Three-hundred million times or more--from the first moment an LS3 engine roars to life in a new base or Grand Sport Corvette to the split-second the odometer celebrates 100,000 miles and beyond--Chevy's modern small-block V-8 crank performs its assigned duties with amazing reliability.
"Thanks to GM's 57 years of small-block V-8 crank-engineering experience, strict manufacturing processes, and precision machining, the LS3 crank is simply a rock-solid, no-fail part,” says GM Technology Communications Powertrain spokesperson Tom Read.
LS3 crank design begins at GM Powertrain Engineering in Pontiac, Michigan, where GM Product Engineers create virtual models of a new crank using 3-D computer-aided-design (CAD) systems. The digital data file is reviewed with GM engineers at Defiance Casting Operations in Defiance, Ohio, and evaluated for manufacturability, and this feedback is incorporated into the product design.
After both engineering teams approve the crank design, product CAD models are transformed electronically, accounting for foundry-process variables (such as shrinkage), to create crankshaft pattern-tooling models. These models are then viewed by a private pattern shop, which will produce the patterns.
The pattern shop uses CNC machines to manufacture these tools and then validates them using a coordinate-measuring machine (CMM). The CMM is digitally linked to the 3-D math data, ensuring strict design tolerances are met.
A GM Tool Engineer inspects and dimensionally accepts the tools prior to shipment to GM Powertrain Defiance Casting Operations, where nodular-iron engine cranks are produced. The tools are used throughout the life cycle of the part or until a new pattern is required (after 500,000 molds, or 3 million cranks).
Once the tooling is in place, Defiance Casting Operations focuses its attention on the first step in the crank-manufacturing process: creating the sand-mold impressions that will yield the world-class nodular crankshafts for the LS3-powered Corvette.
Follow along as we show you some highlights of how it's done.
In our next issue, we'll show you how Defiance Casting Operations transforms iron ore from a solid metal into a molten liquid, transfers it into molds, and performs the other steps necessary to produce an unfinished LS3 crank.
Molding-Sand Ingredients
The molds, which are key to the Corvette crank-creation process, are formed from molding sand, a mixture of the following ingredients:
- Silica sand (also known as silicon dioxide or SiO2): The mechanical and chemical weathering of quartz creates silica sand. GM sources lake and bank sands specifically, which are ideal for iron foundries.
- Sodium and calcium bentonite (also known as Western and Southern Bentonite): These clays are used in varying percentages for hot strength and green (wet) strength.
- Sea coal: This pulverized bituminous coal gives the green sand its black color. It reduces the amount of metal penetration into the sand and improves the surface finish of the casting.
- Cob flour: As the name suggests, this flour is sourced from corn cobs. It serves as an initial combustible to allow for sand-grain expansion.
Green sand molding is the...
Green sand molding is the process used to make LS3 crankshaft molds. In simple terms, sand and water comprise the mold material. The actual recipe is more complex. The green sand’s ingredients include Western and Southern Bentanite clay, cob flour, water, and sea coal, which serves as a repellent to prevent 2,600-degree metal from penetrating the sand grains. Green sand isn’t really colored green; rather, like green wood, it gets its name because it’s wet.
Designed as a large figure...
Designed as a large figure eight, a continuous muller with plows and wheels on a turret mixes the sand and slurry to the proper consistency.
A stainless-steel pattern...
A stainless-steel pattern is mounted on a rapper table via pins and bushings. One pattern will hold the drag (bottom) mold and one will hold the cope (top) mold. The sand mixture is elevated to large tempering bins and sent to Spomatic (Spo) machines (not shown).
The drag flask travels over...
The drag flask travels over the stainless-steel pattern and is located via the previously mounted pins and bushings.
The metering box drops enough...
The metering box drops enough sand for one mold on top of the pattern, and the flask jolts and squeezes the sand into the mold.
Excess sand is wiped off the...
Excess sand is wiped off the flask, the rapper table raps the sand around the pattern, and the squeeze head compresses the sand at approximately 2,100 psi.
The spent sand is recycled,...
The spent sand is recycled, and most of it remains in the foundry’s 1,000-ton sand system to be mulled again.
The drag mold is presented...
The drag mold is presented to the molding line, where operators insert filters and cores into it. The cope mold is made the same way and set over the drag mold in preparation for the pouring of molten iron. vette