IMPROVING MATERIAL REMOVAL RATE OF BRITTLE CERAMICS THROUGH HONING INCIDENTAL TENSILE STRESSES

The stress intensity factors and stress conditions of machining cracks are analyzed by fracture mechanics on the basis of honing characteristics and of brittle ceramic mechanical behavior.Because the honing incidental tensile stresses effectively decrease the critical grinding stresses and increase the stress intensity factors of machining cracks,the honing process can be carried out easily.The results show that honing can be an efficient machining method for brittle materials.

On investigating the soda-lime shot blasting of AZ31 alloy:Effects on surface roughness,material removal rate,corrosion resistance,and bioactivity

In the present study,a novel method of surface finish improvement is proposed using shot blasting of soda lime(SBSL)beads on the Mg-AZ31 alloy.The effect of the soda blasting process parameters,such as blast pressure,stand-off distance,and blast duration,have been studied in-response of material removal rate(MRR)and surface roughness(SR)and corresponding statistical models have been obtained.The multi-objective optimization has also been performed to obtain parameters for maximum MRR and minimum SR.The corrosion behavior of the treated specimens has been performed to study their in-vitro biodegradability in simulated body fluid(SBF)for 1,3,7,10,15,and 21 days.The wettability study of the SBSL treated samples has been investigated using sessile drop methodology.Further,cell adhesion test has also been performed to study the biocompatibility characteristics of the SBSL treated samples using Huh7 liver cell lines.Based on obtained quantitative data as well as scanning electron microscopy analysis of treated samples,the SBSL treatment of the AZ31 alloy has been found highly useful in producing biocompatibility surfaces along with desirable morphological features.

Effect of mechanical anisotropy on material removal rate and surface quality during polishing CdZnTe wafers

The mechanical characters of CdZnTe crystal were investigated by nanoscratch tests, and the effects of mechanical anisotropy on the material removal rate and surface quality were studied by polishing tests. There is a peak of frictional coefficient at the early stage of scratch, and increasing the vertical force will result in the increase of peak value correspondingly. The fluctuation phenomenon of frictional coefficient is generated at high vertical force. The lateral forces show the apparent twofold and threefold symmetries on （110） and （111） planes, respectively. To obtain high surface quality, low polishing pressure and hard direction （〈 T10 〉 directions on （110） plane and 〈 112 〉 directions on （111） plane） should be selected, and to achieve high material removal rate, high polishing pressure and soft direction （〈001〉 directions on （110） plane and 〈 121 〉 directions on （111） plane） should be selected.

Material Removal Rate Prediction of Electrical Discharge Machining Process Using Artificial Neural Network

This article presents an Artificial Neural Network （ANN） architecture to model the Electrical Discharge Machining （EDM） process. It is aimed to develop the ANN model using an input-output pattern of raw data collected from an experimental of EDM process, whereas several research objectives have been outlined such as experimenting machining material for selected gap current, identifying machining parameters for ANN variables and selecting appropriate size of data selection. The experimental data （input variables） of copper-electrode and steel-workpiece is based on a selected gap current where pulse on time, pulse off time and sparking frequency have been chosen at optimum value of Material Removal Rate （MRR）. In this paper, the result has significantly demonstrated that the ANN model is capable of predicting the MRR with low percentage prediction error when compared with the experimental result.

Novel model of material removal rate on ultrasonic-assisted chemical mechanical polishing for sapphire

Ultrasonic-assisted chemical mechanical polishing(UA-CMP)can greatly improve the sapphire material removal and surface quality,but its polishing mechanism is still unclear.This paper proposed a novel model of material removal rate(MRR)to explore the mechanism of sapphire UA-CMP.It contains two modes,namely two-body wear and abrasive-impact.Furthermore,the atomic force microscopy(AFM)in-situ study,computational fluid dynamics(CFD)simulation,and polishing experiments were conducted to verify the model and reveal the polishing mechanism.In the AFM in-situ studies,the tip scratched the reaction layer on the sapphire surface.The pit with a 0.22 nm depth is the evidence of two-body wear.The CFD simulation showed that abrasives could be driven by the ultrasonic vibration to impact the sapphire surface at high frequencies.The maximum total velocity and the air volume fraction(AVF)in the central area increased from 0.26 to 0.55 m/s and 20%to 49%,respectively,with the rising amplitudes of 1–3μm.However,the maximum total velocity rose slightly from 0.33 to 0.42 m/s,and the AVF was nearly unchanged under 40–80 r/min.It indicated that the ultrasonic energy has great effects on the abrasive-impact mode.The UA-CMP experimental results exhibited that there was 63.7%improvement in MRR when the polishing velocities rose from 40 to 80 r/min.The roughness of the polished sapphire surface was R_(a)=0.07 nm.It identified that the higher speed achieved greater MRR mainly through the two-body wear mode.This study is beneficial to further understanding the UA-CMP mechanism and promoting the development of UA-CMP technology.

