Laser welding intelligence for the auto industry

Phil Bates is working to bridge the gap when it comes to laser transmission welding (LTW) — both literally and figuratively.

Bates, who is a professor at the Royal Military College of Canada and the Canada Research Chair in Polymer Processing and Joining, has been researching the laser welding of thermoplastic components as part of an AUTO21 research project.

Generally speaking, laser welding allows the processor to shine the laser through a clear or laser-transparent surface, which is then absorbed by a laser absorbing surface. Unlike friction-based welding processes such as vibration welding, laser welding allows for the joining of complex shapes and high-tech parts with electronic components that may be sensitive to vibratory movement.

“With laser transmission welding, generally there is no vibration,” noted Bates. “Also, because it’s very localized heating, you can in some cases get away with having no flash.”

In particular, Bates’ research focuses on the contour approach, which is well suited for the larger parts and complex seam geometries seen in the automotive industry. With contour LTW, a laser travels once along the weld path, and only short segments along the weldline remain molten at any given instant. By comparison, other laser welding methodologies, like simultaneous welding, involve the use of multiple lasers or fibre optics to irradiate the entire weld seam.

As a result, contour welding prevents the collapse or meltdown of the entire interface, and any gaps at the part interface that exceed critical dimensions could cause weld defects. Additionally, according to Bates, whether a gap will be problematic depends on the weld design and the type of material being used in the application.

“A lot of our early work has been trying to understand the effect of important welding variables such as power and scan speed on resulting joints. Unlike many other joining processes, we have found that this technology is very sensitive to material properties. Understanding the laser material interactions is critical.

The body of research accumulated by the AUTO21 group has allowed Bates and his team to partner and consult with several major Tier 1 suppliers. For example, one major Canadian processor was interested in understanding the behaviour of glass-filled nylon in laser welding applications, while another was working with polycarbonate.

“They’re interested in things like gaps,” explained Bates. “They are the ones that are signing off on the drawings so they need to know, in terms of a gap, what kind of gaps can we live with, and how can we mitigate this problem through design, mold or welding modifications.”

Bates and his team have also worked with three material suppliers, who are interested in providing their customers with comprehensive information about the material through design manuals and technical support.

“They are interested in how their material behaves,” said Bates. “It’s the fundamental understanding of, ‘here’s my material, tell me what happens when you shine a laser through it.'”

Additionally, the group has undertaken new research based on applications by some of the OEMs and Tier 1 suppliers they have worked with. Bates is currently working with an application that has a TPO part with a Class A surface, to determine the key parameters to avoid sink marks on the back of the part.

The group is also looking at novel technologies to weld tubes to plates.

“We are using designs of static mirrors that would allow you to weld tubes to plates, so you could manufacture a heat exchanger or manifold system,” he said. Bates works in collaboration with Drs. Zak and Kontopoulou at Queen’s University, and Drs. Kamal and Walt at McGill University.

Dr. Phil Bates, Royal Military College of Canada (Kingston, Ont.); 613-541-6000 ext. 6609

AUTO21 Network of Centres of Excellence (Windsor, Ont.); www.auto21.ca; 519-253-3000 ext. 4130