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3D robots

A robot system integrator with laser experience can provide guidance and the process, tooling and automation basics can be readily understood

FFJ 1020 face leadOctober 2020 - Q: Can I use a robot with a laser for 3-axis cutting solutions?

A: The marriage of a fiber-delivered laser and a robot has created a powerful and economic 3D cutting system with fiber delivered and non-fiber delivered lasers. Unlike conventional 5-axis laser cutting systems, robotic systems can be one-third the cost, allow fast flow-through automation and have a larger processing envelope.

Robot payload capacity of 12 kg to 25 kg is needed to support the cutting end effector and its umbilical. The key is to have a robot with good accuracy and trepanning capability along with a cutting end-effector designed for robotic applications. An end-effector with non-contact height sensing will ensure that focus is maintained as the robot moves about its pre-programmed path with the cutting-end effector moving above the surface with a tip to part stand-off of about 1 mm to 2 mm.

Q: What accuracy can be expected from a laser robot cell?

A: There are two types of laser cutting end-effectors. First is a laser cutting head with a self-contained surface-following axis. Accuracy is limited to the robot’s inherent capability and motion techniques using its most accurate axes. Approximately 0.15 mm to 0.2 mm repeatability is typical of a good trepanning robot.

The second type of end effector features three self-contained axes that significantly raise system accuracy and speed. Standard motion axes on an end effector typically cause the robot to shake and vibrate with the inertia forces of the trepanner axes. However, this newly designed trepanning unit employs patent-pending inertia-canceling drives that eliminate vibrations, and trepans at two to three times the speed and with a repeatability of better than +/- 0.065 mm—three times better than the robot can achieve on its own.

Q: What are typical cutting speeds with lasers and robots?

A: Robot cutting speeds are typically 150 mm to 200 mm per second for long trim cuts in 1 mm to 2 mm thick material. Using the robot axes, hole trepanning speeds are about 30 mm to 80 mm per second due to limitations in the robot arm motion in fine part trepanning, which results in about 1-second hole cutting cycle times.

If the inertia-canceling trepan head is used, the trepan cutting speeds increase into the 180 mm-per-second range, creating holes up to three to four times faster than when using the robot’s trepanning capability and with roughly three times greater accuracy.

Q: What typical laser power is required?

A: Cutting speeds are limited by the robot’s motion limitations. An accurate robot motion speed limit is 14 m per minute. This tends to set the laser maximum required laser power at 3 kW to 4 kW for 1 mm to 2 mm thick material and 6 kW for thicker materials. For thinner materials, it might be possible to cut with 0.5 kW to 1 kW lasers.

Q: What else is required for a laser-robot cell?

A: A robot, laser source and laser cutting end-effector are the main building blocks. Additional building blocks include a cutting gas pressure control unit, part fixturing/tooling, exhaust system, scrap management system and a safety enclosure.

The assist gas used during cutting can be oxygen at low pressure (0.8 to 2 bar) for mild steels and nitrogen at high pressure (12 to 15 bar) for hot-stamped boron steels, stainless steels and aluminum. Clean and dry air is also an option with aluminum at pressures of 5 to 10 bar, gas control is vital.

Laser robotic cutting tooling serves two purposes. First is to fixture the part during processing for repeatability and quality. Second is its potential for automation and fast cycle time. Fixtures require more features to channel the slugs and convey scrap away from the part.

Q: What should I do to investigate laser and robot cells for my application?

A: Robot simulator software can import a part model, create program paths, identify interference issues and predict cycle times. Simple systems can be designed and integrated by an experienced end-user, but most integrators have standard configurations for higher value. FFJ

Tom Kugler is fiber systems manager for Laser Mechanisms Inc., Novi, Michigan. A physicist, Kugler has spent 36 years working with lasers applications, systems and beam delivery.

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