Aluminum oxynitride (ALON) is a polycrystalline material that has proven difficult to polish due to its grain structure. Bound abrasives are an effective means for polishing ALON, and work is being done with them to obtain good surfaces, with reasonable removal rates. Laps consisting of abrasives bound in epoxy matrices were created for polishing ALON. The effects of varying abrasive type, abrasive concentration, lap shape, coolant and load were studied. Metrology procedures were developed to monitor different aspects of the grain structure and numerically evaluate grain boundary decoration. Strategies were developed to polish ALON at acceptable rates with reasonably good surface quality. Work is directed toward finding optimal bound abrasive lap formulations that can be fabricated into ring and/or contour tools for testing on CNC machining platforms.
Significant research is conducted during the school year and over summer months at the Center for Optics Manufacturing (COM) by undergraduates. Projects are designed with short- and long-term goals, to be carried out by students using advanced CNC machines and sophisticated metrology tools. Five activities are described with emphasis on the individuals doing the work.
The Rochester Section of the Optical Society of America offers a middle school outreach program called the Optics Suitcase. Contents include re-usable demos and give-away experiments that illustrate color in white light. Over 40 suitcases have been shipped, free of charge, to groups in the USA, Canada, Ireland, Germany, Australia and South Africa.
Optical polishing pitch has properties that can be quantitatively examined. These properties may be used to check batches of pitch for consistency, or to evaluate products for differences. In this work we explore the hardness, softening point and viscosity of pitch. The testing methods involved require little preparation, have quick turnaround time, use less than 200 g of pitch, and produce statistically significant results. The tests include: Shore A Durometer hardness test, ASTM Mettler softening point method, and dynamic viscosity measurements via a novel falling needle viscometer. Results from all three tests are given as averages with standard deviations for a variety of wood-based and petroleum-based products.
Magnetorheological Finishing (MRF) is a newly developed and recently commercialized method for finishing optical components. The MR fluid consists of a water based suspension of carbonyl iron (CI), nonmagnetic polishing abrasives, and small amounts of stabilizers. MRF uses both mechanics and chemistry to smooth glass surfaces to less than 10 angstrom rms. Mechanics are responsible for the microscratching of the glass surface which is initially 'softened' by hydration from water in the MR fluid. Experiments were performed to study the separate roles of mechanical abrasion and chemical softening during MRF. Chemical effects were suppressed by introducing a nonaqueous fluid in place of the water. A novel nanoindentation technique was used to determine CI particle hardness, which varied by a factor of five. The mechanics of removal were then investigated with soft and hard CI powders working against soft and hard optical glasses. Chemistry was then 'turned on' by the addition of a small amount of water to the system. Preliminary results of these experiments are presented here.
Magnetorheological Finishing (MRF) is a novel process for deterministic figure correction and polishing of optical materials that utilizes a sub-aperture lap created by moving a magnetic field-stiffened magnetorheological (MR) fluid ribbon against an optical surface. MRF has been successfully applied to a wide range of optical materials. A new research platform has been designed and built that is used to generate sub-aperture polishing profiles, i.e., polishing 'spots,' on optical flats under well-controlled conditions. This platform uses the same fluid circulation and conditioning system as the commercial computer numerically controlled MRF machine, thereby allowing fluid performance issues to be investigated. This new machine complements the capabilities of the original MRF research platform that has been in continuous use for over six years. These two machines have been used to generate polishing spots on a variety of optical materials. The spot profiles were measured to calculate material removal rates and the quality of the polished surfaces characterized by measuring the microroughness within the polishing spots. Examples are presented which illustrate how the evaluation of polishing spots was used to develop MR fluids and operating conditions for calcium fluoride, CaF2, and potassium dihydrogen phosphate, KDP.
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