism of Lapping for Pressureless Sintered Silicon Carbide (SSiC) Microlens Cavity.

Microlens arrays have been widely employed to control the reflection, refraction, and diffraction characteristics of light due to its distinctive surface properties. Precision glass molding (PGM) is the primary method for the mass production of microlens arrays, of which pressureless sintered silicon carbide (SSiC) is a typical mold material due to its excellent wear resistance, high thermal conductivity, high-temperature resistance, and low thermal expansion. However, the high hardness of SSiC makes it hard to be machined, especially for optical mold material that requires good surface quality. The lapping efficiency of SSiC molds is quite low. and the underlying mechanism remains insufficiently explored. In this study, an experimental study has been performed on SSiC. A spherical lapping tool and diamond abrasive slurry have been utilized and various parameters have been carried out to achieve fast material removal. The material removal characteristics and damage mechanism have been illustrated in detail. The findings reveal that the material removal mechanism involves a combination of ploughing, shearing, micro-cutting, and micro-fracturing, which aligns well with the results obtained from finite element method (FEM) simulations. This study serves as preliminary reference for the optimization of the precision machining of SSiC PGM molds with high efficiency and good surface quality.

Design of a novel fixed abrasive petal-shaped lapping tool and material removal uniformity experiments on K9 glass

A novel fixed abrasive petal-shaped lapping tool is proposed to achieve the material removal uniformity based on finite element method (FEM) and mathematical analysis. The cross-sectional profile of the petal-shaped lapping tool is revealed according to the numerical analysis based on the in-plane stress distribution of disk elastomer tools in contact with the workpiece, which is shown and analyzed for the first time. Then, the practical experiments are carried out on the K9 glass plane workpieces to study the characteristic of the surface quality evolution and the material removal uniformity. Results show that the increasing material removal amounts along the radius are all suppressed under different experimental conditions, where the coefficients of variations of the two experimental groups with the better results are as low as 0.077 and 0.085, respectively. Moreover, the surface roughness Sa and Ra along the radial direction after lapping reach as low as 142 nm and 30 nm for the optical glass, achieving a drastic improvement of 77.2 % and 88.8 %. Thus, the design strategy of lapping tool with special structure will explore a new path of fabricating more specific tools in the field of ultraprecision manufacturing.

Investigation on surface evolution and subsurface damage in abrasive lapping of hard and brittle materials using a novel fixed lapping tool

Novel fixed abrasive lapping (NFAL) is used in this study to quickly remove the surface damage layer and control the depth of subsurface damage (SSD), thus saving overall machining time and reducing the costs of large-aperture optical manufacturing. The influence of lapping parameters on the surface and subsurface state is studied through a series of experiments to better understand the material removal and damage mechanisms during NFAL. A surface evolution model for NFAL was established based on indentation fracture mechanics, mathematical statistics, abrasive wear theory and convolution iteration principle. Experimental results show that the model can predict the surface topography well. Further simulation experiments were also conducted to study the effects of the tool load and particle size on the microscopic removal characteristics of the NFAL process. The results show that NFAL can quickly produce submicron-level surface roughness and restrain SSD with the reasonable selection of lapping parameters.

Theoretical and experimental investigation on surface generation and subsurface damage in fixed abrasive lapping of optical glass

Fixed abrasive lapping (FAL) is a promising technology increasingly used for finishing optical mirrors and molds in a number of materials due to its high finishing efficiency, environmental friendliness, and relatively better surface and subsurface quality. A theoretical model for fixed-abrasive lapping of optical glass was developed in this paper by using indentation fracture mechanics, contact mechanics, mathematical statistics, lapping kinematics, and convolution iterative principle to provide an enhanced scientific understanding of the surface microtopography generation and subsurface damage (SSD) control mechanisms. In the modeling, the influence of the shape, size, and spatial distribution of abrasive particles and the ductile and brittle removal mechanisms of the material were considered. A series of lapping experiments on fused silica glass was carried out to quantitatively analyze the feasibility and accuracy of the model and study the influence mechanism of process parameters on the surface and subsurface state. Results indicated that the models could well predict the surface micromorphology and the SSD depth, and the range of sharpness angle of abrasive particles and tool load affected the predicted SSD range. In addition, the material removal mechanism and lapping tool wear characteristics were revealed by the surface structure and element component analysis. Finally, the FAL process was optimized by the evaluation indices of material removal rate (MRR), surface roughness, and SSD.

