Laser-Cut Bevels for Better Welds

Always use the right tool for the work. This maxim sticks with me, particularly when I try to take a shortcut. We have all taken shortcuts, and they sometimes lead us operators to have to start over — a sure-fire route to a much longer job. But the right shortcut can save time, which translates to money in a production environment. You just need to think shortcuts through carefully before starting and, of course, make sure you’re using the right tool.

Shortcuts can dramatically improve weld prep, for example. Bevels can make a huge difference in work quality and production efficiency. Why are bevels such a critical part of welding? Many welds are often just fillets, which are commonplace, but even the common fillet weld has challenges. Fortunately, a few well-placed bevels or design changes in the right place can address potential issues.

Challenges of Fillet Welds

Let’s review some of these challenges, starting with a lifting lug, or eyelet, being welded onto a frame. This is simple, right? The answer to the next question brings some complexity — how large or small is the frame? Is the frame so large you can only weld it with a handheld welding unit? Or could the frame fit in a robotic welding cell? In this case, there are a few different options for welding.

The lug could be tack welded into position and then welded around it. That’s an efficient route, unless the weld is misaligned or completed too quickly. You could clamp down the part to ensure accuracy, but this may create new challenges with torch positioning or robotic systems moving around the eyelet. You could also jig it with fixtures so the eyelet fits in place. These are some of the logistical challenges of welding; however, we must also consider the technical requirements of the weld.

Logistics can make a huge difference in the quality of a finished weld. Better positioning and torch alignment improve movement possibilities and almost always create better results in the finished piece. Another aspect of good part positioning is that it promotes better body positions for the welder. Less awkward positioning for the operator reduces welder fatigue. If the position of the weld looks good, the weld will be good.

Improving Fitup

Now, let’s go back and reimagine the fillet weld. In the world of sheet metal, slotting and tabbing is a commonly used practice. The process allows a tab to be inserted into a slot, a round peg into a round hole, or whatever geometry the design requires. How can this design change help fillet welds? What if a slot is cut in the frame during the laser cutting process? Well, we can.

A laser-cut slot with two angular bevels, along with a tab or key inserted into the slot, will slide into position and self-locate, while the bevel allows the part to sit correctly. This allows the part to be held in place from underneath the top of the weld area, around the fillet weld location. The part and position are now correct, as required, and any clamps used are moved away from the welder or the robot while the weld is performed.

The main idea behind bevel cutting with the laser is to create a better fitup for the welder. A better fitup improves the welder’s torch angles, resulting in better accuracy and more uniform angles on the parts. One new idea for the bevel is to create slots and tabs, which allow the part to be trapped in place by the material itself, as well as by the weld — Fig. 1. This helps reduce failures, because we are using the material itself as a barrier against weld breakdown.

Designing Out Weld Defects

The concept of “designing out defects” in welding is not a unique concept. An article on the root causes of weld defects by Professor R. Carlisle “Carl” Smith, an AWS Certified Welding Inspector and NDE Level III, noted that, “Sometimes weld defects occur less because of welder error or poor instruction and more because the design itself makes the welder’s job difficult. Designers experienced in structural welding know to avoid certain elements when they can, but problems can arise from less experienced design engineers” (Ref. 1).

With the possibilities of improved weld designs, the quantity of welds required can now be reduced. Fewer welds mean a reduction in heat input into the material, which leads to less distortion. Laser welding is often utilized, as this process offers low heat input into the surrounding areas and creates a very narrow, deep, and focused joint penetration that is ideal for certain applications.

All processes, including welding, benefit from fewer steps and less input. Process simplification allows for better focus and control over these inputs. Put simply, if you only have one thing to worry about, it normally gets solved quickly. If you have twenty things, the task grows. Then you must figure out which of these steps is the most critical and solve them in order.

Returning to the eyelet example (Fig. 1), the diagram illustrates new design steps that show how the eyelet is held in position thanks to good design. This design, with integrated bevels, results in better positioning and better access for an easier weld. We can eliminate any clamps that would otherwise interfere with positioning.

Bevels in other areas offer additional benefits, including improved weld appearance for finished goods and less potential for weld cracking due to consistent bevels across a dimension. Bevels lower stress through more consistent heat input enabled by better positioning and design. Bevels also create cost savings, because less wire is used and welders can work faster due to improved access and positioning.

Conclusion

Creating bevels during the laser cutting process eliminates multiple steps and increases safety. It is a real cost-saving shortcut, but it does require a review of your designs and parts to ensure best utilization and overall effectiveness.

Reference

1. Smith, R. C. 2008. The root causes of weld defects. The Fabricator. thefabricator.com/thefabricator/article/arcwelding/the-root-causes-of-weld-defects

GRANT FERGUSSON (grant.fergusson@trumpf.com) is the TruLaser product manager at TRUMPF Inc., Farmington, Conn.