Machinability of rapidly solidified aluminium alloy for optical applications
- Authors: Abbas, Abdalla Abbas Said
- Date: 2020
- Subjects: Aluminum alloys , Mechatronics
- Language: English
- Type: Thesis , Masters , MEng
- Identifier: http://hdl.handle.net/10948/45975 , vital:39402
- Description: The production of metal mirrors and critical components for optical devices and aerospace application requires extreme high accuracy and outstanding surface quality. Thus, to achieve such high dimensional accuracies, they are being mainly produced through ultra-high precision machining. Aluminium alloys have been used in the production of components for optics application as well as spaceborne for so many years but with the advancement in technology and demands for a superior material, a new modified grade of aluminium was developed by a rapid solidification process. These grades exhibit a much better mechanical and physical properties while having a finer microstructure. The only downside is the limited research in the correlation of surface roughness and reflectance when single point diamond turned. In this study, rapidly solidified aluminium RSA 905 were used to investigate the effect of varying the cutting parameters on the machined surface finish and its corresponding surface reflectance. The cutting parameters were cutting speed, feed rate and depth of cut. The surface roughness was measured using Taylor Hopson PGI Profilometer while the reflectance factor was measured by using VERTEX 80v Spectrometer. The results were used to develop two predictive models namely; response surface and artificial neural network which have indicated a very high accuracy to the experimental measurements. Finally, the results were very promising for the diamond turning of RSA 905 where it has achieved a very low values of surface roughness and high reflectance in the visual range without the need of any additional production/fabrication steps and to ensure that bi-metallic binding does not take place in extreme low temperatures. Therefore, RSA 905 is a very promising material for optical applications in the visual spectrum.
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- Date Issued: 2020
Optical diamond turning of rapidly solidified aluminium alloy grade - 431
- Authors: Oyekunle, Funsho Adekunle
- Date: 2020
- Subjects: Aluminum alloys
- Language: English
- Type: Thesis , Masters , MEng
- Identifier: http://hdl.handle.net/10948/46860 , vital:39670
- Description: The high demand for ultraprecision machining systems is increasing day by day. The technology leads to increased productivity and quality manufactured products, with an excellent surface finish. Therefore, these products are in demand in many industrial fields such as space, national defence, the medical industry and other high-tech industries. Single point diamond turning (SPDT) is the core technology of ultraprecision machining, which makes use of single-point crystalline diamond as a cutting tool. This technique is used for machining an extensive selection of complex optical surfaces and other engineering products with a quality surface finish. SPDT can achieve dimensional tolerances in order of 0.01um and surface roughness in order of 1nm. SPDT is not restricted, but mostly applicable, to non-ferrous alloys; due to their reflective properties and microstructure that discourages tool wear. The focus of this study is the development of predictive optimisation models, used to analyse the influence of machining parameters (speed, feed, and depth of cut) on surface roughness. Moreover, the study aims to obtain the optimal machining parameters that would lead to minimum surface roughness during the diamond turning of Rapidly Solidified Aluminium (RSA) 431. In this study, Precitech Nanoform 250 Ultra grind machine was used to perform two experiments on RSA 431. The first machining process, experiment 1, was carried out using pressurized kerosene mist; while experiment 2 was carried out with water as the cutting fluid. In each experiment, machine parameters were varied at intervals and the surface roughness of the workpiece was measured at each variation. The measurements were taken through a contact method using Taylor Hobson PGI Dimension XL surface Profilometer. Acoustic emission (AE) was employed as a precision sensing technique – to optimize the machining quality process and provide indications of the expected surface roughness. The results obtained revealed that better surface roughness can be generated when RSA 431 is diamond-turned using water as a cutting fluid, rather than kerosene mist. Predictive models for surface roughness were developed for each experiment, using response surface methodology (RSM) and artificial neural networks (ANN). Moreover, RSM was used for optimisation. Time domain features acquired from AE signals, together with the three cutting parameters, were used as input parameters in the ANN design. The results of the predictive models show a close relationship between the predicted values and the experimental values for surface roughness. The developed models have been compared in terms of accuracy and cost of computation - using the mean absolute percentage error (MAPE).