Effect of Electrode Materials on Electric Discharge Machining of 316 L and 17 - 4 PH Stainless Steels

Electric Discharge Machining (EDM) is one of the most efficiently employed non-traditional machining processes for cutting hard-to-cut materials, to geometrically complex shapes that are difficult to machine by conventional machines. In the present work, an experimental investigation has been carried out to study the effect of pulsed current on material removal rate, electrode wear, surface roughness and diameteral overcut in corrosion resistant stainless steels viz., 316 L and 17-4 PH. The materials used for the work were machined with different electrode materials such as copper, copper-tungsten and graphite. It is observed that the output parameters such as material removal rate, electrode wear and surface roughness of EDM increase with increase in pulsed current. The results reveal that high material removal rate have been achieved with copper electrode whereas copper-tungsten yielded lower electrode wear, smooth surface finish and good dimensional accuracy.

熔石英元件磁性复合流体抛光去除特性研究

基于磁性复合流体(Magnetic Compound Fluid,MCF)抛光技术开展了熔石英元件抛光工艺研究,对比了传统MCF和超声辅助MCF(以下简称UMCF)抛光对熔石英材料去除特性的影响,探究了不同抛光时间下MCF和UMCF抛光对熔石英材料去除量/去除率和表面粗糙度的影响,并构建了与抛光应力和抛光时间有关的材料去除率模型。研究结果表明,相较于传统MCF,UMCF在提高材料去除率和降低表面粗糙度方面均有优势。两种抛光方式下材料去除机制均为弹塑性去除,UMCF抛光获得的表面粗糙度相比于MCF抛光优化了68.88%。由于流体动压力和超声振动压力的联合作用,UMCF抛光材料去除率最高可达5.74×10^(-3)mm^(3)/min,相比于MCF抛光提升了4.04倍。MCF和UMCF抛光材料去除率与抛光应力和抛光时间均呈现幂函数相关性,且在UMCF抛光中抛光应力对去除率的影响权重大于MCF抛光。

数模联动的多特征工件加工能耗预测方法研究

在实际切削加工过程中材料去除率是不断变化的,现有将其视为恒量的能耗建模方法难以实现能耗准确预测。为了提高切削过程能耗预测精度,提出了一种基于材料去除率的数模联动加工能耗预测方法。首先,基于切削过程刀具与工件的接触关系分析了切入、完全切入和切出阶段材料去除率变化规律,并对相应的加工能耗特性进行了分析;其次,提出了数据驱动的刀具切入,切出阶段加工能耗预测方法,以及模型驱动的完全切入阶段加工能耗预测方法,实现加工过程能耗准确预测;最后,利用实验案例验证了所提模型及方法的有效性,为今后研究能耗预测精度奠定了基础。

多孔异构材料对实验室废水中COD的吸附作用研究

本文以钙基蒙脱土、十六烷基三甲基溴化铵、十二烷胺、正硅酸乙酯为原料制备蒙脱土多孔异构材料,用蒙脱土多孔异构材料作为吸附剂进行实验室废水中COD有机物吸附去除实验,考察不同条件下所合成的蒙脱土多孔异构材料对实验室废水中COD的去除率,并通过智能水质检测仪、热重分析仪等仪器量化分析蒙脱土多孔异构材料的COD去除率。实验结果表明,有机土/十二胺/正硅酸乙酯的摩尔比为1∶24∶160时,合成的蒙脱土多孔异构材料对废水的吸附作用最大。最佳吸附条件为蒙脱土多孔异构材料用量为30g·L^(-1)、吸附混合液pH值为5.0、污水COD浓度为300mg·L^(-1)、吸附时间为150min,该条件下COD的去除率达到45%;蒙脱土多孔异构材料对废水中COD吸附降解性能稳定,可多次使用。

