| Summary: | 碩士 === 崑山科技大學 === 機械工程研究所 === 99 === This thesis is intended to present a new technology in the domain of manufacturing. It presents a numerical study of the possibility of replacing, in the domain of plastic injection molding technology, the traditional method being used for the past thousands of years to produce a wax pattern through injection. To accomplish this, a mold made of a RP plastic material combined with a PCM material will be used to produce wax patterns instead of a mold made out of steel or iron. The system being studied can be described as a one dimensional transient state heat transfer involving a PCM (Phase Changing Material), a mold made of ABS material and melted paraffin wax as the injection material.
The process proposed and studied here uses melted paraffin wax as the injection material. The PCM is placed between two layers of RP plastic material and will be the heat extractor. It is to be noted that once set, the system will be cooled down to a temperature of about 10˚C before the paraffin wax is injected. The step that follows is injecting melted paraffin wax at a temperature of 70˚C into its cavity through a nozzle and then leaves the system exposed to natural internal conduction. Latent heat analysis and numerical methods in heat conduction are used to solve this system in two parts.
The first method used, latent heat analysis, involves the law of enthalpy (internal energy) to determine the total cooling time and temperature gradient in the material. In the process, it was observed that the main heat transfer is done through conduction thus heat transfer through convection and through radiation is neglected in this method.
The second method uses the numerical methods in heat conduction for a one-dimensional transient heat conduction system. This involves infinite series which are difficult to deal with. However, the terms in the solution converge rapidly with increasing time, and for τ=0.2, keeping the first term and neglecting all the remaining terms in the series results in an error under 2 percent.
This system will be simulated using COMSOL under the transient heat transfer physics module. COMSOL is very efficient in solving such systems with a high relativity error. The appearance and the behavior of the melting front can be simulated by modifying the specific heat of the PCM to account for the increased amount of energy, in the form of latent heat of fusion, needed to melt the PCM over its melting temperature range.
Numerical simulation of transient heat transfer was conducted considering both a system exposed to room temperature and to adiabatic condition. The behavior of the melting and heat absorption of PCM was simulated by modifying the specific heat of the material to account for the increased or decrease of the amount of energy in the form of latent heat of fusion over or under its melting temperature range. ABS plastic mold was made through FDM Rapid Prototyping process and a carefully prepared experiment was successfully conducted. To confirm the validity of the work, the data acquired during the experiment was compared with the numerical results through a graph. The outcome was a success. Another experiment with a more complex geometric shape was conducted with satisfying results. An optimization of the current process settings revealed a possibility to have better solidification time result (approx. 10 minutes) than that of the traditional wax pattern process (approx. 15 minutes).
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