High-brightness laser plasma soft X-ray source using a double-stream gas puff target irradiated with the Prague Asterix Laser System (PALS)

High brightness laser plasma soft X-ray source based on a recently developed double-stream gas puff target irradiated with 0.5 ns laser pulses with energies up to 700 J from the Prague Asterix Laser System (PALS) is presented. The gas puff target was created by pulsed injection of xenon into a hollow stream of helium using an electromagnetic valve system with the double-nozzle setup. Soft X-ray emission was measured using the transmission grating spectrograph coupled to a CCD camera and the calibrated silicon photodiodes. The absolute soft X-ray production was determined to be 160 J for 540 J of laser energy, giving the soft X-ray conversion efficiency of about 30%. The source has been used in initial experiments on soft X-ray ablation of organic polymers and elemental solids.     

Welding phenomena and in-process monitoring in high-power YAG laser welding of aluminium alloy

Laser welding of aluminium alloys is difficult because of their low laser coupling, easy formation of welding defects, etc. and thus the establishment of in process monitoring technique is expected in various industries to obtain highly reliable laser welds. In this study, therefore, both the reflected laser beam and radiation light from die molten pool were investigated as monitoring signals during YAG laser welding of A5052 and A5182 aluminium alloy to confirm validity and usefulness of these signals for monitoring. At the same time, laser-welding phenomena were observed through a high-speed video camera to better interpret the monitored signals. Two signals were detected by utilizing photo sensors and band pass or cut-off filters coaxially against a laser beam and from the above-back direction. In this paper, experimental setup, and monitoring and observation results were presented. The correlation between monitoring signals and welding phenomena was clarified when the welding defects such as underfilling and through holes were formed.     

High performance photonic devices made with semiconducting polymers

High performance photonic devices fabricated from conjugated polymers have been demonstrated, including light-emitting diodes, lightemitting electrochemical cells, photovoltaic cells, photodiodes and optocouplers. Performance parameters have been improved to levels comparable to, or better than, their inorganic counterparts. A brief review is given with emphasis on recent progress in Santa Barbara.     

Modeling the radiometric imaging process of weld pool

In the vision monitoring or controlling the arc welding process, it is a prerequisite to get a clear image of weld pool. However, the disturbance of arc radiation makes imaging of weld pool difficult and optical filters are usually used to improve the image quality. In this paper, a radiometric imaging model is established to investigate the influence of the filter on the image quality of the weld pool, in which the spectral distribution of weld pool radiation, the spectral transmittance of the filter, the spectral sensitivity of the camera are all considered. With the proposed model, the influence of the factors on weld pool imaging can be inferred and the selection of optical filters is discussed.     

Effects of pulsing frequencies on macro-particle contamination during pulsed vacuum arc deposition

Offering high deposition rates and being suitable for thin film fabrication, vacuum arc deposition (VAD) has been investigated extensively. However, macro-particles (MPs) emitted from the vacuum arc degrade the properties of the deposited samples and various types of magnetic filters have been proposed to mitigate macro-particle contamination. Unfortunately, the resulting deposition efficiency is inevitably compromised. In this work, we used a direct current (DC) based pulsed vacuum arc to deposit copper on a glass substrate. DC ensures continuous arc burning to achieve better stability, and the pulsed power provides high instantaneous and discontinuous energy that affects the generation of MPs. Four sets of experiments were done, and the relationship between the pulsing frequencies and MPs deposited on the substrate was studied. Our results show that the MPs tend to be smaller when the pulsing frequency increases, and the MP ratios vary with the pulsing frequencies in a different way than duty cycles. Several factors related to this phenomenon are discussed.     

Turbine airfoil degradation in the persian gulf war

Helicopter turbine engines used in the Desert Shield and Desert Storm operations experienced excessive sand ingestion. Fine particles were able to bypass filters and proceed through the combustor or cooling gaspaths. The first-stage turbine vanes were impacted with viscous silicate particles, forming a deposit on the leading-edge root platform and resulting in overheating and oxidation. The chemistry of the raw sand determines that of the ingested powders, the deposits, and the material reactions.     