基于胡麻油工作液电火花成形加工可行性研究

传统的电火花工作液煤油或碳氢矿物油等,存在加工效率低、表面质量差且环境污染和资源消耗等问题。而绿色可持续制造也是当今发展的主要趋势。因此文章提出利用植物油胡麻油为工作液在电火花成形加工中的实验研究,旨在实现绿色可持续电火花加工。研究响应参数电流、脉冲宽度和间隙电压对材料去除率,表面粗糙度值,表面质量的影响规律。实验结果表明,胡麻油在电火花加工过程中表现出显著的性能优势。胡麻油为工作液时,材料去除率显著提高,可获得更好的加工表面,表面裂纹明显减少,重铸层厚度更薄。说明胡麻油具有代替传统工作液的潜质,有望进一步促进绿色电火花加工技术的发展和应用。

金属钼圆基片平面研磨及其表面创成机理研究

目的实现金属钼圆基片高效平坦化加工,获得超光滑表面。方法采用游离磨料对钼圆基片进行平面研磨加工,研究磨料种类及研磨盘转速、研磨压力、研磨时间等工艺参数对研磨效果的影响规律,通过材料去除率(MRR)与表面粗糙度(Ra)的建模分析,对比钼材与高硬脆和高塑性材料,揭示其研磨工艺特性、探究其表面创成机理。结果钼圆基片材料去除快慢和表面形貌受各因素作用的综合影响。CeO_(2)磨料适合钼圆基片的研磨加工,材料去除方式为二体、三体摩擦塑性去除;在研磨过程中,MRR随研磨盘转速、研磨压力的递增而先增大后减小,在研磨盘转速为60 r/min、研磨压力为0.026 MPa条件下MRR达到最大;除磨料因素外,其他工艺因素对表面粗糙度的影响较小;MRR和Ra随加工时间的延长而趋于稳定;使用粒径W1 CeO_(2)磨料在研磨盘转速为60 r/min、研磨压力为0.026 MPa下研磨40 min后,表面粗糙度Ra由46 nm降至9.53 nm,MRR达1.16 mg/min。结论采用游离磨料研磨方法在优化工艺条件下可以有效降低表面粗糙度,获得良好表面。

低温微磨料气射流加工的硬脆材料耐冲蚀性能对比

低温微磨料气射流加工硬脆材料时,其变脆易被冲蚀去除。对碳化硅(SiC)、氮化硅(Si3N4)、钇稳定氧化锆(YSZ)、99氧化铝(99 Al2O3)、石英玻璃5种硬脆材料进行低温微磨料气射流加工对比实验,探究加工压力、冲击加工角度及加工次数等工艺参数对5种硬脆材料的冲蚀去除率、低温冲蚀槽三维形貌及表面轮廓的影响,优选出低温下耐冲蚀性能良好的硬脆材料。结果表明:随着加工压力和加工次数增加,5种材料的冲蚀去除率都不断增大;随着冲击加工角度变化,5种材料的低温冲蚀槽体积也在变化,并在加工角度为90°的垂直加工角度附近时达到最大;在相同的加工工艺参数下,Si_(3)N_(4)材料的冲蚀去除率最小,其最大低温冲蚀槽深度只有20μm,SiC材料的与其相差不大,YSZ和99 Al_(2)O_(3)的冲蚀去除率依次增大,但石英玻璃材料的冲蚀去除率最大且远大于其他4种材料的。同时,Si3N4的低温冲蚀槽槽形不明显,且其表面较平整,去除量最小,因而耐冲蚀性能最佳。

