Lapping Process Research Articles

Evaluation of Y2O3 surface machinability using ultra-precision lapping process with IED

Prospects of Y2O3 have been more extended as a great promising and creditable material for optical, electronic and mechanical purposes. Y2O3 has been more observed as a fine ceramic which has great material properties: high light transparency, excellent thermal resistance and chemical inertness. But in terms of effective application of Y2O3, its hard and brittle nature needs to be overcome during the surface machining process. Therefore, the surface machining control of Y2O3 should be conducted carefully. The evaluation for stable and continuous machining should also be investigated in various industrial fields as there are only limited studies on the subject. The lapping process with in-process electrolytic dressing (IED) is widely used for surface machining of hard and brittle materials. In this study, Y2O3 surface machinability was evaluated by using the ultra-precision lapping process with IED method by changing three major variables: applied force, wheel speed and machining time. The most suitable value of Ra 92nm surface roughness was acquired with smooth surface quality from the following machining condition: 7kg of applied force, 60rpm of wheel speed and 30minutes of machining time. After the lapping process, the machining tendency and surface characteristics were analyzed with fracture toughness and Vickers hardness for the evaluation of Y2O3 surface machinability.

Material Removal Model of Sapphire Substrate in Double-Side Lapping Process

The material removal mechanisms of sapphire substrate in double-side lapping process were studied. The concepts of brittle vs. ductile machining and two-body vs. three-body abrasion were used to classify the processing mechanisms. The material removal models of double-side lapping process in different mechanisms were analyzed and researched. The experiment showed that the material removal model can describe double-side lapping process of sapphire qualitatively.

Computer-Aided Machine Setting for Lapping Optimization

During hypoid gears lapping process, a gear set is running at varying operating positions and under a light load in order to lap the complete tooth surface. The pinions and gears are lapped in pairs. Hence, their tooth surfaces are not only cutters but also workpieces. In the contact region, the contact pressure and sliding speed are different from point to point. This makes lapping to be a very complicated abrasive wear process. So far, knowledge about the relationship between the removed materials and the lapping time as well as how to optimize the lapping process is quite limited. An algorithm was presented (Jiang et al., 2008, “Simulation of Hypoid Gear Lapping,” ASME J. Mech. Des., 130(11), p. 112601) to determine the wear coefficient k for the lapping process of hypoid gears. With the obtained wear coefficient k, a methodology for simulating the lapping process was proposed. Based on the wear coefficient obtained, this work presents a computer-aided machine setting procedure to optimize the lapping cycle in order to improve the lapping quality and efficiency.

Material Removal Model of Sapphire Substrate in Double-Side Lapping Process

Material Removal Model of Sapphire Substrate in Double-Side Lapping Process

Development of Lapping and Polishing Technologies of 4H-SiC Wafers for Power Device Applications

The development of lapping and polishing technologies for SiC single crystal wafers has realized the fabrication of an extremely flat SiC wafer with excellent surface quality. To improve the SiC wafer flatness, we developed a four-step lapping process consisting of four stages of both-side lapping with different grit-size abrasives. We have applied this process to lapping of 2-inch-diameter SiC wafers and obtained an excellent flatness with TTV (total thickness variation) of less than 3 μm, LTV (local thickness variation) of less than 1 μm, and SORI smaller than 10 μm. We also developed a novel MCP (mechano-chemical polishing) process for SiC wafers to obtain a damage-free smooth surface. During MCP, oxidizing agents added to colloidal silica slurry, such as NaOCl and H2O2, effectively oxidize the SiC wafer surface, and then the resulting oxides are removed by colloidal silica. AFM (atomic force microscope) observation of polished wafer surface revealed that this process allows us to have excellent surface smoothness as low as Ra=0.168 nm and RMS=0.2 nm.