Photoconductivity in Langmuir—Blodgett multilayer structures of phthalocyaninato-polysiloxane

The electrical and photoelectrical properties of planar photodiodes based on phthalocyaninato-polysiloxane (PcPS) are presented. Sandwich structures consisting of thin PcPS Langmuir—Blodgett films have been prepared between semi-transparent gold and aluminum electrodes. These structures possess pronounced rectifying behavior. The photocurrent spectra exhibit peaks at 550 and 700 nm. The wavelength dependence of the photoconductivity clearly differs from the linear optical properties.     

Acoustic emission based tool contact detection for ultra-precision machining

Precise tool length measurement and work coordinate setup have been challenging tasks in ultra-precision machining. An acoustic emission (AE) sensor can be used to do both tasks at the same time based on AE generated on contact. First, a parametric study was conducted to identify the relationship between damage on the workpiece and key parameters. Second, two approaches, continuous and incremental, were proposed to minimize the potential damage to the workpiece surface. The incremental method produced much smaller damage while the continuous method minimized the setup time. Proper selection of either method depending on the application would improve the precision of tool length and work coordinate setup.     

Identification of dynamic instabilities in machining process using the approximate entropy method

Chatter instability is a persistent problem in machining process that produces vibrations characterized by nonlinear and nonstationary dynamics. Although traditional fast Fourier transform approaches are typically used for the monitoring of chattering in industry, the method is suitable only for linear and stationary signals. In this paper, methods based on approximate entropy (ApEn) are proposed to identify chatter instabilities in milling process. as entropy is an index of the irregularity and complexity related to randomness from data series. The attractiveness of the ApEn approach is that it can deal with nonlinear and nonstationary data, requires a relatively small number of observations and can be used for noisy signals. For a lab-scale milling experimental setup, the ApEn was implemented under a time-frequency monitoring method, showing that instable chattering is associated with entropy increment for a frequency range. In contrast, stable milling led to an entropy pattern where high-entropy values are concentrated at high frequencies, which are related to the natural dynamics of the cutting tool.     

Stress corrosion cracking initiation under the disbonded coating of pipeline steel in near-neutral pH environment

A novel test setup has been used in this study to simulate stress corrosion cracking initiation under a disbonded coating on an X-65 pipeline steel. In this setup, the synergistic effects of cyclic loading, cathodic protection and soil solution environment under disbonded coatings have been considered. When the X-65 pipeline steel was exposed to the test environment, there existed a wide range of corrosion products on the steel surface in the gradient of cathodic protection. Increasing the test time and the maximum stress increased the possibility of stress corrosion cracking initiation in regions with a high susceptibility to pitting corrosion.     

Sweeping filters and tooth rotation energy estimation (TREE) techniques for machine tool condition monitoring

This paper presents a method for the condition monitoring of the milling cutting process based upon a combination of two techniques; sweeping filters and tooth rotation energy estimation (TREE). Existing spindle speed and spindle load signals from the machine are used thus avoiding the need for any additional sensors. The sweeping filter technique determines the frequency components of the spindle signal using low cost hardware. The filter's cut off frequency is swept across a range of frequencies and its output is acquired and analysed in real time. The variations of individual tooth energies estimated by the TREE technique in the time domain are used to verify the results. The hybrid approach created is based on the verification of any indicated faults before making a final conclusion about the health of the cutting tool. This provides a robust and reliable tool monitoring system that is able to identify tool breakage in real time during machining operations.     

焊接现场脉冲GTAW熔池图像动态检测

通过熔池的动态观测可以获得焊接过程的稳定性和连续性等信息.熔池的动态观测目前基本上停留在试验室阶段,焊接现场对熔池进行观测在改进工艺和指导生产等方面更具意义.针对焊接现场焊接电源不能修改,非计算机可控,电流电压波形未知等问题,在焊接现场建立了一套焊接熔池图像动态检测系统.根据焊接现场脉冲GTAW的特点,采用"外同步取像"方式确定了焊接现场取像的关键制约因素--取像时刻;并利用电弧光谱分析建立了减小弧光干扰的复合滤光系统;在适合的取像时刻,CCD摄像系统配合复合滤光系统,在焊接现场检测到了清晰的熔池图像.     

