Wheel and Tyre Fitment: Manufacturing Techniques

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Manufacturing Techniques

06.23

00:00	With all these different wheel designs and materials, it won't be surprising that there's an equally wide array of manufacturing processes.
00:07	The fact is, these are important to understand as in some cases a wheel can be made to look very similar but made in a completely different process, which has significant impacts on its performance and cost.
00:22	The entry level for aluminium and magnesium alloy wheels is casting.
00:27	In the most basic terms, this is where molten metal is poured into a mould and left to cool and set.
00:33	After the wheel is removed from the mould, it can go through various heat treatment processes.
00:39	Casting usually leaves a rough surface finish, so they'll often be tidied up with some machining.
00:45	This is particularly important on the mounting surface, lug nut seats and the bead seat.
00:51	Chemical treatments and coatings are also used to increase corrosion resistance.
00:55	There of course have been advancements in the casting process for efficiency and in the interest of a better product and these can vary significantly between manufacturers, but there is also a marketing factor here that's good to be aware of.
01:10	Without getting too in the weeds, this mostly concerns the grain structure of the metal.
01:15	At a microscopic level, the structure of the metal is made up of individual crystalline areas called grains.
01:22	In a regular cast wheel, the grains end up in a randomised structure, which put simply, isn't ideal for strength.
01:29	So, heat treatment is used to change the grain structure and increase the strength.
01:35	Next, flow form wheels make up a huge part of the aftermarket performance wheel industry.
01:41	This is where the wheel is cast at a narrower width than the final product.
01:45	Then the wheel is heated and pressure is applied to the inner and outer surfaces of the barrel, essentially stretching it and forming it into the desired shape, in the process called spinning.
01:58	This aligns the grain structure, which greatly increases the strength of the barrel while retaining a relatively cost effective process.
02:06	Next, let's look at forged wheels.
02:08	Although not all so called forged wheels are created through the same process, truly forged wheels really are the pinnacle of single piece or monoblock aluminium wheels.
02:19	The process starts with a billet of aluminium alloy, which is heated intensely and then subject to an extremely high force from a tool to form the part into the rough shape of the wheel.
02:31	This process aligns the grains in the core structure of the wheel and in the correct shape and is followed by the spin forming process we discussed before to form the barrel of the wheel.
02:42	After this there's some machining, heat treatment and chemical treatments to ensure a strong and high quality finish.
02:48	This is a much more demanding and time intensive process and therefore a lot more expensive, but does result in a superior product.
02:57	This is really where the issue with replica wheels comes in.
03:01	To clarify, replica wheels or reps as they're usually called, are copies of a wheel design that has been produced by another manufacturer.
03:09	The problem is that genuine wheels are designed with the manufacturing process in mind.
03:15	For example, the designer understands that if they're going to forge their wheel, it will be stronger than casting and they can make the design suit that, essentially removing material and or changing the shape.
03:28	This is why a forged wheel can be lighter than the equivalent cast wheel.
03:33	So, when a design for a forged wheel is copied, but made with a process like casting, we can run into serious issues.
03:41	You're better off with a wheel that was designed to be cast, which although it may be heavier, will at least be strong enough and not be a safety risk.
03:50	It's important to note here that not all replica wheels are worse than all genuine wheels.
03:56	Some reps might even be better made than some other genuine wheels, especially those made decades ago.
04:03	Ignoring any ethical factors, it's going to be application specific.
04:07	The rigours of motorsport use will require more strength than a street car where aesthetics are the key criteria.
04:14	For multi-piece wheels, the alloy centre disc can be cast, forged or machined entirely from billet.
04:20	The centres for steel wheels are usually stamped however, which greatly limits the flexibility in their design and therefore their appearance.
04:28	The barrels or halves, whether they're made from aluminium steel or stainless steel, will be made using the same spinning process we described for flow forming and forging, also with some machining to finish them off.
04:41	Carbon wheels are naturally a completely different story, which we won't dive too deep into since they're very rarely used due to their price.
04:50	From a very basic standpoint, pre-impregnated carbon fibre is cut into specific shapes and laid into a mould.
04:57	Then an autoclave heats and pressurises the wheel so it cures into a strong structure.
05:04	This is followed by some machining and other finishing processes to achieve the final product.
05:10	We also discussed the use of 3D printing for the titanium centre disc of the HRE wheel in the previous module, but again this is so bespoke it just isn't worth too much attention.
05:21	To summarise, the most commonly used aluminium alloy wheels can be made using a few different methods and the strength, weight and resulting wheel will be significantly different between each method.
05:33	Casting is the most basic and generally the cheapest, but flow forming or spinning can be used to control the grain structure in the barrel, increasing the integrity of the wheel.
05:44	Forged wheels are really the best option for aluminium alloys when it comes to performance in motorsport applications.
05:50	This is where the wheel is formed from a billet, so the internal grain structure of the metal is aligned with the structure of the wheel.
05:57	What's important to understand is that the wheel will be designed with the manufacturing process in mind, which is why a forged wheel can be lighter.
06:06	Wheel designs that have been copied, but made using a lesser manufacturing process can spell trouble.
06:11	While the centres of multi piece wheels can be cast, forged or machined from billets, the barrels or halves are almost always spun.