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Jan 23, 2018

Laser plastic welding gets a quality control upgrade—infrared machine vision

Josh Brown

Laser plastic welding is capable of bonding incredibly complex and difficult assemblies that other methods can’t match. But demanding bonding applications require equally demanding quality control methods, which until recently just didn’t exist.

Despite the advantages, laser plastic welding is still unknown to many companies.

Laser plastic welding is one of the fastest-growing polymer bonding techniques in the medical device, automotive, and consumer electronics industries.

And for good reason.

The list of advantages over other bonding methods is impressive.

But, despite the benefits, technology, and know-how are widely unknown to many engineers and organizations.

Combine an unfamiliar assembly method with applications that have a high degree of complexity and it’s no wonder there is a reluctance to switch from tried-and-true methods like ultrasonic welding.

It’s an issue of trust.

Until now, there were no methods to directly analyze the quality of final welds in process. Quality assurance relied upon either:

  • Indirect methods—essentially monitoring process parameters that correlate to known good welds

or

  • Post-weld, batch testing—i.e. burst, leak, and pressure testing which are all destructive and can’t be implemented in real-time

But new, promising technology is now capable of directly analyzing the quality of the weld in real-time, in-process, and without destruction of an assembly.

Learn more

The solution—infrared machine vision inspection

Machine vision technology is not new and is widely known, but has never been successfully implemented for laser plastic welding production scenarios.

The obvious issue is that—by the nature of laser plastic welding—the joint is obscured by the upper joining layer.

What is needed is a way to see “through” the plastic and into the joint, “X-ray vision” if you will.

Except, in this case, it’s not x-rays, but rather infrared spectrum radiation.

The execution is complex, but the concept is quite simple; laser plastic welding relies on an upper layer being transmissive in the infrared spectrum in order to get laser radiation into the joint.

By utilizing a special infrared camera with a sophisticated illumination of the welded assembly, it’s possible to “see-through” the plastic and right into the joint.

“We now have the ability to directly analyze a weld joint. We no longer need to try to infer quality with indirect process monitoring.” -Dax Hamilton, Director and Global Product Manager – Laser Plastic Welding, Dukane.

Automating the inspection process

The outputted image can be automatically analyzed by image processing software, meaning full real-time, in-process quality control can be 100% automated.

In a fraction of a second, the camera system can snap a “see-through” image of the weld joint, output it into image processing software, and objectively analyze the quality of the weld.

Inspection software: Circular joint with. “Bad” areas in Red/Yellow, “Good” areas in Green

Outputted images can be visually inspected to uncover defects and gaps in weld joints, and while this is excellent for process development purposes, in full production the image needs to be distilled into “pass/fail” criteria an automation line can act on.

By using application-specific criteria and requirements from good and bad parts, the software algorithms can be trained to uncover minute, pixel-size defects that can be as small as a few microns.

Thresholds can then be set within the vision inspection software to either pass or fail a weld based on how grievous of a defect is present.

Criteria that can be analyzed:

  • Gaps
  • Burn marks or occlusions
  • Joint consistency
  • Bubbling or joint deformation (caused by overheating)
  • Contrast ratios (unwelded or under-welded areas)

Even non-weld joint features can be analyzed:

  • Internal part placement
  • Fiducial recognition for assembly locating

What does this mean for the laser plastic welding industry?

Laser plastic welding was already being adopted at an incredible rate across many many industries due to its advantages over other bonding methods. With a reliable method for non-destructive, real-time quality control, there should be even less resistance to companies looking to replace legacy bonding methods in the medical device, automotive, and consumer electronics industries.

Will better quality control methods like infrared machine vision inspection make your organization more likely to adopt laser plastic welding?

Click Here to learn more about Infrared Machine Vision Inspection.

Dukane Corporate Headquarters

.

2900 Dukane Drive St. Charles IL 60174

.

630-797-4900

.

ussales@dukane.com

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