As fuel prices continue to climb, thin tank manufacturers continue the push toward lighter-weight products for road and rail. Whether they are pressure vessels or mobile storage tanks for truck trailers or train cars, the lower the overall weight, the lower the overall cost to ship goods from point A to point B.
New safety regulations for transportation vessels, however, are redefining the standards for impact resistance, challenging thin tank manufacturers to reduce weight in a way that doesn’t compromise strength or performance. In that pursuit, hybrid laser welding has emerged as an ideal manufacturing process for both reducing weight and producing exemplary impact characteristics.
As suggested by the name, hybrid laser welding combines a laser beam and an electrical arc to deliver what many consider an optimal weld pool. Hybrid laser welding differs from standard welding processes through the introduction of the laser beam, which can deeply penetrate the weld joint.
As with standard welding processes, there are three main types of hybrid laser welding: MIG, TIG and plasma. Hybrid laser welding, however, surpasses the performance of standard welding processes by producing very low heat input, low distortion, a very small heat affected zone, small weld beads as well as full penetration welds and more. And, often times, all in a single pass.
To better understand what hybrid laser welding brings to the table for thin tank manufacturing, Shop Floor Lasers had the opportunity to speak with Edward Hansen, global product manager at ESAB Welding & Cutting Products, a manufacturing leader in welding and cutting equipment. To explain hybrid laser welding’s benefits, Hansen began by describing a typical end product: thin tanks with a wall thickness up to 5/8 in. or 16 mm.
Hansen explained that, traditionally, these tanks were produced with mild steel, but today, many manufacturers are shifting to high-strength steels, stainless steel and duplex stainless steel, exotic alloys as well as aluminum. These high-performance materials reduce weight and achieve better corrosion performance, and they just so happen to be an area where hybrid laser welding performs well.
“The key characteristics of a hybrid laser weld include very low heat input compared to a conventional weld,” he said. “It can be about 10 to 15 percent of the heat that a normal weld would put into a part. So that means that it has a very small heat affected zone, which is typically the weakest point. That also means that we have very low distortion. With these high-performance materials, the residual stress from the thermal process is directly proportional to yield strength. So as you start to use stronger materials, the stress that the weld puts into the part goes up proportionally. As these industries are shifting to high-performance materials, welding-induced distortion becomes much more problematic. So by cutting the heat input, we can mitigate the undesirable effects of that.”
So while thinner, stronger materials are the focus moving forward, manufacturers must recognize those challenges and also take into consideration the significant cost impact that comes from shifting to these new structures. Fortunately, another one of the major benefits of hybrid laser welding is its ability to lower production costs. The fact that it’s a faster process is one of many ways that manufacturers can reduce overhead.
ESAB developed a line of automation for the tank industry with HLAW as a key piece of the new approach.
Speed to market
“Depending on the thickness of the material, with a traditional welding process, you might have to do many passes to fill a joint,” Hansen said. “For a 15-mm-thick joint, you might have three to five passes conventionally. We can do that in a single pass or a single pass with a cap. It provides a big reduction in the preparation required and the cleaning between welds.”
Further cost and time savings came to light when Hansen described how thin tanks are produced. “Typically a thin tank is made up of various rings like slices of bananas that are welded together ring to ring to ring via girth welds.”
To create perfectly round rings, manufacturers must manually manipulate them, he explained, injecting more cost into the overall process. With hybrid laser welding, however, plates can be welded in the long direction, up to 28 feet, allowing thin tank manufacturers to execute longer shell sections with fewer girth and round seams.
“The seam welds are easy to automate because they’re straight lines,” Hansen said. “But once you make a ring, they have to line up and they have to be round and they have to be manually manipulated. So the weld of the girth is much more expensive to do than the longitudinal weld. With high productivity and the fully automated capability of hybrid laser welding, we can do longer shell sections. It shifts them from expensive manual girth seams to fully automated long seams. There’s a big reduction in cost, and you can produce more tanks using the same real estate inside a plant.”
The assembly of tanks is also simplified because the weld beads produced by hybrid laser welding are incredibly small and flat. The size of the root of the weld is tiny, like a pencil lead, which makes downstream operations easier. As an example, many tanks, depending on the materials they’ll be moving, have to have their interiors coated with paint or plastic. The smaller the welds, the easier the coating process can be.
