Techn. Hochsch., Diss.--Aachen, 2006.

Zugl.: Aachen, Techn. Hochsch., Diss., 2008.

Zugl.: Aachen, Techn. Hochsch., Diss., 2008

Increasing regulatory pressure to reduce fuel consumption of new vehicles has prompted the automotive industry to seek ways to reduce the weight of their automobiles. The use of steel tailor welded blanks has been successful in reducing vehicle weight while simultaneously reducing manufacturing costs; however, further weight reductions are possible if steel alloys are substituted with aluminum alloys. This has created a need to identify and develop welding techniques that would enable the production of high-quality welds between aluminum sheets of different thicknesses at rates compatible with the demands of the automotive industry. A relatively new welding technique that has been shown to have potential for joining aluminum sheet for tailor welded blank applications is the double-sided arc welding (DSAW) process. In DSAW, an arc is struck between two welding torches situated on either side of the sheets to be welded allowing the aluminum surface oxide to be electrically cleaned simultaneously from both sides of the joint. The demonstrated potential for welding aluminum sheet and the low capital cost compared to conventional laser welding systems typically used for fabricating TWBs makes DSAW an excellent candidate for welding aluminum TWBs. The objective of the research described in this thesis was to assess the feasibility and merits of using a DSAW system to manufacture aluminum TWBs. In this study, a DSAW system comprised of a plasma arc welding (PAW) torch above the work piece and a gas tungsten arc welding (GTAW) torch below the work piece was applied to the high speed welding of 1.0 to 1.5 mm thick AA5182-O aluminum alloy sheets in the butt-joint configuration. A series of conduction-mode DSAW welds were made in the horizontal position to identify the welding conditions that produced good quality welds using visual acceptance criteria and with minimal geometric discontinuity across the weld. Further studies were conducted to determine the influence of the welding process parameters on the hardness, strength, ductility, formability and internal flaws of DSAW welds. DSAW welds were made using a series of welding torch-to-work piece distances, between 1.5 and 6.0 mm, to investigate the influence of varying the relative arc forces acting on the top and bottom of the weld pool on the resulting weld bead dimensions including weld metal drop through. It was found that increasing the torch-to-work piece distance decreased the process efficiency when a constant welding power was used resulting in narrower welds being produced. Weld metal sag or drop through was not observed to be affected by varying the welding torch-to-work piece distance; however, decreasing the PAW torch-to-work piece distance to 1.5 mm was found to produce a pronounced surface ripple pattern on the top surface of the weld. A series of DSAW welds were made to investigate the range of welding speeds and powers that produced visually acceptable welds on 1.0 to 1.5 mm thick AA5182 aluminum sheets. Welding powers ranging from 1.4 to 4.6 kW were found to produce acceptable welds at travel speeds between 10 and 70 mm/s when the net heat input per unit distance was between 60 and 110 J/mm. Above these speeds, unacceptable weld bead quality and lack of fusion defects were observed due to incomplete cathodic etching of the oxide from the surfaces and inconsistent coupling between the welding arcs the sheets. It was found that the visual appearance of the weld was improved and travel speeds could be increased for a given welding power when welding specimens were stainless steel wire brushed prior to welding to break-up and remove most of the pre-existing hydrated aluminum surface oxide. Significant reductions in hydrogen gas porosity were also observed when stainless steel wire brushing was used. The strength, ductility and formability of DSAW welds were found to vary significantly depending on the welding parameters used and the occurrence of porosity defects in the welds. Welds made using welding speeds greater than 30 mm/s were found to exhibit solidification shrinkage micro-porosity and a corresponding degradation in mechanical properties, especially ductility and formability. As the welding speed was further increased, degradation of the material properties continued to increase due to an increase in the quantity of micro-porosity defects in the weld. These defects caused significant strain localization resulting in a marked decrease in ductility and formability. The severity of solidification shrinkage micro-porosity present in the weld metal was found to correspond to the relative length-to-width ratio of the weld pool for all the welding conditions examined. Welds produced at high welding speeds resulted in large length-to-width ratios, a relatively large distance between the liquidus and non-equilibrium solidus and low thermal gradients in the mushy zone at the tail of the weld. These conditions are known to promote micro-porosity in alloys with a wide freezing range. Visually acceptable DSAW welds produced using welding speeds below 25 mm/s were found to have excellent material properties that were nearly indistinguishable from the base metal with excellent ductility and formability. These welds had relatively small length-to-width ratios and little or no evidence of solidification micro-porosity, because the length of the mushy zone at the tail of the weld was much smaller and the thermal gradients were much higher. These conditions are known to prevent solidification micro-porosity during solidification of alloys with a wide freezing range. They also provide more time and opportunity for any hydrogen bubbles that may form during solidification to float up and escape through the top surface of the weld pool thereby further reducing the propensity for hydrogen porosity. The DSAW process has been shown to be capable of successfully producing tailor-welded blanks in 5182 aluminum alloy sheets with excellent ductility and formability provided that all sources of porosity are eliminated. This includes careful cleaning and removal of preexisting hydrated oxides using stainless steel wire brushing prior to welding to minimize hydrogen porosity and welding at slow enough speeds to prevent the formation of solidification micro-porosity at the tail of the weld pool.

