There are essentially 7 methods of construction for aluminum automotive wheels. All methods have pros and cons.
- Gravity Cast
- Low Pressure Cast
- Flow Formed/Rotary Forged/Spun Forged
- 1pc Monoblock Forged
- 2pc Welded Forged
- 2pc Bolted Forged
- 3pc Bolted Forged
The most basic process there is for making aluminum wheels. Molten aluminum is poured into a mold, and gravity is expected to distribute and fill all parts of the mold. The gravity casting technique is very economical. But because the only force being applied to the molten aluminum is gravity, the aluminum is not as densely packed as any other wheel process.
2-Low Pressure Cast
Truthfully the process is nearly identical to gravity casting, except instead of using gravity to fill the mold positive pressure is applied. Resulting in a wheel made of denser aluminum(stronger and lighter) and higher production value. Because the molten aluminum is forced into the mold, it is much less likely to create any voids.
The most modern form of wheel building, combining both the cast and forged processes. The wheel is cast as just face and the the front lip. The wheel is then put into a special machine that heats up the outer portion of the wheel and then stretches it over rollers to create the barrel of the wheel. The result is a wheel with a cast face and a barrel that is essentially forged. Production cost are closer to those of a typical cast wheel, but the weight and strength are closer to that of a forged wheel.
The forging process for the 4 types of forged wheels will be largely the same, so we will condense the explanation of forging to this excerpt. Forging is the process of taking one large piece of metal and smashing it so much it becomes smaller. This creates a much much denser metal, which in turn is very strong, allowing less material to be required, making for a lighter end product. Currently forging is the ultimate process for creating wheels. But that strength and weight loss comes at a price, a starting price of $750 actually.
Monoblock & Multipiece Wheels
We have actually already compared these in our Wheel Building Guide.