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- Date Issued: 2020
The machinability of rapidly solidified aluminium alloy for optical mould inserts
- Authors: Otieno, Timothy
- Date: 2018
- Subjects: Aluminum alloys , Automobiles -- Materials Materials -- Mechanical properties
- Language: English
- Type: Thesis , Doctoral , DPhil
- Identifier: http://hdl.handle.net/10948/23097 , vital:30415
- Description: Ultra-high precision machining is a material removing process under the nanotechnology regime whereby the highest dimensional accuracies are attained. Critical components for optical devices and optical measuring systems are mainly produced through ultra-high precision machining. Their mass production is usually implemented by utilising optical moulds. Aluminium alloys have proven to be advantageous and very commonly used in the photonics industry for moulds. This ever-increasing use and demand within optics have led to the development of newly modified grades of aluminium alloys produced by rapid solidification in the foundry process. The newer grades are characterised by finer microstructures and improved mechanical and physical properties. The main inconvenience in their usage currently lies in their very limited machining database. This research investigates the machinability of rapidly solidified aluminium, RSA 905, under varying cutting conditions in single point diamond turning. The machining parameters varied were cutting speed, feed rate and depth of cut. The resulting surface roughness of the workpiece and wear of the diamond tool were measured at various intervals. Acoustic emissions and cutting force were also monitored during machining. The results were statistically analysed and accurate predictive models were developed. Generally, very low tool wear, within 3 to 5 μm, and very low surface roughness, within 3 to 8 nm, was obtained. Acoustic emissions recorded were in the range of 0.06 to 0.13 V and cutting forces were in the range of 0.08 to 0.94 N. The trends of the monitored acoustic emissions and cutting force showed to have a linked representation of the tool wear and surface roughness results. Contour maps were generated to identify zones where the cutting parameters produced the best results. In addition, a range of machining parameters were presented for optimum quality where surface roughness and tool wear can be minimised. As the machining is of a nanometric scale, a molecular dynamics approach was applied to investigate the underlying mechanisms at atom level. The nanomachining simulations were found to have a correlation to the actual machining results and microstructural nature of the alloy. This research proves that rapidly solidified aluminium is a superior alternative to traditional aluminium alloys and provides a good reference with room for flexibility that machinists can apply when using rapidly solidified aluminium alloys. Efficiency could be improved by reducing the required machining interruption through effective monitoring and performance could be improved by maintaining quality and extending tool life through parameter selection.
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- Date Issued: 2018
Tribocorrosion properties of friction stir welded and laser welded titanium alloy
- Authors: Davoren, Brandon Hilton
- Date: 2017
- Subjects: Chemistry, Technical -- Research Materials -- Mechanical properties , Aluminum alloys
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: http://hdl.handle.net/10948/33250 , vital:32605
- Description: Titanium alloy Ti6Al4V has extensive uses in aerospace, dentistry and the biomedical industry. When used in these applications there is often a need to weld two or more pieces of titanium alloy together. This can be done by either friction stir weld or laser weld methods. These welded regions are often exposed to corrosive environments in addition to factors such as induced additional mechanical wear. Thus to accurately report on the viability of the material in a specific application, the corrosion, wear and their synergistic effects need to be studied. Friction stir welding, which is a well-suited method for joining plates of Ti6Al4V, creates regions in the material that are affected differently. These regions can be described as the parent material, advancing side, retreating side and the weld zone. The tribological properties of the different friction stir weld regions were analysed in air using different loads, frequencies, experimental duration and surrounding environments. When the applied load was increased some of the weld regions showed an increase in the specific wear rate. For example, the weld zone region showed a decrease when compared to the parent material. In this tribology study the effect of the counter material was evaluated. E52100, Si3N4, SS 316 and alumina counter materials were used in the test procedure which was conducted in air on the weld regions. The parent material was found to have the highest average specific wear rates with the four counter materials when compared to the weld zone samples. The regions affected by the friction stir weld process all showed, on average, lower specific wear rates than the parent material. For the various tested samples, the coefficient of friction and material compatibility that was found to be the most stable, was the alumina ball. Owing to this as well as its chemical stability, alumina was determined to be the best material for further tribocorrosion studies. The friction stir welded samples, that were cut from a cross section of a friction stir weld plate, were analyzed in 3.5% NaCl and dilute Harrison’s solution respectively. The effect of wear on the electrochemical properties was studied under open circuit voltage (OCV) and fixed 0.2 V and 0.4 V applied potential conditions respectively. The effect of wear on the corrosion properties was studied using potentiodynamic polarization. From analyzing the friction stir weld regions in both a wear and wear-free environment, the synergistic properties, namely the effect of wear on corrosion and the effect of corrosion on wear, were able to be calculated. The first electrochemical study was performed under OCV conditions. In the presence of applied wear, the open circuit potential of the friction stir weld samples, in both 3.5% NaCl and dilute Harrison’s solution, was found to decrease from the initial stabilized value. Of interest was the rate at which the OCV recovered. It was found to follow a second order repassivation growth model which was explained in terms of an initial film growth stage, followed by a film thickening stage that results in a new OCV. The second synergized electrochemical-wear study was under fixed 0.2 V and 0.4 V applied potential conditions. In both solutions, 3.5% NaCl and dilute Harrison’s solution, a large increase in the current was observed during the applied wear experiment. The samples submerged in 3.5% NaCl were found to have higher average currents during the wear experiment than those in dilute Harrison’s solution. The rapid decrease in the current, after the applied wear ceased, was found to also follow the second order repassivation model. The electrochemical-wear synergism was done by using potentiodynamic polarization tests. The friction stir weld regions as well as the laser samples were analysed in a wear as well as a wear-free environment in order to determine the effect that wear had on the corrosion properties. In both 3.5% NaCl and dilute Harrison’s solution the corrosion rates were found to increase by 100-fold when the wear was present. The effect of the wear process on corrosion could also be described by synergistic factor, where values close to 1 would imply that applied wear had little effect on the corrosion properties and vice versa. The synergistic factors showed that the corrosion rate was greatly affected by the presence of wear with corrosion synergistic factors of 20 and upward for the friction stir welded samples. The results showed that the weld zone region had a lower corrosion rate than the parent material. This implied that the main weld zone was shown to have the least effect of wear on corrosion and would therefore show the lowest likelihood of failure due to corrosion when compared to the parent material. The wear synergistic factor was found to be between 1 and 1.6 for the friction stir weld regions. This implied that the wear rates of the friction stir welded samples were slightly affected by the presence of a corrosive environment and that the wear properties of the laser welded samples were enhanced by the presence of a corrosive environment. Similar studies performed on laser welded samples showed unusually different results due to the small nature of the laser weld region, with inconclusive results when compared to the friction stir welded samples.
