November 2008 Edition

WELDING

Robotic Welding Gives a Lift to Production

A manufacturer that makes parts as few as one at a time for its electric lift trucks discovered its parts could be welded more consistently with robotic welders

Customers get a lift from Crown Equipment Corp.’s products – electric lift trucks – but in a plant where small-quantity production is necessary, Crown found its welding productivity was falling down. Until, that is, it investigated automated welding.

Fabricators, such as Crown, are discovering the benefits of robotic welding in areas they never before suspected. In fact, more job shops and contract manufacturers are finding productivity gains moving to welding automation in applications once ignored.

Robotics was once considered exclusive to mass production. Now, companies such as Crown have burst that myth to find productivity gains in automated welding in as few as one unit for a variety of separate parts.

Crown manufactures electric lift trucks in its Greencastle, IN, plant. The company’s trucks are used to transport materials and goods in warehouses, distribution centers, and manufacturing facilities worldwide. The units often can be seen in big-box retail stores, such as Home Depot and Lowe’s, restocking shelves.

The company produces almost 92 percent of all its truck parts onsite. Each part is made in small quantities – as few as one at a time – to meet real-time demand of the assembly line.

Historically, the company manually welded more than 1,500 miscellaneous parts in nine welding stations using MIG and stick processes. Two years ago the company reevaluated that strategy.

A Recommendation, a Review, Robots

Dan Miller joined Crown from Oxford Automation, an auto parts manufacturer that relied on robotics. After Miller’s recommendation to explore alternatives, Crown invited Fanuc Robotics, Rochester Hills, MI, and The Lincoln Electric Co., Cleveland, to review its operations.

The companies performed a two-day review of Crown’s complete robotic operations and welding procedures and discovered hundreds of parts could be welded better, faster, and more consistently with robots, despite the small unit quantities. The data showed Crown that the investment would pay for itself in months.

Lincoln Electric tested its proposal in its headquarters’ laboratories and presented Crown with the results. Crown engineers took the findings to their senior management team and purchased two Fanuc robots and two Lincoln welding cells, both powered by Lincoln’s Power Wave 455M power sources with Super Arc L-56 MIG wire.

Crown engineers then built dozens of universal fixture mounts for the welding cells. They were built on common frames and pinpoints for easy installation and removal from the robotic cells so the welding fixtures could be changed in and out quickly, as needed.

The engineers found the average fixture change-out time was about five minutes using the universal plates and pinpoints. Crown put the system to work on parts identified by the survey, such as engine mounts, cross braces, break pedals, and battery retainers, and saw immediate savings.

Crown then devised a system of 20" high industrial shelves on which to store the fixtures, which can weigh several hundred pounds. The fixtures are retrieved from the shelves with a forklift as needed and placed in a short-term staging area for installation as soon as a robotic cell becomes available.

This decreased downtime and minimized the amount of time an operator needed to locate a fixture. Once a fixture is changed, the same workers who arrange and coordinate the fixtures in and out of the welding area return the used fixtures to assigned storage areas on the shelves.

When a new fixture is installed into the welding cell, an operator enters a stored programming code into the robot’s teach pendent that corresponds to the specific fixture. From there, the operator places and removes raw part material as many times as needed.

Working Well Together

Fanuc robots and Lincoln Electric power sources interface with each other so that operators only need to enter one code into the robot. The code retrieves the programmed instructions for that part for both the robot and power source, including travel path, travel speed, and arc characteristics such as constant voltage or pulse-on-pulse.

The programs can be designed to change arc characteristics within a single program. For instance, the robot and power source can switch to pulse-on-pulse process when the arm shifts to a vertical weld. When the arm swings back to a horizontal weld, the power source can change back to constant voltage.

Programming storage and variety are the reasons that, despite the small unit production, robotic welding has helped Crown’s overall process.

"The process improved our productivity by a factor of at least five," Randy Spitzer, Crown’s senior manufacturing engineer, said. "The welds are more consistent and are of better overall quality. We perform destructive testing on each run, and the improved quality is clear."

Spitzer said the robot’s speed outperforms manual welding so well that it compensates for the downtime associated with automation, even when producing a single unit. The new fixtures eliminate the need for tack welding used in manual operations, providing additional time savings.

Welding Evaluations Save Money

Companies such as Lincoln Electric and Fanuc Robotics perform free welding evaluations for companies, such as they did at Crown. The process can increase productivity and, in some cases, improve the quality of the finished product without increasing costs.

The survey begins when robotic welding specialists audit operations and identify cost-saving opportunities and productivity gains. If automation is a viable option, Lincoln Electric simulates an automated welding process in its laboratories and determines cost savings.

"Customers appreciate seeing their parts welded. It lets production personnel see how a proposed welding process performs with actual travel speeds and cycle times – and how forgiving a process might be for expected gaps and fixture tolerance, or if improvement in component part fit-up is needed to make the application successful," Geoff Lipnevicius, automation manager for Lincoln Electric, said.

This gives companies a sense of expected productivity gains in an effort to avoid any surprises after the purchase. It also lets the finance committee, prior to the commitment of an investment, make an informed decision with real data to insert into payback or return-on-investment calculations.

For Crown, the robots paid for themselves in four months. The company is considering adding more. The automation survey provided Crown with due diligence and an independent assessment, which its engineers provided to senior management to support their own estimates.

Throughout the survey, Lincoln Electric, Fanuc Robotics, and Crown identified other production issues, such as bottlenecks and weld quality. Fixtures used in manual welding were scattered throughout an unorganized storage area, and in some cases located offsite.

Newfound Productivity

Today, the robotic fixtures are mostly built on standardized 24"×36" plates, which are stored in assigned locations, catalogued in a spreadsheet, and maintained with programming packets and operating instructions for each part.

Miller said he programmed more than 70 welding instructions for the two robots. He designed the programs so when an operator prepares a robotic weld, the operator enters the corresponding code into the robot, sets the raw material into the fixture, and hits the "Start" button.

"The operators love it because there’s no more sweat and spatter, it’s much safer, and the overall fatigue is low," Miller said.

Robotic welds tackle a variety of Crown’s work on carbon steel in thicknesses ranging from 16 gauge to 3/4". Crown uses Lincoln Electric Super Arc L-56 wire in 0.035 and 0.045 diameters.

Raw plate steel first enters the plant, where it is laser cut, formed, machined, and in many cases welded into the final part. From there, it is painted and sent to assembly for final installment.

Parts production had been slow before automation, but organizing the entire process accomplished several improvements, Spitzer said. First it organized the production process overall, as well as precise procedures for each part. Then, it reduced the space of the welding area, organized the fixtures for easy retrieval, and increased product flow to assembly.

He said the average welding time of each part dropped from five to 10 minutes down to two to three minutes. The Lincoln Electric robotic cells are System 30 and System 30 HS. Both are dual station cells, which let the robotic arms alternate between two work areas.

As work is replaced on one side, the robot welds on the other, and vice-versa. The operator replaces finished product with raw material to be welded next. In doing so, the robot is always kept in motion resulting in total time savings of nearly 80 percent.

This new productivity let Crown begin production on a fifth product in the Indiana facility without adding employees.

"Lincoln Electric and Fanuc Robotics helped us realize this change, but we chose these companies because of their experience finding these kind of opportunities and making them work," Spitzer said. "We have not had a single equipment failure with any of these products." The Lincoln Electric Co.

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