半导体碳化硅衬底的湿法氧化

半导体碳化硅(4H-SiC)材料具有硬度高、脆性大、化学性质稳定等特点,一般使用化学机械抛光工艺来加工4H-SiC以获得超光滑平坦表面。湿法氧化作为单晶4H-SiC化学机械抛光的重要过程,直接影响着化学机械抛光的速率和表面质量。本文综述了目前单晶4H-SiC湿法氧化的研究现状,讨论了4H-SiC湿法氧化工艺所选用的氧化剂,如KMnO_(4)、H_(2)O_(2)、K_(2)S_(2)O_(8)等。在此基础上,进一步总结了常用的氧化增效方法,如光催化辅助氧化、电化学氧化、芬顿反应等,并从理论计算的角度分析了单晶4H-SiC湿法氧化的机理,最后展望了4H-SiC湿法氧化未来的研究方向。

单晶碳化硅电化学机械抛光液的组分设计与优化

单晶碳化硅具有高硬度和高化学惰性,化学机械抛光方法难以同时保证其加工效率和表面质量。电化学机械抛光具有较高的材料去除率,是加工碳化硅的一种有效方法。然而,目前针对碳化硅电化学机械抛光液的相关研究还较为缺乏。为此,首先通过单因素实验确定电化学机械抛光液中导电介质和磨粒种类,然后分析导电介质和磨粒浓度以及抛光液pH值对材料去除率和表面粗糙度的影响规律,最终确定抛光液的最佳参数。结果表明:在抛光液以NaCl为导电介质,SiO_(2)为抛光磨粒时,碳化硅具有较好的抛光效率和表面质量,其材料去除率和表面粗糙度随着NaCl浓度的增大而增大,随着磨粒浓度的增加先增大后趋于稳定;当NaCl浓度为0.6 mol/L、SiO_(2)质量分数为6%、抛光液pH值为7时,可以兼顾碳化硅抛光的材料去除率和表面粗糙度Sa,其值分别为2.388μm/h和0.514 nm。

单晶SiC基片干式摩擦化学机械抛光初探

针对碳化硅(SiC)基片在抛光过程中效率低、费用高、环境污染大等问题,提出了一种在干式状态下对SiC基片进行摩擦化学机械抛光的方法(dry tribochemical mechanical polishing,DTCMP)。探究不同工艺参数(磨料种类、磨粒粒径、磨粒含量、抛光盘转速、抛光载荷、固相氧化剂含量)对单晶SiC基片抛光效率和表面质量的影响规律。研究结果表明:金刚石磨粒更适合SiC的摩擦化学机械抛光;当磨粒粒径为W1,磨粒质量为4 g,抛光盘转速为70r/min,抛光载荷为20.685 k Pa,固相氧化剂过碳酸钠添加量为10g时,其为最优工艺参数。采用最优工艺参数对表面粗糙度约为20nm的单晶6H-SiC基片进行干式抛光加工,最终获得表面粗糙度R_(a)为3.214 nm。DTCMP方法抛光SiC基片比水基抛光法热量损失少,所产生的界面温度更高,反应所需的活化能更低,可以实现SiC基片的绿色、高效和高质量抛光。

蓝宝石衬底CMP中氧化硅磨粒粒度分布对抛光液体系性能影响研究

目的 化学机械抛光(CMP)包含化学腐蚀和机械磨削两方面,抛光液p H、磨粒粒径和浓度等因素均会不同程度地影响其化学腐蚀和机械磨削能力,从而影响抛光效果。方法 采用30~150 nm连续粒径磨粒抛光液、120 nm均一粒径磨粒抛光液、50 nm和120 nm配制而成的混合粒径磨粒抛光液,分别对蓝宝石衬底晶圆进行循环CMP实验,研究CMP过程中抛光液体系的变化。结果 连续粒径磨粒抛光液中磨粒大规模团聚,满足高材料去除率的抛光时间仅有4 h,抛光后的晶圆表面粗糙度为0.665 nm;均一粒径磨粒抛光液中磨粒稳定,无团聚现象,抛光9 h内材料去除率较连续粒径磨粒抛光液高94.7%,能至少维持高材料去除率18 h,抛光后的晶圆表面粗糙度为0.204 nm;混合粒径磨粒抛光液初始状态下磨粒稳定性较高,抛光9 h内材料去除率较连续粒径磨粒抛光液高114.8%,之后磨粒出现小规模团聚现象,后9h材料去除率仅为均一粒径磨粒抛光液的59.6%,18 h内材料去除率仅为均一粒径磨粒抛光液的87.7%,但抛光后的晶圆表面粗糙度为0.151 nm。结论 一定时间内追求较高的材料去除率和较好的晶圆表面粗糙度选用混合粒径磨粒抛光液,但需要长时间CMP使用均一粒径磨粒抛光液更适合,因此,在工业生产中需要根据生产要求配合使用混合粒径磨粒抛光液和均一粒径磨粒抛光液。

