Sunday, April 10, 2011
Thursday, April 15, 2010
Laser Safety Classification
Class 1: A Class 1 laser is considered safe based upon current medical knowledge. This class includes all lasers or laser systems which cannot emit levels of optical radiation above the exposure limits for the eye under any conditions inherent in the design of the laser product. There may be a more hazardous laser embedded in the enclosure of a Class 1 product, but no harmful radiation can escape the enclosure.Class 2: A Class 2 laser or laser system must emit a visible laser beam. Class 2 laser light is too dazzling to stare into for extended periods. Momentary viewing is not considered hazardous since the upper radiant power limit on this type of device is less than the Maximum Permissible Exposure for momentary exposure of 0.25 seconds or less. Intention extended viewing, however, is considered hazardous. Class 3: A Class 3 laser or laser system can emit any wavelength, but it cannot produce a diffuse (not mirror-like) reflection hazard unless focused or viewed for extended periods at close range. It is also not considered a fire hazard or serious skin hazard. Any continuous wave (CW) laser that is not Class 1 or Class 2 is a Class 3 device if its output power is 0.5 W or less. Since the output beam of such a laser is definitely hazardous for intra-beam viewing, control measures center on eliminating this possibility.Class 4: A Class 4 laser or laser system is any that exceed the output limits (Accessible Emissions Limits, AELs) of a Class 3 device. As would be expected, these laser may be either a fire or skin hazard or a diffuse reflection hazard. Very stringent control measures are required for a Class 4 laser or laser system. Ultrafast lasers fall into this classification.
Ultrafast lasers possess safety hazards not associated with light from conventional sources. Among potential injuries, eyes are the most vulnerable. Damage to the retina cannot be repaired and does not heal by itself.Why is eye safety so critical? Compare the output of femtosecond lasers with the radiation that the human eye can receive from the sun on a clear day. The sun’s image on the retina is approximately 160 microns. This yields a radiation density of around 30 W/cm2. A typical Ti:Sapphire femtosecond oscillator is capable of producing intensity in excess of 50 GW/cm2, while an amplifier will easily exceed 1014 W/cm2. Obviously, very weak laser reflections, or even scattering from rough surfaces, can be extremely bright - dangerously bright - to the eyes.You are urged to read carefully the safety section found in the user manual of any laser product you use and to strictly adhere to those instructions.
Ultrafast lasers possess safety hazards not associated with light from conventional sources. Among potential injuries, eyes are the most vulnerable. Damage to the retina cannot be repaired and does not heal by itself.Why is eye safety so critical? Compare the output of femtosecond lasers with the radiation that the human eye can receive from the sun on a clear day. The sun’s image on the retina is approximately 160 microns. This yields a radiation density of around 30 W/cm2. A typical Ti:Sapphire femtosecond oscillator is capable of producing intensity in excess of 50 GW/cm2, while an amplifier will easily exceed 1014 W/cm2. Obviously, very weak laser reflections, or even scattering from rough surfaces, can be extremely bright - dangerously bright - to the eyes.You are urged to read carefully the safety section found in the user manual of any laser product you use and to strictly adhere to those instructions.
