FASTENINGS & ADHESIVES FEATURE


The drive for lightweighting in automotive manufacture has brought a variety of alternative materials and bonding techniques to the fore. Dr Antonio Pagliuca of


the Automotive division of 3M, summarises the challenges, highlights the benefits of structural adhesives and looks ahead to the future of multi-material bonding


Structural adhesives: a key to lighter vehicles


Adhesive bonding distributes loads evenly across the whole joint surface and absorbs energy from impacts


bolting and welding. Adhesive bonding distributes loads


M


uch of the pressure to reduce vehicle weight comes


from regulatory demands for lower carbon emissions. European Commission statistics blame cars for around 12% of the EU’s CO2


emissions. Under


new rules, manufacturers have until 2030 to achieve a 30% reduction. At the same time,


“If vehicle weight and production costs


are to be minimised, it is important to adopt new materials and


drivers want more miles per gallon, or per charge in the case of electric vehicles, without compromising on performance or comfort. Reducing weight answers all those needs, provided there is no loss of structural safety. To this end, we are seeing traditional


pressed steel replaced by lightweight alternatives such as aluminium, high-strength steel, carbon fibre, magnesium, plastics and composites. These are put together in carefully selected combinations that best meet the individual needs of each part of the vehicle. The days of constructing a car from one material are long gone.


WHY USE STRUCTURAL ADHESIVES? When it comes to joining assemblies, structural adhesives are proving to have major advantages over traditional fixing techniques such as riveting,


/ DESIGNSOLUTIONS


evenly across the whole joint surface and absorbs energy from impacts. Adhesives also provide designers and engineers with options for management of stress in their assemblies and structures. The strength and durability of modern adhesive technologies can even be applied to joining parts of a vehicle’s fundamental ‘body-in-white’ structure. Furthermore, they can help manage and prevent galvanic corrosion problems, and the possibility of thinner and lighter panels tearing or distorting around bolts and rivets. To give some idea of the scale of the


shift, today’s equivalent of a 2001 car containing 30ft of adhesives may now contain more than 400ft.


manufacturing practices in the early stages of development”


DESIGN ISSUES If vehicle weight and production costs are to be minimised, it is important to adopt new materials and manufacturing practices in the early stages of development. With seemingly infinite possibilities for varying the materials, joint geometry and adhesives, many combinations need to be considered, tried and tested before


a final design is settled. Use of multi- material structures adds to that variety and to the testing needed.


Each area of the car has different


requirements in terms of strength, so designers must take a holistic approach to lightweighting. This requires an understanding of the impact energy implications of every material and adhesive combination used, both for specific areas and for the vehicle as a whole. Consultation with a specialist will


identify suitable adhesives and ensure that bonded structures are fully tested under real-life conditions. Facilities could include bespoke fatigue test equipment that synergistically combines factors such as vibration (or cyclic loading), extreme temperature variation, water immersion and salt spray. Its constantly evolving methodologies help to predict stresses and life cycle performance.


THE FUTURE Although the growth of adhesive bonding in automotive manufacture seems rapid, its adoption by the aerospace industry has been much faster – it has been well-established here for many years. The relatively cautious attitude of car designers relates largely to the constraints posed by much shorter product cycles, higher volumes and faster assembly than their aerospace counterparts face. For example, plenty of time is


available in aerospace manufacture for preparation of difficult substrates before bonding. To meet automotive assembly’s time challenges, adhesive developers have produced solutions that bond effectively with little preparation. The most recent advances from 3M


include next-generation adhesives that cure at much lower temperatures. Instead of curing in an oven at 180˚C or so, they require just 80˚C. This averts the risk of panel distortion and enhances the potential for using light materials that are less tolerant of heat.


3M www.3M.co.uk


DESIGN SOLUTIONS | FEBRUARY 2019 25


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56