PERFORMANCE OF BRAZED DIAMOND CUP-TYPE WHEELS WITH DEFINED GRAIN PATTERN IN GRINDING CEMENTED CARBIDE

A new cup-type grinding wheel of the brazed monolayer diamond is developed with a defined grain pattern on the wheel surface. Grinding performance of the brazed wheel in the surface grinding of cemented carbide is studied. Experimental results show that when continuous dry grinding is employed, grits of the brazed diamond grinding wheel fail mainly in attritious wear and fracture modes and no pull-out ones are found in conventional electroplated and sintered diamond wheels. It indicates the strong retention of brazing alloy to diamond grits and the longer service life of the wheel. In addition, the ground surface has good roughness. The theoretical surface roughness agrees well with experimental results.

New Vitrified Bond Diamond Grinding Wheel for Grinding the Cylinder of Polycrystalline Diamond Compacts

In this work, a kind of new vitrified bond based on Li2O-Al2O3-SiO2 glass ceramics was used to bond the diamond grains, which is made into grinding wheel and the cylindrical grinding process of polycrystalline diamond compacts （PDCs） by using the new vitrified bond diamond grinding wheel was discussed. Several factors which influence the properties of grinding wheel such as amount of vitrified bond and the kinds and amount of stuff in grinding wheel were also investigated. It was found that the new vitrified bond can firmly combine diamond grains, when there are only diamonds and vitrified bond in the structure of grinding wheel, the longevity of the grinding wheel is about 2.5-3 times as that of resin bond grinding wheel for processing PDCs. The grinding size precision of PDCs can be improved from 4-0.03 mm to 4-0.01 mm because of larger Young＇s modulus of vitrified bond than resin bond. The grinding time of a PDC product can be 1.75-2.0 min from 3.25-3.5 min, so this kind of grinding wheel can save much time for processing PDCs. Also, there is hardly noise when using this new vitrified bond diamond grinding wheel to process PDCs. The amount of vitrified bond in grinding wheel influences the longevity of grinding wheel. When the size of diamond grains is 90-107 μm, the optimal amount of vitrified bond in grinding wheel is 21% （wt pct）. When the amount of vitrified bond exceeds 21%, there are many pores in grinding block, which will decrease the longevity of grinding wheel. The existence of addition stuff such as Al2O3 or SiC can reduce the longevity of grinding wheel.

Precision Grinding of Reaction Bonded Silicon Carbide Using Coarse Grain Size Diamond Wheels

Reaction bonded SiC（RBSiC） is attractive for optical application because of its favorable properties and low fabrication cost. However, the difficultness and cost involved in RBSiC grinding limit its application. The investigation on high efficient and low-cost machining with good grinding quality is desired. Generally, high efficient machining for RBSiC is realized by using coarse grain size grinding wheels, but serious grinding damage is inevitable. In this paper, monolayer nickel electroplated coarse grain size diamond grinding wheels with grain sizes of 46 μm, 91 μm, and 151 μm were applied to the grinding of RBSiC. An electrolytic in-process dressing（ELID） assisted conditioning technique was first developed by using cup shape copper bonded conditioning wheels with grain sizes of 15 μm and 91 μm to generate the conditioned coarse grain size wheels with minimized wheel run-out error within 2 μm, constant wheel peripheral envelop as well as top-flattened diamond grains. Then, the grinding experiments on RBSiC were carried out to investigate the grinding performance and material removal mechanism. The experimental results indicate that the developed conditioning technique is applicable and feasible to condition the coarse grain size diamond wheels under optimal conditioning parameters, and the material removal mechanism involved in RBSiC grinding is the combination of brittle fracture and ductile deformation to generate smooth ground surface. This research is significant for the high efficient and low-cost precision grinding of RBSiC with good ground surface quality.

Orientation variation along growth direction of millimeter free-standing CVD diamond thinned by mechanical grinding

A free-standing diamond film with millimeter thickness prepared by DC arc plasma jet was thinned successively by mechanical grinding. The orientation and quality of the diamond films with different thicknesses were characterized by X-ray diffraction and Raman spectroscopy, respectively. The results show a random grain-orientatinn distribution during the initial growth stage. As the film thickness increases, the preferred orientation of the diamond film changes from （111） to （220）, due to the competitive growth mechanism. Twinning generated during the nucleation stage appears to stabilize the preferential growth along the 〈110〉 direction. The interplanar spacing of the （220） plane is enlarged as the film thickness increases, which is caused by the increase of non-diamond-phase carbon and impurities under the cyclic gas. In addition, the quality of the diamond film is barely degraded during the growth process. Furthermore, the peak shift demonstrates a significant inhomogeneity of stress along the film growth direction, which results from competitive growth.