Simulation of Hypoid Gear Lapping

In the lapping process of hypoid gears, a gear set is run at varying operating positions and under a light load in order to lap the complete tooth surface. Because of the rolling and sliding motion inherent to hypoid gears, the lapping compound acts as an abrasive and refines the tooth surface to achieve smoothness in rolling action and produce high quality gear sets. In this paper, the lapping process is reproduced using advanced modeling tools such as gear tooth vectorial simulation for the tooth surfaces and reverse engineering to analyze the tooth contact pattern of existing gear sets. Test gear sets are measured using a coordinate measurement machine prior to a special lapping cycle where the position of the gear sets on the lapper does not change, and then are remeasured after lapping in order to establish how much and where material was removed. A wear constant named “wear coefficient” specific to the lapping compound is then calculated. Based on the obtained wear coefficient value, an algorithm for simulating the lapping process is presented. Gear sets lapped on the production line at AAM are used for simulation case studies. Initial results show significant scattering of tooth distortion from tooth to tooth and from gear set to gear set, which makes the simulation process difficult. However, it is possible to predict a confidence range within which actual lapping should fall, thereby opening the door to the optimization of the lapping process.

The lapping mechanism of hypoid gears

Based on the analysis of the transmission errors and the effect contact ratio under lapping, the mean boundaries of the lapping contact of tooth surface are determined and the lapping paths are schemed. The relative lapping rate of the tooth surface is estimated by means of the synthesis of the sliding coefficient, the lapping probability and the dynamic lapping force. The mechanism of the tooth flank modification on the errors corrected mutually and averaged dynamically in the lapping process are presented and investigated. The teeth precision and the dynamic mesh behavior before the lapping have been compared with these after lapping, the results of which show that the lapping may reduce the teeth form errors and spacing variations to some extent and improve greatly the teeth meshing precision and the dynamic mesh behavior.

Subsurface damage distribution in the lapping process

To systematically investigate the influence of lapping parameters on subsurface damage (SSD) depth and characterize the damage feature comprehensively, maximum depth and distribution of SSD generated in the optical lapping process were measured with the magnetorheological finishing wedge technique. Then, an interaction of adjacent indentations was applied to interpret the generation of maximum depth of SSD. Eventually, the lapping procedure based on the influence of lapping parameters on the material removal rate and SSD depth was proposed to improve the lapping efficiency.

D21 枚葉ラップ盤を用いた大口径工作物のラッピング加工(OS-10 研磨技術)

The lapping process is a processing method to improve waviness or bow of the sliced wafers using slurry. The silicon wafer for LSI or IC to improve the productivity has been required larger size diameter every each year. Therefore, the lapping machine size becomes large in proportion to the enlargement of the wafer size. As the results, the upsized lapping machine brings some problems about deflection of the lapping plate by self-weight, and so on. This study aims to develop the single wafer lapping machine to process the large sized silicon wafer by the small sized machine. This report describes the basic lapping characteristics at the single wafer lapping machine.

Theoretical Analysis and Experimental Verification of Triangular Fracture Defects of MgO Single Crystal Substrate in Lapping or Polishing Process

MgO single crystal is mainly used as substrate for high temperature superconductor film. Surface quality of MgO substrate has significant effect on the function of high temperature superconductor film. MgO single crystal is a typical hard and brittle material, and is easily cleaved along the {100} face, so some defects are always generated on the substrate surface while lapping and polishing, which badly affects the surface quality of the substrate. In this paper, a kind of typical defect, the triangular fracture defect which is on the substrate surface after lapping and polishing, is analyzed in detail. According to the structure characteristics of the MgO single crystal, and based on the dislocation reaction theory, a formation mechanism of the triangular fracture defect in lapping and polishing processes is explored. Through the single grain scratch test in different directions on the polished surface of MgO{100} single crystal substrates, the formation mechanism of triangular fracture defect in lapping and polishing processes is verified. And during the scratch test, the plastic flow of the MgO single crystal material beside the scratch was observed.

Research and Simulation on the Wear Uniformity of Lapping Plate

Lapping plate wear is of great influence on shape precision of workpiece. Investigation on the wear uniformity of uncertain eccentricity plane lapping was carried out in this research. The relative velocity function of the plate to the workpiece is obtained through kinematic analyses in the mode of uncertain eccentricity plane lapping, and material removal rate (MRR) function and wear uniformity function were deduced based on Preston equation. Effects of the ratio and eccentricities on the wear uniformity are discussed in detail through MATLAB simulation. Theoretical analysis and simulation results show that the ratio k1 of workpiece revolution speed to lapping plate is the key to decide whether the lapping plate is lapped uniformly. Theoretically, when k1<0, the greater |k1| is, the better the lapped uniformly of lapping plate can be. The ratio k2 of workpiece rotation speed to lapping plate has great influence on the lapped uniformly when k1 approximate 1, and k2 has little influence on the lapped uniformly when k1<0 or k1>1, Besides, a bit bigger eccentricity e1 is propitious to the lapping uniformly of the lapping plate, and bigger eccentricity e2 are also helpful to lapping uniformly of the lapping plate. And the conclusion could be extended to single-side plane lapping and double-side plane lapping process.

