Hi-Lok Pins Shearing During Install

[itskylecook]

Good afternoon,

I am running into an issue when installing HL12VAP5 Pins with HL1087ATW5 Collars of varying grip lengths but generally between 3's and 5's. When torqueing the Collar there are instances (at least 20%) where the Pin will shear off at the point where the allen key is engaged. We install 100s of Size 5 Hi-Loks per day and 1000s per build so a minimum of 20% failed installs is a pretty significant number.

After searching through the forum I came across a thread where Will Taylor (WKTaylor) stated "An 'integral-washer-collar' will likely induce a significantly higher torque-tension for 'same torque' relative-to a 'plain' collar [due to lower torque-turning friction]." I am under the impression that this is the root cause however I am not sure what the most effective and practical way would be to address it. I also believe that Size 5 Hi-Loks must be an unlucky thickness because we do not have any issues with Size 6 Hi-Loks and greater.

We tested how much torque is being applied to the Collar when the Pin shears off and there were instances when it occurred at 30 in-lb which is the minimum for a HL1087A Collar. We also applied additional lubricant to the Pin and Collar to no effect. Additionally, we used a Plain HL1087A-5 Collar with a .016" thick aluminum washer to simulate the HL1087ATW5 and all Hi-Loks were installed successfully.

Our current solution is to increase the grip length by (1) and install a .032" thick aluminum washer under the HL1087AWT5 Collar in order to move the Collar closer to the solid shank part of the Pin. We successfully install Hi-Loks in this configuration however I am wondering if there is a better solution instead of a reactive approach to the Pins shearing off. As of right now, the only option I can think of is to install HL1087A-5 Collars with .016" aluminum washers in place of HL1087ATW5 Collars as a proactive way to avoid sheared Pins.

Any help or inside would be greatly appreciated,
Kyle

 

[SWComposites]

Well, this is certainly a new failure mode. Perhaps a manufacturing defect with -5 grip length pins?

 

[RoarkS]

Holy crap.

You should be calling your vendor and very shortly be talking to an engineer at the manufacturer.

I had a failure like this once in a stainless fastener and ended up in a high end metrology lab Chicago... halfway across the country from me, in a matter of hours. Turned out the bar stock they used had radial grain structure flaws from the mill. Apparently it was an extrusion before they rolled it. They told us they were able to duplicate the issue with bar from the start of a continuous heat treat process... essentially an uncontrolled Jominy end quench. Corrective action, a nice dinner... was a fun week. Maybe they broached it too deep? grab a pin gage and check depth to spec.

I'm of the opinion the right answer is the right fastener combination. Not knowing the root cause is terrifying to me.

Dumb question: Did you try a different torque wrench? Hopefully a Torque-o-meter/Digital? Check units? /sorry for asking, but needs to be asked.

 

[3DDave]

Similarly - had a dowel pin develop a significant (20% of diameter) Z-bend over a <1D gap. I know, I know, should be a shear plane; not my circus, not my monkeys. Turned out the entire batch had missed heat-treat and hardening. They were precision ground and dead soft. We checked some for hardness and then discarded the rest from stock. Not a life-critical problem but also not the sharpest management. Sigh.

 

[verymadmac]

Have you sent some out for metallurgy? Or otherwise checked the shear capacity

How long have you been using this batch (new stock or old stock).

Looks like a fun problem to solve

 

[rb1957]

I wonder if this is a new "bogus bolts" thing ? As above, I'd check metallurgy.

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[WKTaylor]

I concur with everyone-else... the failure of pin threads looks very ductile and entirely unique.

Look at the HL pin heads 'Mfr code' to confirm they were made by LISI... or whatever company. CALL the HL-Pin OEM ASAP and demand tech-engineer and met-lab support immediately. CAUTION: at one time HL parts were licensed to be manufactured/sold by several other fastener OEMs... unsure about 'now'.

