This article illustrates that factories and machine shops use automated controls, sensors, and continuous electric arcs to make faster welds better. Welding system manufacturers, such as Lincoln Electric Co. of Cleveland, work with robot manufacturers, including ABB, to integrate their products and tailor automated welding systems that make faster precision welds. At the same time, instrumentation companies, such as LMI Selcom of Gothenburg, Sweden, have developed sensors to improve the precision of automated welding systems even further in high-volume applications. LMI Selcom Robotic Guidance of Gothenburg, Sweden, developed its SeamFinder laser measurement systems to improve the welding quality and cycle times of robotic. A key component to the Power MIG 200 is its Diamond Core technology, an internal assembly that provides a constant electrical current to the welding torch. A Michigan-based welding company taking advantage of the Power MIG 200’s smooth arc is Midstate Utility in White Cloud. The company fabricates machinery used to install telephone cable. Midstate Utility has been using the Lincoln unit since October of 2000.
Metal fabricators seek to increase their productivity and quality by upgrading their welding processes. In response, welding system manufacturers, such as Lincoln Electric Co. of Cleveland, work with robot manufacturers, including ABB, to integrate their products and tailor automated welding systems that make faster precision welds.
At the same time, instrumentation companies, such as LMI Selcom of Gothenburg, Sweden, have developed sensors to improve the precision of automated welding systems even further in high-volume applications.
Despite the popularity of robotic welding in high-volume applications, many machine shops continue to thrive because of the skills of their human welders. By combining continuous electric arc technology and smooth wire feeding mechanisms in its Power MIG 200 system, Lincoln Electric is enabling welders to increase their productivity by 20 percent, while reducing the reworking of finished parts.
Luitink Manufacturing Co. has been producing metal parts at its Menomonee Falls, Wis., plant since 1888 and, until August 1997, never had used robotic welding. However, that month, Luitink won a contract to supply shock caps for Ford Motor Co.'s Ranger light-duty trucks. The shock caps ride above the front coil spring to reinforce the frame in the area where the spring rides, and hold the spring in position.
The shock caps consist of 0.176-inch-thick carbon steel, ring-shaped reinforcement brackets welded to the bottom half of the O.156-inch-thick shock caps. The total circumference is 7.5 inches, and the hole to be plug welded measures 5/ 16-inch.
To fulfill the order for the Ford parts suppliers, Luitink would have to weld more than 16,000 parts per week, a task beyond the skills of even its virtuoso welders. They decided to go robotic and, upon a recommendation, contacted Rob Stinson, the Milwaukee representative of Lincoln Electric Co., and Gayle Roofe of Lincoln 's local distributor, Bentley Welding Supply.
Luitink described to the Lincoln Welding representatives the type of parts it had to weld for the Ford Ranger shock caps. Lincoln Welding used a software program to visually simulate how robots would weld the parts in the required parameters of the job.
Lincoln was given a relatively tight deadline for the robotic cell-two weeks from initial investigation to purchase of the cell, and another 10 weeks for delivery and installation. They worked closely with Luitink to meet this deadline.
First, Luitink built all the customized tooling and fixtures at its Menomonee Falls plant, then shipped them to Lincoln's headquarters. There, automation engineers mounted robots directly onto the welding tables, progranmled the robots to weld the shock caps, and shipped them back to Wisconsin. They were installed in the spring of 1997, and running two days later.
Several Luitink employees, including Ernie Muehlenberg, the maintenance supervisor, were given formal training on the cell at Lincoln Electric in Cleveland, as well as hands-on training at the Luitink plant after installation.
The automated welding cell that Lincoln built includes two Fanuc ArcMate robots, each equipped with an R-J2 controller, Lincoln Power Wave 450 power source, and wire feeders. The feeders use 0.045-inchdiameter Lincoln L-50 wire and a shielding gas mixture made of 85 percent argon and 15 percent carbon dioxide. Most of the welding parameters are supplied by Luitink's auto parts client. A single operator oversees the welding cell.
Welding Two Parts at Once
During their operation, the Fanuc robots weld two parts simultaneously. Robot arms move to the first fixture, where two right shock caps are positioned, their location verified by sensors. After welding the right parts, the mechanical arms shift to the second fixture to weld the left parts, already in positions checked by sensors. This arrangement cuts downtime and results in four completed parts without resetting the tooling.
The welded caps are sent through a gauge that measures their height and tests them for burrs, weld buildup, or other flaws that would cause them to be removed. Production- quality caps are counted and dropped into a holding basket.
As an added safety measure, Luitink laid a pressure sensitive mat around the welding cell to shut off the robots if anyone steps too close to them. The welding company also recommended customizing the robots' movements to help in their maintenance. This means that after a predetermined number of welding cycles, the robots automatically move to a torch-cleaning station, where their nozzles are cleaned and an anti-spatter spray is applied to the nozzles and torch tips. "We have also programmed in an automatic tip check, and the robots recalibrate themselves automatically with the help of Lincoln's TorchMate recalibration program," said Muehlenberg.