“We weld from the outside in, so that tiny root bead is on the inside,” Hansen explained. “They’re so small and uniform and clean that they require little or no preparation after the weld is done. Conventional welds might require a considerable amount of manual grinding to get them smooth enough for food or chemical grade containment. So there’s an advantage there.”
That small bead size – as tiny as 1 mm – is also beneficial for the end user in terms of warranties. The bigger or rougher the weld is, the more difficult it is to coat and then clean. This aids in a product’s lifecycle, warranty exposure and the overall durability of the coating.
Hybrid Laser Welding Process:
1. Newly formed weld bead
2. Insert shielding gas
3. Focused laser beam
4. GMAW torch
6. Electric arc
7. Molten pool
Going back to the case of government regulations regarding impact resistance, thin tank manufacturers that leverage hybrid laser welding are able to create stronger end products. Because of the high cooling rate and the fine grain structure of hybrid laser welds, manufacturers achieve high productivity without high heat input, which Hansen described as deleterious to impact performance.
Because of hybrid welding’s low heat input, it also produces a small heat-affected zone. Additional key characteristics include improved low-temperature impact performance, better cosmetic quality of external weld beads, reduced weld repair and post-weld preparation, as well as one-sided, single-pass welds for material up to 12 mm. These characteristics allow manufactures to produce their products smarter and faster, keeping long-term welding costs down.
In terms of the one-sided welding process, Hansen explained that hybrid laser welding can eliminate the need for manufacturers having to access the back side.
“There doesn’t need to be any backing material,” he said. “Typically on a one-sided weld, you’d have to either have a backing material behind the weld if you wanted to weld from one side, or you’d have to weld from two sides, which means you would have to weld from one side and then go around to the other side and often grind back to good metal and then re-weld from the other side. There’s a lot of manual preparation in welding for the second side.”
As technologies have evolved, existing barriers to adoption have been removed. Some of those initial barriers included welding codes, but hybrid laser welding is now capable of being qualified by ASME and AWS codes, among others.
And, in recent years, more barriers have been overcome through technology implementations. Smarter systems have been created by companies like ESAB to help the user develop welding parameters and pre-developed parameter sets. Instead of making machine operators do the heavy lifting, there is sophisticated software available that can take on the brunt of it.
“We’re continuing our development and are focusing on smarter systems, reducing the learning curve for adoption, coming up with synergic and smart welding parameters for customers. We can make controls easier to manage and all of these measures have been addressing some of the remaining adoption issues that some customers may have.”
In fact, ESAB has developed an advanced adaptive control system that broadens the process window for handling joint gaps and mismatch by a factor of five when compared with conventional welding controls. This allows the use of conventional cutting processes to manufacture tank shell sections rather than machining, which is again, more cost effective.
To further illustrate the advancements being made with hybrid laser welding, Hansen used the analogy of switching from an old flip phone to an iPhone. “Even though the iPhone is more sophisticated, it’s easier to use,” he said. “The old phones were difficult to use and had embedded menus. You had to go from one menu to another menu and you had to remember how to configure things. And it is that kind of change that we’re making to the controls. Operators don’t have to learn G code and ladder logic and all of the things that you needed to know in the past.”
In today’s technological day and age, Hansen explained that computing power is cheaper than it’s ever been. “It would be more expensive to make it hard to use,” he mused.
One of the biggest changes that Hansen sees coming is direct diode laser reaching a point where it has the beam quality to be industrially relevant. Additionally, laser costs are dropping at a rapid rate, he said. “As solid-state lasers get cheaper, the form factor improves,” Hansen continued. “They’re becoming smaller and more compact, and it just makes the hard parts of adopting laser welding even more approachable. Going forward, it’s nothing but a good scenario for widespread adoption.”
So now that so many barriers have been overcome, it’s not surprising to hear that thin tank manufacturers are giving the process major consideration. And equally, it won’t be surprising to see hybrid laser welding make its way into other manufacturing environments, such as those for ship building, truck trailer beams, truck chassis frame systems, rail car panels and beams, automotive frames and chassis components, and suspension systems.
Overall, welding productivity coupled with lower operating costs – which can be as low as one tenth of that of GMAW per foot of weld – are driving hybrid laser welding toward greater prominence. And with technology advancements easing the process, it’s sure to be the go-to method for manufacturing in the transportation industry today and for years to come.