TC4钛合金短电弧钻孔工艺性能研究

为了提高小孔钻削的加工效率和尺寸精度,文章提出了一种新颖高效的管电极短电弧钻孔方法。然而,由于电弧放电能量过大与进给速度不匹配,使得高效、高尺寸精度的小孔加工困难重重。文章揭示了基于脉冲电源的短电弧钻孔的工作原理,分析了SEAD的电压电流波形和截面形貌。此外,还研究了不同电极极性、电压、脉冲频率、占空比和电极进给速率对材料去除率(MRR)、电极相对磨损比(REWR)、平均直径和锥度的影响。最后,通过工艺参数优化实验,得到了小孔SEAD参数的最优组合,验证了小孔SEAD的加工性能。实验结果表明,在最佳加工参数下,小孔SEAD的材料去除率最高,为84.51μm/s,电极相对磨损比较低,为29.34%。加工小孔的最小平均直径和锥度分别为698.49μm和0.001 1°。

横向旋转磁场辅助电火花铣削加工烧结钕铁硼的效果研究

为了更好地解决电火花铣削加工烧结钕铁硼过程中蚀除颗粒排出困难的问题,文章引入横向旋转磁场。通过无磁场加工、横向恒定磁场辅助加工、横向旋转磁场辅助加工的加工效果对比试验,分析加工参数对材料去除率、表面粗糙度和电极损耗率的影响。从正离子的受力角度,分析无磁场、横向恒定磁场辅助、横向旋转磁场辅助电火花铣削烧结钕铁硼方法的材料去除率、电极损耗率和表面粗糙度的差异。结果表明:横向旋转磁场辅助电火花铣削烧结钕铁硼的材料去除率更高,表面粗糙度更好,电极损耗率更低。

研磨压力对聚晶金刚石表面质量的影响

使用金刚石平磨盘对聚晶金刚石(polycrystalline diamond,PCD)复合片的金刚石层进行高速研磨实验,研究研磨压力对PCD研磨去除率、表面粗糙度和表面形貌的影响。结果表明:当研磨压力为0.10~0.18MPa时,随着研磨压力的增大,PCD的研磨去除率增大,表面粗糙度减小。PCD研磨表面缺陷主要包括沿晶破碎、微小凹坑、机械划痕、微裂纹等,且随着研磨压力增大,研磨表面平滑面积扩大,机械划痕变小。

弹性基体软固结磨料磨具的材料去除机理

基于弹性磨具的磨抛工艺为硬脆材料超精密加工效率与加工质量的兼顾平衡提供了新的解决思路,但其磨抛过程的材料去除机理尚未明确。为研究弹性磨抛过程中的材料去除行为,以硅橡胶作为磨具基体材料,混合微米级金刚石磨料制备弹性基体软固结磨料磨具,利用有限元仿真分析方法研究弹性基体软固结磨粒的受力状态,结合接触力学与运动学分析建立考虑单颗磨粒磨损行为与有效磨粒数量的材料去除模型,通过石英玻璃试件的弹性磨抛加工试验验证预测模型的准确性。结果表明:石英玻璃试件的材料去除率随着磨抛压力、主轴转速、磨具偏角的增大而显著增加,而磨料粒径对其影响程度较小;当工艺参数组合为磨料粒径100μm、磨抛压力7 N、主轴转速1500 r/min、磨具偏角20°时,经60 min磨抛后,工件已加工表面粗糙度由1.069μm降至0.089μm,材料去除率为8.893×10^(8)μm^(3)/min;该试验条件下,建立的材料去除模型预测准确度相比Preston经典模型提高36.7%。研究成果可为实现硬脆材料的确定性材料去除提供技术支持和理论依据。