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Arc Welding and Spot Welding Arc Welding and Spot Welding

Melded Together: Welding Robotics

POSTED 12/02/2005

 | By: Bennett Brumson, Contributing Editor

Arc and spot welding are some of the oldest and most established applications in robotics. Despite this, they continue to be an important part of the mix of automation for many manufacturers and have a future in robotics due to developing technology.

‘‘Welding is growing because it is a difficult job that fewer people are willing to do manually, so it is harder to find skilled people to do it,’‘ says Daniel Allford, President of ARC Specialties, Inc. ‘‘Also, manufacturers are demanding more out of their products, so they need a greater level of precision than a human welder can provide,’‘ Allford says. ARC Specialties, of Houston, Texas, is a welding integrator.

Think Before you Weld
Getting a welding cell to perform properly and consistently is one of the primary tasks that integrators perform. As with other applications, there are potential challenges to meet, some are process-based, but most stem from materials being welded.

‘‘The challenges today are the new materials and metals. Nachi serves the automotive sector, where high-strength steels and coatings present some challenges to spot welding,’‘ says Michael Bomya, Executive Vice President of Nachi Robotic Systems, Inc. a robot manufacturer headquartered in Novi, Michigan.

Bomya continues by saying that when aluminum was initially introduced on a large scale in automotive manufacturing, it posed a set of issues that have since been overcome. ‘‘Aluminum is soft compared to steel, so it presents some unique challenges in feeding the wire. We at Nachi know how to weld aluminum and stainless steel, but there is definitely a much smaller experience base,’‘ Bomya says. ‘‘We have to grow the knowledge base of the engineers working with these materials.’‘

Bomya adds that arc welding is subject to more variables that influence the quality of a weld than spot welding. ‘‘Controlling all those variables presents quite the challenge,’‘ Bomya says.

Lynn Swanson, President of PRI Robotics, Minneapolis, Minnesota, agrees that aluminum is more of a challenge to weld robotically. ‘‘Aluminum is a more difficult material to weld depending on its thickness. Recent developments such as servo-torch technology and improved welding power sources have made robotic welding of aluminum feasible,’‘ Swanson says.

‘‘By controlling the wire feed rate accurately with a servo motor we are able to improve process control and reliability, said Mike Sharpe, Manager of Materials Joining, FANUC Robotics America, Inc., Rochester Hills, Michigan. ‘‘New features such as intelligent retract start will not allow for a false start on aluminum.  Conditions that may have caused a burn-back, and or a stubbed wire at the start are a thing of the past.’‘

The U.S. has benefited in process developments as a result of the global economy, according to Chris Anderson, Market Segment Technology Leader for Welding at Motoman Inc., West Carrollton, Ohio.  ‘‘We have seen improvements in aluminum welding applications by applying some of the European technology that was developed to weld thin aluminum car bodies. The technology continues to advance to the point where we are able to apply robotics to thin-gage aluminum parts not possible years ago. The robot is also able to reproduce the ‘‘layered-penny’‘ cosmetics of a manually produced quality GTAW weld,’‘ Anderson says.

In addition Swanson says that stainless steel can be MIG, TIG or plasma welded depending on the application and PRI has welded copper successfully.

Process-oriented demands that integrators face when setting up a welding cell includes the repeatability and accuracy of the part to be welded. David DiBiase, Vice President of Welding Systems at Robotic Production Technology (RPT), Auburn Hills, Michigan, addresses this issue.

‘‘The biggest challenges are in the welding process itself, such as repeatability and uptime. The challenge is not in the equipment, which is hardened. Robotic welding equipment really works,’‘ DiBiase says. ‘‘In a lot of manufacturing, welding is the last process. If there are problems fitting parts, welding integrators have to deal with them.’‘

DiBiase went on to say that fitting parts to be welded must be within some measurable tolerance. ‘‘If a part needs to be welded, integrators have to receive that part within an acceptable tolerance band. Integrators cannot expect to weld parts if the tolerances are using more of the band,’‘ DiBiase says. In short, DiBiase says, ‘‘Tolerance is critical. If the parts do not fit, there is not a lot you can do. The gaps have to be within the diameter of the weld wire.’‘

Tolerance issues were also on the mind of Hartmut Boegel, Vice President and General Manager of Cloos Robotic Welding, Inc., a robot manufacturer and engineering services firm based in Schaumburg, Illinois. ‘‘Repeatability and deviation of the part are the major challenges. Cloos utilizes laser vision and adaptive welding to overcome deviation and tolerance problems,’‘ says Boegel.

