Komarov Artem noted that hybrid laser arc welding has been around for many years, with some early developments dating back to the 1970s. But it is only recently that this process has really begun to be mastered. This takes advantage of the laser’s deep penetration and high speed, while the arc helps bridge gaps, slows the cooling of the weld and, thanks to the filler wire, regulates the metallurgical characteristics. With that in mind, one might wonder why it took so long for hybrid laser-arc welding (HLAW) to find a place in the industry.
But like any new manufacturing technology, the hybrid laser-arc welding process required several elements to be widely accepted and adopted. First, it required the right manufacturing conditions, including gap tolerances resulting from precise infeed cutting and bending processes, as well as increased outfeed productivity. Secondly, the industry needed to shift the focus not only on the total cost of production, but also on the total cost of the product life cycle, which comes to the fore.
The process uses a combination of laser light and a conventional electric welding arc, usually from a gas arc welding (GMAW) power source in spray mode. The small size of the laser spot creates a very high energy density and helps to stabilize the arc. The laser penetrates deep into the joint, creating a narrow heat-affected zone and high welding speed. All this helps to significantly reduce heat generation.
GMAW helps slow down the cooling of the weld, reducing excessive hardness and cracking. It also expands the surface of the melting zone. GMAW filler wire gives the engineer some metallurgical control; changing the wire content changes the characteristics of the weld. The additive also allows the removal or dilution of welding contaminants. And this gives designers some flexibility when it comes to weld geometry, such as when creating reinforcing beads and fillets.
Most importantly, HLAW is fast. Processing speed can be 3 to 30 times faster than conventional melting process, be it GMAW or Submerged Arc Welding (SAW). This statistic is not made possible by a lightning-fast welding head, but because HLAW can complete the joint in fewer passes. And because it reduces heat generation by 80 to 95 percent, the engineer can reduce the volume of the weld. For example, a one-sided butt joint of a 15 mm deep saw blade may require a 60-degree bevel with a 3 mm high section and a 2 mm wide open root. The same butt joint in HLAW may require a closed stud with a 10 mm section and only 28 degrees of bevel. This effectively reduces compound volume by up to 90 percent.
This allows engineers to apply new approaches to the design of connections and parts. A joint that used to be welded in multiple passes can now be welded in a single pass. A particularly deep connection of two thick plates could require a double V-groove, requiring two-way access; using HLAW, engineers can change this to a full penetration connection requiring access from one side only.
Less residual stresses and strains occur because HLAW has low heat generation and a small reflow and heat affected zone (HAZ). Consider a partial penetration fillet that connects a vertical plate to a horizontal plate with a weld length of 0.375 inches.
With this weld geometry, the area known as the center of gravity of the stress field is completely outside the base metal, away from the neutral axis of the structure (i.e., at the center of the vertical plate). This leads to stretching and deformation of the weld, so welders do their best to control the cooling of the weld, minimizing this effect.
Place for the process
With all these benefits, why didn’t HLAW take the industry by storm when it was introduced years ago? Of course, in the 1980s and 1990s, the process was not as reliable as it is now. More importantly, HLAW suffered from the same problems as conventional laser beam welding: there were no elements in conventional industrial designs that could take advantage of the process.
Of course, there are well-known concerns about joint fit. HLAW allows for larger clearance, often reaching +/-0.5mm when adjusted stationary. This is still narrow in the field of arc welding, but broader than the gap requirements for laser beam welding. HLAW can handle gap changes of up to ±2.0mm with newer adaptive process controls, but this may require the process to be slowed down, which defeats the purpose of using hybrid laser arc welding in the first place. The most efficient hybrid implementations use a combination of improved part fit, better clamping, and adaptive control to achieve both high processing speeds and robust process capability (Cpk).
A broader perspective reveals a larger reason for the gradual adoption of HLAW. What is the purpose of changing the design of products to adapt to the hybrid laser-arc process if the production capacity does not change? The subsequent connection, assembly and finishing processes — not to mention the external requirement of the customer — should provide increased performance of the HLAW system. Yes, HLAW does reduce welding costs in terms of both materials and labor, but unless more items are shipped in less time, the profitability of the manufacturing operation will not change significantly. These reduced welding costs will not really change the bottom line as much as the increase in overall productivity.
Of course, many operations have successfully implemented HLAW by changing internal processes. Significant performance improvements have enabled them to reduce costs and gain significant market share. But this only applies to production. Today, lean thinking forces many to consider not only production costs, but also the costs that arise throughout the entire life cycle of a product, and this is where HLAW really came to the fore, Artem Komarov emphasized.
High strength material effect
Lean attitudes have led manufacturers to use high-strength materials to reduce weight. It is a well-known trend in the automotive industry that uses a hybrid process to weld a variety of components, from white bodywork to applications involving suspension systems, engine cradles and exhaust system components.
