M.Ing. / A large number of machine tools in use today are worn and can not produce the correct tolerances as a result of the inaccuracy of the structure. A device was developed to assist in the solution to the problem. The study of the development of this device includes several different fields. An entire prototype scale model of a grinding device is developed, with components including a control system and a developed sensor. The control system consists of circuitry and programming. The programming has been done in Visual Basic. The circuitry includes driver circuits for DC motors as well as pulse width modulation circuits and filters, amplifiers and comparators for the newly developed sensors. The sensor developed is an optical device, which can sense the deviation of a cable for reference for the movement of the device. A combination of the above components into a unit and the provision for factors, such as grinding forces and vibrations, which influence the operation of the device, are presented. Furthermore, an analytical model is suggested for the prediction of the system's behavior.

No description available.

<p>Unexplained acoustic emission spikes have been reported to occur at the workpiece entry and exit in interrupted machining operations, most notably during grinding. These AE spikes have yet to be fully explained in terms of their cause, or interpreted to yield useful information regarding the grinding process. This thesis research hence focuses on investigating this phenomenon. What started as a curiosity-driven project has resulted in an experimental technique to measure the actual contact length between the workpiece and the grinding wheel, as well as a technique for detecting grinding burn, which are of remarkable practical significance.</p> / Master of Applied Science (MASc)

No / Wheel structure has a critical influence on grinding performance especially active cutting edge density. Experiments were carried out to find out the relationshipbetween active and staticcutting edge density. It was found that there are many more active cutting edges in grinding than expected based on chip thickness formulae mainly due to wheel deflection in grinding.

Two new technologies, for polishing and testing large optics, are presented in this dissertation. The first is a new approach to generating and polishing aspheric surfaces which utilizes a full size stressed lap. The lap specifications are chosen to automatically generate a specific amount of spherical aberration. The required comatic distortion of the lap is induced by a system of levers and springs which are stretched and relaxed as the lap moves. A lap was constructed to grind and polish a 20cm glass blank. The resultant polished surface, in agreement with the predicted asphericity, has 28 microns of spherical aberration at its edge, appropriate for a F/2.0 convex paraboloid. The average radial profile has a residual peak-to-valley error of 200nm and an rms error of 60nm. This experiment serves as a first successful test of the stressed lap concept and as a demonstration of a new method for generating aspheric secondary mirrors. The second new technology is concerned with testing large optics where vibrations can be a serious problem. A modification to the usual phase shifting interferometry reduction algorithm permits measurements to be taken fast enough to essentially freeze out vibrations. Only two interferograms are needed with an exact phase relationship; and these can be recorded very rapidly on either side of the interline transfer of a standard CCD video camera, prior to charge transfer readout. The third required interferogram is a null. An analysis of potential phase errors was performed for this "2 + 1" algorithm. In the developed implementation, two frequencies, dν/ν≈10⁻⁸, are generated with orthogonal polarizations. A Pockels cell rapidly switches the frequency entering the interferometer, resulting in a phase shift over the long path difference of the interferometer. The two time critical interferograms are acquired with a 1ms separation resulting in a reduction in sensitivity to vibration of one to two orders of magnitude. Laboratory tests were performed to compare this "2 + 1" system with a commercial phase shifting package. Similar phase determination accuracies were found when vibrations were low. However, the "2 + 1" system also succeeded when vibrations were large enough to wash out video rate fringes.

MPH, Faculty of Health Sciences, University of the Witwatersrand, 2006

Hemp, one of the fast-growing plants with strong, durable fibers is being used for industrial applications, including papermaking, as a biodegradable reinforcing material for plastics as well as in construction. A series of tests has been conducted grinding hemp with the SM-220 Szego Mill equipped with three helically grooved, 30 cm long rollers with 8*8 or 4*4 mm grooves. A range of flow rates and rotational speeds has been covered in both dry and wet operation to determine the best processing conditions for various potential applications of refined hemp fibers. Particle size distributions and power consumption have been measured. Fiber length and diameter measurements allow an evaluation of fiber aspect ratio. For dry grinding, these are relatively low, typically in the 6-10 range. Wet grinding generally favors higher aspect ratios due to reduced fiber cutting and greater clearing action in the mill. Measured values are in the 60-80 range

Hemp, one of the fast-growing plants with strong, durable fibers is being used for industrial applications, including papermaking, as a biodegradable reinforcing material for plastics as well as in construction. A series of tests has been conducted grinding hemp with the SM-220 Szego Mill equipped with three helically grooved, 30 cm long rollers with 8*8 or 4*4 mm grooves. A range of flow rates and rotational speeds has been covered in both dry and wet operation to determine the best processing conditions for various potential applications of refined hemp fibers. Particle size distributions and power consumption have been measured. Fiber length and diameter measurements allow an evaluation of fiber aspect ratio. For dry grinding, these are relatively low, typically in the 6-10 range. Wet grinding generally favors higher aspect ratios due to reduced fiber cutting and greater clearing action in the mill. Measured values are in the 60-80 range

Abstract In order to understand ball motions of new ultra-precision ball grinding machine, this study presents an mechanical model using a transparent acrylic container to simulate ball motions. The effects of float material, load, and process condition on the ball grinding characteristics at low shaft speed. The ball motions can be observed by the CCD camera to calculate the ball¡¦s circulation speed , the ball¡¦s spin angular speed and the ball¡¦s spin angle . Furthermore, the kinematic equations of ball motion is derived with different rolling sliding condition. The theoretical values of , , and are compared with the experimental values under pure rolling condition. Results show that the theoretical values are in good agreement with the ball¡¦s spin angular speed, but with larger error for and .This error is still in range of engineer error. Hence, at low shaft speed, contacts between balls and container, or shaft or float are close to the pure rolling conditions. Because the higher friction force between ceramic balls and alumina float, the ball¡¦s circulation speed with alumina float than that with acrylic float since fluid thrusts balls at low shaft speed, the ball¡¦s circulation speed in working fluid than that without working fluid. Since mass of float is light, it can be drive easily. Hence, with increasing the load which also increases the float mass, the float angular speed is decreased and the ball¡¦s circulation speed is also decreased.

Cutting fluids are mainly used for cooling, lubricating, and chip removing. The use of minimum/minimal quantity lubrication (MQL) in machining processes not only reduces the cost of cutting fluids but also has the potential to alleviate the environmental impact. In addition, the MQL technique could be a viable choice to decrease the damage to the miniature machines due to the near-dry lubrication. Therefore, the objective of this study is aimed at the mechanical performance of MQL for micro-grinding of SK3 steels based on surface finish and tool life. In this study, it is observed that tool breaks in dry grinding or air blow grinding, and it is also found that workpiece surface is burned in dry grinding. However, these phenomena are not observed in MQL grinding. The reason is that the use of MQL reduces the friction between the tool and workpiece and improves the chip removal in micro-grinding. The use of MQL in micro-grinding also leads to better surface roughness and the tool life is more than seven times compared to dry grinding. Experimental results show that the best surface finish is achieved in MQL grinding when the use of cutting fluids is 1.88 ml/hr with the air flow rate of 30 l/min among the lubrication conditions in this study.