Any company that makes or uses molds knows the value of repairing them. Mold repair reduces costs and downtime when compared to making a new mold or mold components. Typical mold repairs include building up worn or damaged surfaces, filling in small voids, repairing parting lines or thin walls, fixing cracks and accommodating engineering changes or fixing mistakes.
Welding is the go-to operation for making these repairs. Gas tungsten arc welding (GTAW), also known as tungsten inert gas (TIG) welding, and micro-TIG welding that requires a microscope and thin filler rod traditionally have been used. These technologies involve an electric current being applied to the mold to generate heat at the point of the arc gap. At the point, a molten pool is created and the filler rod is introduced into the molten pool.
Laser welding is also commonly used for mold repair. This technology involves placing a filler rod between the worn or damaged surface and the laser beam, which fuses the filler rod with the base material, creating the repaired area. A microscope is used to view and target at the weld point, and a filler rod (typically up to 0.02 in.) is used to fill in voids.
“If you are repairing a large mold or the mold has a large worn or damaged area, typically you use conventional TIG welding,” says Pete Mourouzis, founder and president of Wicked Welding Inc. “Micro-TIG welding mold repair is for smaller damaged areas or small engineering changes, and even smaller molds with even smaller damaged areas or changes, that is when go to laser welding. If you are going to repair molds, it is pretty essential that you are able to perform all three types of welding.”
Wicked ways
And Mourouzis should know. He started Wicked Welding in 2002. Occupying a 4,000-sq.-ft. facility in Dayton, Ohio, about 70 percent of the company’s work is repairing plastic injection molds, particularly for the automotive industry. The rest is dies and stamping equipment and aviation and medical devices.
“We typically limit the molds we repair to 500 lbs., but our niche is smaller molds and smaller inserts, cores and pins,” he says.
Wicked Welding owns two LaserStar laser welding machines. LaserStar Technologies Corp. offers several laser welders for mold repair applications. These come in different power levels, laser types (Nd-YAG and fiber) and different packages to accommodate various mold sizes, from small inserts to very large molds. The most common series are the 7700 series, 7800 series and 1900/1900 XL series with power ranging from 80W to 200W.
“With laser welding, one can lay beads anywhere from 0.0020 in. to 0.025 in.,” says Jim Gervais, LaserStar president and COO.
The smaller 1900 series is the first laser welder Wicked Welding purchased. “It’s a really good first laser for small molds,” Mourouzis says. “The advantage is you don’t need any fixtures or jigs or tooling, because you are holding the mold to apply the filler rod. That reduces costs to my customers and speeds up the time needed to do the repairs. It is definitely faster than having a bigger laser machine where you have to put the mold in the rotary fixture and set it up.”
The shop later invested in a larger LaserStar 7700 series welder with a universal jig for swinging the laser head out over parts.
“The 7700 is semiautomatic,” Mourouzis adds. “I’m still applying the filler rod by hand but using a joystick controller for the X,Y,Z motion.”
Laser benefits
Laser welding offers several advantages over conventional TIG and micro-TIG welding methods.
“Lasers are user friendly and require minimal training,” Gervais says. “They offer high return on investment due to quick turnaround, reduced labor, no rework and reduced finishing costs.”
Each laser pulse duration is only a few milliseconds, which offers a high degree of heat localization and controllability. This reduces the heat-affected zone considerably over the other two welding methods.
The benefit of localized heat is that the rest of the mold remains unaffected. The entire mold remains cool to the touch and in its original form and shape, which means it can be held with bare hands and there is no distortion or warpage.
Also, because the amount of heat is minimal, the metal drawn into the melt pool is minimized, reducing sink of the base material surrounding the welded area.
“When you put weld on the mold, as the weld cools, it contracts and pulls some of the surrounding base material that you haven’t welded with it,” Mourouzis says. “When you mill or grind that off, it leaves a depression around the welded area and you have to polish that reduced area so the surface appears flat. If you TIG weld it, you may be able to get that sink down to 0.001 in. or 0.002 in. If you micro-TIG weld, maybe down to 0.005 in. With laser, it is down to about 0.0002 in.”
Therefore, “in a thin-wall mold where you can’t remove that extra material, you are going to have that sink line,” Mourouzis notes. “If you are working on a high-quality mold or one with a really high finish where you can’t remove material to hide the sink, the laser is the only way to go.”
Another benefit of minimal heat is no discoloration of the weld and the surrounding base material. Laser welding also reduces the amount of finishing, machining and handwork required.
“And sometimes it reduces it to only handwork,” Mourouzis says. “TIG and micro-TIG welding are always going to leave a bigger buildup than laser welding so most of the time there is going to be some kind of secondary process performed. It may require putting the mold in a mill and machining the weld off or making an electrode and burning it off with a wire EDM. But with laser welding, you could end up with a 0.0005-in. or 0.0010-in. buildup that you can just handwork out and be done.”
Mourouzis adds that laser welding is better, too, for deep holes or slots, especially ones that are narrow.
Laser welding also provides the ability to repair a variety of materials, such as tool steels, aluminum, copper, titanium and powdered metals. The lasers have 1064-nm wavelength so they interact with and melt most elements in the metals family on the periodic chart, according to Gervais.
“Lasers have a distinct advantage with nonferrous materials such as aluminum and copper,” Mourouzis says. “Those materials don’t really micro-TIG weld very well. You can TIG weld them but you have to put a big wad of filler rod material on there and deal with the aftermath or you can laser weld them and add a small amount of material.”
Mourouzis notes that laser welding allows dissimilar filler rod metals to be applied to the base material.
“For example, with copper repair, we can use stainless steel as a filler material,” he says. “Moldmakers use copper for its thermal conductivity; it dissipates heat so the plastic parts cool quickly. But if we apply stainless in a small area of the mold to repair a worn surface instead of copper, it provides a higher wear surface in that spot and the mold lasts longer. That small amount of stainless is not going to affect that thermal conductivity and those dissimilar metals fuse together nicely.”
Ask the expert
And that is why you go to a mold repair expert – they know what metals work together. “I have the years of the experience, through trial and error and consulting filler rod manufacturers and people that make the mold steel, to know what works,” Mourouzis says. “I find out what the customer needs the mold to do and provide the best solution.”
Mourouzis believes the biggest advantage of laser welding for his shop is speed. “No one builds spare molds and no one has any inventory,” he says. “It is all just in time. So they have one mold and if it gets damaged, they have to get it repaired and up and running before they run out of parts. With the laser, as long as the damage is minimal, we can get it welded, do a little handwork and polishing, and turn it around quickly.”
Check out these videos showing laser welding mold repair with LaserStar welding systems.
