光学玻璃超声振动维氏压痕中位裂纹的实验研究

为了进一步掌握光学玻璃材料超声振动辅助磨削亚表面损伤机理,设计常规和超声振动条件下维氏压痕实验,调查两种情况下K9光学玻璃压痕形貌特征;采用磁性复合流体抛光方法检测K9光学玻璃压痕区域的中位裂纹深度,对常规压痕系统中位裂纹模型进行两次系数修正,获得超声振动条件下的维氏压痕系统中位裂纹深度模型.通过超声振动维氏压痕实验计算静态和动态断裂韧性,得到两种加载条件的一次修正系数分别为0.08和0.06;结合检测中位裂纹深度实验结果拟合获得的两种条件下二次修正系数数值接近,分别为94.75和94.50.结果表明该模型对超声振动和加工条件具有良好的识别度.     

基于散粒磨料振动抛光非球面加工技术研究

鉴于非球面光学元件的应用日益广泛,非球面加工技术成为研究热点,提出一种基于散粒磨料振动抛光非球面的加工方法。非球面元件待抛光表面与磨粒均匀接触,通过振动抛光装置为游离磨粒提供抛光作用力,使材料去除均匀,降低表面粗糙度。以材料为ZK-10L、尺寸为Φ55 mm的光学元件为实验对象,分析了振动幅度、抛光液浓度、磨粒粒径和抛光时间对抛光效果的影响,当振动幅度为5 mm、抛光液浓度为80 g/L、磨粒粒径为1 mm时,振动抛光8 h后试件的表面粗糙度从84.4 nm降低到9.4 nm,而试件的面形精度基本不变,从而在保证面形的前提下达到抛光的目的。     

螺旋锥齿轮超声研磨的试验研究

介绍了螺旋锥齿轮超声研磨加工的方法,利用声学和超声空化的相关理论分析了超声研齿的材料去除方式,在齿面接触区具有旋转超声加工的特点,在非接触区,超声空化对齿面产生空蚀或者直接激励磨粒撞击和滑擦齿面,引起材料的去除。进行了超声研齿和普通研齿的对比试验,结果表明超声研齿的材料去除率可达到普通研磨的3倍,齿面粗糙度低至Ra0.2μm,水平截距c1.2μm。齿面研磨后的SEM照片证实,齿面质量明显提高。     

熔融石英玻璃无水环境固结磨粒抛光特性

为了克服游离磨粒抛光的随机性、磨料浪费以及产生的水合层等问题,提出了一种无水环境下熔融石英玻璃固结磨粒抛光技术。研究实现了稳定的抛光轮烧结工艺,并应用于熔融石英玻璃抛光加工,通过对加工产物和抛光轮粉末进行EDS能谱分析和XRD衍射分析,从微观上初步阐述了固结磨粒抛光的去除机理;从宏观上探索压力和转速对去除效率和表面粗糙度的影响。实验结果表明:加工过程中,在法向力和剪切力作用下,CeO₂磨粒和熔融石英发生化学反应,CeO₂将SiO₂带出玻璃,实现材料去除;同时,压力和转速对加工效率影响并不遵循Preston公式,温升和排屑成为决定去除效率的关键。     

脆性光学材料的超声磨削实验研究

分别采用超声磨削和普通磨削加工方法加工了几种脆性光学材料,研究了几种主要工艺参数对工件加工表面粗糙度的影响。结果表明,超声频率和振幅、金刚石磨料粒度、切深、工具的横向进给速度和旋转速度等工艺参数对表面粗糙度的影响较大。通过比较发现,超声磨削方法比普通磨削方法具有更好的加工表面粗糙度,更高的材料去除率,以及更低的工具磨损量。     

超声辅助磨削杯形砂轮变幅器设计与试验*

超声辅助磨削在硬脆材料的加工中应用广泛。为研制以杯形砂轮为加工工具的超声辅助磨削主轴附件式工具系统,建立了杯形砂轮变幅器的理论模型,推导了其频率方程,并通过Matlab开发了杯形砂轮变幅器设计软件。利用该软件结合有限元分析对杯形砂轮变幅器进行了设计。将研制的杯形砂轮变幅器与BT40刀柄一体化外套筒、导电滑环装配组成了杯形砂轮超声辅助磨削主轴附件式工具系统。对该超声振动系统进行了阻抗分析试验及超声谐振试验,结果表明,该超声振动系统阻抗性能较好,能够使杯形砂轮产生稳定的超声振动,验证了所提出的设计方法的正确性,为主轴附件式超声磨削装置的设计提供了理论参考。     

