Grinding Characteristics of MoS_(2)-Coated Brazed CBN Grinding Wheels in Dry Grinding of Titanium Alloy

As an important green manufacturing process,dry grinding has problems such as high grinding temperature and insufficient cooling capacity.Aiming at the problems of sticking and burns in dry grinding of titanium alloys,grinding performance evaluation of molybdenum disulfide(MoS_(2))solid lubricant coated brazed cubic boron carbide(CBN)grinding wheel(MoS_(2)-coated CBN wheel)in dry grinding titanium alloys was carried out.The lubrication mechanism of MoS_(2)in the grinding process is analyzed,and the MoS_(2)-coated CBN wheel is prepared.The results show that the MoS_(2)solid lubricant can form a lubricating film on the ground surface and reduce the friction coefficient and grinding force.Within the experimental parameters,normal grinding force decreased by 42.5%,and tangential grinding force decreased by 28.1%.MoS_(2)lubricant can effectively improve the heat dissipation effect of titanium alloy grinding arc area.Compared with common CBN grinding wheel,MoS_(2)-coated CBN wheel has lower grinding temperature.When the grinding depth reaches 20μm,the grinding temperature decreased by 30.5%.The wear of CBN grains of grinding wheel were analyzed by mathematical statistical method.MoS_(2)lubricating coating can essentially decrease the wear of grains,reduce the adhesion of titanium alloy chip,prolong the service life of grinding wheel,and help to enhance the surface quality of workpiece.This research provides high-quality and efficient technical support for titanium alloy grinding.

THE EFFECT OF THE CBN WHEEL DRESSING AND THE GRAIN HEIGHT PROTRUDING FROM THE BOND ON THE GRINDING PERFORMANCE

CBN (Cubic Boron Nitride) is a highly efficient abrasive and has unique properties (highhardness, high thermal stability and high chemical inertia). As early as 1969 CBN Wheels had al-ready been made and showed excellent performance for grainding high speed steels and othermaterials hard to be ground. So far, however, CBN Wheels are still not popularly utilized in theindustry, the writer considers the main reason being the inadequate study for practical applica-tions and especially the suitable dressing technique. The dressing of resinoid CBN Wheels discussed in the paper, is different from that ofconventional ones. It has to be divided into two operations, truing and sharpening, each of whichhas its specific and independent functions. A simple dressing method with a lot of informationsuitable for production is studied; finally, the grain height protruding from the bond is taken asan index for evaluating the dressing results, and the effect of grain height on the grinding per-formance is discussed. By selecting proper conditions according to the workpiece requirements, abetter technical and economical benifit can be obtained.

APPLICATION OF CBN WHEEL IN CONSTRAININGWORKPIECE BURNING DURING CREEP FEEDGRINDING OF TITANIUM ALLOY

The burning mechanism during creep feed grinding of titanium alloy with SiC wheel is stud- ied. A CBN intermittent creep feed grinding technology combining the advantages of CBN, intermittent grinding and creep feed grinding is recommended. The results show that the intermittent CBN wheel has a bright future in resolving the problem of workpiece burning during creep feed grinding of titanium al- loys

EXPERIMENTAL RESEARCH ON SLOTTED & PERFORATED ELECTROPLATED CBN GRINDING WHEEL WITH RADIAL JET

A creative conception is proposed to enhance heat transfer in grinding contact zone through jet impinging on the basis of analysis on the mechanism of burn during creep feed grinding, and a new apparatus of slotted & perforated electroplated CBN grinding wheel with radial jet is developed, the effect on heat transfer is studied through the experiment of intermitted creep feed grinding. Experimental results show that the technology of enhancing heat transfer through jet impinging is valid to raise the efficiency of heat transfer in grinding contact zone and it is widely applied to solve the problem in grinding burn for difficult to machine materials.

Design and grindability assessment with cup shaped electroplated CBN wheel grinding turbine disc slots of powder metallurgy superalloy FGH96

The machining surface integrity of aero-engine turbine disc slots has a significant impact on their fatigue life and service performance,and achieving efficiency and high-precision machining is still a great challenge.The high machining requirements of future aeroengine turbine disc slots will be difficult to satisfy using the broaching method.In addition,existing methods of slot machin-ing face difficulties in ensuring surface integrity.This study explored a cup shaped electroplated Cubic Boron Nitride(CBN)abrasive wheel for profile grinding the turbine disc slots of FGH96 powder metallurgy superalloy.The matrix structure of the cup shaped abrasive wheel was designed and verified.A profile grinding experiment was conducted for fir-tree slots on a five-axis machining center.The accuracy and the surface integrity were analyzed.Results show that the key dimension detection results of the slots were within the allowable tolerance range.Meanwhile,an average sur-face roughness Ra of 0.55μm was achieved,the residual stress was compressive,the plastic defor-mation layer thickness was less than 5μm,and the hardening layer thickness was less than 20μm.The research findings provide a new approach to machining the slots of aviation engine turbine discs and guidance for the high-quality processing of complex components.

