Stress-Induced Deformation of Thin Copper Substrate in Double-Sided Lapping

Double-sided lapping is an precision machining method capable of obtaining high-precision surface.However,during the lapping process of thin pure copper substrate,the workpiece will be warped due to the influence of residual stress,including the machining stress and initial residual stress,which will deteriorate the flatness of the workpiece and ultimately affect the performance of components.In this study,finite element method(FEM)was adopted to study the effect of residual stress-related on the deformation of pure copper substrate during double-sided lapping.Considering the initial residual stress of the workpiece,the stress caused by the lapping and their distribution characteristics,a prediction model was proposed for simulating workpiece machining deformation in lapping process by measuring the material removal rate of the upper and lower surfaces of the workpiece under the corresponding parameters.The results showed that the primary cause of the warping deformation of the workpiece in the doublesided lapping is the redistribution of initial residual stress caused by uneven material removal on the both surfaces.The finite element simulation results were in good agreement with the experimental results.

Strengthening strategy for high-performance friction stir lap welded joints based on 5083 Al alloy

During aircraft,ship,and automobile manufacturing,lap structures are frequently produced among Al alloy skins,wall panels,and stiffeners.The occurrence of welding defects severely decreases mechanical properties during friction stir lap welding(FSLW).This study focuses on investigating the effects of rotation rate,multipass welding,and cooling methods on lap defect formation,microstructural evolution,and mechanical properties.Hook defects were eliminated by decreasing welding speed,applying two-pass FLSW with a small welding tool,and introducing additional water cooling,thus leading to a remarkable increase in effective sheet thickness and lap width.This above strategy yielded defect-free joints with an ultrafine-grained microstructure and increased tensile shear force from 298 to 551 N/mm.The fracture behavior of FSLW joints was systematically studied,and a fracture factor of lap joints was proposed to predict their fracture mode.By reducing the rotation rate,using two-pass welding,and employing additional water cooling strategies,an enlarged,strengthened,and defect-free lap zone with refined ultrafine grains was achieved with a quality comparable to that of lap welds based on 7xxx Al alloys.Importantly,this study provides a valuable FSLW method for eliminating hook defects and improving joint performance.

Bulging Distortion of Austenitic Stainless Steel Sheet on the Partially Penetrated Side of Non-Penetration Lap Laser Welding Joint

Non-penetration laser welding of lap joints in austenitic stainless steel sheets is commonly preferred in fields where the surface quality is of utmost importance.However,the application of non-penetration welded austenitic stainless steel parts is limited owing to the micro bulging distortion that occurs on the back surface of the partial penetration side.In this paper,non-penetration lap laser welding experiments,were conducted on galvanized and SUS304 austenitic stainless steel plates using a fiber laser,to investigate the mechanism of bulging distortion.A comparative experiment of DC01 galvanized steel-Q235 carbon steel lap laser welding was carried out,and the deflection and distortion profile of partially penetrated side of the sheets were measured using a noncontact laser interferometer.In addition,the cold-rolled SUS304 was subjected to heat holding at different temperatures and water quenching after bending to characterize its microstructure under tensile and compressive stress.The results show that,during the heating stage of the thermal cycle of laser lap welding,the partial penetration side of the SUS304 steel sheet generates compressive stress,which extrudes the material in the heat-affected zone to the outside of the back of the SUS304 steel sheet,thereby forming a bulge.The findings of these experiments can be of great value for controlling the distortion of the partial penetrated side of austenitic stainless steel sheet during laser non-penetration lap welding.

Anti-reverse rotation startup method for sensorless brushless DC motor

In order to start up the brushless DC motor （BLDCM） without reverse rotation and smoothly switch the running state of the motor, a novel startup and smoothly switching method for a sensodess BLDCM is presented. Based on the saturation effect of the stator iron, six short voltage pulses are applied to determine the initial rotor position and the rotor can be found within 60°. After that, a series of short and long voltage pulses are used to accelerate the motor and the variation of the response current is utilized to detect the rotor position dynamically. When the motor reaches a certain speed at which the back-electromotive force （EMF） method can be applied, all the power devices are turned off and the running state of the motor is smoothly switched at the moment determined by the relationship between the terminal voltage waveform and the commutation phases. The experimental results verify the feasibility and validity of the proposed method.

