| Summary: | 碩士 === 國立高雄應用科技大學 === 模具工程系 === 97 === Conventionally, the major products of aluminum extrusion product makers are windows and doors, tubes, rods and structures. The requirements of product quality are not critical, the price and profit are also very low. The die design technology of the local extrusion product makers is still based on experience and try-out method. Due to insufficient knowledge of the plastic analysis of the extrusion process, the material flow can not be considered and controlled during the die design stage, as a result, distortion or the bending defects occurred frequently during the extrusion process. Therefore, lot amounts of experiment and the die amendments are required to fix the poor design results. In such condition, the lead time of die design to extrusion production is increased. In order to meet the market requirements of low volume and high variety, the die amendment times and the trial-and-error process must be reduced if not avoidable. To produce the high quality and dimension precision of electronic products, the process analysis ability must be improved to establish the optimal criteria of the die and process designs.
A hot extruded fin-type cooling part was studied in this research. The parameters of the hot extrusion process, such as the temperature of the billet and the ram speed, should be controlled properly and coped with well designed die geometry to obtain the sound extruded product (called extrudate). The thin-fin features around the solid center of heat sink result in a large velocity difference from center to the surface of product. A porthole die design with the cylindrical mandrel was proposed to cope with the bearing length in order to balance the velocity distribution of material flow. The finite element method was adopted to simulate the extrusion process and study the effects of die design parameters. The extrusion speed, the billet temperature, the bearing length, and the length of mandrel were studied in terms of the extrusion load and the central burst defect. Extrusion experiments were carried out to validate the proposed design and analysis methods. A standard L type extrusion benchmark was announced by the Germany Benchmark Extrusion Workshop, which was used to validate the accuracy of the simulation. The hot extrusion experiment results of the fin-type heat sink showed the round mandrel was able to reduce the velocity variation of the fin and the center areas dramatically. The extrusion die was frequently damaged in the thin-fin area due to the small die features. Further research is required to solve the above mentioned problem.
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