微型轴承内滚道超声辅助超精研磨系统的设计研究*

为了提高5G基站中微型轴承的精度和使用寿命,基于微型轴承外套圈结构特征提出一种超声振动辅助研磨轴承外圈滚道的加工工艺。通过坐标变换及运动合成,获得了振动研磨轴承外圈滚道的工作面轨迹特点,阐明了振动高效研磨的本质特征;之后,分别采用等效电路法和有限分析法,建立了振动系统的等效电路图与频率方程,分析了该系统模型的固有模态与谐响应特性;最后,通过对自行研制的超声辅助研磨系统分别进行振动特性测试和加工效果测试。结果表明,加工系统振动频率相对设计频率的误差率为10‰,超声振幅为12.95μm,加工轴承滚道的粗糙度和轮廓度较传统研磨加工分别降低了27.17%和24.1%。     

单颗金刚石切削无氧铜的声发射关联维特征*

声发射技术可以实现无氧铜切削加工特征的监测与评价。采用声发射技术监测单颗金刚石磨粒旋转切削无氧铜，利用G-P算法重构出声发射时域信号相空间，采用自相关函数法计算出相空间时间延迟参数，通过相空间双对数曲线的计算，得到不同切削工况下的关联维数。研究结果表明，进给速度和切削速度对声发射信号影响较不显著，切深与声发射信号振幅呈正效应关系；声发射信号双对数曲线呈现阶段性增加趋势，并逐渐收敛于饱和状态，关联维数随着嵌入维数的增加先快速下降后趋于平稳；金刚石切削无氧铜的声发射信号具有混沌运动变化特性，在较小嵌入维数时，关联维数与切深和切削速度呈现线性负效应关系，与进给速度呈现线性正效应关系。该研究为无氧铜的切削加工提供理论参考。     

超声辅助加工系统的刀具状态自感知算法

超声波振动台内含压电材料,可以拾取切削过程产生的振动信号,实现不借助外部传感器刀具工作状态的自感知。为了从刀具振动信号中获取有效信息,该文提出一种基于经验模态分解的时频域重构算法。首先,采用经验模态分解算法将原始信号分解,得到多个固有模态函数分量和残差分量;其次,计算原始信号与各分量之间的时频域互相关系数;再次,归一化时频域互相关系数作为权重值,将固有模态函数分量和残差进行重构;最后,通过数值仿真和超声辅助加工实验,验证了基于经验模态分解的时频域重构算法的去噪性能,提取了信噪比为5.03 dB的目标信号,从而实现了超声辅助加工系统的自感知功能。     

基于环摆式双面抛光法加工预测模型的去除均匀性研究

针对环摆式双面抛光难以建立稳定去除函数并进行加工面型预测这一问题,提出了基于磨粒运动学的环摆式双面抛光加工预测模型,并通过预测模型分析不同参数影响下元件表面去除均匀性,针对不同特征面型给出优化策略以指导加工实验。首先,根据环摆式双面抛光机理,探究了环摆式双面抛光中影响去除均匀性的主要因素,提出了元件上、下表面磨粒运动学模型,结合Preston方程给出了基于磨粒运动学的环摆式双面抛光去除均匀性预测模型。根据实际加工工况,分析了不同抛光均匀性影响因素下的磨粒轨迹分布与抛光去除非均匀性,最后通过加工实验验证环摆式双面抛光加工预测模型。实验结果表明：环摆式双面抛光加工预测模型的预测结果与实际加工结果基本吻合,其面型去除特征相同。元件上表面是元件去除非均匀性的主要来源,通过改变中心偏心距、径向摆动距离等参数能改变元件上表面的去除非均匀性,从而影响元件整体面型特征,并实现基于预测模型指导下元件表面面型的快速收敛。     

