Shells are parametric features used for cast and molded parts. Material from the part interior is removed, leaving a hollow cavity. Changes to the dimensions of either the part or the shell automatically resize both.
By default, Autodesk Inventor provides a precise shell feature. If a precise solution does not exist and approximation is enabled, an approximation is attempted.
How shells are defined
To define a shell, you specify one or more part faces to remove from one or more bodies, leaving the remaining faces for shell walls. You set the thickness of the shell wall and indicate the direction relative to the current part face. If no faces are specified for removal, the shell creates a hollow part.
Uniform thickness of shell walls
It is a good practice to specify a uniform wall thickness, because uniform wall thickness helps prevent distortion during manufacture and cooling. If necessary, specific walls can have a different thickness.
Precise and approximate solutions
In a precise solution, each point of the original surface has a corresponding point on the offset surface. The distance between the two points is equal to the specified thickness. An approximate solution enables Autodesk Inventor to deviate from the specified distance in an attempt to find an acceptable solution.
You can control where the deviation is allowed to occur, as well as the accuracy of the approximation. Keep in mind that the more accurate the approximation, the longer it takes to compute. Approximate solutions are provided only when a precise solution does not exist and when an approximate solution can be found. If approximate solutions are not acceptable, you can turn off this option .
Each time approximation is used, the tolerance of the deviation is reported upon selecting OK.
Features included in shell
Because shells remove material from the entire part, features added to a part after the shell is applied is not shelled. For example, if you sketch and extrude a solid feature on a shell wall, the extrusion is not shelled.
To make sure that all features are included in a shell feature, use one of the following methods:
- Sketch all features on the part before you create the shell.
- Use the browser to reorder features. Move all sketched features above the shell in the hierarchy.