Subframe bolt install ssue 1

[Brittany Farley]

I am a supplier representative. I have front subframes that are having issues. We have nuts in the subframe with nycote. The bolt being installed is started by hand and they operator uses a tool to turn the bolt 3 times before sending it to the machine to finish bolting down. Sometimes it will fail and cause the operator to either reshoot it the bolt or to re tap the nut. The supplier insist they're thread checkers are checking the nuts and no issues on their end. The operator doesn't think it's a cross thread issue. Other theories are that the nycote is to thick in the nut. Do you all have any other suggestions?

 

[lucky-guesser]

Perhaps galling from too much material as you have already eluded to would be my guess. Have you had success in the past and this just started to happen or is this a new process off to a rough start?

 

[TugboatEng]

There are a few different products that use the Nycote name. Is this the masking product?

 

[Brittany Farley]

This isn't a new issue. Its like a lock tight nycote layer on the nuts .

. The white nut is the nycote issue

 

[lucky-guesser]

Preface: I've never used any type of thread coating like this, professionally or personally.

With that much gunk in the threads it would seem like it would be hard NOT to cross thread it. Oper might be saying its not to cover for themselves but I would certainly want someone else to verify. That said, its not necessarily their fault. That coating *seems* excessive and I would wonder if you could get them with a thinner application.

 

[3DDave]

It's probably not cross threaded, but could be stripped.

At the least it is just so filled with contaminant to exceed normal installation forces, at worst some spot cuts through and the force that is now uneven forces the materials to gall from the side load.

Are bolts available with a groove on the first couple of threads to carve out the excess material, similar to a thread chasing operation?

 

[Brittany Farley]

These are the bolts

 

[Brian Malone]

I have commonly used the pre-applied Loctite STS 2045 ECO without issue and not familiar with details of the Nycote product, but consider a thinner application of compound or if possible by the application process and your assembly process have the first two threads masked and installed toward the assembly lead-in side to ensure proper fastener thread engagement without thred compound. Certainly, the masking and orientation add some cost but that probably would be less than the cost of the rework of stripped sub-assemblies.

 

[Brittany Farley]

Brian. I'm newer to this stuff. What does masking the first two threads mean?

 

[3DDave]

Oh, good a patch of locking compound to further fill the tiny clearance in addition to Nycote. It looks like there is taper to act to force the Nycote radially, increasing the interference.

Since Nycote is apparently a teflon coating, what is the locking compound patch supposed to bond to?

 

[Brian Malone]

Just saw your photos of the bolts. You have all the good stuff there: unthreaded lead-in nose, and pre-applied thread lock patch. Your assemblers are using automated driver tools and don't feel the odd resistance until the damage is done?

 

[Brittany Farley]

3d- I'm not sure why the locatite is there. I didn't know that it wouldn't bind to the nycote. It does make since that this would make less room for the bolt.

 

[Brittany Farley]

Brian- the operator who first hand starts the bolt about 3 turns and can feel it resist. Sometimes they hammer the bolt into place. The bolt then goes to an automated machine that will shoot the bolt down. Sometimes it fails in the machine. Then another operator will either reshoot the bolt, or Sometimes re tap the nut with a threaded bolt.

 

[Brian Malone]

Brittany, have a plug inserted into the nuts to cover the first two threads prior to application of the Nycote. The plugs are removed and this leaves bare metal threads exposed to work with the lead-in nose already on your bolts. To work properly the bare threads have to be position to the lead-in side to accept the bolt.

 

[Brittany Farley]

Brian- this suggestion makes sense. I was hoping for a easier solution. I am just the representative for this supplier who makes the nuts. It would be a long process to get approval to change the design. But I will definitely mention this as a resolution to our daily problem on the assembly line

 

[Brian Malone]

Wow, the use of a hammer strike sounds excessive and if the threads are properly engaged I would think that is not necessary. Are the hammer-struck subassys more prone to failure than those that aren't?

 

[Brittany Farley]

When the operator hammered in the bolt, it failed through the automation also. We also think it's not necessary and causes more issues.

 

[MintJulep]

Nycote IS a masking material. It's there to protect the threads during the e-coat application.

 

[3DDave]

The hammer is probably to clear excess material on the minor diameter.

Nycote 88 data shows it should be a 0.4 mil / 0.0004 inch thick film, so a reduction of roughly 0.0008 in thread diameter.

Find out what film thickness is actually happening.

 

[TugboatEng]

It's important to be specific about the products you are using. You've got the aerospace group in here thinking you're using a completely different product from an entirely different manufacturing.

Clearly you are using Nycote masking.

https://nylok.com/pre-applied-processes/nycote-nycote-plus/

You should be able to verify the effective application of the Nycote as hole should have a bright white coating and no black e-coat.

This is a clamp for a rubber bushing that is compressed over a spring. If you fully install one bolt before the other this may cause misalignment of the bolt holes. There does appear to be some amount of cross threading as the coating wear favors one side of the bolt in your picture.

The bolt you showed has an inorganic zinc coating such as Dacromet. These coatings so add thickness to the fasteners and can prevent it from running freely. They need to be used with looser clearances.

The yellow coating on the bolt is likely a Loctite product. It's primarily intended for sealing or the threads to prevent corrosion and may provide some locking depending on the specific product.

Are these nuts welded to the frame or are the captive so they can float a bit. If welded, are they properly seated? This misalignment may also lead to cross threading.