iClad: A Wonderful Laser Cladding Head
In the race against time, the specialists at Stork Gears & Services BV, Rotterdam, have a global reputation in sectors like the shipbuilding, petrochemical, wind power, and steel industries where the maximum uptime of efficient gearboxes and associated drive systems is of crucial importance. As quickly as possible, the experts at Stork repair damaged or failed gearbox-related components, rebuilding them or replacing them with new parts. In this line of work, laser cladding is used as a tried-and-tested technology to prevent wear-out and unwanted material changes. The team led by Jelmer Brugman, head of Stork's laser cladding department, successfully applies this technique on more than 20 gear repair or modification jobs per month. However, in about 10% of the cases, inaccessible internal surfaces could not be treated with conventional laser processing heads. Until about a year ago, there was no alternative but to replace the damaged parts with new ones. The solution to this problem is iClad, a laser processing head developed by Pallas GmbH the treatment of internal contours from a diameter of 26 mm and to a depth of 600 mm. By using this innovative processing head, the Dutch company has opened up new possibilities for the repair of critical components. Compared with the previously unavoidable effort involved in such cases, several weeks of repair time can be saved. In the maritime industry, in power stations, or wind power plants, gearboxes and gearwheels have to operate reliably over long periods of time under the hardest of conditions. In many different sectors, corrosion, abrasion, and erosion put such drive systems under extreme pressure. This results in broken or damaged gearwheels, leading to unplanned downtimes or, in the worst case, complete failure. Since last year, however, Stork Gears & Services has been successfully using the new iClad processing head for the preventative maintenance, modification, and repair of such heavily stressed drive systems. Now, both damaged and new components can be optimally coated with low distortion using a 2-kilowatt diode laser. The surface of the component and the powder jetsprayed onto it are melted by the laser and joined together metallurgically with minimal dilution. The previously available processing heads were only deployable for internal contours with an access aperture of at least 100 mm diameter or were limited to the treatment of freely accessible surfaces. The iClad processing head, developed by the company Pallas in collaboration with the Fraunhofer Institute for Laser Technology (ILT), can be used from a diameter of 26 mm and to a depth of 600 mm for the complete range of laser cladding tasks. Whether hardening, alloying, or coating, even in the tightest of internal spaces, iClad renders the most demanding internal surface treatments possible. For Brugman, laser cladding with iClad has significant advantages. Using the new processing head, highly strained critical components that were previously inaccessible can now be optimized or repaired with a coating specifically designed to meet their respective stress loads. As one of the first industrial-scale users, Stork Gears & Services deployed the newly developed processing head, a prototype of iClad with integrated collimation as a special feature. This was a fixed head with a working depth of 500 mm for the internal coating of 50 mm bores. In addition to gearwheels and clutches, gearbox casings are also treated using the new technology. On average, Stork deals with three gearbox repairs per month. One-piece gearbox casing models used to pose a real problem, as laser cladding by means of the standard processing heads was not an option. Before iClad was deployed, the alternative, the production of a completely new casing, used to take several weeks. Now, the filigree processing head for laser cladding of internal contours makes it possible to save time on the repair of a damaged gearbox and thus to reduce the duration of downtimes, a factor of great market relevance. So far, Stork has successfully used iClad on about 20 jobs – most of them demanding single-piece projects, i.e. not serial production. The new technology has proven itself both for repairs and for the production of new components. After just one year of deployment, the slender optical processing head for the laser treatment of hard-to-access inner contours has already significantly enlarged Stork's scope of service. Previously inaccessible surfaces and structures of critical components are now being successfully equipped in record time with specific coatings to meet the challenges of their wear-intensive daily lives.
Sunday, November 1, 2009
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.
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.
Ten Frequently Asked TIG Welding Questions
Experienced welders know that without the right information, it’s easy to sacrifice quality, lose time, and generally become frustrated with TIG welding. And while there is merit in learning by trial and error, if you want to move toward precision TIG welding, getting answers to 10 very basic questions can ease the transition.
1. Should I use an air-cooled or water-cooled torch?
For low-amperage applications, an air-cooled torch cooled by shielding gas works well. These torches are simple to operate and require minimal setup. For high-amperage applications, you can still use an air-cooled torch, but the cable and torch must be much heavier and may be cumbersome to manipulate.
A water-cooled torch, which circulates water through the torch and cable, works equally well, but requires additional equipment and maintenance. These torches use clean, de-ionized water with filters that prevent contaminants from entering the cooling supply or the inner-diameter tube of the torch. You also may need to use additives to prevent algae growth.
Whether you choose a water-cooled system depends on your willingness to invest in additional equipment, as well as additional time and money for maintenance. Many welders, however, prefer these systems because the smaller torch configuration provides better maneuverability and reduces operator fatigue.
2. When should I use a gas lens?
A gas lens should be used when your application requires increased shielding gas coverage. The gas lens reduces turbulence and provides lengthier, undisturbed gas flow and allows you to move the nozzle farther away from the workpiece while still keeping the arc or weld puddle in view. Using a larger nozzle with a gas lens—which consequently produces a larger blanket of shielding gas—can help when welding on materials such as stainless steel and titanium.
