Roy Chambers, of RC Automotive, gave me a quick once-through on the process of making a forged crank. It may have been brief, but this guy knows how to explain crankshaft technology.
This is the basic crankshaft forging process (as I very crudely understand it). The forges used by Ford and RC Automotive (and also by Cummins, Mack, and many other manufacturers) were located at Wyman-Gordon's Harvey, Illinois facility:
1) Square steel ingot (steel type SAE1046 is used in the 427's case, a good steel but nothing fancy) is heated white-hot in a furnace, then plucked out by a robotic arm and placed between the faces of the forge tooling (a series of probably three progressively deepening dies).
2) Forge repeatedly slams tooling faces together, sandwiching the ingot until it fills the form and all excess material squeezes out at the tooling parting line (about a 1/2" or 3/4" gap all the way around, I imagine). When this is done, the forged crank is placed back into the furnace by the robotic arm.
Note: The 427 crank is forged "flat" so that all rod journals are placed flat on the parting line plane. I would guess this allows the tool to be simple and very durable. This method forces certain counterweight size constraints on the centermost sides of the #2 and #4 main journals, but I'll dig into this when I get to step 4.
3) Next, the white-hot flat crank is removed from the furnace again and placed in a stamp, where the excess material around the perimeter of the crank gets "stamped" away in one massive chop from a taylor-fitted cutter tool. This creates what I call (probably incorrectly) the "parting line". I understand the crank is allowed to cool somewhat after this step.
4) The "flat crank" is then reheated white-hot and then placed in another tool of some sort which grabs the center section of the crank and rotates it 90 degrees from the rest of the crank, twisting only at the #2 and #4 main journals. If you look at the #2 and #4 journals of a raw 427 forging you can see the twist marks. Note that smaller counterweights are located on the inner sides of the #2 and #4 main journals. This is probably because the forge can only make certain shapes of counterweights, and full-sized counterweights on the inboard side would not be optimally positioned for a zero balance after "twisting".
Some V-8 crankshafts are forged in their fully bent shape (known as "non-twist" forgings). There are benefits and drawbacks to both types of forgings. I suspect that cost, quantity, strength, and counterweight capability are four driving parameters behind which type of technology is chosen in a particular application.
5) The raw forging is then hardened and tempered (to improve grain structure in the metal), and then cooled.
6) Next Wyman-Gordon fixtures the raw forging on each end and spins it to find the "center of mass", at which time each end of the crank gets center-drilled. Lastly, they use a "multi-fingered" apparatus to find an optimal position for all journals. Using this apparatus, they hand-punch two "locating" points into the crank: The first point is punched to the upper left of the FoMoCo symbol and it references a specific distance where the #3 main journal center should be roughed-in. The second locating point is punched onto a front throw to reference where the rod journal is to be roughed-in. Wyman-Gordon guarantees the crank will finish-up to these locations or you can exchange it for a replacement raw forging.
The raw forging is now done and ready to ship. Wyman-Gordon does no machining in house, so the rest is done at a crankshaft machining facility.
The first step performed at the crankshaft machine shop is to machine the flange and snout. Next, the main and rod throws are machined to a semi-finished (roughly .020 to .040 oversize) state. Then the oil passages are drilled and the throws hollowed out (drilling at this stage assures the passages are properly located in the finished crank). Lastly, the crank journals are finish ground and polished.
I recognize I still don't have the process described quite right, but I did discuss the topic with Roy a second time tonight, and have revised this post to suit.
Also note also that the "I" part of Wyman-Gordon's "$" trademark symbol has some sort of arrow or blunt feature on both ends, so if you see a little artifact in at the tips in the forging, it's supposed to be there.
Shoe.
