用物理实验绽放课堂的精彩

螺纹加工方法最常见的是数控车削加工。探讨数控车削加工时根据不同的加工精度、不同的加工材料，分别选取不同的编程指令、不同的工件装夹方式、不同的加工刀具、不同的切削参数等，在实际螺纹数控车削加工中的合理性。     

钛合金切屑形成过程的高速摄影研究

钛合金是航天、航空工业中的重要结构材料,但由于钛合金的切削加工性差、刀具摩损严重,加工易发生振动等原因,限制了加工质量和生产率的提高。而对于钛合金切屑形成过程的动态研究,为解决钛合金的难加工性将提供充分的依据。     

螺纹数控车削加工的工艺分析

螺纹加工方法最常见的是数控车削加工.探讨数控车削加工时根据不同的加工精度、不同的加工材料,分别选取不同的编程指令、不同的工件装夹方式、不同的加工刀具、不同的切削参数等,在实际螺纹数控车削加工中的合理性.探析螺纹数控加工的特殊性,探索如何实现精确控制螺纹数控车削加工,以及在实际加工中生产出高效、高精、稳定可靠的螺纹产品.     

KDP光学零件超精密车削加工误差的频谱特性与控制

超精密车削技术适于加工KDP(磷酸二氢钾)等频率转换类型的强光光学零件,但车削表面存在明显的加工纹理,导致抗激光损伤阈值降低。以加工表面误差幅值及其频谱分布为对象,分析了KDP光学零件超精密车削的加工特征和误差形态,采用功率谱密度(PSD)评价方法研究了工艺参数与误差频谱的内在关系,结果表明:不同进给速度及主轴转速将使螺旋形刀痕的间距发生变化,进而影响KDP表面误差的频率成分;切削深度虽然对误差频谱影响很小,但会改变PSD的幅值;当主轴转速高于500 r/min、进给速度小于2 mm/min、切削深度小于2 μm时能够加工出rms值优于20 nm的KDP面形。在此基础上,以典型KDP光学零件加工为例,通过超精密补偿车削方法将低频误差的PSD控制在300 nm2·mm以内,中高频误差的PSD控制到国家点火装置(NIF)标准线以下,满足强光系统的工作要求。     

切削参数对新型光学铝级金刚石车削刀具磨损的影响

光学器件和光学测量系统的关键部件主要通过超精密加工制造。铝合金具有很多优势,通常用于光子产业。光学领域对铝合金使用和需求的不断增加,促进了在铸造过程中采用快速凝固技术对铝合金等级重新改良的发展。优异的微观结构和改进的机械和物理性能是新型铝合金等级的特点。目前主要问题在于采用金刚石车削时,由于在切削性方面缺乏对铝合金性能的充分研究,导致机械加工数据库非常有限。本文通过改变金刚石的切削参数,测量切齿安装距超过4km时金刚石刀具的磨损,研究了快速凝固铝合金RSA 905的切削性能。改变的机械加工参数为切削速度、进给速度和切削深度。结果表明切削速度对金刚石刀具的磨损影响最大。主轴转速为500rpm、进给速度为25mm/min、切削深度为15μm时,刀具磨损达到最大值12.2μm;主轴转速为1750rpm、进给速度为5mm/min、切削深度为5μm时,刀具磨损达到最小值2.45μm。通常,较高的切削速度、较低的进给速度和较短的切削深度的组合可以减少金刚石刀具磨损。建立了模型统计以分析金刚石刀具磨损。通过该模型可以生成磨损图,从而确定切削参数产生最小磨损的区域。结果证明,快速凝固铝是更好的选择,为机械工程师使用这种材料提供了参考。     

切削参数对新型光学铝级金刚石车削刀具磨损的影响（英文）

光学器件和光学测量系统的关键部件主要通过超精密加工制造。铝合金具有很多优势,通常用于光子产业。光学领域对铝合金使用和需求的不断增加,促进了在铸造过程中采用快速凝固技术对铝合金等级重新改良的发展。优异的微观结构和改进的机械和物理性能是新型铝合金等级的特点。目前主要问题在于采用金刚石车削时,由于在切削性方面缺乏对铝合金性能的充分研究,导致机械加工数据库非常有限。本文通过改变金刚石的切削参数,测量切齿安装距超过4 km时金刚石刀具的磨损,研究了快速凝固铝合金RSA 905的切削性能。改变的机械加工参数为切削速度、进给速度和切削深度。结果表明切削速度对金刚石刀具的磨损影响最大。主轴转速为500 rpm、进给速度为25 mm/min、切削深度为15μm时,刀具磨损达到最大值12.2μm;主轴转速为1 750 rpm、进给速度为5 mm/min、切削深度为5μm时,刀具磨损达到最小值2.45μm。通常,较高的切削速度、较低的进给速度和较短的切削深度的组合可以减少金刚石刀具磨损。建立了模型统计以分析金刚石刀具磨损。通过该模型可以生成磨损图,从而确定切削参数产生最小磨损的区域。结果证明,快速凝固铝是更好的选择,为机械工程师使用这种材料提供了参考。     

