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Cal-Fab Swingarm question XR200R

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I have a Cal-Fab aluminum swingarm that I ran on my 1982 XR200R. It cracked and I had it heli-arced. Do I need to get it heat-treated again and if I do was it constructed of 6061 or what was it so I can get it treated appropriately? Anyone know where I could send it to get heat-treated? I miss that swingarm-running the stock boat-anchor swingarm. At least it will never break! Love my XR200R- Simons 38mm forks w/ Fox single shock in rear. K&N aircleaner-rejetted stock carb-White Bros. exhaust. Great woods bike!

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Man I can't answer you questions on the aluminum heat treatment. I would say any machine/fabrication shop that works with aluminum could answer that for you. I would love to see pics if your bike. Aftermarket forks & SA on a XR200 has to be cool!

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The welding process applies a lot of heat to the surrounding area and the slow cooling anneals the aluminum, the next failure will be adjacent to the weld. Whether you need to heat treat the swing arm because you welded it really depends on if the factory heat treated the swing arm after they welded it ( I suspect not for cost reasons). Heat treating causes warpage and followon straightening operations are usually needed so I suggest just using the swing arm and keep an eye out for future cracks. What follows is a bit technical but it expalains in general terms the heat treating process for aluminum alloys.

Heat treating AL alloys is a complex process which differs by alloy and level of temper originally specified, both of which can be difficult for a consumer to find. Heat treating alters the size and structure of compounds in the alloy to change its strenght and hardness, measuing the hardness of the metal provides a direct indication of the 'state' of heat treatment. Here is an abstract on heat treating from a website, the link follows:

Abstract:

The term “heat treating” for aluminum alloys is frequently restricted to the specific operations employed to increase strength and hardness of the precipitation-hardenable wrought and cast alloys. These usually are referred to as the “heat-treatable” alloys to distinguish them from those alloys in which no significant strengthening can be achieved by heating and cooling.Heat treatment to increase strength of aluminum alloys is a three-step process:

Solution heat treatment: dissolution of soluble phases

Quenching: development of supersaturation

Age hardening: precipitation of solute atoms either at room temperature (natural aging) or elevated temperature (artificial aging or precipitation heat treatment).

http://www.keytometals.com/Article39.htm

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Posted (edited)

I just read that article.  Was it English?

Edited by socalxr
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Yes English but geeky. It is a short article that glosses over a lot of details and makes assumptions about the reader.  Do a wiki search of the heat treating terms  and you should find more readable discussions.

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Posted (edited)

2 hours ago, Chuck. said:

Yes English but geeky. It is a short article that glosses over a lot of details and makes assumptions about the reader.  Do a wiki search of the heat treating terms  and you should find more readable discussions.

Yea I was just kidding.  I've been reading a lot lately and there are no simple explanations.  I read one that had a about a half page of mathematical formulas. I have a swingarm, I may or maynot need to treat.  I saw that you wrote that 6xxx series softens to 4xxx after being welded, which still strong enough.  So I'm think I'm going with that.

garbage.JPG

Edited by socalxr

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What is interesting about aluminum are the unique characteristic of each alloy series, and which heat treat processes are best for each.  I doubt I would have equated a 6 series alloy to a 4 series alloy, anyway 6061 has 3 tempers, usually measured as hardness, they are -0, -4, and -6.  The heat and slow cooling from welding will reduce the 4 or 6 temper towards 0 temper.  6061 can be purchased in any of the 3 tempers but if you intend to weld it why pay the premium for other than 0 temper? And if the design was based on 0 temper strength you can save on the cost of heat treating.

Most  of this alloy stuff comes from aircraft design and manufacturing, and while nice to know the processes are too expensive to utilize for other applications.  I ran across a well written  article by a Marine Engineer about the strength of aluminum vs steel: http://www.kastenmarine.com/alumVSsteel.htm   

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Yea, I think I misread what you wrote: "I think the welding heat anneals it to T4, if that temper is OK for the application then why bother taking it to T6."  It was back is 2012.  I was read A few posts about heat treating on here.    I think I'm go to just run it.  I don't ride very hard anymore.  

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Im a welder and try to avoid aluminum repairs because of all these issues. When possible I do a repair with additional reinforcement because it was obviously not strong enough in the first place. I did assume and maybe Im wrong that all OEM stuff is heat treated. I know that BBR heat treats their frames. I run a swingarm I extended without heat treat but I added a plate over the splice, I inspect it constantly and I wouldn't sell it that way but its fine for me to use.

As chuck stated heat treating is fussy and they will not only want to know the exact alloy but also the welding rod alloy used for old and new welds.

