Over the last few decades, miniaturization of the product became a necessity for many industries to achieve successful technological development, satisfy customer needs, and stay economically competitive in the market. Thus, many medical, aerospace, and electronic devices tend to decrease in size. Along with the strong demand for miniaturization, new cutting-edge micromanufacturing techniques are developing in order to produce microcomponents with a smooth surface finish and high dimensional accuracy. In the medical industry, some devices require manufacturing of fluidic microchannels on biocompatible materials for transportation of exact amount of medicine to a defined location. Often such microchannels must be manufactured to achieve a high aspect ratio, a submicron surface finish, and an anisotropic controlled profile. The fabrication of such channels on biocompatible materials still poses a challenge. This study developed micromanufacturing technique to produce the microchannels and satisfy all the requirements listed above. Computer controlled micromilling on a high speed machine system in minimum quantity lubrication was used to remove most materials and define a channel pattern. Microchannels were machined with ball end mills of diameters from Ø152μm to Ø198μm on NiTi alloy, 304 and 316L stainless steels. Assessment of microchannel was performed with optical microscopy, scanning electron microscopy, and white light interferometry. The theoretical surface roughness in ball end milling was derived using geometrical approach. The theoretical surface finish model was compared and validated with the experimental surface finish data. Meso- and macro-scale milling confirmed the validity of the model, but surface finish in micro-scale milling was measured to be a few orders of magnitude higher due to size effect and build-up edge. The build-up-edge was reduced when using AlTiN coated tools and milling in minimum quantity lubrication. The empirical surface roughness model obtained in this study shows the dependence of surface finish on chip load in micromilling. In order to further enhance the surface finish of milled microchannels additional finishing technique was identified. A separate study developed an effective electrochemical polishing technique to remove burrs and enhance surface finish of milled microchannels. When applying to 304, 316L stainless steel alloys and NiTi alloy, this hybrid technique can repeatedly produce microchannels with an average surface finish less than 100nm.

Ultra precision single point diamond turning (SPDT) is a machining process used to produce optical grade surfaces in a wide range of materials. Aluminum is of primary interest as a workpiece material because it is easily diamond turnable, highly reflective and corrosion resistant. The cutting tool used is made from a single crystal diamond honed to a very sharp cutting edge. The machines used in this process are extremely precise and stiff. The nature of the cutting parameters used in SPDT changes the process physics substantially over conventional machining. The underlying reason relates to the relative size of the uncut chip thickness and the cutting edge radius of the tool in comparison to the grain size of the workpiece. When performing SPDT, there is a functional limit to the achievable surface finish. This is predominately due to material side flow and the opening up of material defects. Thus the machined surfaces have to undergo post processing operations like lapping or polishing, which increase cost and production time. Thus, the objective of this study was to improve the surface finish of the SPDT process to minimize the amount of post processing. The approach involved addressing the ratio between the tool cutting edge radius and the microstructure. Realizing the limitations associated with sharpening a diamond tool further, efforts have been made to mechanically or thermo-mechanically induce dislocations into the workpiece to refine the microstructure and in so doing enhance machinability. As dislocations act as a point of defect, it is observed that higher dislocation density offers less side flow and leads to better surface roughness. A special tool with a flat secondary edge was then developed to address the remaining side flow issue for planar surfaces. The combination of thermo-mechanically produced ultra fine grained material with the special tool provided a substantial reduction in surface roughness from values typically reported at 3nm [Roblee, 2007] Ra to 0.75nm R0 • In addition to this the use of the custom designed tool can improve the productivity associated with machining a flat face by a factor of one hundred times by allowing the feed rate to be increased while still achieving the desired surface finish. / Thesis / Doctor of Philosophy (PhD)