A gas lens also allows more direct and broader gas coverage on tight joints, such as an inside corner, where access can be limited. In critical applications that have potential for atmospheric contamination, a gas lens can help to reduce the likelihood of weld discontinuities.
3. What are the causes of an unstable arc, and how can I remedy them?
Using the wrong size tungsten, whether in AC or DC applications, is one of the more common causes of an unstable arc. If the tungsten is too large for the amperage, the arc may rotate around the end of the tungsten. Conversely, if the tungsten is too small for the amperage, the current can melt the electrode and cause an erratic arc. To remedy either of these conditions, match your welding current to the tungsten size recommended by the manufacturer.
Contaminated tungsten—caused by debris on the base metal, oxidation from inadequate shielding gas, or gas impurities from a leak—also can cause an unstable arc in both AC and DC applications. To resolve this problem, replace or regrind the tungsten, make sure the base metal is clean, or increase the shielding gas flow after making sure all your hoses are intact and leak-free.
4. How do I prevent tungsten contamination and discoloration?
Allowing the tungsten to touch the weld pool is one of the most common causes of contamination. This problem can be resolved by moving your torch farther away from the workpiece, which in turn lengthens the arc. Touching the filler metal to the tungsten also can be a source of contamination, but there is no clear solution to this problem other than practice; trial and error will determine your best technique.
If you feel your technique is not the culprit of tungsten contamination or discoloration, check to see that you have adequate gas flow, and allow adequate postflow time as well. Allow several seconds of postflow—about 1 second for every 10 amps of weld current. Finally, you may want to consider using a power supply that offers high-frequency starts if you think using the scratch-start method is causing the contamination.
5. What are the causes and solutions for excessive electrode consumption?
Using too much current on a given application is a major cause of excessive electrode consumption and is most easily solved by increasing the tungsten size, changing the type of tungsten you are using, or decreasing the amperage.
Using the wrong polarity also can result in excessive tungsten consumption. During AC welding, for example, using more electrode-positive current may provide more cleaning action, but it also subjects the tungsten to more current and thus consumption. Instead, it is best to set the power source more toward electrode negative on the balance control to minimize the amount of current and time spent on the electrode.
Using an incorrect or contaminated shielding gas can lead to high electrode consumption. Be sure to use pure argon, and check for leaks in the hoses, either from cracks or loose fittings.
6. What causes porosity in a TIG weld bead, and how can I prevent it?
A loose hose or torch component is a primary cause of porosity. It is remedied by tightening the fittings. If you cannot find loose hose connections by doing a visual check, you might want to place the hose in soapy water until you find the leak and tighten the fittings accordingly.
Using the wrong shielding gas or one that has impurities also can lead to porosity. This is remedied by using pure argon after using nitrogen to purge the line of air and any condensation that may have accumulated. Drafts from fans or open doors also can lead to porosity, so be sure that your working environment is well-isolated from drafts or use a gas lens to provide better gas coverage.
To prevent porosity caused by inadequate shielding gas flow, follow the recommended flow rate, which is approximately 10 to 20 cubic feet per minute (CFM), depending on the application. Doing so helps ensure quality welds.
7. What type of tungsten should I use?
There are several tungsten choices for TIG welding, including 2 percent thoriated tungsten, 2 percent ceriated tungsten, and 1.5 percent lanthanum tungsten.
Two percent thoriated tungsten is a good choice when using a DC power source because it maintains a pointed shape, resists melting, and has a high current-carrying capacity. When welding thin aluminum—0.09 in. or less—thoriated tungsten is also a good alternative to pure tungsten because it creates a more focused arc. It is recommended that thoriated tungsten be used in a properly ventilated area and measures be taken during preparation to capture dust from grindings.
Two percent ceriated tungsten is a good alternative to thoriated tungsten and provides good arc starts at low currents, along with greater arc stability. This type of tungsten is recommended for aluminum AC welding with an inverter-based power source.
A 1.5 percent lanthanum tungsten is most commonly used for applications in which long weld times and multiple arc restarts are necessary.8. What is the proper procedure for cleaning base metals?The base metal should be free of all contaminants, including dirt, paint, and oil. Wipe the base metal with a cloth or scrape it with a wire brush dedicated for use on a particular material. Before welding on aluminum, in particular, you need to remove oxides with a stainless steel brush manually; using a power brush is not recommended as it can re-embed contaminants into the metal. You can also use a caustic solution to clean aluminum. If you are considering using this method, your local welding distributor is the best resource to provide you with product options. You can also discuss several scraping methods with your distributor if you do not want to use chemicals.
