Lightweight alloy wheels are made from aluminum, which is light weight and great at dissipating heat, that has been "doped" with small amounts of more rigid metals. This mix is called an alloy. By varying the amounts of the alloying metals in the 'mix', the properties of the wheel material can be set to the desired standards. A wheel made out of pure aluminum would be too soft and too prone to crack to be usable. The aluminum alloy on the other hand is very rigid and resistant to cracking.
Alloy metals provide superior strength and dramatic weight reductions over ferrous metals such as steel, which makes them ideal materials for high performance wheels. Minimizing the unsprung weight of a wheel is crucial to the road holding properties of a vehicle. They are less prone to bounce and give a the shock absorbers an easier job than heavy steel wheels do. This is why steel wheels are no longer seen on racing, sports or performance cars.
Casting is the most efficient way to produce high-quality, strong alloy wheels. Two different methods are employed in casting alloy wheels: gravity casting and low pressure or negative pressure casting.
In gravity casting the molten material is simply poured into a mold and allowed to cool. The molds are CNC machined to very exacting measurements and produce wheels that only requires minor finishing, minor trimming of excess metal and drilling of bolt patterns and center bores, to be considered complete.
Negative Pressure Casting
In low pressure casting, also called negative pressure casting, the molten alloy is drawn up into the mold using a high-pressure vacuum. This process makes for a slightly different, more compact structure of the metal. Thus wheels cast in this process can be made with thinner profiles without any sacrifice in strength. The molds for this process are also made to very precise measurements and thus the wheels coming out of the process are of the same finish as the gravity cast wheels.
The choice of process is determined by the design and intended use of the wheel to give customers the best possible value for money. For some high performance wheels König has chosen a more advanced, and also slightly more expensive process for strengthening the rims, the M.A.T. Technology Wheel Process.
M.A.T. Technology Wheel Process
The demands on the center and on the rim of the wheel are very different. The forces on the center are almost exclusively straight pressure on the spokes or center disc from the perimeter to the hub. The bending forces are relatively small. This makes cast aluminum alloy a good choice for wheel centers, especially taking into account the greater design freedom and economy of casting compared to forgings.The wheel barrel, on the other hand, is subject to a very different set of forces. It is the rim that has to take the brunt of potholes and bridge joints, it is the rim that takes the hits from curbs. So rims have to be made tough. It is also desirable to have very light rims, as peripheral weight on a wheel gives it a flywheel or gyroscopic effect, making it less responsive to steering input and more difficult to brake. The M.A.T. Technology, licensed to König by the machine manufacturer Enkei, solves this problem. The cast wheel is set up in a roll forging machine, where the wheel is spun at high speed while rollers apply high pressure to the rim. This makes the metal in the rim "flow", which transforms the crystal structure of the metal as in a forging process. The end result is a one-piece cast wheel with a rim that is as light and strong as the rim of a much more expensive forged wheel.The König one-piece cast wheels with rims spun in the M.A.T. Technology process give customers the best of both worlds, the economy and design freedom of casting and the rim strength and light weight of forgings.