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- Date Issued: 2017
Characterisation of dissimilar friction stir welds between 5754 Aluminium alloy and C11000 copper
- Authors: Akinlabi, Esther Titilayo
- Date: 2010
- Subjects: Friction stir welding , Aluminum alloys , Copper alloys
- Language: English
- Type: Thesis , Doctoral , DTech
- Identifier: vital:9629 , http://hdl.handle.net/10948/1536 , Friction stir welding , Aluminum alloys , Copper alloys
- Description: Friction Stir Welding (FSW) is a solid state welding process invented and patented by The Welding Institute (TWI) in 1991, for joining ferrous and non-ferrous materials1. The FSW of Aluminium and its alloys has been commercialised; and recent interest is focused on joining dissimilar materials. However, in order to commercialise the process, research studies are required to characterise and establish process windows. This research work through material characterisation of the welded joints establishes a process window for the Friction Stir welding of 5754 Aluminium Alloy and C11000 Copper. Furthermore, preliminary studies83,85 on the FSW of aluminium and copper have revealed the presence of intermetallic compounds which are detrimental to the weld qualities. This research work is also aimed at establishing process parameters that will result in limited or no intermetallic formation in the weld. The joint integrity of the resulting welds will also be correlated with the input process parameters. Based on the preliminary investigations conducted, a final weld matrix consisting of twenty seven welds was produced by varying the rotational speed between 600 and 1200 rpm, and the feed rate between 50 and 300 mm/min using three different shoulder diameter tools – 15, 18 and 25 mm to compare the heat input into the welds and to achieve the best results. The welds were characterised through microstructural evaluation, tensile testing, microhardness profiling, X-Ray Diffraction analysis, electrical resistivity and statistical analysis – in order to establish the interrelationship between the process parameters and the weld qualities. viii Microstructural evaluation of the weld samples revealed that the interfacial regions are characterised by mixture layers of aluminium and copper; while 33 percent of the tensile samples are within the acceptable range (> 75 percent joint efficiency). High Vickers microhardness values were measured at the joint interfaces, which corresponded with the intermetallic compounds. The Energy Dispersive Spectroscopy analysis revealed the presence of thin layers of intermetallics in nanoscale at the interfacial regions. The diffractograms of the X-Ray Diffraction analysis showed small peaks for intermetallics in some of the welds. Low electrical resistivities were measured at the joint interfaces. The statistical analysis showed that the downward vertical force, (Fz) can significantly influence the resulting weld qualities. An overall summary of the analysis of the weld qualities - with respect to the shoulder diameter tools employed showed that the 18 mm shoulder diameter tool is most appropriate among the three shoulder diameters considered, and a process window of medium spindle speed of 950 rpm and low-to-medium feed rate between 50 and 150 mm/min is established for FSW of Aluminium and Copper. Welds produced at 1200 rpm and 300 mm/min with low heat input did not have intermetallics formed at the joint interface.
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- Date Issued: 2010
Optimisation of cold rolling process parameters to improve surface quality of the AA 3003-H22 treadbright coils
- Authors: Makhanya, Lehlohonolo
- Subjects: Aluminum alloys
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:9611 , http://hdl.handle.net/10948/554 , Aluminum alloys
- Description: The main objective of this dissertation was to investigate how cold rolling process parameters could be optimised to improve surface quality of the AA 3003 H22 treadbright coils. This treadbright product is one of Hulett Aluminium’s main products and is exported mainly to the North American market. One of its critical requirements is a defect-free bright surface. The literature review was conducted with particular focus on the effects of selected parameters or settings with respect to surface quality and a chapter outlining these aspects has been included. It was clear from the literature review that selected parameters do affect the surface quality and if adjusted accordingly can improve surface quality on treadbright coils. Subsequent chapters after the literature review outline how the tests were conducted, procedures followed and equipments used from the cold rolling machine to laboratories. Surface appearance results after each parameter was adjusted, showed that the surface quality did improve and even got better when other parameters like the colouring roll angle and percentage reduction were adjusted. Correct working limits within which each parameter would yield acceptable surface quality were also established. All experiments conducted had no influence on the microstructure of the metal as it remained the same throughout each experiment. The same has been found with the mechanical properties as percentage reductions experiments led to no change in tensile strength, proof strength and percentage elongation. In conclusion, this research has proved that cold rolling process parameters selected did affect the product surface quality. If controlled they can be used to optimise the surface quality on the treadbright product as required by Hulett Aluminium and its customers.
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