The purpose of this study was to develop a composite manufacturing process that would be able to deliver Class A surface finished products in the context of mould manufacturing methods. The problem required solving was to overcome the time needed to prepare Class A surfaces, by developing a composite manufacturing process that will deliver Class A surface finished products straight from the mould. The process was aimed at the entire development process, from mould and plug design up to the finished product. A literature study and a factory mould survey were conducted with a view to obtain the necessary insights into surface finishing and composite manufacturing. These surveys were followed by seven constructional tests which determined the most appropriate solutions for the proposed manufacturing processes. Test 1 was used to determine a quality finish standard for composites from the sanding grits used to finished composite surfaces versus surface roughness values used in other industries. The standard determined that a P800 finish has a roughness between 0.200 and 0.150 um and constitutes a Class A3 finish. P1000 to P1200 have a roughness between 0.150 um to 0.100 um and constitutes a Class A2 finish. Finally a P2000 and higher have a roughness of 0.100 um and lower and constitutes Class A1 surface finish. After the standard was set, the tests for finishing of the moulds, plugs and parts commenced. Test 2 was conducted on the CNC manufacturing of plugs out of Nuceron651 tooling board. Tool path parameters were varied in a matrix. The samples with the best surface finish value were cut with a step-over of 0.5 and feed of 800 mm/min. These parameters were found to be the most influential. Test 2 and 4 revealed that the plug surface finishing should commence with conventional 2K paint finishing, with a possibility of acrylic split surface. This process produced projected mould surfaces between 0.150 um and 0.200 um, which can be categorised as Class A-3. Test 5 and 6 determined methods for improving the mould surface quality and durability. It was established that the tooling gelcoat should be applied whilst being heated and backed with at least two layers of glass veil and a steady increase of GSM of structural glass fibres to prevent print-through. Test 3 determined that the mould corners could be strengthened with rovings pressed into the corner. It was also established that the moulds surfaces will require finishing after demoulding. The final moulds were manufactured from a fibreglass composite structure with tooling gelcoat surface. A number of guidelines and a set process were developed in order to produce moulds with a surface finish of average 0.9 um, equivalent to Class A1. Release agents were tested in Test 7, and the Loctite Frekote 770-NC release system was deemed appropriate for use with In Mould Coating (IMC) of 2K Paint. These elements were all synthesised into plug, mould and part manufacturing processes. The proposed processes were validated by the manufacturing of a JS instrument panel, which delivered a Class A2, 0.175 um, finish with IMC of 2K paint. With only a minor sanding of P3000 grit and polishing, the part was made into a Class A1 surface, measured at 0.63 um. The study proved that it is possible to produce Class A finished part with IMC. This method can provide a solution aimed at the elimination of P600 and lower finishing of composite parts manufactured with IMC. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

