Lightweighting process developments are helping automotive engineers to meet incoming legislation

According to the European Commission, cars are responsible for around 12% of the EU’s total CO2 emissions. However, by 2021, phased in from 2020, the fleet average of all new passenger cars needs to produce no more than 95g of CO2 per km, which is a 40% reduction in comparison to the 2007 fleet average of 158.7g of CO2 per km. This demands a fuel consumption of around 4.1L per 100km (65mpg) for petrol and 3.6L per 100km for diesel (57mpg).

If average CO2 emissions of a fleet exceeds these limits, manufacturers will have to pay an excess emissions premium for each car registered, at a cost of €95 from the first gram of exceedance onwards.


With such a daunting target looming, it’s clear that automotive manufacturers will need to continually reduce the mass of their vehicles. In recent years, there has been a major shift in body materials from conventional steel to aluminium. To help facilitate this step-change, customised pre-treatment and coating solutions from bonding specialists Henkel have helped provide improved corrosion protection and enhanced process efficiency.

In chassis applications, for example, its BONDERITE MN-T 1800, a zirconium-based product, is already replacing traditional zinc phosphate at many automotive plants throughout Europe. Used for processing car bodies through pre-treatment systems prior to painting, the product is having a significant role in lightweighting initiatives.

Henkel claims MN-T 1800 requires fewer process steps and a shorter contact time (with very little process control changes) than traditional zinc, which helps increase production rates. Furthermore, there are no heavy metals and the process runs at room temperature – minimising energy consumption. Over eight million vehicles on the road are already using this technology.

The shift towards lightweight aluminium wheels is also facilitated by Henkel pre-treatment and coating technologies. For instance, the improved formulation available with BONDERITE M-NT 4595 not only reduces overall process cost, but enables the development of wheels with improved properties and lower weight.

Audi surface treatment

In cooperation with Audi, Henkel has also developed a two-step process that enables surface treatment of multi-metal auto-bodies with an aluminium content of up to 100%.

In zinc phosphating, which was the conventional process, the volume of waste products increases as the aluminium content of mixed material bodies rises. These are costly to remove from the pre-treatment bath and the treated surfaces.

Due to the different surface properties of steel and aluminium body components, the two-step process pre-treats them in two stages. This allows more aluminium to be used, while reducing the disadvantages of the current process, i.e. energy and chemical use decrease during the production process. In addition, servicing expenses, associated downtime, and waste volumes also reduce.

Audi was the first company to integrate this method into its processes. The two-step process has now become the global standard for pre-treatment of auto bodies with a high aluminium content.

Peter Kuhm, business director automotive surface treatment Europe at Henkel Adhesive Technologies, explains: “The BONDERITE two-step metal pretreatment process for multi-metal bodies provides superior corrosion performance while reducing investment and processing costs. We are very proud of our collaboration, not only with Audi, but also with other global leading automobile manufacturers.”

Crash structures

There also exists further opportunities to reduce metal weight in vehicles by using structural adhesives for crash resistance applications. Structural bonding in the automotive industry already takes place, such as the anaerobic heat-shrink bonding of ring gears to crankshafts on Volvo’s SI6 engine. Offering high torque transmission capability, it reduces the need for clamp rings and fasteners, thus reducing weight – all at a much lower investment cost than laser welding.

In another application, this time involving a driveshaft, the bonding of carbon fibre to aluminium using proven epoxy technology again affords a lightweight design, not to mention the elimination of weld distortion.

Electric vehicles

Of course, there is another major trend to throw into the vehicle lightweighting mix: the world’s increasing desire for more hybrid and electric vehicles. Lightweighting is particularly important here as it can improve efficiency and increase range.

Key components include inverters, electric motors and batteries. Here, electrically-conductive primer coatings and sealing technologies are being used for lithium-ion batteries and ultra-capacitors.

Applications include LOCTITE adhesives for bonding battery modules and pack elements, and TECHNOMELT low-pressure moulding compounds for reinforcing flexible cells and protecting sensitive electrical components. Furthermore, BONDERITE surface treatments are deployed to provide long-term corrosion protection to battery trays, cylindrical and prismatic canisters, as well as battery pack assembly structures. Among the major benefits is reduced weight with the ability to use multi-substrate materials such as aluminium, magnesium, plastics and composites.

Growing opportunities exist across the automotive electronics application range, including parts such as ECUs, sensors and converters. Indeed, reflecting this trend, Henkel has developed a range of specially adapted adhesives, which can be electrically and/or thermally conductive for example. In addition, these can be formed-in-place, cured-in-place and moulded-in-place.

Although the miniaturisation of in-vehicle electrical and electronic components has helped to reduce both space and weight, the increasing power densities involved have led to higher local temperatures. And these need to be effectively dissipated. For such applications, a selection of specialised potting and encapsulation compounds based on epoxy silicone and urethane technology, combining thermal conduction with electrical insulating properties has also been developed.

Vehicles will continue to lose weight as automotive OEMs head towards the 2021 emissions target and look to steer clear of penalties. And it is assembly and joining technologies that are being utilised to enable the multi-material and lightweighting mantra to become realised and established.

Engineering Materials

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