Mechanically welded and solidworks static analysis

Simulation Generality
1

Hello

I just remade the assembly below with 2 aluminum plates of 1cm thick and 4 tubes of 21.3 x 2.3 (I put alloy steel, I don't know what is normally used for these tubes?)  welded to these plates and I have several questions about the quality of my design and its solidity.

In addition, since I'm completely new to SW simulation, I have a lot of questions for which I haven't found answers in the different video tutorials I've watched.

So already from a point of view of the mechanically welded structure , I would like to know if solidworks should not automatically transform the angles between the tubes into an elbow, because there it seems to me not very realistic to bend a tube like that (but I'm wrong p-e, I'm not an expert ^^).

In case it is up to me to do it manually, do I have to do it at the level of my 3D sketch with sketch fillets? Or is it done when I turn my sketch into a "welded construction"?

And still in the case where I have to do this work myself, how do I determine the angles to use for the fillets, can solidworks help me choose appropriate values (and if so, how?)? Or are there "known" values (and that I don't know :D)? 

2nd point, I would like to rework the mechanically welded structure in order to size it correctly so that it can withstand a load of 50kg on the brown plate.

So I tried to do my first static analysis with SW Simulation. To try, I left only gravity and there I got the result below with the deformed plate (as if it had melted..), which surprises me a little since I haven't even put any force (other than gravity) yet.

If I understood correctly, SW shows a deformation no matter what happens by accentuating what I imagine is given to it (so here there gravity?)  and to see the "reality" you have to right-click on the result go to "Modify definition", then change the "Distorted" parameter from "Automatic" to "True scale"? If that's right, we can say that it's not very intuitive ^^. By the way, I have a bit of trouble understanding the difference between the different results listed by default: Constraints (-vonMises-), Displacements (-Resulting Depl.-), Deformations (-Equivalent-), Displacements (-Displacement-). The only one I understand is the safety factor (which I add).

So after adding my 50kg force and putting the "normal" scale, I notice that my plate bends, but my mechanically welded never moves.

Since it's not the plates that interest me, I removed the gray one, and I went rigid the brown one, and when restarting the simulation, I finally had a folding of the mechanically welded, but when I go back to real scale, it doesn't move a hair.... I increased the force up to 500,000 newtons, and nothing, it started to bend at 5,000,000 NoO. So I must have done something wrong, is it because I took alloy steel?

Last question about this study, if I understood correctly, the green/pink dots are the connections? If the green ones are the fixed ones, shouldn't I have indicated that they were weld seams? And what do roses mean?

Finally, last point, Without talking about solidworks, what do you think of such a "chassis", would there be an obvious way for someone in the business to make such a structure (I imagine that the question must have arisen for chairs/stools in particular)? 

2

Hello

First, the bending radius should be set on your 3D sketch. The value depends on the tools used for bending but it seems to me that you should choose an inside radius of 1.5 or 2 x the diameter. In any case, you can find charts on the internet.

Second point, with a load of 50 kg on the plate, it is normal that the tubes do not flinch because they are made of steel. By the way, we can ask ourselves the question of the welding between your aluminum plates and your steel tubes. Why not make your whole structure in aluminum, I think it should be more resistant, you can define the section of your tubes according to your calculations.

For the results of the analysis, the visual is indeed exaggerated so that we can distinguish the deformations.

The pink dots on your structure are the knots that symbolize the junction between your pieces of tube (which are welded in your case but should disappear if you make a bending radius in your 3D sketch.

Finally, I don't know the cross-section of your tubes but it's normal that they don't move with 50 kg, you should know the cross-section, see the elastic resistance in your material,...

It all depends on the application of your stool, but what shocks me is the welding between steel and aluminum.

I hope I haven't told too much nonsense and have guided you a little.

Have a nice day.

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3

Hello

 

Quick question and without going into too much detail... but you weld aluminum on steel? Because it seemed to me that it was not possible

So, find out about your metals before you start an analysis, because it can completely change the results

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Also remember to simplify your study, because you have 2 axes of symmetry.

And if you're only interested in tubes, then simplify it even more by removing your plate (you'll add it to your applied force)

If your tubes are welded, they can have this shape. If you want to bend them, you'll have spokes instead of your fittings.

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5

For me too, the welding of steel tube on aluminum plate shocks me a little.

Personally I would use the same material for the plate and the tubes.

Next, why bend the tubes? Wouldn't it be easier and more economical to install it at an angle with a miter cut?

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Wow, thank you very much for your answers which contain a lot of information:)

So, for the aluminum/steel welding, I didn't know it wasn't possible, but in fact as I said at the beginning,  the plate I know will be aluminum, but the tubes I had no idea of the materials I commonly encounter.

I'm looking to make a part that is as economical as possible (in terms of material and manufacturing processes), so if it's better to use aluminum, iron, plastic, in short, whatever you advise me, I'll take :)

So I'll try to answer each one in order^^

@dargaud.anthony

Ok for the bending radius, with what you just told me I was able to search a little and come across this page which completes the explanation : http://www.guillot-pelletier.fr/cintrage-theorie.html

For the 50kg load ok, but for 500,000 newton (that's 50 tons, isn't it?)  ? If SW is right, steel is stronger than I imagined.

I don't find it very intuitive that Solidworks exaggerates the visual like that, because in the end we tell it that we have 50kg, and the 1st thing you see when you have the result is that your thing bends, so you tell yourself that your part doesn't hold the 50kg, and in fact not at all...  

the tubes are those of 21.3 x 2.3 supplied as standard in SW.

@opiep27 it's true that for the moment neither tube is linked to the other, so analyzing 1 tube is the same as the 4, but I was thinking of doing it at the 1st angle at the bottom

@Frédéric Ok so what I did is feasible if it's a cut + soldering, but I didn't want to cut/solder here originally. I wanted to have it all in one tube. Now if you tell me that cutting + welding is cheaper than bending, I'm interested, but I'm skeptical about the resistance to other forces that would not be applied on the brown plate (for example, someone pulling one of the tubes, while the brown plate already supports 50kg).

 

Edit: for your information, even if in my case, it's not possible, there are apparently some advances on the welding of aluminum/steel together: http://www.usinenouvelle.com/article/souder-l-aluminium-et-l-acier-n-est-plus-impossible. N157533

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@liohau, I was thinking of removing the hangers and making straight tubes. And not to make butted and welded tubes. 

If you want an angle in a tube, the cheapest is the bending 

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Ah ok, well I'm going to go for bending then.

9

Hello

 

I see that the others answered just about everything except the interpretation of the results. and in my opinion this is the most complicated part of the simulation! And for that no secret, you have to do some, do it again but also do it again!

Concerning the displacements you can draw the results of the resulting displacements, i.e. the total displacement of each node in space. But sometimes it is also interesting to see the displacement projected on one of the 3 axes.

Regarding the real scale, we almost never use it for the simple reason that we can't see anything! The amplification of the deformation of allows you to see how, in which tendency your model deforms. It's thanks to this that we generally see if our initial assumptions are right or wrong!

When it comes to sizing your tubes, it's not only the movement that counts, but also and above all the constraints! Imagine your glass structure (so very rigid but fragile) your structure will break by barely deforming. The same titanium structure (soft and solid) will deform enormously without breaking...

each material has a maximum breaking stress that should not be exceeded (example for standard steel it is 235Mpa or 355Mpa depending on the grade)

 

 

 

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I will admit that I did not fully grasp the principle of the result of constraint. For me, constraints are gravity, forces, torques etc. that I defined, so I don't really understand the meaning of this result.