The purpose of this study was to develop a composite manufacturing process that would be able to deliver Class A surface finished products in the context of mould manufacturing methods. The problem required solving was to overcome the time needed to prepare Class A surfaces, by developing a composite manufacturing process that will deliver Class A surface finished products straight from the mould. The process was aimed at the entire development process, from mould and plug design up to the finished product. A literature study and a factory mould survey were conducted with a view to obtain the necessary insights into surface finishing and composite manufacturing. These surveys were followed by seven constructional tests which determined the most appropriate solutions for the proposed manufacturing processes. Test 1 was used to determine a quality finish standard for composites from the sanding grits used to finished composite surfaces versus surface roughness values used in other industries. The standard determined that a P800 finish has a roughness between 0.200 and 0.150 um and constitutes a Class A3 finish. P1000 to P1200 have a roughness between 0.150 um to 0.100 um and constitutes a Class A2 finish. Finally a P2000 and higher have a roughness of 0.100 um and lower and constitutes Class A1 surface finish. After the standard was set, the tests for finishing of the moulds, plugs and parts commenced. Test 2 was conducted on the CNC manufacturing of plugs out of Nuceron651 tooling board. Tool path parameters were varied in a matrix. The samples with the best surface finish value were cut with a step-over of 0.5 and feed of 800 mm/min. These parameters were found to be the most influential. Test 2 and 4 revealed that the plug surface finishing should commence with conventional 2K paint finishing, with a possibility of acrylic split surface. This process produced projected mould surfaces between 0.150 um and 0.200 um, which can be categorised as Class A-3. Test 5 and 6 determined methods for improving the mould surface quality and durability. It was established that the tooling gelcoat should be applied whilst being heated and backed with at least two layers of glass veil and a steady increase of GSM of structural glass fibres to prevent print-through. Test 3 determined that the mould corners could be strengthened with rovings pressed into the corner. It was also established that the moulds surfaces will require finishing after demoulding. The final moulds were manufactured from a fibreglass composite structure with tooling gelcoat surface. A number of guidelines and a set process were developed in order to produce moulds with a surface finish of average 0.9 um, equivalent to Class A1. Release agents were tested in Test 7, and the Loctite Frekote 770-NC release system was deemed appropriate for use with In Mould Coating (IMC) of 2K Paint. These elements were all synthesised into plug, mould and part manufacturing processes. The proposed processes were validated by the manufacturing of a JS instrument panel, which delivered a Class A2, 0.175 um, finish with IMC of 2K paint. With only a minor sanding of P3000 grit and polishing, the part was made into a Class A1 surface, measured at 0.63 um. The study proved that it is possible to produce Class A finished part with IMC. This method can provide a solution aimed at the elimination of P600 and lower finishing of composite parts manufactured with IMC. / MIng (Mechanical Engineering), North-West University, Potchefstroom Campus, 2014

No description available.

Electrochemical machining (ECM) is a non-conventional manufacturing process, which uses electrochemical dissolution to shape any conductive metal regardless of its mechanical properties and without leaving behind residual stresses or tool wear. Therefore, ECM can be an alternative for machining difficult-to-cut materials, complex geometries, and materials with improved characteristics, such as strength, heat-resistance or corrosion-resistance. Notwithstanding its great potential as a shaping tool, the ECM process is still not fully characterised and its research is an on-going process. Various phenomena are involved in ECM, e.g. electrodynamics, mass transfer, heat transfer, fluid dynamics and electrochemistry, which occur in parallel and this can lead to a different material dissolution rate at each point of the workpiece surface. This makes difficult an accurate prediction of the final workpiece geometry. This problem was addressed in the first part of the present thesis by developing a simulation model of the ECM process in a two-dimensional (2D) environment. A finite element analysis (FEA) package, COMSOL multiphysics® was used for this purpose due to its capacity to handle the diverse phenomena involved in ECM and couple them into a single solution. Experimental tests were carried out by applying ECM on stainless steel 316 (SS316) samples. This work was done in collaboration with pECM Systems Ltd® from Barnsley, UK. The interest of studying ECM on stainless steels (SS) resides on the fact that the application of ECM on SS typically results in various different surface finishes. The chromium in SS alloys usually induces the formation of a protective oxide film that prevents further corrosion of the alloy, giving the metal the special characteristic of corrosion resistance. This oxide film has low electrical conductivity; hence normal anodic dissolution often cannot proceed without oxide breakdown. Partial breakdown of the oxide film often occurs, which causes pits on the surface or a non-uniform surface finish. Therefore the role of the ECM machining parameters, such as interelectrode gap, voltage, electrolyte flow rate, and electrolyte inlet temperature, on the achievement of a uniform oxide film breakdown was evaluated in this work. Experimental results show that the resulting surface finish is highly influenced by the over-potential and current density, and by the characteristics of the electrolyte, flow rate and conductivity. The complexity of experimentally controlling these parameters emphasised the need for the development of a computational model that allows the simulation of the ECM process in full. The simulation of ECM in a three-dimensional (3D) environment is crucial to understand the behaviour of the ECM process in the real world. In a 3D model, information that was not visible before can be observed and a more detailed realistic solution can be achieved. Hence, in this work a computer aided design (CAD) software was used to construct a 3D geometry, which was imported to COMSOL Multiphysics® to simulate the ECM process, but this time in a 3D environment. This enhanced simulation model includes fluid dynamics, heat transfer, mass transfer, electrodynamics and electrochemistry, and has the novelty that an accurate computational simulation of the ECM process can be carry out a priori the experimental tests and allows the extraction of enough information from the ECM process in order to predict the workpiece final shape and surface finish. Moreover, this simulation model can be applied to diverse materials and electrolytes by modifying the input ECM parameters.

