Everything2Stroke - Hydroforming Expansion Chambers
  • Hydroforming Expansion Chambers

    Just a very quick rundown:

    With free form hydroforming (pressure washer style, not die forming), the smoother the outside radius the better. A pipe with lots of twists and turns isn't going to be best for free form hydroforming but there are some cheats around that I'll discuss later.

    Mgty3whlr, you basically hit the nail on the head. The only thing I have to add is to not skimp on the cutting method, hand shears are going to make a more jagged edge which is going to make it more likely to buckle during inflation.

    I used a woodward fab rotary shear:



    It works like a gigantic can opener, rolling the metal between a smooth roller and a serrated roller. It's throatless and the work side is the one rolled against the smooth roller so it's smooth. The leave has a serrated edge on it but it's not a huge deal.

    This was going to be an OOF pipe for a drag trike so shape was, for the most part, unimportant but I can tell you I shaped and reshaped the inside and outside radii several times to make it easier to cut and pump up.



    There are several things to keep in mind here. When you pump it up the difference in inside radius and outside radius means that the pipe will "contract" in on itself. I'm sure there are some very complicated mathematics that can quantify the amount of change but I left passed trig a while back and have no desire to revisit that crap....my advice? Just wing it, the more change between the inside and outside, the more it's going to contract.

    The other thing that changes is the tuned length based on the cone angles. The pipe designing program does NOT take into account the changes so I had to do them offline. I did some real quick and dirty math to figure out the difference, pythagorean theorum states that the square of the hypotenuse is equal to the square of the other two sides. We know the other two sides of each cone, Length and Radius (radius being half of the given Diameter) so I figured out how much longer the hypotenuse (the outside metal of the pipe) needed to be roughly and added the extra metal to the sheet before I cut it. Now I say "roughly" because unlike a rolled multi stage cone, the cones on this pipe are smooth transitioning (not a real difference in power, just a difference in the "start" and "stop" of the right angles). For the purpose of this discussion lets assume that the calculations were perfect and lay out a table of "corrected" Length and Diameter for the given pipe.

    Now, we still can't start cutting.... we don't actually need Diameter now, do we? The pipe we're drawing needs to be half of the circumference wide and the "corrected" length, long. Recalculate (promise, this is about all of the math which, so far, has only been marginally harder than balancing your checkbook) the table by multiplying given Diameter by Pi and deivide by 2. Then record the new pipe design table as Length and Circumference (really, half circumference but I need something to call it that makes sense!).

    Start off with a full sheet of 18-20 gauge steel. 18 is easier to weld, 20 is easier to pump. I had a BOSS 11hp honda pressure washer at my disposal so I went with 18 gauge sheet steel so I wouldn't have to fret about the weldling as much.

    Draw the "center" of the pipe in a shape which you think you can make your pipe work with. Remember that we're making a 2D "ballon" so 3D turns will have to be sliced and turned later to make the pipe fit into tight areas. Just go into the drawing stage with an idea of what the 2D balloon would need to look like to include the turns needed. Make the center line the "corrected length" long and put a mark at each of the Length measurements as you go.

    At each Length measurement, using a ruler, measure out from the center line at a right angle to the Circumference measurements and make marks. This is where a well laid out pipe design will shine and the first time you make one you'll realize how far down the rabbit hole you actually are Alice... If everything is the correct shape, you should be able to connect the Circumference lines by drawing a nice smooth transitional line between each mark. What you end up with should look, more or less, like this:



    Obviously that's a VERY simplified pipe and I've already plasma cut it out from the main sheet but you can sort of get the idea.

    A few notes: Leave a little "tail" at the tip of the tail cone for the puckering that will happen. The tail cone won't be perfectly round (more pictures in a bit) and leave a "spade" at the headpipe end for forming around the fitting and drawing in that will happen as a result. You can see the spade left in the picture above but I didn't leave enough of a tail on the tailcone for this pipe.
    This article was originally published in forum thread: Hydroforming Expansion Chambers started by sicivicdude View original post
    Comments 18 Comments
    1. sicivicdude's Avatar
      sicivicdude -
      Now, using the shear, go right down the outside line. Work slowly and if you make a mistake, don't go back and start another shear line because you won't be able to weld the new shear line to the old on in any meaningful way, just continue on and slowly get back onto the line (OBVIOUSLY patience is a virtue on this part of the process).







      Now, once pipe half #1 is all cut out, it's time to duplicate. I paid it down on the rest of the sheet and drew it out with a marker carefully. I thought about using lineman's paint to spray it real quick but didn't figure I could hold the original down tight to the sheet well enough not to get overspray. Anyway, just make sure the two cutouts are friggin identical because it makes welding on the edge much harder later if they're not....

      #2 drawn out and plasma'd from the sheet:



      AND two copies:



      Aside from the math, this process should have taken about an hour or two. Obviously if you have a very complicated pipe in mind, the initial drawing might take much much longer but using the hand rolled cone method, in this amount of time you'd have a handful or rolled and tacked cones laying there and not much else....

      Lay the two sheets down on a flat workbench (You see I switch over to my presto worktable for welding, plywood is just for manipulating and plasma cutting out of the whole sheet) and see if the shear warped them too bad. The woodward fab shear I was using did a pretty slick job but once the shear gets out of whack, it can roll the edges of the sheets down pretty bad resulting in a little "break" which will then twist the sheets. The fix here is a light smack with a flat nosed hammer to tweak the sheets back flat before continuing.



