Wheel Tech

Wheel Construction

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All Wheels Are Round. Or Are They?

Though not enforced, there are quality standards to govern the production of wheels. Some countries though, like Germany and Japan, have government regulations requiring aftermarket wheels to meet certain criteria and ensure proper fit. The United States has taken steps to establish guidelines but it will be some time before they can enact regulation of any kind.
Consequently, all wheels are not made the same. The performance of an alloy wheel is a direct result of the manufacturing technique employed.
The Tire Rack offers a wide range of wheel choices from manufacture's that have adopted the manufacturing processes that meet the strict O.E.M. (Original Equipment manufacturers) requirements. Wheel companies that supply to the O.E.M. market must follow certain procedures during the manufacturing process to maintain the quality and integrity of their product.
"...all wheels are not made the same. The performance of an alloy wheel is a direct result of the manufacturing technique employed."
There are many factors to consider when purchasing an alloy wheel.
What Is a Wheel and What Is a Rim? Are They the Same Thing?

It may seem obvious, but a wheel is comprised of a hub, spokes and rim. Sometimes these components will be one piece, sometimes two or three. The hub is the center portion of the wheel and is what attaches the wheel to the suspension. The spokes radiate out from the hub and attach to the rim. The rim is the outer part of the wheel that holds the tire. While many people refer to wheels as "rims," this is technically incorrect. We'll discuss several ways that wheels are manufactured below.
One-Piece Cast Wheels

This is the most common type of aluminum wheel. The casting of wheels is the process of getting molten aluminum inside a mold to form a wheel. There are different ways this can be accomplished and although it sounds simple, this is truly an art when done properly.
Gravity Casting
Gravity casting is the most basic process of pouring molten aluminum into a mold utilizing the earth's gravity to fill the mold. Gravity casting offers a very reasonable production cost and is a good method for casting designs that are more visually oriented or when reducing weight is not a primary concern. Since the process relies on gravity to fill the mold, the aluminum is not as densely packed in the mold as some other casting processes. Often gravity cast wheels will have a higher weight to achieve the required strength.
Low Pressure Casting
Low pressure casting uses positive pressure to move the molten aluminum into the mold quicker and achieve a finished product that has improved mechanical properties (more density) over a gravity cast wheel. There is a slightly higher production cost over gravity casting, but low pressure casting is the most common process approved for aluminum wheels sold to the O.E.M. market. Some companies offer wheels that are produced under a higher pressure in special casting equipment to create a wheel that is lighter and stronger than a wheel produced in low pressure, but there's a higher cost associated with the process. Low pressure cast wheels offer a good value for the aftermarket while still maintaining strength and a lighter weight.
Spun-Rim, Flow-Forming or Rim-Rolling Technology

This specialized process begins with a low pressure type of casting and uses a special machine that spins the initial casting, heats the outer portion of the casting and then uses steel rollers pressed against the rim area to pull the rim to its final width and shape. The combination of the heat, pressure and spinning create a rim area with the strength similar to a forged wheel without the high cost of the forging. Some of the special wheels produced for the O.E.M. high performance or limited production vehicles utilize this type of technology resulting in a light and strong wheel at a reasonable cost. O.Z. has used this technology for several years in their production of racing wheels for Formula One and Indy cars. O.Z.'s Formula HLT wheel for the aftermarket is an example of a wheel produced using spun-rim technology.
High Light Technology (HLT)

The High Light Technology (HLT) process used in the manufacturing of select O.Z. Racing wheels uses rollers to compress and elongate the material along the barrel of a low-pressure cast aluminum wheel to obtain the desired profile. This process, which is directly derived from O.Z.'s experience in F1, produces wheels that are extremely light and strong.
The flow-forming process and the HLT technologies combine to create mechanical characteristics similar to those of a forged wheel. This permits a dramatic reduction in wheel weight while enhancing structural rigidity vs. a standard cast wheel.

