No description available.

No description available.

Friction stir welding (FSW) is a modern solid state welding technique developed at the welding institute (TWI) in 1991. The joining is achieved by heat generation, material softening and plastic deformation following the travelling of non-consumable pin through the gap between the two work pieces to be joined. In present study, joining of AA 2024-T3 aluminium alloy, is achieved by FSW. The influence of the FSW on the alloy microstructure and corrosion behaviour is determined. The effect of laser surface melting (LSM) treatment on the improvement of corrosion resistance of friction stir welded alloys is investigated. Further, heat treatments to simulate the welding process with controlled cooling rate are performed to assess the effect of cooling rate on the microstructure, consequently, the corrosion performance of the welds. It is revealed that FSW process introduces elevated temperatures at the weldment, resulting in distinct regions with modified microstructures. The regions are named as the TMAZ (thermomechanically affected zone) and the HAZ (heat affected zone). TMAZ, positioned at the weldment centre, is featured by a central nugget with dynamically recrystallised fine, equiaxid grains, that is surrounded by heavily deformed grains. HAZ, positioned as narrow bands just outside TMAZ, has grain size similar to parent alloy. Corrosion testing shows that the as-welded alloy is highly susceptible to corrosion, particularly at the bands just outside the TMAZ (i.e. HAZ). Welding process resulted in the preferential precipitation of copper and magnesium rich particles at the grain boundaries within the HAZ, which reduces the corrosion resistance as a result of the galvanic coupling of the sensitised grain boundaries and the adjacent matrix. Laser treatment resulted in a melted near-surface layer, up to 6 μm thick, where normal constituent particles are absent. Corrosion testing showed that laser treatment reduces the degree of localized corrosion due to the removal constituent particles. However, scrutiny of the melted near-surface layer revealed continuous segregation bands, approximately 10nm thick, containing mainly copper. The presence of such segregation bands promoted localised corrosion of the laser melting layer due to microgalvanic action. From the areas where melting layer is corroded, localised corrosion propagated further into the weld intergranularly. The severe intergranular corrosion beneath the laser melting layer undermines the laser melting layer, resulting delamination of the surface layer from theunderlying bulk alloy. The simulated heat treatments show that the cooling cycle of the welding process has a significant influence on the alloy's microstructure and corrosion behaviour. Slow cooling can result in formation of a continuous network of second phase particles at the grains boundaries, leading to significantly reduced corrosion resistance. Rapid cooling tends to prevent the formation of second phase particles at grains boundaries, resulting in improved corrosion resistance.

No description available.

No description available.

Several axi-symmetric EN3B steel components differing in shape and size were forged on a 100 ton joint knuckle press. A load cell fitted under the lower die inserts recorded the total deformation forces. Job parameters were measured off the billets and the forged parts. Slug temperatures were varied and two lubricants - aqueous colloidal graphite and oil - were used. An industrial study was also conducted to check the results of the laboratory experiments. Loads were measured (with calibrated extensometers attached to the press frames) when adequately heated mild steel slugs were being forged in finishing dies. Geometric parameters relating to the jobs and the dies were obtained from works drawings. All the variables considered in the laboratory study could not, however, be investigated without disrupting production. In spite of this obvious limitation, the study confirmed that parting area is the most significant geometric factor influencing the forging load. Multiple regression analyses of the laboratory and industrial results showed that die loads increase significantly with the weights and parting areas of press forged components, and with the width to thickness ratios of the flashes formed, but diminish with increasing slug temperatures and higher billet diameter to height ratios. The analyses also showed that more complicated parts require greater loads to forge them. Die stresses, due to applied axial loads, were investigated by the photoelastic method. The three dimensional frozen stress technique was employed. Model dies were machined from cast araldite cylinders, and the slug material was simulated with plasticene. Test samples were cut from the centres of the dies after the stress freezing. Examination of the samples, and subsequent calculations, showed that the highest stresses were developed in die outer corners. This observation partly explains why corner cracking occurs frequently in industrial forging dies. Investigation of die contact during the forging operation revealed the development of very high stresses.

