Investment casting tolerances are determined by the size and shape of the casting, as well as by different process factors. From foundry to foundry these different factors and allowances can vary by the experience of the foundry or their capabilities of process control.
Investment Casting Tolerances Process Factors:
- Design Configuration
- Firing Temperature
- Number of Coats applied
- Pouring Temperature
- Pressure of Wax Injection
- Rate of Cool
- Shell or Mold Backup Sand Composition
- Type of Wax
- Wax Temperature
Other factors that can effect casting tolerances are:
- Angles and angularity of the surface and location in the casting
- Concentricity is when the casting has more than one spherical feature that share a common axis.
- Cost of the part is increased the more precision required in the tolerance requirements of the part.
- Flatness
- Hole Tolerances apply to the roundness of the hole in conjunction with the surrounding metal.
- Parallelism is determined by the surface condition being equidistant from specific points.
- Perpendicularity involves 90 degree angles in surface, axis or line.
- Position tolerance depends upon the symmetry of the parent casting.
- Roundness tolerance is determined by the normal variations in shrinkage the metal in which each round element must conform.
- Standard linear tolerances are ± .005 (.127 mm) with a few exceptions
- Straightness tolerances are ± .005 (.127 mm per 25 mm)
- Surface finish alludes to the type and number of flaws on the casting surface.
- Tolerance variables are determined by a number of factors, such as: wax temperature, pressure of injection, temperature of die, firing temperature, shell composition, cooling rate and variation between raw material lots.
- Wall thickness is determined by the alloy and travel distance for the molten alloy.
Learn more about Investment Casting Tolerances and Shelmet Precision Castings tight tolerances.
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