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How To | How kart rims are manufactured

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HOW KART RIMS ARE MANUFACTURED

07 August 2019
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INTRO

Rims are the part of the kart directly in contact with the tires and play a fundamental role in managing their temperature. For this reason there are various models on the market, which vary in materials (aluminum or magnesium) for quality and shape. With the help of AMV (Alluminio Magnesio Veneto) an Italian company which makes components for karts and specializes in the manufacturing of rims, we are going to discover the particular production process for the manufacturing of a kart rim.

1 DESIGN

The first step to create a rim for karts is in its design, which at AMV is performed by the technical professional’s utilizing CAD software. The project starts by designing the rim in 3D, calculating the volume of air between the tire and the rim via a computer and defining the dimensions. Theory says that a low air content rim allows for a greater control of the temperatures which is definitely an advantage, but not in all conditions. For example, a driver needs to spend more time warming up the tires, a rim with a higher quantity of air can help. The dimension’s, therefore, should be evaluated right away, depending on the type of rim that is being developed.
Another important parameter to differentiate one model from the other is the rigidity of the rim-hub connection.  This is partially influenced by the thickness of the rim in that area. Fundamentally the decisive alternative is between a three-spoke rim and a flat-flanged one. The first features a more rigid structure and is typically used in the shifter category where engines have a lot of power (which translates into to faster lap times) this requires absolute maximum traction. Conversely, the rim without spokes provides the kart with a “softer” layout which gives the advantage to the kart’s smoother drivability.
All these variations are already analyzed and developed in the CAD design drawing, from which the 2D views and all the dimensions are obtained, these are useful for making the moldings destined for the foundry. After having defined the design of the rim, the C.N.C machine language is generated to correctly program the machinery of the production department.

2 CASTING

Both aluminum and magnesium rims are produced by casting and the companies which carry out this process in-house are rarely found. AMV has two ovens, one for magnesium and one for aluminum accessories. Besides directly managing this phase, the Veneto region company has introduced a low-pressure casting system, a process used in the past for magnesium rims dedicated to F1 and rally vehicles which reduces the porousness of the metal eliminating the need to paint the rim’s surface that eliminates potential tire air leaks.  The advantage is that paint has a thermal exchange coefficient much lower than magnesium, it acts as an insulator, while the unpainted magnesium can disperse heat quicker, this avoids overheating of the tires and keeping their internal pressure constant. The optimal temperature to start the casting phase is 700 °C and to reach it, the ovens take 3 to 4 days to get to that point of proper heat. In the meantime, depending on the type of rim to be manufactured, the dedicated mold is prepared. For all castings, operators first insert a filter. This is an important operation that allows to collect any impurities present in the materials and guarantee an excellent quality for the finished product. When the rim completes the casting phase it needs to be cooled down. Then the filter is removed, and the next step is the C.N.C. machining.

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