Running the robot

IN the late 1980s and early 1990s, arc-welding robots accounted for an estimated 5% of total robotics sales.

By 1995, that number had doubled.

Now, it's up to 15% — with some estimates going as high as 30% within the next five years.

Arc-welding robots have gotten more cost effective, and more OEMs are preferring that completed subassemblies are brought in to their lines rather than building on the line, leading to more work by suppliers. And more robots purchased. Last September, FANUC Robotics North America in Auburn Hills, Michigan, completed what it called the largest-ever order for robotic arc welders and laser cutters: 450 robots from Formet Industries for use in producing 5000 truck frames a day at its plant in St Thomas, Ontario.

More robots used means more robot accidents. Jeff Noruk, chairman of the American Welding Society's D16 Committee on Robotic and Automated Welding, says that there is no tracking mechanism to document the number of injuries or deaths due to arc-welding robots, with all machine incidents lumped into one category. But he says that with the committee consisting of robot manufacturers, integrators, and users, there has been a keen awareness of the dynamics involved in the growth.

So in 1999 — 14 years after the committee was organized to provide a centralized source for the exchange of technical information between manufacturers, installers, integrators, and operators of robotic and automated equipment — it began work on developing a safety standard for manufacturers and operators. And in January, it released AWS D16.1M/d16.1:2004: Specification for Robotic Arc Welding Safety.

It is the first document to focus on safety aspects unique to robotic arc-welding applications. The standard, prepared under the direction of the AWS Technical Activities Committee and approved by the AWS Board of Directors, identifies hazards involved in maintaining, operating, integrating, and setting up robot systems for gas metal arc welding (GMAW) and flux cored arc welding (FCAW) processes.

“We realized that safety with arc welding was quite a bit different than for robots used for handling or spot welding,” says Noruk, president of Servo Robot. “We thought we needed a specific standard to handle those issues with arc flash and the fact that you're very close to the robot. With an automatic machine, you know where it's going to go. A robot adds another aspect. If something drastic happened, theoretically it could take off and move in any location, even outside of where you programmed it.

“Anybody who uses a robot, before he actually welds a real product, will weld the first one by hand and he'll go through a dry-run mode, and he's fiddling inches from the robot and welding torch. That's very different than spot welding or virtually any other process, where you're never that close to the action. Robots are big enough that they can do some real damage at the speed they move at.”

Committee lauded

David Sytkowski, an electrical engineer for Tower Automotive — which builds structures for the automotive industry, including frames for small pickups — says he recognizes the benefits of the new standard and lauds the committee's work.

“As robots have come from a stand-alone novelty into an environment where they had to interact with other equipment that already had standards, the need to have a standard kind of evolved,” says Sytkowski, whose plant runs two lines that produce 400 frames each in an eight-hour shift. “This new standard defines the guidelines to help keep men separate from machines. It also specifies certain procedures that need to be followed when men interact with machines.”

And there is a lot of interaction.

The typical robotic arc-welding cell is quite sophisticated and can include: a robot controller, teach pendant, remote operator panel, positioning table, work fixture, welding torch, wire feeder and control cable, welding wire guide and supply, electrode lead, wire feeder, control cables and hot gas supply, torch-cleaning station, weld-control interface, water cooler, welding power supply, shielding gas supply, weld interface cable, operator panel interface, robot arm power, work lead, and common base.

“The robot actually is sometimes not the biggest risk,” he says. “The risk is those big positioners that work in concert with the robot. Those can be 10,000 lb. If that thing takes off, it can easily crush somebody.

“There are issues that are unique to robots. When you run a robot in any kind of production, the same things happen as when you're welding by hand. You have to change the contact tips and nozzles. You have to baby-sit. And if it stops welding, you can run in there and do things you don't do with other processes where you troubleshoot from a distance. A lot of injuries happen when people are running in, trying to fix something quickly in a production line and get the robot back in service.”

Key facets

The 26-page document includes a diagram of a typical robotic arc-welding cell and a comprehensive list of definitions. Noruk says the three most important sections of the standard are:

Section 4.4: Attending Weld Program Verification: Robot welding programs can be verified visually by trained operators and technicians. The procedures for verifying the robot welding shall include the following requirements:

  1. Personnel shall be trained on the safe use of the robot, the welding process, and the system requirements prior to performing program verification.

  2. The program shall be executed without the welding arc being on to verify the actual weld path and control function of the robot.

  3. One trained individual shall observe the actual welding process in the restricted space. The individual shall be equipped with an enabling device and the overall speed of the robot shall be restricted to a maximum TCP speed of 250mm/sec (10"/second).

  4. Active safeguards shall be in place prior to the initiation of automatic cycle start to prevent any personnel, other than the individual programming the robot, from occupying the restricted space of the robot during verification.

“This section is one example of why arc welding is different,” he says. “You wouldn't see this in spot welding.”

Section 5: Weld Fixture Requirements.

Design, Construction, and Use. Weld fixtures shall be designed to avoid the following hazards:

  1. Burn hazards associated with weld spatter and hot surfaces.

  2. Impact and pinch points associated with fixture motion, clamp actuator motion, and broken parts.

  3. Flying projectiles, such as unrestrained parts that can come out of their fixtures during system or part loading operations.

The section goes on to recommend that: fixtures should fit within the guarding provided on the weld table, positioner, or within the safeguarded space; guards should be provided over all mechanisms; impact and pinch-point hazards associated with fixture setting and handling shall be safeguarded.

“It's just people safety,” Noruk says. “We're not worried about the robot per se. Some of this also affects the robot because if you don't do things right, you could be swinging things and crashing the robot arm because you didn't take everything into account.”

Says Sytkowski, “You want to have enough room around the robot so that when people have to get in and adjust it or maintain it, there are minimal pinch points and enough room to walk around and work. You determine that by doing a hazard analysis and/or risk assessment. It's a pre-planning, what-if scenario that determines the level of safeguarding you need.

“Generally, we don't like robots that have the capability to reach beyond what they're fenced in to do. There should be about an 18" cushion between the guarding and the robot. There's a formula for the stopping time of the equipment that generally comes from OSHA. If you need to interact with the robot and the parts in front of it, you need to specify how far away the curtain is from where the robot is, based on the stop time of the machine. For a smaller robot, it might be in 400 milliseconds. For a larger robot, one to two seconds.”

Section 6.1: Ancillary Equipment.

The installation and use of any ancillary equipment shall not reduce the level of safety embodied in the standard. All ancillary equipment shall be interlocked to achieve safe, controlled operation and to prevent hazardous motion when the arc welding robot system is not in a predetermined ready state. Electrically powered ancillary equipment shall be installed in accordance with NFPA 70, National Electrical Code, and all local codes.

“People think, ‘Oh, a robot is a power source,’” Noruk says. “But there are a lot of things in the cell that are ancillary devices — little things like torch cleaners. It has its own set of hazards.”

The standard is available for $24 for AWS members and $32 for nonmembers. To purchase it, order online at www.global.ihs.com or call Global Engineering Documents at 1-800-854-7179. This standard, like most AWS publications, also is available in electronic format or as part of a subscription or licensing agreement.

The AWS welcomes comments or suggestions for the improvement of the standard. They should be sent to: Secretary, AWS D16 Committee on Robotic and Automated Welding, American Welding Society, 550 N.W. LeJeune Road, Miami, FL 33126.

Official interpretations of any of the technical requirements of the standard may be obtained by sending a written request to: Managing Director, Technical Services Division, American Welding Society. A formal reply will be issued after it has been reviewed by the appropriate personnel following established procedures.

TAGS: Fabrication
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