Some level of automation has come to almost every part of ground based, wind-tower construction except the welding of the door frame. Most door frames remain long manual processes.
The rest of the tower is the exact opposite. For instance, after metal plate is first cut to size using CNC tables, it’s rolled into a tower section whereupon automation seam welds it into a “can”. Multiple “cans” are welded together using an adaptive fill laser tracking system in conjunction with motorized slides and a submerged arc welding head. However, get to the door section and suddenly, automation takes a long smoke break while a single welder goes to work for eight to ten hours welding the humble door frame in place.
It doesn’t have to be that way, say the engineers at Lincoln Electric. “The biggest bottleneck in tower construction is the attachment of the door frame,” says the company’s General Manager of Mechanized Automation Mike Morgan. “Most companies today are still hand cutting the shell for the frame using a simple template that lacks accuracy.”
Most tower fabricators then manually weld the frames in place using a hand held sub-arc gun that can take up to eight hours or longer depending upon the skill of the operator. The curvature of the door “can” is never the same and the typical 2-in. thick and more frames are hard to maneuver so it’s difficult to get accuracy and repeatability.
With some advancement, Morgan suggests, it is possible to weld door frames in place with a submerged-arc robot arm. “We can take that one step further by putting the robot on the end of a manipulator. The robot can then speed the process with advancement in scanning software,” he says. In a video during a recent welding workshop, Morgan showed how much automation the company has developed just for tower-door frames.
He narrates a video that shows a robot first scanning a tower door sitting on a nearby pallet. The controlling computer then
compares the door with engineering drawings. Then it scans the inside of the tower because inside wall curvature will change. “At this point in the process, we have generated a custom program just for this tower and door,” says Morgan. After the scan, the robot picks up a plasma cutting torch using one of several tools from a tool changer. “Now it can accurately cut an opening for the door frame in the tower without big gaps, so we can reduce the amount of weld filler and therefore weld time. After that, the robot can start cutting an inside and outside bevel. This is huge time saving,” he says.
Now, he asks: how do we get the door frame to the tower? “It is heavy and 2-in. thick. We can use a rail-car-based scissor lift to bring the frame under the can before lifting it through the cut hole to the correct mounting height. Change the tool again to a welding torch and weld around the frame. It’s still multi-pass work. Then use the precision manipulator to lift the robot to the top of the can to complete the outside weld once the “can” has been turned on turning rolls to the 12 o’clock position.
If you’ve welded door frames, you appreciate this automation,” he says. Manually, the job can take a full day and more, just for the door. Automation cuts the job to about 1.5 hours with all the passes, including cuts. “It’s a huge advantage all around saving consumable usage, improving quality, and time.”
The other thing, says Morgan, is that companies often buy all the most up-to-date and advanced equipment, but nobody thinks about feeding the weld wire to the job. A 60 lb coil gets one or two can sections completed with change over times of between 5 to 30 minutes per coil. So the next thing would be to put a 250 lb coil of wire on the side or back end of the manipulator. “Make sure it has the weight capacity. If the manipulator is not of a suitable capacity an option would be a ground based 1,000-lb drum or a reel. The problem encountered here is that the manipulator boom is going in and out and up and down creating resistance in the conduit so there are a few designs concepts that are required depending on the application to overcome that.”
Filed Under: Towers