Guys who weld cracked rims or things like brake pedals, shifters and levers are nuts. A lot of welds aren't stressed but its important to know which ones are. If an existing part broke, Assume it needs some additional reinforcement along with the new weld. 

I just can't imagine anyone would sell a non heat treated Hayabusa stretched swingarm but I've been wrong before. I think distortion during heat treat is actually because the stresses are relieved. An OEM arm would of course be machined after heat treat. 

Aluminum is a poor choice for dirt bikes in my opinion because of the fatigue life. You can build a frame or swingarm from higher strength steel that will match the strength and stiffness of aluminum and it will last much longer. Steel is also easier to repair and modify. Kudos to KTM for not going along with the market hype and staying with steel frames. Their cast swingarms however are on the heavy side and fairly brittle but they look sexy and cost less.

Anyone pondering an engine swap project should start with a steel framed donor bike to make life easier.

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All good points. I do like my aluminum frame CRF250X for its stiffness but for a  conversion I prefer a steel frame.  My background is aerospace Manufacturing Engineering and I just can't imagine the OEMs spending the time and money to heat treat and then straighten their aluminum stuff. Plus if you design for T-0 material  you can avoid those cost.  Also the OEMs weld cast and extruded material together so they are working to the lower cast strength.
It is modern aircraft design that has all of the esoteric alloys and mfg processes, and the alloys used are a very small part of the total aluminum market.

Some of small J aluminum parts are pressure cast and contain a lot of hydrogen and as a result are very difficult to weld.

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Chuck, your logic sounds good but I still wonder,.. my BBR frame is built heavier than an OEM frame and its still heat treated. A frame with its closed loops pretty much contains the welding distortion and subsequent stress relief of heat treating. As long as you machine the headstock and swingarm pivots after I don't think there is a straightening process?? These are all assumptions on my part.  My bike came with a broken motor mount because the previous owner left out a small spacer. BBR had a flat $200 fee to fix any repairable frame and send it through heat treat again. Presumably the only distortion was limited to the newly repaired area because they never mentioned straightening or machining. I welded it myself with reinforcement and no heat treat.

I remember that the warranty rate for Cannondale bicycle frame was many times higher than steel frames. Honda at one point went too far with stiffness and factory riders preferred previous year frames. Now all the OEMs are slimming down the frames again and preaching selective compliance. They do this with careful FEA to eliminate stress points. Moto GP is all about selective compliance in the swingarm and front downtube to allow lateral flex only while maintaining torsional stiffness

With aluminum its a fine line to walk between stiffness and deflection that results in fatigue. The engineers keep staggering back and forth across that line until they find the limits. Its a shame because every ounce of weight loss these days just goes to compensate for added technology so bikes from the 70's are still lighter than today. KTM just avoids the issue and has the lightest most reliable frames using thinwall forged areas with tubing. KTM sticks with cast swingarms but the failure mode is terrifying, see youtube for proof.

Aluminum done right can be very good but so can steel at a lower price and longer life. There are new steels optimized for frames like Docol R8 which is what I plan to use for my next frame. Its 10-15% stronger than 4130 with better properties in the weld area.

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BBR's home in Auburn WA is in the middle of the PNW Aerospace Industry so I can understand the influence.

A simple hardness test will indicate the temper of aluminum; Brinell Hardness for 6061-T6 is about 90, 6061-T4 about 60, and 6061-T0 in the 30s.

If I were to do a clean sheet chassis design/build it would not be aluminum, it would be steel. Aluminum can save about 35% weight for the same stiffness but IMO the fabrication complexities and fatigue resistance make steel a better choice.

 

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On 3 May 2009 at 11:33 AM, Footy said:

Man I can't answer you questions on the aluminum heat treatment. I would say any machine/fabrication shop that works with aluminum could answer that for you. I would love to see pics if your bike. Aftermarket forks & SA on a XR200 has to be cool!

Lets see some pics please.

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I had the swing arm heliarced after it cracked in 1989 and then it cracked again in same spot right away. Then I put the boat anchor stock swingarm back on where it remains today. About twenty years ago I contacted Scott’s down in Pasadena about the swingarm and they referred me to a person who heliarced it again for free but this welder told me I needed to get it re-heat treated or it would crack again. Hence my search for someone to do just that. I sure as hell don’t want to go through the work of putting it back on to just have it crack

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Good luck finding someone. Its a very specific treatment and they will want to know the alloy of the swingarm and welding rod used before they can do it. Even then, the factory weld was heat treated and it cracked so no reason to expect the problem to go away unless you reinforce it. 

 

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On 7/5/2018 at 11:59 AM, Chuck. said:

BBR's home in Auburn WA is in the middle of the PNW Aerospace Industry so I can understand the influence.

