磨料粒度对电镀CBN砂轮磨损影响的有限元仿真分析

以单颗CBN磨粒的磨损为例,对电镀CBN砂轮的磨损进行研究。针对磨削淬硬轴承钢GCr15,将单颗CBN磨粒适当简化成圆锥体,建立楔形滑擦模型,利用Deform 3D软件对单颗CBN磨粒的磨耗磨损进行仿真分析。仿真结果表明:不同粒度磨粒的磨损形式相似,均为前端面磨成弧形月牙洼形,尖端逐渐磨成平台;相同条件下磨粒的最大磨损量随着磨料粒度号的增大而减小。同时也说明了细粒度的电镀CBN砂轮的磨损较小。研究结果对进一步研究电镀CBN砂轮制造工艺有指导意义。     

新型小直径端面CBN砂轮开发及其磨削性能研究

基于电镀小直径端面CBN砂轮磨削沟槽的试验结果,为减小沟槽底面与侧面过渡圆弧半径,开发了一种新型小直径端面CBN砂轮,在试验研究其磨削性能的基础上提出了改善措施,取得了良好的磨削效果。新型端面CBN砂轮加工沟槽的过渡圆弧半径达到0.2mm以下,比电镀CBN砂轮减小60%以上。新型端面CBN砂轮磨削过程中,由于有效CBN磨粒发生的后面磨损及其破碎,使磨粒切削刃凸出高度降低,而砂轮表面所有CBN磨粒均先后依次成为有效磨粒,因此提高单个CBN磨粒的耐磨性和韧性,减小破碎,是提高新型CBN砂轮寿命的有效措施。选用多晶强韧的CBN磨粒(通用电器GE550型产品)使砂轮寿命提高到了原来的6.75倍。     

Grain wear of brazed polycrystalline CBN abrasive tools during constant-force grinding Ti�C6Al�C4V alloy

Constant-force grinding experiments of titanium alloy Ti?C6Al?C4V were carried out with brazed polycrystalline cubic boron nitride (PCBN) abrasive wheel heads. Stock removal and tool wear of PCBN abrasive tools were evaluated by comparison with that of monocrystalline CBN counterparts. Grain wear of the brazed PCBN abrasive tools were examined using optical microscopy and scanning electron microscopy. Fracture mechanism of the PCBN abrasive grains was discussed. The results show that the brazed abrasive tools with PCBN grains give larger stock removal by 25% and the longer service life by 30% than the tools with CBN grains. PCBN abrasive grains have the capability to maintain sharp cutting edges by means of the fracture behavior of microcrystalline CBN particles. In case of strong fixing of the PCBN grains in the Ag?CCu?CTi filler layer, the crack of PCBN abrasive grains are mainly dominated in the intergranular mode dependent upon the joining effects of AlN binder material among the adjacent microcrystalline CBN particles.     

A precision grinding method for screw rotors using CBN grinding wheel

Aiming at the high precision machining of screw rotors, a new grinding method for screw rotors using cubic boron nitride (CBN) grinding wheel is presented in this paper. Small electroplated CBN grinding wheel is firstly used to grind screw rotors. The mathematical model for the axial profiles of CBN grinding wheel is developed based on gear engagement theory. Taking the backlash of screw rotors and the coating thickness of CBN layer into consideration, the modification of the base body of the wheel shape is introduced into the design of the CBN grinding wheel. Wire cut electrical discharge machining low speed (WEDM-LS) was used to machine the base body of the CBN grinding wheel. The formed turning tools of the base body of CBN grinding wheel using WEDM-LS and the wheel shapes of CBN grinding wheel using the formed turning tool were performed. The CBN grinding wheels for the screw rotors were made to verify the validity and effectiveness of the presented method. The electroplated CBN grinding wheels were used to machine the screw rotors, and the machining experiments were performed. The data obtained in the experiments reach the fifth class of Chinese Standard GB10095-88.     

