If you think about it, crankshafts are really treated badly. I mean – along with the heat – the forces they must endure are pretty extreme. So I wonder: How they are made?
I guess if I was going to make one myself, I’d use a casting technique. I’d make a mold, pour in the metal, then fine tune the surface and dimensions with machining, followed by case hardening. But it seems like some kind of forging technique might be better. I’m not even sure a cast crank shaft could even stand up the forces at all. Casting produces a more brittle product than forging, and it seems like a brittle crank shaft is not what you want. You don’t want it shattering and pieces going flying in all directions.
On the other hand, crankshafts have such a complicated shape, it seems like it would be close to impossible to bend a rectangular bar of steel into the shape of a crankshaft by pounding on it.
Just curious. Anybody know how crankshafts are made by the auto manufacturers?
I would imagine a crankshaft would have to be turned after getting forged or cast, but My gut says forged is better agree @Tester though no scientific evidence, but in my life forged is stronger than cast.
@Tester … thanks for you comment, any idea how one would go about forging something into a shape so complicated as a crankshaft? I can see pounding a rectangular bar into the shape of a horseshoe. But a crankshaft? A special bending/pounding machine just for crankshafts maybe? Plus, don’t crankshafts have counterweights on the opposite side, to balance out the inertia of the pistons ? It seems nearly impossible to forge counterweights. Maybe those are welded? Just seems like an interesting problem, how to make one. The auto manufactures must have it down to a fine science, and they rarely fail in normal driving as long as the routine maintenance is kept up to date.
Basically they take a red hot billet of the metal and place into a drop forge with different dies. They start at one end to start making the shape and move along the different dies as the forging hammer pounds the metal into the desired rough shape.
They are usually cast but sometimes forged for strength. They are then milled, drilled, and ground until they are of the desired final shape, features, and finish.
Over the years, the auto industry has developed some very specialized tooling to forge and machine crankshafts…Visit your local automotive machine shop and ask them to show you a crankshaft grinder in operation and you will see what I mean…Yes, they are tricky to forge, but the process has been perfected…Back in the 60’s, Ford developed “nodular cast iron crankshafts” first used in the 221, 260, 289, 302 series of engines…These were a big improvement over the regular cast-iron cranks…The 289hypo-boss302’s were equipped with forged cranks however…
Elly, Making a crankshaft takes a great deal of technology, equipment, and knowledge. Unless you have the specialized machinery to at least do reverse-gravity casting, as well as the specialized machinery to do the machining and grinding, as well as the metallurgical knowledge to understand the behavior of the metals in the heating, casting, and cooling processes, and the knowledge of metal cutting (machine set up, speed & feeds, etc etc etc), than it’s impossible to make a crankshaft in your garage.
A few of the countless questions you’d have to be able to answer:
how do you verify the chemical and physical properties of the metals that you’ll be either alloying or ordering?
What alloy should you use?
How tightly do you need to control the casting temperatires?
How quickly to you need to heat the letal?
What temperature do you cast the metal at?
How quickly should you cool it?
How do you control the temperatures of the metal throughout the process?
By what process would you create the mold?
By what process would you release the cast part from the mold?
When machining the crankshaft,
How do you prevent the weight of the shaft combined with the pressure of the cutting tool from causing the center of the crankshaft to sag during machining, throwing the dimension out?
How much material can you cut with each pass?
At what speed?
How do you relieve the stresses introduced to the metal during the cutting process?
And these questions are just the tip of the iceburg. Things done well look simple once done. But actuallyy doing them is often surprisingly difficult.
TSMB, pretty sure EE was being sarcastic…but it does remind me of the poster several years ago that wanted to recreate his Mercedes’ engine in his home shop, castings and all…
While Elly was joking, I don’t see why the thread’s at all ridiculous. There are very interesting reasons why forged is better than cast, and they’re not obvious. But then, I’m old, and an engineer…
To: the same mountainbike, If you can, find the movie " The Words Fastest Indian ". It ia about a man named Bert Monroe who built a highly modified 1920s Indian in his shed in Australia and brought it to Bonneville in the 60s and set speed records that stand today. The movie is fictionalized, but not much. I remember the account in Hot Rod magazine at the time and he made his pistons by digging holes in the sand and casting them from Ford tractor axles. He said they had the best metal he could get. He then filed them to size and roundness by hand.
Never underestimate what a determined man can do.