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Autodesk Inventor 2011 is capable of designing anything. There are some limitations to the software, and we use our skills and talents to guide Inventor in order to deliver what we need.

There is one things that Inventor can’t do for us. It can’t make up for limitation in the production facilities. It can however prepare for them.

Limitations of Manufacturers and Methods

All Manufacturing methods carry with them some form of limitation. Most manufacturing companies have state of the art equipment, but many are still biased to one form of production or another. Developing a good working relationship with the production company can give you knowledge of what can or cannot be accomplished to bring your design to life.

Another more obvious concern is material limitations. We always have to keep a material’s capabilities in mind, and that brings us back to the manufacturing process. Some materials just can;t be manipulated by certain methods.

Design with the limitations in mind

Design with the end processes in mine. Whether you are a separate design firm, or tied to a manufacturing facility, keeping the design within the bounds of the manufacturer’s capabilities can keep you away from needless and painful design revisions.

If possible, create the base skeleton file with an understanding of these limitation.  I often try to limit my design to the lowest common denominator of a designated manufacturing practice. I know that my local capabilities are a 3 axis CNC vertical mill. With that in mind, I steer away from tight undercuts.

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In the image above I am having to limit a ramp in order to mill a critical track in the component. Stress Analysis will help me determine if this change will actually perform properly. Another option will be to invert the ramp, or buy new tooling. If I do invert it, I’ll need to know what tool geometries will be used to create the slot.

Top Level Adaptive Limiters

One thing that has worked on numerous occasions is to plug in parameters at the top level base part file, that represent typical limitations that production is faced with.  Sometimes we understand that limitations exist, but not to what degree. We can still design the product with these in mind, and prepare to adjust when the specs arrive.

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Tooling

For example I like to add a parameter named ‘MinToolingDia’, and set it for what I have on hand.  Often a 0.063” endmill is usually acceptable, however in a recent tool prototype, the tooling on hand was a bit too limiting. So I designed the components around a ‘MinToolingDia’ parameter, and later when I determined what tooling would work in the shop conditions, I revised the parameter value accordingly.  All the dimensions and data updated automatically.

If you needed some corners and relief holes as tight as possible,  but also need to keep nominal design radius that is independent, then assign both.

MinToolingDia = 0.125   NomRadius = MinToolingDia

You can tie one to the other, and later when and if tooling permits, make their values independent.

MinToolingDia = 0.063   NomRadius = 0.125

You could even use Min/Max in a user rule variable that keeps general fillets tied to MinToolingDia so long as it does not drop below NomRadius, and vice-versa.

Materials

All wall thicknesses and ramps are run from a ‘MinWallThick’ value. I do this for material stability. When we get to Stress Analysis, the global values are in place for adjustment. Again, Min/Max in certain situations provide flexibility, while limiting it above critical thickness.

Comments

I used knowledge of what process would be used to create the parts, and what those limitations were. I designed with those factors in mind, and when the limitations finally eased up, the design relaxed accordingly. Conversely, when Stress Analysis begins to crunch down, the Parameters and design are in place from the get-go.

Read more…Multi-Body Parts