The one joining technology ABB sees as growing and becoming more accepted by automotive OEMs is gluing or chemical bonding, Nidamarthi said. "Suppliers are coming up with new glues that can bond different materials. Dow Chemical's research is showing that such gluing can help achieve both lighter car weight and higher structural stiffness."
For example, Dow Automotive Systems' BETAFORCE two-component polyurethane adhesives are particularly well suited for bonding carbon fiber composites to other composites or to metals such as aluminum. These products have prolonged work times, adhere quickly, and require little surface preparation.
Dow Automotive Systems' BETAFORCE adhesives, shown here joining carbon fiber composite automotive panels, are two-component polyurethane bonding systems designed to join carbon composites to each other or to materials such as aluminum in vehicle bodies. (Source: Dow Automotive Systems)
However, applying glue quickly and accurately is a challenge, especially when it is incorporated into an automated process. "In mass production, you need accurate and fast methods for applying glue, like dispensing a continuous ribbon or a bead versus applying it in spots," said Nidamarthi. The correct timing of mixing and application is important, and the temperature of heated glue must be carefully managed.
It is thus extremely important for the robots that apply the glue and their controllers to be accurate. To coordinate the speed of the robot and the speed and accuracy of glue dispensing, ABB is integrating dispensing controllers into a robot controller. The system simultaneously manages mixing, temperature, dispensing flow or glue volumes, and robot speeds so that the correct amount of glue is dispensed quickly in the right place. ABB has customers using this integrated dispensing system in automotive applications, and aerospace customers are conducting pilot research, Nidamarthi said.
Fascinating story, Ann, on how to join materials that can't be welded. One thing that gives me pause is that as they develop appropriate adhesives, it will still only be a guess on how the joining materials will hold up after 20 years. Only time will tell whether the adhesives will hold the car together over decades.
These are structural adhesives, and many of them are being adapted from aerospace applications, where they've been used with composites for some time. We covered structural adhesives here http://www.designnews.com/document.asp?doc_id=237011
I did some work at Raytheon (Beech) quite a number of years back. They routinely used adhesives to bond aluminum aircraft parts together. The parts were also riveted (sparingly), but the engineers referred to the rivets as "chicken rivets", because they insisted the glue was more than strong enough. Supposedly the FAA wouldn't let them get rid of all of the rivets. I don't know how it ages, however. We had to disassemble some of the parts that were glued, and the aluminum would tear before the glue would let go. As I remember it, the stuff was basically inseparable.
That's very encouraging, Ttemple. Was that a number of years ago? I would guess if adhesives had any durability problems we would know by now. In manufacturing, I would think using adhesives is more efficient than welding.
I would say around 1996 or so. They were manufacturing the (Kingair?)"1900D" heavily at that time. It says on wikipedia that the 1900D was introduced in 1991, and produced through 2002. I'm sure that many 1900D's are still in use as regional commuters.
I don't know when they started using adhesives though. The part I remember specifically was the window attachment to the fuselage skin. There was sort of an aluminum porthole looking piece that was glued to the fuselage. The joint had the appearance of a weld, and it held together like it.
I think they use adhesives in the wing compartments too, at least in the areas where there is going to be fuel stored. The adhesives seal the compartments, I think. They also use special fuel resistant coatings on the skin inside those areas.
Ttemple, it sounds like there is an good long track record on the adhesives, at least a couple decades. So, while these adhesives may be new to the auto industry, they seem to be well tested in aerospace.
ttemple, thanks for telling us about your direct experience. Anything going into the construction of commercial aircraft has very strict specifications and requirements, including extensive testing on the ground and in the air, and everything is 100% traceable. Whether structural adhesives or fasteners are used in a particular part of the plane depends on several factors, but stresses in aircraft are much more extreme than in cars.
It certainly is a valid question, adhesive lifetime, and how does one speed the aging process so as to find a correct answer? And the very important question is how reliableare the bond lifetime results? Many adhesives primarily fail through long term creep type of fault, while in others t6he ridgid bond becomes brittle and does not stand up to shocks. Two different failure mechanisms, it seems. And he experience of how things stick to a composit is not the level that we are looking for. So the solution is to understand the failure mechanism, and use that information.
A lot of research has been done on structural adhesives, as we've covered here http://www.designnews.com/document.asp?doc_id=237011 and here http://www.designnews.com/document.asp?doc_id=236816 Fabrico, which doesn't make adhesives, but uses them assembling all kinds of structural components, has articles and a Q&A on many of these subjects here http://fabricoforum.com/2012/06/structural-adhesives/
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