RESEARCH ON PARALLEL GRINDING METHOD OF NON-AXISYMMETRIC ASPHERIC LENS

In order to resolve the problems of machining non-axisymmetric aspheric lens,which is short of flexibility in mould grinding and needs high accuracy CNC machine center in globediamond wheel grinding, a new parallel grinding method that utilizes common arc diamond wheel isput forward. Base on the approach calculation of machining locus, the advantages of parallelgrinding that machines non-axisymmetric aspheric lens by 2.5-axis CNC machine center have beenobtained. The results of grinding experiment show the new method can meet the need of grinding highaccuracy non-axisymmetric aspheric lens.

High Efficiency Axial Deep Creep-Feed Grinding Machining Technology of Engineering Ceramics Materials

Axial deep creep-feed grinding machining technology is a high efficiency process method of engineering ceramics materials, which is an original method to process the cylindrical ceramics materials or hole along its axis. The analysis of axial force and edge fracture proved the cutting thickness and feed rate could be more than 5-10 mm and 200 mm/min respectively in once process, and realized high efficiency, low-cost process of engineering ceramics materials. Compared with high speed-deep grinding machining, this method is also a high efficiency machining technology of engineering ceramics materials as well as with low cost. In addition, removal mechanism analyses showed that both median/radial cracks and lateral cracks appeared in the part to be removed, and the processed part is seldom destroyed, only by adjusting the axial force to control the length of transverse cracks.

Material Removal Behavior and Surface Integrity in Grinding of UltrafineGrained WC-Co Materials

Due to the excellent combination of wear resistance and fracture toughness,the ultrafine-grained WC-Co composites can significantly improve the durability and reliability of industrial tools.However,the grinding of ultrafine-grained WC-Co remains a challenge.In order to provide an experimental basis for improving grinding quality of ultrafine-grained WC-Co,a series of surface grinding experiments on ultrafine-grained WC-Co hardmetals were conducted by diamond wheel under various grinding conditions,and the material removal behavior and surface integrity in grinding of ultrafine-grained WC-Co materials were characterized by means of scanning electron microscopy(SEM),X-ray microstress analyzer and surface roughness analyzer in this paper.The results indicate that the material removal behavior in grinding of ultrafine-grained WC-Co materials is determined not only by the abrasive grain size on the wheel,but also by the depth of cut.The roughness values of ground surface increase with increasing grit size of diamond wheel,and increase initially,then decrease with increase in depth of cut.Grinding causes the residual compressive stress in the surface layer of ground cemented carbides under various grinding conditions;the magnitude of residual surface stress increases with increasing grit size of diamond wheel,and isn't changed obviously along with the change of depth of cut.

Unsteady-State Grinding Technology (I) Theoretical Generalization and Research on Grinding Mechanism

In conventional grinding theory, it is obvious that there must be a very high hardness difference between grains of the grinding wheel and workpieces. The best grinding wheels are those giving the lowest "natural limiting surface roughness" while cutting at appreciable plunge velocities. With the development of new materials and new machining processes, conventional theories of grinding techniques are no longer suitable to explain many phenomena in the course of grinding procedures. In dealing with precision or ultra-precision grinding processes of advanced ceramics, many results of experiments and practical production have shown that grinding with super hard materials wheels is not the only method to machine advanced ceramics. This paper is intended to propose a new grinding theory named as unsteady-state grinding technique evolved from some phenomena that can not be explained by conventional grinding theory. Unsteady-state grinding technique means the technique which can make the surface roughness of the materials, especially hard and brittle, be up to the standard of ultra-precision machining by utilizing common wheels characteristic of inferior self-sharpening and wear-resistance. In the process of machining, the common wheel need to be redressed about 3～5 times and the time between two redressings is about 3～5 minutes. As a validation of the new grinding technology, experimental work was performed to prove the existence of the unsteady state in the process of ultra-precision grinding with common abrasive wheel-pink fused alumina wheel. From the results of the observation of the wheel topography, the whole grinding process in unsteady state was separated into three stages namely cutting by grains peaks, micro-cutting by micro edges of the broken grains and rubbing without material removal, which is different from conventional grinding theory. For the difference of hardness between grinding wheel and workpiece material is not so apparent, some people have doubts about whether the cutting especially micro-cutting actions exist in the process of unsteady state grinding. By utilizing the common abrasive wheel newly redressed to grind the finished surface of silicon nitride glut and comparing the finished surface with the damaged surface in SEM pattern and surface roughness, the existence of cutting and micro- cutting actions in the unsteady state grinding process was confirmed.