Wear behavior and mechanism of single-layer brazed CBN abrasive wheels during creep-feed grinding cast nickel-based superalloy

Wear behavior and mechanism of single-layer brazed CBN abrasive wheels during creep-feed grinding nickel-based superalloy K424 was investigated. Grinding force and temperature acting on the abrasive wheels were measured. Optical microscopy and scanning electron microscopy were utilized to detect grain protrusion and wheel wear morphology. The normal distribution of the protrusion height of the brazed CBN grains on the wheel surface was determined. The results show that, though the grinding zone temperature is merely about 180°C during creep-feed grinding nickel-based superalloy, the grinding heat still has an important effect on the grain wear owing to the high temperature of the individual grain up to 500–600°C. Wear patterns of brazed wheels are composed of mild wear (attritious wear and grain micro-fracture) and severe wear (grain macro-fracture, erosion of the bonding layer). Strong joining of brazed CBN grains and Ag–Cu–Ti bonding layer improves significantly the resistance to grain pullout.     

感应钎焊温度对立方氮化硼砂轮磨削性能的影响

利用超高频感应钎焊在不同钎焊温度条件下制备立方氮化硼(CBN)砂轮,采用扫描电子电镜（SEM）和能量分散谱仪（EDS）对磨粒表面新生化合物进行观察与分析,并通过与电镀CBN砂轮进行比较,对感应钎焊CBN砂轮的磨削性能进行评价。结果表明：CBN磨粒界面新生化合物主要组成元素有N、B、Ti三种,活性元素Ti发生扩散并与N和B发生化合反应;当感应钎焊温度为940℃时,磨粒表面生成物致密覆盖在表面,且所制备的CBN钎焊砂轮的磨削力和磨削比能较小。在相同磨削用量下,对电镀CBN砂轮和感应钎焊CBN砂轮的磨损形式进行对比分析发现,电镀CBN砂轮的磨损形式为黏附磨损,钎焊CBN砂轮的磨损形式为破碎磨损。     

平面磨削中金刚石砂轮有效磨粒数的研究

采用4个不同排布方式的钎焊金刚石砂轮和1个电镀金刚石砂轮磨削天然黑色花岗石，用薄片热电偶检测磨削弧区温度信号，同时测量了磨床主轴的功率。通过分析温度信号中高频热脉冲的个数，确定金刚石砂轮实际参与磨削的磨粒数量和有效磨粒比，并计算出磨削过程中单颗金刚石磨粒的实际最大切削厚度及其消耗的切削功率。     

Some remarks on the chemical wear of diamond and cubic BN during turning and grinding

Previous experiments using simple grinding wheels consisting of a single layer of cubic boron nitride (CBN) or diamond grits on an electroplated rod have shown that the production of wear flats on the grits leads to an increasing grinding force which eventually results in the destruction of the nib. In one of the present experiments, similar worn areas are observed on the grits in a conventional type grinding wheel. The wear of the flats appears to be similar in type to that observed on the flanks of turning tools fabricated from single crystals of diamond and CBN. Experiments with such turning tools show wide variations in the rates of wear between diamond and CBN and between different difficult metal workpieces. These and previous results imply that the flats are formed by an attritious wear process conditioned by the chemical constitution of the tool, workpiece and environment. Further consideration of these various points should lead to the enhanced performance of diamond and CBN grinding wheels.     

金刚石磨盘磨削的磨粒损伤特性研究

研究了钎焊金刚石磨盘和电镀金刚石磨盘磨削花岗岩的磨粒损伤形式及其与法向磨削力之间的相互关系。实验结果表明，钎焊金刚石磨盘的磨粒损伤形式为磨粒尖端因磨耗变成平台、切削刃破损；电镀金刚石磨盘的磨粒损伤不但具有上述两种形式，同时还有磨粒脱落，因而其使用寿命大为缩短；金刚石磨粒形态对磨削力有较大影响，磨削力的变化加速了磨粒形态的转化。阐述了三种磨粒损伤产生的机理和磨削力变化的成因。     

电镀小直径CBN环形砂轮端面磨削沟槽底面

在对小直径环形砂轮端面磨削沟槽底面过程中的磨粒切屑厚度进行解析的基础上,设计了电镀小直径ＣＢＮ环形砂轮端部结构尺寸,作为提高砂轮寿命的措施,实验分析磨削冷却液供给方式和倾斜砂轮轴磨削法的效果。     

Study on precision grinding of screw rotors using CBN wheel

With increasing demands for high-speed and high-precision machining technology, CBN shape grinding is an effective means in the field of precision machining for screw rotors. Aiming at the high precision machining of screw rotors, a mathematical model for the axial profiles of the CBN wheel for machining screw rotors is developed based on theory of gear engagement. Small electroplated CBN wheel is firstly used to grinding screw rotors. Taking the backlash of screw rotors and the coating thickness of CBN layer into consideration, the modification of the base body of the wheel shape is introduced into the design of CBN wheel. For reducing the tooth profile errors of screw rotors induced by mounting errors and wears of CBN wheel, a mathematical model of the error analyses is established and the influence curves of the profile errors affected by mounting errors and radius error of grinding wheel are proposed. The electroplated CBN wheels for the screw rotors are made to verify the validity and effectiveness of the presented method and the machining experiments were performed. Results of this study reveals that the method proposed in this paper can be used as the precision grinding of screw rotors.     