9. How do I solve high-frequency-interference problems?
Malfunctioning electrical equipment, such as computers, telephones and radios, is often a sign that you are experiencing high-frequency interference from your welding power source.
To remedy such high-frequency interference, start by verifying that the power source is grounded according to the installation instructions provided in the operator’s manual. Keep your torch cables and work cables as short as possible, and place them close together. Physically separating your welding equipment from devices that may experience interference is also an option, but doing so can be time-consuming and space-prohibitive.
If all else fails, you could switch to an inverter-based power source that provides a high frequency for arc starting only.
10. What are the cause and solution for arc rectification?
Arc rectification occurs when the surface oxide of a nonferrous metal acts as a barrier, making it more difficult for electrons to flow from the workpiece to the tungsten than from the tungsten to the workpiece. Excessive arc noise, unstable weld pools, or a weld pool that appears to dry up are all signs of arc rectification.
You can either increase your travel speed or decrease the amperage for the application. Another option is to adjust the balance control on your power source toward electrode negative, which provides more penetration.
1. Should I use an air-cooled or water-cooled torch?
For low-amperage applications, an air-cooled torch cooled by shielding gas works well. These torches are simple to operate and require minimal setup. For high-amperage applications, you can still use an air-cooled torch, but the cable and torch must be much heavier and may be cumbersome to manipulate.
A water-cooled torch, which circulates water through the torch and cable, works equally well, but requires additional equipment and maintenance. These torches use clean, de-ionized water with filters that prevent contaminants from entering the cooling supply or the inner-diameter tube of the torch. You also may need to use additives to prevent algae growth.
Whether you choose a water-cooled system depends on your willingness to invest in additional equipment, as well as additional time and money for maintenance. Many welders, however, prefer these systems because the smaller torch configuration provides better maneuverability and reduces operator fatigue.
2. When should I use a gas lens?
A gas lens should be used when your application requires increased shielding gas coverage. The gas lens reduces turbulence and provides lengthier, undisturbed gas flow and allows you to move the nozzle farther away from the workpiece while still keeping the arc or weld puddle in view. Using a larger nozzle with a gas lens—which consequently produces a larger blanket of shielding gas—can help when welding on materials such as stainless steel and titanium.
A gas lens also allows more direct and broader gas coverage on tight joints, such as an inside corner, where access can be limited. In critical applications that have potential for atmospheric contamination, a gas lens can help to reduce the likelihood of weld discontinuities.
3. What are the causes of an unstable arc, and how can I remedy them?
Using the wrong size tungsten, whether in AC or DC applications, is one of the more common causes of an unstable arc. If the tungsten is too large for the amperage, the arc may rotate around the end of the tungsten. Conversely, if the tungsten is too small for the amperage, the current can melt the electrode and cause an erratic arc. To remedy either of these conditions, match your welding current to the tungsten size recommended by the manufacturer.
Contaminated tungsten—caused by debris on the base metal, oxidation from inadequate shielding gas, or gas impurities from a leak—also can cause an unstable arc in both AC and DC applications. To resolve this problem, replace or regrind the tungsten, make sure the base metal is clean, or increase the shielding gas flow after making sure all your hoses are intact and leak-free.
4. How do I prevent tungsten contamination and discoloration?
Allowing the tungsten to touch the weld pool is one of the most common causes of contamination. This problem can be resolved by moving your torch farther away from the workpiece, which in turn lengthens the arc. Touching the filler metal to the tungsten also can be a source of contamination, but there is no clear solution to this problem other than practice; trial and error will determine your best technique.
If you feel your technique is not the culprit of tungsten contamination or discoloration, check to see that you have adequate gas flow, and allow adequate postflow time as well. Allow several seconds of postflow—about 1 second for every 10 amps of weld current. Finally, you may want to consider using a power supply that offers high-frequency starts if you think using the scratch-start method is causing the contamination.