Damage mechanisms during lapping and mechanical polishing CdZnTe wafers

CdZnTe wafers were machined by lapping and mechanical polishing processes,and their surface and subsurface damages were investigated.The surface damages are mainly induced by three-body abrasive wear and embedded abrasive wear during lapping process.A new damage type,which is induced by the indentation of embedded abrasives,is found in the subsurface.When a floss pad is used to replace the lapping plate during machining,the surface damage is mainly induced by two-body abrasive and three-body abrasive wear,and the effect of embedded abrasives on the surface is greatly weakened.Moreover,this new damage type nearly disappears on the subsurface.

Optimization experiment on eccentric lapping of cylindrical rollers

Cylindrical rollers are important elements of bearings,and their machining accuracy and consistency affect the bearing quality.Using a GCr15 cylindrical roller ofФ11×12 as the processing object in this study,the effects of loading pressure,abrasive concentration,and speed combination on cylindrical roller machining precision were investigated using the orthogonal experimental design method on a double-side eccentric pendulum lapping and polishing machine.The machining parameters of the lapping stage were optimized,and the lapping optimal process parameters were determined by S/N response analysis and analysis of variance(ANOVA).The results show that when the experiment was optimized using loading pressure of 10 N/roller,abrasive concentrationof 20.0 wt%,and rotational speed combination,the material removal rate(MRR)of cylindrical roller reached 0.0896μm/min;the average roughness of the batch decreased from 0.056μm to 0.027μm,51.8%lower than the original batch average roughness,and the deviation decreased from the initial 0.022μm to 0.014μm;the batch average roundness error decreased from 0.47μm to 0.28μm,40.4%lower than the original batch average roundness error,and the deviation decreased from the initial 0.19μm to 0.038μm;and the batch average diameter variation decreased from 4.5μm to about 3.6μm,20%lower than the original batch average diameter variation.The double-side eccentric lapping of cylinder rollers does not only lead to improvement in the surface quality and shape accuracy of rollers,but also improvement in the batch consistency.

Modeling and Validation of Indentation Depth of Abrasive Grain into Lithium Niobate Wafer by Fixed-Abrasive Lapping

The prediction of indentation depth of abrasive grain in hydrophilic fixed-abrasive(FA)lapping is crucial for controlling material removal rate and surface quality of the work-piece being machined.By applying the theory of contact mechanics,a theoretical model of the indentation depth of abrasive grain was developed and the relationships between indentation depth and properties of contact pairs and abrasive back-off were studied.Also,the average surface roughness(Ra)of lapped wafer was approximately calculated according to the obtained indentation depth.To verify the rationality of the proposed model,a series of lapping experiments on lithium niobate(LN)wafers were carried out,whose average surface roughness Ra was measured by atomic force microscope(AFM).The experimental results were coincided with the theoretical predictions,verifying the rationality of the proposed model.It is concluded that the indentation depth of the fixed abrasive was primarily affected by the applied load,wafer micro hardness and pad Young′s modulus and so on.Moreover,the larger the applied load,the more significant the back-off of the abrasive grain.The model established in this paper is helpful to the design of FA pad and its machining parameters,and the prediction of Ra as well.

MINITYPE MACHINING SYSTEM FOR DIAMOND LAPPING & POLISHING BY USING BRUSHLESS DIRECT CURRENT MOTOR AS PRECISE SPINDLE

A minitype precise spindle system which can machine precisely and stably in the process of diamond lapping and polishing is designed. In such minitype spindle system, the brushless DC spindle motor is used to drive the lapping finish table, which is built with fluid dynamic bearings. Some measures have been taken to make the lapping system dynamic balance, and a servo controller which can adjust the speed of motor from 1200 r/min to 5400 r/min is designed. Experiments show that the spindle system is reliable and stable for diamond polishing, and the detection results by atomic force microscope（AFM） show that the surfaces of diamond edge＇s Ra is 6.725 nm and whole diamond average Ra is 3.25 nm.

