Pressure Tightness
Most diecastings can be cast pressure tight, however, in some cases impregnation may be required. Consultation with the die caster in the early design stages is recommended where a requirement for pressure tightness exists in order to take advantage of the basic knowledge of the design and processing factors which will help him to cast pressure tight diecastings.
Important considerations relating to the economic production of pressure tight diecastings include the following:
1. Design
Successful casting of pressure tight die castings requires conformance to the principles of good diecasting design.
- Recommendations concerning fillets, ribs and corners should be followed very carefully.
- Sections should be as uniform as possible.
- Holes and passages requiring pressure tightness should be cored to reduce the effect of porosity.
- Ample draft should be allowed in cored holes and passages which are not machined. Heavy sections should be avoided.
- Careful consideration of the factors of good design will aid in the economical casting of pressure tight castings.
2. Machining
The nature of the diecasting process is such that the outer surface of a diecasting is usually dense and relatively free from porosity
- A minimum amount of machining stock should be allowed to avoid cutting deeply into a diecasting where porosity may be present.
- Avoid large draft angles which would require the removal of a large amount of stock from surfaces to be machined, particularly where holes are cored.
- Where machining is required, both sides of the same section of a diecasting should not be machined.
- Where a large amount of machining must be done, impregnation probably will be required after machining.
3. Size
Larger diecastings are generally more difficult to cast pressure tight and will require pressure testing by the diecaster to assure adequate process control. Impregnation is more generally required for large diecastings.
4. Pressure
Pressure requirements for diecastings are generally in the order of 5-15 psi.
Pressures in excess of 100 psi will require special consideration.
5. Alloy
Certain alloys are better for making pressure tight diecastings.
