Electrical-static discharge in single point diamond turning machining of contact lens polymers
- Authors: Kadermani, Mohamed Munir
- Date: 2015
- Subjects: Electric discharges , Electrostatics , Contact lenses , Polymers
- Language: English
- Type: Thesis , Masters , MEngineering (Mechatronics)
- Identifier: http://hdl.handle.net/10948/4055 , vital:20508
- Description: Single Point Diamond Turning (SPDT) is a technology widely applied for the fabrication of contact lenses. One of the limiting factors in polymer machining is wear of the diamond tool due to electrostatic discharge resulting in poor surface quality of the machined products. The research work presented in this dissertation highlights the electrostatic properties of contact lenses during machining operations and the effects these properties have on the surface quality of the work piece materials. Two contact lens samples were experimented on, Definitive 74 (Silicone Hydrogel) and Tyro 97 (Rigid Gas Permeable). The electrostatic surface potentials (ESPs) were measured during turning operations using an electrostatic voltmeter and the surface roughness measurements were taken using a surface profilometer. Response Surface Methodology (RSM) techniques were employed to create predictive models for both surface roughness and ESPs with respect to the cutting speed, feed rate and depth of cut. Predictive surface roughness models were successfully generated for both materials and the cutting speed and feed rate were identified as the parameters with most effect on surface roughness. In addition, an electrostatic model was successfully generated for the Definitive 74 contact lens material which cited the cutting speed and feed rate as the most effective parameters on the material’s electrostatic behaviour. However, no relationship was evident between the machining parameters and electrostatic behaviour of Tyro 97.
- Full Text:
- Date Issued: 2015
- Authors: Kadermani, Mohamed Munir
- Date: 2015
- Subjects: Electric discharges , Electrostatics , Contact lenses , Polymers
- Language: English
- Type: Thesis , Masters , MEngineering (Mechatronics)
- Identifier: http://hdl.handle.net/10948/4055 , vital:20508
- Description: Single Point Diamond Turning (SPDT) is a technology widely applied for the fabrication of contact lenses. One of the limiting factors in polymer machining is wear of the diamond tool due to electrostatic discharge resulting in poor surface quality of the machined products. The research work presented in this dissertation highlights the electrostatic properties of contact lenses during machining operations and the effects these properties have on the surface quality of the work piece materials. Two contact lens samples were experimented on, Definitive 74 (Silicone Hydrogel) and Tyro 97 (Rigid Gas Permeable). The electrostatic surface potentials (ESPs) were measured during turning operations using an electrostatic voltmeter and the surface roughness measurements were taken using a surface profilometer. Response Surface Methodology (RSM) techniques were employed to create predictive models for both surface roughness and ESPs with respect to the cutting speed, feed rate and depth of cut. Predictive surface roughness models were successfully generated for both materials and the cutting speed and feed rate were identified as the parameters with most effect on surface roughness. In addition, an electrostatic model was successfully generated for the Definitive 74 contact lens material which cited the cutting speed and feed rate as the most effective parameters on the material’s electrostatic behaviour. However, no relationship was evident between the machining parameters and electrostatic behaviour of Tyro 97.
- Full Text:
- Date Issued: 2015
An evaluation of a strategy of lean manufacturing as a means for a South African motor vehicle assembler to achieve core competence
- Authors: Maritz, Louis Wiehahn
- Date: 2000
- Subjects: Automobile industry and trade -- Management , Automobile industry and trade -- South Africa , Manufacturing industries -- Management
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10834 , http://hdl.handle.net/10948/26 , Automobile industry and trade -- Management , Automobile industry and trade -- South Africa , Manufacturing industries -- Management
- Description: South African businesses are facing unforeseen opportunities and threats following the country’s remarkable political transformation that culminated in its first non-racial, democratic elections in April 1994 (Krüger, 1997: 138). The objective of this paper was to understand what core competences a South African motor vehicle assembler requires to survive this era of declining protectionism and increasing competition. It is argued in this paper that organisations that want to compete with the best in the world market needs to adopt lean manufacturing principles. This paper is concerned with the core competences of an organisation and how an organisation identifies and utilises these in order to become a lean enterprise. The qualitative research method was identified as the most appropriate for the study. Two methods of data collection were used i.e. interviews with senior and middle management and a detailed literary study on the subject. The senior management interviews were aimed at identifying what they perceived to be the core competences a motor vehicle assembler requires in order to be a world-class lean manufacturing enterprise. The literary study was the base for the understanding of core competence and lean manufacturing. Finally, a second round of interviews with middle management was conducted to obtain clarity on the perceived role of middle management in the selected organisation’s quest to be a lean manufacturing concern. This paper concludes that if an organisation wants to survive it needs to identify and assess its core competences. These competences need to be developed or discarded in the organisation’s aims to be a lean manufacturing enterprise by eliminating all forms of non-value added activity. The programmes or projects that the selected organisation embarked on were primarily driven from the top down, placing middle management in the centre with the resistance coming from the lower levels in the organisation. Middle management should be given the necessary tools to overcome the resistance and assist the company to make smooth transitions.
- Full Text:
- Date Issued: 2000
- Authors: Maritz, Louis Wiehahn
- Date: 2000
- Subjects: Automobile industry and trade -- Management , Automobile industry and trade -- South Africa , Manufacturing industries -- Management
- Language: English
- Type: Thesis , Masters , MTech
- Identifier: vital:10834 , http://hdl.handle.net/10948/26 , Automobile industry and trade -- Management , Automobile industry and trade -- South Africa , Manufacturing industries -- Management
- Description: South African businesses are facing unforeseen opportunities and threats following the country’s remarkable political transformation that culminated in its first non-racial, democratic elections in April 1994 (Krüger, 1997: 138). The objective of this paper was to understand what core competences a South African motor vehicle assembler requires to survive this era of declining protectionism and increasing competition. It is argued in this paper that organisations that want to compete with the best in the world market needs to adopt lean manufacturing principles. This paper is concerned with the core competences of an organisation and how an organisation identifies and utilises these in order to become a lean enterprise. The qualitative research method was identified as the most appropriate for the study. Two methods of data collection were used i.e. interviews with senior and middle management and a detailed literary study on the subject. The senior management interviews were aimed at identifying what they perceived to be the core competences a motor vehicle assembler requires in order to be a world-class lean manufacturing enterprise. The literary study was the base for the understanding of core competence and lean manufacturing. Finally, a second round of interviews with middle management was conducted to obtain clarity on the perceived role of middle management in the selected organisation’s quest to be a lean manufacturing concern. This paper concludes that if an organisation wants to survive it needs to identify and assess its core competences. These competences need to be developed or discarded in the organisation’s aims to be a lean manufacturing enterprise by eliminating all forms of non-value added activity. The programmes or projects that the selected organisation embarked on were primarily driven from the top down, placing middle management in the centre with the resistance coming from the lower levels in the organisation. Middle management should be given the necessary tools to overcome the resistance and assist the company to make smooth transitions.
- Full Text:
- Date Issued: 2000
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