On the formation of a quick-stop chip during single grit grinding

An experimental method is described for the provision of quick-stop chips in an authentic grinding grit-workpiece situation. Metallographical and scanning electron microscopical examinations of the chips have provided information to aid the elucidation of the mechanism of metal removed during grinding with abrasive particles having large negative rake angles.     

Material removal mechanism of precision grinding of soft-brittle CdZnTe wafers

Cd_0.96Zn_0.04Te (111) wafers were precisely ground by #800, #1500, #3000, and #5000 diamond grinding wheel. For comparison, Cd_0.96Zn_0.04Te (110) wafers were machined by lapping, mechanical polishing, and chemical mechanical polishing. High-resolution environmental scanning electron microscopy equipped with energy dispersive spectroscopy and optical interference surface profiler both were employed to investigate the surface quality and material removal mechanism. The results show that the material removal mechanism of #800 grinding wheel is abrasive wear, fatigue wear, and adhesive wear, and that of #1500 is abrasive wear and fatigue wear. Both the material removal mechanism of #3000 and #5000 grinding wheel are abrasive wear, leading to the excellent ductile removal precision grinding. While the material removal mechanism of CMP on CdZnTe wafers is firstly chemical resolving reaction and secondly mechanical carrying action. Moreover, precision grinding exhibits high-efficiency character and eliminates the imbedding of free abrasives of Al₂O₃ and SiO₂.     

基于单颗磨粒的高速外圆磨削成屑机理研究

高速磨削是解决磨削效率和磨削质量完美统一的一种可能途径,但对于高速外圆磨削机理的研究并不多见。基于切削仿真软件,构造了单颗磨粒高速外圆磨削仿真模型,对高速外圆磨削机理进行了仿真试验研究,研究结果表明:钛合金在单颗磨粒高速磨削作用下经历了滑擦→耕犁→成屑→滑擦4种状态变化;工件在磨屑形成之前,力与温度均呈上升趋势,随着工件温度的升高,磨削力出现拐点并急剧下降,成屑过程中磨削温度达到最高值时,磨削力降至最小值。     

Simulation study on chip formation mechanism in grinding particle reinforced Cu-matrix composites

Based on the coupling method of finite element method and smoothed particle hydrodynamics method, the process of single abrasive grain cutting particles reinforced Cu-matrix composites with small volume fraction of particle phase is simulated, and the chip formation mechanism of particle reinforced Cu-matrix composites was analyzed. It can be concluded that the plastic removal of the Cu-matrix is still the main removal form of the composite, but the existence of the reinforced particle phase affects the cutting deformation behavior and the chip morphology. During the cutting process, the interfaces between part of reinforced particles and the Cu-matrix are broken, and resulting in the particles falling off into chips, but most of the particles will form continuous mixed chips with copper alloy, with the plastic deformation of the Cu-matrix. The extrusion of abrasive particles leads to pile-up of dislocation producing in Cu-matrix around the reinforced particle, which interferes with the continuous plastic deformation of Cu-matrix, thus affects the cutting force and cutting temperature of the abrasive grain. The simulation results show that with the increase of cutting speed, the cutting force decreases, but the cutting temperature increases. As the cutting depth increases, the cutting force and cutting temperature increase. The increase of reinforced particle content will lead to the increase of cutting force and cutting temperature.     

超高速磨削切屑去除机理的分子动力学仿真研究

利用分子动力学建立了超高速磨削的物理模型和数学模型,模型包括边界原子层、牛顿原子层和恒温原子层。运用Tersoff势函数对磨粒原子和工件原子之间的相互作用力进行计算。建立了模拟的运动方程,对其进行数值求解,从而获得工件原子变化后的位移和速度。模拟了不同磨削深度下切屑的形成情况。讨论磨削深度对切屑形成过程的影响,研究了超高速磨削冲击成屑的机理。     

Material phase transformation at high heating rate during grinding

The modeling of maraging steel phase transformation in grinding process is presented in this article. Specifically, heating rate and contact zone temperature are examined to quantitatively link material properties, wheel topography characteristics and process parameters to the kinetics of diffusion-controlled transformation and diffusionless transformation. Physics-based modeling and prediction for the volume fractions of phase transformation in continuous heating under anisothermal conditions are developed based upon the addition of volume fractions in sequential segmented isothermal processes of grinding. The predictive model is validated by 18Ni (250) maraging steel grinding experiments, X-ray diffraction measurements and regression analyses. Results are compared to the model predicted of martensite and ferrite phase volume fractions after grinding. The physics-based model is experimentally validated as viable to predict the occurrence and extent of phase transformation related to material properties, wheel topography and grinding thermal-mechanical loading. Finally, correlation analysis is used to quantify the importance of the input variables to both model-predicted and X-ray diffraction measured phase transformation results.     

