High-deposition welding with vision.
The welding of aluminum ball-port sections for the Bradley Fighting Vehicle served as a beta test site for the system. Based on its performance to date, we believe it offers significant opportunities for improving weld quality and reducing production costs, while significantly expanding the range of practical robotic arc-welding applications.
Why adaptive control
Our Ordnance Div produces a variety of armored vehicles with aluminum hulls and structures. We began investigating automated welding five years ago when robotic technology had advanced to where it made possible high deposition rates with fewer torch passes on jobs requiring larger welding wire. Real-time adaptive control of process parameters and weld path was required to make this a reality.
There are thousands of parts used in the manufacture of armored vehicles. Even slight variations in part tolerance can create fitup inaccuracies that require the torch and process to adapt. Prior to CyroVision, we lacked this capability.
The harsh welding environment had rendered earlier vision systems useless. We prefer using 3/32" wire for these applications because it yields the best weld. However, this requires over 450 amps, and creates extreme heat, light, and smoke.
We evaluated several through-the-arc seam trackers, but none could respond adequately to the electrical resistivity of the aluminum, and this precluded precise control. The intense arc-light emission and high reflectivity of aluminum result in a signal-to-noise ratio too low for most vision systems to perform satisfactorily.
The system we needed had to be capable of adapting in real time to variations in joint geometry and position. After an exhaustive search, we have concluded that CyroVision is the only system that meets our requirements 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 and Oldelft, a European supplier of optics and laser-related products. It makes 2500 depth measurements per second and reproduces the seam profile 10 times/sec.
During welding, the vision system precedes the torch, gathering and processing data on both the weld path and the seam profile. By correcting for weld path and joint volume variances in real time, it enables a robotic work cell to produce quality welds in applications previously considered impractical for robotics. Weld parameters can be adjusted in direct proportion to joint deviations without affecting weld quality. The system identifies tack welds according to their individual volumes. The compact camera is air purged and water cooled.
The advantages of this system over manual welding became apparent at once. The number of welding passes were reduced. The extreme amount of light and heat generated by high-density welding make manual operations impossible. Manual welding with low-density wire required as many as five passes to complete the weld. With robotics, we can use 3/32" wire to complete the weld in a single pass, even for parts 3" thick. Thus, we achieve dramatic savings in production time.
Secondly, robotic welding eliminates many of the quality problems normally encountered with manual welding in this situation, it eliminates brushing, bubbles, and grinding, while providing excellent consistency 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 requirements and our need to know the precise location of the part. Adjustments for part tolerance are made without affecting weld quality. When working manually, a welder normally must accommodate fitup inaccuracies and joint changes by adjusting torch travel speed. Now, adjustments are made in voltage and wire feed so a constant torch travel speed is maintained, resulting in greater consistency in weldment quality.
The systems proved to be very reliable. Productivity increased dramatically due to increased arc on-time, faster torch travel speeds, and higher deposition rates. Also, the need for finish grinding has been reduced or eliminated. Arc on-time averages better than 85 percent, and we expect to increase this to 90 to 95 percent as we gain more experience with this equipment. Torch travel speeds are 60 to 80 percent faster, and deposition rates are up more than 200 percent over manual methods.
We anticipate a significant increase in the number of units produced per day, based on production levels achieved during beta-site testing 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 welding the entire outside of the Bradley vehicles. We look forward to the time--very soon--when robotic arc welding can demonstrate its full potential by performing all the welding operations required in full-scale production.
During testing, we found that intensive employee education is necessary to successfully implement any stage of welding automation. Our educational program includes seminars, training sessions, and lectures for management and engineering staffs as well as machine operators.
These programs emphasize that people are essential in robotic arc welding. We stress the fact that there will always be a need for skilled people with the experience and expertise to properly evaluate weld quality. Our program also stresses to employees how important robotics will be to help FMC stay competitive in the future.
For more information on CyroVision arc-welding systems from Advanced Robotics, circle E62.
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|Author:||Young, Robert N.|
|Publication:||Tooling & Production|
|Date:||Mar 1, 1985|
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