High-technology applications which are using high precision optic components in high and medium quantities
have increased during recent years. One possibility to mass-produce e.g. such lenses is the precision glass molding
(PGM) process. Especially for aspheric and free-form elements the PGM process has certain advantages. Premise
is to manufacture accurate press molds, which have to feature smaller figure errors as the required lenses and
may be made of materials, which are difficult to machine, like silicon nitride ceramics. These work pieces
have to be machined in economical and steady process chains. However, due to the complex shapes and the
corresponding accuracy an error dependent polishing is required. The Magnetorheological Finishing (MRF) as a
high precision computer controlled polishing (CCP) technique is used and will further be presented in this work.
To achieve the postulated demands a previous study of the material removal at selected machining parameters
is needed. Changing machining parameters modify the removal, which is presented through values like the peak
and volume removal rate. The value changes during the controlled variation of process parameters are described
and discussed. Magnetorheological Finishing (MRF) provides one of the best methods to finish PGM molds that
are relatively inaccurate to high precision in an economical, steady and efficient way. This work indicates the
MRF removal selection and removal interference for the correction and finishing of precise silicon nitride molds
for the precision glass molding.
Computer-controlled polishing has introduced determinism into the finishing of high-quality surfaces, for example those used as optical interfaces. Computer-controlled polishing may overcome many of the disadvantages of traditional polishing techniques. The polishing procedure is computed in terms of the surface error-profile and the material removal characteristic of the polishing tool, the influence function. Determinism and predictability not only enable more economical manufacture but also facilitate considerably increased processing accuracy. However, there are several disadvantages that serve to limit the capabilities of computer-controlled polishing, many of these are considered to be issues associated with determination of the influence function. Magnetorheological finishing has been investigated and various new techniques and approaches that dramatically enhance the potential as well as the economics of computer-controlled polishing have been developed and verified experimentally. Recent developments and advancements in computer-controlled polishing are discussed. The generic results of this research may be used in a wide variety of alternative applications in which controlled material removal is employed to achieve a desired surface specification, ranging from surface treatment processes in technical disciplines, to manipulation of biological surface textures in medical technologies.
Magnetorheological finishing is a computer-controlled polishing technique that is used mainly in the field of
high-quality optical lens production. The process is based on the use of a magnetorheological polishing fluid
that is able, in a reversible manner, to change its viscosity from a liquid state to a solid state under the control
of a magnetic field. This outstanding characteristic facilitates rapid control (in milliseconds) of the yield stress,
and thus the pressure applied to the workpiece surface to be polished. A three-axis dynamometer was used to
measure the forces acting between the magnetorheological fluid and the workpiece surface during determination
of the material removal characteristic of the polishing tool (influence function). The results of a testing series
using a QED Q22-X MRF polishing machine with a 50 mm wheel assembly show that the normal forces range
from about 2 to 20 N. Knowledge of the forces is essential, especially when thin workpieces are to be polished
and distortion becomes significant. This paper discusses, and gives examples of, the variation in the parameters
experienced during a programme of experiments, and provides examples of the value of this work.
Magnetorheological finishing (MRF) is a commonly used computer-controlled polishing (CCP) technique for
high precision optical surfaces. The process is based on a magnetorheological abrasive fluid, which stiffens in a
magnetic field and may be employed as a sub-aperture polishing tool. Dependent upon the surface error-profile
of the workpiece and the polishing tool characteristic (influence function) an individual polishing procedure is
calculated prior to processing. However, determination of the influence function remains a time consuming and
laborious task. A user friendly and easy to use software tool has been developed, which enables rapid computation
of MRF influence functions dependent on the MRF specific parameters, such as, magnetic field strength or fluid
viscosity. The software supersedes the current cumbersome and time consuming determination procedure and
thus results in considerably improved and more economical manufacture. In comparison with the conventional
time period of typically 20 minutes to ascertain an influence function, it may now be calculated in a few seconds.
An average quality improvement of 57% relating to the peak-valley (PV) value, and approximately 66% relating
to the root-mean-square (RMS) of the surface error-profiles was observed during employment of the artificial
computed influence functions for polishing.
The main objective of this article is to introduce a novel power device for electrical-assisted micro-grinding, which could
reduce the ambiguities reported and experienced during grinding. For example, the device's software is equipped with a
knowledge database that automatically sets suitable electrical parameters for the instructed fine grinding parameters. The
parameters are controlled throughout the process in order to achieve the stringent specifications required for further
advanced polishing processes or establishing mirror surface finish on optical components.
