Single- and dual-carrier microwave noise abatement in the deep space network

The NASA/JPL Deep Space Network (DSN) microwave ground antenna systems are presented which simultaneously uplink very high power S-band signals while receiving very low level S- and X-band downlinks. Tertiary mechanisms associated with elements give rise to self-interference in the forms of broadband noise burst and coherent intermodulation products. A long-term program to reduce or eliminate both forms of interference is described in detail. Two DSN antennas were subjected to extensive interference testing and practical cleanup program; the initial performance, modification details, and final performance achieved at several planned stages are discussed. Test equipment and field procedures found useful in locating interference sources are discussed. Practices deemed necessary for interference-free operations in the DSN are described. Much of the specific information given is expected to be easily generalized for application in a variety of similar installations. Recommendations for future investigations and individual element design are given

Fabrication of the 23-ft Collimating Mirror for the JPL 25-ft Space Simulator

Optical, structural, and thermal design criteria and fabrication techniques for collimating mirror in space simulato

Laser transmission welding of Acrylonitrile-Butadiene-Styrene (ABS) using a tailored high power diode-laser optical fiber coupled system

Laser transmission welding (LTW) of polymers is a direct bonding technique which is already used in different industrial applications sectors such as automobile, microfluidic, electronic and biomedicine. This technique offers several advantages over conventional methods, especially when a local deposition of energy and minimum thermal distortions are required. In LTW one of the polymeric materials needs to be transparent to the laser wavelength and the second part needs to be designed to be absorbed in IR spectrum. This report presents a study of laser weldability of ABS (acrylonitrile/butadiene/styrene) filled with two different concentrations of carbon nanotubes (0.01% and 0.05% CNTs). These additives are used as infrared absorbing components in the laser welding process, affecting the thermal and optical properties of the material and, hence, the final quality of the weld seam. A tailored laser system has been designed to obtain high quality weld seams with widths between 0.4 and 1.0mm. It consists of two diode laser bars (50W per bar) coupled into an optical fiber using a non-imaging solution: equalization of the beam quality factor (M2 ) in the slow and fast axes by a pair of micro step-mirrors. The beam quality factor has been analyzed at different laser powers with the aim to guarantee a coupling efficiency to the multimode optical fiber. The power scaling is carried out by means of multiplexing polarization technique. The analysis of energy balance and beam quality is performed in two linked steps: first by means ray tracing simulations (ZEMAX® ) and second, by validation. Quality of the weld seams is analyzed in terms of the process parameters (welding speed, laser power and clamping pressure) by visual and optical microscope inspections. The optimum laser power range for three different welding speeds is determinate meanwhile the clamping pressure is held constant. Additionally, the corresponding mechanical shear tests were carried out to analyze the mechanical properties of the weld seams. This work provides a detailed study concerning the effect of the material microstructure and laser beam quality on the final weld formation and surface integrity

Automatic re-contouring of repair-welded tool moulds

The process of repairing damaged tool moulds is conducted manually in the industry. This results in long process times as well as a high dependence of the repair result on the experience of the worker. After a visual inspection, the detected damages are removed by metal cutting and the missing material is filled by a build-up welding process. Afterwards, the target geometry is restored via machining re-contouring process. Because of the individual tool mould surface and welded seam, each repair case requires an individual machining strategy as well as toolpaths and process control parameters to ensure high surface quality and shape accuracy. This paper introduces an innovative design for re-contouring of repair-welded tool moulds, which takes into consideration the individual mould surface, repair welding and material properties. For that purpose, the actual geometry of the tool mould is measured directly in the CNC machine using an optical profile line sensor. Based on the measurement, the re-contouring process is planned automatically by means of a computer aided manufacturing (CAM) software. A material removal simulation with cutting force prognosis is carried out to adapt the process parameters individually with regard to repair time and surface quality. To set up the force and surface simulation model with high model quality, re-contouring experiments are carried out on welded seams made of 1.2343 (AISI H11) as well as on Toolox 44 and 1.2343 workpieces for comparison

Use of the Plasma Spectrum RMS Signal for Arc-Welding Diagnostics

A new spectroscopic parameter is used in this paper for on-line arc-welding quality monitoring. Plasma spectroscopy applied to welding diagnostics has typically relied on the estimation of the plasma electronic temperature, as there is a known correlation between this parameter and the quality of the seams. However, the practical use of this parameter gives rise to some uncertainties that could provoke ambiguous results. For an efficient on-line welding monitoring system, it is essential to prevent the appearance of false alarms, as well as to detect all the possible defects. In this regard, we propose the use of the root mean square signal of the welding plasma spectra, as this parameter will be proven to exhibit a good correlation with the quality of the resulting seams. Results corresponding to several arc-welding field tests performed on Inconel and titanium specimens will be discussed and compared to non-destructive evaluation techniques

Defect Detection in Arc-Welding Processes by Means of the Line-to-Continuum Method and Feature Selection

