Welding Trends For The 21st Century

Lighter Metals Will Push Low-Frequency TIG Welding
Collision shop welders will be dealing with lighter metals and new technology as the auto industry advances into the new millennium. In addition to keeping up with day-to-day concerns, there will be other changes to deal with as today's popular metal inert gas (MIG) systems will likely face increasing competition from tungsten inert gas (TIG) welding and resistance spot welding.
There is a trend to do a lot more replacement work and less repair. I see a lot more parts that are being classified structural or HSLA (high-strength, low-alloy). Straightening alloy steel just isn't done anymore, although a lot of that has been done with the malleable steel in the past.
Chesterland Auto Body is a complete service and collision shop servicing all makes. There are eight employees in the shop, including two paint teams working in one downdraft and one cross-flow room. All welding work is done on three units: two Hansen hand-helds and one Lincoln AC/DC Stick Welder. Every job is MIG welded at Chesterland and it is expected to continue that for a long time. There is no more brazing or acetylene welding done anymore. Everything is MIG. The Hansen units are 160 amp units; the Solar is 175 amps.
One of the things paramount to doing a good job is proper use of a good weld-through primer. It's really important to stay on top of the technology to keep the seams from corroding. You don't want to get sued 15 years from now because the car started coming apart at the seams.
In the 1970s, unitized body construction became the rage, saving weight by using thinner material. When high-strength steel became widely available, its use forced body shops to go to MIG systems to handle the welds. Smaller and less expensive 110 amp machines became commonplace.
MIG or "squirt-gun" welding grew in popularity over the past 15 years as shop owners were attracted by its quick training time and ease of use. The downside with MIG is the difficulty controlling MIG's high deposition rate with the electrode wire and the time required to grind down welds. Still, it remains the most popular aftermarket repair welding technique.
More recently, because of the high cost of high-strength steel, auto makers have begun going back to mild steel, using thicker steel in the car's body construction. The added weight is being offset by more fuel-efficient engines, however, it changes the repair strategy. As the structural panels on the newer cars become heavier, it requires more amps to do the job. The upper panels generally remain lighter.
Toyota, Honda and similar manufacturers now insist on a minimum 200 to 250 amp power supply. Another typical difficulty is with feed problems. A good feeder costs more than a MIG welder.
Cost, both for equipment and training, is probably the main factor that has kept resistance spot welding equipment out of many shops. All car manufacturers use resistance spot welds, therefore shops should consider them for any application where high-strength steel is being fused or where a factory-look weld is required. Resistance spot welding will let a technician work four times faster than MIG. The grinding task associated with MIG will disappear. Why should one fill up and then have to grind down a weld?
Today, resistance spot welding has about 1 percent of the market. That will change over the next 24 months as repair shops find themselves dealing more with high-strength steel. MIG will not go away, he concedes, but will be used for butt welding or structural welds in places where a resistance spot welder cannot reach.
TIG welding is another leading contender for handling the new materials shops will encounter. While not a new technique, as the auto industry moves to lighter metals in construction, TIG promises to play a larger role in welding shops. Wyatt Swaim, a consultant for Lincoln Electric who is best known for his work at the Indianapolis 500, is a big proponent of TIG, especially in lightweight, high-strength applications. "TIG is versatile ... it can do aluminum, steel, stainless steel or titanium. It is much like gas welding but with more precise control, lower metal distortion, more precise disposition of material and not a lot of after-welding cleanup," Swaim said. As manufacturers move to lighter vehicles, shops will face the need to handle metals like aluminum and titanium.
Aluminum Is ComingAs part of the move to lightweight cars, many manufacturers are looking at aluminum. Ford already has paraded an all-aluminum Taurus at several shows. Chesterland Auto is set up for aluminum with the wire and argon gas. "We don't get into a lot of aluminum yet," Mader said, adding that he expects more down the road.
"I haven't seen it in the lower-end vehicles. It's more in the top-of-the-line cars like Mercedes and Jaguar," Mader said. "Occasionally you'll see it in a first-run hood on the Fords, but the replacement will be steel." He adds that aluminum also can be found in bumper components.
Ron Kuehn, business development manager for the Inter-Industry Conference on Auto Collision Repair (I-CAR), agrees that the market is headed to aluminum. "It is still the next evolution of the unibody program," he said. To this point, he feels MIG will be the tool of choice for welding aluminum because of the high-frequency nature of TIG. "High-frequency welding machines and cars' on-board computers are not compatible," Kuehn said.
Kuehn points out that plasma cutters had the same problem when they first came out in the early 1980s. The industry quickly went from big machines to smaller, low-frequency units. Similarly, emerging TIG technology may make it possible to do low-frequency TIG welding on aluminum.
Neal Borchert, TIG product manager for Miller Electric Manufacturing, Appleton, Wis., agrees that TIG's biggest problem is the high-frequency interference with computers. Miller has a low-frequency unit that sells at $7,700, a price tag that puts them beyond the reach of the typical collision shop. Called the Aerowave, it can operate at single-phase or three-phase, with or without high frequency.
In Europe, high frequency is frowned on for a number of reasons, including technical ones. In the U.S. market, however, there is a constraint on primary power input because single-phase is used everywhere. In Europe, three-phase is typical. For that reason, the largest market potential for a low-frequency unit is overseas. In the United States, the strongest interest in low-frequency TIG units comes from the racing world, where $12,000 aluminum blocks and $10,000 testers are commonplace.
However, emerging technology generally drops in price as demand increases. Borchert says there will be a full-featured, downsized version of the Aerowave on the market later this year at a lower price than today's Aerowave.
