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Mass properties via "Geometry and Parameters" not updating inertias

KM_10927337
4-Participant

Mass properties via "Geometry and Parameters" not updating inertias

(I'm using Creo 8.0.3.0.  Thanks in advance for any help with this!)

Hi, my situation is the following:
I start with a simple single body part file. It starts out with a default PTC_SYSTEM_MTRL_PROPS material assigned. The density field is blank. When I access "Model Properties > Mass Properties > change", I see that "Assigned Material Density" is "missing" and I can't calculate the mass properties. So I adjust the Material Definition to have an arbitrary density value (1e-6 kg/mm^3). This enables me to calculate the mass properties, including mass and inertia.

 

Next, I want to specify that the part body be 1 kg in mass. So I go to "Model Properties > Mass Properties > change > Define Properties by > Geometry and Parameters". This lets me type in a mass value of "1 kg", and when I click "calculate", it calculates the correct density, given the geometry of the part, to achieve the target mass.

 

At this point I expect the new density of the geometry to also affect the inertia values. But it is still displaying inertia values from before I assigned the 1 kg mass, from the older, arbitrary density value. This breaks my expectations, because I wanted to use Creo to assist in calculating the inertia of parts and assemblies, simply by assigning target mass values to the part geometries. Instead, I need to manually calculate the required density given a target mass and the particular geometry volume and create+assign a new material with that calculated required density.

 

It feels like this functionality is just a step away for the CAD software, since it's clearly already figured out the new density given the geometry and the mass target. Can this be enabled or achieved in native Creo Parametric?

I've attached a pictorial of a simple test I performed, for others to reproduce the issue.

(I am aware that Creo Simulate/Mechanism has a different mass properties feature that may do a similar thing, but it's not a scalable workflow for our team).

1 ACCEPTED SOLUTION

Accepted Solutions

Thanks for the help everyone. I asked PTC support and was directed to this article CS180789. The solution is to toggle a config.pro setting.

 

If config.pro part part_mp_calc_ignore_alt_mp is yes (default)

  • Assigned mass is only considered for the transformation portion of the equation

Set part_mp_calc_ignore_alt_mp to no in order to

  • Override user defined density
  • Use single density value derived from assigned mass

View solution in original post

3 REPLIES 3

Recalculate Inertia Manually… After changing the mass by defining properties by “Geometry and Parameters,” try manually recalculating the inertia. This can sometimes refresh the calculations and update the inertia values.

 

Sounds like a bug, upgrade to latest version possibly. 

Michael P Bourque
Boston Regional User Group

I would suggest that you review this article (if you are not well versed in how Creo deals with assigned mass properties) as well as the supporting docs you will find in the links. You need to do some up front planning on exactly how you would like to handle the mass props and develop a plan that supports your workflow.

 

Article - CS189205 - About Computed and Assigned options in Mass Properties analysis dialog box in Creo Parametric (ptc.com)

========================================
Involute Development, LLC
Consulting Engineers
Specialists in Creo Parametric

Thanks for the help everyone. I asked PTC support and was directed to this article CS180789. The solution is to toggle a config.pro setting.

 

If config.pro part part_mp_calc_ignore_alt_mp is yes (default)

  • Assigned mass is only considered for the transformation portion of the equation

Set part_mp_calc_ignore_alt_mp to no in order to

  • Override user defined density
  • Use single density value derived from assigned mass
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