There has been
a lot of discussion over the years between various
suppliers of investment castings regarding tolerance
that is appropriate for the process. While there continues
to be some debate, what follows is meant to be a general
guideline. An investment casting is meant to be a
"near net-shape" part that offers the most value.
If the buyer and producer maintain a high level of
communication, the design requirements and cost efficiencies
will be met by processing capabilities.
Linear Tolerance
The general rule-of-thumb for linear tolerance
of investment castings is usually expressed as +/-.005
per inch of length. As with any such rule, there are
always exceptions required by process capabilities.
The chart below can be used for most applications.
Premium tolerances can be made available for a few
selected design characteristics such as holes and
slots. One should keep in mind however that tighter
tolerances sometimes require special procedures and/or
secondary operations which can increase the cost of
the casting and increase the need for longer production
times. |
