Utrasonic Assisted Vibration Grinding(UAVG) Of Ultra-low Expasion(ULE)Optical Glass

Glass materials possess properties that are highly needed in various areas of today’s and future innovation applications. However, machining glass to a required structure and surface for the intended purposes has frequently posed various difficulties. Their nature of being hard and fragile makes them extremely hard to fine machine using ordinary methods without cracking them and significantly affecting the subsurface structure. As a result, their widespread applications have been hindered by the high cost of machining as most of the material goes to waste.In this research, a hybrid process of grinding; Ultrasonic Assisted Vibration Grinding(UAVG), has been proposed as an alternative to solving the current problems with machining glass. In order to justify this hybrid grinding process it has to be compared to the already existing and frequently used technologies i.e. Conventional Grinding(CG). Ultrasonic Assisted Vibration Grinding(UAVG) combines the material removal mechanism with ultrasonic vibration, this process adds an axial ultrasonic vibration which can lead to reduced cutting temperatures and thus tool wear reduction and at the same time maintaining a high surface quality which is not the case with conventional machining. This hypothesis has been tested in this research.The research aims at providing new knowledge of Ultrasonic Assisted Vibration Grinding(UAVG) on Ultra-Low Expansion(ULE) optical glass. This material is of interest as it finds its applications in the space industry such as Hubble telescope; the telescope’s optical glass is the UltraLow Expansion(ULE) glass due to its superior properties which has been further analysed in this paper. This glass has also been widely used in the semi-conductor industry. Various machining processes have been used over the years to machine glass, however, most of them can be very time consuming e.g. polishing method. This method is able to achieve the desired surfaces without substantial damage but the time consuming factor makes it expensive and therefore does not meet the requirements of ultra-precision machining; precise and fast.A brief literature review on the subject has been presented to show what has been done in this field. An attempt to simulate the whole experiment using DEFORMTM software and already existing models was made but due to time limitation results were not achieved. The grinding experiments were conducted so that CG can be compared to UAVG. The air spindle(grinding spindle) was installed on a planar grinder for both processes. When conducting UAVG, a piezoelectric transducer(PZT) in the spindle to give it the desired vibration. Analysis tests such as surface roughness, subsurface damage, force analysis, Acoustic Emissions(AE) and tool monitoring were carried out for both processes.The results have been discussed and presented in this research; UAVG produced a better surface finish in comparison to ultra-precision(conventional) grinding, the subsurface damage analysis further show that UAVG left a better subsurface due to the periodical separation of the tool, grinding forces were reduced to approximately 45% with the additional ultrasonic axis. The Acoustic emissions(AE) analysis has shown a proportional relationship between AE and material removal rate(MRR), Ultrasonic Assisted Vibration Grinding(UAVG) had a higher removal rate.The paper further concludes the research based on the objectives set. Future works recommended on the subject include an analysis of the tool wear and a complete simulation of the experiment.