Laser welding isn’t exactly new. After all, it’s been used in automotive manufacturing for many years. Outside of the auto plant, however, laser welding (and its potential for savings) is less familiar. When parts made of thin-gauge sheet metal need nice-looking welds, lasers don’t immediately come to mind; labor-intensive TIG or MIG welding, grinding and careful finishing are the norm. It doesn’t have to be that way and Estes’ Laser Welding Development Manager, Jay Reddick, wants you to know why.
Add Lasers to your Welding Toolbox
Laser welds can be used in manufacturing metal furniture, shelving and cabinets, industrial and commercial appliances like ovens, refrigerator doors or washing machines, counters, trays, tubes and ducts, medical or other hermetic enclosures and even turbine parts.
Reddick and his team welcome the challenge of discovering how to convert TIG or MIG welded parts to laser welding; however, often it’s so far into the development process that a redesign delays time-to-market or affects too many other components. That’s why it’s so important for engineers and designers to think about laser welding from the earliest stages of a project, before it’s too late to make changes.
Can laser welding replace conventional welding for your application? What weld options will work? What changes to the joints and overall design are necessary? What equipment is needed to prep the materials?
We believe your next project can benefit from the improvement in throughput, aesthetics, and possible cost savings that laser welding offers. But before starting a project, here are some things to consider.
1. Joint design
Part fit-up is critical: gap tolerances are tight as there is usually no filler metal added in laser welding. If you keep fit-up in mind, you can reduce the number and type of joints needed. Flanges, for example, can be made narrower or even replaced with butt joints. Further, because a laser-welding robot only needs access to one side of a piece, welding in tight or closed areas is possible.
One approach to part design and improved fit-up is building in special features like positioning tabs, interlocking joints (i.e. bayonet or tab-and-slot), and connector tabs to improve alignment and fit-up before welding. If your design ensures accurate alignment with minimal gapping (e.g. less than 5-10 percent of the thickness of the thinnest component for butt joints), your welded seams can look good and stay strong.
2. Conduction vs. keyhole welding and the heat-affected zone
Your application determines the type of weld used. For parts where appearance is important, conduction welding results in a wide, shallow joint that looks smooth. According to Amada Miyachi America’s Geoff Shannon, “Conduction welding is performed at low energy density, typically around 0.5 MW/cm2, forming a weld nugget that is shallow and wide. The heat to create the weld into the material occurs by conduction from the surface.”
Penetration or “keyhole” welding is narrow and deep for thicker sheet metal or areas needing high strength. Shannon explains, “increasing the peak power density beyond around 1.5MW/cm2 shifts the weld to keyhole mode, [where the laser creates] a filament of vaporized material, known as a keyhole, which extends into the material and provides a conduit for the laser light to be efficiently delivered into the material. This … maximizes weld depth and minimizes the heat into the material, reducing the heat-affected zone (HAZ) and part distortion … The keyhole is surrounded by molten material that acts to close the keyhole.”
Reddick notes that “the [laser’s] focal point is adjusted based on the type of weld needed. A higher focal point produces a more defocused beam for slower, more cosmetic welds; a lower focal point produces a small spot size for faster welds that aren’t appearance-critical.”
In both types of welding, energy from the focused and directed beam is absorbed at the precise weld site and the surface temperature rises. In mere milliseconds, the metal begins to melt. But because the energy is concentrated on a tiny area and because the laser passes by so quickly, the HAZ surrounding the weld site is much smaller than in traditional welding. This means there is less residual heat to distort, discolor or otherwise damage the workpiece. Watch the video below to see the difference between traditional welding and laser welding.
3. Setting up for the best possible weld
Precision is the name of the game when designing for laser welding. Blanks need to be cut and formed correctly so that joints fit tightly together. “Standard tolerances that apply to MIG and TIG joints will not hold the weld position as consistently as necessary for the laser beam,” says Reddick.
Estes uses top-of-the-line technology to automate the forming process, enabling them to hold tight tolerances. “Since we are dealing exclusively with fusion across the weld point with no filler being used, the weld location position needs to be held to +/- .005” and that at the point of the weld, both surfaces must be in contact with each other within +/- .0025”,” Reddick says. Careful fixturing is just as important as joint design. Reddick’s team can develop fixtures that can “hold joints accurately enough for the 4-kW, gantry-style laser system, which can position the processing head to within ±0.003 in. in the X, Y, and Z dimensions,” says Tim Heston in his profile of Estes’ work in The Fabricator.
Creating a Better Corner Weld
Estes developed much of the team’s expertise with laser welding in-house. Because so much of the research and writing on laser welding focuses on the auto industry, there was little guidance for the kinds of light-gauge sheet metal projects in which their shop specializes. Thus, in the late 2000’s a journey to a new territory began with Reddick experimenting on corner welds in cold rolled steel, which are usually slow and labor-intensive due to manual welding, grinding and cleanup.
In addition to higher throughput, laser welding reduces post-weld labor like grinding away built-up fillers common to TIG and MIG welding (not to mention a cleaner shop with far less dust and better air quality). The automated equipment means repeatability, part consistency and quality are increased, resulting in cost savings to pass along to the product’s sales base.
Writing in Fab Shop, Ed Huntress says that while laser welding has been in use since the 1980’s, “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.” But benefits like higher throughput, reduced grinding and finishing, cosmetic welds, less distortion and cost savings mean laser welding belongs in the engineer’s standard toolbox.