Clarification of abrasive jet precision finishing with wheel as restraint mechanisms and experimental verification

According to the critical size ratio for the characteristic particle size to film thickness between grinding wheel and work, the machining mechanisms in abrasive jet precision finishing with grinding wheel as restraint can be categorized into four states, namely, two-body lapping, three-body polishing, abrasive jet machining and fluid hydrodynamic shear stress machining. The critical transition condition of two-body lapping to three-body polishing was analyzed. The single abrasive material removal models of two-body lapping, three-body polishing, abrasive jet finishing and fluid hydrodynamic shear stress machining were proposed. Experiments were performed in the refited plane grinding machine for theoretical modes verification. It was found that experimental results agreed with academic modes and the modes validity was verified.

金刚石砂轮与金刚石滚轮磨削接触的声发射监测

为了实现金刚石砂轮磨削加工金刚石滚轮过程的自动化,需要对磨削接触状态进行准确识别。由于磨削过程中材料去除率较小导致声发射信号幅值变化不显著,仅用有效值对磨削接触状态识别的准确性受噪声影响很大。针对此问题,通过模态分解和相关性分析相结合的方法对采集的声发射信号进行处理,再计算各分量的有效值和方差值完成特征提取,最后利用支持向量机对磨削接触状态进行识别。实际应用发现:该方法对滚轮的磨削接触状识别准确率达到了98.3%,准确实现了对磨削接触状态的识别。

粗粒度金刚石砂轮的放电赋能磨削修整试验研究

针对粗粒度金刚石砂轮磨粒出刃形貌难以控制的问题,提出了放电赋能磨削修整技术,旨在实现出刃磨粒的等齐性。系统研究了该复合修整技术的材料去除机理,建立脉冲放电传热数值模型,以金刚石热软化深度作为磨削深度,最大限度发挥放电赋能磨削的修整优势。探究了机床运动参数(待修砂轮转速、刀具轮转速、进给速度、磨削深度)对砂轮修整精度和刀具轮损耗深度的影响规律,并优化了工艺参数以实现粗粒度砂轮的高效高精修整。磨粒粒度为180目的金刚石砂轮修整后轮廓误差PV值为11.97μm。修整砂轮表面形貌检测结果表明,放电赋能磨削修整可将磨粒部分去除,使得砂轮表面磨粒具有较好的等齐性。磨削的碳化硅陶瓷工件表面粗糙度达412 nm,表明了修整砂轮具有优异的磨削性能。

超精密晶圆减薄砂轮及减薄磨削装备研究进展

在芯片制程的后道阶段,通过超精密晶圆减薄工艺可以有效减小芯片封装体积,导通电阻,改善芯片的热扩散效率,提高其电气性能、力学性能。目前的主流工艺通过超细粒度金刚石砂轮和高稳定性超精密减薄设备对晶圆进行减薄,可实现大尺寸晶圆的高精度、高效率、高稳定性无损伤表面加工。重点综述了目前超精密晶圆减薄砂轮的研究进展,在磨料方面综述了机械磨削用硬磨料和化学机械磨削用软磨料的研究现状,包括泡沫化金刚石、金刚石团聚磨料、表面微刃金刚石的制备方法及磨削性能,同时归纳总结了软磨料砂轮的化学机械磨削机理及材料去除模型。在结合剂研究方面,综述了金属、树脂和陶瓷3种结合剂的优缺点,以及在晶圆减薄砂轮上的应用,重点综述了目前在改善陶瓷结合剂的本征力学强度及与金刚石之间的界面润湿性方面的研究进展。在晶圆减薄超细粒度金刚石砂轮制备方面,由于微纳金刚石的表面能较大,采用传统工艺制备砂轮会导致磨料发生团聚,影响加工质量。在此基础上,总结论述了溶胶–凝胶法、高分子网络凝胶法、电泳沉积法、凝胶注模法、结构化砂轮等新型工艺方法在超细粒度砂轮制备方面的应用研究,同时还综述了目前不同的晶圆减薄工艺及超精密减薄设备的研究进展,并指出未来半导体加工工具及装备的发展方向。