Characterization of chip formation during machining 1045 steel

A deep understanding of the generation and characterization of chip formation can result for practical advices of chip type controlling in engineering applications. The chip formation is divided into the continuous chip and the serrated one in this study. The characterization of the continuous chip formation is expressed as the chip deformation and that of the serrated chip formation is expressed as the frequency of serration, the degree of segmentation, and the deformation of serrated chip. The chips of 1045 steel under different cutting speeds (100–3,600?m/min) are collected during machining. After inlay and polishing of the collected chips, the chip morphology is observed with VHX-600 ESO digital microscope. It is found that at the cutting speeds of 100–400?m/min, the chip type is continuous, at the cutting speeds of 600–2,200?m/min the chip type is serrated, and at the cutting speeds of 2,500–3,600?m/min the chip type is segmented. The quantitative relations between the characterization parameters of chip formation and the cutting speed are obtained. The chip deformation increases with the cutting speed, and the influence of the cutting speed on the shear strain rate is more sensitive than that on the shear strain during the continuous chip formation. All the characterization parameters including the shear strain rate, the frequency of serration, the degree of segmentation, and the shear strain increase with the cutting speed during the serrated chip formation. The sensitivity of influence of the cutting speed on these parameters is in the following: the shear strain rate, the degree of segmentation, the frequency of serration, and the shear strain.     

Surface formation and damage mechanisms of nano-ZrO2 ceramics under axial ultrasonic-assisted grinding

Journal of Mechanical Science and Technology - In this study, the surface formation and damage mechanism of hard-brittle materials in axial ultrasonic-assisted grinding (AUAG) were revealed using...     

Morphology evolution and micro-mechanism of chip formation during high-speed machining

In this paper, the morphology and micro-mechanism of chip formation during high-speed machining aluminum alloy 7050-T7451 is investigated based on the combination of dislocation theory and plastic deformation theory. Experiments of quick stop stoppage for turning and special method (Buda) for milling process were carried out in order to obtain shear angle in different cutting speeds. The results show that effective flow stress and temperature in front edge zone is higher and more concentrated than that in other deformation zones. The shear front-lamellar structure was observed and analyzed in the front edge zone which influences the chip formation directly. The influence of cutting speed on chip formation was analyzed by simulation and experiments. Cutting speed is an important factor affecting the morphology evolution and chip formation. When the cutting speed is below 1500 m/min, the concentration of shear stress and the shear front-lamella structure of cutting deformation are more remarkable and easier for forming continuous ribbon chips. With the cutting speed increase, the ribbon chip transforms into serrated chip when a critical cutting speed (2500 m/min) is reached. Finally, microscopic mechanism of chip formation has been revealed and critical condition of the shear front—the layer structure formation—has been determined.     

负前角磨粒磨削过程磨屑形成的有限元仿真分析

磨削过程是由成千上万个磨粒的微小切刃完成的,实验观察和分析磨削过程十分困难.运用有限元法对负前角磨粒的磨削过程进行仿真,分析负前角磨粒磨削时的成屑机理,并将各仿真结果进行比较分析.结果显示,磨粒以小负前角和大负前角磨削时的成屑机理并不相同,与小负前角相比,大负前角磨削时,剪应变、最大等效塑性应变和模型应变能都较大;与前角为正和小负前角时最高温度出现在前刀面上距刀尖一定距离处不同,大负前角时最高温度出现在刀尖和工件接触处.所得结果可为砂轮修整、磨削表面质量研究提供理论依据.     

Study on formation mechanisms of serrated chip based on valence electron structure

Abstract

High-speed machining experiment of pure copper and aluminum bronze (QAl9-4) is carried out at the same cutting condition to obtain the different chips. The valence electron structure (VES) parameters that affect adiabatic shearing sensitivity were studied in this paper. The results show the bond energy and lattice electron number are related to adiabatic shearing sensitivity. Adiabatic shearing sensitivity increases with the increase of bond energy, and the decrease of lattice electron number. For pure copper, the bond energy is smaller and the lattice electron number is higher, so its adiabatic shearing sensitivity is low. The shape of chip is approximate ribbon. For aluminum bronze (QAl9-4), the bond energy is increased and the lattice electron number is decreased due to aluminum (Al) addition, so its adiabatic shearing sensitivity is higher than that of pure copper. The serrated chip divided uniformly by Adiabatic Shear Band (ASB) was formed. The basis can be provided for optimizing process parameters, improving and selecting materials with different cutting performance by studying the specific alloy elements on the influence of adiabatic shearing sensitivity to predict the chip morphology to some extent in VES level.     

