TIG Welding Repair is Best For Extending Tool Life, Quick Return to Production
Tools, dies and molds have a hard life. Normal wear takes its toll. They crack, the metal wears away or a screwdriver is used one too many times to pry a part from the mold. Soon, they no longer function well or cannot hold the tolerances necessary for quality.
That's when customers call on Five Star Tool Welding Corp. of Butler, Wis. "There aren't too many tool and die welding service houses around-we're probably one of five in the entire state," says Joe Canfield, president and owner of Five Star Tool Welding. "We specialize in tool and die welding, including micro-welding, and that's all we do. We don't do any fabricating, building or machining."
Five Star provides its customers with three major benefits. "Welding lowers part replacement cost, extends tooling service life and gets your jobs operational faster than any other option," Canfield says. "Time and cost usually go hand in hand, but it seems time is more important than cost. They come to us because they don't want to build a new die, they want it repaired and they need it done quickly," Canfield says. "A lot of people will tell us, 'I don't care what it costs, just get it fixed right now!'"
In addition, tool repair requires highly specialized knowledge; it's a bit of black magic. When tool steel companies produce a new grade of steel, such as the 9V and 10V crucible powdered metals (CPMs) or 300 or 400 series stainless steels, Five Star devises a welding procedure based on consulting with the metal producer and its own experience.
"CPMs are a bear to weld because they're so brittle," says Canfield. "They're especially prone to cracking when the weld cools and puts pressure on the surrounding area" (see "No Crack" below). "The first few times we welded CPMs we had no idea what we were in for. There are always recommendations from the steel manufacturer, but we vary that according to what we think is best. And we devised a way, after doing it three or four times and failing maybe once or twice, to the point where we've got it well under control as far as preheating and the type of rod to use," Canfield says. Five Star works with all grades of tool metals, including H13 (the highest volume), S7, D2, A2, all AMPCO metals (aluminum bronze), Be Cu alloys, copper, bronze, aluminum, magnesium and zinc. Parts repaired include plastic injection molds, die cast dies, blow molds, compression/transfer molds, Dynacast and Techmire dies, stamping and forming dies and related components.
Precision TIG Welds
Five Star almost exclusively uses the TIG welding process. With the heat input (amperage) controlled by a foot pedal that functions similarly to a car's accelerator, the operator can observe the area needing repair and adjust the amperage accordingly...even down to 1 amp DC or 5 amps AC. The company's "micro-TIG welding" occurs at these amperages. Other welding processes simply do not provide this level of control over heat input or the width of the weld bead.
"With TIG, we can pinpoint the arc at the area being welded," says general manager Steve Coleman. "We can direct the weld puddle so it doesn't destroy the surrounding area or require the customer to perform extra machining. Further, TIG does not produce the spatter that MIG welding does, which keeps the tool clean."
As an example pinpoint control, Five Star once received a micro-weld sample from a competitor that had a weld bead on top of the head of an ordinary shirt pin. Coleman put a new weld bead on top of their weld bead and mailed the pin back to them.
While Coleman performed that feat with a traditional Syncrowave® AC/DC TIG power source from Miller Electric Mfg. Co., the company's newer TIG machines feature an advanced squarewave output and use inverter technology. This technology achieves greater penetration; narrows the weld bead; increases travel speeds up to 20 percent; may permit using smaller diameter tungsten to more precisely direct the heat or make a narrower weld bead; and reduces the size of the etched zone for improved cosmetics. It also produces a more stable arc and the positive arc starts at 5 amps or less that are critical for micro-TIG welding.
Most of Five Star's TIG welding equipment comes from Miller. This includes several Syncrowaves of varying vintages, an Aerowave® AC/DC unit, a Maxstar® DC TIG inverter and a Dynasty® 200, Miller's newest AC/DC TIG inverter featuring Auto-Line™ technology.
Overall, the methods Five Star uses to create a sound TIG weld do not differ greatly from other precision TIG welding operations using the newest technology and techniques. Operators strike an arc, establish a weld puddle and add filler metal as necessary. The education section of Miller's Web site, MillerWelds.com, offers a free, downloadable PDF called Guidelines to Gas Tungsten Arc Welding (GTAW) that covers the newest technology (look under "Books & Pamphlets"). For detailed fundamentals, examine the 84-page TIG Handbook (look under "Resources for Sale").
However, some special techniques and cautions are particularly important for tool welding repair. Five Star offers the following advice.
Gas Lenses - Use Them
Always use a gas lens. This screen inserted inside the cup prevents turbulent gas flow, which in turn provides a wider area of shielding gas coverage. If necessary, it allows increasing electrode extension from 1/4 to 3/4 in. beyond the cup. Extending the electrode permits reaching into corners and better visibility of the weld area. Shielding gas is 100 percent argon for all metals. Note that thicker sections of aluminum may benefit from a helium/argon mix. Consult with your local welding supply distributor for more information about shielding gases.
