机械工程英语——Lesson 30 Welding Systems Get Smarter and More Versatile

Although the basic resistance welding process remains unchanged, there is plenty of evolutionary change. Among the major trends are: Systems integration. Blending the parts of a welding system to create a stand-alone cell or a system that can be integrated into a larger manufacturing operation is a major change. Most users don''t want the responsibility of buying and blending welding system components.

The buyer may work with a robot or welding equipment manufacturer, or to ensure the widest possible range of products will be considered, use an independent integrator. Smaller companies that are getting away from traditional manual welding operations for the first time may need help in creating automated systems.

As an example of integration between robot and a welding component supplier, ABB Automation (Fort Collins, CO) has an arrangement with Miller Electric Manufacturing Co. (Appleton, WI). "We supply equipment ranging from simple hand-held units to robotic welding equipment," says Bruce Albrecht, Miller''s vice president and general manager, industrial products.

In another case, "We have a relationship with Lincoln Electric (Cleveland) in using their Powerwave 455 R," says Mike Sharpe, Manager, Material Joining Group, Fanuc Robotics North America, Inc. (Rochester Hills, MI). "This power supply, developed with Fanuc, allows the user to have a common user interface before you needed two interfaces: one on the robot and one on the welding equipment."

Pre-engineered welding system, the 20A, combines Lincoln welding system and Fanuc robot control.

With this arrangement the operator has more control over data, and the ability to select and configure different processes. It opens ways to share information, including remote troubleshooting, remote diagnostics, and the ability to develop procedures and download off the Internet.

Changing materials. Improvements in arc control have allowed users to do more with thin materials. "Demand in two of our three major markets remains rather flat," says Richard Litt, president and CEO, Genesis Systems Group (Davenport, IA). "First is automotive, a traditionally high-volume, low-mix market that generally uses fixed systems. Next is the industrial market, or those applications that chiefly fabricate parts from plates .25" [6 mm] or greater thickness. This includes off-road construction and agricultural-equipment manufacturers. However, most of the action is with the light-gage or sheet-metal users. These companies make products such as RVs, golf carts, and enclosures."

Another change that may influence the welding industry is greater use of aluminum. This will require major changes in both equipment and training.

Small shop needs. "We see strong growth in sales of robotic systems to small and medium shops," says Litt. "In bigger companies, automated welding has been a way of life for some time, while at job shops and sub-contractors, most of the work has been, at best, semiautomated."

Tim Morehead, spokesman for Lincoln Electric, also sees more automatic welding as smaller shops convert from semiautomatic to robotic applications.

"One factor encouraging this move is that the price of robots has dropped about 35% over the last eight years," explains Litt of Genesis. "Another is that it is now easier to integrate the elements of a welding system because the technology is more robust and almost problem free."

ABB Robots can be configured in a variety of welding systems. Fixturing is designed to allow maximum welding with minimal setup.

Software simplification is another factor encouraging the small shop owner to automate. There is less fear of complex programming.

"A standard-cell concept is very popular," comments Lincoln''s Morehead. "Manufacturers are looking for immediate solutions to meet their production needs. This is often a prepackaged stand-alone cell that takes little floor space and is as close to plug-and-play as possible."

In this cell from Genesis, an operator loads half the indexing table while a robot-carried welder works on the other half.

Buying more. The trend to greater automation means that US companies are buying more robots for welding systems. Although the US continues to lag behind Japan and Western Europe in the number of installed robots, we are catching up. "Last year, we bought 46% more arc-welding robots than in 1998," says Morehead. "A major push for this change is an ever-shrinking manpower pool. At the same time, it is becoming obvious to the shop owner that ''If I don''t automate, my competitor will.''"

No need to see. Vision systems, which made a major splash a few years ago, have not taken over a large share of the market as predicted. "Vision is a very important technology," says Litt of Genesis. "But it''s not mainstream and not headed in that direction. Although the price of vision equipment has dropped dramatically, the engineering content can be staggering."

Vision systems are currently used chiefly in niche applications such as large-part fabrication where the operation takes advantage of the system''s ability to measure joint geometries and adapt the gun position to the weld.

"The need for vision has also been reduced by more reliable fixturing which ensures the weld joint is properly positioned and improved arc-sensing technology that eliminates the need for vision systems," according to Lincoln''s Morehead. "The better arc seam-tracking software allows you to weld smaller fillets at higher speeds. Current programs can track lap welds at speeds up to 70 ipm [1.8 m/min]."

Axis sweepstakes. When considering low-volume or very complex parts, system versatility, or where the welding head can reach, is critical. The number of axes a robot welding system provides is certainly not fixed.

Equipment suppliers caution that potential buyers should carefully evaluate product needs before setting up a system, and not be unduly impressed by the number of axes offered. Another caution is to determine how the axes are controlled. Are they coordinated with robot motion and does the controller have the power and speed to handle all the axes required at the necessary speed? According to Sharpe of Fanuc Robotics, "The problem comes down to the amount of load you can put on your CPU. Currently we can supply a system in which one robot supports 16 axes."

"Our systems can handle up to 16 axes in a coordinated fashion," says Lincoln''s Morehead. "For the majority of our work, we have six with the robot and two or three extra take care of most situations." Sometimes an integrator will add additional axes using other equipment. Reis Robotics (Elgin, IL) puts the maximum number of axes at 24, while Motoman (West Carrollton, OH) says it can offer up to 27 axes, and operate two robots with one controller.

Time crunch. Welding operations in many shops are now facing the same time constraints as machining operations. Therefore, every effort is made to shave time from the welding process.