Longitudinal ultrasonic vibration assisted guillotining of stacked paper

Ultrasonic vibration assisted cutting is a complex process with high dynamics. The interaction between cutting tool and workpiece is of key interest to understand the entire process. Experimental investigations are limited by the dynamics of the measurement system, and thus appropriately modeling of the ultrasonic vibration assisted cutting process is essential. In this investigation, a dynamic model regarding the ultrasonic vibration assisted guillotining of stacked paper sheets is developed. A Kelvin–Voigt material model, representing the individual sheets, is chosen, with its stiffness and damping parameters being empirically determined. A novel measurement strategy for studying the contact time and interaction between cutting tool and workpiece is introduced. It allows the verification of the highly dynamic behavior of the developed model. With the dynamic model, the experimentally observed cutting forces can be calculated. It is found that the dynamic forces cause a quicker failure of the material, which leads to a lower compression of the stack prior to reaching the critical cutting force.     

Autoresonant control of nonlinear mode in ultrasonic transducer for machining applications

Experiments conducted in several countries have shown that the improvement of machining quality can be promoted through conversion of the cutting process into one involving controllable high-frequency vibration at the cutting zone. This is achieved through the generation and maintenance of ultrasonic vibration of the cutting tool to alter the fracture process of work-piece material cutting to one in which loading of the materials at the tool tip is incremental, repetitive and controlled. It was shown that excitation of the high-frequency vibro-impact mode of the tool-workpiece interaction is the most effective way of ultrasonic influence on the dynamic characteristics of machining. The exploitation of this nonlinear mode needs a new method of adaptive control for excitation and stabilisation of ultrasonic vibration known as autoresonance. An approach has been developed to design an autoresonant ultrasonic cutting unit as an oscillating system with an intelligent electronic feedback controlling self-excitation in the entire mechatronic system. The feedback produces the exciting force by means of transformation and amplification of the motion signal. This allows realisation for robust control of fine resonant tuning to bring the nonlinear high Q-factor systems into technological application. The autoresonant control provides the possibility of self-tuning and self-adaptation mechanisms for the system to keep the nonlinear resonant mode of oscillation under unpredictable variation of load, structure and parameters. This allows simple regulation of intensity of the process whilst keeping maximum efficiency at all times. An autoresonant system with supervisory computer control was developed, tested and used for the control of the piezoelectric transducer during ultrasonically assisted cutting. The system has been developed as combined analog-digital, where analog devices process the control signal, and parameters of the devices are controlled digitally by computer. The system was applied for advanced machining of aviation materials.     

Rotary ultrasonic machining of CFRP: A mechanistic predictive model for cutting force

Cutting force is one of the most important output variables in rotary ultrasonic machining (RUM) of carbon fiber reinforced plastic (CFRP) composites. Many experimental investigations on cutting force in RUM of CFRP have been reported. However, in the literature, there are no cutting force models for RUM of CFRP. This paper develops a mechanistic predictive model for cutting force in RUM of CFRP. The material removal mechanism of CFRP in RUM has been analyzed first. The model is based on the assumption that brittle fracture is the dominant mode of material removal. CFRP micromechanical analysis has been conducted to represent CFRP as an equivalent homogeneous material to obtain the mechanical properties of CFRP from its components. Based on this model, relationships between input variables (including ultrasonic vibration amplitude, tool rotation speed, feedrate, abrasive size, and abrasive concentration) and cutting force can be predicted. The relationships between input variables and important intermediate variables (indentation depth, effective contact time, and maximum impact force of single abrasive grain) have been investigated to explain predicted trends of cutting force. Experiments are conducted to verify the model, and experimental results agree well with predicted trends from this model.     

Theoretical and experimental investigations on rotary ultrasonic surface micro-machining of brittle materials

