Page 60 - Australian Paint & Panel March-April 2020

Bonding
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PAINT&PANEL MARCH / APRIL 2020
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ABOVE: Robotic joining on the production line at the BMW plant in Dingolfing, Germany.
JOIN FORCES
LIKE EVERY OTHER ASPECT OF VEHICLE TECHNOLOGY, JOINING IS NOT GOING TO GET SIMPLER A SAYS ANDREW HOOKER, ADVANCED REPAIR PROJECTS MANAGER AT THATCHAM RESEARCH.
A DECADE AGO THE MATERIAL
mix was simpler. Typically a car body could be 20% high strength steels (HSS), the re- mainder mild steel. More recently we are seeing a greater mix of materials. This includes advanced high strength steels (ADHSS), ultra-high strength steels, and press hardened steels. The use of HSS has decreased as it's been re- placed by stronger, more advanced steels (or even aluminium). Quite often though, this can come at the expense of
repairability.
We’ve recently seen some new cars
launched that have not taken significant steps forward in terms of body structure as higher grades of ADHSS cannot be used, because of their strength and stiff- ness properties, and also because of their cost. Simply put, you cannot al- ways use a high percentage of higher
grade steels as they’re too expensive for smaller, cheaper, high volume cars.
ENGINEERING CARS
FOR THE FUTURE
As a result, car makers are having to give serious thought to engineering cars for the future. Composites are one solu- tion, but for smaller cars this means cheaper sheet moulding compound plas- tics, certainly not carbon fibre yet. It could also mean cheaper plastics rein- forced with carbon fibre tapes. Alumini- um use is increasing, but again is still expensive when compared to steel prod- ucts. The typical solution for aluminium application is to make bigger single com-
ponents that replace many smaller steel components, but this in turn leads to a need for deeper structural replacement.
Steel will remain the predominant ma- terial for higher volume vehicles for the current and forthcoming generation of cars and trucks, but make no mistake, some very different vehicles are coming our way. We’ve already seen some joining challenges, such as the demanding stack of materials for the B Pillar of the Honda Fit; 4 sheets of steel, including a 1500MPa hot formed steel, the others all high strength steels. Honda’s solution in pro- duction at the factory was a multi-tip spot welder; not a solution for a bodyshop.
Different car makers will have different strategies and will have preferences for what material direction to take. Some clearly prefer aluminium, others prefer the better-known properties of steel, all are in- vestigating carbon fibre. We can expect a similar level of diversity for joining.
With such a range of steels, including press hardened steels, computer con- trolled adaptive welding is very much the future. Eventually we can expect many car makers to mandate this in order to guarantee the quality of each weld.
But what you can’t see is that as the car makers are ‘pushing the envelope’ of cur- rent steel capability. Panels are cut and pressed with consideration to the molec- ular grain of the material; much like wood. So, joining two steel parts may be affected by the orientation of the panels. Some joining of the newer steels is prov- ing very difficult to control consistently on the production line, so is likely to need careful managing for repair.
We need to be very mindful of the pro- cesses for steel panel production today too. A panel could very well have ‘soft zones’ applied in production to enable controlled deformation; crumpling and bending in specific directions in a crash. These soft zones are not visible, but can