Аналіз конструкцій плоскопритиральних верстатів

One of the methods of material processing is considered, which allows to obtain high geometric accuracy and low surface roughness of parts, namely their abrasive finishing. The high quality of machining of parts in this way is due to the use of coordinated relative movement of the workpiece and the cutting tool. According to the kinematic features, most lapping machines can be divided into two groups: machines with oscillating working motion and machines with rotating lapping motion. The machines of the first group are more common due to the simplicity of their design and versatility. However, the possibility of their use is limited by the size range of the workpieces and uneven wear of the cutting tool and, as a consequence, the uneven surface treatment of the part. The machines of the second group are considered the most versatile, as they allow processing a wide range of parts, varying in shape and size, but they are also not without such a disadvantage as uneven wear of the cutting tool with all the corresponding consequences. Improving the efficiency of abrasive finishing by complicating the trajectory of the relative movement of the tool and the part, ie the formation of a unique mutual working movement of the lapping and the movement of the workpiece, is one of the most common areas. The main disadvantage of equipment that provides processing of parts on this principle is, in most cases, limited regulation of the operating parameters of the cutting process, so this area remains promising and has broad prospects for development. The constructive scheme of the hydraulic-pulse flat-lapping machine offered in work thanks to a combination of advantages of the hydraulic-pulse drive with use of numerical program control will allow to provide unique mutual multi-movement of preparation and the lapping tool with a possibility of adjustment of its parameters in the course of processing. Purposeful choice of the shape and density of the trajectory of the working movement of the tool will form a micro relief of the treated surface with the necessary statistical parameters and low roughness.

Features of Calculating Kinematic and Roughness Parameters at Abrasive Finishing of Shut-Off Surfaces of Gate Valve Bodies Connecting Pipes

Introduction. The author defines main provisions for peculiarities of the kinematics of plant lapping in the process of finishing shut-off elements of the valves, as well as methods for determination of operating parameters and values of roughness in the process of abrasive finishing of sealing surfaces of valves. Materials and Methods. The kinematic scheme of grinding machines was developed to determine the angular velocity of rotation of an instrumental disc and lapping machine. Based on the developed kinematic scheme, we obtained analytical expressions to determine the capacity of the machine’s drive motor and cutting elements, as well as the angular and linear speeds of rotation of tool drive and laps. There were also developed trajectory traces of grid points of the lapping tool at its movement along with the treated surface details of pipe fittings. Results. There are given examples of calculation of kinematic parameters and roughness of the treated sealing surface of gate valves with the diameter DN = 100 according to established analytical dependencies for rough and finish lapping. The coordinates of the moving tools were calculated with visualization of trajectory points using special software Lazarus. The coordinates were calculated and the trace of the moving point tool was built. The specific space which characterizes the capacity of the sealing surfaces was calculated. Discussion and Conclusion. Calculations allowed us to determine how to place the lapping tool relative to the machine’s sealing surface for optimization of the treatment process. Preliminary calculations showed that the area of lapping tool’s contact with the workpiece and the optimum angle of contact would change slightly within the relative probability of error of 5% and 10%.