Naslund points out that much of the aluminum fraction in today's street cars is not in the panels, but in the castings for the engine and gear box. While the typical car has only 17 pounds of aluminum in the panels, he agrees that aluminum is the metal of the future. He notes that electric cars, gaining popularity particularly in California where he works, will be all aluminum when they finally hit the market in five or 10 years. Resistance spot welding can be used for aluminum, although the technique requires using a larger nugget.
Swaim agrees that electric cars are coming and that they will drive aluminum body panels into the general market. However, he says titanium material is also showing up. "Titanium has gone down in price and you'll start to see more of it in car parts," Swaim said. "Technicians need to understand the metal and how to shield for it."
Corrosion is always a consideration - remember, it induced DeLorean to use stainless steel in his car bodies. Swaim forecasts a Mercedes-quality electric car will be built with titanium body parts. "Don't be surprised if you see titanium panels, rather than aluminum," he said. "It is non-corrosive and salt resistant. Titanium will be the metal of choice since it is so tough." TIG technology works well with titanium, he adds.
Training is the key to proper use of TIG equipment, Swaim says. It will take about a half-semester of night school classes to make a technician proficient with TIG. That's a lot of training compared to the several hours required to get a technician working with MIG or an AC/DC buzz box.
"One day's worth of training with TIG will just get a technician frustrated," Swaim said. "They'll put the tools down and say they'd just as soon grind." But Swaim says such workers, and shop owners, are missing a bet. "I'd absolutely recommend TIG, and I do all processes," he said. "When it comes to working with thin materials, TIG is the only way to go."
A TIG system such as Lincoln Electric's Square Wave TIG 175 will run about $1,300, including accessories. Shipped as a complete package, all a welder has to do is connect the power, add gas and go to work. It provides single range, continuous control from 12 to 175 amps (although operation around 30 to 45 amps will handle most body shop jobs).
An upgrade kit to convert AC/DC to TIG is available for $249. Added to the $350 cost of a typical buzz box, a shop can get into TIG for about $600.
"There is no 25-pound spool of wire needed," Swaim points out. "You'll find you were using about five times as much material with MIG as you do with TIG. Plus, there is five times less grinding with TIG." Where TIG shines is in its focused hot spot. The heat-effective zone with a TIG weld is between 1/16 inch and 1/8 inch, contrasted with 1/2 inch for a typical MIG weld.
Some of the money saved on materials and grinding will have to be spent up front in training. Swaim is working with the Lincoln Foundation on a video that will teach proper TIG technique. It should be available in the fall of 1997 at a nominal cost through suppliers or from Lincoln Electric in Cleveland.
I-CAR has offered several classes on aluminum welding. "The guys interested in being leaders, being in the forefront of the field, will be ready for aluminum when it comes," Mader concludes.
Miller Electric announced in January a package for its Econotig TIG welder, including a heavy-duty current and contactor foot control for industrial-type uses. The TIG/Stick package produces small, high-penetration TIG weld beads with no spatter and can be used on any weldable metal 18 gauge to 3/16 inch thick. In the Stick mode, it can weld 3/32-inch and 1/8-inch electrodes.
Miller also offers the Millermatic 185, a MIG welder with 30 to 185 amps power and the ability to weld stainless steel and aluminum, according to product manager David Anderson. While I-CAR generally looks for 200 amps when welding aluminum, the complete 185 package, at $1,199, is versatile enough to provide intermittent support around a shop. Anderson also notes the SpoolMatic 30A spool gun is handy for aluminum repair and use with other metals. It uses a two-pound spool, not the usual 30-pound spool, making it versatile for occasional jobs.
Safety ConcernsAnother major concern in welding shops is safety. Many manufacturers now coat metals with toxic materials to prevent rusting in such susceptible areas as the rocker panels, according to Hansen. "The result is more toxic fumes," he said. "The guys complain that the smoke is making them sick."
Shop managers like Mader agree that they have encountered some vapors as they burn through the coatings. However, Mader says that it has not been a problem for them.
Both steel and aluminum panels can produce toxic fumes that should be filtered away from the workplace. Hansen recommends the articulating MIG arms that his firm produces as a practical solution. "The trend is to be cleaner, bigger, more professional," he says. "The goal is to eliminate sloppy work spaces."
Hansen's MIG arm has a smoke extraction system that sucks fumes through the welding gun, up the hose and out the arm. The fumes are either vented to the outside or trapped in a filtering system. Hansen acknowledges that there are other solutions, as well. Audi, in its European operations, has developed a special overhead gantry system for their repair bays. "The goal is the same - to get hoses and other things off the floor," he said.
Naslund agrees that vapors can be a problem. He points out that new cars are dipped in vats and receive an electro-coating of zinc. The E-coating generally includes some plastic, but it is the zinc that can cause trouble for the worker. "The auto aftermarket shops are one of the only industries that weld zinc," Naslund said. "The manufacturers weld first, then apply the zinc."
Naslund, whose firm deals in resistance spot welding equipment, says resistance spot welding - unlike MIG welding - does not take off the E-coating because it can weld right through the coating. "The machine that creates more heat will create more fumes," he said. Since the resistance spot weld creates less heat, Naslund says it is less hazardous.
TIG also has advantages over MIG. Because TIG uses an inert process with argon gas, it does not put off as much smoke, Swaim notes. The more focused heat-effective zone also means there is less zinc material burned off.
Hansen says that even such a minor improvement as using a central vacuum system, rather than a broom, can make the shop more productive and safer.
Naslund cautions against destroying the film between two panels since that is the likely spot for corrosion to start.
The bottom line, of course, is to have the safest possible weld for both the vehicle owner and for the technician working on the car.

