Geometry optimized adhesive joining for sustainable production

Project time: 2013 – 2015

Budget: 11 825 000 SEK

Funding: FFI – Strategic Vehicle Research and Innovation

"Geometry Optimised adhesive joining for sustainable production” in Swedish (Geometri Optimerad LimFogning för hållbar produktion, "GOLF") is a project within the Swedish research program FFI for Sustainable production. It has as its mission to develop technology and methods to get the right amount of adhesive on the right place. The drivers behind this are the overall strive to decrease weight in vehicles and moving machines to minimize the amount of CO2 in the atmosphere.

The CO2 hunt, forces development of new material combinations in products that got to be more efficient. This material combinations causes some new joining situations where old knowledge of joining components of the same material are overruled by material combinations that can´t be welded or joined together with rigid joint methods that don´t take the different behavior of the joint material in account. Using adhesive as an joining method is not an new technology, but the use of adhesive in the way that the new material conditions put the demands on the parts and products is a new thing.
The car industry has used adhesive bonding for over thirty years. It has mainly been used as a sealing material in welded or riveted joints where the forces in the joints between the materials should have been carried out by the spot welds or rivets. The adhesives strength has been looked at as some kind of bonus in the total strength of the joint. This are shown in the facts around the data of stress analyses with FEM where there are very little traces’ of how to involve the strength of the adhesive in the structural analyses. Look at the thesis work (Effects of Cyclic Thermal Loadings on Distortion of Dissimilar Joined Materials) in the appendix A. There are almost no evidence of how to model the adhesion in the FEM solutions. Because of the history of joining technology the demands of which forces a joint should be able to wear there are no real design demands on the joint. The knowledge of how much stresses and in which directions it should work are based on the destructive testing that almost all car manufacturers uses to investigate that the joints are correct. One problem is that with the new materials and material combinations. The part price becomes much more expensive than with an all steel component. From around €5 to €20 per sheet metal part to €80 to €100 per multi material part, which means that destructive testing is not manageable any longer. This also means that process control to assure that the joining method delivers the joint that the designer intended is of most importance.
FFI Fordonsstrategisk Forskning och Innovation | www.vinnova.se/ffi 5
The process to create a more design directed requirements will take some time. In the mean while the knowledge around the process parameters to be controlled and monitored to be able to produce correct adhesive beads with placement control is of great importance.
The “GOLF” project had its start point from state of the art knowledge and technology of adhesive characterization, collision free path planning and advanced fluid simulation. The project aimed to through the rheology status of the adhesive create optimized robot programs to fulfill coming requirements of placement, amount and compensation. To meet the effects of assembly parts that have joining surfaces that are not geometrical optimal due to the theoretical ideal to mount the meeting surfaces parallel in normal direction. The deviations could come from parts that are deviating from the nominal form, it is not held in its nominal shape during assembly or the shapes of the parts can´t be assembled with all joints in normal direction. There will be sliding or tilting conditions during closing the gap between the parts. This has been studied in the project in a comparable small study to investigate which forces the parts puts on the bead and which forces the bead reacts with, that can change the shape and imply stresses in to the parts during fixation and curing. The study showed how complex the forces in the gap directs the effects on the adhesive and the parts which must be carried out in a continuation project.

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