Taptite Screws not Fully Seated. 3

[Luis91]

Hello guys! (I'm new here!)

Basically the post is related to a problem with this type of screws where I have a high ocurrance rate on not getting fully seated when installed (Using an specific torque Target: 24Nm).

According to the information I had review, we are suppose to be forming the threads on the bore (These are machinned and the material is Aluminium) but when I remove the screw I see material from the bore literally welded to the Edge of threads, meaning I'm cutting instead of forming.

Here's a picture of the threaded bolts torndown. (The black things is just sealant from the joint surfaces to clamp.)

This is a photo of the equipment used to install the screws. We use an atlas copco nut runner mounted on a CNC.

This is a picture of the part seated on a pallet, later to be processed on the station (I'm showing the bolts where we have higher ocurrance of screws not fully seated.

One Hypothesis I have is that there's excesive axial load applied by the tool to push the screw against the bore during installation leading to higher friction. This one added to a mis-allignment of the screw due lack of thread leads where we might be forcing our way in?

Making a comparison from Conti-Reminc data sheet vs the Internal drawing I have for these parts. There's a difference on the spec (Thread Leads), since the dimension suggested for a MR7 is 4-5 Threads and the internal drawing only marks 2-2.5mm of thread lead (which it represents about 1-1.5 threads), don't know if these could be a variable that contributes to the failure.

Any thoughts? Process / Product?

 

[hydtools]

The predrilled hole diameter needs to be larger to allow space for the metal displaced during threading with the bolt.
On edit: And add a lubricant.

Ted

 

[mfgenggear]

hydtools nailed it, rolled threads require that the minor diameter for rolled threads calculated at a minor diameter before rolled or formed tapped.
to allow displacement of the material to the required minor diameter. a coating on the bolts would also may help for the galling.
please advise the material of the bolts.

 

[Luis91]

Material Specification is listed like this:

SAE 1022 (Currently used)
Neutral Hardened to RC 33-39

There's a coating involved and it's according the PS-11036.

 

[EdStainless]

We used similar fasteners. The holes that we drilled were oversized, and they also flared a bit at the start. Sometimes you get enough material displaced that if the top of the hole is tight it will prevent seating.
A lubricant is necessary.

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P.E. Metallurgy, consulting work welcomed

 

[hydtools]

Thread forming in cast material can be a challenge. Casting quality can make a difference.

Ted