Welding of Pure or Low Alloy Materials: Difficulties and Solutions

Pure metallic materials or low alloyed materials find many engineering applications and has many potential applications. For example aluminum alloys find extensive applications as thermally conducting fuel cladding materials in nuclear research reactors. Another important material is TZM (Titanium Zirconium Molybdenum); which contains more than 99.5% Mo. There are many applications where pure or nearly pure (or low alloy) materials need to be welded and welding of these materials is not so easy. So what are the problems and what could be potential solutions.
Difficulties:
1. High thermal conductivity:
Pure or nearly pure metallic materials exhibit high thermal conductivity. Therefore, the heat deposited at the joint line runs away quickly from the joint and thus entire component gets heated up at the cost of fusion of the material near the joint. Whether high energy density process like Laser Beam Welding or Electron Beam Welding will help? It helps to some extent but there are other problems.
2. High reflection:
The metallic materials which exhibit high thermal conductivity have high reflectivity as well and this acts as double whammy for laser beam welding of such materials – First, they will reflect most of the energy and then they will conduct away whatever was absorbed. But this is not all there is one major metallurgical issue.
3. Narrow liquidous:
Low alloy materials have narrow liquidous and therefore melt solidifies quickly leading to entrapment of gases / vapors and thus formation of porosity.
So what are the solutions?
Solutions:
1. Twin Spot Laser Beam Welding:
In this technique, the laser beam is focused at two spots – one leading and another trailing. Now many things can be varied to suit the purpose like power of the leading and the trailing beam and the distance between the two. The leading spots serves the purpose of melting the materials surface for promoting the absorption of the trailing beam and the trailing beam penetrates deep and prolongs the melt life and thus enables the release of the entrapped gas / vapor and thus minimizes occurrence of porosity.
2. Laser Arc Hybrid Welding:
Here the arc creates a shallow melt skin and the falls in this molten skin leading to deep penetration. Arc welding has longer melt life and thus occurrence of porosity is minimized. Additionally, arc welding has larger gap tolerance between the work pieces and therefore edge preparation is reduced to that extent.

