Technological change comes to the collision repair industry much the same way it does to most other business markets – first as a trickle then a rush when businesses are confident that the change will benefit them.
Collision repairers most recently experienced such widespread change with the adoption of waterborne paints. Many repairers first balked at these finishes, believing their promised benefits to be too good to be true. Others decided they would wait to make a transition only when the law mandated they do so. Once an initial group of shop made the change and raved about the results, shops waited in line with their vendors to buy in.
Nitrogen welding, arguably, is going through much the same process. It promises financial benefits such as lower costs and shorter cycle times by allowing shops to quickly perform plastic repairs in lieu of ordering, refitting and replacing damaged plastic parts. Additionally, it provides repairers with the opportunity to boost their revenue even further with convenient bumper and other repairs. Like waterborne paints, it offers repairers another scenario where the potential benefits seem a little too good to be true, leaving most shops waiting to be convinced and therefore losing out today on what could be a significant upgrade to their operations.
Should your shop get ahead of the curve and buy into this technology today? Let's delve into nitrogen welding a bit deeper with a look at all the benefits it promises and the steps your techs soon could be taking to perform state of the art plastic repairs.
Proof positive
If you're not convinced that nitrogen welders are ready to take their place in collision repairs, consider the fact that they've been an integral part of the industry for years, most notably in automotive bumper remanufacturing facilities. If you've ever installed a remanufactured bumper, you've utilized a part likely repaired by nitrogen welding.
This fact is one of the driving forces for having this technology in your shop. By performing this work yourself, you'll reduce the cycle times involved with ordering and receiving a replacement part. You'll also collect revenue since you'll be performing work that would otherwise go to someone else.
These factors help play into further benefits. By reducing cycle times and offering more repair options, you'll make your operation more appealing to customers and insurers. You'll also set your business up to add additional profit lines such as fast lane bumper repairs.
Some plastic repairs can be handled with two-part adhesives, but welding manufacturers note that nitrogen welding provides a stronger repair (manufacturers also declare nitrogen builds a stronger repair than other hot air welding methods). Further, nitrogen welding can be performed on part areas impossible to repair with adhesives, including slots, mounting holes and tabs (thick or thin), grille bars, high-stress areas, flexible tabs and fender liners.
Nitrogen welding also can provide other benefits over adhesive. Welding can generate greater profits and be completed more quickly. The Urethane Supply Company says that an average 6 in. (15 cm) welding repair costs less than $2, with typical welding speeds of 4 in. (10 cm) to 6 in. (15 cm) per minute. There's also no wait time for curing. When the weld is complete, the work can immediately be given to a painter who cools the weld area with water, then sands and primes the part before finishing.
If you still need more convincing, consider that the number of plastic parts incorporated into vehicles continues to grow – translating into even greater repair opportunities.
The basics
Hot air welding is performed by using extreme heat (usually 345 degrees C) to melt two pieces of plastic together – the base plastic on the part and a plastic filler rod/ribbon. The welder typically cuts a V-groove into the damaged part and sets the filler rod/ribbon into the groove. The welder melts the two plastics together with extreme heat, usually 345 degrees C, produced by blowing compressed air over a heating element. (Unlike other welders, nitrogen welders don't use a feeder tube-type or flat shoe tip.)
Nitrogen is used since it eliminates oxygen from the weld area, thereby removing contaminants (while producing less smoke) and creating a stronger bond.
Welders must stick to two rules when using this technology:
- Identify the plastic in the part. Nitrogen welding can only be performed on thermoplastics such as polypropylene/thermo plastic polyolefin (PP/TPO), which is used to make most bumper covers. The type of plastic can be determined from the ISO code, usually located on the back of a part. If no code is present, check the vehicle manufacturer information. Next, select the appropriate filler rod, which usually is made of pure plastics like thermoplastic olefin (TPO), polypropylene (PP) or acrylonitrile butadiene styrene (ABS). Note that filler rods are available in different widths, diameters and shapes.
- Keep the air flowing. Maintain the airflow over the welding heating element at all times, whether you're preheating, welding or cooling. To help conserve the nitrogen supply, nitrogen welders only release it during the actual welding.
