Material removal characteristics of 20CrMnTi steel in single grit cutting

The single grit cutting test was regarded as an important approach for understanding a complex grinding process, and revealed the connection between grinding wheel state, grinding parameters, and the surface integrity of workpieces. To investigate the formation mechanisms and morphology of grinding chips of 20CrMnTi steel, experiments on the high-speed grinding of a single grit on the surface of 20CrMnTi steel were performed by the finite element method. Combining this with the analysis of scratch morphology and the use of the finite element method, the authors showed that the process included sliding friction, ploughing, and produced fragmented, and continuous chips which changed with the cutting depth. Moreover, the distributions of physical quantities including stress, strain, heat, and temperature fields in the three areas subjected to cutting deformation were analyzed in greater detail. Moreover, combined with the deduced theoretical formulae, finite element simulation tests were conducted to analyze the undeformed chip thickness, shear angle, chip shape, strain in the formation process of chips from a single grit grain, and its changes with grinding parameters and the shape of abrasive grains.     

郑州市邙山输水系统改造设计

郑州市柿园水厂的原水由邙山输水系统引黄河水输送供给。邙山干渠是综合性输水系统，经过多年运行使用，其取水口、滩区沉砂池、提升泵站、明渠等均存在不少问题，直接影响了柿园水厂的原水水质和水量，故亟需进行改造。介绍了邙山输水干渠系统的改造设计方案及设计参数，可供类似工程参考。     

Thermal residual stress analysis of coated diamond grits

Residual stresses of coated diamond grits were analyzed by a finite element unit cell model.Diamond grits coated with four types of metals, W, Mo, Ti, and Cr, were considered.The numerical results show that compressive stress occurs in the diamond particles and tensile stress occurs in the metal matrix; compressive stress is concentrated in the diamond sharp comer; interface stresses decrease by more than 1000 MPa with a metal interlayer; plastic deformation of the matrix begins near the sharp comer of diamond grits and extends toward the peripheral zone.Stress concentration dramatically decreases due to plastic deformation of the matrix.The deposition of transition metals on a diamond surface can dramatically promote the adhesion between diamond grits and the metal bond.     

铁基粉末触媒的粒度及其均匀性对合成金刚石的影响

本文利用铁基粉末触媒在国产六面顶压机上进行了金刚石单晶的合成。研究了高温高压条件下（5.7GPa，1370～1650℃），筛分的6种不同粒度（140／170，170／200，200／230，230／270，270／325，325／400）以及未经筛分的混合粒度的铁基粉末触媒生长金刚石的形貌特征。同时研究了粉末触媒粒度均匀性对合成金刚石的影响。结果表明，触媒粒度越均匀，合成金刚石单晶的粒度越集中。触媒粒度以及合成的金刚石晶体分别通过扫描电镜和光学显微镜进行了观测。     

OPTIMIZATION OF DRESSING CONDITIONS FOR A RESIN-BONDED DIAMOND WHEEL BY TOPOGRAPHY ANALYSIS

The macro-geometry (run-out, shape, profile, etc.) and the micro-geometry (density, distribution, and shape of the grains) of a grinding wheel are measured after both truing and dressing. The effectiveness of the truing is studied by analysing the topography of the wheel to characterize the tool and its effect on workpiece surface quality during the grinding process. Using wheel replicas, the surfaces are analyzed with a non-contact interference microscope and the measurements are processed with MountainsMap Software. For different truing and dressing conditions, the dressing efficiency, the grain density, and its effects on the roughness and wear of the wheel in the grinding process are investigated.     

