Alloy Wheels

Alloy wheels are mostly made from the alloys of magnesium and aluminum. Alloy wheels are common used in vehicle wheels and are far much lighter compared to the other commonly used wheels. Alloy wheels are stronger and have a significant more favorable heat conduction than normal wheels. Their great cosmic appearance makes them the wheels of choice for vintage cars and most luxury vehicle models. The earlier version and models of the aluminium wheel alloys were not as a success as the current ones since the first version that traded in the 1960s was brittle due to their low ductility. The same fate was shared even when the magnesium alloys were used thus the use of the wheels was a far from safe affair. The status and the improvement of the aluminium alloy for the wheel alloy came about when the aluminium casting was improved giving them their original purpose and position in motorsport as a high performance wheel yet low cost. The aluminium alloy wheels are characterized by their good grip as a result of the un-sprung mass that gives way to good suspension in following the terrain closely. With this reduced weight of the wheels, there is general reduction in the weight of the vehicle which may lead to a reduced consumption of the fuel. The heat conductance of the alloy wheels are especially handy in heavy trucks as braking produces a lot of heat which is dissipated by the wheel hence reducing the possibility of brake failure. The manufacture and availability of the aluminium alloy wheels was not taken as a factory standard in the manufacture of vehicles. Aluminium alloy wheels were generally categorized as add on owing to the costs involved in the manufacture of an alloy wheel. However in the advent and rise in demand of the aluminium alloy wheel, the manufacture and inclusion as a standard has been increasing in the motorvehicle manufacture industry aluminium alloys are now common in economy cars compared to when they were mainly found only on expensive vehicles. An increase in the uptake of the aluminium alloy wheels can also be attributed to the availability of the wheels as a substitute to the normal steel wheels and an increase in the number of the aluminium alloy wheel manufacturers.  The main purchase since the year 2000s to date has been for cosmetic value even though the alloys that are commonly used are not resistant to corrosion. To protect them from corrosion, they are usually painted or covered with wheel covers. The possibility of having custom and a wide range of designs on of the aluminium alloy wheels is another fast for their sharp increase in uptake. The designs made are intricate and very bold. The downturn with the aluminium alloy wheels however is their likely corrosion, i.e. galvanic and the difficulty in their repair compared to steel wheels. The cost of producing an alloy wheel is far much above that of the steel wheel hence the reason for the continued marketing of the alloy wheel as an add on. The sports car, which are relatively expensive compared to economy cars, don the alloy wheels and have been an inspiration for the increased customization of economy cars to spot alloy wheels. Alloy wheels are subject to theft owing to their high cost a factor that led automakers and garages to design a special locking wheel nut without which prevents one from removing the wheel unless they have a key. The alloy wheels are mainly cast or forged in the manufacturing process but the forged alloy wheels are more expensive than the casting. There are visually attracting and very appealing wheel alloys that are light called “mags” that are custom fitted to automobiles. Most of the customers purchasing these wheel alloys also believe that it will increase the performance of the vehicle as larger wheels have been hugely associated with better suspension and handling of the vehicle. This notion has helped the drivers, regardless of the vehicle model, generally save on the fuel as a test showed that use of wheel alloys that have better suspension lead to an overall reduced fuel economy. The illusion in this however is that compared to the cost of the wheel, the fuel economy reduction is insignificant also coupled with the reduced comfort of the vehicle and increased noise levels. The integration of the wheel alloys into the pop music culture can be attributed to the allure that they showcase luxury and unmatched comfort. Majority of the wheel alloys in the market are cast and only a few manufacturers forge their wheel alloys. The increased demand in the wheel alloys has been partially contributed by the increasing number of speed vehicle racing games funs who want to replicate the same on the streets. This demand from the enthusiast has seen a significant increase in the number of wheel alloys manufacturers in the recent year. The hip hop music artists’ adoption of wheel alloys with large diameter has been an accelerating factor in the demand of the wheel alloys. A number of modifications have been made on the wheel alloys to give better visual impressions. Amongst these additions are the inclusion of the spinners that give the impression that the vehicle is on movement even after stopping and the floater that gives the impression that the wheel is not moving when it is on the move. These are some of the major driving factors in the increase in popularity of the wheel alloys and especially their integration into the pop culture. The cast wheel alloy market is very saturated in the United States due to the increased influx from cheaper Chinese companies. The major players in the wheel alloys industry American racing company and Wolfrace of Britain which are also some of the oldest firms in this industry dating to as early as the late 1950s. 

The first magnesium alloy wheels were die cast and their trade name was mag wheel. The magnesium alloy wheels were however susceptible to corrosion and their production has since stopped. The current real magnesium alloy wheels available are only found in classic cars that were manufactured at the time of the production of the ‘mag wheels’. The susceptibility of magnesium to corrosion and pitting gave the magnesium alloy wheels a short life span. The magnesium alloy wheels would easily crack and could even burst into flames. This is as a result of the properties of magnesium which would easily catch fire if the rubber tyre caught fire. The only reprieve with this problem came with the development of alloys of magnesium. Previously the wheels had to be kept polished regularly. Magnesium wheels originally found their footing in racing cars whose popularity led to interests in the development of aluminium alloys which was die cast.

High quality wheel alloys are produced by forging and thus an understanding of the process is critical in understanding wheel alloys, i.e aluminium wheel alloys.