Understanding the residual stress distribution in brazed polycrystalline CBN abrasive grains

This article investigates the brazing-induced residual stresses in the polycrystalline cubic boron nitride (PCBN) abrasive grains based on finite element simulation. The effects of embedding depth and gap thickness on the residual stress distribution in brazed PCBN grains are discussed. Results obtained show that, compared with the Ag-Cu-Ti alloy joining CBN grains and AISI 1045 steel substrate, the AlN binder materials in the polycrystalline CBN grains always have a greater effect on the brazing-induced residual stresses; meanwhile, large residual tensile stresses usually exist at the interface between the microcrystalline CBN particles and AlN binders. In comparison to the embedding depth, the gap thickness has little influence on the brazing-induced residual stresses. Furthermore, compared with the other embedding depth, in the case of the embedding depth of 40 %, the residual stresses in the brazed PCBN grain are generally the lowest in the grain bottom and the largest in the grain top surface. Finally, the finite element model applied in the current simulation work is validated through measurement experiments of the brazing-induced residual stresses in the monocrystalline CBN grain.     

单层钎焊金刚石砂轮的修整实验研究

为满足单层钎焊金刚石砂轮高效精密加工的性能要求,对磨粒有序排布单层钎焊金刚石砂轮的修整进行了实验研究。采用磨粒有序排布的钎焊金刚石修整工具对钎焊砂轮进行了修整,该修整方法通过修整工具粒度的变化以及修整速比的调整来控制砂轮形貌,从而使氧化锆的磨削表面粗糙度达到了精密加工的水平。对砂轮形貌进行了观测统计,数据表明,砂轮磨粒的等高性得到明显改善且避免了磨粒端部的严重钝化。     

钎焊超硬磨料工具的研究进展

介绍了单层钎焊超硬磨料工具的特点及优势,综述了国内外钎焊金刚石和立方氮化硼(CBN)工具的研究现状和研究成果。在此基础上探讨了磨粒优化排布问题,并展望了钎焊超硬磨料工具的发展前景。     

Sensor elements made of conductive silicone rubber for passively compliant gripper

Grinding is regarded as a special multiple edge cutting process, in which the abrasive grains remove the workpiece material at the microlevel. The grain–workpiece interaction, which resembles the microcutting process, directly modifies the workpiece surface and dominates all the output measures of grinding process. Recently, a virtual single-layer cubic boron nitride (CBN) grinding wheel model is developed by simulating each wheel fabrication step, which makes the estimation of the single grain material removal mode possible in grinding. Therefore, the study of the grain–workpiece interaction through microcutting behavior on the abrasive grains becomes necessary for the quantitative investigation of grinding processes. In this paper, the influence of the grain orientation on the microcutting performance of CBN grains is studied through finite element method (FEM) simulation based on response surface methodology (RSM). The FEM simulation helps in both qualitative and quantitative understanding of microcutting process. And the RSM analysis is proved to be an effective tool for factorial analysis in this paper. The results indicate that the single grain microcutting force is sensitive to the grain wear condition and orientation status, and there exists preferable orientation condition for microcutting with abrasive grains to achieve minimum cutting force.     

Tool wear, chip formation and workpiece surface issues in CBN hard turning: A review

Steel parts that carry critical loads in everything from automotive drive trains and jet engines to industrial bearings and metal-forming machinery are normally produced by a series of processes, including time-consuming and costly grinding and polishing operations. Due to the advent of super-hard materials such as polycrystalline cubic boron nitride (PCBN) cutting tools and improved machine tool designs, hard turning has become an attractive alternative to grinding for steel parts. The potential of hard turning to eliminate the costs associated with additional finishing processes in conventional machining is appealing to industry. The objective of this paper, is to survey the recent research progress in hard turning with CBN tools in regard of tool wear, surface issues and chip formation. A significant pool of CBN turning studies has been surveyed in an attempt to achieve better understanding of tool wear, chip formation, surface finish, white layer formation, micro-hardness variation and residual stress on the basis of varying CBN content, binder, tool edge geometry, cooling methods and cutting parameters. Further important modeling techniques based on finite element, soft computing and other mathematical approaches used in CBN turning are reviewed. In conclusion, a summary of the CBN turning and modeling techniques is outlined and the scope of future work is presented.     

