In the wheel industry monoblock and 3 piece are two of the most popular types of forged wheels. The terms "monoblock" and "3 piece" refer to the construction of the wheel, but the similarities end there. In fact, there are many differences between the two types that make each ideal for different kinds of automated applications.
Monoblock wheelsare also referred to as "one-piece" wheels, meaning that they are forged into a single part without any removable components. During the manufacturing process a monoblock wheel begins as a single, round block of 6061-T1 aluminum alloy. The aluminum block is compressed and subjected to intense heat which creates a dense grain structure and forms a round, blank piece of metal. The single piece of aluminum alloy is then flow-formed and placed in a CNC milling machine where the spokes are formed to finish the manufacturing process.
Being that monoblocks are made from a single piece of aluminum alloy, they are the lightest of forged wheels. Their low weight is bought after as they help to reduce unsprung mass which can reduce acceleration times, enhance braking, and improve handling. Monoblock wheels are often less expensive than their 2- or 3-piece forged counterparts, as few parts are used for construction. However, if a monoblock wheel is damaged or bent they are difficult to repair, often requiring a complete wheel replacement.
3 piece forged wheels offer different advantages over monoblocks, mostly from a styling point. A 3 piece wheel has three main parts: a center, the outer hoop or "lip", and the inner hoop. The manufacturing process of 3 piece wheels is similar to that of a monoblock, except more aluminum alloy blocks are used due to the increased number of parts. After all of the pieces are milled, they are fasted together using a number of perimeter bolts and sealed using Silicone RTV.
The construction of 3 piece forged wheels allows manufacturers the ability to offer a wider range of widths and fitments for customers. 3 piece wheels are also the most customizable as any of the components can be easily painted or chromed to create a unique color scheme. If they sustain any damage it can be readily replaced. In addition, 3 piece forged wheels retain the highest resale value among used wheels. 3 piece wheels are not without their disadvantages. They are the most expensive forged wheels because of their multi-piece manufacturing, and if the RTV Silicone seal is broken, leaks can form.