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  1. #1
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    What is a 'Forged' dropout?

    People talk about 'Forged' parts, and I have absolutely no idea what that means.

    What is 'Forging'? And what's the difference between that and the 'other' sort of drop out?

    Lastly, does the 2007 Chameleon have that?
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  2. #2
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    I am immune to your disdain.

  3. #3
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    Forged aluminum dropouts..they pretty much compress all the molecules in the metallurgy process. It makes them less prone to cracking and more prone to bending, as well as stronger overall and potential for less weight.

    The counterpart would be a cast dropout, basically just pouring molten metal into a mold and letting it harden. Much cheaper
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  4. #4
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    Quote Originally Posted by kuksul08
    The counterpart would be a cast dropout, basically just pouring molten metal into a mold and letting it harden. Much cheaper
    I think forged dropouts are usually steel.

    Also, my guess would be that the cheaper counterpart to forged dropouts is going to be stamped. Just cookie cutter a piece of steel.

  5. #5
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    Aluminum is forged as well. The lower VPP links are now forged rather than extruded.
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  6. #6
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    I didn't mean to imply aluminum can't be forged.
    I guess I really mean dropouts are usually steel.

  7. #7
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    Quote Originally Posted by zfeldman
    I didn't mean to imply aluminum can't be forged.
    I guess I really mean dropouts are usually steel.
    Depnds on what the rest of the frame is made from usually.

  8. #8
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    Forging is a process where, basically, you take a lump of metal and smash into between two hardened dies that have the negative shape of the thing you want to come out. Basically you smush the metal into the shape in the two dies using a huge press.

    Forging does change material properties, but its not simple how. It depends on the material, and the heat. "cold forging" is when the material is below 1/2 of its melting temperature when its forged. The terms "warm" and "hot" forging are used also. Hot forging is when you don't get any mechanical property enhancement because the material is so hot, the atoms just move around back to where you smushed them to. Its the smushing when they can't move that makes the material stronger.

    Lots of times, wrenches are cold forged. Sometimes bicycle cranks are cold forged. Why? Because you want the added material strength, and it makes a part that is close to the shape you want in the end. Cold forging requires much larger presses, and it also limits the shape of the finished part, and the amount of "flow" the material can go through.

    Hot forging is how a lot of aluminum bicycle frame parts are made (shock mounts, dropouts, etc). Since the frame is welded and heat-treated, any strength you can add by cold forging is canceled after welding and heat-treating. So you'd just waste money.
    Why forge instead of machining? You can get complex shapes that are hard to machine (think swoopy surfaces), and its more friendly for medium to high volume production. Most small manufacturers don't want to invest a bunch of money in tooling up front, so they stick with machining. The parts cost more, you don't have to pay for tooling up front, and the shapes are limited. Forging costs more up front, the parts are cheaper to buy, and the shaping is not limited.
    Forged parts get machined afterward, so you can have machined surfaces as well on a forged part.

    Steel frames typically use cast parts, not forged. Again, heat, welding, and cost issues.
    Aluminum frame parts are never cast, since casting is not a good choice for high-strength and low weight. The alloying impurities caused in a slow cooling process (from sand or investment casting) would come out during welding and alignment. Plus its not any cheaper.
    Die-casting, which is a lot like plastic injection molding, requires very expensive tooling. Imagine a molten stream of aluminum shooting out at high pressure! Its sketchy, so the tools are very nice, and very expensive. Die-casting gets less impurities in the final part, but limits part geometry, because like injection molding, the wall thicknesses have to be very close thru the entire part or part shrinkage isn't uniform during the fast cooling that is possible when using a cooled die in a production die-casting environment.

    Often, the only difference between an "extruded and machined" part and a "forged" part is the process used. That is typically decided based on part cost, tool cost, expected number of units to be produced, as well as the possibility of different shapes. For instance, an extruded and machined lower link would have lower tooling cost, but higher part cost, and it has to be a constant cross-section in one direction (at least initially).
    The forged part has to be able to be pulled out of a simple die, would have lower part cost, but probably around 3-5 times the tooling cost.

