This thesis presents a collection of theoretical and experimental investigations into various geometrical aspects of hybrid laser-MIG welding. The work is divided up into four parts; A review of the hybrid laser-MIG welding technique with brief summaries of the three papers which make up the remainder of the thesis. A paper entitled "Fundamental analysis of hybrid laser-MIG welding". This paper provides a theoretical insight into the hybrid laser-MIG welding process. This fundamental analysis includes a description of the effect of process parameters on the cross-sectional geometry of the weld. A paper entitled "The influence of joint geometry and fit-up gaps on hybrid laser-MIG welding" This paper analyses the effect of the geometry of the pre-welded joint on the final weld cross-section. This paper specifically investigates the influence of gaps between the workpieces and their effect on the welding process. From this work, guidelines on the achievement of successful welds have been developed. A paper entitled "The influence of joint gap on the strength of hybrid Nd:YAG laser-MIG welds". This paper looks into a specific feature of weld geometry; the effect of different size gaps at the root of partial penetration butt welds. It was postulated (and confirmed) that an optimum range of fit-up gaps gives maximum weld strength. If the gap is smaller than this optimum then the fit-up gap acts as a sharp "crack" at the base of the weld. If the gap is larger than the optimum range then the root of the weld takes on a more complex geometry which, once again, includes stress raising features. / <p>Godkänd; 2005; 20061213 (haneit)</p>

In Laser Material Processing of metals, an understanding of the fundamental absorption mechanisms plays a vital role in determining the optimum processing parameters and conditions. The absorptance, which is the fraction of the incident laser light which is absorbed, depends on a number of different parameters. These include laser parameters such as intensity, wavelength, polarisation and angle of incidence and material properties such as composition, temperature, surface roughness, oxide layers and contamination. The vast theoretical and experimental knowledge of the absorptance of pure elements with smooth, contamination-free surfaces contrasts with the relatively sparse information on the engineering materials found in real processing applications. In this thesis a thorough investigation of the absorption mechanisms in engineering grade materials has been started. The Licentiate thesis consists of 5 papers. Paper 1 is a short review of some of the most important mathematical models used in describing the interaction between laser light and a metal. Paper 2 is a review of a few experimental methods of measuring the absorptance of an opaque solid such as a metal. Papers 3 and 4 are experimental investigations of the absorptance of some of the most frequently found metallic alloys used in Laser Material Processing today. Paper 5 is a co-authored paper on the cleaning of copper artefacts with the use of second harmonic generated Nd:YAG laser light. / <p>Godkänd; 2005; 20061213 (haneit)</p>

Milling is a processing technology massively applied in the metal manufacturing industry. The continuous demand for higher productivity and product quality asks for better understanding and control of the machining process. A better understanding can be achieved through experimental measurement and theoretical simulations and modelling of the process and its resulting product. In particular process monitoring and control is desirable for automated control and optimization of the process and in turn of productivity and product quality. However, due to the high complexity of the process, in particular of the interaction system/process/product, the above goals have only partially been achieved today, to a limited, unsatisfactory extent. The here presented research addresses the above needs and their progress by developing and starting to implement and study a highly sophisticated sensor and analysis platform for machining with the objectives of (i) advanced measurement and analysis of the milling process and (ii) advanced process monitoring and control. For a certain highly advanced high speed machining centre a comprehensive concept has been developed for the integration different kinds of sensors to the system. In particular the complex concept takes into account sophisticated analysis, research and development through the cooperation between different experimental and theoretical methods. The present thesis presents the developed platform concept. Due to the complexity of this sensor and analysis platform and its early stage of development, the here presented research work focuses on the implementation and investigation of selected sensors and analysis methods. Paper I screens and discusses the possibilities of the applied machining centre for sensor integration, particularly aiming at process monitoring. From the large variety of relevant sensors, particularly promising turned out to be acoustic emission sensors, force sensors, accelerometers, temperature sensors and optical sensors. Their potential and limitations are discussed. The specific concept developed for the addressed high speed machining centre is described in Paper II. Force sensors measuring the spindle force components, flexible accelerometers measuring the vibrations at almost any desired spindle or product location and Laser Doppler Vibrometry (LDV) for non-contact measurement of vibrations turned out to be the most promising sensors, to be implemented and studied in more detail in the following. Moreover, the concept recommends the cooperation of the sensors with modelling, simulation and analysis at different levels. Experimentally, the simulation of a static load to the spindle or even oscillating load through a magnetic shaker was realised in order to simulate the processing conditions for measuring and characterizing the spindle behaviour. The LDV- measurement enables precise identification of spindle oscillations at different locations. A particular challenge is the identification of stable operating points at high rotational speeds through stability lobes. For this purpose the vibrations of a certain complex, thin walled aerospace structure were measured by LDV and in good agreement simulated by FEA for different machining process stages in order to derive stable lobe areas. Beside implementation and first testing of the above mentioned methods, the paper describes and discusses possible concepts for a closed loop control of the process. In Paper III the LDV method is for the first time and successfully applied for measuring the fee-running rotating spindle of a high speed machining centre. In particular the roundness of the dummy tool applied was measured at high accuracy during rotation, as verified by mechanical measurement. Moreover, the LDV permits the measurement of misalignment of other geometrical and kinematical imperfections of the spindle rotation. Paper IV describes in more detail the verification of FEA through LDV for the complex aerospace structure, presented in Paper II. Both, vibrations of the unconstrained and of the clamped workpiece are studied. Moreover, the workpiece vibration characteristics was studied at four different machining stages, starting from aluminium stock and ending in a thin walled structure after removal of 97% of the material. In particular the corresponding stability lobes were predicted by the aid of the FEA, compared with modal analysis and with selected milling experiments. When machining a monolithic structure that reduces it's volume to such an extent gives several problem: Clamping of a thin walled structure is hard due to its flexibility, The changing dynamics of the workpiece has the affect that prediction of the vibrational properties is very hard to realise and finally the milling is hard because of the fact that the walls of the structure bends when a force is applied from the milling tool. Paper V discusses the suitability of different sensors for process monitoring, by applying them on-line during machining experiments for steel and aluminium, each at three different feed rates. The signals of force sensors in three dimensions arranged below the workpiece, of accelerometers in two directions mounted at the spindle housings and of LDV spotting the tool fixture ring were acquired on-line. The six signals were analysed, extracting mean values that were compared to the achieved surface roughness for the six different milling conditions. From evaluation of the stability of the signal and its coherence with the surface roughness trends the suitability of each sensor was discussed. While the sensors lateral and vertical to the feeding direction were not suitable, the sensors measuring in feeding direction were most promising, in particular the accelerometer and the corresponding LDV. The context between the roughness, process and sensor signals is discussed. Summarizing, a sophisticated sensor and analysis platform concept was developed. Selective sensors and methods have been implemented and studied with the purpose of system characterization, process understanding and process monitoring. The promising results encourage for continuation of this research programme. / Godkänd; 2006; 20070109 (haneit)

