A model was devised and used as the basis of a computer simulation to predict the shape of and physical phenomena in the keyhole during deep penetration laser welding. The shape of the weld cavity was determined as a part of the solution, and a convection-dominated vaporization model was utilized. Deep penetration welding is characterized by the formation of the keyhole. Beyond a certain threshold laser power, the laser beam rapidly evaporates material creating a strong back pressure, which pushes the molten material sideways forming a cavity. Hence, the laser power is effectively transferred to the bottom of the cavity and penetrates into the material until an energy balance is achieved around the keyhole. Around the keyhole three different regions (solid, liquid, and vapor) are analyzed, each region with its most suitable method. The heat transfer within the solid region is solved by Boundary Element Method. A thin layer approximation is made to simplify the analysis in the liquid region. A scaling analysis shows that fluid dynamics in the liquid region does not contribute significantly to the heat transfer in the liquid region. In the vapor region, a one-dimensional gas dynamic model is adopted from the literature. The solutions in the three regions are matched to satisfy conservation of mass at the liquid-vapor interface and of energy at the solid-liquid interface. Specifically, the matching technique of energy at the solid-liquid interface is called the matching scheme, and with it the shape of the solid-liquid interface is calculated. Then the shape of the liquid-vapor interface can readily be obtained from the shape of the solid-liquid interface and the thin liquid layer approximation. The matching scheme and the use of modules combine to make a model which is capable of predicting the shape of the solid-liquid interface; depth of penetration; surface temperature of the keyhole; pressure acting on the keyhole; energy distribution, such as the energy of vaporization, fusion, and conduction; and the thickness of the liquid layer. As a model material, pure iron was analyzed in this study. The calculated penetration depths are compared to empirical data, in order to verify the current study, and good agreement was observed.

Thesis (M.S.) in Mechanical Engineering--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 141-145).

No description available.

In laser transmission welding (LTW), a laser beam passes through the laser-transparent part and is absorbed by carbon black (CB) in the laser-absorbent part. This causes a temperature rise at the interface between the parts which leads to melting, diffusion and ultimately joining of the two components. Weld temperatures increase with laser power at a given scan speed. However at higher temperatures, it has been observed that weld strength of LTW starts to decline due to material thermal degradation. Thermal degradation of materials is a kinetic phenomenon which depends on both temperature and time. Therefore there is no specific temperature for thermal degradation. Thermal gravimetric analysis (TGA) is used to study the thermal degradation of two commonly used thermoplastic materials: polycarbonate (PC) and polyamide 6 (PA6). Each material was studied at two levels of CB. It is shown in this work that increasing the carbon black (CB) level from 0.05 to 0.2wt% has no significant effect on the thermal stability of PA6. However, it is observed that increasing the CB level from 0.05 to 0.2wt% has a noticeable effect on the thermal stability of PC. The TGA data were then used to obtain the kinetic triplets (frequency factor (k_0), activation energy (E), and reaction model (f(α))) of the materials using a non-linear model-fitting method. These kinetic triplets were combined with temperature-time data obtained from a Finite Element Method (FEM) simulation of the LTW process to predict material degradation during LTW. The predicted degradation was then compared with experimental data. It is found that the predicted onset of material degradation is in good agreement with experimentally observed thermal degradation (of both visually observed degradation onset and weld strength decline) for PC and PA6. A semi-empirical model based on the FEM temperature data is also developed in this work as a simpler alternative for obtaining LTW maximum temperature-time profiles for prediction of material thermal degradation during LTW. Comparison of the predicted material conversion using temperature-time profile obtained by FEM and the semi-empirical model shows good agreement. / Thesis (Master, Chemical Engineering) -- Queen's University, 2013-09-27 10:45:24.688

Laser transmission welding of polymers is a relatively new joining technique. It is based on the fact that the majority of thermoplastics are transparent to infrared radiation. A laser beam passes through the transparent part, and is then absorbed by a part rendered absorbent by additives such as carbon black. Absorbed laser energy is transformed into heat that melts the polymer at the interface between two parts, thus forming a weld. Many industrial applications have quite a complex geometry. This may often make it impossible to irradiate small elements of the joint interface directly. One of the possible solutions for this problem is to employ an oblique mirror to redirect a laser beam to the desired direction. In present work, transparent nylon tubes were welded to absorbing nylon plaques using a conical mirror inserted in the tube. The effects of the laser power, the angular motion speed, and the number of cycles on the joint shear strength were examined. Additionally, a two–dimensional axi-symmetric transient finite element heat transfer model was developed and evaluated. It simulated the temperature developed in the specimen during the welding cycle; the model was validated with the welding and mechanical testing results. The experimental results demonstrated good joint strength, confirming the feasibility of this technique. It was also found that welding at a lower laser beam power and a higher rotational speed allowed higher maximum weld strengths to be achieved at the expense of longer cycle time and higher energy consumption. Simulation of the temperature demonstrated that varying of the rotational speed at constant laser power does not change the overall temperature rise trend. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-08-14 23:12:18.491

No description available.

Thesis (M.S.) in Mechanical Engineering--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 129-130).

Thesis (M.S.)--Oregon Graduate Center, 1986.

We investigate the post-weld-shift(PWS) induced fiber alignment shift in butterfly laser packaging. For high-speed laser modules in lightwave communication systems, the butterfly laser modules are widely used. When laser welding is applied to assemble a butterfly package, it is usually necessary to have mechanical elements such as substrates, fiber ferrule, and clip of house materials to facilitate fiber handing and retention within the package. However, during the process, rapid solidification of the welded region and associated material shrinkage often cause a post-weld-shift between welded components. The PWS significantly affects the package yield. A novel measurement and compensation technique employing a high-magnification camera with image capturing system (HMCICS) to probe the post-weld-shift (PWS) induced fiber alignment shifts in high-performance butterfly-type laser module packages is studied. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded butterfly-type laser module packaging can be quantitatively determined and then compensated. The increased coupling efficiency after this PWS compensation was from 3% to 10%. This HMCICS technique has provided an important tool for quantitative measurement and compensation to the effect of the PWS on the fiber alignment shifts in laser module packages. Therefore, the reliable butterfly-type laser modules with a high yield and a high performance used in lightwave transmission systems can be developed.

A notch clip approach to compensate post-weld-shift(PWS) induced by laser welding process in butterfly type laser module packages is investigated. For high-speed laser modules in lightwave communication systems, the butterfly laser modules are widely used. When laser welding is applied to assemble a butterfly package, it is usually necessary to have mechanical elements such as substrates, fiber ferrule, and clip of house materials to facilitate fiber handing and retention within the package. However, during the laser welding process, rapid solidification of the welded region and associated material shrinkage often cause a post-weld-shift between welded components. The PWS significantly affects the package yield. A notch clip approach and measurements employing a high-magnification camera with image capturing system (HMCICS) to probe the PWS induced fiber alignment shifts and welding compensation on notch in high-performance butterfly-type laser module packages are studied. The results show that the direction and magnitude of the fiber alignment shifts induced by the PWS in laser-welded butterfly-type laser module packaging can be quantitatively determined and then compensated. The overall coupling efficiency after this PWS compensation was from 80¢H to 90¢H. This notch approach and HMCICS technique have provided an important tool for quantitative measurement and compensation to the effect of the PWS on the fiber alignment shifts in laser module packages. Therefore, the reliable butterfly-type laser modules with a high yield and a high performance used in lightwave transmission systems can be developed.