Investigation on induction brazing of profiled cBN wheel for grinding of Ti-6Al-4V

Profiled monolayer cBN wheel was induction brazed for grinding of titanium dovetail slot in this study.Aimed at acquiring a uniform temperature distribution along the profiled surface and reducing the thermal deformation of the brazed wheel,a finite element model was established to investigate the temperature uniformity during induction brazing.A suitable induction coil and the related working parameters were designed and chosen based on the simulation results.Ag-Cu-Ti alloy and cBN grains were applied in the induction brazing experiment.The results showed geometric deformation of the brazed wheel was no more than 0.01 mm and chemical reaction layer were found on the brazed joint interface.Further validation tests were carried out by grinding of Ti-6 Al-4 V alloy.Compared to the electroplated wheel,the brazed wheel showed better performance such as low specific grinding energy and good ground quality in grinding of Ti-6 Al-4 V alloy.Abrasion wear was found to be the main failure mode for the induction brazed wheel,while adhesion and grains pull-out were the main failure mode for the electroplated wheel.

STUDY FOR INCREASING ACCURACY OF INTERNAL CYLINDRICAL GRINDING

Internal cylindrical grinding is much more difficult than other grindings, because of its lowproductivity and poor quality, e. g. taper often occurs in hole after grinding, which has an effect onthe service life of the workpiece. It is a pity that internal cylindrical grinding is rarely studied. Inthis paper. aimed at the above conditions, factors affecting the accuracy of internal cylindricalgrinding are theoretically analyzed. The roller shell of the ring spinning frame(as mass part)aretaken as an example, of which internal cylindrical grinding tests are made. Tests show that thetheory conforms with practice.

Comparative investigation on high-speed grinding of TiCp/Ti–6Al–4V particulate reinforced titanium matrix composites with single-layer electroplated and brazed CBN wheels

In order to develop the high-efficiency and precision machining technique of TiCp/Ti - 6Al-4V particulate reinforced titanium matrix composites （PTMCs）, high-speed grinding experiments were conducted using the single-layer electroplated cubic boron nitride （CBN） wheel and brazed CBN wheel, respectively. The comparative grinding performance was studied in terms of grinding force, grinding temperature, grinding-induced surface features and defects. The results display that the grinding forces and grinding temperature obtained with the brazed CBN wheel are always lower than those with the electroplated CBN wheel. Though the voids and microcracks are the dominant grinding-induced surface defects, the brazed CBN wheel produces less surface defects compared to the electroplated wheel according to the statistical analysis results. The max mum materials removal rate with the brazed CBN wheel is much higher than that with the electroplated one. All above indicate that the single-layer brazed CBN super-abrasive wheel is more suitable for high-speed grinding of PTMCs than the electroplated counterpart.

Prediction on grinding force during grinding powder metallurgy nickel-based superalloy FGH96 with electroplated CBN abrasive wheel

In this article,a grinding force model,which is on the basis of cutting process of single abrasive grains combined with the method of theoretical derivation and empirical formula by analyzing the formation mechanism of grinding force,was established.Three key factors have been taken into accounts in this model,such as the contact friction force between abrasive grains and materials,the plastic deformation of material in the process of abrasive plowing,and the shear strain effect of material during the process of cutting chips formation.The model was finally validated by the orthogonal grinding experiment of powder metallurgy nickel-based superalloy FGH96 by using the electroplated CBN abrasive wheel.Grinding force values of prediction and experiment were in good consistency.The errors of tangential grinding force and normal grinding force were 9.8%and 13.6%,respectively.The contributions of sliding force,plowing force and chip formation force were also analyzed.In addition,the tangential forces of sliding,plowing and chip formation are 14%,19%and 11%of the normal forces on average,respectively.The pro-posed grinding forcemodel is not only in favor of optimizing the grinding parameters and improving grinding efficiency,but also contributes to study some other grinding subjects(e.g.abrasive wheel wear,grinding heat,residual stress).