Magnetorheological finishing (MRF) is a computer controlled polishing (CCP) technique for high precision
surfaces. The process uses a magnetorheological fluid which stiffens in a magnetic field and thus acts as the
polishing tool. A standard MR fluid consists of magnetic carbonyl iron (CI) particles, nonmagnetic polishing
abrasives and liquid. To delaying oxidation of the iron particles and avoiding agglomeration the liquid consists
of water completed with stabilizers. For the material removal and smoothing of the surface mostly cerium
oxide or diamond is used. The materials to be polished may tend toward to different sedimentations of
the MR fluid on the machined surface. These sedimentations result from the machining and may develop a
polishing layer with MR fluid components. At the University of Applied Sciences Deggendorf analysis of the
machined surface are made by the scanning electronic microscope (SEM) to determine the sedimentations
of the finishing. The results of the research display the influence for the surface properties due to developing
polishing layer by magnetorheological finishing.
Magnetorheological finishing (MRF) is a computer controlled polishing process (CCP), which is commonly used in the field of high quality optical lens production. The process uses the material removal characteristic of the polishing tool (influence function) and the surface error-profile to calculate individual, surface error-profile dependent polishing sequences. At the University of Applied Sciences Deggendorf a testing series with a magnetorheological finishing machine has been performed, and effects of the influence function size and its removal capacity on the polishing quality and the process time have been investigated. The result of the research shows that the influence function size has a major effect on the process time, whereas the polishing quality is nearly independent of the influence function size. During the testing series the process time was significantly reduced using an appropriate influence function size. The process time decreased about 9% relating to the original influence function.
Magnetorheological Finishing (MRF) is commonly used to finish high quality optical surfaces. The process is based on a magnetorheological fluid, which stiffens in a magnetic field and thus may be used as a polishing tool. The fluid removal characteristic depends on several parameters, for example the magnetic field strength or the relative velocity between workpiece and polishing tool. Another parameter is the fluid itself. Different compositions of polishing abrasives result in different removal characteristics. At the University of Applied Sciences Deggendorf, five different magnetorheological polishing fluids have been analysed. The results of the research are scanning electron microscope analyses as well as spectra analyses. The removal characteristic for each fluid has been determined for different glass materials. Finally, the fluid conditions during polishing have been analysed. For this purpose, the fluid flow rate, the fluid pressure and the fluid viscosity have been investigated.
In Magnetorheological Finishing (MRF) a magnetic field is applied to a stream of abrasive magnetorheological fluid, in order that the fluid behaves as the polishing tool. The process may be used to finish the surface of high quality optical lenses. The fluid viscosity is one important parameter the polishing tool characteristic depends on. At the University of Applied Sciences Deggendorf a new viscosity measurement, which uses the inductance of the fluid had been tested. The result of the research is a close relationship between viscosity and inductance. The new viscosity measurement is not an absolute, but a comparative system, based on inductance of the flowing fluid and the fluid age.
Magnetorheological finishing (MRF) is a computer controlled polishing (CCP) technique for high quality surfaces. The process uses a magnetorheological fluid which stiffens in a magnetic field and thus acts as the polishing tool. At the University of Applied Sciences Deggendorf thermal sources in a MRF polishing unit have been analysed using an infrared camera. The result of the research is a warming of the fluid in the fluid conditioner caused by the mixer motor. The existing cooling is therefore essential, in order to ensure a constant polishing tool characteristic during polishing runs. A new fluid conditioner, which was developed at the University of Applied Sciences Deggendorf, with the aim of an extended fluid lifetime may be used without cooling, because an increase of the fluid temperature in the conditioner could not been detected. Furthermore, a warming of the workpiece during the polishing process was not ascertainable.
A novel approach to handle and quantify a computer controlled polishing process will be introduced. This approach will be compared to real data. This comparison indicates the correctness of this approach. Based on it a formula has been developed to predict the results of a computer controlled polishing process. The formula will be used to predict real polishing processes and the results will be compared to the real results. The limits when using this formula will be shown along with suggestions when the formula would be useful. This rough prediction of the computer controlled polishing results may be used to enhance the automation of a computer controlled polishing process. Also a way to improve the formula itself will be introduced. It is the opinion of the author that by further stabilizing of the whole computer controlled polishing process the whole system becomes more robust, the prediction more accurate and the whole system improves in reliability and the results become better.