New demands for passenger safety, vehicle performance and fuel economy have led to an increase in the use of advanced high strength steel. An increase in strength decreases the formability of the material and increases the spring back behaviour. Recently the development of high strength steel has rapidly advanced, requiring verification of earlier material models suitable for describing the plasticity behaviour in sheet metal forming. The aim of the here conducted numerical simulations is to verify the deep drawing process and the shape of the final component of a simple hat profile geometry for studying spring-back of high strength steels. Four advanced high strength steels were selected for detailed investigation, namely the dual phase steels DP600 and DP750, the triple phase steel TRIP700 and the stainless steel HYTENS800. The plastic properties of these steels have been assessed through intrinsic and simulative tests, leading to verification and comparison at different levels. The hat profile serves as a simple test geometry for deep drawing due to elimination of the lateral dimension in first order. The corresponding simpler plasticity behaviour in space facilitates systematic analysis Experiments and simulations were carried out, leading to comparison of the resulting draw in, strain, thinning, final shape and spring-back. The verification and analysis concerns the friction coefficient, two software codes, Finite Element properties and the two material models Hill48 and Hill90. The simulation provides a good qualitative coincidence with experimental results, which enables to develop a process theory and to study the individual mechanisms involved. The friction coefficient, varied from 0 to 0.1, shows very low sensitivity on the process. The simulation underestimates the spring-back by 8-12° at the flange edge. Among the four materials studied basically the stainless steel HYTENS800 shows the largest deviations during comparison. In general the results partially reveal distinct quantitative discrepancies, in particular in the critical bending regions, demanding for improved material models and better knowledge of the boundary conditions. / Godkänd; 2005; 20070102 (haneit)

No description available.

This thesis presents an investigation into the laser cladding process using CO2 and Nd:YAG lasers. The work is divided into four papers: Paper one is a literature review of the subject of laser cladding. This presents a general overview of the subject from a practical and theoretical point of view. Paper two is an investigation about the energy redistribution during CO2- laser cladding. Experimental absorption measurements by calorimetry were carried out to separate and analyse how much of the energy is lost by reflection etc. It was found that approximately 60% of the original laser power is lost by reflection. Paper three extends the work of paper two and compares the process efficiency of Nd:YAG and CO2 laser cladding. The energy redistribution during cladding has been analysed for both processes. The Nd:YAG laser cladding process was found to be considerably more energy efficient than CO2- laser cladding process. Paper four presents preliminary experimental results from two new processes; Laser casting and Laser clad-casting. Laser casting is a process similar to blown powder laser cladding but without the final product joined to the substrate. The substrate acts as a mould and the casting retains topological features of the substrate. Laser clad-casting involves the production of a clad layer between machined copper blocks. Clad tracks can therefore be achieved with large depth to width ratios and pre determined cross sections. / Godkänd; 2002; 20070222 (ysko)

