4WD MODIFICATIONS - TECH TORQUE
The amount of aluminium content in 4WDs is steadily increasing and some makers have adopted all-aluminium bodywork. What’s driving this trend?
Since the late 1980s vehicle design directions throughout the world have been increasingly directed by global emissions standards. The first step was easy enough: tidying up exhaust gas pollution by improving combustion efficiency and reducing the amount of burnt engine oil coming out the tailpipe.
As the emissions screws tightened the engine designer’s task became more difficult, until exhaust after-treatment was essential. Today’s internal combustion engines – both petrol and diesel – now have catalytic converters, exhaust gas recirculation and particulate filters, and exhaust gases can’t be made much cleaner.
The early emissions reduction laws ignored carbon dioxide, but that by-product of hydrocarbon fuel burn is now on the statute books, either as a shrinking target for specific CO2 emissions or in terms of progressively-reducing fuel consumption targets.
Parallel with developments in engine technology, vehicle designers spent a lot of time making vehicles more streamlined, to reduce the amount of engine power needed to overcome wind resistance. But that path has now been pursued to the point where significant drag reduction is no longer possible, other than the eventual replacement of external rear vision mirrors by cameras.
Modern road tyres have less rolling resistance and lubricants reduce powertrain and rolling chassis friction, to reduce power demands.
Given that today’s new 4WD – SUV or ‘real’ 4WD – is streamlined, powered by a clean engine and with low rolling resistance, designers have had to shift focus to meet ever tightening CO2 targets. The new goal is weight reduction, so that a same-size vehicle can be powered by a more frugal powerplant.
According to studies by the IFEU Institute in Heidelberg a weight saving of 100kg, achieved by using lightweight materials in a medium-sized vehicle, results
in an average saving of 0.35 litres of petrol per 100km. In this way, CO2 emissions are reduced by about 10g/km, taking into account the energy consumed in the total fuel-supply chain. Over a 200,000km vehicle life that means 700 litres less fuel.
Aluminium alloys are ideal materials for automotive body structures, because while steel is ultimately stronger, comparable or better body strength can be achieved in aluminium at about one-third the weight. In addition, aluminium is much more corrosion resistant, giving it excellent life and recycling properties.
Europe currently recycles around 85 percent of automotive aluminium, using only five-percent of the energy used to produce the original aluminium from bauxite (aluminium ore).
A plus for Australian exports is that this country is by far the world’s largest producer of bauxite.
In the 4WD world Land Rover/Range Rover has been the design innovator since the first Range Rover was released in 1970. Even then, the company had been building 4WDs with aluminium panels over steel body frames and chassis for more than 20 years.
It’s not surprising that this company produced the world’s first aluminium-monocoque, civilian 4WD wagon in 2013, with a typical-specification weight reduction of around 400kg. This landmark Range Rover is being joined by additional aluminium Range Rover products.
A switch to monocoque aluminium construction was less of a radical move for Range Rover, given the company’s background, than it is for traditional welded-steel body makers. Also, Land Rover/Range Rover vehicles are premium products, making it easier for the maker to pass on the significantly higher cost of
In the USA aluminium has been used extensively in military vehicles – the Humvee being the best known aluminium monocoque machine – and this trend continues with developments such as the new FED. However, civilian 4WD makers in the USA have been slower to adopt aluminium bodywork.
Ford stole a march on the world’s ute makers when it released the 2015 aluminium-bodied F-150. Ford claimed that a typical F-150 2015 model weighed around 340kg less than a 2014 model. The ladder frame of the all-new F-150 is still constructed of high-strength steel, but 95-percent of its body structure is pressed from high-strength, military-grade, aluminium alloys.
“There’s isn’t an automotive manufacturer that makes vehicles in North America that we’re not talking to,” said Tom Boney, in a June 2014 interview with The Detroit News. Mr Boney is head of North American automotive business for Novelis, one of the USA’s largest aluminium suppliers.
Making an aluminium monocoque
Pure aluminium is most usually alloyed with copper, manganese, silicon, magnesium, silicon or zinc, depending on the intended application.
Aluminium-alloy sheet is numbered in different series: 1000 series are essentially pure aluminium, with a minimum 99-percent content by weight and can be work hardened: 2000 series (formerly referred to as duralumin) are alloyed with copper and can be precipitation hardened to strengths comparable
to steel; 3000 series are alloyed with manganese and can be work hardened; 4000 series (silumin) are alloyed with silicon; 5000 series are alloyed with magnesium; 6000 series are alloyed with magnesium and silicon, are easy to machine and can be precipitation hardened to medium strengths; 7000 series are alloyed with zinc and can be precipitation hardened to the highest strength and 8000 series are alloyed with other elements (aluminium-lithium is an example).
The common alloys used for external automotive body panels are 6111 and 2008, and 5083 and 5754 are used for inner body
panels. Bonnets have been manufactured from 2036, 6016, and 6111 alloys.
Aluminium bodywork can’t be produced by existing steel-welding robots that specialise in spot-welding, because the melting point of aluminium is much lower and it has a higher thermal conductivity, meaning that traditional welding techniques can damage the panels. In addition, an aluminium panel’s corrosion-resistant oxide layer can produce a weld that is weak, with low fatigue resistance, while the oxide reaction contaminates the spot-welding tip.
Current aluminium panel attachment methods include self-piercing rivets (SPR), flow drill screws (FDS) and clinch-rivets – all with or without adhesive bonding. As with aircraft and marine construction, controlled-process welding is also used. Robots have been adapted to handle repetitious aluminium-fixing work.
There are some OH&S issues with aluminium, in vehicle production and panel repair. For instance, in dust form it can be flammable and can spontaneously combust. Aluminium dust plays a vital role in the manufacture of fireworks!
For that reason, any sanding equipment used needs to be operated by a brushless electric motor, with waste filter and catchment. Long-term inhalation of aluminium powder or dust has been associated with pulmonary fibrosis and lung disease.
Aluminium doesn’t change colour as heat is applied and melts at a significantly lower temperature that steel. Generally, it should not be heated above 230°C and has a melting point of 660°C.
The recommendations of the OEM should be followed and proper welding processes adhered to, with the correct shielding gas, correct wire and correct technique.
I-CAR’S Live Course ALI01 provides a comprehensive overview of working with aluminium-intensive vehicles: www.i-car.com.au