凹坑减阻表面拓扑磨削几何形状变异机理的研究

为了揭示结构化凹坑减阻表面的拓扑磨削过程中,被磨削出的表面与设计表面之间的几何变异规律,通过对磨粒间相对运动状态分析,确定拓扑磨削形成凹坑长度及中间截面形状并通过仿真验证。首先,建立球冠凹坑数学模型并将中间截面拓扑变换得到磨粒簇中间截面;其次,确定影响砂轮磨粒簇长度的两个参量—砂轮基体半径、砂轮转速与工件进给速度之比,在砂轮基体半径确定的条件下,建立凹坑长度和磨粒簇长度间的精确的数学表达;最后,设计仿真实验,分别改变速比和磨削深度进行磨削得到凹坑表面,并提取中间截面数据拟合曲线与设计凹坑曲线对比。结果表明,定半径条件下满足磨粒簇长度与速比对应关系时,其形成的凹坑表面形状与设计形状相比几乎不存在变异,误差远小于其他速比所形成表面,而磨削深度略浅会使凹坑按比例缩小。

偏转激光切向修整凹形面金刚石倒角砂轮的研究

为了减小凹形面金刚石砂轮的激光修整误差,建立激光遮蔽效应和激光斜面分散效应误差模型,分析了激光切向修整凹形面金刚石砂轮的误差来源,提出了偏转激光修整凹形面成形砂轮法,并通过理论分析和实验验证,探索了修整参数对凹形面砂轮轮廓精度和圆弧半径的影响。结果表明,在1°~1.5°的偏转角范围内,斜边轮廓修整精度为8μm;在合适的偏转角度下,圆弧半径误差小于10μm;在修整凹弧半径为0.2 mm和0.5 mm、补偿半径分别为0.03 mm和0.06 mm时,凹弧半径误差分别缩小0.02 mm和0.03 mm。偏转激光修整法有效地提高了修整精度,减小了修整误差,为凹形面金刚石修整提供了新思路。

一种3-DOF并联机械手的研制

提出了一种采用(U+UPS)P+UPS弱耦合并联机构的3-DOF机械手。首先,推导出机构的位置反解,建立机构的速度映射模型,并建立了机构的驱动、约束静力学传递方程。然后,对机构的工作空间进行分析,绘制出工作空间三维分布图以及雅可比矩阵条件数在工作空间内的三维分布图。通过定义运动灵活性评价指标对机构进行运动灵活性分析,绘制出结构参数与运动灵活性评价指标之间的关系曲线;通过定义静力承载性能评价指标对机构进行静力学分析,绘制出结构参数与机构静力承载性能评价指标之间的关系曲线。采用蒙特卡罗法进行结构参数设计,选取了一组综合性能较好的结构参数:机械手的固定平台万向副分布直角边长为240mm,运动平台球面副与参考点间距为80mm,中间连接杆球面副与主UP支链轴线间距为90mm,主UP支链与中间连接杆的固接点到万向副间距为600mm。最后,研制出机械手的实验样机,对机械手实验样机进行了力学标定,验证了机械手样机结构的合理性。

陶瓷磨削用多层钎焊金刚石砂轮的研制

为解决传统树脂、电镀金刚石砂轮磨削陶瓷材料时存在的磨削寿命短、砂轮易堵塞烧伤等问题,分析利用钎焊金刚石技术制备陶瓷磨削用多层钎焊金刚石砂轮的可行性。结合钎料组分优选,制备具有开槽结构的多层钎焊金刚石砂轮,并对99.9%高纯度的Al_(2)O_(3)陶瓷进行磨削性能试验。结果表明:树脂、电镀金刚石砂轮分别存在磨削效率低和磨削寿命不足的问题,单层钎焊金刚石砂轮磨削效率较高但磨削寿命有限,多层钎焊金刚石在保持高磨削效率的同时磨削寿命优势明显,较单层钎焊金刚石磨轮提升约60%。在陶瓷材料磨削过程中,多层钎焊金刚石砂轮磨削效果显著,虽磨粒出露高度有限,但开槽设计的排屑效果显著,砂轮表面不易发生陶瓷粉末黏结、堵塞。

