An approach to improve the quality of offline programming for laser beam welding is described. A CAD-dataset is combined with technological information using a feature model. A feature consists of the basic geometry, process parameters, a set of strategies in which way it can be processed, and rules to select the optimum strategy depending on the boundary conditions. The resulting welding task is represented by a list of features from which an NC-dataset is generated, containing all process information. The aim of the development is to design a feature based technology module which is integrated into a flexible, fault tolerant and process near planning tool.
Software supported process planning and quality assurance are of primary importance for the realization of a manufacturing method in laser beam welding. A novel software tool for process planning and prediction of the properties of laser welded seams named CALAS, i.e. computer aided lasering, is presented. Its structure and performance are described in detail. The software tool connects a physical model of welding by carbon-dioxide laser radiation to an interactive man/machine-interface by simulation and visualization. The model considers five fundamental physical processes, absorption of laser radiation at the keyhole surface including multiple reflexion, heat conduction in liquid and solid phase, melt flow, gas flow and heat conduction in the vapor phase, and absorption of laser radiation inside the keyhole volume (plasma absorption). The effect of processing parameters and the resulting geometry of the welded seam are calculated and displayed. The interface provides a three dimensional visualization of the keyhole and the melt pool. Cross sectional views and longitudinal sections may be displayed two-dimensional. Besides typical parameters the beam characteristics, such as power density distribution, and material properties, such as temperature dependent surface tension and heat conductivity, are included in the calculation too. Due to direct and fast prediction of process parameters and seam geometry CALAS serves as a controlling tool for the operator at the machine tool, and in a more general view, it serves as a tool for processing planning and quality assurance in industry.
Coated ZnSe optical components are irradiated with high-power, pulsed CO2 laser radiation at fluences up to 250 J/cm2. The components are characterized at various stages of irradiation by optical microscopy, interferometric microscopy, profilometry, surface chemical analysis (x-ray photoemission and Auger electron spectroscopy), and surface structural analysis (micron-Raman spectroscopy). Two types of coating damage occur within the irradiated area of the component: a breaking apart of the ZnSe overlayer of the coating system over relatively large areas resulting in a network structure, and the formation of isolated craters of diameter approximately 30-50 micrometers extending in depth of approximately 5 micrometers through the coating system down to the ZnSe substrate. Chemically, the irradiated area is characterized by an oxidation of both Zn and Se and an increase in the stoichiometric ratio of Zn and Se. These effects are especially pronounced at the crater defects, and are attributed to localized optical absorption, leading to thermal stress and chemical reactions of Zn and Se with atmospheric or absorbed water and/or oxygen. Structually, the coatings exhibit a polycrystalline structure with no orientation of the individual grains. During irradiation the grain size diminishes giving, in addition, indication for built-in stress and partial melting at high laser fluences.
Si/Ge superlattices provide the possibility to create a novel direct band gap semiconductor. The energies and oscillator strength of interband transitions are strongly affected by strain individual layer thicknesses and superlattice periodicity. We report on photoreflectance (PR) studies of SimGen superattices with a layer thickness ratio m/n1/3 and period lengths of 8 12 and 16 monolayers. Between 1. 9 and 2. 5 eV transitions which are related to the E1 gap are observed for all samples. In the infrared region between 0. 9 and 1. 2 eV superlattice induced interband transitions are observed for Si2Ge6.