Assembly Weights

I am going through a large assembly and assigning specific gravities
to all the parts so i can get a correct total weight and center of
gravity for the part. All the parts are working fine with the
relations I am using but in the assemblies and sub assemblies I am
getting weights that are not even close to being right. Is there
something that I can do to fix this. I have put all the desired
relations in the initial and post regeneration relations box. If any
one can help I would really appreciate it.

 

A couple of random points first: I've always assigned material to parts. This comes with a set of properties useful in all kinds of calculations, especially density. The material files also contain the name of the system of units which is required for interpreting values like density, thermal conductance, stress limits.

The only times I've not assigned material is when I've inherited a surface model that can't be solidified. Then I've gone into 'Edit>Setup>Mass Properties' to assign a density and/or mass. To complete this process, it's necessary to hit the 'Generate Report' button. And what is little known and poorly understood about the value stored in MP_MASS or PRO_MP_MASS is that it's a measure, a record from that report generation function. It is not dynamic, does not update automatically; so, while it is parametric to the extent that it can pass its value in a relation, it does not update, even when set to post regen. If the mass of a part changes after that 'Generate Report' button is pressed, it'll be necessary to go back into the Mass Props dialogue and hit the button again to recalculate the mass. Then, hopefully, the relation involving pro_mp_mass will also update with a part regen.

So, unless the relation is needed for something besides mass property calculations, it really isn't needed at all to get assembly mass properties. Parts with material assigned and units set do 'Analysis>Model>Mass Properties' calculations just fine without ever touching 'Edit>Setup>Mass Properties' or doing anything with relations and pro_mp_mass. And assemblies with those parts in them do assembly mass props calculations equally flawlessly.

If you are using the relation to create a parameter to put in a note, e.g., &WEIGHT, the parameter can be more easily and directly created using 'Analysis>Model>Mass Properties'. Instead of leaving the analysis type at Quick, click the Feature radio button and create an analysis feature. Click the eye glasses and see the analysis data. Then go to the Feature tab and see the parameters it created, three by default, including one called MASS, which you can use directly in a note as &MASS.

David Janes

 

There's a config pro option which forces a massprops calculation after
every regeneration, do you have it set?

 

Right. It's mass_property_calculate with by_request and automatic choices for when to recalculate. Anybody know what this does? Does it update the value of pro_mp_mass with a part regen?

David Janes

 

I think if this option is set to 'automatic' it will prompt you for
the mass of any part in the assembly that does'nt have one assigned to
it. Even parts from the library or commonspace without the mass
assigned to it, will prompt you to assign one. And then you might not
have the permission to save it back to the library.This can be a bit
of a headache whe you have a few thousand parts in an assy. I have
that set to 'by request' and just regen after every change .

Gary Miglionico