Will a robotic laser system cut it?

Robotic Laser Cutting Systems

A typical robotic laser cutting system consists of a servo-controlled, multiaxis mechanical arm that has a laser cutting head mounted to the robot's faceplate. The cutting head has focusing optics for the laser light and often an integral height control mechanism.

An assist gas delivery package distributes a cutting gas, such as oxygen or nitrogen, to the cutting head. Most systems use an Nd:YAG laser generator, which can deliver the laser light to the robot cutting head through a fiber-optic cable.

Some systems use a CO₂laser generator that delivers the laser light to the robotic cutting head through a mechanical flexible arrangement with mirrors at each joint. CO₂lasers require a laser gas, either precharged and sealed or through a delivery system.

Why Use a Robot for Laser Cutting?

Features that can make robots attractive for laser cutting include flexibility, integration and automation, reusability, and return on investment (ROI).

Flexibility. With a minimum of six axes of freedom, robots can perform 3-D cutting by reaching in and around tooling to cut required features into a part. Cut features can range from simple round holes to complex contours.

Integration and Automation. Robots typically have a small footprint, so small workcells can be designed that have one or several robots close to a part. Adding one or more robots to the same cell can increase future production. Often two robots can share one laser.

The footprint of the laser system also should be considered. Typically, CO₂lasers have a larger footprint than Nd:YAG lasers, for example.

A robotic laser system also can be set up to perform multiple applications, such as cutting and welding, with the same laser and cutting head.

Reusability. Because the robot uses a flexible programming method, it can cut different parts within the same workcell or be moved to a new workcell.

ROI. The initial capital expenditure typically is higher for a robotic laser cutting system, but improved quality and elimination of multiple workstations can yield process and quality ROI values of two years or less for many systems.

Applications for Robotic Laser Cutting

Not all applications are suitable for robotic laser cutting. Some key factors to consider are:

• Geometry. Some parts, such as draw stampings, have complex shapes that require the cutting head to achieve many different attitudes to cut specified features. These parts may have ideal robotic applications, provided enough access space exists for the cutting head.

  High-volume flat-sheet cutting can be done more cost effectively by a dedicated 2-D laser cutting machine. However, if both 2-D and 3-D cutting are required, a robotic laser cutting system can be suitable.

• Access. Parts such as hydroformed tube sections used in automotive frames that have closed sections where holes can't be punched because of limited access to the back of the material are another candidate for a robotic system.

• Volume. Part volume should justify the cost of robotic laser cutting equipment and fixtures. Because a robot is flexible, it can cut a family of parts in the cell. Typically, part volumes should be 50,000 to 100,000 or more, depending on the number of features to be cut.

• Thickness. For most robotic laser cutting applications, aluminum and steel parts should be 0.02 to 0.2 inch (0.5 to 5 millimeters) thick.

  Cutting thickness capacity depends on laser performance and power; for example, aluminum requires more power than steel to cut the same thickness. As the power of the laser increases, so does the cost of the laser generator.

• Material coatings also play a role in cutting. For instance, zinc-coated steel can reduce cutting speed, while anodized aluminum can improve cutting speed.

• Fixtures. Part location must be repeatable and allow access to all areas to be cut. Some parts are difficult to locate because they lack defined features or gauge holes. Also, fixturing must not interfere with the cutting process, which often is an engineering challenge.

Vendor Capabilities

Robotic laser cutting system vendors must provide repeatable robots. To achieve high-quality cutting, the robot must be able to locate cut features in the parts to ±0.009 in. (0.25 mm) or better.

Your robotic laser cutting system should have the capability to streamline the process of creating and maintaining robotic programs. It should accept parametric data entry for the size of standard shapes it will produce, such as round holes, slots, and rectangles.

Once it performs production cutting, it also should be able to adjust the feature location and size without interrupting production. In addition, the system vendor should be able to create robot programs offline to reduce programming time and validate the application before building the system.

Your vendor also should be able to address all laser cutting issues, including fixture design, integration into an automated cell, and mechanisms to reposition parts.

Process control also is an issue. Controlling a robotic laser cutting system requires more than just turning the laser on and off. The vendor must be able to control cutting process parameters such as laser power, assist gas pressure, and cutting head height settings. Automated recovery from errors should be integrated into the control to maximize system uptime and prevent downtime.

Tips for Success

As an end user, you must begin with a hands-on approach. You should be involved from the beginning and have intimate knowledge of the overall system, especially the details of the parts to be produced. While the vendor is responsible for developing a system that meets your expectations, you will work with the system daily.

Process knowledge is important too. One person or a team should be identified as the process experts. The team doesn't have to have process expertise before using the first system, but it should grow into the expert role with training and hands-on experience. The process expert should then maintain and fine-tune the system for optimal performance.

Like knowledge, training is critical when working with a robotic laser cutting system. Training should be integrated into the project from the beginning and should be done as early as is practical.

Mike Erickson is senior engineer, Materials Joining Segment, at FANUC Robotics, 3900 W. Hamlin Road, Rochester Hills, MI 48309-3253, 800-477-6268, mike.erickson@fanucrobotics.com, www.fanucroboticscom. FANUC Robotics designs, engineers, and manufactures robots and robotic systems.