A simple hardness test will indicate the temper of aluminum; Brinell Hardness for 6061-T6 is about 90, 6061-T4 about 60, and 6061-T0 in the 30s.

If I were to do a clean sheet chassis design/build it would not be aluminum, it would be steel. Aluminum can save about 35% weight for the same stiffness but IMO the fabrication complexities and fatigue resistance make steel a better choice.

 

The way I understood was that Aluminum is a third the weight and a third the stiffness of steel when looking only at the properties and not the construction. If the frames were built exactly the same that is what you would get. A super light noodle.

Nobody wants a noodle frame so you add back some more aluminum to increase tubing diameters and thickness to gain some stiffness. Its a juggling act to trade weight for stiffness but by the time you match the stiffness of steel you usually end up the same weight or slightly heavier depending on the design. That is the common situation with bike frames now. Assuming they have similar stiffness. KTM frames are the same or slightly lighter than the average Alloy frame. 

There are good and bad examples of frames in both materials but on average over many years Its been about a tie. The aluminum is preferred by marketing guys because its sexier but the manufacturing and warranty guys hate it. Steel is boring but cheaper and more durable. I like steel because I can repair or modify it more easily.

With aluminum,.. castings worry me the most by being brittle,.. billet is better with no porosity or inclusions but forged is by far the best . Ever try to straighten a forged KTM brake pedal, pretty impressive strength and ductility. Forgings are also the best way to shape steel parts when possible. KTM uses thinwall steel forgings in their frames, then they blow it with heavy cast aluminum swingarms. People are so used to seeing massive swingarms now I don't think they could accept a steel one even if it was stronger and lighter. Sadly the styling, accounting and manufacturing guys dominate the design process these days. 

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The Marine Architect article in my previous post explains how differences in the characteristics between aluminum and steel affect dimensions and weights, and while aluminum is 1/3 the weight of steel its strength and flex values are much lower so more material is needed to equal the performance of steel. This results in only about a 35% overall weight saving with aluminum.

The 84-95 XR250R and 84-02 XR200R swing arms all interchange but the aluminum versions, for drum or disc brake, are about 35% lighter than the steel versions.   

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Posted (edited)

Chuck,.. You got me on that swingarm example but it was a bad example. You won't find two modern MX frames for instance that are anywhere near 35% difference. Other than a thickness difference, those two swingarms have pretty much the same physical design which means one or the other is not optimized for its material.. I suspect in that instance they are not even close in stiffness. I think the stylists oversized the steel arm to "look" more like aluminum. The part that shocks me most is the massive cast steel suspension rocker on the xr200. There is no way in the world to justify that blatant use of excess weight other than ignorance or cost. It appears to be designed for aluminum and then cast in steel to save money.

Bicycles being essentially all tubing can better take advantage of larger diameter thin wall tubing to use the aluminums extra available volume of material. In that case aluminum frames can reliably come out a tiny bit lighter than steel but nowhere near a 35% difference.

The only time you can find that kind or weight difference between aluminum and steel frames is if you compare a modern alloy MX race frame with say a steel  XR or DR trail bike frame where weight savings was not a priority. Apples to oranges. In Moto GP where cost is no object and weight means everything, a Ducati steel frame is still closely matched in weight and stiffness with aluminum. 

Sorry for the ramble,.. when it comes to weight savings you just have to be obsessive to make a big difference. I would trade a kidney for a 35% weight savings if it were that easy.  

Edited by woodsryder

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In the marine link above the 35% weight saving is the result of converting steel designs to aluminum for the hulls, and is similar to the differences in the swing arms I posted. The examples are not a complete MC or boat so the savings will be a much smaller proportion of the total vehicle weight.   Because aluminum has less fatigue life than steel it must be designed for less flex which means more material and more weight than if designed for strength only, which is probably why the aluminum MX frames weigh so much. Also they are stiffer than typical steel frames so design goals may have been different.  Have said that I have a Honda Montesa Trials bike and the the aluminum twin spar frame  weighs 14.3lbs.  

I don't have a lot of swing arm weights but here are a few:
84 XR250R steel   x 11.44lbs (86+ XR200R weigh the same).
89 XR250R AL (drum brake) x 8.09lbs
90 XR250R AL (disc brake) x 7.89lbs
89 RM125   AL x 8.60lbs
98 XR600 AL (1" longer than 88 XR200) x 8.6lbs
And a Trial bike; Montesa 315R  AL   6.46lbs

Yes I was astounded when I first examined the linkage on a 90 XR200R, it was as if Honda did a U turn on the little R and decided cost was more important than weight. However 84-85 XR200R/250R and 86-88 XR200R linkage are aluminum and weigh 2lbs less than the 90+ steel version (close to 50% difference).

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