Point About Tungstens
Select a 2% ceriated tungsten for all metals, including non-ferrous metals. Five Star has experimented with pure, thoriated, zirconiated and ceriated tungstens and has determined that a 2% ceriated tungsten best maintains a point on the end of the tungsten. It provides more consistent arc starts and produces a narrower arc cone.
"The only tungsten that we use now is the 2 percent ceriated in different diameters," says Coleman. "Larger diameters for AC welding (typically 1/8-in.), 3/32-in. for normal welding and 1/16-in. or .040 in. for micro-welding." Proper tungsten preparation is critical. "We have a special sharpener with a diamond wheel that puts a smooth finish on the tip that we grind onto the tungsten, which will ensure an even better start," he notes. "If you have any rough spots, the current will catch that rough spot and carry it somewhere else."
Canfield also points out, "When I work on aluminum, I try to sharpen the electrode and put a small land on the end. Otherwise it balls up and starts wobbling. When you're running really high amperage, if the electrode is wobbling it could blast right into the weld and contaminate it."
Finding the Right Filler
Matching the filler metal to the base metal seems like a straightforward task: just pick two metals of the same type. However, the parent metal's hardness and tempering current state throw a monkey wrench into that equation.
"For welding A2 steel," says Canfield, "we use an M2 rod because it produces a finished weld with a Rockwell hardness of 60 to 62. If we were to use an A2 rod in its hardened state, the weld would come out with about a 54 Rockwell. Then the customer would have to heat treat the whole piece to obtain the right hardness, which they don't want to do." This type of knowledge is why customers come to Five Star instead of repairing tools themselves.
Five Star operators value positive arc starts more than any other TIG machine attribute.
"The arc needs to start instantly, and it must start precisely where I direct it," Coleman says. "If the arc misfires, it can do more harm than good."
The next most important feature is directional control. "If the arc dances around when I'm trying to make a delicate repair in the bottom of a mold cavity, it can damage fine edges the customer doesn't want touched or lead to excess machining," adds Canfield.
For positive arc starts at low amperages and for welding aluminum, a TIG inverter will provide the best results and better directional control (Miller's downloadable PDF provides a good explanation). Also, most of today's inverters and conventional TIG machines have set up options to tailor arc starts for low amperage welding.
Clean and Hot
Remove all dirt, grease and foreign material from the tool. Use a neutral alcohol or acetone for grease or a sandblaster for hard coatings or "the big gunk." To prevent damage to adjacent surfaces, protect those areas with masking tape before sand blasting. Cracks with excessively rough edges will be removed with a hand grinder or carbide tool.
Cleaning the tool doesn't just prevent weld contamination, it also keeps the shop from smoky grease fouling the shop air. And any grease will smoke, because the tools are then preheated, usually to just below the last tempering temperature.
"An S7 steel was last heated to about 700 degrees Fahrenheit, so we have to stay below that or we'll soften the whole piece," says Canfield. "With H13, we heat it to around 1100 degrees without worrying about harming the hardness of the steel." Customers generally indicate the type of tool steel, but sometime Five Star operators need to perform a harness test with a Rockwell hardness tester.
Pre-heating the tool minimizes the temperature difference between the weld and the surrounding area. If the temperature difference is too extreme, the sudden cooling and contracting of the weld pool can cause the tool to crack. For these same reasons, operators keep welds shorter. For welding thin pieces, operators clamp the part to keep it from warping.
Operators peen the weld after each pass. This swages out the weld bead, relieving the metal from the natural shrinkage that occurs as the weld cools. Before striking the punch with the hammer, operators yell "fore!" The last thing someone making a micro-weld wants to hear is an unexpected hammer blow.
If the steel type dictates, Canfield says he, "cannot over-emphasize the importance of post-weld heat treatment in preventing cracking, especially for difficult to weld metals like CPMs." A third party may perform this treatment, which involves heating a part, holding it at a specified temperature and cooling it at a precisely controlled rate.
Despite the new trends in the types of tool steels being used today, Canfield says welding techniques are "pretty much the same, no matter what you're welding. It's up to the person operating the machine and how they do it best. As far as weave beads and that sort of thing, it all depends on the job. It depends on the amount of weld that has to be built up, how large of an area you have to cover and how fast you want to do it. I'd say everybody has his or her own signature. I can look at a finished weld and tell who did it. Everyone here can do that," Canfield says. Of course, not everyone works at Five Star Tool Welding.
For more information on TIG power sources, visit MillerWelds.com or call 1-800-4-A-MILLER. For more information on Five Star Tool Welding, call (262) 783-5822, (800) 894-5822, fax (262) 783-6380 or e-mail firstname.lastname@example.org.