March 11, 2008
Welding workpieces with circular components can leave welders spinning, literally. By keeping three considerations in mind, welders can stop spinning and start welding.
It's easy to overlook equipment used to position a workpiece for welding, but turn for turn these machines make welding circular assemblies easier on welders. Whether for a short or long production run, a large assembly with a unique geometry, or a small circular piece, weld positioners in many cases promote flat or square welding, provide an ergonomic welding environment, and increase welder productivity.
Practical Welding Today spoke with two rotary weld positioner manufacturers to get a better idea as to what these units offer job shops.
The premise behind rotary positioning equipment is simple: Move the part, not the welder. Regardless of the size of the workpiece, welders can stay in one spot versus walking to where the weld needs to be laid, said Tom Rankin, vice president and general manager, Jetline Engineering, Irvine, Calif. Jetline manufactures positioners with load capacities from 75 to 500 lbs.
"Say a part is a 3-foot piece of stainless. What commonly happens is the welder will have to weld, walk a little bit, weld, and walk a little bit more to get around the part. If it's on a positioner, the welder sits, has a brace for his arm, pushes a foot pedal, and rotates the positioner so he can keep on welding. The benefit for the employer is an increase in productivity," Rankin said.
Keith Honhart, vice president of Atlas Welding Accessories Inc., Troy, Mich., which offers positioners in 100-, 200-, and 500-lb. load capacities, said rotary positioners can aid in the welding of any assembly that has a circular feature, and can fit in short-run or long production environments.
"If it's millions of parts, then I think you'd probably want to find something different. However, we have customers out there who are welding on these things every day and sometimes it's the same job for an entire month," Honhart said.
Many positioners have a tilting base that allows for vertical welding of at least 90 degrees. A foot pedal almost always comes standard to initiate rotation in either the forward or the reverse direction. For manual welding, a bracelike arm rest supports the handle of any hand-held welding device to help relieve arm and hand strain and to help the welder lay a steady bead.
"The welder wouldn't be carrying the weight of the gun at that point. It's like shooting a rifle from a bench as opposed to off-hand," Honhart said.
The weight of a workpiece must not exceed a machine's specified load capacity. Rankin said users must remember to take into consideration not only the weight of the part, but the weight of the tooling used to hold the part.
After determining the load capacity, users must then calculate the necessary revolutions per minute (RPM) for the job. Honhart refers customers to a simple formula that will help them target the appropriate RPM according to workpiece size. First calculate the welding speed in inches per minute (IPM). To do so, Honhart recommends running a test bead for 15 seconds and multiplying the number by 4. If GMAW is used, keep in mind that wire feed speed does not indicate how fast the arc passes over the weldment. Then divide the IPM by the circumference of the part.
"The larger the part diameter, the slower you have to turn the machine," Honhart said.
Honhart suggests users find a machine with a speed range that will accommodate an increase or decrease in workpiece size.
"Speed ranges and RPMs can vary from job to job depending on the speed of the arc and the circumference of the part."
While standard workholding accessories are made available by most positioner manufacturers, Honhart has found that many fabrication shops build their own workholding fixtures to accommodate their jobs, and some, he admits, are quite clever. For quick part setup and removal, Honhart suggests building a fixture for each part on a base plate that can be quickly attached and removed from the positioner.
For users positioning multiple jobs with differing workpiece diameters on one machine, units with an LED readout eliminates the guesswork involved in determining RPM after the job is set up originally.
"Typically by trial and error they would have to figure out the speed. With a digital readout on the machine, they can see the optimal rotation speed and record the RPM for the next time the job is set up," Honhart said.
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