Increasing regulatory pressure to reduce fuel consumption of new vehicles has prompted the automotive industry to seek ways to reduce the weight of their automobiles. The use of steel tailor welded blanks has been successful in reducing vehicle weight while simultaneously reducing manufacturing costs; however, further weight reductions are possible if steel alloys are substituted with aluminum alloys. This has created a need to identify and develop welding techniques that would enable the production of high-quality welds between aluminum sheets of different thicknesses at rates compatible with the demands of the automotive industry. A relatively new welding technique that has been shown to have potential for joining aluminum sheet for tailor welded blank applications is the double-sided arc welding (DSAW) process. In DSAW, an arc is struck between two welding torches situated on either side of the sheets to be welded allowing the aluminum surface oxide to be electrically cleaned simultaneously from both sides of the joint. The demonstrated potential for welding aluminum sheet and the low capital cost compared to conventional laser welding systems typically used for fabricating TWBs makes DSAW an excellent candidate for welding aluminum TWBs. The objective of the research described in this thesis was to assess the feasibility and merits of using a DSAW system to manufacture aluminum TWBs. In this study, a DSAW system comprised of a plasma arc welding (PAW) torch above the work piece and a gas tungsten arc welding (GTAW) torch below the work piece was applied to the high speed welding of 1.0 to 1.5 mm thick AA5182-O aluminum alloy sheets in the butt-joint configuration. A series of conduction-mode DSAW welds were made in the horizontal position to identify the welding conditions that produced good quality welds using visual acceptance criteria and with minimal geometric discontinuity across the weld. Further studies were conducted to determine the influence of the welding process parameters on the hardness, strength, ductility, formability and internal flaws of DSAW welds. DSAW welds were made using a series of welding torch-to-work piece distances, between 1.5 and 6.0 mm, to investigate the influence of varying the relative arc forces acting on the top and bottom of the weld pool on the resulting weld bead dimensions including weld metal drop through. It was found that increasing the torch-to-work piece distance decreased the process efficiency when a constant welding power was used resulting in narrower welds being produced. Weld metal sag or drop through was not observed to be affected by varying the welding torch-to-work piece distance; however, decreasing the PAW torch-to-work piece distance to 1.5 mm was found to produce a pronounced surface ripple pattern on the top surface of the weld. A series of DSAW welds were made to investigate the range of welding speeds and powers that produced visually acceptable welds on 1.0 to 1.5 mm thick AA5182 aluminum sheets. Welding powers ranging from 1.4 to 4.6 kW were found to produce acceptable welds at travel speeds between 10 and 70 mm/s when the net heat input per unit distance was between 60 and 110 J/mm. Above these speeds, unacceptable weld bead quality and lack of fusion defects were observed due to incomplete cathodic etching of the oxide from the surfaces and inconsistent coupling between the welding arcs the sheets. It was found that the visual appearance of the weld was improved and travel speeds could be increased for a given welding power when welding specimens were stainless steel wire brushed prior to welding to break-up and remove most of the pre-existing hydrated aluminum surface oxide. Significant reductions in hydrogen gas porosity were also observed when stainless steel wire brushing was used. The strength, ductility and formability of DSAW welds were found to vary significantly depending on the welding parameters used and the occurrence of porosity defects in the welds. Welds made using welding speeds greater than 30 mm/s were found to exhibit solidification shrinkage micro-porosity and a corresponding degradation in mechanical properties, especially ductility and formability. As the welding speed was further increased, degradation of the material properties continued to increase due to an increase in the quantity of micro-porosity defects in the weld. These defects caused significant strain localization resulting in a marked decrease in ductility and formability. The severity of solidification shrinkage micro-porosity present in the weld metal was found to correspond to the relative length-to-width ratio of the weld pool for all the welding conditions examined. Welds produced at high welding speeds resulted in large length-to-width ratios, a relatively large distance between the liquidus and non-equilibrium solidus and low thermal gradients in the mushy zone at the tail of the weld. These conditions are known to promote micro-porosity in alloys with a wide freezing range. Visually acceptable DSAW welds produced using welding speeds below 25 mm/s were found to have excellent material properties that were nearly indistinguishable from the base metal with excellent ductility and formability. These welds had relatively small length-to-width ratios and little or no evidence of solidification micro-porosity, because the length of the mushy zone at the tail of the weld was much smaller and the thermal gradients were much higher. These conditions are known to prevent solidification micro-porosity during solidification of alloys with a wide freezing range. They also provide more time and opportunity for any hydrogen bubbles that may form during solidification to float up and escape through the top surface of the weld pool thereby further reducing the propensity for hydrogen porosity. The DSAW process has been shown to be capable of successfully producing tailor-welded blanks in 5182 aluminum alloy sheets with excellent ductility and formability provided that all sources of porosity are eliminated. This includes careful cleaning and removal of preexisting hydrated oxides using stainless steel wire brushing prior to welding to minimize hydrogen porosity and welding at slow enough speeds to prevent the formation of solidification micro-porosity at the tail of the weld pool.

