For over 30 years research has been done concerning the solidification and quenching of light metal alloys for the purpose of improving material properties. This thesis is concerned with an interesting new process for casting metals, by spraying water onto a sand mould, removing the sand and the directly quenching the part. This process is challenging since the component during solidification is extremely fragile, and the rate of cooling that is needed could seriously damage it. The water flow rate to the component needs to be quickly and precisely controlled. Additionally as this a new method there is very little prior art.
The purpose of this thesis to develop a control system for the water sprayers flow rates. With this system the flow rate through the nozzles will be controlled indirectly using pressure feedback. The material properties and casting process, and how they influenced the design and construction of the spraying apparatus, are explained first. The hydraulic plant being controlled consists of three proportional valves connected to six spray nozzles. Based on experiments, the plant is extremely nonlinear making it difficult to control.
Several controllers were developed and compared experimentally. The best performance was produced by extending a proportional plus integral plus derivative controller by adding an empirical nonlinear feedforward component; smoothing the setpoint; bounding the integration term; adding one bias at time zero and a 2nd bias for the remaining time (to mitigate valve stiction and to prime the hoses). This extended PID controller produced a 0.7% mean error and 1.9% mean absolute error for a multi-step setpoint covering a range of 0 to 80 PSI. Its performance was also highly repeatable. The standard deviations of the mean error, mean absolute error and maximum absolute error were less than 0.2 PSI over five runs. / Thesis / Master of Applied Science (MASc) / During the sand casting of aluminium and magnesium rapid cooling will greatly improve the material properties. By containing the liquid metal in a water soluble sand mould, and spraying it with water; the desired part shape and rapid cooling can be achieved. Removing the mould requires a powerful high flow rate jet. During the solidification of the metal, the flow rate must be reduced or the part would be demolished. This necessitated the development of a high speed, high flow rate controller to adjust the flow rate to remove the sand but not damage the part, and to maintain a smooth continuous cooling rate. The hydraulic system being controlled consists of three electronic valves connected to six spray nozzles. Several controllers are developed and compared experimentally. The best controller is shown to provide a quick and precise response.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/18225 |
| Date | 11 1900 |
| Creators | Pringnitz, Hino K.H. |
| Contributors | Bone, Gary M., Shankar, Sumanth, Mechanical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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