Automatic way to offset surfaces

[Paul_Brown]

Hi,

We design painted parts and parts with surface finishes, where dimensions on drawings and annotated parts, are for the finished part. This causes a problem because when we send a step file to a supplier for machining, they must recreate a model and offset the surfaces to be the part "before manufacturing", they also need to create a control drawing with all of the corrected dimensions to control the part before painting or surface treatement.
Does Creo propose an automated way to correct the 3d model and drawings to adjust the dimensions with a given offset?

The same question goes for offset tolerances (10mm-0+0.1 for instance), suppliers will recreate a model and offset the surfaces to have a model with only mid-tolerance dimensions. 

Does Creo propose an automated way to correct dimensions to have only mid-toleranced parts?

[Patriot_1776]

No automatic way I know of.  We just put a note on there specifying that the dimensions apply to finished (anodized typically) surfaces unless otherwise specified.  Since your vendor is far more familiar with the thickness of the coatings they apply than you, I'd send them the finished part STEP files and let THEM figure out the offsets needed.  If they whine about it tell them that there's other vendors out there you can do business with.

[Tdaugherty]

I agree. We do the same thing. 

[Paul_Brown]

I agree that is our current practice, and the suppliers whine about it!

However i'm exploring the use of MBD for our company and feel that the supplier having to recreate their own model to be able to manufacture and control completely defeats the purpose of MBD because there is a rupture of digital continuity.

Any thoughts?

[StephenW]

I would like to think we could precisely control all aspects of the parts, but sometimes we can not. 

IF you have only one supplier for that part and it's processes for manufacturing are not being changed or adjusted, you may be lucky enough to be able to make it work.

In my experience, even with parts built in house with known tooling, processes and procedures, manufacturing always needs to make adjustments to the "details" to make sure the final product meets the requirements. I don't know the reasons why but I usually just attribute it to wear and tear and/or maintenance along with changing opinions of those responsible for the manufacturing the product. Having to go back to engineering to make adjustments to the drawings/models every time there is a change to the process is a daunting task and so often engineering is not able to keep up with the timeframe for these adjustments.

These are my opinions, based on my experience and may or may not be applicable to your products and processes.

Your mileage may vary!

[tbraxton]

Creo supports application of a shrink feature in the mold design extension (add on module). I am not sure that is what you are asking for here though.

If you can define mathematically a nominal value for the surface offset, then you can include this design intent into your design model. If you can clarify in more detail what you need to do with a simple example it would help with proposed solutions.

[Patriot_1776]

'Sup Tom!  I thought about that, but then there's an issue if one side (as is typical) is NOT painted or plated.  Also, from what I remember (long time ago), it works on a percentage of shrink, or a shrink of distance per distance (i.e. .001" per .100"), not sure which.  So, dunno if this would work for him.  I think as mentioned it would be best for the actual painter/plater to offset the selected surfaces as needed because they're more intimately familiar with the thickness of the coating/plating.  My $.00002.

[tbraxton]

I agree with @Patriot_1776 , @StephenW , & @Tdaugherty in practice. I would not typically model paint, plating, or other applied coatings in the CAD model. We would address it in specifications or drawings using the as delivered part inclusive of finishing geometry dimensions.

We have had to model geometries associated with the stages of parts as they migrate through the manufacturing process where the geometry does change, and the Inheritance feature is what I would default to for that to capture the design intent driven by a master model representing the finished component.

[tbraxton]

Assuming you determine that you need 2 or more dimensional variants of a design model available as Creo parts, then the Inheritance feature would support this directly. You would have at the top level the "as finished design model" model and then use the Merge/Inheritance function to create derivative models representing the different geometries associated with the manufacturing processes.

When done intelligently this would allow you to modify the top-level model and the derivative models would update automatically with the required offset dimensional changes. You should be able to address the tolerance assignment using annotation elements.

For prismatic geometries this should be quite simple to manage. If you have more complex form factors on parts, then offsetting them may require some manual intervention in Creo.

[StephenW]

I've always had trouble with trying to specify the "before finish/coating/plating/etc" dimensions because different vendors or processes have always needed different #'s based on their equipment. It seems to create a never ending do-loop of "required changes" since there is a never ending set of processes/vendors/machines. Unless forced, my go to has always been to only supply the finished dimensions...of course that never works for internally supplied parts but that is usually a more controlled setting.

[kdirth]

No automatic way that I have seen.  You can copy all surfaces (select a surface, hold shift and select surface again, hold ctrl and select any non-finished surfaces if needed, ctrl+c, ctrl+v) offset quilt, remove material with solidify.  If there are any unfinished surfaces you may need to extend the quilt to fully intersect the model.