Today's post is a review of a NADCA presentation titled, "A Study in Aluminum Die Casting Housing for a Thermo-Electric Fan." You can find the entire presentation here.
- In cold climates, military personnel need warm shelter for protection from the elements. In tents, sheds, and buildings without central heating, the shelters use individual space heaters to provide warmth.
- In such uninsulated structures, the hot air from the heaters rapidly rises to the ceiling without warming the actual living space.
- The comfort level in these shelters is markedly improved if the warm air is directly circulated throughout the shelter, as compared to natural convection conditions.
- High thermal conductivity in the housing is a key performance factor to maximize heat transfer from the thermoelectric generator.
- The housing needs to have controlled wall thickness and uniform metal fill for structural integrity and rigidity.
- Machined features must be free of porosity for good thermal conductivity and to prevent off-tolerance drilling and tapping.
- Dimensional tolerances for precision machined features are +/- 0.005" to meet form and fit requirements
- The fan housing is a 14" diameter open top cylinder with a complex slotted and finned base. The cylinder is 10" high and has a weight of 7.5 lbs. The wall thickness of the housing ranges from 0.880" at the base to 0.124" on the side walls
Die casting is the production method of choice for this fan housing, meeting the requirements for complex shape, close tolerances, high quality, appearance, and low cost production.
Critical Design Issues
The requirements for performance, manufacturability/ castability, and cost are closely interconnected. Four design issues played a major role in meeting the three design imperatives for the fan housing:
- Choose a metal alloy that best meets the performance and castability requirements.
- Optimize the die casting process to reduce porosity.
- Refine the gating and overflows to eliminate shrinkage porosity in critical areas.
- Tailor the thermal management process to ensure quality and reproducibility.
- For thermal performance, the alloy should have high thermal conductivity.
- For mechanical performance, the alloy has to be both strong and stiff.
- The alloy has to be easily machined.
- From the die casting perspective, the thin walls of the fins and ribs in the base require an alloy that will flow and fill the die cavity rapidly and easily, but will not solidify too quickly. Early solidification in the die can produce defects (lack of fill, cold shuts, etc.) in the casting.
Die Casting Process in Google News:
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