造孔剂对陶瓷结合剂CBN砂轮组织结构及性能的影响

为研究不同造孔剂对陶瓷结合剂CBN砂轮组织结构及性能的影响,在一定条件下,制备添加不同造孔剂的陶瓷结合剂CBN砂轮试样,对其进行抗折强度、抗冲击强度和气孔率的分析,并对其进行磨削实验。结果表明:同等条件下,添加玻璃空心球的CBN试条气孔率最高,抗折强度和抗冲击强度下降程度较小,兼顾了强度和锋利性的两方面要求;通过磨削实验得到,当加入体积分数约20%的玻璃空心球时,砂轮磨削时的功率最小,同时能得到粗糙度低、表面质量优异的工件。

陶瓷CBN砂轮的研究进展

陶瓷CBN砂轮在成形加工和精密加工等领域广泛应用,对其进行研究在提高工件加工质量和加工效率方面具有重要意义。分别从CBN磨粒、改性剂的添加、陶瓷CBN砂轮的制备和磨削性能方面,综述近些年陶瓷CBN砂轮的研究进展,并对其未来发展前景进行展望。在CBN磨粒方面,论述了CBN单晶的合成,介绍了CBN磨粒表面处理和加入强磁场时的处理方式;对于改性剂,分别论述了成孔剂、氧化物、金属物质、纳米材料的添加对陶瓷CBN砂轮性能的改善;在陶瓷CBN砂轮制备方面,介绍了其成形和烧结的方法。此外,还介绍了陶瓷CBN砂轮在钢类材料、镍基合金、钛合金等难加工材料上的磨削加工应用,并提出影响其磨削性能的因素。

基于Shannon熵与声发射信号的CBN砂轮性能监测方法研究

为了在磨削加工过程中能够有效判别CBN(Cubic Boron Nitride)砂轮的磨削性能,提出了一种基于Shannon熵理论与声发射信号的CBN砂轮性能监测方法。首先,利用声发射传感器采集CBN砂轮磨削加工过程中的声发射信号,基于最大信息熵对CBN砂轮磨削加工过程中的声发射信号进行概率密度估计,获得磨削加工过程中声发射信号的最大熵概率密度分布。然后,通过分析研究CBN砂轮在修整过后循环磨削以及不同直径剩余磨削时的声发射信号特征,根据交叉熵原理分析CBN砂轮不同磨削性能时声发射信号最大熵概率密度分布,并通过设定交叉熵阈值来辨别磨削加工过程中CBN砂轮的磨削性能。最后,为验证该方法的实用性,在某工厂CBN砂轮磨削产品生产线上进行大量实验研究,结果表明,该方法对CBN砂轮磨损状态及CBN砂轮剩余寿命进行有效监测,验证了该方法监测CBN砂轮在磨削加工过程中磨削性能的有效性。

Characterization and Analysis of Inconel 718 Alloy Ground at Different Speeds

Inconel 718(IN718)alloy is widely applied to fabricate high temperature resistant or corrosion resistant parts due to its excellent mechanical performance.However,the machining of IN718 alloy is difficult as it may cause serious tool wear and poor surface quality(SQ)of the workpiece.In this work,grinding experiments on IN718 alloy at different speeds were conducted by using a CBN grinding wheel.The relationship between grinding speed,SQ and subsurface damage(SSD)was well studied.With increasing grinding speed,surface roughness decreased,and SQ was greatly improved.Meanwhile,the microhardness of the grinding surface declined as the grinding speed increased.The SSD depth was almost unchanged when the grinding speed was lower than 15 m/s,then it decreased with higher grinding speeds.It was attributed to the mechanical-thermal synergistic effect in the grinding process.The results indicated that increasing grinding speed can effectively improve the SQ and reduce the SSD of IN718 alloy.The conclusion in the work may also provide insight into processing other hard-to-machining materials.

镀镍cBN磨料对树脂结合剂cBN砂轮磨削性能的影响

通过树脂结合剂cBN砂轮中所使用的cBN磨料按不同质量比,将裸料cBN和镀镍cBN-N60 (镍层质量分数60%,下同)磨料混合后制备成端面磨削用树脂结合剂cBN砂轮,探究不同比例的镀镍cBN磨料对树脂结合剂cBN端面砂轮的磨削性能的影响。使用端面磨床对砂轮进行磨削测试,从修整后砂轮表面状态,以及磨削过程中磨削效率和工件粗糙度等方面进行探究,研究不同比例的cBN磨料对磨削空调压缩机气缸的影响。试验结果表明:当裸料cBN磨料与cBN-N60的比例为1∶2时,树脂结合剂cBN砂轮具有较好的锋利度和自锐性。

18CrNiMo7-6钢发射率值标定及外圆磨削温度研究

为研究齿轮钢外圆横向磨削过程中工件温度受加工参数变化的影响,以18CrNiMo7-6齿轮钢作为工件材料,CBN砂轮作为磨具进行试验,使用红外热像仪对磨削过程温度进行检测。提出一种增设气幕装置的热辐射发射率值标定方案,通过气幕生成的高速气流减缓外界空气进入加热炉,防止标定过程中试样被氧化,保证高温条件下标定得到的发射率值的准确度;依据检测结果,分析工件转速v_(w)、工件每转的磨削深度f_(a)、砂轮磨粒粒度d_(g)、砂轮直径d_(s)和磨削宽度b对温度的影响。结果表明:f_(a)对温度变化影响最显著。通过拟合得到磨削温度与试验参数间的经验公式,其误差为9.27%。将磨削温度的试验测量结果与运用移动热源理论、瑞利分布模型和干式磨削热分配比模型进行理论推导的结果作对比,偏差为8.51%。