泡沫陶瓷过滤器净化原理及含过滤器浇注系统的设计

对浇注系统、夹杂产生物来源及金属液体流态进行分析，氢气泡流体动力学实验表明，在浇注系统中过滤器的主要功能是对液态金属产生“整流”净化作用。采用相似理论通过水力模拟实验利用最小二乘法得到过滤器流动阻力的表达式，提出泡沫陶瓷过滤器在浇注系统中放置位置和放大截面积的设计方法。     

基于被动视觉的管子-管板GTAW熔池检测及处理

针对换热器管子-管板自动焊的特点,设计了一套适应于管子管板钨极氩弧焊(GTAW)的CCD视觉传感器和减光/滤光系统,实时获取管子管板焊接液态熔池图像。开发了一套基于部件树的图像特征点提取算法,能够有效获取管子管板GTAW熔池边缘图像,通过曲线拟合方法,可获取完整的熔池轮廓曲线和熔池特征尺寸信息,进一步实现管子-管板自动焊远程监控。     

An approach to measure the pose of RHJD4-1 arc welding robot for calibration

A measurement setup used for robot calibration was designed to meet the requirement of off-line programming technique. The robot end-effector pose (position and orientation) can be calculated indirecdy by using this setup. The setup has been applied to RHJD4-1 arc welding robot. The experimental results show the method of pose measuring using the measurement setup is simple and reliable to finish pose measuring.for robot calibration. In addition, the setup can measure the position repeatability of robot.     

Quick 3D Modeling of Machining Environment by Means of On-machine Stereo Vision with Digital Decomposition

The paper describes a three dimensional vision-based modeling system, which can efficiently and accurately construct solid models of a machining environment including the workpiece setup with jigs and fixtures on the machine table. The unique methods of the object recognition with various key technologies have been developed based on the simultaneous real and virtual stereo image processing. Since the constructed model accurately matches with the real setup, real time NC program verifications can be performed for 100% collision-free machining simulation. The prototyped system has been successfully verified by implementation on several real machining systems.     

A Study on Tribology in Minimal Quantity Lubrication Cutting

Despite the fact that minimal quantity lubrication (MQL) machining produces almost similar cutting performance to conventional flood supply machining while using much less metal working fluid (MWF), it has not been fully utilized in industry due to lack of understanding of the fundamental process physics. To take full advantage of MQL machining and expand its applicability, an understanding of its tribological behavior is critical. Hence, in this study, the adsorption characteristics of MQL media during orthogonal cutting was investigated using two experimental setups; one in a high vacuum chamber with a mass spectrometer to observe mass changes of MQL media during cutting, and another setup in an atmospheric chamber where the supply of MQL media can be controlled. The former is mainly for analysis of the tribological behavior of MQL media, and the latter for cutting performance monitoring. It was found that the adsorption amount of MQL media was closely related to lubrication behavior. Oxygen in MQL supply plays a significant role in lubrication. Ultrasonic vibration cutting tests with MQL were conducted for further understanding of lubrication mechanism.     

Innovative measurement technique to determine equibiaxial flow curves of sheet metals using a modified Nakajima test

Since an inhomogeneous punch pressure distribution occurs in the Nakajima test, equibiaxial flow curves have been determined solely in the hydraulic bulge test so far. By using an innovative measurement technique, it is possible to determine both the punch pressure and strains that occur in the Nakajima test. In this paper, a calibration and realization strategy is presented that allows to determine accurate equibiaxial flow curves for sheet metal materials using a modified Nakajima test without inverse parameter identification. This setup is suitable to substitute the expensive and time-consuming hydraulic bulge test by a simple and common experimental setup.     

中高速柴油机曲轴锻件RR弯曲镦锻工装的模式化设计

简要介绍了中高速柴油机曲轴锻件的RR弯曲镦锻工艺。在分析了RR弯曲镦锻工装结构特点的基础上提出RR弯曲镦锻工装模式化设计方案