Materials Processing - Diode lasers test their mettle in surface treatment

Most everyone has heard the old adage, “If it ain’t broke, don’t fix it.” But history has repeatedly demonstrated that technology advances can often improve a process or outcome we didn’t even realize needed fixing. (Then it’s just a matter of waiting until it becomes affordable.)

Advances in high-power diode lasers are a case in point, especially when it comes to materials processing. During the past 20 years, multimode diode-laser bars and individual single-emitter diode devices have achieved increasingly higher output powers and better power-conversion efficiencies, allowing semiconductor lasers to evolve from the scientific arena into true industrial tools. In fact, interest in direct-diode materials processing has been a key factor in the development of high-power diode lasers. While diode lasers are still a few years away from being practical ablation or cutting tools for heavy metals, they are gaining traction in materials-processing applications in which beam quality and brightness are not critical to the outcome, such as surface treatment.

Surface treatment is one of the most efficient uses of laser energy and one of the most controllable heating processes when working with metal components. Laser-based techniques such as heat treating, cladding, alloying, and welding have become well-established in the automotive, aerospace, energy, defense, and machine-tool industries for applications ranging from increasing wear resistance of turbine blades to improving corrosion resistance and performance in car engines. Historically, these applications have been served by Nd:YAG and CO₂ lasers, both of which are well-accepted materials-processing tools. Displacing these lasers would require a solution that brings not only operational but financial advantages.

This is where high-power diode lasers come in. While engineers continue to work out a few remaining kinks-such as how to offset the thermal issues that arise in a compact package as it churns out 3 to 4 kW of power in a single shot-the diode laser offers a number of advantages for industrial surface-treatment applications as compared to the Nd:YAG or CO₂ laser. In particular, the shorter wavelength of the diode laser enables much better absorption of the laser energy, leading to an overall lower power requirement for surface treatment applications. A diode-laser cladding system can typically perform cladding with half as much laser power as a CO₂ laser (see table). The diode laser typically has 25% to 30% wall-plug efficiency, compared to about 10% for the CO₂ and the Nd:YAG laser. In addition, the diode laser can be fiber-delivered, which makes it more attractive for automated applications. Also, there is no need to precoat the metal to increase absorption-a necessity with the CO₂.

Electrical energy costs
	CO2	Nd:YAG (diode pumped)	Diode
Required laser power	5 kW	3 kW	3 kW
Average wall-plug efficiency	10%	10%	30%
Approximate electrical power consumption of the lasers	50 kW	30 kW	10 kW
Electrical power cost per hour @0.09$/kWh	4.50 $/h	2.70 $/h	0.90 $/h
Source: Fraunhofer

“Most laser-cladding operations use the CO₂ laser, but there are inherent disadvantages compared to the diode laser or other lasers with the same wavelength as the diode,” said Eric Stiles, laser-division manager at the Fraunhofer Center for Coatings and Laser Applications (Plymouth, MI). “But the diode laser is interesting for applications like cladding because of the low cost for kilowatt power. A 3 to 4 kW diode-laser system can do the same work as a 6 to 8 kW CO₂-laser system because a lot of the energy of the CO₂ is lost. With the diode you get much better absorption with a lot of materials, especially at lower power intensities where CO₂ absorption is poor.”