5. What are the causes and solutions for excessive electrode consumption?
Using too much current on a given application is a major cause of excessive electrode consumption and is most easily solved by increasing the tungsten size, changing the type of tungsten you are using, or decreasing the amperage.
Using the wrong polarity also can result in excessive tungsten consumption. During AC welding, for example, using more electrode-positive current may provide more cleaning action, but it also subjects the tungsten to more current and thus consumption. Instead, it is best to set the power source more toward electrode negative on the balance control to minimize the amount of current and time spent on the electrode.
Using an incorrect or contaminated shielding gas can lead to high electrode consumption. Be sure to use pure argon, and check for leaks in the hoses, either from cracks or loose fittings.
6. What causes porosity in a TIG weld bead, and how can I prevent it?
A loose hose or torch component is a primary cause of porosity. It is remedied by tightening the fittings. If you cannot find loose hose connections by doing a visual check, you might want to place the hose in soapy water until you find the leak and tighten the fittings accordingly.
Using the wrong shielding gas or one that has impurities also can lead to porosity. This is remedied by using pure argon after using nitrogen to purge the line of air and any condensation that may have accumulated. Drafts from fans or open doors also can lead to porosity, so be sure that your working environment is well-isolated from drafts or use a gas lens to provide better gas coverage.
To prevent porosity caused by inadequate shielding gas flow, follow the recommended flow rate, which is approximately 10 to 20 cubic feet per minute (CFM), depending on the application. Doing so helps ensure quality welds.
7. What type of tungsten should I use?
There are several tungsten choices for TIG welding, including 2 percent thoriated tungsten, 2 percent ceriated tungsten, and 1.5 percent lanthanum tungsten.
Two percent thoriated tungsten is a good choice when using a DC power source because it maintains a pointed shape, resists melting, and has a high current-carrying capacity. When welding thin aluminum—0.09 in. or less—thoriated tungsten is also a good alternative to pure tungsten because it creates a more focused arc. It is recommended that thoriated tungsten be used in a properly ventilated area and measures be taken during preparation to capture dust from grindings.
Two percent ceriated tungsten is a good alternative to thoriated tungsten and provides good arc starts at low currents, along with greater arc stability. This type of tungsten is recommended for aluminum AC welding with an inverter-based power source.
A 1.5 percent lanthanum tungsten is most commonly used for applications in which long weld times and multiple arc restarts are necessary.8. What is the proper procedure for cleaning base metals?The base metal should be free of all contaminants, including dirt, paint, and oil. Wipe the base metal with a cloth or scrape it with a wire brush dedicated for use on a particular material. Before welding on aluminum, in particular, you need to remove oxides with a stainless steel brush manually; using a power brush is not recommended as it can re-embed contaminants into the metal. You can also use a caustic solution to clean aluminum. If you are considering using this method, your local welding distributor is the best resource to provide you with product options. You can also discuss several scraping methods with your distributor if you do not want to use chemicals.
9. How do I solve high-frequency-interference problems?
Malfunctioning electrical equipment, such as computers, telephones and radios, is often a sign that you are experiencing high-frequency interference from your welding power source.
To remedy such high-frequency interference, start by verifying that the power source is grounded according to the installation instructions provided in the operator’s manual. Keep your torch cables and work cables as short as possible, and place them close together. Physically separating your welding equipment from devices that may experience interference is also an option, but doing so can be time-consuming and space-prohibitive.
If all else fails, you could switch to an inverter-based power source that provides a high frequency for arc starting only.
10. What are the cause and solution for arc rectification?
Arc rectification occurs when the surface oxide of a nonferrous metal acts as a barrier, making it more difficult for electrons to flow from the workpiece to the tungsten than from the tungsten to the workpiece. Excessive arc noise, unstable weld pools, or a weld pool that appears to dry up are all signs of arc rectification.
You can either increase your travel speed or decrease the amperage for the application. Another option is to adjust the balance control on your power source toward electrode negative, which provides more penetration.
Sunday, October 12, 2008
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.
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.
Saturday, September 13, 2008
Materials Processing - Diode lasers test their mettle in surface treatment
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
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
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 (
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 (
Laserline’s expertise is also in fiber-delivered high-power diode lasers up to 6 kW. According to Klaus Kleine, vice president of
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