基于力信号的砂轮磨削状态在线监测研究

磨削过程监控是实现磨削加工智能化与保证制造质量的关键.磨削力是磨削加工过程中一个重要的伴随信号特征,它直接跟砂轮磨损程度、磨削热、砂轮与工件接触状态等事件之间有着密切联系.为了提升微晶刚玉砂轮磨削齿轮工艺的精密化、自动化与智能化水平,开展砂轮磨削状态在线监测与砂轮磨损机制研究,建立磨削力时频两域信号与砂轮–工件接触状态、砂轮磨损程度事件之间的内在关联,提出一种基于实时力信号的砂轮磨削状态的在线监测新方法.同时,采用激光共聚焦显微镜与扫描电镜表征分析了微晶刚玉砂轮形貌蕴含的磨损机理.研究表明,磨削力时域波谱的峭度、波形指标、峰值指标、脉冲指标等波形特征指标分布规律呈现为变切深磨削状态≥显著磨损砂轮的稳态磨削状态≥轻度磨损砂轮的稳态磨削状态>未接触状态的鲜明态势.然而,磨削力幅频谱的峭度、脉冲指标两项波形特征值在不同磨削状态下的变化规律却与时域信号截然相反.砂轮工作表面三维粗糙度随磨损演变呈现出先略微减小后增大的变化规律,而微晶刚玉磨粒的聚微晶结构使其拥有沿微晶界面呈现逐层解理剥落的更新自锐能力.

激光修整青铜金刚石砂轮预测模型与优化研究

为了根据实验规律获得更多激光修整青铜金刚石砂轮的工艺参数,采用反向传播(BP)神经网络和粒子群遗传混合优化算法(PSO&GA),建立了激光修整青铜金刚石砂轮的预测模型。首先通过分析激光修整的原理得出砂轮型面角度、激光偏转角度、入射角度和光斑重叠率为主要影响参数,并以砂轮型面角度误差和峰谷(PV)值为评价指标修整了192组工艺实验数据;建立了4×9×2的3层BP神经网络预测模型,通过PSO&GA混合优化算法对预测模型进行训练优化;最后选取16组实验数据测试BP神经网络预测模型,预测结果比较准确;并对比了梯度下降法(GD)、粒子群优化算法(PSO)和遗传算法(GA)的BP神经网络的训练效果。结果表明,经PSO&GA-BP预测模型角度误差预测偏差在0.2°以内,PV值预测偏差在1.6μm以内,相较于其它优化算法,收敛速度更快、精度更高。该研究为激光修整青铜金刚石砂轮提供了良好的预测模型。

弧形金刚石砂轮机械修整研究进展

弧形金刚石砂轮因特有的弧形轮廓,常用于陶瓷、光学玻璃、硬质合金等难加工材料光学元件的精密超精密磨削加工。然而,在光学元件磨削加工过程中,由于砂轮与工件表面间的相互作用,砂轮表面受到挤压破坏,长时间磨削后会产生砂轮堵塞、砂轮磨损、砂轮尺寸和形状精度下降等问题,进而降低了磨削后光学元件的表面粗糙度、面形精度和损伤厚度等。修整弧形金刚石砂轮是解决上述问题的有效途径之一,机械修整因具有修整效率高、便于实现等特点,仍是弧形金刚石砂轮在位修整的主要应用方法。对弧形金刚石砂轮的机械修整方法进行了综述,探究了不同修整方法的修整机理与特点,分析了修整效果的评价方法,并对弧形金刚石砂轮机械修整的发展方向进行了展望。

不同造孔剂树脂金刚石砂轮对硬质合金球阀的精密研磨

为改善硬质合金球阀的加工效果,在树脂金刚石砂轮中引入造孔剂,对其力学性能、微观形貌及磨削性能进行分析,研究空心玻璃球和塑料球造孔剂对树脂金刚石砂轮性能的影响。结果表明:随着造孔剂体积分数增加,树脂砂轮的抗折强度逐渐下降,且2种造孔剂对抗折强度的影响基本一致;砂轮的硬度随造孔剂体积分数的增加亦逐渐下降,但空心玻璃球造孔剂对砂轮硬度的影响显著大于塑料球的;加入造孔剂明显提升了砂轮的锋利性,空心玻璃球体造孔剂体积分数为15%和塑料球造孔剂体积分数为20%的砂轮综合性能最好,且后者的综合性能优于前者的。