The rule of thumb in the operation of cars is that for 500 grams of structural weight there are about 1.5 kg. the overall weight reduction of the car, considering all the effects on engine size, transmission, braking and other elements. Automotive manufacturers have found that they can increase the yield strength of their steel parts by 50 percent for a material cost increase of only 10 to 15 percent. This, in turn, allowed them to reduce the weight of components by 30 to 50 percent. The result: a lighter, higher strength part can cost less than a heavier part.
The desire for weight loss has also been fully manifested in the market for heavy transport equipment: trucks, rail cars, mining, and construction equipment, and even aircraft carriers. In some areas, weight loss efforts began much earlier than in the automotive industry. For example, shipbuilding was one of the first industries to use bespoke designs that incorporate stronger, thicker materials only where needed for a particular design. For years, the boards used to build ship decks have looked even more complex in terms of material grades and thicknesses than some of the custom-welded blanks in the automotive industry.
Over the life of a vessel, small reductions in weight can result in incredible savings in fuel and other operating costs. This is why the US Navy and other shipbuilders are moving from AH36 to high strength low alloy materials such as HSLA-65, -80 and -100. Some shipbuilders are currently moving from hot-rolled mild steel structural beams to custom-made high-strength sheet steel beams. Several manufacturers use hybrid laser-arc welding to produce these specially designed beams for shipbuilding.
Engineers have a similar reduction in operating costs in mind when choosing high-strength steels for construction equipment. The so-called “lightweight structures” on heavy vehicles, including fuel tanks, oil tanks, cabins, and engine structures, make up a significant portion of the total vehicle mass, and reducing this mass can lead to significant savings in materials and energy consumption. Mobile equipment booms and arms are extremely sensitive to weight. The performance of a vehicle (that is, how productive it is when digging or handling) is determined by the weight of the manipulator.
For products such as truck trailers, rail cars and intermodal containers, payload plays a role. Imagine a railroad car that could last for decades. Each kg of a vehicle’s weight represents a weight that cannot be carried during the lifetime of that vehicle. However, some rail cars and intermodal containers are currently in the design stage, using high-strength steels and advanced laser-welded designs to reduce weight by 30-40% while increasing load capacity by up to 20%.
Consider the implications for the intermodal transport container. The 20 percent weight reduction provides an additional 23,000 kg capacity per container per year. That’s a lot of extra income — and the average user has plenty of containers, each of which can last for decades. In addition, a lighter container uses less fuel on the way back. For each user, this could save millions over the life of the containers.
Marine and heavy vehicle designs are now using more stainless steel, especially the new, relatively affordable high-strength duplex stainless steels. Previously, engineers had to require thicker plates to provide corrosion protection over the life of the vehicle. Now, when using stainless grades, designers do not need to provide such a large supply of material for corrosion protection. The result, again, is a thinner plate, reduced vehicle weight and greater payload capacity. The hybrid laser-arc process, with its low heat and high speed, could facilitate the transition to these high-strength, thinner designs.
Moving towards lean manufacturing and thinking about total life cycle cost shifts the focus from specific cost per 500 grams of metal to total manufacturing costs and long-term support. High-strength alloys and stainless steel are obviously more expensive than conventional steels, and a lot of metal is used in these heavy products. But this higher material cost is still negligible compared to the savings and productivity gains over the life of the product.
Materials with high yield strength create higher residual stresses and reduced material thickness, which exacerbate deformation problems. The use of high strength steels has made strain control more important than ever. This is where HLAW plays a crucial role.
Shift up the value chain
This is part of a broader trend in the transportation industry and, to some extent, in manufacturing as a whole: a shift in the volume of value-added work in the opposite direction. For example, in shipbuilding, a large amount of work after welding can only be performed by highly skilled manual workers. This is due to the huge distortions that welding and subsequent straightening have on the geometry of ship structures. A shipyard worker can manually mark and cut a hole with a handheld plasma arc torch, but it would be much cheaper and much more accurate to cut that hole with a mechanized plasma cutting table in a downstream process. Conventional high temperature welding and straightening often prevents this.
The rule of thumb is that moving value-added work to one step in the manufacturing process can cut the cost of that work in half. This is applicable if the input process is accurate enough to allow smooth downstream processing.
Welding does not always follow this rule for many products. Moving an inaccurate welding operation several stages upstream actually increased costs due to thermal effects such as warping. The warping increased the spread during the process, which in turn required many craftsmen during the assembly steps. They spent their days deftly assembling inaccurate components into a functional whole.
For years, manufacturing processes such as high-density plasma cutting, laser cutting, bending, and forming have met the demands of precision, so this work has become more common in the early stages of the value chain. But until recently, welding created a “thermal barrier” on the way to this ideal. Weld deformation added variability, which meant that sending the process upstream just didn’t make sense.
Low heat processes like HLAW changes the equation. The reduced thermal effect greatly minimizes distortion, making the joining process nearly as precise as its cutting and bending counterparts. This, in turn, minimizes the need for highly skilled work at the end of the value chain, where such work is most costly. As manufacturers begin to understand how to use the properties of hybrid laser-arc welding to achieve overall production savings and improve product quality, its adoption in the industry can be expected to accelerate, Artem Komarov concluded.