Bulk forming and cutting are widely used to shape metals in industrial production. Bulk forming is characterized by large strains, extensive plastic deformation and large surface expansions. Cutting is characterized by high speeds, high pressures and high temperatures. The prevailing conditions during these processes lead to transfer of work material to tools. In bulk forming this is a significant problem. The transferred work material is hardened and becomes harder than the work material, causing galling. This leads to high friction and high forming forces, bad surface finish of the formed products and significant difficulties to produce complicated geometries. In cutting, transfer of work material can be desired for protection of the tool surface. However, the transfer film has to be of the correct type to provide a stable and predictive behaviour during operation. In this thesis the influence from tool material and surface treatment on work material transfer has been studied for both applications, with the use of simplified laboratory test methods followed by extensive surface studies. Both the tendency to, appearance of and chemical composition of work material transfer is evaluated. The results are compared with real industrial examples, to ensure that the correct mechanisms are mimicked. In forming, the problems arise when poor lubrication prevails, due to high forming forces or large surface expansions. The transfer of work material can then be avoided with the use of a galling resistant coating, offering low adhesion. However, the coating has to be as smooth as possible, to avoid activation of the work material and subsequent transfer. In cutting, the desired transfer film can be obtained by choosing the correct cutting parameters. The geometry and material of the fabricated component is often predetermined, setting the general cutting conditions, but the cutting speed influences the formation of the transfer film. Too low speed or too high speed leads to an unstable cutting process and poor surface finish of the piece. The speed intervals for each mechanism are partly determined by the tool material and thus by the tool coating.

Este trabalho apresenta resultados de testes com processo de usinagem para diferentes ferramentas de torneamento. Foram realizados ensaios para avaliar a diferença de comportamento quantoa esforçosde cortee acabamentosuperficialem operaçãode torneamento para um mesmo tipo de ferramenta, com variação na superfície de saída, sendo uma com quebra cavaco com outra de superfície de saída lisa. O material usinado foi aço ao carbono 1045 recozido, testado para duas diferentes velocidades, variando-se também a profundidade de corte e avanço para cada ensaio. Os testes foram executados em um torno mecânico convencional, onde as variáveis do processo foram coletadas com um sistema de aquisição de dados, através de um dinamômetro piezoelétrico para avaliação das forças de corte e um rugosímetro portátil para medida da rugas idade superficial. Observou-se nos resultados, uma forte diminuição dos esforços quando aplicada a ferramenta sinuosa com quebra-cavaco, bem como melhoria nas características do cavaco. Em relação à rugas idade superficial houve uma pequena melhora quando utilizada a ferramenta com superfície de saída lisa, situação decorrente das condições de remoção do cavaco. / This wark presents the results af machiningpracess tests with different turning tools. Tests were done to evaluate behaviors differenceson cutting efforts and surface finishing in turning operations to a same type of tool, with a variation on rake face, where one had a chipbreaker groove and the other are flat. The machining material was 1045 annealed carbon steel, tested to two different cutting speeds, changing also the depth of cut and the feed rate for each case. The tests were done in a conventionallathe, where the process variances were collected by a data acquisition system, through a piezoelectric dynamometer to evaluate the cut efforts and a portable rugosimeter to measure the surface roughness. The results show a strong reduction of the efforts when grooved tools with chip-breaker were applied as well an improvement on the chip characteristics. In relation to the surface roughness, it was observed a slight improvement when the tlat tool was used, because ofthe conditions of chip remova!.