Observations in the flat lapping of stainless steel and bronze

Lapping is a finishing process, in which material removal takes place due to relative motion between the workpiece, loose abrasive grains, and the lapping plate. This process is used in achieving finer surfaces and closer fits, correction of minor imperfections, and maintaining close tolerances. Although a significant underlying science-base exists with regards to the physics, mechanics, dynamics, and thermal effects, lapping has been considered an art, rather than a science. Exploring lapping at a fundamental level will help improve its application. This study discusses the effects of using various abrasive materials on surface topography via flat lapping. Stainless steel and bronze specimens were lapped using a set of different abrasives. Topography of the surfaces generated by lapping is investigated using a scanning electron microscope. The surface generated as a result of abrasive particles has been characterized based on concepts in tribology. The goal of this research was to quantify the influence of abrasives material properties in flat lapping with an application in reconditioning valve seats. The lapping process using different abrasives as applied in this study showed no significant material removal rates. However, the surface roughness and the surface topography are seen to be readily affected by the use of different abrasives. The results on MRR obtained by lapping stainless steel and bronze with garnet, alundum, and crystolon indicate that, even though crystolon is harder than alundum, alundum abrasive was more efficient in removing material than crystolon. In general, the surface finish and flatness was observed to improve with the hardness of the abrasive grit.

Parameters Optimization on the Lapping Process of 9Cr18 with Taguchi Method

9Cr18 is a type of martensite stainless steel. It has high hardness, chemical stability, fine anticorrosion, wearable and quench stability. It has been used in different areas with high-anticorrosion and high polishing surface as mirror. So it requires for the high level surface quality after lapping and polishing. In this paper, the surface quality (surface roughness and flatness) of 9Cr18 is discussed with lapping parameters which include velocity, load and time distribution of two lapping steps(rough lapping and Ultra-precision lapping). In order to optimize those parameters, an optimization experiment for lapping 9Cr18 with Al2O3 was designed by Taguchi method. Finally, the optimum condition of each factor can be determined that speed: 80rpm, load:3.0kPa, and time distribution: rough lapping time=15min, Ultra-precision lapping time＝45min are the optimum conditions for both Ra and Wt.

High Throughput SiC Wafer Polishing with Good Surface Morphology

We report SiC wafer polishing study to achieve high throughput with extremely flat, smooth and damageless surface. The polishing consists of three process, wafer grinding, lapping and chemical mechanical polishing (CMP), which are completed in shortest about 200 minutes in total for 2 inch wafer. Specimens of 4H- and 6H-SiC were provided from slicing single crystal as wafers oriented (0001) with 0 or 8 degrees offset angle toward to <112 _ 0>. By the first grinding using a diamond whetstone wheel, we realized flat surface on the wafers with small TTV error of 1 μm in 15 minutes. After second process of lapping, the wafers were finished by CMP using colloidal silica slurry. AFM observation showed not only scratch-free surface but also atomic steps on the wafers after CMP. Rms marks extremely flat value of 0.08 nm in 10 μm square area.

Simulation of a ceramic ball lapping process under dual rotating plates lapping mode

To study the lapping process and sphere-shaping mechanism of ceramic ball under Dual Rotating Plates (DRP) lapping mode and reduce the experiment trails, a simulation method utilising the section-dividing conception that special surface is divided into zones by latitude circles and longitude circles with certain step lengths and the lapping process is simulated in MATLAB with the calculated of lapping trace and given material removal rate. The effects of velocity parameters and material removal rate on the sphericity after lapping is analysed.

Experimental Study on New Bonding Materials for Developing Nano-Grinding Plates

This paper describes a method for experimental development of a novel fixed abrasive nano-grinding plate (FAG-plate) which is proposed for lapping some rigid brittle materials, such as quartz crystal and silicon. The FAG plate is developed with ultraviolet-cured resin by rapid prototyping technology. The analysis shows that such FAG-plate can keep its grinding ability constant and continuous and it can make the roughness of machined surface reach to nanometer level. Based on experimental comparisons with conventional free abrasive slurry lapping plates, the lapping process using FAG-plate has several distinct advantages. One is that the machining efficiency is significantly improved. The second is that it improves the surface roughness of machined work-pieces, although it decreases the flatness tolerance of materials. Furthermore, the fixed abrasive nano-grinding plate is made by the new bonding materials- ultraviolet curing resin and thus the fabrication of FAG-plate is convenient and economical.

