A Confocal Probe based on Time Difference Measurement

A low cost confocal probe based on time difference measurement has been developed. A tuning fork is used to modulate the focal length of the probe. An auxiliary arm is introduced to the optical system. This arm can be utilized for carrying out lateral measurement or for providing a reference signal. The position of the surface is determined by measuring the time difference between two successive peak intensities of the measuring signal or that between peak intensities of measuring and reference signals. Some key problems in probe design are discussed. A correlation based technique for determining the time difference between two peak pulses is developed. Error compensation technique for nonlinearity and other errors is introduced. The excellent performance of the probe has been proven by experiments.     

Accurate two-dimensional modelling of piezo-composite array transducer elements

The assumption of piston-like behaviour is widely applied when modelling ultrasonic transducers. Experimental measurements of the directivity patterns of piezo-composite array transducers have shown that this assumption is not valid for small element sizes. An alternative modelling approach has been developed based on the assumption that the variation in pressure across the face of each array element can be described by a Hanning window. The effect of inter-element cross talk has been included in the model by using a window larger than the nominal size of the element. This approach has been shown to produce excellent results via validation against experiment for directivity patterns and array surface displacement.The improved modelling method has been used to quantify the errors introduced by the assumption of piston-like behaviour by comparison of modelled beam profiles generated using simple delay and sum beam forming. This has been performed by simulating a variety of different beam types and monitoring the following parameters: beam width, maximum amplitude, and beam angle. These simulations show that the only parameter significantly affected is the relative amplitude of different beam angles. The improved directivity model predicts that the maximum beam amplitude decreases with increasing beam angle at a higher rate than directivity models based on piston-like behaviour; the maximum error recorded was approximately 3 dB.     

Development of a 45° tilted on-machine measuring system for small optical parts

A new contact type of on-machine measuring system is developed in order to measure aspherical optical parts with steep surface angle for large numerical aperture (NA). A ceramic air slider made of SIALON is adopted for the measurement probe because of its low thermal expansion coefficient, high rigidity and light weight. A high accuracy glass scale is employed to reduce the thermal drift of the displacement gauge. The air slider or the measuring probe is tilted for 45° against the aspherical workpiece axis, and the probe is scanned over the workpiece surface, so as to keep the contact angle between the probe axis and the contact surface constant in order to reduce the change in the probe friction force.     

合金铸铁光束熔凝处理后的组织和硬度

采用自研的ＳＲ－Ⅱ型５ｋＷ聚焦光束加热设备对珠光体合金铸件进行了表面熔凝强化处理。借助扫描电镜、光学显微镜、显微硬度和表面硬度计研究了采用不同聚焦模式的光束熔凝处理的合金铸铁的表面硬度、显微硬度分布及光束热作用区的组织转变特点。结果表明,当采用单一模式的反光镜聚焦时,功率密度较低、热作用区的奥氏体发生了托氏体－索氏体转变;而采用透镜与反光镜配合的复式聚焦模式时,由于功率密度的提高,奥氏体转变为马氏     

On-machine three-dimensional monitoring technique using machining laser

An on-machine three-dimensional monitoring system has been developed that uses machining YAG laser as a source of light for monitoring. In the monitoring stage, the output of the laser is decreased. The reflected light from a workpiece is taken out with a beam sampler on the way of the optical system, and observed by CMOS image sensor. This system can measure both Z-direction depth and the position of X–Y-direction. Because the same laser and the optical system are used, the system has no gap of an optical axis between the measurement and the machining, and also has no limitation of viewing angle. Every three-dimensional shape which can be machined by laser beam can be measured. In this paper, system configuration, monitoring technique and the experimental results are described.     

A quantitative alternative to the Vickers hardness test based on a correlation between thermal diffusivity and hardness—applications to laser-hardened carburized steel

A quantitative non-destructive test technique for characterizing heat treated steel based on a theoretical model was developed and verified by experiments using the optical beam deflection technique at metallic samples, heated by a Gaussian beam. The analytic solution of the heat equation with appropriate approximations provides a theoretical expression of the surface temperature, which is an important guide to optimize the experimental process. Measurements have been focused on determining both, mechanical parameters and thermal local properties, in order to find correlations. The theoretically described thermal diffusivity was experimentally measured by using the new developed photo-thermal deflexion inversion procedure. A simple correlation between the micro-hardness according to Vickers and the thermal diffusivity was found for laser-hardened specimens depending on their microstructure and individual chemical composition.     

