High-deposition welding with vision Essay

As part of an effort to use automation to reduce costs, improveproductivity, and increase profitability, the Ordnance Div, FMC Corp’s Defense Systems Group, San Jose, CA, tested the capabilityof a robotic arc-welding system developed by Advanced Robotics Corp,Columbus, OH. Called Cyro Vision, it is an advanced 3-D laser-based,real-time adaptive system. The welding of aluminum ball-port sections for the Bradley FightingVehicle served as a beta test site for the system. Based on itsperformance to date, we believe it offers significant opportunities forimproving weld quality and reducing production costs, whilesignificantly expanding the range of practical robotic arc-weldingapplications. Why adaptive control Our Ordnance Div produces a variety of armored vehicles withaluminum hulls and structures.

We began investigating automated weldingfive years ago when robotic technology had advanced to where it madepossible high deposition rates with fewer torch passes on jobs requiringlarger welding wire. Real-time adaptive control of process parametersand weld path was required to make this a reality. There are thousands of parts used in the manufacture of armoredvehicles.

Even slight variations in part tolerance can create fitupinaccuracies that require the torch and process to adapt. Prior toCyroVision, we lacked this capability. The harsh welding environment had rendered earlier vision systemsuseless. We prefer using 3/32″ wire for these applications becauseit yields the best weld. However, this requires over 450 amps, andcreates extreme heat, light, and smoke. We evaluated several through-the-arc seam trackers, but none couldrespond adequately to the electrical resistivity of the aluminum, andthis precluded precise control. The intense arc-light emission and highreflectivity of aluminum result in a signal-to-noise ratio too low formost vision systems to perform satisfactorily.

The system we needed had to be capable of adapting in real time tovariations in joint geometry and position. After an exhaustive search,we have concluded that CyroVision is the only system that meets ourrequirements of real-time process control, seam finding and tracking,uses large-diameter wire, and allows changes in process parameters. How it works This system is a joint development of Advanced Robotics andOldelft, a European supplier of optics and laser-related products. Itmakes 2500 depth measurements per second and reproduces the seam profile10 times/sec. During welding, the vision system precedes the torch, gathering andprocessing data on both the weld path and the seam profile. Bycorrecting for weld path and joint volume variances in real time, itenables a robotic work cell to produce quality welds in applicationspreviously considered impractical for robotics.

Weld parameters can beadjusted in direct proportion to joint deviations without affecting weldquality. The system identifies tack welds according to their individualvolumes. The compact camera is air purged and water cooled. Test results The advantages of this system over manual welding became apparentat once. The number of welding passes were reduced. The extreme amountof light and heat generated by high-density welding make manualoperations impossible. Manual welding with low-density wire required asmany as five passes to complete the weld.

With robotics, we can use3/32″ wire to complete the weld in a single pass, even for parts3″ thick. Thus, we achieve dramatic savings in production time. Secondly, robotic welding eliminates many of the quality problemsnormally encountered with manual welding in this situation, iteliminates brushing, bubbles, and grinding, while providing excellentconsistency in fill height. Thirdly, because it accommodates seam-location tolerances of up to[plus-or-minus]2, it allows us to re-evaluate our tooling requirementsand our need to know the precise location of the part. Adjustments forpart tolerance are made without affecting weld quality. When workingmanually, a welder normally must accommodate fitup inaccuracies andjoint changes by adjusting torch travel speed. Now, adjustments aremade in voltage and wire feed so a constant torch travel speed ismaintained, resulting in greater consistency in weldment quality. Productivity boost The systems proved to be very reliable.

Productivity increaseddramatically due to increased arc on-time, faster torch travel speeds,and higher deposition rates. Also, the need for finish grinding hasbeen reduced or eliminated. Arc on-time averages better than 85percent, and we expect to increase this to 90 to 95 percent as we gainmore experience with this equipment. Torch travel speeds are 60 to 80percent faster, and deposition rates are up more than 200 percent overmanual methods. We anticipate a significant increase in the number of unitsproduced per day, based on production levels achieved during beta-sitetesting so far. Translated to direct cost savings, we expect to save$400,000 per robot per year.

By 1986, FMC expects to rely exclusively on robotics for weldingthe entire outside of the Bradley vehicles. We look forward to thetime–very soon–when robotic arc welding can demonstrate its fullpotential by performing all the welding operations required infull-scale production. Education required During testing, we found that intensive employee education isnecessary to successfully implement any stage of welding automation. Oureducational program includes seminars, training sessions, and lecturesfor management and engineering staffs as well as machine operators. These programs emphasize that people are essential in robotic arcwelding. We stress the fact that there will always be a need forskilled people with the experience and expertise to properly evaluateweld quality.

Our program also stresses to employees how importantrobotics will be to help FMC stay competitive in the future. For more information on CyroVision arc-welding systems fromAdvanced Robotics, circle E62.

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