Study on Lapping Characteristics of Silver using Brittle Material (1st Report)

The authors have recently researched interesting phenomena on lapping tests for a glass on a silver lapping plate using different quaternary ammonium chloride solutions. The silver lapping plates were not worn during the lapping process even under the condition of large stock removal of the glasses. In this research, glasses, silicon wafers and ceramics were used as lapping plates for lapping test in the various quaternary ammonium chloride compound solutions as suspensions with aluminium oxide abrasive grains. It inquired into relations between the phenomena and concentration of NaCl, KCl, NH4Cl and ZnCl2 solutions, too. The surfaces of silvers were observed by SEM and EDX after lapping test. In the case when NaCl, KCl, NH4Cl and ZnCl2 lapping solutions were used on glass lap plate, also stock removals of silvers become zero. Any differences of structures on the silver surfaces were not observed after lapping by SEM and EDX even if this phenomenon occurred or not.

An Experimental Study on Laser Cutting Mechanisms of Polycrystalline Diamond Compacts

The objective of this study is to experimentally investigate the cutting mechanisms of polycrystalline diamond compacts (PDC) using two different lasers: (a) a near infrared Nd:YAG laser (Neodymium-doped Yttrium Aluminum Garnet) of 1064 nm wavelength and 100 μs pulse width; and (b) a green light KTP (Potassium Titanyl Phosphate)/Nd:YAG laser of 532 nm wavelength and 120 ns pulse width. To realize the objective, the study applies polishing, lapping and etching processes to the cut-surfaces of the PDC samples. It further observes and analyzes the processed cut-surfaces with scanning electron microscopy (SEM) and Raman spectroscopy. A discussion is provided to reveal the underlying physics of the laser cutting mechanisms, and a conclusion is drawn based on the outcomes from the experimental investigation and the discussion.

The ultimate sharpness of single-crystal diamond cutting tools—Part II: A novel efficient lapping process

As the theoretical predictions presented in Part I, the ultimate sharpness of (1 1 0)–(1 0 0) oriented diamond cutting tool can reach up to 1∼6 nm, and the (1 0 0)–(1 0 0) oriented cutting tool up to 2∼5 nm [W.J. Zong, K. Cheng, D. Li, T. Sun, Y.C. Liang, The ultimate sharpness of single-crystal diamond cutting tools—Part I. Theoretical analysis and predictions, International Journal of Machine Tools and Manufacture 2005, submitted]. In order to validate the theoretical predictions, a novel efficient lapping process, namely thermo-mechanical lapping, is developed in the present work, which is regarded as an effective extension of the traditional mechanical lapping process. By this developed lapping method, a large number of lapping experiments are carried out on the (1 1 0)–(1 0 0) oriented cutting tools. AFM measurement results illustrate that lapping time has little effects, but both lapping compression force and lapping velocity have enormous influences on the finished cutting-edge radius. Furthermore, based on the optimized lapping compression force and lapping velocity, an elegant diamond cutting tool oriented along (1 1 0)–(1 0 0) is sharpened. Atomic force microscope (AFM) and scanning electron microscope (SEM) measurement results indicate the cutting-edge radius has been sharpened down to 2∼9 nm, which agrees well with the theoretical predicted value, i.e. 1∼6 nm.

Parameters Optimization on the Lapping Process for Advanced Ceramics by Applying Taguchi Method

The surface quality is a critical factor affecting the performance and reliability of advanced ceramics. This paper focuses on the application of Taguchi method for optimization of advanced ceramics lapping process parameters to obtain the best finish. An optimization experiment for lapping silicon wafer with Al2O3 was designed by Taguchi method. Surface roughness Ra and Rt are considered as criteria for optimization. Influence of parameters involving load, speed, and slurry concentration for a given workmaterial with given abrasive (material and size) are discussed, and the optimum lapping conditions are figured out. Compared with single parameter experimental results, it illustrates that the experiment design based on Taguchi method can successfully applied to determine the optimum processing conditions for advanced ceramics lapping process.