Billet & Forged Crankshafts

[tommac95]

{ i penned this after only reading the first page of the thread ... sorry }

Metallic properties are determined by various means: alloy composition, heat treatments, and physically distorting/forming the grain structure.

I would agree with R.J. that (for the same/comparable) composition alloy, forged pieces are far superior due to the fact that the grain structure follows the shape .

R.J. is also clearly correct that for small runs {especially small shops} a forging process is unmanageable expensive (particularly large item like a crank).

I will unequivocally assert that the increasing prominence [to current dominance] of so-called "billet" manufactured articles represents the wide acceptance of CNC or computer-controlled tooling and cheap computers and software . The software program is much easier to pay off than a forging mechanism, and the tooling+software are more versatile to apply to form many different products.

Enter the variable of composition.... Being mindful that most pure metals have extremely limited applications [as gold and copper for electrical conductors] , and that most metal components are employed in the form of engineering alloys [as 14-Carat gold for strong jewelry, or silicon-bronze for corrosion-resistance]... note that there are whole classes of alloys [ie, commercially proven (initially proprietary) admixtures of metals] which can be cast , but are not capable of being forged , or cold-worked.

There are some heat-resistant alloys [also corrosion-resistant , etc] which cannot be forged/hotworked/coldworked ... yet have very, very fine mechanical (or other) properties in the AS CAST condition. It is quite possible that niche manufacturers can use CNC/billet fabricating techniques to create small production runs of very high-quality crankshafts {possibly superior to production forged cranks incorporating cheap commercial alloys} . These would command the $3000 price (or whatever).

Automobile manufacturers can only sell competitively-priced articles in the mass-markets. Thus the first (proven) cranks were forged ... then creative/experimental research developed cast steel cranks , now cast iron cranks are adequate for many purposes {and use only CHEAP cast iron (with appropriate heat treatment) instead of the superior alloys in the forged cranks ... or the even more dear admixtures in the quality billet cranks}.

And soooooo ..... One cannot a crankshaft properly classify , by production process alone. Composition matters .

I always wanted to have stainless alloy wire welded onto production (forged) cranks prior regrinding , for corrosion-resistance , but ... never got that far!