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Tubing for a car

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  • Tubing for a car

    When I was in high school I was in a class where we learned about technology, especially green technology, and we made an electric car. It was a one passenger car and we raced it against electric cars from other schools. It's been two years since then and I was thinking of doing it again on my own except making it a two passenger car but I don't know what size tubing I should use. We used aluminum tubing to lessen the weight and used tig welding for the frame. I love to tig weld but I don't know if its absolutely necessary for a car frame. Any suggestions for tubing size and welding processes and feedback or other comments would be greatly appreciated, thanks in advance.

  • #2
    Hi foreverAstudent

    In general aluminum tubing is not preferred for chassis material, especially for home built/backyard vehicles. Without knowing what type of vehicle you are designing (will it have suspension front and rear?) it is rather difficult to go into the different reasons why aluminum is usually not a good choice.

    When it comes to car chassis design the name of the game is torsional stiffness. That is how the chassis resists twisting between the front and rear suspension inputs. Theoretically you want the chassis to be so stiff that it will not flex during operation (primarily cornering). Then the question becomes what is stiff enough and what is to stiff, casing extra material to be used and thus extra weight.

    For vehicle performance what you really care about is your power to weight ratio. Therefore the lighter you can make a chassis for a given power package the "faster" your car will be.

    Although aluminum is much lighter than steel, its stiffness is ~1/3 of that of steel's stiffness (young's modulus). So in the end not much weight is truly saved when a specific stiffness value needs to be obtained. Additionally a few other things need to be taken into consideration with aluminum as well, including fatigue (both pre and post welding), fracture resistance, yield strength, etc....

    Unless you plan on doing some rather in depth analysis of your chassis I would highly recommend that you use 1020 or 1018 DOM steel tubing. These are both very common and suitable materials for chassis building. Furthermore you may have heard of 4130 or "chrome moly" as it is also called. Some principle applies to 4130 as it does to aluminum, unless you plan on doing an in depth analysis of your chassis, you will never really benefit from using these materials.

    Few other things that you want to keep in mind for chassis building.
    1.) Try to keep tubing members non bent, and load them in compression or tension only, not bending.

    2.) Increasing the diameter of a tube instead of increasing the wall thickness is a more weight effective method of substantially increasing "strength".



    As for welding.....

    Without knowing the specifics of your vehicle or what wall thickness tubing you will be using. I would look at either the TIG or MIG welding process. You could definitely TIG weld the entire chassis, no matter what the wall thickness is. If the tubing has thick enough walls you might be able to MIG weld it, just watch out for burn through. Also depends on what equipment you have available.

    Hope this helps.

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    • #3
      Thanks for the info, I was planning on having suspension in the front and rear, because I'm not a large manufacturer of cars or an engineer who knows how to use aluminum for a car chassis, I'll just go with the DOM like you suggested. All I have at the moment is a tig/stick welder anyway, I just asked about the mig to see what people would say. I'll post pictures when I begin making this thing.

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