While designing castings, the most important thing to consider is the effect of shrinkage during cooling. Some other critical factors include the flow of metal and porosity.Some general casting design rules are -
- Avoid sharp corners - they may result in hot tearing during cooling.
- Fillets should be used with care – they lead to stresses as they shrink. Radius in the range of 1/8” to 1” is acceptable.
- Use uniform cross sections – they keep the cooling rate relatively uniform and keep off stresses.
- Avoid internal features – they require additional steps in mold making and may cause problems in metal flow.
- Place parting line near corners – they will hide the flash.
- Use straight parting lines wherever possible – It makes the mold making easier.
- Avoid large flats - large flat areas tend to deflection.
- Machining Allowances - allow excess material for later machining of critical dimensions.
- Use a draft angle - A small angle of 0.5-2° on the vertical walls makes it easier to remove the pattern.
- In the designing of cast shapes, an understanding of finished part dimensional prerequisites is essential to attain near net dimensions at most economical cost. The designers should apply as high a tolerance as possible.
- Fix geometric tolerances, like profile of a surface for complex blended surfaces.
And most important of all, consult and work with your casting manufacturer to improve the performance, effectiveness and quality of your casting designs.