    Hope that helped clear things up a bit.

  9. #9
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    thanks 11 yo. that was very informative.

  10. #10
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    Quote Originally Posted by SC_Eric
    thanks 11 yo. that was very informative.
    I second that.

    Thanks dude.
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  11. #11
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    Quote Originally Posted by eleven-yo
    Forging is a process where, basically, you take a lump of metal and smash into between two hardened dies that have the negative shape of the thing you want to come out. Basically you smush the metal into the shape in the two dies using a huge press.

    Forging does change material properties, but its not simple how. It depends on the material, and the heat. "cold forging" is when the material is below 1/2 of its melting temperature when its forged. The terms "warm" and "hot" forging are used also. Hot forging is when you don't get any mechanical property enhancement because the material is so hot, the atoms just move around back to where you smushed them to. Its the smushing when they can't move that makes the material stronger.

    Lots of times, wrenches are cold forged. Sometimes bicycle cranks are cold forged. Why? Because you want the added material strength, and it makes a part that is close to the shape you want in the end. Cold forging requires much larger presses, and it also limits the shape of the finished part, and the amount of "flow" the material can go through.

    Hot forging is how a lot of aluminum bicycle frame parts are made (shock mounts, dropouts, etc). Since the frame is welded and heat-treated, any strength you can add by cold forging is canceled after welding and heat-treating. So you'd just waste money.
    Why forge instead of machining? You can get complex shapes that are hard to machine (think swoopy surfaces), and its more friendly for medium to high volume production. Most small manufacturers don't want to invest a bunch of money in tooling up front, so they stick with machining. The parts cost more, you don't have to pay for tooling up front, and the shapes are limited. Forging costs more up front, the parts are cheaper to buy, and the shaping is not limited.
    Forged parts get machined afterward, so you can have machined surfaces as well on a forged part.

    Steel frames typically use cast parts, not forged. Again, heat, welding, and cost issues.
    Aluminum frame parts are never cast, since casting is not a good choice for high-strength and low weight. The alloying impurities caused in a slow cooling process (from sand or investment casting) would come out during welding and alignment. Plus its not any cheaper.
    Die-casting, which is a lot like plastic injection molding, requires very expensive tooling. Imagine a molten stream of aluminum shooting out at high pressure! Its sketchy, so the tools are very nice, and very expensive. Die-casting gets less impurities in the final part, but limits part geometry, because like injection molding, the wall thicknesses have to be very close thru the entire part or part shrinkage isn't uniform during the fast cooling that is possible when using a cooled die in a production die-casting environment.

    Often, the only difference between an "extruded and machined" part and a "forged" part is the process used. That is typically decided based on part cost, tool cost, expected number of units to be produced, as well as the possibility of different shapes. For instance, an extruded and machined lower link would have lower tooling cost, but higher part cost, and it has to be a constant cross-section in one direction (at least initially).
    The forged part has to be able to be pulled out of a simple die, would have lower part cost, but probably around 3-5 times the tooling cost.

    Hope that helped clear things up a bit.
    You've got it right guys.. "
    Die-casting, which is a lot like plastic injection molding, requires very expensive tooling. Imagine a molten stream of aluminum shooting out at high pressure! Its sketchy, so the tools are very nice, and very expensive. Die-casting gets less impurities in the final part, but limits part geometry, because like injection molding, the wall thicknesses have to be very close thru the entire part or part shrinkage isn't uniform during the fast cooling that is possible when using a cooled die in a production die-casting environment. "



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  12. #12
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    One way to think of it in terms most people will get instantly is the difference between particle board and solid wood. (I'm not getting technical here...)

    Take a 1' length of 2x4 particle board and bend it. It'll snap because there are little chunks of sawdust glued together. That an example of how most parts are down at the microscopic level. Now take the same 2x4 and bend that puppy. You probably can't but if you could, it would not just snap. That is because of the 'wood grain' - which is similar to how forging manipulates the granular structure in forged aluminum and steel parts. There is a lot more to it but that's the basic principle.
    "It looks flexy"

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