3D metal removal simulation to determine uncut chip thickness, contact length, and surface finish in grinding

The two most important geometric parameters that describe the mechanics of grinding are the uncut chip thickness and the contact length. Currently, analytical approaches are used to estimate these parameters. The accuracy of these approaches, however, is limited because they do not take into account the random shape, size, and protrusion height and placement of the abrasive grains around the circumference of the grinding wheel. In this paper, a simulation technique was used to gain new insight into the effect of the stochastic nature of grinding wheels on the geometric properties of the grinding process. The simulator was used to calculate the number of active grains, uncut chip thickness, and contact length for a stochastic wheel model of Radiac Abrasive’s WRA-60-J5-V1 grinding wheel. These values were then mapped to every grain on the grinding wheel and used to determine the instantaneous material removal rate of the wheel and workpiece surface finish. There was excellent agreement between the predicted and experimentally measured surface topology of the workpiece. The results suggest that only 10–25 % of the grains on the grinding wheel are active and that the average grinding chip may be as much as ten times thicker and ten times shorter than would be produced by a grinding wheel with a regular arrangement of cutting edges as assumed by existing analytical approaches.     

Material removal mechanism of silicon nitride during rubbing in water

The material produced at the friction interface and the material removal mechanism were investigated for the rubbing of silicon nitride in water. The material removal rate estimated by the contact time of the specimen was constant at all rubbing speeds, which suggested that the material removal mechanism was attributable to the chemical reaction at the rubbing interface. The analytical results from the ion microprobe analysis spectra indicated that many ions of silicon with hydrogen and oxygen remained on the polished surface. Also, the rubbing remnants in the water were shown to be an amorphous material and were converted into α-cristobalite (SiO₂) by a heat treatment in air at 1170 K for 1 h. These results suggested that the oxidized silicon nitride was changed by friction to an amorphous hydrate SiO₂·xH₂O during rubbing in water and, after that, the amorphous hydrate was removed from the rubbing interface.     

Modeling of metal removal during an internal grinding in view of kinematics cutting features

A new model of the metal removal in internal grinding permits calculation of the margin actually removed, the internal radius, the time for complete removal of the margin, and other parameters. In the model, the metal removal is determined with specified machining parameters; elastic deformation and the cutting kinematics are taken into account. The calculation is based on the model of the cutting force in internal grinding, which covers most of the factors affecting the cutting force (such as changes in the programmed and actual radial supply, the mechanical properties of the workpiece, the geometry of the wheel–workpiece contact zone, the wheel characteristics, and the blunting of the abrasive grains). Types of wheel–workpiece contact with inclination of the wheel axis on account of elastic deformation of the system are noted.     

Direct examination of chip formation during metal machining by scanning electron microscopy

New insights into the mechanics and morphology of chip formation in metal cutting have been obtained by direct observation of an orthogonal cutting process in progress in a scanning electron microscope. A specimen stage specifically designed for this purpose is described. This stage permits dynamic viewing of all accessible areas of interest at magnifications up to ×5000 during cutting. Permanent records are obtained by videotaping each experiment. A brief summary of results is given, and extensions of the technique of dynamic scanner observation are suggested.     

有机磨削液在氮化硅陶瓷磨削过程中的清洗机理研究

通过一系列试验考察了不同有机物的乳液作为冷却液时金刚石砂轮磨削氮化硅陶瓷的堵塞效果.试验结果表明:短链有机物及烷烃作为磨削液时,金刚石砂轮磨削氮化硅陶瓷会发生堵塞,而包含较强极性基团的长链有机物可以很大程度地降低砂轮堵塞.其原因是烷烃在氮化硅陶瓷表面形成的非极性油膜对非极性的氮化硅磨屑产生较强的吸引而聚集在磨削区,进而导致砂轮堵塞.油膜表面具有一定的极性可以很大程度地缓解磨屑的积聚并降低堵塞现象的发生.通过对几种极性有机物的清洗效果进行分析,探讨了有机物的分子结构特征与其清洗性能的关系.     

Reduced models of grinding wheel topography and material removal to simulate dynamical aspects in grinding

Increasing competition and short product life cycles make it necessary to optimize and evaluate the outcome of manufacturing processes. In tool grinding, models for the final workpiece geometry and cutting forces are of particular interest. To establish a valid general grinding model, we investigated the cutting process and the influence of local grinding wheel engagements on the material removal. We consequently developed models of material removal and grinding wheel topography, which capture the main correlations in grinding. In combination, temporal cutting forces and final workpiece geometry are predictable and are in excellent agreement with experimental data. The introduced models are valid for grinding in general, since they are solely based on the geometry and process parameters, and hence are applicable for manufacturing process optimization.