Boegel went further, saying that robotic welding is to the point where it can overcome almost every issue encountered. ‘‘The challenges are the materials to be welded, the way they go together, and how they are presented to the robot.’‘

‘‘Our greatest challenge is mimicking the skilled manual welder who can compensate for part inaccuracies,’‘ agrees Sharpe.  ‘‘Adaptive weld control through arc sensing allows for a more tolerant process where the robot compensates for varying joint volume changes on large weldments.’‘

Motoman’s Anderson adds that there have been changes in the robot itself to improve the issues related to process uptime. Robots have very high uptime, normally stopping because of process-related issues.  Typically, process equipment is mounted on a generic robot arm configuration. Now robot arms are being designed for specific applications. ‘‘The arc welding arm has hollow passages through the upper arm and wrist to allow the weld wire to be fed through the arm to an in-line torch.  This reduces the feed distance to less and one meter and reduces cable flexing. The result is improved feeding and longer cable life. There is a side benefit of improved torch access into confined spaces,’‘ Anderson explains.   

 ‘‘Similarly, spot welding robots are now available with an integrated harness for utilities. Water and air lines, weld power and I/O signal cables, and even servo motor cables (for servo guns) are integrated into the harness. This integrated harness can last six times longer than traditional dress packages,’‘ Anderson continues. Side benefits include the ability to use the full range of motion with the robot, no interference from external cabling, and less teaching time during product launches thanks to off-line programs that can be downloaded and run. 

Welding On
The evolution of welding robotics had led to the development of new processes. ‘‘There is friction stir welding, where the robot creates friction between two pieces of metal, generating much of the heat that welds them together,’‘ says Joseph Campbell, Director of Strategic Alliances at KUKA Robotics Corporation, Clinton Township, Michigan. Friction stir welding and hybrid welding are processes will start to show up in the robotics market,’‘ Campbell says. Hybrid welding combines, for example, laser and MIG welding.

Cloos’ Hartmut Boegel also sees laser hybrids becoming the norm in robotic welding, but not just yet.  ‘‘Laser hybrid welding is still too expensive for the average the customer. It will not be used widely unless companies like General Motors use laser hybrid welding for automotive applications.’‘

Campbell sees robotic welding becoming more widely available to smaller job shops. ‘‘New technology enables robotics for fabrication projects that were never considered for automation because they were very low volume or just making parts for custom fabrication,’‘ Campbell says. ‘‘One of KUKA’s smaller customers is using a robot to automatically weld single piece parts with no previous programming,’‘ Campbell said. These new technologies open up a whole new class of applications that have yet to be tapped into by robotics.

For Hartmut Boegel, one of the most significant recent developments in robotic welding is the tandem welding technology. Here, two weld wires are used simultaneously rather than the traditional one wire. Again, Hartmut Boegel: ‘‘Tandem wire welding has welding wires that are independent and separate from each other. This doubles the amount of material put down in the seam, and can be more than twice as fast as a single wire system.’‘

Boegel predicts that dual wire will become the norm in robotic welding in the not-so-distant future.  ‘‘Tandem wire welding will become the standard, because it saves money, uses less floor space, requires less maintenance, capital equipment, and labor.’‘ Boegel says that 40 percent of Cloos’ current orders are for tandem wire welding cells. ‘‘I predict that tandem wire will be used for aluminum and for sheet metal applications in the next five or so years,’‘ Boegel concludes.

For ARC Specialties’ Dan Allford, the most significant change in robotic welding over the past few years has been the increased power of Off-Line Programming (OLP). ‘‘Off-line programming allows integrators to create programs without cutting into production time. This is how automatic machine tools have become to dominate the machining industry. OLP is now becoming viable for robotics make robots essential in the fabrication industry,’‘ Allford says.

