TIG welding-Best Practice

World-renowned dragster chassis fabricator Murf McKinney Chooses TIG Inverters as Part of Best Manufacturing Practices

The TIG welded 4130 chrome-moly frame of a NHRA Top Fuel dragster weighs less than 300 lbs., yet it withstands almost incomprehensible forces. The supercharged, fuel-injected, nitromethane-burning engine produces an estimated 7,000 horsepower, rocketing the vehicle down a quarter-mile track in 4.4 seconds and at speeds up to 335 mph. The forces cause the 300-in.-long frame to bow up 10 to 12 inches, while the large rear wing on a dragster develops upwards of 8,000 pounds of downforce.

The allure of such power makes even non-racing fans aware of the sports legendary names: “Big Daddy” Don Garlits, Shirley Muldowney, Don “the Snake” Prudhomme, Larry Dixon and John Force.

When these legends purchase a dragster chassis and body or need an existing car refurbished, they turn to Murf McKinney. While not recognized by the general public, everyone in the dragster and funny car business knows McKinney, who captures more dragster chassis sales than any other fabricator. Top fuel chassis costs around $55,000, a funny car chassis costs $35,000 to $40,000 and the body for a funny car costs another $55,000.00.

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 A chassis has dozens of welded tabs, which hold down a variety of parts. Notice that the weld bead is only as wide as it needs to be.

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To obtain this stack of dimes appearance, welder/fabricator manually pulses the amperage with the foot control.

 

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In the hands of a skilled welder  advance squarewave output enables creating weld beads that look like they were made with a machine.

 

Best Chrome-Moly Welding Practices at McKinney Corp.

• Set argon flow to 18 to 22 cfh and check the flow each day. More is not better, as turbulence could suck oxygen into the weld.
• Set gas pre-flow at .4 to .6 seconds; set post-flow to 6 to 10 seconds. Hold the torch in place at the end of the weld for the entire duration of the post-flow.
• Whenever joint access permits, use a gas lens to improve gas coverage. Keep the screen free of debris and spatter.
• For the majority of thin tabs and brackets, use a 1/16-in. tungsten and .045-in. filler rod.
• For welding tube joints, use a 1/16-in. tungsten and 1/16-in. filler rod.
• For welding roll cages (larger, thicker tubes), use 3/32-in. tungsten and 1/16-in. filler rod.
• Most chrome-moly welding is on tubing and parts .035- to .090-in. thick. Set the maximum amperage output to 120 to 130 amps, DC electric negative, HF start only.
• A dirty-looking weld may indicate poor argon coverage or too much heat.
• Keep tack welds small and ideally longer in length than width. A good tack has root penetration.
• Keep welds to within their specified size. A weld needs to be no larger than its thinnest section, which will be the “weakest link” in the chain. Larger welds may add excess heat and waste gas, filler rod and time.
• Avoid pinholes by tapering off heat input at the end of the weld and maintaining a constant distance between the tungsten and the weldment.
• Weld in one continuous motion, pulsing the foot control and adding filler rod to create the stack of dimes appearance. Do not stack separate puddles on top of each other, as this may lead to incomplete fusion.

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