Theoretical and experimental analysis of material removal and surface generation in novel fixed abrasive lapping of optical surface

Abstract Fixed abrasive machining, which overcomes the lack of determinacy and efficiency of current loose abrasive polishing or lapping processes, is an alternative technology for fabricating large-aperture aspheric surfaces with high finishing efficiency and high-quality surface finish. A novel fixed abrasive lapping (NFAL) tool, which combines computer-controlled optical surfacing and conventional fixed abrasive lapping process, is introduced in this study to produce off-axis aspheric surfaces efficiently while surface state is controlled and subsurface damage (SSD) is avoided. The removal mechanism analysis shows that fused quartz glass is primarily removed in ductile regime and the SSD depth is 14.7 μm when the tool load is 25 N. The material removal volume is linear with the machining time under the ductile removal mode. The material removal and surface generation models are developed on the basis of the calculation of the spatial distribution of abrasive particles, the pad–particle–workpiece interactions, the single-particle abrasion mechanism, and the linearly cumulative removal of surface generation in the NFAL process. The models are verified through a series of spot and surface lapping experiments. Results show that the theoretical model can be successfully used to predict and optimize the NFAL process. The spot lapping experiments indicate that the material removal volume is linear with the rotation speed, and the maximum depth is limited to the specific value that depends on the stiffness of lapping tool. The surface roughness Ra and Rz values of the measured and simulated surface data decrease with the increase in feed rate and increase with the increase in raster spacing. The power spectral density analysis indicates that high feed rate can distinctly improve the high-frequency errors, and the selection of the raster spacing can principally affect the low-frequency and middle-spatial frequency errors.

Investigation and optimization of the internal cylindrical surface lapping process of 440c steel

A new lapping method is proposed for internal cylindrical surfaces finishing. Regression analysis and artificial neural network (ANN) were used for modeling this lapping process and predicting the effects of parameters of rotational speed of the lapping tool (ω), the length of the lapping tool (L) and difference in external diameter of the lapping tool and internal diameter of the workpiece (D) on the material removal rate (MRR), out-of-cylindricity (C) and surface roughness (Ra) of the lapped holes. Comparison of the results of the regression and ANN models with the values obtained from the experiments indicates that the MRR, Ra and C are more accurately predicted using ANN models. MRR, Ra and C of the lapped holes have been optimized using genetic algorithm (GA) and particle swarm optimization (PSO) algorithm. The results show that the highest MRR, which is equal to 2029 μg/min, has been achieved at ω of 400 rpm, D of 0.1 mm and L of 45 mm. The lowest Ra of the lapped hole is 64 nm which has been obtained at ω of 100 rpm, D of 0.1 mm and L of 20.82 mm. The minimum C of the lapped hole is 3 μm, which was obtained at ω of 212 rpm, D of 0.1 mm and L of 28.3 mm. The most important problem in the lapping process is the low MRR which causes increased cost and production time. Therefore, in the lapping process, the selection of conditions, that in addition to the production of pieces with geometric accuracy and surface roughness needing a high MRR, is very important. In this study, MRR, Ra and cylindricity of the lapped holes was optimized using multi-objective PSO (MOPSO) algorithm and non-dominated sorting genetic algorithm II (NSGA II), and the Pareto optimal solutions were obtained. Comparison of the results obtained from NSGA II and MOPSO shows that both of these algorithms can achieve optimal Pareto front with the same accuracy, but the time required to reach the MOPSO algorithm to the optimal Pareto front is 25 % less than the NSGA II.