High Speed Lapping of SiC Ceramic Material with Solid (Fixed) Abrasives

An experimental investigation is carried out to machine SiC ceramic material through the method of high speed plane lapping with solid(fixed) abrasives after the critical condition of brittle-ductile transition is theoretically analyzed. The results show that the material removal mechanism and the surface roughness are chiefly related to the granularity of abrasives for brittle materials such as SiC ceramic. It is easily realized to machine SiC ceramic in the ductile mode using W3.5 grit and a high efficiency, low cost and smooth surface with a surface roughness of R_a 2.4?nm can be achieved.

EFFECT OF LAP SURFACE PROFILE ON LAPPING EFFICIENCY

To meet the requirements of improving the efficiency in lapping operat ion, the effect of lap surface profile on the efficiency is analyzed theoretical ly and an experimental study is carried out on lapping of Mn Zn ferrite. It is f ound that the profile of lap surface affects significantly the efficiency by mea ns of its capacity to keep loose grains and fixed grains during lapping, and tha t the efficiency can be increased by several times by using a lap with proper surface profile, while the same work surface roughness can be finally obtained.

CVD Micro-diamond Coated Tool Lapping with Sapphire Wafer

Micro-diamond films were prepared on YG6 substrate by hot filament chemical vapor deposition method.An innovative micro-diamond coated tool was used to the lap sapphire wafer.The effect of load,rotating speed,and lapping time on material removal rate(MRR)and surface roughness was investigated.The results showed that the best process parameters were 3N,100r/min and 15 min.The surface quality of sapphire improved significantly after lapping.The coating after lapping adhered well and did not show any peeling.The innovative micro-diamond coated tool was feasible and suitable for the lapping of the single crystal sapphire wafer.

Finite Element Analysis for Grinding and Lapping of Wire-sawn Silicon Wafers

Silicon wafers are the most widely used substrates for semiconductors. The falling price of silicon wafers has created tremendous pressure on silicon wafer manufacturers to develop cost-effective manufacturing processes. A critical issue in wafer production is the waviness induced by wire sawing. If this waviness is not removed, it will affect wafer flatness and semiconductor performance. In practice, both lapping and grinding have been used to flatten wire-sawn wafers. Although grinding is not as effective as lapping in removing waviness, it has many other advantages over lapping (such as higher throughput, fully automatic, and more benign to environment) and has great potential to reduce manufacturing cost of silicon wafers. This paper presents a finite element analysis (FEA) study on grinding and lapping of wire-sawn silicon wafers. An FEA model is first developed to simulate the waviness deformation of wire-sawn wafers in grinding and lapping processes. It is then used to explain how the waviness is removed or reduced by lapping and grinding and why the effectiveness of grinding in removing waviness is different from that of lapping. Furthermore, the model is used to study the effects of various parameters including active-grinding-zone orientation, grinding force, waviness wavelength, and waviness height on the reduction and elimination of waviness. Finally, the results of pilot experiments to verify the model are discussed.

Subsurface Damage of Monocrystalline Germanium Wafers by Fixed and Free Abrasive Lappings

The subsurface damage(SSD)layers of monocrystalline germanium wafers lapped by three different ways were measured and compared by the method of nanoindentation and micro morphology.Three ways such as ice-fixed abrasive,thermosetting fixed abrasive and free abrasive lappings are adopted to lap monocrystalline germanium wafers.The SSD depth was measured by a nanoindenter,and the morphology of SSD layer was observed by an atomic force microscopy(AFM).The results show that the SSD layer of monocrystalline germanium wafer is mainly composed of soft corrosion layer and plastic scratch and crack growth layer.Compared with thermosetting fixed abrasive and free abrasive lappings,the SSD depth lapped with ice-fixed abrasive is shallower.Moreover,the SSD morphology of monocrystalline germanium wafer lapped with ice-fixed abrasive is superior to those of two other processing ways.

ANALYSIS ON LAPPING AND POLISHING PRESSURE DISTRIBUTION OF HARD MAGNETIC DISK SUBSTRATE

The contact model of lapping and polishing for magnetic disk substrate is presented. Based on elastic contact theory, pressure distribution for this model are analyzed. Further, the effects of various parameters, such as the material properties of the PVA(polyvinyl acetate),grinding stone, the polishing pad and the base plate, the thickness of the pad or the stone on the pressure distribution have been discussed.