FANUC Robotics’ Sharpe states that customers understand the benefits of off-line programming and the ability to maximize cell utilization as well as ‘‘teach the perfect joint’‘. However, many users do not understand the round-trip tools to send this perfect virtual welding program to the robot. To do this, robots and work cells must be calibrated to match the mathematical models where they were initially created.

Communication Is Everything
In the past five years, there has been an increase in the digital communication between the robot and its controller. This makes for faster and more reliable transfer of data and power input flowing from the controller to the welding robot.

‘‘Digital communication and faster processing speeds between the robot, the power source and the wire feeder have expanded the capabilities for robotic welding,’‘ says Swanson of PRI. Swanson believes that digital communication will spread through welding robotics industry to become the de-facto method of controller-to-robot contact.

‘‘Looking at communications is only one aspect when considering power supply interfacing,’‘ replies Sharpe. ‘‘To interface means to bridge and when you understand today’s digital communications they are only bridges.  One exception is a digital protocol that works on a different level where the robot and welder do not interface, but are one on the same object from a device perspective. The benefits are a pure method of control with no bridges or gateways, maximum speed, and robustness of arc starting and ending.  Complete diagnostics available on the robot’s web server allows for complete access and maintenance monitoring, and updates can be carried out remotely.’‘

Likewise, David DiBiase of RPT looks to see more digital communication. ‘‘Digital communication between welding power supplies and robots is relatively new. Before digital, communication was analog and integrators had to scale it,’‘ DiBiase says. Integrating analog was difficult and communication time was much longer, making for less control over the weld process than with digital.

The improvement in processing speed and digital communication has allowed a single robot controller to operate multiple arms. A single controller can operate up to four arms simultaneously, programmed from a single teach pendant which complies with the robot safety standard. There is a single E-Stop circuit and I/O processing boards for all robots so multiple robot control reduces integration costs. Software keeps the arms from colliding with each other. The integrated control also allows unique processing methods by having material-handling robots position parts for welding robots. Anderson explained, ‘‘We saved cycle time by using a robot to position a manifold for another welding robot. The motion is coordinated between the robots so that as the handling robot turns the part, the second robot follows the geometry. This allows the welding to be done in the optimum position for higher welding speeds.’‘

Michael Bomya of Nachi likes what he sees with digital pulse welding becoming the basic power supply for robotic welding systems. Coupled with digital communication, Bomya believes that improvements in software have made welding robotics more capable and user-friendly.

‘‘Software is now extremely capable, becoming more fault tolerant,’‘ Bomya says. With welding software that is not fault tolerant, should the robot stop, an operator has to figure out what was the cause.

‘‘When an expert human welder has a problem, he stops to fix it and goes on. He overcomes a problem with his brains and expertise, and gets parts welded,’‘ Bomya says. With more powerful software, welding robots will not just stop and indicate a problem. ‘‘A more intelligent machine will be able to solve a problem without human interference. The software will be capable of self-diagnosis and take action to get back to welding. Welding is the goal. Software is how to get there,’‘ Bomya stresses.

An example would be an arc restart feature. ‘‘The robot will do what a human welder would do, which is to back up in order not to leave a gap in the bead, restart the arc and continue welding,’‘ Bomya says. Good welding software embodies the intelligence of a person and processes as much information as possible into the robot controller. ‘‘Take the mind of a great welder and make that accessible to the robot control,’‘ concludes Bomya.

Joe Campbell of KUKA believes that increased software power will translate into increased power and flexibility in welding robotics. ‘‘Software can take Computer Aided Design (CAD) files and process-in knowledge to generate-out robot welding parameters,’‘ Campbell says. ‘‘Robotic welding software carries a lot of functionality, controlling power supplies, wire feeders, tool center point adjusters and other devices that are peripheral to a welding cell,’‘ says Campbell.

Can’t Live Without it
With technology developments, today’s flexible welding robots successfully address material and process-based issues.  Although considered a mature application, welding robots will always be in demand. Assisting with dull, dangerous and dirty jobs, flexible robotic welding fills the needs of a growing application.