Precision Machining of Silicon Substrates

Brittle nonmetallic structural materials, such as quartz, glass, silicon, ceramics, ferrites and glass ceramics, are widely used in mechanical engineering, instrument making and radio electronics, as well as in optical, clock and jewelry industries. These materials have high hardness, strength, wear resistance and brittleness; therefore, their machining is a complicated problem. For production of piezoelectric resonators and filters, semiconductor devices, solid-state lasers, optoelectronic devices and other parts of electronics, plates made from monocrystals of quartz, lithium tantalate and niobate, silicon, germanium, sapphire, etc. are used. Semiconductor plates, which were obtained after cutting of a boule, have a number of defects, such as presence of a mechanically affected layer, nonflateness of sides, twisting and large variation of thickness. Therefore, after cutting it is necessary to carry out grinding and polishing. Grinding (abrasive finishing) is machining of semiconductor plates by means of hard finishing grinding discs (lapping tools) using abrasive flour grains. Finishing discs (lapping tools) are usually made from cast iron, glass, steel, copper or tin. The grain size of flour grains for grinding of semiconductor plates is selected from M14 to M5. Finishing machining of silicon substrates is complicated by a number of factors, such as provision of stable sizes, and, which is more important, the required microrelief of a machined surface, and unacceptability of machining marks and micro fissure on a surface. In Perm National Research Polytechnic University, the method of abrasive finishing and polishing of surfaces of silicon substrates by means of “Rast-350” flat-finishing machine was developed. The feature of the machines is in sliding movement of a tool (lap) along a nonrecurring trajectory, which has a form of a grid of complicated configuration. At that, the speeds of movement of all points of the working face of the lapping tool are the same. The studied and proposed technological recommendations for operations of finishing and polishing of silicon substrates allowed determining the main technological regimes (time, specific pressure, and density of the grid of tool marks), as well as the required abrasive material of corresponding grain size, which allowed providing the required microrelief of substrates (Rz 25 nm, Ra 5 nm) and eliminating machining marks and micro fissures on a polished surface.

Lapping Performances of a Stainless Steel Mesh Lap

In a rough lapping process of substrates made of SiC or sapphire, a cast-iron lap is generally used. However, the cast-iron lap has some problems, which it has low corrosion resistance and low removal rate. We developed a fiber lap as an alternative lapping tool for solving these problems. The fiber lap is a tool containing stainless-steel fibers in the epoxy resin. A stainless-steel mesh (called as a “mesh lap”) was used as a lapping tool to optimize the dimensions of the fibers. As a result, the removal rate of the mesh lap was very high compared with the cast-iron lap. Then, the lapping mechanism on which a high removal rate could be obtained was investigated. The lapping performances of the mesh lap can be changed depending on the wire diameter and the pitch interval. The difference in the lapping performances was examined by observing the moving behavior of the abrasive grains on the tool. It was found that there were two types of abrasive-grain behaviors, meandering motion and linear motion. Finally, by reflecting the results obtained using the mesh lap on the fiber lap, we improved the lapping performances of a fiber lap.

Pressure variation of developed lapping tool on surface roughness

Improving the surface roughness is always one of the major concerns in the development of lapping process as high precision machining caters a great demand in manufacturing process. This paper aims to investigate the performance of a newly designed lapping tool in term of surface roughness. Polypropylene is used as the lapping tool head. The lapping tool is tested for different pressure to identify the optimum working pressure for lapping process. The theoretical surface roughness is also calculated using Vickers Hardness. The present study shows that polypropylene is able to produce good quality and smooth surface roughness. The optimum lapping pressure in the present study is found to be 45 MPa. By comparing the theoretical and experimental values, the present study shows that the newly designed lapping tool is capable to produce finer surface roughness.

金属短繊維含有ラッピング工具の開発

A new high-performance lapping tool consisting of short metallic fibers and epoxy resin was developed to overcome the low lapping performance of conventional tools for grinding difficult-to-cut materials. The short metallic fibers were compressed and impregnated with epoxy resin to produce the new lapping tool. By using these different wear-resistance materials, the tool surface could maintain the uneven shape continuously even when its surface was worn and this makes it possible to maintain long-term high lapping characteristics and enough effective slurry supply. In this research, we examined the optimization of the shape and the material of fibers. Moreover a 40 vol% fiber lap could be produced by using a coupling agent. The results of the tests showed that the lapping efficiency was improved by 28 % and that the durability was equal to that of the conventional cast-iron lap.

