How to bend aluminum i beams?

Discussion in 'Materials' started by Steve W, May 11, 2008.

  1. Steve W
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    Steve W Senior Member

    So i want to build a large aluminum sailboat trailer and have been looking a commercially made tandem and triple axle examples around the marinas and taking dimensions and what strikes me is that
    a/ they are all bolted together,this is obviously because aluminum welds are not as strong as the parent metal.
    b/they are typically made from sizeable i beams rather than channel or rectangular sections like the typical steel trailer.
    c/The outer fore and aft members run parallel to the centerline from the aft end and then are take a gentle bend in to the tongue.
    This is where im having trouble,how do they do that? so i was wondering if anyone here has any knowledge of how this is done.I havnt been able to find anything online.
    Steve.
     
  2. Steve W
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    Steve W Senior Member

    Sorry, i should have mentioned that what i want to bend is 8"x4" beam in the sideways dimension,the 4" dimension.
    Steve.
     
  3. murdomack
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    murdomack New Member

    They probably heat it up to anneal it and bend while it is in the annealed state. Different grades have different annealing temperatures. I haven't done anything like this for over 40 years when I assisted my journeyman to bend some large bore aluminium pipe.
    They had all sorts of tricks back then to get the right temperature which involved soot and certain types of wood, but today a Tempil stick for the required temperature will tell you when it is hot enough. How all this affects the structural strength, given it's a trailer, you will need to research as well.

    It might be possible to cold bend it in a series of small bends by setting up a hydraulic bending jig that will keep the flanges in line as you apply the bending force. As it is only 4" flanges, I would try this way first. You may find that it forms without applying heat.

    Setting up to bend the beams will need some equipment and if you do not have it there should be fabrication shops near you who will do this kind of work. It may be cheaper to get them to do your bends than acquire the tools to do it yourself.
     
  4. rwatson
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    rwatson Senior Member

    I have seen the types of trailers you mention - none of them were annealed as I recall.

    My gut feeling is that you could build a jig out of timber and then use large cramps to pull the bend into the beams quite easily. I would also fasten some strong timber to the sections that are meant to stay straight so the bending didnt induce curves into the straight bits.

    The type of aluminium would be very malleable, and as you say, the bends are fairly gentle.

    The big bonus on these trailers is not just the rust free beams, but the rubber mounted suspension instead of those problem prone steel leaf springs.

    The MacGregor yacht company now uses them as standard equipment for their 26 footers

    http://www.macgregor26.com/aluminum_trailer/aluminum_trailer.htm

    Their sections are I beams, 3 ½” x 5” with .280" flanges
     

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    Last edited: May 15, 2008
  5. PAR
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    PAR Yacht Designer/Builder

    I've seen these beams bent and it's done with a cleverly arranged set of rollers in a press. The aluminum is bent just like a mandrel pipe bender, except the "I" shape is maintained by shaped rollers, both male and female. It takes a huge amount of force to do this and I don't think you could do it with wooden dies or backyard methods.
     
  6. murdomack
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    murdomack New Member

    I agree with what PAR says here. If you look in the MacGregor website attached above and blow up the photograph of the bent rail you will see that the flanges are losing their shape and seem to be flaring out on the inside radius. These were probably done on a proper machine and are still not too good.
    If you have the equipment, a solid steel baseplate to weld off, powerful hydraulic ram and plenty of heavy steel and pipe to make your former and flange guides then you could try it. If you don't have all this then it will be cheaper to get them done in a fabricator's. I've checked the UK websites and there are about 20 companies spread around the country who bend aluminium beam.
    Why not weld them and add doubler plates if you think that it would not be strong enough with normal welding.
     
  7. Steve W
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    Steve W Senior Member

    Hey,thanks for the comment guys,i tend to think the bends are probably done with rollers as PAR said.I looked at one in our marina again and it is a fairly big one,triple axle about 18000gvw,and the bend is very neat with no kinking or buckling,what i did notice though is that at the point of the bend there is a galvanized steel crossbeam with ends that are shaped like they may serve as a former for bending the i beam around.The aluminum i beams are 8"x4". Im starting to think that with some kind of jig to keep the flange from buckling as rwatson suggests may work,what i would have working for me is leverage,my beams would be about 25ft long with the bend in about the center.I would certainly consider having a fab shop do it if i could find someone capable but so far no luck.We actually have at least 4 such trailers in our marina from several different manufacturers an all are with bolted together any weling done on steel members that are then galvanized.What i havnt seen yet is a sailboat trailer for deep keel boats made from alluminum.
     
  8. rwatson
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    rwatson Senior Member

    I cant prove it, but I would be surprised if the MacGregor beams werent just bent manually.
    They used to do it with the old steel rails, so I imagine they would want to be able to manufacture their own trailers still.

    The buckling is very minor, but if that is a problem for a fastidius trailer owner, you would probably be able to 'adjust' the buckle with a suitable piece of steel to lever it into shape *after* the bending has been done.

    I think the secret is to keep the radius as large as possible and do it very slowly. Aluminium, being so light, would be too difficult to keep at the right temparature to make heat treatment useful.

    I think if you are needing to load a deep keel trailer, you would probably have a suitable steel edifice built to sit on top of the aluminium, and bolt it on. Sort of destroys the aim to rust proof the whole trailer, but at least the steel structure could be unbolted and thrown away for a new one when the time comes.

    Of course, you could go along to one of the trailer manufacturers and just buy one! A novel concept, but it has worked for me in the past :)
     
  9. Petros
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    Petros Senior Member

    there is no easy way to re-heat treat a beam that big if you anneal it. there are different alloys and different heat treats that can be cold worked. My guess is that it is a T-5X heat treat which is not at strong as a T-6 but it can be cold worked without ill effect and still have its strength. There are also weldable alloys too, so yes alumnium can be welded without heat treat too, you just need the right kind.

