The floowing excerpt rang true with my metallurgical learning from years back:
Alan Davis Of Eagle:
?People think billet is stronger than a forging, but that?s not true. Billet got that reputation from back when forged aftermarket cranks weren?t readily available, and billet was the only way to go for a performance crank. With a forged crank, the forging process creates an interwoven grain structure. With a billet crank, the grain structure just runs parallel with the crank. Billet is a better option if you need a custom one-off crank since it doesn?t require expensive tooling equipment. On the other hand, the 200-ton presses required for forgings cost at least six figures, so they?re more suited for large production runs.?
As a designer I had to be aware of all the manufacturing processes and choose the one that corresponded to the component and its loadings and stresses, cost of course was a major factor.
That said my old world has been turned on its head since I changed fields, the advent of CAD/CAM means that most stuff is machined from solid which would have been commercial suicide in my day except for a one off, shapes and forms that could not have been machined, only sculpted by hand can now be. I have an Airbus factory opposite me, I am aghast to see huge components that should be forged for strength alone not to mention avoiding removing 95% as machining swarf, in fact most of the volume of the machining plants is concerned with the processing and removal of the swarf.
Closer inspection reveals that these components are much thicker in section in certain areas than if they were forged so have an equal strength but critically the strength of the billet material is consistent and regular in all directions, weaknesses or changes to the structure are not created by forging which was in fact the raison d'?tre of forging, the ability to move the grain structure in the direction to oppose the service loadings.
Whilst the machined from solid components look heavier which is undesirable in an aircraft CADCAM stress analysis means that other non critically loaded areas can be made thinner to compensate, much thinner than forging or casting would involve.
A long ramble but other than for price a forged crank I believe will always be a safer bet than a billet machined one, however price is the most important thing for a company selling the component.
Long out of production components can be remanufactured with little or no tooling costs by laser scanning and then CNC machining to create a visually identical component, I was once involved in this but walked away when I realised that the non technical sales people running the company could not accept that copying a forged suspension upright for a historic racing car (just one example of many) with a dimensionally identical machined from solid item could and probably would result in death.
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a) truck engineering: nothing forged, as weight "up front" wasn't a criteria and the rest is for the coach builders, so to say! b) aerodynamics in reg. automotive parts (gfrp): weight is determined by the laminator and no-one cares, c) racing components in cfrp and honeycomb as we needed for audi and porsche tec..: all of OUR (Nobrac) parts weighed less than our competitors did! and d) aircraft like airbus (MBB) use all of the technologies: lots of new reinforcable fibers (no whiskers etc..) and forgings AND the machined aluminum parts where 97% of the material needed turns into scrap! ------------- i sure wish we could of used more forged parts!! sandy
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