In forged wheels, computer numerically controlled (CNC) mills add the cosmetics and the bolt circle to exacting tolerances.

Forged

The ultimate in one-piece wheels. Forging is the process of forcing a solid billet of aluminum between the forging dies under an extreme amount of pressure. This creates a finished product that is very dense, very strong and therefore can be very light. The costs of tooling, development, equipment, etc., make this type of wheel very exclusive and usually demand a high price in the aftermarket.
Multi-Piece Wheels

This type of wheel utilizes two or three components assembled together to produce a finished wheel. Multi-piece wheels can use many different methods of manufacturing. Centers can be cast in various methods or forged. The rim sections for 3-piece wheels are normally spun from disks of aluminum. Generally, spun rim sections offer the ability to custom-tailor wheels for special applications that would not be available otherwise. The rim sections are bolted to the center and normally a sealant is applied in or on the assembly area to seal the wheel. This type of 3-piece construction was originally developed for racing in the early 1970s and has been used on cars ever since. The 3-piece wheels are most popular in the 17" and larger diameters.
There are now many options for 2-piece wheels in the market. The 2-piece wheel design does not offer as wide a range of application that a 3-piece wheel allows; however, they are more common in the market and the prices start well below the average 3-piece wheel. Some 2-piece wheels have the center bolted into a cast or cast/spun rim section and other manufacturers press centers into spun rim sections and weld the unit together. When BBS developed a new 2-piece wheel to replace the previous 3-piece street wheel, they used the special rim-rolling technology (originally developed for racing wheels) to give the rim section the weight and strength advantages similar to a forged rim. On the high-end of the 2-piece wheel market you can find wheels using forged rims and forged centers. Since these are only sold in small volume and due to the high development and production costs associated with the forging process, they tend to be on the high end of the price scale.

The Difference Between Casting & Forging

Casting is the process where metal is heated until molten. While in the molten or liquid state it is poured into a mold or vessel to create a desired shape.
Forging is the application of thermal and mechanical energy to steel billets or ingots to cause the material to change shape while in a solid state.
Why use castings?

We use castings for a wide range of wearparts and components that are too large, complicated, intricate or otherwise unsuitable for the forging process. We can forge parts up to 50kgs but the sheer energy required to forge larger items make casting a much more viable alternative.
We currently cast mining and earthmoving components to 580 kg. We can cast up to 3000 kg if required. Manganese work hardening screens are one of our specialities. We have found that by carefully choosing alloys and applying proven methods of heat treatment, we can produce castings of high quality, strength and wearability. The casting process better lends itself to making parts where internal cavities are required.
The advantages of casting include:

• No real upper size limit in casting weight
• Large range of alloy choices
• As forgings remain solid, custom alloys are far more difficult to get into production whereas with casting, alloys including Chrome, Nickel and Moly can be added at the molten stage.
• Tooling is often less expensive than forge dies
• Smaller production “runs” required
• Complicated/complex parts are no problem

For general GET as well as large and complex components - casting is a fantastic method of manufacture.

Why use forgings?

Forging offers uniformity of composition and structure. Forging results in metallurgical recrystalisation and grain
refinement as a result of the thermal cycle and deformation process. This strengthens the resulting steel product particularly in terms of impact and shear strength.
Forged steel is generally stronger and more reliable than castings and plate steel due to the fact that the grain flows of the steel are altered, conforming to the shape of the part.
The advantages of forging include:

• Generally tougher than alternatives
• Will handle impact better than castings
• The nature of forging excludes the occurence of porosity, shrinkage, cavities and cold pour issues.
• The tight grain structure of forgings making it mechanically strong. There is less need for expensive alloys to attain high strength components.
• The tight grain structure offers great wear resistance without the need to make products “superhard” We have found that, on a blank HRC 38-42 forged grinder insert wear/wash is about the same as a high alloy HRC 46-50 cast grinder insert. The difference being a HRC 46-50 casting does not have the ductility to handle high impact grinding.