oversize hole repair

[brin]

I'm looking for other experience on repairing oversize bolt holes. Our typical repair is to ream and install aluminum freeze plugs (interference fit). However, this results in removing more material to allow for minimum wall thickness (.03 to .05), which can be a major issue in some locations.

Oversize bolts (NAS6603X or NAS6603Y, etc.) and Hi-Loks are preferred depending on the degree of damage, but availabilty is usually a problem.

1. Has anyone worked with thin wall stainless steel sleeves or repair bushings on structural joints? Corrosion problems?

2. We usually source from the following list of oversize bolts. Any other recommended additions? Specialty bolt manufacturers?

NAS6603 thru 6620 X or Y (.0156 or .032 oversize)
NAS6203 thru 6220 " "
BACB30US (Boeing) " "
BACB30FD (Boeing) " "
BACB30LC (Boeing) " "
HL63 (HiLok)
HL64 (HiLok)

Thanks

 

[chuck1]

Have you considered using Acres Sleeves? These are grooved sleeves made from either 5052 1/2 hard, 6061-T6 and A286. The grooves allow the sleeves to be broken off to the necessary length.
Acres Sleeves are a J.O. King product. Their address is 711 Trabert Ave N.W., Atlanta, GA 30318, CAGE Code 24973. I don't know if they have a website or not.
I'm also pretty sure that Boeing has a standard for this.

 

[johnfalky]

My viewpoint is that if .03 to .05 becomes an issue, you have other problems as well. I have seen attempts to use solutions "other than" the repair interference-fit bushings, but getting approval was very difficult, er, impossible, and took far too much time, i.e. while you are designing the "custom bushing repair" other folks are standing around idle. The freeze plug repairs are actually very effective and durable and can be accomplished in any facility that has a decent machine shop. Also, if you have many oversized holes, you have to ask yourself the question; "why?" more than likely there is a workmanship problem, so the likelihood of fabricating a freeze plug, getting it installed correctly and then reaming again will not be successful. In my personal experience, I have seen some repairs done over "n" number of times at massive expense until a light went on somewhere and a check was made of skill levels at the shop floor. Please note that these days, many techs are poorly skilled and might not even read or speak English

 

[rguil]

What is your parent material? Would a weld build-up help? I recently had the same problem and I performed a build up on a Mg casting. Approval and substantiation was not a problem since this is not a new technique and it is used extensively during manufacturing. Before you begin such a project you must know your base material, condition and treatments etc...

 

[liaisoneng]

A point I would also make, which you may already be aware of - the absolute necessity to plug each layer independently, so that the plug does not act as a fastener itself.
A problem we have had even beyond the X oversizes, the complete lack of Z (3/64) oversize fasteners.

 

[WKTaylor]

Guys... a few observations...

Obviously oversized fasteners are the elegant repair solution when oversized holes are mandatory: IE: structural repairs or mods. If doing "depot" type work, it pays to stock these fasteners in anticipated quantities, for immediate future use.

Regarding Fastener sleeves... be careful. Some acft tech data and engineers allow them everywhere... including fatigue-critical locations... others acft/engineers say "absolutely NOT. There are various issues, including installation-fit [they don't tolerate interference fit very well], they have a fixed ID that is generally designed for a substantial cleartance fit, have and very little engineering data to support their use, etc. NOTE: I have carefully used ACRES Sleeves [A286], installed in very light interference thru the hole [not separated for each layer]... with a precision fastener in light clearance down the center. They seemed to work OK... If anything sealing was "best" this way. I also held a batch of sleeves in reserve for "emergency repairs" that I would control use stringently.

I have used interference fit bushings with undersized ID's[or plugs] in each layer as suggested by liaisoneng... but again final hole diameters required for acceptable bushing wall thickness is always an issue... especially with thin edge margins [drift hole center away from edge where-ever possible]. The ID is always line-reamed last for a precision fit of fastener thru the stack-up. Note: the real reason for bushing wall thickness limitations is due to practical issues: thin-walled bushings placed in significant interference tend to wrinkle/distort on instl; thick walked bushings reamed to final size may dislodge and spin when reamed; or they are made of bar-stock that could crack longitudinally. CAUTION: certain materials such as 7075-T6 and 7178-T6 cannot tolerate too much interference [without cold-working], due to high potential for Stress Corrosion Cracking [SCC].