Repair steps
The key to a proper plastic repair job is proper technique. This involves the coordination of both hands, with one controlling the welding torch and the other feeding the rod. Typically, you'll need to melt the bottom surface of the rod and the top of the base plastic. Do not “puddle” the rod like you would in metal welding since keeping the basic structure of the rod intact creates a stronger weld.
Nitrogen welding incorporates four factors: Temperature, angle, pressure and speed – or TAPS, for short.
Temperature. Set the temperature on the welder to the proper setting. For example, the PP/TPO setting will generate an air flow of about 550-600 degrees F. Adjust higher or lower for varying thicknesses of plastic.
Angle. Use a 45 degree angle between the welder and the part. Aim the stream of hot air a little in front of the rod. For thicker rods, focus the heat back toward the rod.
Pressure. Especially when working on bumpers, put as much downward pressure on the rod as possible to help the rod fuse with the part. Place steady, downward pressure on the rod and keep the rod moving slowly. Do not overheat the rod and allow it fold over backwards.
Speed. Maintain welding speed of about 4 to 6 inches per minute. Note, however, that it will be difficult to move this slowly with thinner rods while thicker rods may require you to move more slowly. Regardless of the rod being used, always move steadily while keeping proper downward pressure on the rod and a small bead of melted plastic in front of the rod.
Most nitrogen welders use the same basic following steps to repair a bumper:
- Identify the part plastic. As already noted, you'll need to identify the damaged plastic (1) to see if it can be repaired and (2) to match it will the appropriate filler rod.
- Clean the weld area. Wash the area thoroughly with automotive soap and water. Next, apply a cleaner recommended by the welding manufacturer. Be sure to wipe the area in one direction to avoid creating static electricity, which can draw contaminants to the repair area. Also, do not apply any solvent cleaners since they can become trapped in the repair area and produce bubbles when the area is baked or exposed to sunlight.
- Align the part. Because the plastic in the damage area usually has been stretched or distorted, try to get the crack back yo pre-damaged shape as closely as possible. (If the plastic is dented or stretched, heat with a heat gun and push the plastic back into position.) Use aluminum tape to realign the damaged area and hold it in place. After the front of the part is realigned, sand the back with P80 grit paper. Use clean, oil-free compressed air to blow the area clean.
- Weld the back of the bumper first. For maximum strength, use a wider rod that offers more surface area and/or thicker stock for greater strength. Begin the weld by focusing the heat of the welder about ½ in. past the crack on a solid part of the bumper. After the plastic starts to turn glossy., stab the end of the ribbon rod down into the plastic and bend it toward the welder.
- Prepare the front of the bumper After the back has cooled, remove any aluminum tape from the front. Using a ½ in. ball cutter in a die grinder, grind out a V-groove in the plastic ½ in. wide about 1/16 in. deep. Put some sanding scratches in the plastic with a 50 grit Roloc or 80 grit paper in a dual action sander. Blow any dust away.
- Weld the front side of the crack. On the front, it’s usually best to use a more narrow rod so it can be tucked down into the V-groove and retain most of its strength even after it’s been sanded flush. Use the same process as on the backside to weld it. Focus the heat from the welder a little farther in front of the point where the rod meets the bumper to prevent the rod from becoming too weak. Apply about a pound of downward pressure on the rod as you weld to make sure the rod fuses properly with the bumper plastic.
- Finish the weld. Once the weld is completely cool, sand with 50-80 grit paper. Do not sand too quickly since this will melt and smear the plastic. Instead, use a sharp, new piece of paper and slow the sander a bit to keep the plastic from melting. Sometimes the repair may be finished out and feathered with the welding rod. Most often you’ll use filler paper to fill in any low spots.
One word of caution: this type of repair can have a very bad effect if it is not used in the right way. For example, if the bumper cover comes off a highly optioned Lexus with rear blind spot radar, and your plastic repairs to the rear bumper cover change the thickness of the plastic, is the shop prepared to warranty that? Will the system still work? Plastic repair, just like metal repair, is case by case. Research how the vehicle and related systems are designed and how they work. Only then, determine the best repair plan.
Getting your techs up to speed on plastic welding will require some practice and experience. Consider starting this journey by letting them practice on damaged plastic parts that you'll be tossing out. Shops that take this direction report that it doesn't take long to “sell” this technology to skeptical workers – and skeptical owners, as well.
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