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Can we design Multi Body Part../?

SOLVED

Re: Can we design Multi Body Part../?

Marco,

What you have described is essentially a Top Down approach, normally utilized in an Assembly with one of the procedures described above. Managing all the surfaces, merges, quilts can get a bit tedious, essentially if you are referencing offset surfaces (I.E. body gaps, reveal lines, etc... with merges) With a single change it can go pear shaped quickly.

Am I reading correctly you do this in a .PRT file? IMHO, I believe you are making more work for yourself in the long run.


Re: Can we design Multi Body Part../?

Francis,

Multi body is really a "what one is used to doing" type thing. I have worked on both types of software and, IMHO, one does not have an advantage "technically" over the other. Each method gives the same results, with the same amount of control as the other.


Re: Can we design Multi Body Part../?

It's true - this technique makes more work with some restrictions. And I can't see the benefit inside Creo. So I prefer a clear top-down-solution with skeleton, publish and copy geom with clear downstream and replace options. But not everybody have an essentials team or advanced assembly license.

And what I'm doing with Creo is always playing. I'm not paid to build up CAD data. I use it for fun.

Re: Can we design Multi Body Part../?


That's fair. I forget not everyone will have all the license capability. But, even with simple Assembly Mode you can get the results without all the extra surface work and management. Both methods work....just depends how much "Fun" one wants to have, I guess.

Cheers.

Re: Can we design Multi Body Part../?

Dean

Thanks for your views. I too have used both types. I just get on better with the direct, nudge to surface, lock to feature that SE provides, I just find it so more fluid and much quicker to use than traditional ordered, parametric modelling where topology can mean that the thing that you want to reference from is often just not there without the extra operations of setting up a special reference plain higher up in the tree along with another sketch at the top with all the references detached, so you can lock onto things, but that can most of the time get out of date rather quickly too.

Re: Can we design Multi Body Part../?

Francis Greensides wrote:

... Sorry PTC but Solid Edge wins here again with the syncronous technology, multi-body modelling, automomous re-referencing, again and again, time is saved in bucket loads.

I'll strongly disagree with that statement. We have both SE & Creo here (and SW too for that matter). Our team will take skeleton driven top down design in Creo every time, especially if we have to move fast,  In the past 24 months, our team of 6-8 engineers have brought 6 complex consumer products from concept to tooling release because of the TDD techniques available in Creo.  No way we could have gotten there with SE or SW.  That is in part due to what we are familiar with, but we haven't seen anything in SE that looks even close to the power. We know SW quite well and the tools simply don't exist there.

--
Doug Schaefer | Engineering Manager
Crow Works

Re: Can we design Multi Body Part../?

Hi Doug

Im open and always interested to see different ways to do things. Which parts of Creo you are using to do your "skeleton driven top down design" would very much like to see some video samples, possibly on youtube, maybee.... I do not know everything and your comments interest me a lot.

Kind regards

Francis

Re: Can we design Multi Body Part../?

It's not a single technique, but rather a system of modeling techniques that work together. The core of it is:

  • Using skeletons to define the design intent
  • Creating Publish Geometries in the skeleton to define sets of geometry to pass on to the parts or sub assys
  • Creating External Copy Geometries in the parts and sub assy skeletons to retrieve the data
  • Careful, intentional reference selection that explicitly capture your design intent

A skeleton is a special part that is used to define your overall product's design intent.  It has to be created in the context of an assy and you have to have the advanced assembly extension.  The top level assy skeleton contains the geometry needed to be shared at that level.  The main outside shape and major fastening or motion items, for example.  Each sub-assy has it's own skeleton that contains more detailed information that needs to be shared between the parts in that sub assy.  Depending on the complexity of the entire product, we typically only go 1 or 2 levels down with sub assy skeletons to keep things more manageable.

In the skeletons, we create a publish geometry feature for each part or sub assy that contains the geometry that item needs.  A publish geom is like a bucket you put a set of geometry in for passing on to another part.  In the sub assy skeletons and the parts, we create an external copy geometry that references that publish geometry, pulling the relevant skeleton model data in.  It's like reaching in that bucket and pulling that geometry into that part.

In most cases, we use the default CS for both assembling the component and locating the external copy geom. In cases where default assy position doesn't make sense for a given component (the origin of the assy would be far outside the envelope of the part, for example), we create a CS for that component in the skeleton and use that CS both for assembling it and for the external copy geom.  It's important that the assy CS and the external copy geom CS match.

We make very heavy use of the skeleton, putting in geometry for every instance where two parts or sub assys need to share geometry. Everything from the outside shape, parting lines and major mechanism features like pivots down to screw boss locations and heights go into our skeletons.  Again, if it's shared geometry, it goes into the skeleton.  Some will say keep them simpler, but we've had great success with our method.

A major consideration, however, has little to do with the actual TDD technique and more to do with the modeling and creation of individual features. If you are careful with reference selection and model to capture your design intent, you will be rewarded with very robust and very responsive models.  Think as if you are baking your design intent into your feature construction. 

We've been able to make major size changes to overall dimensions of very mature assemblies (in some cases live in a client meeting!) with very few feature failures.  It's quite satisfying to change an early skeleton feature effecting 6 or 8 parts, regen your 3800 feature assy and have no failures.  Make the whole product an inch shorter and still release for tooling on Tuesday? No problem.

There are some good KB articles on skeleton modeling, search for them.  I cannot link to them because my company's maintenance agreement has expired.  I searched a bit for videos, but didn't find any that show exactly what we are doing, but there are some out there that show the basics of creating a skeleton and creating publish & copy geometry features.  Part of the problem is that it's very specific to your design. Learn the basic techniques and you can then apply it to what you do.

That's an intro (there's a lot more) but I hope that helps.

--
Doug Schaefer | Engineering Manager
Crow Works
Highlighted

Re: Can we design Multi Body Part../?

Thanks to all of you...

I got the answer from your discussion...

and also learn something new from these all discussion...

In short, if we want multi body modeling, then Skeleton and Published Geo are the best option... and from this we can solve all the problems.....

Re: Can we design Multi Body Part../?

Hi Doug

Thank you so much for your introduction, most interesting. I will have to read it a few times to get into that mindset of assembly Skeleton control. This actually reminds me of a top down way of working that I have found very sucessful particularly with boundry surface modelling, where I have a control sketch at the top of the tree that everything relates back to it via referencing. From that I have used these reference dimensions and entered these into Family Tables for the vairable factors that create the instances. I have had a look on youtube on the advanced assembly module and have found something that I will need to see a few times by Leo Greene from ECogintion that includes the use of skeleton control modelling system. I have also found a useful bit of detail on intent selection, that could help provide a more stable model, all very interesting. I understand the feeling when whole assemblies update, reject unwanted sub-family table assemblies and end up with a complete machine at the end. I feel that I might be able to apply your setup into my family table setup and create something really more spectacular than I already have.

Regards

Francis