In the 1990s I was at an airbase in Japan doing a repair. I spotted a parts-bin partially-filled with very off/odd looking HL20-6-x [3/16 cadmium Plated steel]: the shank surfaces appeared to have been 'pitted' prior to Cd plating. I had the shop 'set-aside' that LOT of parts and get replacements sent ASAP.

I knew the lead HL engineer for Hi-Shear [HS] so I called him from overseas. I described the HL20-6-X pin condition and indicated these Pins were 'entirely inconsistent' with quality standards I expected of Hi-Shear... but the HL mfr's logo on the head was a valid Hi-Shear marking. He was concerned so I sent him [10] randomly selected PIN for analysis.

Then waited... and waited... and waited. So, about a month later, I called my friend back to get a straight answer.

He told me "Yep HS made these pins. It appears that the pre-plating cleaning/etching bath chemistry was 'way-off' the pitting was squarely HS's fault. From my 'sample' it was apparent that thousands of these Pins likely 'escaped' internal QA. They were assessing the probability for field failures."

I asked for a written report... But NEVER received one. Called my POC back... and asked a second time for the report... and he politely told me 'management' put a lid on the report... since the PIN LOT was 'small' and the PINs passed strength and fatigue tests. I reminded him that precision fit, smooth shank, was also required to prevent pressure/fuel leaking around the pin shank. In this call I asked him to do the right thing and contact DLA [MIL parts procurement] with the info... and got a tepid response.

Next day, I called the airbase sheet-metal section MSgt and asked that they send a QDR [quality discrepancy report] to DLA with PIN samples... but guess what?!/!... Yep, those pins were 'long-gone': installed in other jets. Aw-Cr*p. My work 'was done'... but the problem was never truly resolved. Hoops and red-tape and lots of other 'hot jobs' defeated me.

#1 Lesson Learned. Fastener OEM 'Aw-Sh*ts' happen... and can escape the factory. when something is 'off with any parts' CONTACT THE OEM DIRECTLY, ASAP!!!!

#2 Lesson Learned. Even though the mechanic installing these parts is 'ultimately responsible for the installation', the shop is usually in-a-hurry and will blindly 'trust the packaging'... and rarely ever give any of these 'trusted parts' a 'hard visual inspection'. Heck most mechanics 'do well-enough' to inspect installed-parts, during/after installation... rarely before any job.

#3 Lesson Learned. Openness and candor and humor and calm 'adult conversations' can do wonders for attaining solid technical support and building life-long relationships with people who will help YOU over the long-haul. NEVER scream or rage or VENT at who ever You are dealing with... that is highly/grossly counter-productive. BUT BE ASSERTIVE and proactive and do Your duty thru other channels... a parts-problem NEVER goes away on it's own.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov

 

[rb1957]

"Openness and candor and humor and calm 'adult conversations' " ... tru dat

"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.

 

[3DDave]

I worked with a really good materials engineer who had worked a gun program. To increase the strength of the barrel it was wound with some ultra-high strength alloy that was to have been carefully tempered. When tested, the barrel blew to smithereens.

He said his approach was simply to explain that the problem wasn't to find someone to blame but to understand what happened. In this case it turned out that a couple of hours of tempering ended up being the entire weekend because the timer on the oven didn't get set. He said that had they gone after the "who" they would not have gotten the "what" leaving the rest of the program in jeopardy as the predicted results had been replaced by fragments. I presume a new barrel was wound and so forth and worked, but that wasn't the point of him telling me this story.

 

[WKTaylor]

One thing that struck me yesterday late-late...

I pulled-up the data sheet for HL1087 collars. WOW... the collars and the optional integral washer have an unusual variety of materials they can be made from.

Collars: 302HQ [ASTMx]; or 302, 305 per [AMSx]; or 303Se [ASTMx or AMSx]

Opt Washer: '300-series SStl'; or 2024-T6

IF the collar had any defects in the threaded barrel area... such as distorted/imperfect threads or excessive locking-crimp... or there are alloy shear-strength variations... any of these may allow over-torqueing the smaller Dia HL pin threads, before/at collar-break.

Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov