Since 2008, GM Powertrain Defiance Casting Operations in Defiance, Ohio, has produced more than 45,000 nodular-iron LS3 crankshafts, the bulletproof backbones of the engine rotating assemblies in all base and many Grand Sport Corvettes.
Last month we showed you the first step in the crankshaft-manufacturing process: green-sand casting, which creates the recyclable molds from which the cranks are born.
“Defiance has decades of experience casting small-block cranks,” says Tom Read, GM’s Technology Communications Powertrain spokesperson. “Its quality procedures and checks ensure the cranks last virtually forever, while handling the LS3’s 424 lb-ft of twisting force and 430 horsepower.”
Defiance pumps out approximately 1,000 cranks an hour. It casts LS3 cranks in batches as needed for Corvette production demands.
How does the facility transform iron ore into a molten liquid, transfer it into green-sand molds, and perform the other tasks necessary to produce a ready-to-be-machined LS3 crank? Follow along as we show you some highlights of how it’s done.
1 A 10-ton magnetic crane...
1 A 10-ton magnetic crane loads a mixture of iron scrap, also known as “frag,” into the skip bucket for loading the cupola. One bucket amount is called a cupola “charge.”
2 The skip bucket enters...
2 The skip bucket enters the cupola with 11,000 pounds of charge material to be melted. The cupola holds 10 charges.
3 Iron Technician Dennis...
3 Iron Technician Dennis Okuley takes a temperature reading from the cupola. It ranges from 2,500 to 2,640 degrees (F).
4 Molten metal travels through...
4 Molten metal travels through a hole at the bottom of the cupola and into a trough. Here, Okuley “rubs down” the iron trough to ensure the liquid is properly transported.
5 The trough delivers the...
5 The trough delivers the liquid metal to a porous plug vessel (shown), where it’s desulfurized through the introduction of nitrogen.
6 The hot-metal crane, which...
6 The hot-metal crane, which is used to transport large quantities of iron to the pouring station, prepares to receive alloy. The alloy is a mixture of carbon, silicon, manganese, and copper.
7 Its next stop is a holding...
7 Its next stop is a holding furnace, where it receives 10,000 pounds of iron.
8 After the fill from the...
8 After the fill from the holding furnace, the crane transports and pours the iron into the line-rod furnace.
9 The iron from the line-rod...
9 The iron from the line-rod furnace fills the Rotary Mechanical Iron Pour (RMIP) ladles for transport to the sand molds. Shown here, the ladle then pours iron into a sand mold. When the gray iron hits the magnesium inoculant alloy pocket in the mold, its conversion to nodular iron takes place.
10 Cranks cool in the molds...
10 Cranks cool in the molds for 150 minutes. Then the cope flask is then picked off, and the drag flask rolled over. The castings slide into a basement oscillator known as the “shake-out area,” where they cool for approximately 90 more minutes.
11 The rough crankshafts...
11 The rough crankshafts travel to the hard-iron breaking conveyor, where the excess metal, which was needed to cast the crank, is separated from the casting. The cranks are then transferred via a bucket conveyor to a processing department.
12 Iron Technician John Kramer...
12 Iron Technician John Kramer prepares to remove scrap castings or fragments (both of which are called “sprue”) from the conveyor.
13 Scrap castings are transported...
13 Scrap castings are transported to the 10-ton crane area to be melted down again.
14 Crankshafts are sent through...
14 Crankshafts are sent through a drum shot-blast cabinet for a first clean, and an in-line blast cleaner for a second.
15 Casting Processor Dan...
15 Casting Processor Dan Casarez inspects the crankshaft and removes excess material at the “chip station” on the process belt. He then performs a “ring test,” which, as its name implies, involves striking the crankshaft with a hammer and listening to the resulting sound. LS3 (and other nodular-iron) cranks should ring like a bell. Afterwards, any excess metal remaining on the cranks is removed with a hand grinder.
16 Voila--a processed cast...
16 Voila--a processed cast nodular-iron crankshaft.
17 Defiance employee Gary...
17 Defiance employee Gary Gustwiller hoists processed cranks from the belt and into containers for shipping to an intermediary facility. There, technicians will remove 2 mm from every crank’s rod and main journals, drill and tap the holes for the flywheel, and add counterweights for internal balancing. These machined cranks are then delivered to GM’s St. Catharines Powertrain Operations, where engine assemblers lower them into waiting LS3 blocks and secure them in place with six-bolt main-bearing caps. You probably know the next step: The finished LS3 engines are delivered to the Bowling Green Assembly Plant and installed in new Corvettes! vette