单点金刚石车削加工切削距离的计算

讨论了大型金属反射镜在金刚石车削中,金刚石刀具的磨损对加工精度的影响;详细介绍了超精密加工中几种典型零件形状单点金刚石车削加工的切削距离计算方法,经计算在加工直径为1000mm的圆盘工件时,当刀具的进给量为2μm/r,切削距离达到近400km。通过计算为加工大型光学元件刀具磨损规律的研究提供分析基础。     

脉冲电流冲击力对电极间距的影响

利用时变场理论和瞬态动力学方程建立了电极及其支撑结构的瞬态耦合模型,分析了瞬态电磁场各参数的分布特点,并求解了电极及其支撑结构的动态响应状态参数。计算结果表明:玻璃钢支撑结构对于脉冲电流形成的冲击力载荷具有很好的缓冲作用;低弹性模量支撑材料在脉冲上升沿和峰值阶段均会产生波动性形变,但该波动性形变对电极间距不会造成太大的影响。     

几何光学 光学镜头、光学零部件

TH703 2005020883 红外线聚光非球面透镜的单点金刚石镜面切削方法=Single-point diamond mirror turing of infrared aspheric lens [刊,中]／谢晋(华南理工大学机械工程学院．广东,广州 (510640)),耿安兵…//光学精密工程．-2004,12(6)．- 566—569 根据硬脆性材料的延性域加工机理和面形误差补偿 加工方法,研究了圆弧形和平头形刀具的单点金刚石延性 域切削方法,在加工中直接获得了镜面切除面。利用数控     

单点金刚石飞切KDP晶体表面缺陷深度的研究

基于印压断裂力学理论分析了磷酸二氢钾晶体表面缺陷面积与中位裂纹深度的关系.在刀具参量和主轴转数一定的情况下,采用不同切削深度和进给速率对磷酸二氢钾晶体进行单点金刚石飞切加工实验,并计算晶体表面单位面积缺陷的占比系数.实验结果表明,晶体表面缺陷深度与面积占比系数成正相关,与理论分析结果相符,进而提出了利用计算晶体表面缺陷占比系数估测缺陷深度的方法.最后基于该方法得到高效率切削步骤,并加工获得了表面粗糙度算术平均值优于5nm的超光滑晶体表面.     

Condition monitoring of turning process using infrared thermography technique – An experimental approach

In metal cutting machining, major factors that affect the cutting tool life are machine tool vibrations, tool tip/chip temperature and surface roughness along with machining parameters like cutting speed, feed rate, depth of cut, tool geometry, etc., so it becomes important for the manufacturing industry to find the suitable levels of process parameters for obtaining maintaining tool life. Heat generation in cutting was always a main topic to be studied in machining. Recent advancement in signal processing and information technology has resulted in the use of multiple sensors for development of the effective monitoring of tool condition monitoring systems with improved accuracy. From a process improvement point of view, it is definitely more advantageous to proactively monitor quality directly in the process instead of the product, so that the consequences of a defective part can be minimized or even eliminated.In the present work, a real time process monitoring method is explored using multiple sensors. It focuses on the development of a test bed for monitoring the tool condition in turning of AISI 316L steel by using both coated and uncoated carbide inserts. Proposed tool condition monitoring (TCM) is evaluated in the high speed turning using multiple sensors such as Laser Doppler vibrometer and infrared thermography technique. The results indicate the feasibility of using the dominant frequency of the vibration signals for the monitoring of high speed turning operations along with temperatures gradient. A possible correlation is identified in both regular and irregular cutting tool wear. While cutting speed and feed rate proved to be influential parameter on the depicted temperatures and depth of cut to be less influential. Generally, it is observed that lower heat and temperatures are generated when coated inserts are employed. It is found that cutting temperatures are gradually increased as edge wear and deformation developed.     

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.     

数控裁剪机切割刀壳体振动噪声预测分析

高频往复式切割刀是柔性材料数控裁剪机的核心部件.该文对切割刀壳体的振动噪声改进措施进行研究.首先对切割刀进行刚体动力学分析,获取其所受动载荷情况,并通过数值计算验证了切割刀刚体动力学模型的可靠性.其次,基于有限元法获取切割刀壳体模态特性,并通过锤击激振实验验证了有限元模型的准确性.然后基于模态仿真结果进行谐响应分析,将...     

