What’s Different About Laser Welding

We sometimes forget how mature laser welding is. It’s been around since the ‘80s, and the applications, properties and advantages have accumulated into an extensive technology.

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As long as laser welding has been used in industry, there’s still a tendency to think of it as something for special circumstances – difficult materials, awkward locations that can’t easily be reached with MIG or other common processes, very small parts, and high-volume applications, such as specialized automotive applications.

In fact, we could do better by thinking about it the other way around: it should be the first choice as often as not. The advantages in metallurgy, versatility, and design flexibility are considerable. Some of them are unique, but many are just better than the alternatives.

TRUMPF has long been on an education crusade for laser welding, and we’re borrowing heavily here from one they present at trade shows and other events. If you’ve not been to one of those, this is just the highlights. David Havrilla, TRUMPF’s Manager of Products and Applications, gave us a personal presentation. We hope it will encourage you to see it in person, where you can ask questions about your specifics.

First, though, we want to pull something out of the regular presentation order: Laser welding gives you an opportunity to redesign parts for more efficient production. Some of the greatest advantages come from simpler joints, reduced overlaps, and welding in places that might otherwise be inaccessible. Often you can gain more by thinking about laser welding before a part or assembly is designed, rather than applying it as an afterthought.

Beyond that, a big advantage results from reduced heat input. The depth/width ratio of a weld can be greater, and the heat-affected zone (HAZ) can be much smaller. The result is less distortion and less shrinkage. A smaller weld bead improves appearance.

A narrower weld bead can result in a stronger weld. Coupled with the reduced amount of heat input into the metal, and the narrower HAZ, a laser weld can be a much stronger weld.

In terms of access, not only can a laser reach deeper, it also involves no contact. The control of the weld width allows single-side welding in cases where it wouldn’t otherwise work.

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Single-side welds and other inaccessible conditions are much more often doable with laser welding

Some of lasers’ big differences

* Lasers produce a very intense heat, which is the basis for less heat getting into the parent metal. So the reduction in distortion often is a very big issue. It’s also very consistent and predictable. It generates less scrap.

* Uptime with a laser can be on the order of 98%. It’s time-efficient. And it’s labor-efficient. Laser welding lends itself exceptionally well to automation.

* A lot of laser’s advantages and developments have come from automotive applications, and they spread out and apply to non-automotive applications as the practice becomes better known. For example, butt welds and flangeless welds save those fractions of weight that car makers clamor for. But they also simplify other kinds of assembly. The ability to make a weld with a narrow flange, or no flange at all, not only saves material, but it also may eliminate some bends.

* In one continuous operation, lasers can switch from stitching to continuous welds. Stitching can be a replacement for spot welds. In an automobile door frame, a laser can make one continuous path that switches from continuous seam welding on the front and rear of a door frame, where hinge loads and side-impact resistance are critical, to stitch welds at the roofline and the door sill. Not having to change methods or machines to complete an assembly can have applications in many aspects of fabricating.

* Some issues that are unique to laser configuration include the focus spot size and the light frequency. The first influences joint gaps, especially for butt welds, where the general guideline is for a gap 3% to 10% of the thinnest sheet.The second has to do with the reflectivity of the metal being welded. Highly reflective metals can be more efficiently welded with the short wavelengths characteristic of semiconductor lasers – disc, fiber, and YAG.

* Because the heat of a laser is intense and focused, most laser welding is autogenous – it’s done without filler. But metals that are prone to hot cracking, such as 2000-series aluminum grades, generally require a filler.

* Laser welding is suited to a wide variety of materials, including stainless, titanium, and difficult materials such as the advanced high-strength steels that are used in cars, including parts and subassemblies made throughout the supply chain. This includes the boron-containing alloys that are used in hot-stamping operations. As long as the carbon content is below 3%, roughly, or 3.5% – 4% carbon potential, as with chromium steel alloys, laser generally has no trouble with it.

* Aluminum in series 1000, 3000, 4000, 5000, and 6000 are commonly and successfully welded.

* Laser’s accuracy makes complex tube joints relatively easy. Likewise, interlocked joints in sheet metal, which require exceptional accuracy in parts with multiple bends.

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Lasers allow the use of narrower flanges, or, given the good properties of laser butt-welds, no flange at all.

From TRUMPF’s extensive list, we’ve selected just the highlights that address the essential concepts that distinguish laser welding. These are the basic points to think about when comparing laser welding with other general-purpose welding methods.

There are more that aren’t general-purpose. The list of special issues is extensive: Remote scanner welding, joint types, localized annealing, welding galvanized metals, and many others have been developed through experience over the past few decades.

If anything here catches your attention, it’s worth a deeper look.

TRUMPF

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