Robotic Welding Resolves a Challenge

Metal fabrication job shops are faced with a constant challenge: produce high-quality, highly specialized work in limited production quantities, while being responsive to ever-changing customer demands.

This is actually the challenge of the job shop industry as a whole. And the ways job shops meet this challenge epitomize the benefits that OEM's obtain from outsourcing to America's job shops.

In one example, Sherman-Reynolds of Chicago, Illinois acquired high technology processing equipment to meet this challenge. The company's customers now benefit from speedier turnaround of high quality work, and Sherman-Reynolds improved its capability to cost-effectively handle increased production volumes.

Established in 1930, Sherman-Reynolds employs 75 people in the custom metal fabrication business. Roughly half of its work involves stainless steel fabrication for the food processing industry. The other half is small-quantity production runs and prototypes for heavy industry.

As with all job shops, the company's success depended upon its ability to meet customer's exacting specifications for a variety of materials and processes. Shop methods must be readily adapted to the needs of new and changing markets.

The Technical Challenge

One of Sherman-Reynolds' customers within the transportation industry recently requested welding repairs as a critical step in the re-manufacturing of heavy, complex-shaped, steel parts. The welding process was extremely important because most of the parts were previously repaired in the field. Field repairs often subject the parts to unknown heat effects, which can alter metallurgical properties.

In the Sherman-Reynolds repair process, parts are initially inspected to determine suitability for re-manufacturing. Welding is then used to replace metal lost to wear. After the metal surfaces are built up, a significant amount of machining is needed to finish the parts. The structural integrity of the weld is critical to the success of these machining operations.

Sherman-Reynolds drew upon their years of welding expertise to determine the best method to build up the worn surfaces. The part being repaired was a complex, contoured shape, roughly 30 inches in diameter -- with no true radius. Up to 1/8 inch thick weld material has to be applied to a variety of surfaces before machining of keyways and wear surfaces. In some areas, multiple weld passes are required.

The company established that gas metal arc welding with flux-core welding wire provided the structural integrity needed to prevent metal 'peeling' during finish machining.

After manually welding one to five pieces per week, the customer needed Sherman-Reynolds to increase production to 40 parts per week.

The customer has 20,000 parts in service, all of which will eventually need to be re-manufactured. Clearly, an automated welding method was needed to achieve the volume requested by the customer.

Automation Meets the Challenge

Tom Owens, President of Sherman-Reynolds, attended the 1994 International Machine Tool Show in Chicago where he watched demonstrations of several welding robots. "At the time, we weren't exactly sure a welding robot would be able to do what we wanted," Owens said. But after evaluating several units, Owens decided to go with an ArcWorld 1000 robotic welder manufactured by Motoman of West Carrollton, Ohio.

It was a good decision. Robots are able to weld complex parts and perform multiple welds efficiently and with high quality. Since robots can be reprogrammed easily, changes in product mix and volume can be efficiently accommodated without changes in shop floor tooling.

Robotics for a wide variety of applications are available from Motoman. These include welding, assembly, dispensing, laser, plasma, and waterjet cutting, material handling, material removal, painting and spot welding. Stand-alone robots, robotic application packages, standard "World" systems, and turnkey custom systems are all available.

Sherman Reynolds' ArcWorld 1000 is a standard, off-the-shelf, six-axis, robotic welder. It includes Motoman's K6S robot and an ERC controller, an integrated welding package with water-cooled torch, an operator-controlled station, a part positioner, and safety components.

"Engineers from Motoman analyzed the task and mounted a part on their robotic welder at their factory. They verified that the part could be welded as needed before we made the purchase," Owens said.

Since the manual process required frequent starts and stops to allow heat and fumes to dissipate, robotic welding had an advantage. It is not affected by fumes and can withstand higher ambient temperatures.

The welding speed and accuracy of the robotic welder also contribute to this substantial productivity increase. The robot manipulator moves the welding torch at precise velocities while accurately negotiating complex contours. "Doing this manually was taking us about six hours per unit," said Owens. "With our robot, we cut that down to about 45 minutes."

Work-piece fixturing is critical in any application. "The robot controller has to know at all times where the part is. If you're going to move the part, you have to make sure you logically explain that to the controller," explained Owens. "We made a turntable and interfaced it to the robot controller to make the welding operation even more efficient," said Owens.

The combination of well-designed fixturing and the robot's accurate repetitive positioning accuracy (± 0.004 inch) assure high quality of the finished product.

Keys to Success

Robots are relatively new to the job shop environment. Sherman-Reynolds found the welder a good choice for entry into robotic production techniques. An integrated, pre-packaged system presented less risk than a custom-designed system would have. Installation was simple, and engineers helped ensure a successful application through run-off testing at the manufacturer's factory.

Tom Owens pointed to ease of programming as an important performance issue. "We have to be geared-up for short runs and prototypes. We don't want a cumbersome programming job and only produce a couple of pieces," said Owens. Sherman-Reynolds sent an operator, a maintenance foreman, and a plant automation specialist to courses at Motoman's training facility. Owens was impressed with the results. "We were programming the robot the day the operator came back from class."

The maker of the robotic welder helped interface the Sherman-Reynolds' custom work-piece turntable, which mounts on welder's part positioner, to the robot welding system controller. "With a lot of help from the manufacturer, some of our own ingenuity, and the ease of interfacing to the robot controller, things went smoothly," said Owens. "We are very pleased with the results."

Sherman-Reynolds is now more prepared for business growth as a result of the flexibility of their robotic system. Production capacity of the robotic welder exceeds the current workload. "We're one of very few custom metal fabricating job shops in the Chicago area with a welding robot," said Owens. "We're entering a new market. We can be very competitive on short welding runs because programming the system is easy, welding costs are lower, and the welds are consistent."

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