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Wheel Anatomy: Part I

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Arguably one of the most aesthetic components of any vehicle, wheels reflect the owner’s style, personality and, in many cases, the size of his or her bank account. But wheels encompass much more than just good looks.

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Looking beyond the final product all the way back to the beginning, we discover an idea or inspiration dwelling in the mind of the wheel’s creator. That’s where we want to take you. We see and appreciate the final product, but how does it get here? This month begins a series on the various ways of constructing wheels, from concept to final product.

Inspiration comes from all around us. Some wheels, like the Torque-Thrust, are rooted deep in the history of custom wheels, relying on a five-spoke design that is simple, clean and timeless. Other styles evoke architectural designs, with arches, long curves and sharp edges. Still others derive their shape from form following function, using direct lines and simple angles to minimize weight but still maintain load capacity.

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The first chapter in our design and anatomy lesson is the one-piece aluminum wheel. This wheel is constructed by pouring molten metal into a mold, which, when cooled, becomes a raw casting.

To show you how the process works, we’re going to walk through it step-by step. MHT Wheels and Ultra Wheels are two major design and manufacturing companies in the U.S. Here are some of the designs they unveiled at the SEMA Show just a few weeks ago.

Once the design concept is conceived, these wheels were sketched on paper. After some revisions, the drawing and dozens of others were submitted to a committee. At this stage, the sales staff, the person who created the design and production personnel come together to discuss the feasibility and longevity of the design.

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A side note: A few years ago, a wheel design would have a life of three to five years before being discontinued. Today, a wheel design’s lifespan can sometimes be as short as just 18 months. Like clothing, a trendy wheel design will be a must-have today and a boat anchor tomorrow. The cost of designing, engineering, testing and building the tools and molds all has to be considered against sales potential. Short production runs drive the per-unit cost skyward.

Once the concept drawing is approved, the next step is to develop a 3D rendering with a computer model. High-tech models like these help the overall design concept move more quickly to actual production. Using special software, the computer model can test strength and rigidity as well as troubleshoot design issues.

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When the rendering is complete and any engineering issues have been addressed, the information is transferred to a CNC milling machine. This machine is loaded with a chunk of billet steel. Over the course of a day, the CNC can chew away steel a few thousands of an inch at a time and hold tolerances within 0.0005-inch. The result is a segmented investment mold, as shown below.

Notice that there is a top, bottom and sides. Only two sides are shown here, but, in reality, it takes four of these to make up the sides of a wheel. The light color shown is a ceramic coating. Molten aluminum is highly corrosive, so to protect the mold itself, this coating is applied before the mold is put online.

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How expensive is a mold? Some cost as much as $20,000! That’s one mold for one size. Now multiply that by the number of diameters and then by the number of widths.

With the mold in place, the casting can start. Ingots of A356 – virgin aluminum – are melted down and mixed with other alloys (the choice of which depends on the properties desired), and then is poured into a vat, which is then slid under the bottom of the mold machine. From there, the molten metal is injected upward into the mold cavity. This method is called a counter-pressure injection mold system.

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After the wheel is cooled and removed from the mold, it goes on to heat treatment. This process hardens the aluminum to prepare it for a multi-step machining process. Bolt holes, center bore, back and front half of the wheel must undergo a machining process, as well.

To the right, we see an aluminum mod with the rear half cut on the lathe. The wheel will be conveyed to the next machine, which is set up to cut the front half.

With all of the machine work finished, the wheel then goes through first-stage inspection. One part of the inspection process is the leak test. The wheel is sandwiched between two flat panels and submerged in water. Compressed air is forced into the center of the wheel, and if a leak exists, an air bubble will seep through to the outer side. The technician can mark the spot for repair or discard the leaky wheel entirely into the reject pile.

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Wheels that complete this inspection stage go to the final finishing stages of painting, polishing or chrome plating. A final inspection checks for finishing flaws, and then it’s off to packaging, warehousing and shipping.

The final, final ending comes when you mount the wheel on your customers’ rides and see their faces light up. That’s a look most wheel designers – and all of the production crew – never get to see, but it is their artistry, imagination and craftsmanship that made it possible.

I hope that you now have a fond appreciation for the amount of time and energy that goes into manufacturing a wheel. Next month, we’ll delve into two-piece wheels.

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