【转帖】defining a weight for a specific part for analysis

yang686526

defining a weight for a specific part for analysis....
lets say you have a solidworks part and it's completely solid.
in the real world the part is not solid but complicated; has mechanical parts and space inside, for example a pump and it's motor.
you're not concerned about this now. the sw parts are for layouts and general shop drawings. in the future though the engineers want to do an analysis and are concerned that there would be inaccuraces because of this.
can you define a weight for the part regardless of the volume, density, etc.
i'm thinking you can do this.  
"can you define a weight for the part regardless of the volume, density, etc"
??
make a 2d drawing and add a note "weight: (###)".
or, as most do, model the part as it is in real world.
my model, do it right the first time.
chris
solidworks/pdmworks 08 3.1
autocad 08; catia v5
i've always measured the volume of my envelope model and calculated a "pseudo" density to make the weight come out right.
timelord
with the part open, go to tools > mass properties > assigned mass properties

i meant for something like fea analysis.
so, even if you don't manufacture the pumps and motors you should still model the interior parts?

do as cbl suggests, as long as you are not performing any analysis on the "less detailed" itself.
"art without engineering is dreaming; engineering without art is calculating."
one limitation to cbl's method is that the center of mass may not be in the center of the volume.  my recommendation however is to use cbl's method and leave the mass center concern to the person doing the analysis.  it would be ashame to expend effort to get the mass center right and then have it not be necessary.
also, in older versions of sw, cbl's method does not exist... in that case, use timelord's recommendation.  timelords method  along with changing the density of different bodies of a multibody part (i seem to recall this being possible but have not done it) is how you would move the center of mass.
-dustin
professional engineer
certified solidworks professional
certified cosmosworks designer specialist
certified solidworks advanced sheet metal specialist

to clarify, on the real part, the center of mass may not be in the center of the volume.  in the solidworks model, using cbl's method, the center of mass would be in the volume center.
-dustin
professional engineer
certified solidworks professional
certified cosmosworks designer specialist
certified solidworks advanced sheet metal specialist

thank you guys. i knew it was something simple like that.
the cog can also be specified in the tools > mass properties > assigned mass properties section.

awesome... i was wondering about that... i am still stuck in 2006.
-dustin
professional engineer
certified solidworks professional
certified cosmosworks designer specialist
certified solidworks advanced sheet metal specialist