Actually, it would work, but it would likely weigh more than an entire cheap bicycle weighs today. You'd have to get Tony Little to sell it as an exercise machine.
If you _could_ make a bike frame entirely by casting, and it _didn't_ weigh a ton, the founder would surely win a prize.
Today's safety bicycle is a highly evolved product, not likely to change in any major way ...
... until its replacement shows up and kills the market overnight.
Casting is probably not a good way to make a bicycle frame, or someone would have done it. But it might be the best way to make the frame of the bicycle's replacement, whatever that turns out to be, so don't feel limited by what I said above.
The world is overflowing with unlimited opportunities, disguised as insoluble problems. Some of the disguises are very good....
Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA
Back in the days of hand brazed Reynolds 531 steel frames, often the lugs (which hold the ends of the tubes that make the two main triangles) were cast. Tubing is cheap and can easily be made with different thicknesses around the circumfrence and through the length.
Hmm, don't know about bicycles, but I believe Yamaha's sportbike frames (motos) are made from aluminum casting. Deltabox frames they're called. And hell, they're light. Fully equipped bike at less than 400#. Just look up the YZF R6 or YZF R1 and it should give some background.
I have seen injection molded frames.
Instead of tubular sections they are all H beam sections.
This could easily be cast, but I don't see the advantages.
It would be an interesting study to do.
It sure takes some re-thinking of the geometries.
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Corrosion never sleeps, but it can be managed.
a very big issue will be grain structure. castings have large grains and they are oriented perpendicular to the outer surfaces (those surfaces cool first and start nucleating from the outside, in. Toughness in such configuration suffers. also, castings have not undergone any strain hardening like rolled product has. you'd have you use a much more exotic alloy to get a similar strength to a cold worked lower alloy. There is also the issue of piping, inclusions, and segregation that you don't have with cold rolled product.
The Yamaha frames are not forged, they are cast. I'm sure a quick search of the Aluminum Association website or even a google search would yield information and photos about this.
frankiee,
One reason for not casting bicycle frames is that the tooling cost for some processes like high-pressure die casting are quite high, which is a problem because the number of frames of one style/size that can be sold is limited, which makes amortizing the cost difficult. A recent article by Josh Deetz in the June? issue of JOM described some of this as it relates to magnesium for bike frames.
So TVP,(or any one else), what would be the advantages of casting a bike frame. Will the grain stucture be tough so a minimum amount of metal could be used? I thought it would be cheaper if there were enough of them sold? I seen the first page of the article you pointed out. Interesting.
For aluminium alloys bike frame, die casting route can be used. This will give good finish, soundness in the casting and a fine grain size. However, this may still be bulkier than the extruded ones.
Costs can be lesser if there is a greater acceptance for a bulkier bike.
Folks-
It looks like everyone missed the mark on this one. Aluminum castings are much more brittle than other forms of aluminum. Structural failure happens with little notice with castings because they are not ductile. The stress strain curve is almost entirely a straight line; there is no nonlinear strain-hardening segment following the straight line portion. Ductile materials always experience a taffy-like HIGH STRENGTH yielding event before failure. These materials are less likely to fail and, when they do, there is often an obvious sign that failure is going to occur!
tunalover,you seem to sound that all cast products are brittl and do not exhibit sufficient ductility. This is not correct. The straight line curve is observed in grey irons only and not other cast alloys. All of them exhibit different levels of ductility thus undergoing plastic deformation before failure.
I do agree that in the cast form there can exist mcro shrinkages and other forms of defects rendering the metal weak. But certainly not causing it to be so brittle, to break at being dropped.
arunmrao-
I intended only to make a general statement. There are certainly exceptions to the rule. I am only going on my experience with aluminum diecastings. Aluminum diecastings are certainly more brittle than other forms of aluminum due to porosity and the lack of strain hardening inherent with molding and casting methods.
