Intelligent laser processing

A newly designed cutting head produces a remarkable increase in cutting speed

As a machine tool manufacturer or producer of manufactured parts, you decide how intelligently your production units will operate. Interaction is essential today when it comes to production, whether you want to manufacture industrial machines to cut, weld, or glue component parts. Fresh ideas and strong collaboration with the customer, cooperation with institutes, universities, and skill centers provide the basis for services that will be “state of the art” tomorrow.


FIGURE 1. Various intelligent cutting head configurations.
Click here to enlarge image

Laser cutting has become the standard for a wide and steadily growing range of types, gauges, and forms of materials. All of these applications require a high flexibility of the machine as well as the interface between the workpiece and the machine.

During the years many cutting heads and nozzle body designs have been developed to meet an end-user’s specific needs and allow for flexibility in the machine. These sensors produce consistent cutting quality even with coated workpiece surfaces and, when incorporated into the cutting heads (see Figure 1), increase process safety and keep processing time to a minimum.

Three-dimensional applications utilize continuous turning linear drives and require slim nozzle body designs. As the applications become more sophisticated, the sensor controls must be able to compensate for plasma, speed, and fault signals in case of collision with the nozzle electrode or other surfaces. Today process monitoring by a microcontroller is used to regulate the process to maintain parameters that will guarantee consistent product cut quality.

A new development in sensor technology for laser cutting is Velocity-Dependent Cutting. The PS 130 process sensor was originally developed for laser piercing and was intended to control the piercing and cutting process in combination with Lasermatic or Lasermatic Z focusing heads from Precitec for CO2 laser cutting machines. This system of sensors-consisting of evaluation unit, preamplifier, and sensors-evaluates the emissions in the visible and infrared spectrum that occur during the cutting process. This is especially true when dealing with stainless steel or thick sheets because occurring errors may be corrected immediately. The use of the PS 130 is advantageous to reducing rejected or incomplete cuts.


FIGURE 2. W.A. Whitney Co. PlateLASER system.
Click here to enlarge image

Last year, W.A. Whitney Co. included the PS 130 in its PlateLASER systems (see Figure 2). These systems are designed from the ground up to process thick plate as well as thin sheet in a production environment. One critical component to this processing is the feature on every system of an independent lens axis capable of rapidly adjusting the focal position in real-time. Whitney’s Intelligent Laser Control automatically accomplishes this lens position adjustment, as well as the adjustment of virtually any process parameter. All parameters can be set in Material Parameter Libraries allowing real-time adjustments during automatic piercing, automatic lead-in, automatic cornering, and Velocity-Dependent Cutting.

In the initial stages of system development a pierce detection system was not implemented as the pierce process in PlateLASER systems is so fast and consistent through 1-1/4 in. material that it was deemed unnecessary. By moving the focal position down during piercing to follow the ignition point, a precise small hole is created in the material. This minimizes the pierce time and also keeps the surrounding material cool allowing for small feature cutting. No separate nozzle, cutting head, or time-consuming pre-pierce cycle is needed for rapid piercing (see Figure 3).


FIGURE 3. Sample cut quality.
Click here to enlarge image

However, in order to push the cutting process to the limit in thickness or feed rate (or both), and still maintain a stable production-level process, a mechanism to monitor the system is required. Whitney developed a real-time adaptive process control option and implemented the PS 130 piercing sensor as the feedback mechanism with a signal based upon parameters set in the Material Parameter Library.

During the pierce process, a signal level is set to trigger an end to the pierce routine once the signal level drops to indicate that the material has been completely pierced.

During the cut process, several signal level triggers are set. If problems occur during the cut process (due to material defects, difficult programmed geometry, etc.), the signal will climb above a normal level. At this point the cut process is automatically slowed or halted until the signal returns to a normal level. After the signal drops below the resume cut trigger level the feed rate is ramped back up to normal cut speed. If the PS 130 signal climbs again the process is repeated. If a catastrophic event occurs, which causes an unrecoverable degradation in the cut process, an emergency signal level is reached, which triggers an abort to the cut process and signals an alarm.

The Adaptive Process Monitor produces a number of end user benefits. Material can be processed more quickly without the need for constant supervision. Feed rates may be pushed above conservative levels with confidence the process will continue at a robust production level. Even the rapid pierce times available with a Whitney system can be shortened by from 0.1 to 2.0 seconds. Over many pierce cycles this adds up to large production time benefits.

Problems are prevented allowing either automatic recovery or operator intervention precluding the scrapping of material and wasted production time. Damage to nozzles, lenses or other system components may be avoided. In addition to producing rapid pierce times, the sensor, as implemented in the Adaptive Process Monitor Option, provides an extra measure of performance and reliability in both thick plate and thin sheet cutting.

Highly accurate, contact-free sensor systems are key components in technologies today. With their electro-optical measuring technology, these sensors enable modern processing methods to be used reliably. Companies will push forward the development of outstanding solutions for optronics and image processing through innovative optical, electronic, and mechanical components for laser material processing and process control monitoring to allow for a more productive environment.

Don Sprentall is president of American Laser Enterprises Inc. (www.a-l-e.net), a Precitec company.

Reference

Ira E. Cole III, W.A. Whitney Co., “PlateLASER Adaptive Process Monitor,” July 2004.

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