磨削弧区采用径向射流冲击强化换热的试验研究

在分析缓进给磨削烧伤机理的基础上,提出了高压射流冲击强化磨削弧区换热的创新构想,研制了带径向射流的ＣＢＮ 开槽砂轮试验装置,并通过缓进给断续磨削时采用径向射流冲击弧区的磨削试验研究其换热效果。结果表明,射流冲击强化换热技术可有效提高弧区换热效率,在解决难加工材料磨削烧伤方面具有广阔的应用前景。     

钛合金Ti6Al4V高速磨削试验研究

为实现难加工材料钛合金的高效磨削,进一步发挥高速磨削的潜力,开展了钛合金Ti6Al4V高速磨削工艺试验研究,对磨削过程的磨削力、磨削比能以及磨削温度随单颗磨粒最大切屑厚度agmax的变化特征进行了分析。研究结果表明：不同砂轮线速度vs条件下,磨削力、磨削比能及磨削温度三者随单颗磨粒最大切屑厚度agmax变化的特征曲线略有不同,具体表现为,单颗磨粒最大切屑厚度agmax一定条件下,磨削力及磨削比能随着磨削速度的提高呈减小趋势,磨削温度则呈上升趋势,同时钎焊CBN砂轮的磨削力、磨削比能低于陶瓷结合剂及电镀CBN砂轮的磨削力、磨削比能,因此,利用钎焊CBN砂轮磨料有序排布的优势,选择合理的单颗磨粒最大切屑厚度,可在提高砂轮线速度的同时提高进给速度,从而提高磨削效率,实现钛合金的高速高效磨削。     

Improvement in tool life of electroplated diamond tools by Ni-based carbon nanotube composite coatings

Ni-based CNT composite (Ni-CNT) coatings were applied for improving the grain bonding strength of electroplated diamond tools. Further, since it is extremely important for the coatings to have good surface roughness for applications to micro-electroplated diamond tools, ultrasonic-vibration stirring was employed for improving the surface roughness of the coatings. The effects of the amount of CNTs in the plating bath on the hardness and grain bonding strength of Ni-CNT coatings were evaluated. Finally, we evaluated the tool life of microelectroplated diamond tools comprising Ni-CNT coatings as the topcoat layers by conducting experiments involving side machining and hole-drilling. The Vickers hardness of Ni-CNT coatings electroplated in a bath that contained more than 1-g/l CNTs exceeded 500 HV. The grain bonding strength can be improved by codepositing CNTs in Ni coatings and was almost 1.3 times in our estimations. In the case of the side machining of glass plates, electroplated diamond tools composed of the Ni-CNT coatings had a tool life approximately eight times longer than that of normal tools. Moreover, micro electroplated diamond tools also had a longer tool life for drilling holes in fused quartz glass. This represents the first experimental verification of the efficacy of Ni-CNT coatings in improving the grain bonding strength. In this manner, we have demonstrated that Ni-CNT coatings are extremely effective for improving the grain bonding strength of electroplated diamond tools.     

Wear of CBN Tools in Ultra-Precision Machining of STAVAX

CBN cutting tools are widely used in ultra-precision machining of STAVAX (specialized stainless steel) mould inserts for injection moulding of optical lenses. This paper will report on experiments carried out to investigate the wear of CBN tools with different grain sizes and various CBN/TiN ratios in ultra-precision machining of STAVAX. The tool-wear characteristics were observed to be greatly dependent on the tool type, hardness of the STAVAX and cutting parameters used. In the machining of STAVAX with a hardness of 55 HRC, fine-scale cavities were formed on the rake face and as such the surface damage acted like a chip breaker resulting in formation of cracks. While the flank faces of all tool types showed a similar wear resistance, it was observed that a combination of a higher percentage of TiN binder and smaller grain size led to greater wear resistance on the rake face. It was found that the formation of cracks on the rake faces could be prevented by means of either increasing the cutting speed or reducing the hardness of the machined workpiece.