Threaded Connection of Aluminium Components

[_psp]

Hi,
It's Pawan.

I'm designing a product containing many aluminium parts and lost in their mounting selection. I want to use thread-based mounting of components.
Now I've to mount one aluminium part with another using threads.

The problem is that the product will be in constant vibration of varying frequencies and all the components will experience tension which means if I use inserts there are chances of them getting pulled out.

I'm looking to strengthen the threads on aluminium as the weakest part of the product.

There are various components of aluminium and steel -

1. Thread engagement length varies from part to part but the least is 10mm and the dia. is 30mm
2. The material (specifically AL) is not finalized yet.

Also, I've seen a product that is a damper made of aluminium not sure of the specifics but the components were directly mounted by threads. The damper was a heavy truck damper.
Is it okay to directly mount the aluminium components by using threads?




I'd appreciate all the suggestions and answers. Also, I'm still learning and new to the industry so please help.

 

[drawoh]

Pawan,

Threads in aluminium are weak, which is why thread inserts are used extensively. I am not aware of thread inserts failing in vibration. Read up on fasteners failing under vibration. The website for Bolt Science is a good place to start.

In general, assume that lock washers do not work. Torque your screws down as hard as you can. Use thread-locker if possible.

 

[Gr8blu]

@Pawan
If I read your post correctly, you have an assortment of threaded fasteners of different diameter, with different thread engagement lengths. What is unclear is whether your statement (10 mm engagement and 30 mm diameter) apply to the same fastener or not.

Remember that a good engineered joint requires at least two things: 1) at least 75% of the threaded length is engaged, and 2) the engagement length is at least 1.0x - and preferably 1.5x - the fastener diameter.

 

[Orange_kun]

Nobody has mentioned galling yet?

Aluminum on aluminum threads is asking for trouble, particularly where vibration is present. It's a virtual certainty your threads will gall together, possibly even with an excellent anti-seize compound being used.

That's not to say it can't be done. Just be aware that you might destroy the threads if you need to disassemble the joint.

You say you're worried about inserts backing out? Are you not able to install something like PEM nuts from the other side? Or install nutserts from the front. Better than aluminum on aluminum threads. If you have material thickness, you could install a helicoil insert. With the correct retaining compound, they won't go anywhere, and you'll get a much better steel thread that won't gall. For the male thread, if you can't change material I think you need to look into hard anodizing. A coarser thread is also better for resisting galling, assuming the surface finish is still good.

 

[ShataCastings]

Thread inserts like we common used in aluminium castings are more stronger than aluminium threads, you can make the inserts much bigger than thread size, and add multiple groves to avoid to be pulled out.

 

[MintJulep]

Here's an example of aluminum to aluminum threads in about the size described that works fine for long time without galling.




If your thing is different, perhaps some detailed specifics would be useful.

 

[Jboggs]

I've used helicoils for similar applications for years.
Key locking inserts are a step up and work really well.
Both are available as stainless steel if that is an issue.

 

[BrianPetersen]

Automotive/motorcycle engines and transmissions use steel fasteners threaded into aluminium everywhere. Thread inserts are only used for repair purposes but if you anticipate frequent dismantling, they may be a good idea. Thread sizes are commonly M6x1.0, M8x1.25, M10x1.25 (this appears to be JIS, if you are using ISO then use M10x1.5).

Don't use fine thread pitch. Don't use screws smaller than M6. Use lots of thread engagement length. Don't use lockwashers. DO use flat washers. DO make sure your parts fit well together (machined surfaces) and are located using multiple screws and dowel pins where appropriate so that the screws aren't responsible for carrying any torque loads in the completed assembly.

 

[_psp]

Automotive/motorcycle engines and transmissions use steel fasteners threaded into aluminium everywhere. Thread inserts are only used for repair purposes but if you anticipate frequent dismantling, they may be a good idea. Thread sizes are commonly M6x1.0, M8x1.25, M10x1.25 (this appears to be JIS, if you are using ISO then use M10x1.5).

Don't use fine thread pitch. Don't use screws smaller than M6. Use lots of thread engagement length. Don't use lockwashers. DO use flat washers. DO make sure your parts fit well together (machined surfaces) and are located using multiple screws and dowel pins where appropriate so that the screws aren't responsible for carrying any torque loads in the completed assembly.

Thanks, Brian

I apologize for not giving a better explanation.

As per my application, the product is 'maintenance-free', and the lifecycle is around 20 years under constant tension and vibration. Also, the product will be facing only axial loading. I'm more worried about a long lifespan without any maintenance.
Also, I don't know if it is that long for the industry or not.
I'm worried that the fasteners or inserts will be loose which can endanger human life and will be an economic loss too.

Some of my aluminium components are threaded and will be joined with other aluminium components via threads. So, they'll be the weakest part.

 

[drawoh]

Pawan,

Aluminium's galling has been noted above. You can thread aluminium parts into other aluminium parts only if they are anodized. Bare aluminium and chemical conversion filmed aluminium will gall. The parts will not be fully tightened, and you will not be able to take them apart. Been there, done that.