Aluminum Weldment Design Help 4

[Andre3]

I have recently moved from a mechanical design role into engineering at my small R&D company figured I would try reaching out to you folks for some help and direction as I do not have other colleges to consult with. I am looking to design a weldment between two 6061-T6 components supporting a very strong solenoid magnet. This had been a bolted connection but the bolts failed after the system was overloaded and now we would like to weld them together for a stronger, permanent connection. My thought was to chamfer the parts to make for a groove weld to hold them together but I am mostly unfamiliar with weldment design.

From what I have seen it looks like to be conservative I can expect the welded area to behave like 6061-O which is dramatically weaker. There is an axial magnetic force of about 250 kN downward and an outward radial force that is still being evaluated, for now I am treating it as 0.5 MPa acting on the inside wall of the support. Where should I start with evaluating the stress experienced at the weld and how it will behave? I have attached some snips of a simplified model for discussion.

 

[desertfox]

Andre3

Can you confirm bolt stiffness you quote 1.88 * 10^8 N/m that seems high to me ?

Also what is the grip length of the bolt you used in the calculation?the overall length you gave was 35mm and last but not least what values of modulus of elasticity for bolt and joint are you using

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Andre3]

IFRs

No I do not have a pattern other than hitting them twice in a star pattern, where can I find information on establishing a pattern?

desertfox
The grip length is 24mm

Here is how I got Kb
Eb = 194.6 GPa 316 stainless at 293K
length of shank = 11mm
length of thread in grip = 13mm
K = A*E/L
Kb = Kshank*Kthread/(Kshank+Kthread)

Em= 70.4 GPa 6061-T6
Ewasher = 151.9 GPa invar 36

 

[desertfox]

Hi Ande3

From the information you have given I cannot get the same bolt stiffness as you so just post what length you used in the formula for stiffness along with the bolt area which I had from the inconel bolt as being 20.1mm2

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Andre3]

I wrote the Kb formula wrong, I corrected it.

There are two areas we need, one for the shank and one for the threaded section, the new bolts will be partially threaded. The threaded section area is 20.1mm^2 and the shank area is 28.3 mm^2. The length of the threaded section in the grip is 13mm and the shank is 11mm long. To get the total bolt stiffness Kb, you combine the stiffnesses like this : Kshank*Kthread/(Kshank+Kthread)

 

[hydtools]

I don't think the thread length should be consider in calculating the stiffness. Any change in thread length is resisted by engagement in the helicoil/aluminum.

Ted

 

[Andre3]

Hydtools
Please see the section on bolt stiffness here :

https://mechanicalc.com/reference/bolted-joint-analysis

The thread length I am referring to above is the length of the thread within the grip. The bolt is 35mm long, 11mm shank and 24mm thread, but only 13mm of threaded length is in the grip and contributes to the bolt stiffness.

 

[desertfox]

Hi Andre3

Okay I checked the stiffness and I think the calculation you did for tightening the bolt using the angle method is correct.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Andre3]

desertfox

Thank you, I have presented the concept and it has been well received.

I plan to make a test fixture for our Instron with a scaled down bolt pattern of 4 or 8 bolts and test the separation force. I think it will be a nice way to prove out the torque method and wrap up the solution. Does anyone have a suggestion on identifying the separation load during testing? I am hoping the slope change of the load curve at separation will be clear enough for me to identify when the bolts start taking the full load but it will be a first for me.

 

[desertfox]

Hi Andre3

You’re very welcome, it’s been a very interesting problem and I think we’ve hopefully solved the problem and it’s always worth trying to understand why a failure as occurred because in doing so it usually leads to a better solution.
I am pleased that your design as been well received and all I would ask is that you keep us posted when you have tested the product, it’s always good to hear what happens in the end.

I will have a think about how you might get indication of joint separation, it’s not something I have any experience of.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[desertfox]

Hi Andre3

Not sure whether you could use these bolts that change colour when the reach a certain tension?
You could contact them and talk to their technical people.

http://www.smartbolts.com/dti/

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Andre3]

desertfox
Yes I will post updates as we test and implement the solution, I am very grateful for everyone’s time and consideration.

That is an interesting idea I have never seen a product like that. At a quick glance it appears that they do not have any M6 A4-80 options, I am still tied to that bolt spec.

 

[desertfox]

Hi Andre3

Thanks for the response, shame they don’t go down to the bolt size you are looking for but I will have another look to see what I can find.

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[desertfox]

Hi Andre3

Is there any news yet on this project?


“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[Tmoose]

No survivors.

 

[Andre3]

Yes! I have a layout for a 6 bolt test fixture to be used in our Instron and will be ordering the hardware shortly. There have been some programmatic challenges that put this problem in the background but we are still moving forward!

 

[desertfox]

Hi Andre3

Thanks for the update

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein