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dynamic simulation, separate a part from a 'welded group' for FEA

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Message 1 of 24
nac69
3403 Views, 23 Replies

dynamic simulation, separate a part from a 'welded group' for FEA

Hi All,

 

I am doing a dynamic simulation in which I have a shaft attached to a gear by some screws, so when the gear rotates the shaft rotates as well. Then when I carry out a dynamic simulation, both the gear and shaft appear as a welded group, but I want to export only the shaft for a FEA. Currently this is not possible because this cannot be done with welded parts (that is the error message I get).

How do I take out the shaft out of the welded group so I can do the FEA?

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Message 2 of 24
JDMather
in reply to: nac69

In this case do not use the Automatic conversion of assembly constraints to DS Joints.

You can retain the Joints already created (when you change the option for automatic conversion), delete the ones you don't want and then manually add the necessary joints to hold the part together (without converting to a Welded Group).

or

Are these parts a sub-assembly?

if so, a bit more work.

 

(I'm working from memory and might have missed a detail in the steps.)  (it could be as simple as Right Mouse Button - Retain DOF)

Can you attach the assembly here?


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Message 3 of 24
nac69
in reply to: JDMather

Attached is the assembly. How do you remove the automatic conversion?

 

The propeller,shaft, gears are not a sub-assembly since I thought that by assembling everthing in one file I would have the welded groups problem. 

 

What I want to be able to do is simulate the motor driving the propeller in a dynamic simulation and then export different pieces of the whole set-up to analyze their stresses i.e. the shaft, the gear, or any other part connected to the propeller shaft. 

Thanks!

Message 4 of 24
JDMather
in reply to: nac69

Before moving on to an advanced topic like Dynamic Simulation - you should understand that -

 

An assembly file (*.iam) is only a list of hyperlinks to the part files (*.ipt) and a record of assembly constraints (and a bit more).

You must include the part files.


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Message 5 of 24
nac69
in reply to: JDMather

I thought so but then maybe it would include the fiels automatically.. here are the files, sorry for that.

Message 6 of 24
JDMather
in reply to: nac69

You have M5 fasteners going into 6mm blind holes.

I don't think the design will work without an engineering change.

 

Failure.PNG


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Message 7 of 24
nac69
in reply to: JDMather

I forgot to change that. I correted that to 5mm holes with m5 threading. But was that change necessary to remove the automatic joint?

Message 8 of 24
JDMather
in reply to: nac69


@nac69 wrote:

...... I corrected that to 5mm holes with m5 threading. But was that change necessary to remove the automatic joint?


Attach the corrected file here.

 

The change was not needed for DS, but I never allow my students to progress to DS without mastering the basics.

When I worked in industry out on the shop floor - nearly every project somehow made it out to the shop with basic mistakes like this.  It always bothered me that I was resolving the mistakes made by engineers earning twice my pay.

 

Attach the corrected file. 


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Message 9 of 24
JDMather
in reply to: nac69


@nac69 wrote:

The propeller,shaft, gears are not a sub-assembly ...


On opening the assembly I got an error that a sub-assembly was missing?

 

 

Automatic Joints.PNG


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Message 10 of 24
nac69
in reply to: JDMather

Hi JDMather,

 

Sorry I took so long to reply, I went on an internship and had no access to Inventor. Attached is the file with the edited holes. I checked again and there were more holes that were 6mm not 5mm for the M5 screws.

 

Also before continuing into dynamic simulation, since you mentioned there were more mistakes, if it's not too much work for you could you let me know which are the mistakes so I can fix them? This is all a learning process for me and I want to get it right.

Thanks so much for your help.

 

Message 11 of 24
JDMather
in reply to: nac69

Imagine you had this part in one hand and an M5 fastener in the other hand.

You PUSH the M5 fastener into the 5mm hole.  What happens?  What is the normal behavior of threaded fasteners?

 

You have made a beginner mistake of using the wrong hole size for a tapped hole - not leaving any material for the threads.

DO NOT use the Thread feature tool for internal threads.  Use the Hole feature tool with the Tapped Hole option and Inventor will select the correct Tap Drill size for your threaded fastener specification.  This might be the most common mistake I see beginners make (besides not including part files with an assembly).

 

I will get back to you on the main (DS) problem as my time permits.

 

M5.png The fastener will fall into the hole.


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Message 12 of 24
nac69
in reply to: JDMather

I didn't know that, thanks for the tip. I did this on every hole and now all of them are the right size (I changed to M6 instead). For the unthreaded holes I made them Clearance holes again using the window commands to set the right size for M6 automatically. I attached the new file below for when you get a chance to help me with the D.S.