钎焊单层金刚石砂轮关键问题的研究

概述了用活性钎料将金刚石磨料钎焊到钢基体表面制作单层金刚石砂轮，比传统的单层电镀金刚石钞轮具有明显的工艺优势。分析指出了钎焊工艺用现存的关键问题，即如何实现金刚石磨料与合金钎料层高的结合强度，钎料层厚度的均匀性和金刚石磨料的有序排布。给出了可行的解决方案，即利用Ag-Cu-Cr或Ni-Cr等活性钎料与金刚石界面化学反应生成的Cr7C3和Cr23C7，实现钎料层与金刚石间的高强度结合；通过化地貌优化，优化出磨粒排布方式，然后按优化的结果排布磨料。     

ON CUMULATIVE DEPTH OF TOUCH-DRESSING OF SINGLE LAYER BRAZED cBN WHEELS WITH REGULAR GRIT DISTRIBUTION PATTERN

The present work deals with a single layer brazed type cBN grinding wheels, which have been developed in-house. Grits were actively brazed on the working surface of the wheels in a regularly distributed pattern so that it could perform grinding without loading. In general, such a wheel produces substantially high transverse roughness. This happens because of its low active grain density. A touch-dressing technique, developed in-house, has been successfully applied on these brazed wheels so that most of the grits did participate and the average roughness could be brought down to an acceptable magnitude. This work investigated the co-relation between the grit size and cumulative depth of dressing required to achieve an acceptable magnitude of transverse roughness. It was found that the required cumulative depth of dressing was dependent on the size of cBN grits. This paper also shows the effect of gradual touch-dressing on improvement of roughness of the surface ground by such new class of recently developed wheels. Experiments were conducted with microcrystalline cBN grits of three different sizes.     

Effect of abrasive grit shape on polishing of β-Ga2O3(100) substrate

β-Ga₂O₃ can be cleaved easily, where the (100) surface is the main cleavage surface. This surface encounters local stress concentration during ultra-precision machining and is prone to local fragmentation, resulting in formation of micro-cleavage pits. The effects of different abrasive grit shapes on polishing are studied in order to ensure smooth processing of β-Ga₂O₃(100). First, a contact mechanics model for different shapes of abrasive grits and crystal surfaces is established in accordance with the theory of elasticity. Then, the contact mechanism between the abrasive grits and the crystal surfaces is analyzed using a theoretical model. Finally, the feasibility of the theoretical model is verified in experiments. The results show that blunt spherical abrasive grits are more suitable for polishing of β-Ga₂O₃(100) than sharp diamond-shaped abrasive grits. Compared to sharp abrasive grits, the crystal surfaces processed using blunt abrasive grits are smoother, with surface roughness (Ra) of approximately 14 nm. During polishing, the sharp and blunt abrasive grits remove brittle and plastic material, respectively. Therefore, blunt abrasive grits are more suitable for the polishing of β-Ga₂O₃ than sharp abrasive grits.     

砂石过滤器在微灌工程中的应用

砂石过滤器应用于微灌工程中 ,既能提高微灌的农业质量 ,又能保证微灌设备的完好性及良好的使用性 ,减少作物的病虫害发生 ,有利于农业的稳产、增产。     

金属结合层包覆单列磨粒小直径CBN砂轮端面磨削过程研究

金属结合层包覆单列磨粒小直径CBN砂轮在端面磨削过程中突出高度不同的CBN磨粒相继发生后面磨损、切削刃破碎和脱落,产生了砂轮自锐效应。砂轮磨削力呈现低频起伏和高频波动变化的特征,这是由于磨削过程中CBN磨粒后面磨损钝化使磨削力增大以及随后磨钝磨粒破碎变得锐利使磨削力减小的综合作用结果。砂轮磨削过程受到CBN磨粒性能及其切削刃状态的支配,多晶强韧CBN磨粒(BORAZON550,GE产品)耐磨性改善、磨粒微细破碎保持了砂轮的锐利性,延长了单个磨粒服务时间,突出高度不同的磨粒加入磨削过程的批次效应显著,磨削力低频起伏明显,单晶CBN磨粒(BORAZON500,GE产品)破碎范围大有效降低了磨粒切削刃突出高度、新磨粒加入磨削的过程具有连续性,磨削力高频波动明显。