Re: Forged vs. ?

* * Chas wrote:
<frkrygow@xxxxxxxxx> wrote in message
news:1190691450.182659.323440@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Sep 24, 3:46 pm, "* * Chas" <verktygj...@xxxxxxxxxxxxxxx> wrote:
"Melt forged" was/is a BS term for injection molding, a method for
making
high quality castings.
I think you meant die casting, not injection molding. Although the
processes are conceptually very similar, when it's done with metal,
it's called die casting. When it's done with plastic, it's called
injection molding. At least, that's true everywhere I've come across
it.

A casting is still a casting and doesn't have the benefits of
increased
metal density that comes from forging.
Hmm. Well, forgings definitely tend to be stronger per unit weight,
but there are a wide variety of casting processes. Some are clearly
better than others regarding accuracy, finish, mechanical properties,
etc.

As Andrew noted, it's certainly possible to make perfectly acceptable
parts by casting. The cast parts may be a bit heavier, but the
difference is probably undetectable to most riders.

When you get to the point where you're counting grams, then yes, you
probably want forged parts.

Unless you go with carbon fiber. ;-)

- Frank Krygowski


You're right, the process is called Die Casting. I was in a hurry when I
wrote that. I guess that I'm getting old and the memory gland doesn't
always work as well as it once did. ;-)

Die casting is used to make castings from aluminum, magnesium, zinc alloys
(zamac), and copper and it's alloys (brass & bronze).

I object to the term "melt forged" which is a misleading misnomer rather
than castings in general.

it's not. "casting" is used for liquid solidification. "melt forged" or thixoforming does in no way produce the same product as casting.



Someone at a LBS showed me a hollow Shimano crank arm that had been cut in
half. He said Shimano told him it was a forging. I looked it over and
could tell it had been cast.

what features led you that conclusion? i ask because those things are most definitely forged - and the above illustrates that you have some confusion on this subject. if you have access to metallography, it would be good for you to use it - you'll see what i mean the moment you look down the microscope.

.

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  • Re: Forged vs. ?
    ... I think you meant die casting, not injection molding. ... metal density that comes from forging. ...
    (rec.bicycles.tech)
  • Re: Forged vs. ?
    ... The term injection molding usually refers to the plastics industry but it ... molding and metal die casting. ... I was unfamiliar with the term thixoforming. ...
    (rec.bicycles.tech)
  • Re: Forged vs. ?
    ... I think you meant die casting, not injection molding. ... Die casting is used to make castings from aluminum, magnesium, zinc alloys ... Someone at a LBS showed me a hollow Shimano crank arm that had been cut in ...
    (rec.bicycles.tech)