Many brittle materials, such as single-crystal materials, amorphous materials, and ceramics, are widely used in many industries such as the energy industry, aerospace industry, and biomedical industry. In recent years, there is an increasing demand for high-precision micro-machining of these brittle materials to produce precision functional parts. Traditional ultra-precision micro-machining can lead to workpiece cracking, low machined surface quality, and reduced tool life. To reduce and further solve these problems, a new micro-machining process is needed. As one of the nontraditional machining processes, rotary ultrasonic machining is an effective method to reduce the issues generated by traditional machining processes of brittle materials. Therefore, rotary ultrasonic micro-machining (RUμM) is investigated to conduct the surface micro-machining of brittle materials. Due to the small diameter cutting tool (<500 μm) and high accuracy requirements, the impact of input parameters in the rotary ultrasonic surface micro-machining (RUSμM) process on tool deformation and cutting quality is extremely different from that in rotary ultrasonic surface machining (RUSM) with relatively large diameter cutting tool (∼10 mm). Up till now, there is still no investigation on the effects of ultrasonic vibration (UV) and input variables (such as tool rotation speed and depth of cut) on cutting force and machined surface quality in RUSμM of brittle materials. To fill this knowledge gap, rotary ultrasonic surface micro-machining of the silicon wafer (one of the most versatile brittle materials) was conducted in this study. The effects of ultrasonic vibration, tool rotation speed, and depth of cut on tool trajectory, material removal rate (MRR), cutting force, cutting surface quality, and residual stress were investigated. Results show that the ultrasonic vibration could reduce the cutting force, improve the cutting surface quality, and suppress the residual compressive stress, especially under conditions with high tool rotation speed.     

Ultrasonic excitation affects friction interactions between food materials and cutting tools

In the food industry, ultrasonic cutting is used to improve separation by a reduction of the cutting force. This reduction can be attributed to the modification of tool–workpiece interactions at the cutting edge and along the tool flanks because of the superposition of the cutting movement with ultrasonic vibration of the cutting tool. In this study, model experiments were used to analyze friction between the flanks of a cutting tool and the material to be cut. Friction force at a commercial cutting sonotrode was quantified using combined cutting–friction experiments, and sliding friction tests were carried out by adapting a standard draw-off assembly and using an ultrasonic welding sonotrode as sliding surface. The impact of material parameters, ultrasonic amplitude, and the texture of the contacting food surface on friction force was investigated. The results show that ultrasonic vibration significantly reduces the sliding friction force. While the amplitude showed no influence within the tested range, the texture of the contact surface of the food affects the intensity of ultrasonic transportation effects. These effects are a result of mechanical interactions and of changes in material properties of the contact layer, which are induced by the deformation of contact points, friction heating and absorption heating because of the dissipation of mechanical vibration energy.     

Ultrasonically assisted turning of aviation materials: simulations and experimental study

Ultrasonically assisted turning of modern aviation materials is conducted with ultrasonic vibration (frequency f approximately 20 kHz, amplitude a approximately 15 microm) superimposed on the cutting tool movement. An autoresonant control system is used to maintain the stable nonlinear resonant mode of vibration throughout the cutting process. Experimental comparison of roughness and roundness for workpieces machined conventionally and with the superimposed ultrasonic vibration, results of high-speed filming of the turning process and nanoindentation analyses of the microstructure of the machined material are presented. The suggested finite-element model provides numerical comparison between conventional and ultrasonic turning of Inconel 718 in terms of stress/strain state, cutting forces and contact conditions at the workpiece/tool interface.     

Built-up edge investigation in vibration drilling of Al2024-T6

Adding ultrasonic vibrations to drilling process results in an advanced hybrid machining process, entitled “vibration drilling”. This study presents the design and fabrication of a vibration drilling tool by which both rotary and vibrating motions are applied to drill simultaneously. High frequency and low amplitude vibrations were generated by an ultrasonic transducer with frequency of 19.65 kHz. Ultrasonic transducer was controlled by a MPI ultrasonic generator with 3 kW power. The drilling tool and workpiece material were HSS two-flute twist drill and Al2024-T6, respectively. The aim of this study was investigating on the effect of ultrasonic vibrations on built-up edge, surface quality, chip morphology and wear mechanisms of drill edges. Therefore, these factors were studied in both vibration and ordinary drilling. Based on the achieved results, vibration drilling offers less built-up edge and better surface quality compared to ordinary drilling.     

超声波加工盲孔的研究

本文以超声波加工机对玻璃等硬脆材料元件的加工工艺为主要研究对象,阐述了超声波加工的原理、变幅杆和刀具的设计以及加工工艺的研究,并将它应用在空间光学系统中光学元件的轻量化的加工。同时对加工后的表面微观特性——表面微裂纹和表面微应力进行具体测试分析,以解决在复杂的空间环境中元件的表面质量对使用精度和应力变形的影响,从而提出适于大型光学元件轻量化的工艺技术方法。