Pros and cons

Despite these advantages, however, diode lasers still need further refinement in terms of being reliable enough for intensive industrial applications like laser cladding, a process in which laser energy is used to melt or weld a metallic or ceramic powder onto a substrate to create a wear- or corrosion-resistant layer on a metal component (see Fig. 1). While the current generation of high-power diode lasers has resolved many of the reliability issues that plagued earlier generations, random failures remain a problem when a diode-laser system is used in high-volume production applications, particularly when pulsing is required. Thus, while the overall cost of an industrial diode-laser system should be lower, the need to replace the diodes more frequently disrupts production cycles and increases overall cost of ownership.

“The main specificity of this market [materials processing] is the operating regime,” Franck Leibreich, director of marketing at Newport’s Spectra-Physics Lasers Division (Mountain View, CA). “Long micropulses-one second on, one second off-is the most difficult operating regime for the diode because it stresses the diode very much, which leads to random failures. So we and others are working to make the lasers more robust by focusing on the interaction between the soldering material and the heat sink in order to compensate for the coefficient of expansions. The goal is to optimize the thermal exchange between the materials.”

Brightness is another factor. According to Leibreich, the need to transform inherently low-brightness, highly asymmetric diode lasers have led to the development of several important beam-shaping and beam-combining technologies (see www.laserfocusworld.com/articles/250394). As a result, diode-laser devices that produce 4 kW from a 600-µm-diameter-core fiber are now being used in applications such as cladding and annealing.

“As diode lasers continue to evolve, we can predict that there are two areas where this technology will grow in attraction for industrial applications,” said Phillip Anthony, manager, macro business unit at Rofin-Sinar (Plymouth, MI). “The life of the diodes and diode bars will get longer, and as this happens the long-term cost of ownership becomes less of an issue. Second, a lot of time and energy is being spent on improving the beam quality, which should lead to becoming more realistic for fiber delivery. In the end this will be driven by the cost of ownership and the predictable life of the diode that can be measured in tens of thousands of hours.”

The real world

While efforts are under way to improve the reliability and lifetimes of diode lasers, some companies and organizations are already demonstrating the efficacy of this technology for surface treatment. At Fraunhofer, for example, Stiles and his colleagues have developed a new cladding process that utilizes a 3 kW Rofin-Sinar direct diode laser and a coaxial powder-feeding nozzle. It was initially tested in the oil industry, in which new wear-protective hard coatings were developed, tested, and applied to a number of down-hole drilling tools.

On the commercial front, Nuvonyx (Bridgeton, MO) and Laserline (Mülheim-Kärlich, Germany) have both had some success with their diode-laser cladding systems (see Fig. 2). Nuvonyx, founded in 1998 by former employees from the McDonnell/Douglas Laser Systems Division, has been a pioneer in the commercial introduction of high-power direct-diode and fiber-coupled laser systems for industrial applications in aerospace and defense. In 2005 Nuvonyx was acquired by ICx Technologies, which then acquired Thales Laser Diode (Orsay, France), which has since become Nuvonyx Europe. The company’s newest product, introduced in June 2006, is a fiber-coupled diode-laser system with an optical power density of more than 1 MW/cm², which the company says is an order of magnitude higher than any other commercially available system operating at a single wavelength.

Laserline’s expertise is also in fiber-delivered high-power diode lasers up to 6 kW. According to Klaus Kleine, vice president of U.S. operations, Laserline is beginning to see diode-laser cladding systems replacing CO₂ and Nd:YAG lasers in industrial applications, particularly in the United States. While the aerospace and power-plant industries continue to account for the bulk of laser-cladding applications, Kleine says there is a big push under way in other industries and that the compactness, efficiency, and affordability of the diode-laser systems should begin to attract more customers.

“The automotive applications are much more prevalent in Europe, which is also at the forefront of installed diode-laser systems for surface treatment,” he said. “A lot of these advances are being pushed by diesel-engine technology; the goal (in Europe) is to make diesel engines cleaner and much more fuel efficient via surface treatment.”