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Microchannel process technology (MPT) components are chemical unit operations which exploit highly-parallel arrays of microchannels to process large fluid volumes for portable and distributed applications. Microchannel heat exchangers (MCHXs) have demonstrated 3 to 5 times higher heat fluxes when compared to conventional heat exchangers resulting in proportionate reductions in size and weight. The most common fabrication approach for producing MPT components is microchannel lamination, or microlamination, in which thin layers of metal or polymer are patterned with microchannel features, registered, and bonded to produce monolithic components. Currently, the most common microlamination architecture involves the photochemical machining and diffusion bonding of metal foils. Prior work has established that the yields in diffusion bonding often drive the costs of MCHXs. Laser keyhole welding has been proposed as an alternative bonding technology providing the potential for faster cycle times, smaller weld widths and layer-to-layer evaluation of hermeticity leading to higher yields. Furthermore, laser weldments have small heat-affected zones providing excellent mechanical strength. In this study, efforts are made to evaluate the feasibility of using laser welding in the microlamination of a high-temperature counter-flow heat exchanger made of a Ni superalloy. Preliminary efforts were focused on the development and validation of weld strength estimation models. These models were then used to narrow down the range of process parameters and a final set of process parameters was determined through the use of a full factorial experiment with weld strength, joining efficiency and weld gap as response variables. The most acceptable parameter set was used to demonstrate the fabrication of a Haynes 214 microchannel array with adequate bond strength and hermeticity and minimal thermal warpage. / Graduation date: 2013

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Laser welding is used in modern industrial production due to its high welding speed and good welding performance comparing to more traditional arc welding. To improve the flex-ibility, robots can be used to mount the laser tool. However, laser welding has a high require-ment for the accuracy in positioning the laser tool. There are three main related variables which affect the laser welding accuracy: robot path accuracy, workpiece geometry and fixture repeatability. Thus, joint tracking is very important for laser welding to achieve high quality welds. There are many joint tracking systems which were proposed in recent years. After receiv-ing the joint information, a control system is necessary to control the robot motion in real-time. The open control system for the industrial robot is one trend for the future. A lot of methods and systems are proposed to control the robot motion. Some systems can achieve a high accuracy in the experiments. However, it is still hard to apply them in practical indus-trial production. Thus more commercial solutions appear to overcome the robot motion problem nowadays. They are very useful to realize practical applications. ABB EGM path correction module, a new function of Robotware, is one of the com-mercial solutions for robot motion control in real time. In the experiments presented in this work, a computer is used to simulate a sensor to create a path correction signal. To test its feasibility for the laser welding application, many experiments are conducted. One was to test the robot path repeatability when there is no correction message sent to the robot. Another was to test the level of accuracy EGM can achieve during the correction process. Different types of paths and three different speeds were separately carried out. The results showed that it is possible to use the EGM in the laser welding application. In the EGM feasibility test, there exists deviation in the z-direction. Since these deviations are less than 0.2mm, it will have a minor influence the laser welding performance, implying that the EGM path correction can be applied in practical production.

For getting the position which can obtain the maximum coupling efficiency, fiber array and laser array need to be adjusted while the module of fiber array is packaging, than fastening it on the base. Nowadays, there are some methods for fastening the fiber array like adhesive, soldering and laser welding. But the material will discover some phenomenons like expansion and contraction during the process of heating and solidification. Those phenomenons will lead the system to deviate on the six degree of freedom (D.O.F). Because of the fiber array system will confront with the situation of deviation, the magnitude of coupling efficiency will drop down. It is because that the technique of laser welding will cause smaller deviation than other methods just mentioned, so the research choose the method of laser welding for packaging. The distance between fiber and laser array is too small to fasten the CCD on the directions of X, Y and Z axes while the research measures the deviation. So the research uses a mirror to reflect the image for obtaining the correct position of the space and Post-Weld-Shift measurement the deviation of system. Afterward, the research designs a structure for reducing the deviation and increasing the coupling efficiency of system.

Abstract In this thesis, we have studied the post-weld-shift (PWS) in laser welding technique for laser module packaging. The joining method for packaging of laser module by laser welding technique can offer a number of significant advantages. It provides strong joint strength, therefore, the packaging has good long-term stability. It also provides high-speed and high-volume production, and hence the packaging is potential low cost. However, the laser welding process has caused PWS of laser module, would decay the coupling efficiency of laser module. We investigate the weld-spot by using metallographic method. The PWS in stainless steel (SS304L) plate is studied experimentally and numerically. The metallographic results are in good agreement with the Finite-Element-Method (FEM) results that the PWS in x-y plane can be neglected. Based on the experimentally and numerically results of PWS in SS304L, we investigate the yield improvement of laser module packaging. The laser hammer technique was used to improve the coupling efficiency of laser module. The results show displacement of the z-axis is from 1 to 9 (£gm) that equals to the angle changes of upper parts of laser module from 0.38¡Ñ10-2 to 3.4¡Ñ10-2 (degree). Therefore, the coupling efficiency of laser module can be improved from 4 to 20 (%).

The low cycle thermo-mechanical fatigue of laser beam welded conventionally cast Inconel 738, directionally solidified René 80 and single crystal René N5 has been evaluated. Results have been compared to gas tungsten arc and baseline alloy conditions. Metallographic examination of laser beam welds and the associated heat affected zone were conducted by scanning electron microscopy and energy dispersive spectroscopy. The impact of laser beam welding on thermo-mechanical fatigue properties of Inconel 738, René 80 and René N5 has been evaluated and recommendations for improvements and areas of further research have been presented.

The low cycle thermo-mechanical fatigue of laser beam welded conventionally cast Inconel 738, directionally solidified René 80 and single crystal René N5 has been evaluated. Results have been compared to gas tungsten arc and baseline alloy conditions. Metallographic examination of laser beam welds and the associated heat affected zone were conducted by scanning electron microscopy and energy dispersive spectroscopy. The impact of laser beam welding on thermo-mechanical fatigue properties of Inconel 738, René 80 and René N5 has been evaluated and recommendations for improvements and areas of further research have been presented.

Thesis (M.S.)--Brigham Young University. School of Technology, 2007. / Includes bibliographical references (p. 73-75).

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