陶瓷结合剂CBN砂轮磨削难加工材料时磨削液的作用

通过对单颗 CBN磨粒和普通磨粒磨损特性的比较以及对陶瓷结合剂 CBN砂轮磨损特性和磨削性能的分析 ,研究了 CBN砂轮磨削难加工材料时磨削液的作用 ,提出了陶瓷结合剂 CBN砂轮磨削液的选择依据。研究结果表明 ,CBN磨粒粘附后所承受的磨削力增大 ,由此所造成 CBN砂轮磨粒和结合剂破碎是不利于发挥 CBN砂轮的优异性能的主要因素。磨削液应以抑制粘附、减小摩擦的润滑作用为主。与水基磨削液相比 ,磨削不同的难加工材料时选用极压磨削油可减小磨削力2 0 %～ 50 %、降低磨削温度 70～ 2 0 0℃、提高磨削比 3～

cBN砂轮高速磨削镍基高温合金磨削力与比磨削能研究

磨削力和比磨削能是磨削过程的两个重要参数,也是制定合理的磨削工艺需要参考的两个重要因素。采用陶瓷结合剂cBN砂轮、电镀cBN砂轮以及单层钎焊cBN砂轮[1]进行了高速磨削GH4169高温合金试验,研究了磨削力、比磨削能与单颗磨粒最大未变形切屑厚度的关系,并在此基础上建立了相应的理论公式。研究结果表明,单层钎焊cBN砂轮在高速条件下更适合难加工材料的磨削,同时也验证了"尺寸效应"的存在及作用。针对磨削力与比磨削能的建模对于高速磨削机理研究与高速磨削工艺优化具有参考价值。

ZnO/Na_2O(mol)对cBN陶瓷砂轮性能的影响

通过DSC-TG综合热分析、X衍射分析、线膨胀测试仪、扫描电镜等测试方法研究了ZnO/Na2O(mol)(Z值)对Li2O-K2O-SiO2-Al2O3-B2O3系陶瓷结合剂及立方氮化硼砂轮性能的影响,结果发现:ZnO能够抑制α-石英晶相析出,诱导析出低膨胀晶体Li2OAl2O37.5SiO2,并随着Z值的增加,α-石英减少,Li2OAl2O37.5SiO2晶体逐渐增多,Li2OAl2O37.5SiO2晶型结构趋于完整,晶粒尺寸减小,结构更加致密;当砂轮配方一定时,砂轮的体积密度、抗弯曲强度、洛氏硬度均随着Z值的增加而增大,气孔率减小,磨削(干磨)铸铁(QT400)时磨耗比先增加后减小;当Z=0.75时,结合剂的膨胀系数为6.902 9×10-6 K-1,耐火度为805℃,砂轮的烧结温度为845℃,抗弯曲强度为73.97MPa,气孔率为15.65%,磨耗比最大为156.42%.

超高速陶瓷CBN砂轮纳米陶瓷结合剂性能实验研究

以超高速陶瓷CBN砂轮的结合剂低温高强性能要求为目标,在以化学纯原料为主的R2O+RO-B2O3-Al2O3-SiO2玻璃体系基础上,引入纳米改性剂来对陶瓷结合剂基体进行改良强化。4种成分结合剂性能的测试结果表明,纳米陶瓷结合剂的抗折强度、耐火度、浸润性与普通陶瓷结合剂相比有着显著优势。4号纳米陶瓷结合剂的抗折强度达到了83.75MPa,耐火度降至795℃,其膨胀系数也与CBN磨料更为接近,是一种更适合用于制备超高速陶瓷CBN砂轮的结合剂。

高速磨削用单层钎焊CBN砂轮及其磨削性能

针对钎焊砂轮存在的热变形导致精度降低的问题,提出基于局部加热的超高频感应钎焊工艺方法制备高速磨削用单层钎焊CBN砂轮,采用三坐标测量仪对砂轮及其钎焊前后的尺寸进行测量,最后对该砂轮高速磨削镍基高温合金磨削性能进行评价。三坐标测量结果显示,钎焊CBN砂轮基体的变形量小于16μm,在高速重负磨削镍基高温合金试验中,加工表面未见裂纹和烧伤,表面粗糙度可达Ra0.4μm,砂轮表现为正常磨耗磨损。表明超高频感应钎焊工艺制备的单层钎焊砂轮在高速磨削具有应用潜力。