No description available.

P-aminobenzoic acid (PABA) is a polymorphic compound with two known polymorphs - alpha with a needle morphology and β with a rhombic morphology. It is an enantiotropic compound with a transition temperature at 13.8oC, where alpha is more thermodynamically stable above transition temperature and β is more thermodynamically stable below. At the beginning of this project, crash-cooling crystallisation experiments were conducted to determine the effect of solvent, temperature and supersaturation on the nucleating polymorphs of PABA. Three solvents were tested (water, ethanol and isopropyl alcohol) over a range of supersaturations and temperatures. The results suggested that polymorph appearance of PABA was heavily influenced by kinetics, as opposed to thermodynamics of the system, disagreeing with Ostwald's rule of stages. The project then focussed on the ability of tailor-made additives to select the crystallising polymorph of PABA from supersaturated solutions of PABA in isopropyl alcohol. Crash-cooling crystallisation experiments were performed using two additives: 4-amino-3-nitrobenzoic acid, and 4-amino-3-methoxybenzoic acid. Results showed that alpha PABA crystallised below a critical concentration of either additive, and above that critical concentration, β PABA would crystallise. To determine whether the additives were affecting the nucleation and/or growth kinetics of alpha PABA and β PABA, a series of nucleation and growth experiments were conducted using a Crystal16 multiple stirred reactor and a crystal growth cell respectively. The results showed that both additives greatly reduced the attachment frequency of growth units to alpha PABA nuclei, and inhibited the growth rate of alpha PABA seed crystals. Nucleation data could not be obtained for β PABA, but in terms of crystal growth, both additives did not affect growth rate of β PABA to a noticeable degree. Gravimetric and HPLC experiments were also employed to measure the solubility effects of both additives on PABA in isopropyl alcohol. Results showed that both additives did not appear to affect PABA's solubility to a noticeable degree.

The purpose of this study is to describe and analyze how companies offering tailor made products on the internet, can work with their marketing and their customer relationships. The study will answer the purpose from a service management perspective and there will also be presented theories from an Electronic Commerce perspective. The starting point for this study was the qualitative method. The essay builds its empirical material from interviews with knowledgeable persons in the subject and the owner of the company whose products are tailor made and sold on the internet. It was conducted seven interviews, four of which were face-to-face, two conducted by mail and finally there was made a telephone interview. Conclusions have been drawn based on the empirical material and theory. The study has been able to identify three concepts that are central to this type of product: Site-building, customer involvement and promotion & relationship management.

<p>The purpose of this study is to describe and analyze how companies offering tailor made products on the internet, can work with their marketing and their customer relationships. The study will answer the purpose from a service management perspective and there will also be presented theories from an Electronic Commerce perspective.</p><p>The starting point for this study was the qualitative method. The essay builds its empirical material from interviews with knowledgeable persons in the subject and the owner of the company whose products are tailor made and sold on the internet. It was conducted seven interviews, four of which were face-to-face, two conducted by mail and finally there was made a telephone interview.</p><p>Conclusions have been drawn based on the empirical material and theory. The study has been able to identify three concepts that are central to this type of product: Site-building, customer involvement and promotion & relationship management.</p>

The effect of impurities on crystal morphology is a challenging problem, since even at low concentrations they can have drastic effects on the final habit. Industrially this causes problems with downstream processes such as filtration, processability and even storage. Conversely, structurally related additive molecules may be introduced to a system in order to mimic the effect of an impurity resulting in a beneficial effect on problematic crystal morphologies. The work presented here considers the design and use of tailor made additives on a nonhydrogen bonded crystal, benzophenone. This compound is typical of many agrochemical materials in that the major intermolecular interactions are of the nondirectional van der Waals type. Using crystal packing analysis a selection of additives has been chosen with the intent of specifically hindering certain directions of crystal growth. From an initial group of nine molecules two additives, 4ABP and 4MBP were found tobe particularly effective, both strongly hindering growth. Measured kinetic data suggests that these additives bind to steps in the growth spirals, drastically slowing growth of specific crystal faces altering the crystal morphology to a needle shape. Through nucleation experiments and product analysis the additives were shown to effect only crystal growth becoming incorporated into the crystal structure. Computational modelling of the binding of additives to the crystal surfaces of benzophenone has been used in an attempt to rationalise the experimental effects. In many cases calculated binding energies were in agreement with experimental observation. However, modified attachment energies did not match well with experimental observations.