Dynamic Modeling of the Feed Drive System of a CNC Metal Cutting Machine

Studying the vibrational behavior of feed drive systems is important for enhancing the structural performance of computer numerical control (CNC) machines. The preload on the screw and nut position have a great influence on the vibration characteristics of the feed drive as two very important operational conditions. Rotational acceleration of the screw also affects the performance of the CNC feed drive when machining small parts. This paper investigates the influence of preload and nut position on the vibration characteristics of the feed drive system of a CNC metal cutting machine in order to be able to eliminate an observed resonance occurred at high rotational speeds of the screw, corresponding to high feed rates. Additionally, rational structural parameters of the feed drive system are selected in order to increase the rotational acceleration for improving the performance of the CNC machine. Experiments and analyses showed that by selecting specific parameters of feed drive system and simultaneously applying a certain value of preload, a 97% increase in rotational acceleration and 30% time reduction considering the vibration resistance at high rotational speeds can be achieved.     

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.     

超声振动对光学玻璃加工的锯切力特征研究

超声振动辅助方法已在各种硬脆性材料的加工工艺中得以应用,其优异的加工能力和效果已得到广泛证明。本研究中通过采集有无超声振动条件下锯切光学玻璃的平均锯切力以及单颗金刚石磨粒划擦实验下的力信号,对不同工艺条件下的平均锯切力、单颗磨粒受力特征进行分析。同时通过扫描电镜观察对应力信号下工件与工具加工后表面形貌,进一步通过超声振动下材料去除机理解释超声振动对锯切力影响。结果表明：与传统锯切工艺相比,超声振动辅助使得单颗磨粒划擦过程中的受力降低引起平均锯切力的降低;超声振动改变普通锯切下材料的去除方式;同时可使工具保持良好的锯切状态,降低光学玻璃材料的锯切力比,改善其可加工性。     

Feasibility study of nonlinear tuned mass damper for machining chatter suppression

In order to improve the performance of the tuned mass damper (TMD) for machining chatter suppression, a new-type of nonlinear TMD is proposed in this paper. Compared with the common linear TMD, the nonlinear TMD is equipped with an additional series friction-spring element. The capability of the nonlinear TMD in suppressing machining chatter vibration is investigated in this paper. The harmonic balancing method (HBM) is used to estimate the frequency response function (FRF) of the machining system to which the nonlinear TMD is attached. Considering the special nature of the machining stability problem, the optimal design parameters of this nonlinear TMD are those that minimize the magnitude of the real part of the FRF of the nonlinear TMD damped machining system. This paper also demonstrates the performance of the optimally tuned nonlinear TMD for machining stability improvement by calculating the stability diagrams for the milling of the nonlinear TMD damped workpiece. The calculation results show that more than 30% improvement in the critical limiting cutting depth can be obtained, compared to the optimally tuned linear TMD.     

Regenerative vibration avoidance due to tool tangential dynamics in interrupted turning operations

Linear stability models are often used to predict regenerative vibrations in turning representing continuous operations, simple cutting geometries with constant coefficients and/or dominant modes acting in the feed direction. However, turning of components with interrupted features, such as turbine cases, may lead to large tool overhangs with vibration motions in the cutting speed direction and tool cut-off periods that result in the latter approaches being insufficient. This paper proposes a stability model for chatter in interrupted turning when the dominant vibration is orthogonal to the chip section plane. The method requires the calculation of a dynamic displacement factor that depends on the tool vibration frequency. The simulations of the model are supported by experimental tests for different contact fractions.     

Evaluation of the tool life and fracture toughness of cutting tools boronized by the paste boriding process

The present study evaluates the tool life and the fracture toughness of AISI M2 steel cutting tools boronized by the paste boriding process. The treatment was done in selective form on the tool tips of the steels. The temperatures were set at 1173 and 1273 K with 4 h of exposure time and modifying the boron carbide paste thicknesses in 3 and 4 mm. Microindentation fracture toughness method was used on the borided tool at the temperature of 1273 K and a 4 mm paste thickness, with a 100 g load at different distances from the surface. Also, the borided cutting tools were worn by the turning process that implied the machining of AISI 1018 steel increasing the nominal cutting speed, of 55 m/min, in 10 and 25% and maintaining the feed and the depth cut constants. The tool life was evaluated by the Taylor's equation that shows the dependence of the experimental parameters of the boriding process.