Cadmium coatings are currently applied to steel fasteners used in aerospace applications. At present there are growing concerns, based on cadmium's toxicity and carcinogenicity, which may lead to its eventual banning. The aim of this research, therefore, was to find a possible replacement to electrodeposited cadmium for use on aerospace fasteners. Any replacement coating system should have all of the relevant properties that make cadmium so attractive, but without its obvious shortcomings. These beneficial properties include excellent corrosion resistance in chloride containing media (such as seawater), the ability to offer sacrificial protection to steel, excellent galvanic compatibility with most aluminium alloys and an inherent lubricity. Alternatives proposed and produced in this research are electrodeposited composite coatings containing PTFE particles, based on zinc or zinc alloys. Extensive analysis was carried out in order to characterise the coatings. Composition was determined by a number of methods; gravimetric analysis was used to determine the percentage of codeposited PTFE, while X-ray and X-ray wavelength energy dispersive analysis were used to determine the percentage of alloy element present in these coatings. Coating morphology was investigated by scanning electron microscopy. The sacrificial corrosion performance of each coating in relation to steel was studied using neutral salt-spray tests, while linear polarisation resistance tests gave an indication of their barrier corrosion properties. Galvanic compatibility of the coatings with aerospace grade aluminium alloys was investigated using a zero resistance ammeter. Two different tribological tests, an inclined plane test and a reciprocating wear test, were used to determine the coefficient of friction for the coatings. Finally, linear sweep voltammetry was used to compare the kinetics of electrodeposition from dilute solutions and corrosion in aqueous media for each of the coating systems. The composite coatings were found to offer either similar or slightly reduced corrosion performance to conventional zinc and zinc alloy coatings, but were inferior to commercially electrodeposited cadmium. However, the tribological properties of these coatings demonstrated a marked improvement over cadmium.

The work reported in this thesis has been developed to predict and measure the cutting forces in the gear hobbing process. A review of past research in this area has highlighted the need to adopt a different approach to modelling the process in order to predict the cutting forces. The hobbing process has been described using six different co-ordinate systems and the kinematic relationships between these systems established. A single rack profile has been used to represent the profile of a single cutting tooth from the hob which was then extended to simulate the hob itself. When the hob gashes pass through the cutting region surfaces are generated which, if mapped on a regular grid can give the basis to estimate the depth of cut, i.e. the instantaneous chip thickness produced by that particular tooth. The instantaneous cutting forces generated by that tooth then can be estimated by using the concept of a specific cutting force of the workpiece material. The estimation of cutting forces acting on a single tooth space was used to predict the cutting forces produced during machining of a full gear, by assuming that the forces acting in a particular tooth space are equal to those acting on the adjacent tooth space at an equivalent instant in the cutting cycle. In order to validate predicted results, a Churchill PH1612 hobbing machine was retrofitted with a CNC control system at Newcastle University, utilising a programmable multi axis controller (PMAC). A specially made single toothed gear, and a full gear were machined, and cut on this machine, and the cutting forces measured in real time using a 3-axis dynamometer. The force signals produced by the dynamometer were measured utilising a 12-bit ADC card. Code, written in C, was developed to perform the many functions needed for the overall control of the machine, but additionally was used to capture both the cutting forces and axis position data. The results of the simulation and modelling have shown very good agreement with those obtained experimentally.

The use of insoluble anodes has become critical to the viability of horizontal electroplating equipment. Despite this there have been few reported studies on the impact of using such anodes on the electrochemistry of acid copper plating solutions. A literature search therefore reviewed the different types of insoluble anode that had been previously utilized in sulphuric acid-based electrolytes and from this a number of criteria were established that might be applied when selecting an insoluble anode for horizontal acid copper electroplating. A 'life study' was then carried out to compare two electroplating baths, one operating with standard copper anodes, and the other insoluble anodes.

Spot welding is a process that is widely used in industries worldwide. This project aims to research and develop a control system to improve the strengths of the spot welds. Conventional (pneumatic) spot welding systems do not lend themselves towards in-process control specifically controlling the forging force during welding. The importance of the forging force is that it is related to the dynamic resistance and hence to the rate of heating of the weld as has been shown in this work. The use of the forging force to control weld strengths was investigated by converting the electrode actuating system of a pneumatic spot welder to a motor driven servo system. This enabled the electrode forging force to be varied during welding. The control system was used to vary the forging force during welding by means of various preset force profiles in order to vary the heating during welding. The effects of the various force profiles to heat generation and weld growth were studied by using the dynamic resistance curve. The relationship between resistance and force enables the dynamic resistance to be used as an indicator for weld performance. Experiments were carried out to propose the force profile that will give the highest weld strength. Results obtained from this project shows that two changes in the characteristics of the force profile, viz, the delay time before ramping and the rate of ramping, affects the amount of heat supplied to the weld during welding which causes change in the weld strength. Statistically significant differences between average weld strengths due to the changes in these characteristics are presented. Forging force control was also found to produce stronger welds compared to the conventional electrode clamping force (ECF) condition, which was found to be statistically significant. It was also found possible to extend the weld lobe region of the electrode clamping force (ECF) condition by using forging force control, to produce improved weld strengths at the no weld and expulsion regions of the lobe. The profile that starts with a lower force and ends with a higher force with a longer ramping delay and slower ramping rate was the profile that produces the strongest weld strength among all the profiles tested. This profile with a welding current below the expulsion limit was suggested as the strategy to produce stronger welds at a faster rate.