Meanwhile I will try to make it work too, but at least now the model is better. If you find any more mistakes please let me know to improve it even more (obviously I know you have your own things to do so by what I just said I mean if you just happen to catch one).

Thanks

Message 13 of 24
JDMather
in reply to: nac69

Bump!

 

Just bringing this one back to the top - I keep forgetting to take a closer look.

 

 

Edit:  Hmmm, maybe that is why - I opened latest attachment and got a unresolved file errors.


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Message 14 of 24
nac69
in reply to: JDMather

Hi JDMather,

 

do you mean the zip file above made on '08-21-2014 08:16' ? because I attached everything I have.

 

 

Also thanks to you and the rest of the Autodesk community answering my questions I am starting to understand more the dynamic simulation (DS) environment. Attached below is a labelled diagram of the 4  parts that I need to design, which I will be referring to from now on.

design.PNG

 

At this point, if you run the dynamic simulation on the last zip file you'll see it has 3 degrees of mobility:

1 for the pinion

1 for the base #3 in diagram below

1 for a pin in a pin joint which hasn't been constraint correctly, but I don't care about this for now.

 

From these 3 movable bodies the only one that matters to me is #3(in the diagram below) since I have to design it. This one I should be able to export it into FEA and analyze it because in the ouput grapher I can see the forces involved with this part and the part itself is also a movable body. Now I need to figure out how to carry out FEA on #1,2 & 4.

From what I havelearned so far is that you can't export parts from DS that have no degrees of freedom, grounded or fully constraint into FEA. Now that I think of it maybe parts #1,2 & 4 fall below one of these 3 criteria so that is why I haven't been able to get them to work (i.e. exporting these parts from DS to FEA). So maybe I've been thinking about all of this the wrong way and the way to go about this problem is as follows: from the DS find resultant forces, and then do a static FEA for parts #1,2 & 4 in which I apply these resultant forces and torques. Essentially this is kind of like going around the problem.

 

What do you think? or maybe I don't have to do a separate static and dynamic analysis to design the 4 parts if I set-up everything correctly?

 

Edit: added image in the message instead of as attachment

Message 15 of 24
JDMather
in reply to: nac69


@nac69 wrote:

Hi JDMather,

 

do you mean the zip file above made on '08-21-2014 08:16' ? because I attached everything I have.


You have different files in different uploads.

I could combine them and fix everything myself - I understand exactly what you want - but my time is limited.

Perhaps someone else with more time will come and combine the proper assembly without errors and redo the DS Joints.

Different assemblies.PNG Note that your latest attachment is missing files from previous attachment.


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Message 16 of 24
JDMather
in reply to: nac69

I am not sure of the two base parts in your image.

These are the component names I see in the assembly browser.

 

Component Names.png

 

I assume these are the components that you want to analyze?


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Message 17 of 24
JDMather
in reply to: JDMather

Since you modeled the motor as one material - is the resulting mass approximately correct?  (you can override it if not)

 

What is the mass of the beam?


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Message 18 of 24
nac69
in reply to: JDMather

Hi JDMather,

I completely understand, still I learned a lot from your tips and that is what this is all about, thank you so much for your constant help throughout this.

Right now I'm fixing the assembly folder to have everything in one single upload to post here so that anyone will have all the files needed.

Exactly, those are the 4 parts I want to analyze.

I modeled the motor as one material on purpose because I don't know the exact mass, however the dimensions are accurate so the resulting mass should be approximately correct.

I don't know the mass of the beam because it was already attached to the structure before I started this project. But the dimensions are accurate and I set the material so wood, so again the resulting mass should be approximately correct.

Given your limited time, is it possible you could tell me where to start, or what to look for? Just from that maybe I can find something on the internet or try things myself in inventor until I get it right.

again, thanks so much!
Message 19 of 24
nac69
in reply to: JDMather

Ok so now all the files should be there, I saved everything using 'pack and go', the main assembly is 'assembly 2'.

In DS I just added a belt joint between the pinion and the gear and impossed a motion on the pinion, so if you try to run the DS you will see things moving the right way.

Message 20 of 24
nac69
in reply to: JDMather

I DID IT!! I changed the constraints in assembly mode and that fixed things, look! :

I did it!.PNG

 

I know it doesn't look nice though. When opening DS (prior to performing FEA) there was a warning that the model was overconstrained, but at least I got something! and the numbers look ok too! I'm so excited I finaly made some good progress. However the next part is tricky because I'm not sure on how to fix the overconstrained issue:

 

overconstrained.PNG

 

The problem seems to be on how I constrained the 3 M6 fasteners between the propeller welded group (prop, shaft, gear) and the back base plate. attached is only the assembly file, all the parts are in the zip file above called 'complete system'.

I used align and insert and that seems to have thrown off the DS but I have no idea why, any clue?

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