Exceeding Expectations through Robotics Washington DC

Morton Metalcraft Co.'s corporate strength is embodied in its dedication to craftsmanship, supplier partnerships, technical innovation and delivery of comprehensive solutions providing bottom-line results to its clients. With plant facilities in Illinois, North Carolina, South Carolina and a new plant in Pennsylvania, Morton's resources—more than 750,000 square feet of industrial space and 1,400 employees—provide highly engineered components and assemblies to the agricultural, construction and commercial-equipment industries.

"We are continually driven to excellence by key clients as Deere & Co. and Caterpillar, Inc.," says Peter Ellis, general manager-Morton West (Morton, Ill.). "Both expect smart, beginning-to-end solutions such as small lot sizes, superior engineering, strict adherence to quality standards throughout production, and precise command over logistics in a just-in-time environment."

And robotic welding represented one technology that could satisfy these demands.

TECHNOLOGY AND PARTNERING STRATEGY

"We were experiencing the same problems that all fabricators of any size experience today: difficulty recruiting and training welders in sufficient numbers to increase welding capacity as well as managing excessive turnover and loss of skills due to resignations, retirements and so forth," says Ellis. "Despite extensive training programs, turnover led to an unacceptable loss of people."

The company established three goals: (1) reduce human-resource needs, using arc welding robots to provide the capacity it was unable to hire or train; (2) establish a zero-defect goal for welding errors made with semi-automatic gas-metal-arc welding: arc hitting the wrong location, out-of-spec welds or welds not made; and (3) reduce production costs by improving efficiency and eliminating rework.

Ellis' team met with several companies, including Panasonic Factory Solutions Co. (Buffalo Grove, Ill.). Jeff Wiley, manufacturing supervisor, describes more details of the final review: "An eight-person team of operations, engineers and managers visited [Panasonic's] technical center in Buffalo Grove. Test parts for welding evaluation were chosen from those considered most troublesome. Part-to-part consistency was most critical. After the development of part-specific procedures, these welds were demonstrated in a work cell as readily fabricated in production. We returned at a later date to run the same parts again to assure ourselves that repeated welding would be just as successful," Wiley says.

IMPLEMENTATION STRATEGY

Jeff Ingraham, senior welding engineer at Panasonic, spent several weeks at the Morton, Ill., plants to assist with integration. According to Ingraham, many potential robotic applications had been very challenging for semi-automatic welding. "The immediate task was to develop new robotic procedures for welding parts to achieve the higher quality and consistency required. For example, the rear-frame part was comprised of 10-mm-thick (approximately 3/8-inch) mild steel requiring almost two hours if welding manually with semi-automatic gas metal arc welding. As a result, only 13 parts could be produced per day.

"Our first step was to conduct offline programming and simulation studies to configure a work cell for this part. The original two-hour cycle was reduced in production by almost 50 percent after installation of the customized work cell, thus increasing daily output to about 25 parts per day," says Ingraham.

Says Tim Nacey, Panasonic's general manager, "First efforts were devoted to building a comfort level with the range of tasks to manage the work cell. For each application, the team began welding using basic procedures until the operators were comfortable with programming and operations. Operator training included use of the teach pendant for programming and robot operations. Since this is a Windows CE-based tool, many were already familiar with a Windows interface from home computer use."

The first installations focused on less complicated subassembly weldments. As Ingraham explains, "Morton had many light-to-medium-gauge parts that did not require sophisticated solutions. Initially, we chose the PerformArc 102S model work cell equipped with the tawers robot to weld smaller size, higher volume part," with a basic rotating-turntable configuration.

CYCLE TIME VERSUS ARC-ON TIME

"Most end users make a mistake by concentrating only on arc-on time when considering the opportunities for productivity improvements in robotics," Ingraham explains.

"Rather, the total cycle time from arc-start to arc-start combines time periods for arc striking, arc-on, arc-ending and the non-productive robot arm motion ("air-cut"). During the air-cut period, higher-speed motors provide increased acceleration and deceleration and combine with a 50-percent increase in maximum robot speed to effectively reduce air-cut times by 20 to 50 percent in typical applications."

A lift-arc-ending function, made possible through high-speed bus communications, automatically lifts the weld wire away from the decaying arc through robot arm motion, not reversing the wire feeder. Thus, the ball typically found on the end of the welding wire is eliminated. This allows a more controlled arc start when the next arc ignition takes place. At that moment, the lift-arc start function occurs, aiding starting and reducing downtime.

Designed with a 64-bit processor combined with a 100-kHz primary welding inverter, the system's bus communication permits data communications through an embedded-arc-control technology that merges control for the robot, power source and servo-wire-feeder control functions within a single master circuit. The robot can monitor and correct the welding arc as frequently as every 10 microseconds.

The cells also take advantage of touch sensing, providing a significant quality benefit: error-proofing. The robot ensures that a locating boss was manually welded correctly in a previous operation by determining the correctness of part fitup and tacking. If the locating boss is missing, the system stops the robot and signals the operator to correct the problem before continuing. If the actual part location is not correct, the robot adjusts its welding trajectory or path and then makes the weld correctly.

FUTURE PLANNING

To handle larger parts, the team selected a larger 212S cell featuring twin rotating head-and tail-stocks. The company's plan is to expand capacity to six units, allowing a two-month installation cycle per cell.

According to Wiley, robotic cells will soon be integrated to weld eight smaller parts, each requiring six-minute cycles, including approximately 4.5 minutes arc-on time. The typical 212S work-cell configuration balances the parts loading for the head- and tail-stock on each side of the robot. Parts loading and unloading occurs while one side is actively welding. Wiley explains that the goal is to achieve same cycle time on each side, so that neither side waits for the other. "All works well and our throughput has in fact increased greatly. Typical parts include three 3-mm thickness hood styles and six styles of an 8-mm thickness grill."

Concludes Ellis, "The value of our investment in new technology is easily measured by the perceptions and quality acceptance of customers. For example, our quality approval process of the heavy-gauge rear frame was driven by internal quality demands as well as those required by Deere & Co., which required very high accuracy of weld sizes. AWS [American Welding Society] certified inspectors within our quality laboratory routinely examine welds visually, measure weld geometries and check for any other customer requirements. There have been no rejects in the many months during which we have produced thousands of different parts after implementing the new robot and the various work cells. So, the value is obviously there.

"In addition, we now experience much less spatter and weld smoke. We typically produce components to an internal Class A surface standard requiring a first-quality surface finish. If weld spatter were present, we would incur the labor cost and downtime for removal."

Editor's Note: Sean Walters is marketing product manager at Panasonic Factory Solutions Co., www.panasonicfa.com. Photos courtesy of Panasonic.