Launched in September 2016, the multidisciplinary cross-border project “Laser and Surface Treatment Assisted Metal Polymer assembly (LaserSTAMP)”, coordinated by the University of Luxembourg in collaboration with the Luxembourg Institute of Science and Technology (LIST), the University of Namur and industrial partner company Optec, is coming to a successful end.
Source : uni.lu
Publication date : 08/14/2020
“Joining polymers with metals enables innovative products to benefit from complementary material properties, like lightweight and enhanced strength,” explains Prof. Peter Plapper, the project’s Principal Investigator, “The laserSTAMP team accomplished to expand the understanding of laser joining process and to implement these insights in NC (numerical control) machine.”
Challenge of combining polymer and metal
Combining the very specific material properties of polymers and metals presents different advantages. “Laser joining of metals to polymers has gained tremendous interest among industries and researchers due to its ability to produce lightweight products with customised properties. Compared to conventional joining methods, such as using adhesives or screws, laser beam joining has the advantage of being an autogenous, rapid, and easily automated process,” explains Adham Al-Sayyad, doctoral researcher at the Laser Technology Competence Center (LTCC) who managed the LaserSTAMP project since his arrival in 2017 within the Department of Engineering at the University of Luxembourg.
However, joining metals to polymers is very challenging, particularly because of the materials’ different thermal properties and physical–chemical incompatibility. Whereas successful research projects on thermal joining of polymer-metal structures have shown the general feasibility of selected material combinations, the scientific understanding and explanation of the joining phenomena were still missing. That is why, the objectives of project LaserSTAMP were to provide comprehensive understanding on the nature of physicochemical adhesion at the interface of laser welded metal – polymer joints, understand the factors influencing joint behaviour, and transfer the developed know-how to a tailored industrial laser system.
Multidisciplinary cross-border research project
Funded by the Luxembourg National Research Fund (FNR) and Walloon Region, in the framework of the European Union’s M-era.Net, the project gathered scientists and engineers from the University of Luxembourg, the Luxembourg Institute of Science and Technology (LIST), the University of Namur and Optec, a laser systems SME company based in Belgium.
LaserSTAMP project involves multidisciplinary team of engineers, physical chemists and material scientists. Each partner contributed at different levels: the University of Luxembourg analysed the main factors influencing the joint strength and quality and identified the optimal conditions for promoting the adhesion of laser welded metal to polymer assemblies. The University of Namur worked on uncovering the root cause of the physicochemical adhesion between the joining partners and revealing the nature of chemical bonding involved. Material scientists at LIST supported surface pretreatments and the characterization of treated surfaces and welded joints. The industrial partner, Optec, worked on the industrialization of the developed know-how, through the development of a laser system specialised in surface preparation and joining of metals to polymers.
Through their combined efforts, the project’s scientific consortium investigated the effects of laser welding parameters on the joint strength, benchmarked the effects of several surface pretreatment techniques on joint performance, and revealed the nature of interfacial physicochemical bonding between joining partners.
“The complementary skills of project partners were essential to the project’s success. The multidisciplinary expertise, multicultural mindsets, and collaborative spirit of the team members provided a strong basis for both its scientific and industrial contributions”, Adham says.
New potential industrial innovations
The LaserSTAMP team successfully joined several material combinations including aluminum and titanium alloys to polyamide and PEEK polymers. Using brilliant laser beam source and developing proper surface pretreatment methods, the team managed to create miniaturized joints (0.8 mm wide) reaching relatively high joint strength (up to 80% of polymeric base material). Researchers at the University of Luxembourg employed statistical Design of Experiments methods to generate mathematical models describing relation between laser welding and surface pretreatment parameters with the resulted joint performance. Using state of the art assessment techniques, the team unveiled important aspects on the interfacial physicochemical bonding between joined partners. “It is well known in literature that surface topography has a prominent effect on performance of laser welded metal – polymer assemblies. However, the mechanism was unclear,” explains Adham, “LaserSTAMP team showed that given a sufficient chemical affinity is provided, a smoother treated surface is beneficial for improving joint quality and performance by enhancing interfacial thermal transfer during laser welding process.”
In addition to LaserSTAMP’s very valuable scientific contributions, scientific insights were successfully industrialised through state-of-the-art laser system. The developed laser system integrates continuous wave (CW) fiber laser for welding metals to polymers, along with short pulsed laser for metallic surfaces pretreatment. Combining two processes in one machine significantly increases production efficiency and reduces manufacturing time. Moreover, the versatile design of the developed system permits incorporating atmospheric plasma jet for activating non-polar polymers' surfaces to prepare for laser welding with metals. Such versatile design allows for welding a wide variety of material combinations with various properties, which opens the doors to innovation and design flexibility in many fields.
While laser joining of titanium alloys to polymers has promising potential for biomedical applications, the ability of this technology to join two families of materials involved in lightweight structures, i.e. aluminum alloys on the one side and polymer based composites on the other side makes it promising for future development in transportation industries (automotive, railway, aerospace..) where lightweighting is a great challenge due to the need to reduce greenhouse gases emissions in transportation.