"Like machine tool operations, welders are under pressure to minimize the time per part," explains Litt of Genesis. In response, their company has developed a near-zero time change weld fixture. Typically, when changing parts, the weld fixture is removed and replaced. With the Genesis system, the operator keys in a part number, then servomotors adjust the clamps to accommodate the new part.

"We are introducing a new line of welding machines to take advantage of higher welding speeds," says Chris Anderson of Motoman. "They have unique features including pulsing and AC MIG. Its control keeps the arc link very short. Most gas metal arc welding is done with DC electrode positive, which gives rapid penetration of the base material. Now we are using AC power supplies that reduce penetration so you can weld thinner materials and bigger gaps."

Another way to boost speed is to cut component weight. Miller Electric now offers a low-inertia seam weld head that achieves speeds up to 45 fpm (14 m/min).

Smarter than ever. Controls can now do more, yet without adding much programming or operating complexity. "They can handle more variables than ever before," says Morehead of Lincoln. "You only need to dial in the current, wire feed, and voltage, and away you go. You can weld horizontally or vertically in thick or thin materials. We make it as simple plug-in menus. You can even change a process on the fly.

"We communicate directly from the robot to the power source instead of the old way of going from the robot controller, through the weld controller, then to the power source. This erases a major time lag."

Manufacturers have also looked at programming methods. "For some time the trend has been to reduce the size of the teach pendant and put all the programming functions on the controller," according to Litt. "The industry is going the other way. Almost all the programming features are on the teach pendant with only on-and-off and emergency stop on the controller. This simplifies the work of the programmer who is now next to the equipment."

Multiple robot and weld-head axes make a system that welds complex parts.

"To ensure accuracy, we offer a mechanism that lets you fingerprint the robot," says Fanuc''s Sharpe. "A robot that comes directly from the factory is mastered to a calibration jig. But in the shop, a device called Autocal can fine-tune the robot. It takes out machining-induced tolerances as well as any arm variations. The result is a very tight, accurate robot good for off-line programming. It lets you calculate path accurately so that you can go from virtual time to real-time operation with little touch up."

"The most important element in system accuracy is repeatability," claims Voss of Reis Robotics. "For example, if there is a distance change of only 1 mm between the weld tip and the workpiece, that causes about 0.5 V change, and that can mean a lot of damage to a thin-sheet welding operation. Or, if you are off 0.004" [0.10 mm] with wire that is 0.0030" [0.08 mm] in diameter, you could be off the joint or cause burn through."

Images, not hardware. There is now more simulation being carried out, chiefly by the robot supplier and those doing analyses for the end user. Usually only larger companies have their own systems for frequent evaluations and process planning. Smaller companies tend to use simulation chiefly for initial checkout.

Simulation is a powerful tool in preparing a program. "When a guy powers up a welding system, he wants to weld immediately, he doesn''t want to develop processes and make scrap," according to Fanuc Robotics'' Sharpe. "Our off-line programming for PCs includes a 3-D node-map function that lets you graphically represent the robot path in space."

"Our programming allows the end user to have a PC interface to a robot that is basically a productivity manager," says Sharpe. "It counts such things as production cycles, faults, and number of password users, and integrates them with the data monitor function."

At ABB they use PC-based software with a Windows-type format. It is easily adaptable to a customer''s needs and allows off-line programming, part studies, and simulation. This simulation can include the entire plant, or a single cell. The programs also offer automated weld control software that adapts the system to various joint configurations.

"In addition to greater speed and path accuracy, our controllers include simulation, which has moved to the point where it incorporates robot path planning as well as cycle time," explains Anderson of Motoman. "We now have customers who can go from CAD to part without any touch-up. There is no need to edit the program."

Keep it safe. "One of the reasons behind the interest in smaller robots comes from the safety issue. It is necessary to have an area between a robot and any protective fence wide enough for a person to stand. This is to eliminate any potential "pinch points," but also adds significantly to the robot''s floor space requirements.

"To minimize the area, and total system footprint, we have developed a compact robot," says Mike Bomya, vice president, Nachi Robotic Systems (Novi, MI).

Although robots themselves have a very high reliability, there are potential safety problems when the utilities are not properly protected. Nachi engineers make a special effort to route the lines through the robot or securely fix them to the outside and feed them through a single fixture at the base of the machine. This minimizes breakage from unprotected lines.

"Safety is going to be a more significant issue because of the new safety standards passed last year," says Motoman''s Anderson. "We have until June of next year to comply. A key issue is dual-channel monitoring safety circuits, which will add cost and change some designs."

Another item from the new standard is that safeguards have to be rated as complying with ANSI 15.06, which may add requirements.

No dirty hands. The welding industry, like most of manufacturing, is suffering from a shortfall in both the quality and quantity of new workers. This has forced a stronger interest in robot welding systems. These needs have required the development of newer, smarter, more easily programmed equipment that can take over many welding tasks once performed manually.

Design simplicity is another way to meet the labor problem. Developers are minimizing the number of controls on a unit and, at the same time, making the software smarter and able to handle more of the process variables.

As an example of designing for simple operation, Miller Electric has its MP series for pulse welding of aluminum or steel. The 350 MP has a 60-amp unit that has wave-shaping capability. But because wave shaping can be confusing for the novice, there is a single SharpArc control knob. With it, the operator can make the arc stiffer, or softer, without need for complex training. SharpArc is a feature that allows the operator to tailor the size and shape of the arc cone, bead width, appearance, puddle fluidity and travel speed by turning a single knob. This easy-to-use control helps the operator find the right performance for an application without modifying factory programs.