Forging: Method of producing Magnesium and aluminium alloy wheels

‘Aluminium alloys are produced by all the current forging methods available including open-die forging. Closed die forging, upsetting, roll forging, orbital forging, spin forging, mandrel forging, ring rolling and extrusion. Selection of the optimal forging method for a given forging shape is based on the desired forged shape, the sophistication of the forged shape, the sophistication of the forged design and cost’. (George, 2003)

‘These forging methods are the basics that guide the production of high quality wheel alloys. In many cases, two or more forging methods are used in order to achieve the desired forged shape and microstructure. For example, open die forging frequently precedes closed die forging to pre-work alloy and to pre-shape the metal to conform to the subsequent closed dies and to conserve input metal. Aluminium alloy forging are produced on a wide variety of forging equipment. Aluminium alloys forging are produced on the full spectrum of forging equipment, ranging from hammers and presses to specialized machines. Selection of forging equipment for a given forging shape and type is based on the capabilities of the equipment, forging design sophistication, desired forging design and cost’.

‘Deformation or strain rate is also acritical element in the successful forging of a given alloy. The deformation or strain rate are imparted by equipment varies considerably, ranging from very fast on equipment such as hummers, mechanical presses, and high energy rate to relatively slow on equipment such as hydraulic presses. Although aluminium alloys are not considered to be as sensitive to strain rate as other materials, selection of the strain rate in a given forging process or differences in deformation rate inherent in various types of equipment affect the forging pressure requirements, the severity of deformation possible, and therefore the sophistication of the forging part that can be produced.’ (George, 2003)

‘Open die forging is used to frequently produce small quantities of aluminium alloy forgings when the construction of expensive closed dies is not justified or when such quantities are needed during the prototype fabrication stages of forging application. The quantity that warrants the use of closed dies varies considerably, depending on the size and the shape of the forging and the application for the part. However, open die forging is by no means confined to small or prototype quantities, and in some cases it may be the most cost effective method of aluminium forging manufacture. Open die forgings in aluminium can be produced to a wide variety of shapes ranging from simple rounds, squares, or rectangles to very complex contoured forgings. In the past, the complexity and the tolerance forging of aluminium and other materials depended on the skill of the press operator, however, with the advent of the programmable computer controlled open die forging presses, it is possible to produce such shapes to overall thickness/width tolerance bands of 1.27mm. Because the open die forging of aluminium alloys is also frequently implemented to produce preforms for closed die forging, these state of the art machines produce very precise shapes, improving the dimensional consistency and tolerances of the resulting closed die forging and reducing closed doe forging cost through further input material conservation.’

‘Closed die forging; most aluminium alloy forgings are produced in closed dies. The four types of aluminium forgings shaped in closed dies are blocker type, conventional, high definition and precision. Blocker type forgings are produced in relatively inexpensive, single sets of dies. In dimensions and forged details, they are less defined and require more machining than conventional or high definition closed die forgings. A blocker type of forging costs less than a comparable conventional or high definition forging, but it requires more machining. Conventional closed-die forgings are the most common type of aluminium forging. They are produced with either a single set of finish dies or with block and finish dies, depending on the design criteria. These forgings have less machine stock and tighter tolerances than blocker type forgings, but require additional cost to produce.’

‘High-definition, near net shape closed-die forgings are a result of improved forging equipment and process control. They offer forging design and tolerance enhancement over conventional or blocker type forgings to affect further reduction in machine costs. High-definition forgings are produced with multiple die sets, consisting of one or more blocker dies and finish dies, and are frequently used with some as forged surfaces remaining un-machined by the purchaser. This is the specific forging type inherent in wheel alloy manufacture and more so in the manufacture of racing car wheel alloys and truck alloys.’

‘Precision forgings represent net shape products that require no subsequent machining. Net shape aluminium forgings are produced in two pieces, three piece through-dieand/or multiple segment wrap die systems to very restricted design and tolerance necessary for assembly. Precision aluminium forgings are produced with very thin ribs and webs; sharp corner and fillet radii; undercuts, backdraft, and/or contours; and, frequently, multiple parting planes that may optimize grain flow characteristics. Design and tolerance criteria for precision aluminium forgings have been established to provide a finished product suitable for assembly or further fabrication. Precision aluminium forgings do not necessarily conform to the tolerances provided by machining of other product forms. However, design and criteria are highly refined in comparison to other aluminium alloy forging types and are suitable for the intended application of the product without subsequent machining by the purchaser.’

‘Precision aluminium forgings are typically produced on hydraulic presses, although in some cases mechanical and/or screw presses have been effectively employed. Although many aluminium forgings have been produced on small-to-intermediate hydraulic presses with capacities in the range of 9 to 900kN, the size of precision parts demanded by users increased, and so heavy hydraulic presses in the range of 135 to 310,000kN have been added or upgraded to this product. Forging process criteria for precision aluminium forgings are similar to those for other aluminium alloy forging types, although the metal and die temperatures used are usually controlled to near the upper limits of the ranges.’

‘In wheel alloys, i.e. aluminium the main type of forgings involved is the spin forging and orbital forging. Spin forging is a relatively new aluminium alloy forging technique that combines closed die forging and computer numerically controlled spin forgers to achieve close tolerance axisymmetric hollow shapes. Because spin forging is achieved over a mandrel, inside diameter contours are typically produced to net shape, requiring subsequent machining. Orbital or rotary forging is a variant of  closed-die mechanical or hydraulic press forging in which one or both of the dies is caused to rotate, usually art an angle, leading to incremental deformation of the work-piece. Orbital forging is used to produce parts with surfaces of revolution with both hot and cold aluminium alloy forging processes, and it provides highly refined close tolerance final shapes (George, 2003)’.