    Where do you live? I know a shop not far from where I live than can bend beams like that (there may even be one near you). I am in the north part of Puget Sound in WA state.

    It might be possible to mount the beam between two large trees and pull on it with a winch or even your truck to get the shape you want. The trick I think without heavy tooling is to find a way to hold the beam while you bend it. You need something that will not move while you pull on it. If you do it carefully you might be able to do it with out a hydraulic jig, just a handy truck bumper to pull on it with. If you use lots of blocks of wood to hold it in place, and your bend is not too large it can be done. Perhaps drive a car on it bridged between two large blocks? With the correct alloy (one suitable for cold working) as long as you keep it strait bending it will work fine.

    Wikipeidia has some good general information about the properties of different AL alloys, also a stock supplier can usually tell you what alloy and heat treat are used for your application. Get something that is reasonably corrosion resistant too (not all AL alloys are, the high strength stuff turns to dust in seawater!)

    Good luck
     
  10. murdomack
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    murdomack New Member

    Steve W
    "what i would have working for me is leverage,my beams would be about 25ft long with the bend in about the center."

    Levering the beam round is not a good idea, unless the bend area has been made softer than the rest of the beam, it will not end up as a uniform bend. For cold bending without a properly designed machine you need to push a former at the center point of your bend with the beam held back at two points equidistant on either side. These points should be round or pivoted so that your beam can move freely.
    As an alternative you could remove the flanges from the beam, say 6", at the bend area and bend the web. Bolt on doubler flanges and even add a doubler to the web. Your doubler flanges could be triangular adding even more strength.
     
  11. Steve W
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    Steve W Senior Member

    Thanks for the responses, just to clarify,i cant just buy a trailer of the type i have in mind, to my knowledge no manufacturer in the US makes such a beast so i have designed my own which, if it works out as planned i will try to market.
    What i have designed is a trailer which will be able to pick up a deep keel sailboat up to about 12000 lbs off of jack stands at a marina and allow the owner to transport it to his driveway behind a pickup truck and set it down again on jackstands freeing up the trailer to go move another boat.This will be kind of a simplified consumer version of the hydraulic trailers used by commercial haulers.
    What has prompted me to design this trailer is my personal distaste for having trailers which spend all winter with the boat sitting on it and all summer sitting empty.I have 2 sailboats and 2 such trailers which could be consolidated down to 1,which makes me think that a few boat owners (or a yacht club) could share in such a trailer making it quite economical.
    So,im trying to decide whether to build in steel or alluminum,so i dont mind spending a bit of money building a steel assembly jig which can aid in the bending or as par suggested,building a hydraulic bender which could be similar to the tubing benders you buy from Northern tool or harbor freight but larger and with suitable formers.
    Steve.
     
  12. Steve W
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    Steve W Senior Member

    Oh,and if i could find a fab shop in the Twin cities area in Minnesota who could do the bend for me that would be a good solution but so far no luck.
    Steve.
     
  13. rwatson
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    rwatson Senior Member

    While the big beam aluminium has the ability to stay rust free, I wonder if it is worth the trouble in the scenario you describe.

    In my mind, the big aluminium beams and springless axles were developed for the trailer sailer that only needs a flat bed to store and launch from, and for long reliable highway use.

    For marina use - and especially for large keels boats, the large beam alumunium doesnt seem to be an ideal solution, given that you will need a lot of extra framing to keep the boats supported.

    If the rust problem is severe enough to warrant the expense, then I suspect an aluminium tube space frame type of construction would make a lot more sense, and avoid all this bending angst.

    With galvanizing, and all the modern protection you can get for steel though, and the ease of being able to weld, maybe the steel solution would be best in this situation.

    Rather you than me making the decision :)
     
  14. Steve W
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    Steve W Senior Member

    rwatson,all the aluminum trailers around our marina are large tandem or triple axle with load ratings of 10000lbs or more,indeed one has a 34ft sea ray on it,its rated at 18000lbs, so they are not just for trailer sailers. The reasons that im looking into aluminum are as follows.
    1/ a lighter weight trailer gives a higher load capacity.
    2/ i think that less welding will make for quicker assembly,maybe.
    3/ much less work when you dont need to paint it,this is huge.
    4/ Cost, while aluminum costs more per pound it is 2/3rd the weight of steel coupled with the very real cost of either having to paint or galvanize the steel trailer i think the alloy trailer will cost out cheaper. remember ,there are a lot of man hours in properly prepping and painting steel and paint supplies are not cheap either, most commercially made trailers have half assed prep work which is why they start rusting almost immediatly.Galvanizing which would be preffered is another can of worms,its not going to be inexpensive to do a frame this size,the nearest place with a big enough vat is in the next state and the cost to transport the frame there and back i expect will make it much more expensive than alloy.
    5/ perceived quality,the fact that they dont rust means they always look good wheras a painted trailer is going to take a lot more upkeep if its not to end up an eyesore so maybe its not just perception.
    I have got pricing last week on the 8"x4"x25 ft i beams and was pleasantly supprised, less than $500 per beam(i need 3) A lot of priceing still to do though.
    Steve.
     

  15. murdomack
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    murdomack New Member

    Steve

    This film will give you an idea of what you need. You could make the former and the capstans double wheeled to suit your I beam or just do a bit on top and bottom flanges alternately with this kind of set-up


    http://www.youtube.com/watch?v=dpcDY9UO5vY
     
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