DISCUSSING ON SOLID ABRASIVE LAPPING PATH

Relative motion path between lapping tool and workpiece in plane solid abrasive lapping is dis- cussed and its path model is set up. The paths simulate. by this model are compared with the one got in experiments. The changing relationship of workpiece rotating speed with the main spindle rotating speed and eccentricity is also discussed.

A Research on the UItrasonic Vibration Lapping of Natural Diamond Tools

This paper deals with a new technology for the manufacturing of natural diamond cutting tools. In order to raise the efficiency of lapping natural diamonds, the ultrasonic vibration technology is applied to the lapping process. The experimental resykts show that ultrasonic vibration lapping can greatly raise the abrasion value of diamonds. The efficiency of ultrasonic vibration lapping is 2-3 times higher than that of conventional lapping. Besides, the mechanism of why the abrasion value of diamonds in ultrasonic vibration lapping is high is also discussed in the paper.

Correlation between the Surface Quality and the Lapping Parameters in Loose Abrasive Lapping

As one of the basic finishing operations,loose abrasive lapping is widely used in the surface finishing on metallic parts,non-metallic components,and engineering ceramics.During lapping,lapping parameters have a great influence on surface quality of machined workpiece.In order to provide an experimental basis for the selection of lapping parameters,effects of some important variables such as abrasive size,lapping load,and lapping speed,on surface roughness and residual surface stress of high speed steel workpiece via loose abrasive lapping were discussed in this paper.The results show that the work surface roughness increases with the increasing of abrasives size or decreasing lapping load,and does not change obviously with the lapping speed.Lapping can cause residual compressive stress in the surface layer of lapped workpiece,and the magnitude of residual surface stress becomes larger with increasing abrasive size,lapping load,and lapping speed.

Comprehensive study of microstructure and mechanical properties of friction stir welded 5182-O/HC260YD+Z lap joint

The welding of aluminum(Al)and steel has attracted more and more interest due to the weight reduction trend in vehicle and aerospace manufacturing industries.5182-O/HC260YD+Z lap joint was produced by friction stir welding(FSW),and the microstructure and mechanical property of the joint were systemically characterized.The microstructure in horizontal direction of the Al and steel near interface was similar to their corresponding conventional friction stir welded joint.The joint was divided into stir zone of Al(ST-Al),stir zone of interface(ST-I),thermal-mechanically affected zone of steel(TMAZ-Fe)and base material of steel(BM-Fe)according to their distinct microstructure vertically.Three kinds of intermetallic compounds(IMCs)of FeAl_(3),FeAl and Fe_(3)Al were formed at the interface.The horizontal micro hardness distribution exhibited a hat shape and“M”shape in Al and steel,respectively.The hardest region of the joint was located at the ST-I,with a hardness of 175 HV−210 HV.The joint was fractured along the hook structure,with an average shear strength of 73.9 MPa.Fractural morphology of Al and steel indicted a cleavage fracture mode.

基于LAPS资料的一次江西连续性暴雨过程分析

利用LAPS资料,结合地面和高空常规观测资料、雷达资料,从环流背景、影响系统、物理量场等方面对2013年6月27—29日连续性暴雨过程进行分析,得出结论:(1)LAPS输出的产品时效性好,分辨率高,产品多样化,更好地丰富了对天气过程分析的方法,对中尺度天气具有非常明确的解释能力,有利于从更深层次分析天气发生的成因;(2)高纬有阻高建立,低纬度地区受南亚高压控制,系统稳定少动,中纬度地区不断有短波槽东移,引导冷空气南下,副高西北侧强盛的西南气流将暖湿空气源源不断地输入江西中北部,在此形成冷暖交汇,稳定的形势有利于形成连续性暴雨天气;(3)副高西北侧的强西南急流中,风向风速在江西中北部辐合,为强降水提供了抬升条件,并且急流的脉动与降水强度的变化有着密切关系,强降水往往出现在凌晨前后,下午至晚上逐渐减弱。