"We check four parts each shift to make sure the robot is maintaining penetration and overall consistency of the weld, and what we are finding is that there's very little variation," remarked Mike Krajna, process improvement manager at Luitink. "Because the robot produces minimal smoke and spatter, we don't have to do any grinding or cleanup. We couldn't keep up with the required quantities any other way."
A crash prevention program embedded in the robots' software will stop the robots immediately if one arm moves out of pattern because of a work order and approaches another robot too closely. At the request of its automotive customer, Luitink programmed a repeatability test that causes the robot arms, after a predefined number of cycles, to land on sensors that generate an accuracy report.
Today, the robotic cell at Luitink welds two shock caps in 15 seconds, 20 hours per day, 52 weeks per year. Luitink expects to increase the production of its robot welding to 20,000 parts per week in the near future.
Find that Seam
LMI Selcom Robotic Guidance of Gothenburg, Sweden, developed its SeamFinder laser measurement systems to improve the welding quality and cycle times of robotic welding operations by locating the precise seam position to be welded. Eight SeamFinder systems are fulfilling that mission at an automotive plant in a Benelux country, where they are used by eight ABB Model 2400 robots that arc weld door hinges on car bodies. The SeamFinder systems were installed at the car plant in 1999 by ABB Flexible Automation and were programmed with ABB Robot's Teach pendant.
Each SeamFinder system has a Selcom SLS 2301 laser sensor head mounted close to each robot's welding torch to put them as close to the welding seams as possible, and is integrated with a Selcom controller to the ABB robot's controller. The diode in the sensor head emits a visible laser beam toward the target surface up to 16,000 times a second, so that its light-sensitive detector can record the position of the reflected beam. By taking a series of readings, the SeamFinder establishes the seam's position
The ABB robots are programmed with welding parameters that include the type of joint and plate thickness to be welded. The robot controllers combine this information with the laser sensors' findings and by correcting the parameters to accommodate varying gaps and measurements, direct the welding tip to produce a precise weld.
Half of the laser systems at the Benelux plant are used during prewelding to ensure the quality of welds made on the door frame. This is accomplished by welding a reinforcement upon the body that the hinge door weld would be placed on. The other four sensing systems are used to actually weld the door hinges onto the car body. The SeamFinders locate the three positions needed to properly position the door hinge in less than one second. The sensing system enables the ABB robot to find the requisite seam to within O.1-mm accuracy.
The SLS 230 sensors are designed to operate in the presence of normal welding smoke, and electromagnetic interference generated by high alternating currents or the welding surface. In addition, Selcom engineers equipped the sensor head with a pneumatic shutter to protect it from welding smoke and spatter.
Although automated welding is making inroads on traditional metal working operations, many metal parts will continue to be joined by skilled artisans . Lincoln Electric designed its Power MIG 200 combination wire feeder/ welding machine for welders working in light industrial fabrication, auto body repair, and ornamental ironwork shops, as well as stainless steel and aluminum fabrication.
Like all MIG (metal inert gas) welding machines, the Power MIG 200 uses its wire as both filler material and arc electrode, blanketing the arc in inert gas such as argon or nitrogen to protect the weld from oxidation. The unit requires either single-phase 208- or 230-volt input power, or 460 and 575 volts, to create an electric arc from 30 to 200 amps, with infinite control between those ranges to accommodate varying weld thickness.
The wire drive system feeds from 50 to 700 inches per minute of wire into the arc also to accommodate different welding thickness . Dual drive rolls feed the wire precisely, and split wire guides support the wire as it is fed.
Diamond Core Technology
A key component to the Power MIG 200 is its Diamond Core technology, an internal assembly that provides a constant electrical current to the welding torch. This technology means positive arc starts, a wider "sweet spot" welding range for the machine, and good stainless and aluminum capability.
A tip-in gas bottle platform eliminates the need to lift heavy gas bottles for the unit. A locked storage compartment is used to stow tools or two 10-pound spools of welding wire.
Industrial Metal Cleaning Corp. of Norton Shores, Mich., uses two Power MIG 200s to make the racks, carts, totes, and baskets it supplies to companies that paint, plate, and anodize parts for the automotive, furniture, and aerospace industries. The manufacturer chose the Lincoln welders because of their continuous arc and infinite control, and has been using them for more than a year. "At times we have to weld some very small components, and I believe we are doing this more efficiently," said Gary Link, fabrication manager at Industrial Metal Cleaning. "My fabrication throughput has increased almost 20 percent and rework has dropped to practically nothing."
Another Michigan-based welding company taking advantage of the Power MIG 200's smooth arc is Midstate Utility in White Cloud. The company fabricates machinery used to install telephone cable. Midstate Utility has been has been using the Lincoln unit since October of last year.
George Magoon, a welder at Midstate Utility, has used the Power MIG only on steel so far, but hopes to employ it on welding aluminum soon. "I really like that little toolbox on the unit; I've got it jam-packed with all the tools and parts I need," he added.