The "best" deal Ive heard recently is an innovation coming out of Fatigue Technology [FTI, 206-244-9886] that "force-mates" repair bushings in place [cold-expansion technology, using various bushing materials]. This technology provides temendous fatigue enhancement, along with the potential for installing original [nominal dia] fasteners in transition fit or close-reamed fit in the bushings... without worrying that they will be pushed or spun-out. The bushings are essentially swagged [cold-expanded] into the holes... which also receive the benefits of the generic cold-expansion technology. The undersized ID of the bushing is then reamed to final diameter and a nominal diameter fastener installed. Thin walled bushings can be allowed with high strength materials. Net fit fastener installation is possible... but a very tight close-reamed fit is still advised. Regards, Wil Taylor

 

[donengr]

Oversize hole: Using oversize fasteners or freezeplugs for repair.

Running a stress analysis on a freeze plug runs into the "How brave are you?", scenario. Do you run the analysis using the plug as being homogeneous with the parent material or is your analysis based on the premise that the freeze plug is an oversize fastener in the material? Fatigue analysis has the same problem, is the plug homogeneous or a stress riser? The answers are interesting and depend on the beliefs of the engineer doing the analysis and the faith this engineer has in the emperical data.

Stress analysis is only one problem. Another problem is retention. Will mechanical retention be required or is the plug interference sufficient to retain the plug? A ridged outer diameter, how to calculate the stress risers? Inspection is another problem. If the plug is buried, mechanically retained, hidden, etc., NDI of the area shows the plug as an unknown anomaly and structure may have to be removed to resolve the anomaly.

By far, the greatest problem with freeze plugs is customer acceptance. My experience, with the customer paying money for the part, has shown very limited acceptance with this procedure. You may ask, "Why tell?" Ethics for one and customer inspection will eventually find it.

Oversize fastener repair has its own unique problems. How many can you place in a given area without running into hole out area being a problem? Does the oversize fastener(s) cause a hard point? Do your released processes, listed on the drawing, allow for oversize? If so, how many , what size, will the number cause a quality and/or a customer problem?

Misdrilled holes are a universal problem. The problem can come from machine drilling as well as hand drilling. The approach I recommend is to remove and replace, with repair being a distant second choise. Yes both manufacturing, trying to meet schedules, and management, trying to hold down costs, are going to scream. However, the down stream problems with repair are far worse. Using repair, you are responsible for the part structural integrity as well as the acceptance of the repair.

Donengr.

 

[liaisoneng]

I would agree with Wil, that the FTI cold expanded bushing system does look beneficial. We had a tech rep come out about a month ago to demonstrate. It seemed to address the issues of freeze plugging (is that a verb?) separate layers - i.e. installation of multiple freeze plugs and aligning them with their respective layers before they warm up and expand. The tech rep tried to stress the cold working benefits from the bushing process as well, but it was fairly obvious from his demo with photo-elastic material showing residual stresses, that the degree of expansion was substantially less with much smaller effective zone.

 

[WKTaylor]

liaisoneng...

I just looked at Your Bio... I think our paths have crossed, in our "past-lifes". The last Civil Service position I held was as lead engr (GS-861-13 Aero-Engr) at OC-ALC/LAY-SCP (Kadena AB).

Regards, Wil Regards, Wil Taylor

 

[liaisoneng]

Wil:
Your name doesn't ring a bell with me, but in looking at your bio I'm amazed it doesn't. I do know the current Kadena engineer (Dustin C.) fairly well from his time at Tinker. I'm sure you know Joe R. at Boeing in Midwest City. Since you're no longer in civil service are you with one of the -135 contractors (Boeing:Wichita or San Antonio, PEMCO)?

Best wishes,
Russ Davis

 

[liaisoneng]

Wil:
Forgot to mention that I was at Tinker for an extended TDY in the summer of 98 with OC-ALC/LCRA. Those were in my young and foolish Lieutenant days. We probably know quite a few of the same folks.
Russ

 

[WKTaylor]

Russ...

I'm at B-W.

I'm familiar with all the folks You've "noted"... and they know me. Definitely surprised we haven't met.

Regards, Wil Taylor

 

Look at Acres sleeves. J.O.King and Huck Mfg, (difficult to purchase) or locally fab'd similar subs. See Mil-H-5.

 

[Kenneth]

J.O. King had sold the ACRES Sleeve product line to Huck, who subsequently sold it to CLICK BOND (

http://www.clickbond.com/).

You won't find it advertised at their web site, but they're the people to talk to...