Design of a six-axis high precision machine tool and its application in machining aspherical optical mirrors

The paper presents the design of a six-axis machining system and its application in fabricating large off-axis aspherical mirrors with sub-aperture lapping techniques. The new system is based on computer-controlled optical surfacing (CCOS), which combines the faculties of grinding, polishing, and on-machine profile measuring, has the features of conventional loose abrasive machining with the characteristics of a tool having multiple degrees of freedom moving in planar model. And a novel dual touch-trigger probe profiler is designed, which is composed of a probe, model METRO-MT60 made by HEIDENHAIN Co., is integrated into the system for measuring the shape accuracy of the tested aspherical surface, another probe modeled METRO-MT12 is designed as a calibrating device for minimizing the cosine error caused by assembly inaccuracy. The new CNC machining system with two kinds of moving coordinate systems, dual tool activities and on-machine measuring is presently developed based on the new concept. The general material removal function during machining is analyzed on the basis of the Preston hypothesis. Further, an alignment test of the measuring profiler is carried out using a leveling rule as a specimen. The accuracy of the optical surfaces measured by the dual probe profiler is found to be within 1 μm PV after removing cosine error and error compensating, achieves to the resolving power of the profiler is about 0.2–0.5 μm, so the developed system can be applied to the shape accuracy measuring of aspheric fabrication with micro precision during fine grinding process according to the calibrating results. Finally, the manufacturing experiments are carried out by virtue of an off-axis oblate ellipsoid mirror with rectangular aperture as 770 mm×210 mm and centered 127 mm. The accuracy of the aspherical mirror improved from the initial form error of 17.648 μm rms to the final one of 0.728 μm rms after grinding for 200 h.     

Wire beam electrode: a new tool for studying localised corrosion and other heterogeneous electrochemical processes

Heterogeneous electrochemical processes are very common in industry and are important, but difficult topics in electrochemical and corrosion science studies. Traditional electrochemical techniques which employ a conventional one-piece electrode have major limitations in studying heterogeneous electrochemical processes since the one-piece electrode has major difficulties in measuring electrochemical parameters from local areas of the electrode surface. In order to overcome this problem, a multi-piece electrode, namely the wire beam electrode, has been developed. This new electrode enables the measurement of electrochemical parameters from local areas over a working electrode surface and thus it can be used to study heterogeneous electrochemical processes. This paper describes how this new electrode was applied in studying several typical heterogeneous electrochemical processes including water-drop corrosion, corrosion under non-uniform organic films and cathodic protection.     

A laser straightness measurement system using optical fiber and modulation techniques

In this paper a laser straightness measurement system is proposed. Using the characteristics of travelling straight and parallel, a new diode laser system utilizing optical fiber and modulation techniques was developed. This optically aligned beam is used to establish a reference line for the straightness measurement of any mechanical system. A four-quadrant photo detector was used to receive the laser beam. A phase sensitive detecting technique was adopted to process the opto-electrical signals from the detector. A single board microcomputer employing an 8098 processor was developed to conduct all data acquisition and signal processing. The influence from disturbing lights, circuit drift and beam drift can be removed from the system. The system was calibrated using an HP5528 laser interferometer. Results showed good accuracy of 0.3 μm within the range of ±100 μm and pointing stability of 0.3 μm at a 1 m distance was obtained. Two practical testing examples are carried out on a CMM and a grinding machine, respectively. Repeatability of both tests was found within 0.5 μm. This low-cost system has been successfully applied to the straightness measurement of a precision CMM.     

Development of auto defect classification system on porosity powder metallurgy products

Automatic optical inspection (AOI) has been applied to many manufacturing fields for defect inspection of mass production parts, such as PCB and TFT-LCD, but it has never been applied to the production line of porous powder metallurgy. By its nature, the powder-formed part has inherent non-uniform porosity pattern on the metal substrate. The defect’s images are not easily separated from the substrate surface using the conventional binarization technique. This study develops a new image processing methodology and employs optical system design to build up an on-line surface defect inspection system for powder metallurgy parts. An analysis algorithm is also developed for the auto defect classification technique. It removes the noise signals from the porous image, detects the object edge and uses the hybrid-based method to sort out defects on the surface, such as crevice, scratch, broken corner and dent. Experimental tests show the maximum miss rate can be controlled to less than 5.65%.     

New electron beam gun for welding in space

ABSTRACT

A new design of electron beam gun for welding in open space has been developed. The gun design is based on the application of triode emission system with improved quality of electron beam formation. This provides increased specific power of the beam and, as a result, the high capability to increase the penetration depth of welded joints. To reduce the dimensions of the gun and increase its service reliability, the high-voltage insulation has been provided applying metal-ceramic heat-resistant welded-brazed vacuum-tight components. The original technologies for their manufacture have been developed. The performed tests of the new gun design have proved the possibility of its application under open space conditions.     

Integration of three high power Nd–YAG lasers to one beam and its application in stainless steel welding

Abstract

An Nd–YAG laser processing system has been developed in which the beams of three Nd–YAG lasers (two 2·0 kW continuous wave oscillators and one 1·5 kW pulsed oscillator) were combined at the input end of a single optical fibre and transmitted through the optical fibre. The power distribution of the integrated beam, even at the defocused point of the processing optics, was not split between the three beams. Complex pulse waveform control was therefore possible. The effect of the waveforms on penetration depth was examined. Penetration depth for the rectangular modulated laser beam superimposed on the pulse laser beam with a delay was deeper than that for the rectangular modulated laser beam and the continuous laser beam, even under the same average power condition. The effective delay was 1–3 ms. Deepest penetration depth for the rectangular modulated laser beam superimposed on the pulse laser beam was 1·7 times that for the continuous laser beam.     

Portable nano probe for micro/nano mechanical scratching and measuring

A nano probe system which can measure precise micro parts or optical parts in nanometer range resolution and scratch contact force in mN scale was demonstrated. The nano probe was originally designed for on-machine measuring applications and one kind of contact type measuring probes was designed for miniaturized or microfactory system. It ideally should be of small size and able to measure surface topography in nanometer scale. A commercial capacitive displacement sensor was proposed. It was a new concept i...     

Portable nano probe for micro/nano mechanical scratching and measuring

A nano probe system which can measure precise micro parts or optical parts in nanometer range resolution and scratch contact force in mN scale was demonstrated. The nano probe was originally designed for on-machine measuring applications and one kind of contact type measuring probes was designed for miniaturized or microfactory system. It ideally should be of small size and able to measure surface topography in nanometer scale. A commercial capacitive displacement sensor was proposed. It was a new concept in nano probe systems which can measure the displacement of shaft driven by the variation of surface topography. The nano probe mainly consisted of three parts: a capacitive displacement sensor, a porous type air slide and a contact probe part with various tip radiuses. The porous type air slide assured the shaft slided smoothly with controllable normal force in mN scale and had high positioning accuracy. The probe part which was directly in contact with target surface, can be applied to micro/nanoscale scratching as well as the measurement of sample topography by a simple tip change.     

Vibrational Probing Technique for the Nano-CMM based on Optical Radiation Pressure Control

A microprobe system with a micrometer size probe sphere is required to establish the nano-CMM that is a three dimensional coordinate measuring machine with a measuring range of mm and accuracy of nm order. In this paper, the newly developed vibrational probing technique for the microprobe sytem is presented. The principle is based on the single-beam gradient-force optical trap and the forced vibration method. An optically trapped silica particle in air is vibrated using the laser beam scanning method. Frequency response is examined to estimate the radial spring constant of the microprobe system. Fundamental measurements of a micro-step specimen fabricated using a FIB (Focused Ion Beam) process are demonstrated to investigate the position detection sensitivity.     

光纤引导皮秒激光Al2O3陶瓷精细刻线研究

作为一项基础研究．提出了一种在陶瓷表面加工凹槽的新方法,利用光纤引导激光在陶瓷表面实现加工,并基于有限元分析法,对光通过光纤的电场强度进行了模拟,从实验和模拟两方面证明了光纤对激光具有光强增强效果,及其对光束的引导作用,能达到材料表面微结构的加工效果。与未用光纤引导激光加工的陶瓷表面做对比,光纤对光强的增强效应使得在具有高熔点、高硬脆物理特性的陶瓷表面产生刻蚀成为可能,小于聚焦光束直径（50μm）的增强区域尺寸保证了加工精度的提高。     

A new technique for calibration in frequency of piezoelectric transducers

The calibration in frequency of piezoelectric transducers can be obtained by sending an ultrashort laser pulse (30 ps), generated by a mode-locked Nd:YAG laser, directly on the detector surface. Thanks to its short duration, the mode-locked pulse behaves as an excitation source of wide spectral content, so that the spectral analysis of the recorded electric signal gives direct information about the frequency response of the probe. In particular, we report a series of measurements on various transducers of several nominal frequencies and we show the different response of the probe to a focused laser beam to that of an unfocused one.     

Effect of weakly ionised plasma on penetration of stainless steel weld produced with ultra high power density fibre laser

Abstract

A weakly ionised plasma can be generated in stainless steel welding with a 10 kW fibre laser beam at the ultra high power density of ～1 MW mm^–2 in Ar shielding gas. The objectives of this study are to obtain a fundamental knowledge of optical interaction between a fibre laser beam and the weakly ionised plasma, and to evaluate effects of the plasma on weld penetration. The optical interaction was investigated by the high speed video observation or the power meter measurement of another probe fibre laser beam, which passed horizontally through the weakly ionised plasma induced during bead on plate welding of a 20 mm thick type 304 plate with a 10 kW fibre laser beam of 0˙9 MW mm^–2 in power density. The probe laser observed was refracted at 0˙6 mrad angle in average, which was much lower than the 90 mrad divergence of the focused fibre laser beam. The attenuation of the probe laser was measured to be ～4%, which was not mainly caused by Inverse Bremsstrahlung but by Rayleigh scattering. Moreover, a stable laser welding process could be produced at such ultra high power density that 11˙5 mm deep penetration was obtained even if the laser peak power was modulated 1 ms periodically from 10 to 8˙5 kW. It was consequently considered that the optical interaction between the 10 kW fibre laser beam and the weakly ionised plasma was too small to exert the reduction in weld penetration.     

激光熔覆加工头聚焦性能及成形工艺研究进展

激光熔覆作为一种十分有前途的制造技术,已在工业中广泛用于部件修复、表面改性以及增材制造等领域。在激光熔覆系统中,激光熔覆加工头是其关键核心部件,可以在基材表面实现激光束、熔覆材料和熔池之间的精准耦合并形成连续熔覆层。激光熔覆加工头内置有光学镜组,主要用于激光束的传输、变换和聚焦,可以根据不同的加工需求对光束进行处理。主要从分析激光熔覆加工头聚焦性能对熔覆成形工艺影响的角度出发,综述了加工头的设计及其成形工艺的发展,具体包括光斑尺寸、光斑形状、光斑能量分布、激光功率、光源特性等对材料沉积速度、材料利用效率、熔覆层质量等的影响。首先按照激光熔覆的材料类型和材料与激光束的耦合形式,对激光熔覆光料耦合方式及加工头进行了简要概述,并对成形工艺造成的影响进行了总结。其次分别讨论了连续高斯光束和平顶光束以及脉冲激光的聚焦性能对熔覆层的影响,同时概述了3种不同形状光斑（圆形、矩形、环形）的能量分布特性和光斑尺寸对成形工艺的影响;接着研究了激光能量密度对熔覆层质量的影响;基于超高速激光熔覆技术分析提出透镜长焦深聚焦特性能够大幅提升激光熔覆的加工效率。最后展望了激光熔覆加工头聚焦性能在成形工艺上的发展趋势...     

NanoSurf IV: traceable measurement of surface texture at the National Physical Laboratory, UK

A new surface texture measuring instrument, NanoSurf IV, has been developed at the National Physical Laboratory. Laser interferometers provide traceable displacement measurements in both the vertical and scanning axes enabling surface texture to be measured with nanometre uncertainty. Provided the fidelity of the surface–probe interaction is ensured, NanoSurf IV measures the co-ordinate of a point on the surface. The instrument is designed primarily to calibrate surface texture standard specimens that can in-turn be used to calibrate other instruments. The design of the instrument, its calibration and results obtained from surface texture calibration artefacts are presented.