      Seam weld the edges together using a 1/16" or .040" tungsten on 25 amps or less and using mig .030"-.035" ER70S wire as the filler. Work slowly and DO NOT melt the sheet away, undercut at this point will be a kink in the pipe later.... Start welding at the end OPPOSITE of the end you are going to put the pressure washer fitting into (usually the headpipe end) and work your way, slowly, towards it. As you get to the "spade" weld the outside edges of the spade only to hold the pipe from shifting during the next step.

      I do not have a pexto stake table (but good lord do I wish I did ;) ) so I improvised. I put a piece of 3/4" or 1" round rod in my vise and used that. What you want to do is make two kinks on each side of the very tip of the spade so that you can weld the sheet steel around the pipe fitting as tightly as possible. What you want is the pipe fitting stuck in there with the sheet steel welded up to just beside it with no huge gaps to try to fill in. Fill is going to result in a more uneven surface later. Granted, the spade is designed to be cut off but why tempt fate if you don't need to?

      Once you have the pipe nipple welded into the pipe (get it? ) install an adapter to the hose fitting for the pressure washer.

      For the actual pumping process, I borrowed an additional length of pressure rated hose and purchased an additional adapter for my wand so I had the normal 50' hose from my pressure wash hooked to the handle part of my wand (making the control valve, there) and then hooked an additional 50' or pressure washer hose to the handle instead of the spray nozzle to run out to the pipe.



      Unfortunately, I was working alone that day and didn't get any pics of the actual pumping process but it was uneventful.... The pipe pumped slowly until it got full and then a pinhole opened up on the backside and it released the pressure. No explosions, no loud bangs, not even so much as a funky noise while it was going.





    1. HondaATC's Avatar
      HondaATC -
      Very Cool! Thank you so much for sharing as this is something that has kept my mind curious for a while, couple questions.

      How exactly do you convert the "rolled section" type pipe like I made, dimension wise, into a flat template? I'm atrocious at math, and even trying to figure this out makes my brain turn to mush


      Something you may try I saw on another forum is also bending a a short 90 on the seam and welding it that way, supposedly when it starts forming, it allows the weld bead edges to flatten out a lot more.

      I'd really love to try building one of these next...
    1. mgty3whlr's Avatar
      mgty3whlr -
      beautiful job... just takes finesse..
    1. mgty3whlr's Avatar
      mgty3whlr -
      Did you have issues with specific sections "buckling" ? I saw this technique being done on youtube...years ago..."do it yourself" go figure ! But it was kinking at some areas.
    1. sicivicdude's Avatar
      sicivicdude -
      HondaATC, you have to convert the Length and Diameter table into a corrected length (for the angle of each cone) and Circumference/2. It's not an enormous amount of math but it is some you'll have to sit down and do for this process to work.

      Here are the calculations for corrected length:



      Half of the difference between D1 and D2 is A

      L1 is B

      Corrected length is C
    1. sicivicdude's Avatar
      sicivicdude -
      Once you have each corrected L1, you need half the circumference (you are trying to make a balloon, in order to get a given diameter, you need material equal to half way around the balloon on each side). Getting circumference is the diameter on your 2 stroke wizard printout times 3.14 and then halving that. In this way, you should be able to calculate (with minimal mathematical skills) the desired length and width of the pipe template for laying it out.
    1. FrankieJames7's Avatar
      FrankieJames7 -
      beautiful work.
    1. sicivicdude's Avatar
      sicivicdude -
      And here's the final product:

    1. mgty3whlr's Avatar
      mgty3whlr -
      That pipe came out beautiful !
      Just curious, what was the total amount of time to make the pipe ?
    1. sicivicdude's Avatar
      sicivicdude -
      Half day including drawing the first version about 40 times. It took about 2 hours to cut and weld and about 10 minutes to pump up.
    1. mgty3whlr's Avatar
      mgty3whlr -
      Not too bad for a day's work.
      It's gotta be pretty cool when someone comes up to you and asks.... Who built your pipe ? and you say... I did !

      When the weather gets a little better here, I think I might give it a try.

      Did you use a 2-stroke pipe program like bimotion, tsr...? to get your dimensions or did you just use the formulas from Bell's, Jennings, or Blair's books ?

      Joe
    1. sicivicdude's Avatar
      sicivicdude -
      We already had that happen. The trike was taking out 450's, rappy's, 250cc dirtbikes.... one of the guys walks over and said "my god that things fast, who built it?!"

      I just smiled and Nate just pointed over behind him and then pulled his helmet back down for another pass.
    1. sicivicdude's Avatar
      sicivicdude -
      So as far as the design, the beginning was humble. Tuned length calculations were done for the engine as designed. I then used 2 stroke wizard to get a design I was hapoy with. The hand calculations were used to confirm the 2 stroke wizard design (it lined up quite well) before any drawing took place
    1. HondaATC's Avatar
      HondaATC -
      Great information...I will endeavor to try building one of those hydroform style sometime, has that sectioning mess is for the birds, haha.

      Nice to hear you used the 2 stroke pipe wizard program with good success, as that is what I used on mine also but haven't gotten to run it much yet.
    1. mgty3whlr's Avatar
      mgty3whlr -
      Did you get the Honda/rotax motor fired up yet ? Just wondering how you made out with the hybrid set-up ?
      I know it was a lot of work including the custom pipe...Welding and fitment !
    1. HondaATC's Avatar
      HondaATC -
      I got it to fire off a bit in my test stand, but haven't gotten it in a bike yet. I really do need to update my thread here I guess!
    1. mgty3whlr's Avatar
      mgty3whlr -
      kool ! keep us posted on the progress !
    1. Morph0906's Avatar
      Morph0906 -
      update with pics!!