Manufacturing Technology Explained
Materials and Manufacturing
Other than steel wheels that we are not concerned about, most wheels are made from aluminum or other metal alloys (Mixture). Aluminum is relatively inexpensive and, when compared to steel, exhibits a higher strength-to-weight ratio. In other words, aluminum wheels can be strong and light.
Just how strong and how light they are, though, depends on how they are made. There are only a handful of ways wheels can be manufactured, the most popular of which includes “CASTING”, “FLOW-FORMING” and the most premium, “FORGING”.
3 Main Manufacturing Process
CASTING
FLOW FOAMING
FORGED MONOBLOCK
CASTING
The most common and inexpensive way to mass produce. Wheels can be cast in two ways: by means of gravity or through a low-pressure application. Gravity casting is the simplest and least expensive process. Here, molten aluminum gets dumped into a mold where it is spread, set, hardened and turned into a wheel. No forces other than the Earth’s pull pack the aluminum into place, which means gravity-cast wheels are not the strongest.
Low-pressure casting applies a vacuum onto the molten aluminum, packing its molecules into place, reducing impurities and resulting in a denser, stronger wheel. Whatever car you own, if; originally comes with aluminum rims, chances are they have been low-pressure cast.
As it turns out, aside from being heavy, OEM wheels are not all that bad. Government regulations require original equipment rims to be a whole lot stronger than they really need to be, at least twice as strong as recommendations for aftermarket wheels. Speaking of aftermarket wheels, REGULATIONS ARE NOT ENFORCED IN MOST PARTS OF THE WORLD EXCEPT ONLY LESS THAN 5 COUNTRIES, which means sourcing your next set from a reputable company with some sort of racing pedigree is very critical.
However, there are other advantages to cast wheels, like their ability to yield more detailed designs when compared to other manufacturing methods that result in more angular shapes. Thanks to computer-controlled manufacturing processes, for example, cast wheels can still be quite strong. This is a not a good thing when you are driving, especially spirited driving and can cause a lot of damage, not just to the wheel but to the rest of the car or even worse, it can cause a collision that will damage cause the loss of lives.
The disadvantage of a cast wheel is their failure point. Cast wheels tend to crack under stress and have spectacular failures on track. The porosity of the alloy creates opportunities for the casting to break away.
Cast wheels are designed for a lower load rating and are built to have 400-500 treadwear tires on them. If you put a slick tire on a cast wheel (or even a 200 treadwear tire) with a heavy car, it is possible to break a cast wheel.
Cast Wheel Pros + Inexpensive, better than steel wheels, easy to mass produce
Cast Wheel Cons – Brittle, prone to cracking and failure, need more material to maintain strength, heavy.
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FLOW FOAMING
An upgrade to cast wheels is a process called flow foam, also called flow forged or forged hybrid. (Marketing Terms)
Within engineering technology, in reality; there is NOTHING FORGED about these wheels. The name “FLOW FORGED”, “FLOW FORM”, “FORGED FUSION”, “HYBRID FORGED” SHOULD NEVER BE USED AT ALL. It misleads people who do not have engineering background to think of it as a superior product. Sadly, this is often used by marketers to convey a sense of strength in the product and up sell them with a higher profit margin. (Yes, that is the hurtful truth for you)
But flow forming; regardless of not being forged, does have its own advantage to increase strength in aluminum. This process allows manufacturers to use LESSER material thus creating a lighter wheel.
The process to manufacture a flow foam wheel is to start off with a cast wheel, just like any other cast wheel, however; the die(shape) for the barrel portion of the wheel is narrower than the final dimensions of the final wheel. The unfinished wheel is then heated to 400 degrees and then spun. A spinning disc contacts the wheel and is pressed to flatten out and widen the barrel of the wheel to form the eventual shape. This process of heat and pressure strengthens the aluminum at the core of the wheel barrel.
This process of crafting wheels can create very light weight wheels, which is very suitable for light race cars and super bikes (Mazda Miata etc.) Less weight helps with rotating mass and breaking efficiency, which we will cover that in the “Why Light Weight”
However, there is still some risk with flow foam wheels, because of all the lightness comes some issues with failures. The center of the wheel is still cast and thus still has porosity in it, which makes the center hub brittle.
Flow Foam Wheel Pros + Lighter than cast wheels, less expensive than forged wheels
Flow Foam Wheel Cons – Center of the wheel is still cast, which makes it brittle, unsuitable for heavier vehicles
*Fun Fact – Porsche GT4 comes with original factory Flow Foam Wheels (OEM)*
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FORGED MONOBLOCK
The heavenly KING OF KINGS. Forged rims are light and strong but comes with a high price. The FACT is forged wheels are EXPENSIVE, or rather any forged metals. When you see how these wheels are made and how much material is used, it makes sense why these wheels fetch such a high price.
The forging process involves heat, LOTS OF HEAT, and smashing compressed metal to get the grain of the 6061-t6 aluminum just right for tons of metal strength.
The forging process which creates the high load rating helps the wheel during an impact. If a Forged wheel strikes a wall it will bend. This is different from a cast or flow formed wheel which has granular aluminum so if they hit a wall they will break (brittle) which means their failure mode is catastrophic.
Even though a forged wheel is stronger, but it is still a wearable item. Wheels do not last forever. (Yes, they do not) (Specifically, to dedicated race cars F1, Nascars etc) Wheels are designed with a triangle concept: weight, strength and longevity. According to Dwarf Racing®’s Founder, “I can make a wheel strong and heavy to last forever. Or I can make a lighter wheel that is not as strong but will last 10 years and beyond depending on usage.” These are trade-offs for any wheels, these metal parts are constantly under fatigued stress, it does not matter if a wheel is cast, flow formed or forged, in extreme dedicated racing they will all fail eventually.
Not only Dwarf Racing® Forged wheels are much stronger, but they are also lighter as well as compared to any cast wheel with the same physical dimensional properties.