Quote:
Originally Posted by Don
David, another KMU question, progressing from from 101 to 201......
Basically, the reasons behind a forged aluminum product vs. machined, and the choice of aluminum, heat treat etc. Such as:
" Profil wheels are forged from 6061-T6 aluminum alloy; this aircraft-grade aluminum is heat treated for a higher yield strength than your typical aluminum wheel. This allows us to create stronger, more stable wheels, while maintaining a low weight. "
http://www.fikse.com/2010/profil.html
........thanks |
Forgings are used when grain structure is important. Aluminum is forged at around 800 degrees F (if I remember right) then squeezed in a hydraulic press. You need some 25 tons/square inch to make a good forging. As you can see, that is a tremendous amount of force. The press squeezes the hot, plastic aluminum into the shape of the die making it flow into the die. Curiously, if the temperature is too hot, the aluminum will literally crumble. It is quite interesting to actually see it happen in real life. As the aluminum flows throught the die, the grains tend to line up in the direction of the flow. Usually, (but not always!) the stresses the part sees in life are also in the direction of the flow and so the direction of the grain strengthens the part. Alloys that are typically forged are 6061, 6082, 7075. We have made parts in all these alloys.
Another advantage of a forged part is you don't need to remove so much material to make the part. A forging basically makes the part in the general shape you need. Many times all you have to do is drill some holes and machine a few surfaces and you have a usable part. There is a HUGE drawback, however. Dies are expensive to make. Dies are also expensive to set up. So, it only pays to make a die if you are sure you are not going to be changing anything. But, what do you do if you are into constant improvment--like Shingo? That is why over the years we have gotten away from forgings and gone to machining our parts straight from billet. If we have a better idea today, we don't want to wait until tomorrow (or next year like many companies) when we run out of forgings to implement a new, upgraded part into our proeduction. If we have a better idea today, we want to implement it TODAY.
I imagine, the quote above that 6061-T6 has a "higher yield strength than your typical aluminum wheel" is comparing 6061-T6 (forging alloy) to 356-T6 which is a casting alloy. There is no doubt 6061 T-6 is far stronger than 356-T6. Castings do have their advantages, like you can cast intricate shapes that are quite impossible to make with machining (think about the hollow water jackets in an engine block). However, the strength of 356-T6 is quite low and we really don't like using it for much of anything. As the years have gone by, we have eliminated almost all castings from our car. The only casting left is the differential housing now. Who knows, one day we might billet that too.
Happy to answer any questions, or go deeper if you want.
David