Este trabalho apresenta resultados de testes com processo de usinagem para diferentes ferramentas de torneamento. Foram realizados ensaios para avaliar a diferença de comportamento quantoa esforçosde cortee acabamentosuperficialem operaçãode torneamento para um mesmo tipo de ferramenta, com variação na superfície de saída, sendo uma com quebra cavaco com outra de superfície de saída lisa. O material usinado foi aço ao carbono 1045 recozido, testado para duas diferentes velocidades, variando-se também a profundidade de corte e avanço para cada ensaio. Os testes foram executados em um torno mecânico convencional, onde as variáveis do processo foram coletadas com um sistema de aquisição de dados, através de um dinamômetro piezoelétrico para avaliação das forças de corte e um rugosímetro portátil para medida da rugas idade superficial. Observou-se nos resultados, uma forte diminuição dos esforços quando aplicada a ferramenta sinuosa com quebra-cavaco, bem como melhoria nas características do cavaco. Em relação à rugas idade superficial houve uma pequena melhora quando utilizada a ferramenta com superfície de saída lisa, situação decorrente das condições de remoção do cavaco. / This wark presents the results af machiningpracess tests with different turning tools. Tests were done to evaluate behaviors differenceson cutting efforts and surface finishing in turning operations to a same type of tool, with a variation on rake face, where one had a chipbreaker groove and the other are flat. The machining material was 1045 annealed carbon steel, tested to two different cutting speeds, changing also the depth of cut and the feed rate for each case. The tests were done in a conventionallathe, where the process variances were collected by a data acquisition system, through a piezoelectric dynamometer to evaluate the cut efforts and a portable rugosimeter to measure the surface roughness. The results show a strong reduction of the efforts when grooved tools with chip-breaker were applied as well an improvement on the chip characteristics. In relation to the surface roughness, it was observed a slight improvement when the tlat tool was used, because ofthe conditions of chip remova!.

Este trabalho apresenta resultados de testes com processo de usinagem para diferentes ferramentas de torneamento. Foram realizados ensaios para avaliar a diferença de comportamento quantoa esforçosde cortee acabamentosuperficialem operaçãode torneamento para um mesmo tipo de ferramenta, com variação na superfície de saída, sendo uma com quebra cavaco com outra de superfície de saída lisa. O material usinado foi aço ao carbono 1045 recozido, testado para duas diferentes velocidades, variando-se também a profundidade de corte e avanço para cada ensaio. Os testes foram executados em um torno mecânico convencional, onde as variáveis do processo foram coletadas com um sistema de aquisição de dados, através de um dinamômetro piezoelétrico para avaliação das forças de corte e um rugosímetro portátil para medida da rugas idade superficial. Observou-se nos resultados, uma forte diminuição dos esforços quando aplicada a ferramenta sinuosa com quebra-cavaco, bem como melhoria nas características do cavaco. Em relação à rugas idade superficial houve uma pequena melhora quando utilizada a ferramenta com superfície de saída lisa, situação decorrente das condições de remoção do cavaco. / This wark presents the results af machiningpracess tests with different turning tools. Tests were done to evaluate behaviors differenceson cutting efforts and surface finishing in turning operations to a same type of tool, with a variation on rake face, where one had a chipbreaker groove and the other are flat. The machining material was 1045 annealed carbon steel, tested to two different cutting speeds, changing also the depth of cut and the feed rate for each case. The tests were done in a conventionallathe, where the process variances were collected by a data acquisition system, through a piezoelectric dynamometer to evaluate the cut efforts and a portable rugosimeter to measure the surface roughness. The results show a strong reduction of the efforts when grooved tools with chip-breaker were applied as well an improvement on the chip characteristics. In relation to the surface roughness, it was observed a slight improvement when the tlat tool was used, because ofthe conditions of chip remova!.