Plasma optical spectroscopy is widely employed in on-line welding diagnostics. The determination of the plasma electron temperature, which is typically selected as the output monitoring parameter, implies the identification of the atomic emission lines. As a consequence, additional processing stages are required with a direct impact on the real time performance of the technique. The line-to-continuum method is a feasible alternative spectroscopic approach and it is particularly interesting in terms of its computational efficiency. However, the monitoring signal highly depends on the chosen emission line. In this paper, a feature selection methodology is proposed to solve the uncertainty regarding the selection of the optimum spectral band, which allows the employment of the line-to-continuum method for on-line welding diagnostics. Field test results have been conducted to demonstrate the feasibility of the solution

Optical design and development of a fiber coupled high-power diode laser system for laser transmission welding of plastics

Laser transmission welding (LTW) of thermoplastics is a direct bonding technique already used in different industrial applications sectors such as automobiles, microfluidics, electronics, and biomedicine. LTW evolves localized heating at the interface of two pieces of plastic to be joined. One of the plastic pieces needs to be optically transparent to the laser radiation whereas the other part has to be absorbent, being that the radiation produced by high power diode lasers is a good alternative for this process. As consequence, a tailored laser system has been designed and developed to obtain high quality weld seams with weld widths between 0.7 and 1.4 mm. The developed laser system consists of two diode laser bars (50 W per bar) coupled into an optical fiber using a nonimaging solution: equalization of the beam parameter product (BPP) in the slow and fast axes by a pair of step-mirrors. The power scaling was carried out by means of a multiplexing polarization technique. The analysis of energy balance and beam quality was performed considering ray tracing simulation (ZEMAX®) and experimental validation. The welding experiments were conducted on acrylonitrile/butadiene/styrene (ABS), a thermoplastic frequently used in automotive, electronics and aircraft applications, doped with two different concentrations of carbon nanotubes (0.01% and 0.05% CNTs). Quality of the weld seams on ABS was analyzed in terms of the process parameters (welding speed, laser power and clamping pressure) by visual and optical microscope inspections. Mechanical properties of weld seams were analyzed by mechanical shear tests. High quality weld seams were produced in ABS, revealing the potential of the laser developed in this work for a wide range of plastic welding applications

Rapid Laser Manufacturing of Microfluidic Devices from Glass Substrates

Conventional manufacturing of microfluidic devices from glass substrates is a complex, multi-step process that involves different fabrication techniques and tools. Hence, it is time-consuming and expensive, in particular for the prototyping of microfluidic devices in low quantities. This article describes a laser-based process that enables the rapid manufacturing of enclosed micro-structures by laser micromachining and microwelding of two 1.1-mm-thick borosilicate glass plates. The fabrication process was carried out only with a picosecond laser (Trumpf TruMicro 5×50) that was used for: (a) the generation of microfluidic patterns on glass, (b) the drilling of inlet/outlet ports into the material, and (c) the bonding of two glass plates together in order to enclose the laser-generated microstructures. Using this manufacturing approach, a fully-functional microfluidic device can be fabricated in less than two hours. Initial fluid flow experiments proved that the laser-generated microstructures are completely sealed; thus, they show a potential use in many industrial and scientific areas. This includes geological and petroleum engineering research, where such microfluidic devices can be used to investigate single-phase and multi-phase flow of various fluids (such as brine, oil, and CO2) in porous media

Welding diagnostics by means of particle swarm optimization and feature selection

In a previous contribution, a welding diagnostics approach based on plasma optical spectroscopy was presented. It consisted of the employment of optimization algorithms and synthetic spectra to obtain the participation profiles of the species participating in the plasma. A modification of the model is discussed here: on the one hand the controlled random search algorithm has been substituted by a particle swarm optimization implementation. On the other hand a feature selection stage has been included to determine those spectral windows where the optimization process will take place. Both experimental and field tests will be shown to illustrate the performance of the solution that improves the results of the previous work.This work has been supported by the TEC2010-20224-C02-02 and OPENAER CENIT 2007–2010 projects

Arc welding quality monitoring by means of near infrared imaging spectroscopy

The search for an efficient on-line monitoring system focused on the real-time analysis of the welding quality is an active area of research, mainly due to the widespread use of both arc and laser welding processes in relevant industrial scenarios such as aeronautics or nuclear. In this work, an improvement in the performance of a previously designed monitor system is presented. This improvement is accomplished by the employment of a dual spatial-spectral technique, namely imaging spectroscopy. This technique allows the simultaneous determination of the optical spectrum components and the spatial location of an object in a surface. In this way, the spatially characterization of the plasma emitted during a tungsten inert gas (TIG) welding is performed. The main advantage of this technique is that the spectra of all the points in the line of vision are measured at the same time. Not only are all the spectra captured simultaneously, but they are also processed as a batch, allowing the investigation of the welding quality. Moreover, imaging spectroscopy provides the desired real-time operation. To simultaneously acquire the information of both domains, spectral and spatial, a passive Prism-Grating-Prism (PGP) device can be used. In this paper the plasma spectra is captured during the welding test by means of a near infrared imaging spectroscopic system which consists of input optics, an imaging spectrograph and a monochrome camera. Technique features regarding on-line welding quality monitoring are discussed by means of several experimental welding tests