Experimental study on elastic deformation molding process for generating aspheric surface glass

The elastic deformation machining method has been demonstrated to be a novel optical manufacturing approach which can greatly reduce and simplify the production of large aspheric lens. Upon completion of the machining process, the workpiece under process will be shaped into a desired surface form of mold. The method allows the lapping and polishing of aspheric optical surfaces using a large lapping or polishing tools. The subject of this study is to determine the surface shape of the finished glass workpiece after the lapping process of the elastic deformation machining process associated with molding. The experimental and finite element analysis (FEA) results were compared with the shape of the molded surface form. The form accuracy between the optical glass and mold is within 1.6 μm (within radius 32 mm). The conclusions show that the method proposed is effective for machining the aspheric optical glass with proper elastic deformation machining parameters.

G1300106 鋳鉄ラップと多孔質ウレタンパッドの相似性

In this paper, we examined the processing characteristics of the cast iron plate and the urethane resin porous polishing pads. The similarities between the cast iron lapping plate and the porous urethane resin polishing pad are described. It was known that the conditioning state of tool surface affects the processing characteristics greatly. To improve the performance of conventional tools, we developed the metallic fiber lapping tools and the epoxy resin pads. The metallic fiber tool can grip the abrasives on the lapping area with microasperity. The epoxy resin polishing pad showed higher removal rate and lower surface roughness than a conventional urethane resin polishing pad, because of high hydrophilic property.

Grinding Hyperboloid Part by Bending Method

In view of the machining difficult problem of hyperboloid, a new method is presented that high speed lapping hyperboloid parts using the bended lapping tool, and the principle of high speed lapping by the bending method is discussed. The mathematical model of bended lapping tool has been established using mechanics and higher mathematics, and the expression of width function of lapping tool is deduced. Analysis of the calculating example indicated that this method is possible to design the needed lapping tool. The bending experiment of lapping tool has confirmed the feasibility using this method, the biggest error of face shape was 1.0038μm, the face shape precision can satisfy the majority part request.

Lapping Parabolic Parts Using the Bending Lapping Tool

Lapping the parabolic work-piece with the lapping tool in bending method is a new technology, which has some good characters such as low cost, scope broad, easy operation, and high precision. The lapping tool is formed by the means of bending and forming with solid abrasives on it in the experiment. The experiment shows that parabolic workpiece can be lapped using this method. The experimental result indicates that the work-piece face shape precision is high with the lapping tool, the maximal error is 0.0881mm and the minimal error is-0.0011mm, and lapping efficiency is high and the cost is low.

Lapping Aspheric Workpiece Using Bending Method

A new method is proposed that high speed lapping aspheric surface workpiece using lapping tool by means of bending because there processing difficult, In this study, the principle of high speed lapping has been presented, the mathematical model for the lapping tool has been established, and the equidistance curve error of the lapping tool has been analyzed. The results of the experiment indicate that the forming precision of the lapping tool is high using this method, the surface precision of the workpiece reaches micron grade, furthermore, the aspheric surface workpiece can been machined using this method in lapping, and that it can meet the need of medium precision of machining the aspheric surface workpiece. The experiment result indicates that the the lapping tool shape precision is high, the lapping error of the workpiece is 0.0108mm, and lapping efficiency is high and the cost is low. This aspheric lapping method has incomparable superiority of other processing methods.

Analysis for Force in a New Method of Lapping Brake Pump Master Cylinder

By means of finite element method this paper analyzes a new support method used in lapping with solid abrasive and reearches lapping pressure distribution between workpiece machining surface and solid abrasive in lapping process with lapping tool pressed by three support points.From results we can find that by means of the new method the lapping pressure distribution between workpiece machining surface and solid abrasive is improved obviously in lapping process,which is favorable to increase cylindricity of machined hole.Through actual machining process, new method is demonstrated increasing cylindricity accuracy of machined holes of main cylinder significantly.