Preservation of cultural property in the form of historical artefacts for the future is an important interest in our society. The information which can be obtained from these materials is a valuable key to understand the past. One of the aims of any conservation procedure is to preserve both aesthetic and physical conditions of irreplaceable artefacts. Conservation involves a number of different steps. Cleaning is one of the critical steps needed to stabilise the material and to recover hidden details on the surface. It is therefore very important to choose suitable techniques and methods when cleaning to avoid damage to the artefact. Research and development to find more suitable conservation techniques are still going on. One of the new techniques under investigation is laser cleaning which has shown a good potential as a cleaning tool for many material categories met in conservation work. This thesis presents an investigation of the laser cleaning of metal artefacts using Nd:YAG and TEA CO2 lasers. The first part is a general overview of the laser technique applied to metal conservation and an outline of the practical work. The thesis then continues with four papers. Paper A concerns the removal of adhesives and coatings from iron samples using pulsed TEA CO2- and Nd:YAG-lasers. Trial samples were treated with different kinds of adhesives and coatings typically used in metals conservation and then cleaned using the lasers. The results were compared with cleaning using a conventional technique, micro blasting. Comparison of the different laser-cleaned surfaces was also performed by optical microscopy and Raman-spectroscopy. The comparative study showed that the best cleaning result was achieved by the TEA CO2 laser. The coatings were removed entirely without damage to the substrate. Paper B deals with cleaning of corroded iron samples using pulsed TEA CO2- and Nd:YAG-lasers. TEA CO2 lasers were successfully used to remove organic materials and rust. The Nd:YAG laser was able to clean the corroded samples, however, the risk for surface damage was found to be higher than using the TEA CO2 laser. Analysis of the surfaces cleaned by the two types of lasers was carried out by optical- and scanning electron microscopy, X-ray spectrometry and Raman-spectrometry. Paper C is a comparative study of the cleaning of iron samples using TEA CO2- and Nd:YAG lasers. In the first experiment a comparison of Nd:YAG laser and micro blasting for the cleaning of rust was made. The second experiment dealt with the removal of a wax coating from iron samples using a TEA CO2 laser with different power densities. The first experiment shows that the samples cleaned by pulsed laser retain a better surface structure than those cleaned by micro blasting. The second experiment showed how different energy densities affect the same surface. Paper D is an investigation of the cleaning of silver threads in textile using Nd:YAG laser at wavelengths of 1064 nm, 532 nm and 266 nm. The goal of this work was to find a technique to clean the tarnished silver without damaging the underlying silk. This was necessary since the conventional chemical treatment for cleaning tarnished silver is problematic to apply in this specific instance. The laser wavelength of 266 nm was found to be most appropriate for cleaning the silver threads without causing any damages either the silver or the underlying silk. However, the 1064 nm wavelength caused damage such as melting and burning of both the silver and silk. / Godkänd; 2002; 20070224 (ysko)

This thesis presents an investigation of the interaction mechanism involved in processing of different engineering materials using pulsed TEA CO2- and Nd:YAG lasers. Several methods were used. Digital Speckle Photography (DSP) or Speckle Correlation was used to detect micro-structural changes in the material surface during laser irradiation. Scanning Electron Microscopy (SEM) and optical microscopy were used to obtain information about hole quality; entrance and exit diameters, amount of spatter, cracking etc., when laser drilling. Optimum processing parameters, for example wavelength, pulse repetition frequency and pulse energy were established and are presented in this thesis. In Papers A and B, an evaluation of the interaction mechanism using Digital Speckle Photography (DSP) is presented. Paper C focuses more on the influence of the laser irradiation parameters on the quality of laser drilled holes. To find optimum processing parameters, SEM and optical microscopic investigations of thermoplastic polymers, and thermoset polymers exposed to laser irradiation with different wavelengths were carried out. Thermoplastics PMMA and Polycarbonate and a thermoset epoxy matrix reinforced by glass and graphite fibres were used. The results from the first paper showed that microstructural changes caused by laser pulse impact can be visualised. The results of other two papers showed that, for hole drilling, short wavelengths are most suitable since these give good hole quality in most engineering materials including metals and composites. / Godkänd; 2004; 20070128 (ysko)

This thesis describes the state-of-the-art of off-line programming (OLP) for co-ordinate measuring machines (CMM's) and explores two important aspects of OLP systems; automatic generation of inspection programmes, probing points and movements between these, and data transfer from computer aided design (CAD). A method of generating inspection programmes using a 'feature' based definition of component geometry is described. This has been implemented as both free standing code and as a prototype, known as the Inspection Planning Assistant (IPA), which is based upon the robot simulation software GRASP. Current neutral data exchange formats such as IGES and DMIS are limited in their ability to transfer a toleranced 3D CAD model to OLP systems. The new standard for the exchange of product model data (STEP ISO 10303) offers the potential to resolve these problems. The scope and application of a STEP application protocol for inspection process planning is described / Godkänd; 1996; 20080328 (ysko)

No description available.