Interference Fits
- Where interference is light, (typically 0.001 mm/mm or less) installation can be performed with both members at room temperature
- For heavy interferences, the external member should be heated, the internal member cooled, or both
- The amount of retention is a function of residual stress levels, which can be calculated using classical right cylinder analysis
- Heavy interferences may cause metal removal, reducing retention
- The tendency for either member to remove metal from the other depends on the relative hardness of the metals, the amount of interference, use of lubricant, and the leading edge profiles of the members
- It's advisable to check the effectiveness of interference fits by testing production samples. This will determine the force required to disassemble the members, or the torque required to cause rotation
- Where the die cast alloy has sufficient ductility, crush ribs can be used to develop interference between the internal and external member
- Crush ribs do not require the very close dimensional tolerances required by conventional interference fits
- The design must be verified by testing production samples to evaluate long-term effects such as that of creep and of stress corrosion cracking (AZ91 magnesium alloys only) if either condition is possible
