Technology Spotlight: New laser cutting technology means newfound productivity

Figure 1
This QCW fiber laser is cutting a 10-mm-thick carbon steel automotive component using the latest Prima Power Laserdyne process for piercing and cutting.

Combining advanced laser control, new assist gas hardware, and noncontact part mapping now allows fabricators to significantly reduce the cycle time in cutting 3-D parts produced from high-strength, low-alloy (HSLA) plate, according to the laser experts at Prima Power Laserdyne.

By shortening the time for piercing of 5- to 10-mm-thick steel plate in parts containing several hundred holes, slots, and other shapes, the manufacturer has reduced the cycle time more than 30 percent compared to traditional laser processes, said Prima Power Laserdyne President Terry L. VanderWert.

Fiber lasers with average power of 2,000 W have been commercially available for more than 10 years. In fact, automotive component manufacturers have embraced this technology in a large way. The fiber lasers in this power range, a majority of which have continuous wave (CW) output, are well-suited for automotive metal cutting and welding applications. That may be changing, however.

Greater Laser Power

Quasi-continuous wave (QCW) lasers produce peak power 10 times greater in pulsed mode than CW mode, providing new process opportunities in automotive and many other industries, according to Dr. Mohammed Naeem, Prima Power Laserdyne’s senior manager, applications engineering and technology development. (CW lasers are the result of power sources that continuously emit light. QCW lasers have power sources that emit the laser both continuously and at defined intervals.)

“Major QCW laser enhancements in process speed and quality have been made recently in both aerospace and medical device manufacturing. These are now being adopted in other industries, particularly in the automotive sector,” Naeem said.

For Prima Power Laserdyne, innovation in this area has centered around SmartTechniques™, a suite of hardware, software, and control technology that is designed to improve productivity and quality in laser processing and provide unique capabilities for high-power laser cutting, welding, and drilling using both CW and QCW fiber laser systems (see Figure 1). In particular, SmartPierce™ and SmartSense™, along with a patent-pending gas assist nozzle—all developed for aerospace applications—hold great promise for the automotive industry, VanderWert said.

The Automotive Fabricating Challenge

Automotive applications typically differ from aerospace applications in a few important ways. Most automotive parts are fabricated from cold- or hot-rolled steel, instead of stainless steel and specialty alloys, and production processes are not as lengthy when compared to aerospace applications, such as an aerospace combustor that requires laser-drilling thousands of holes.

In fact, because of the quantities of the components required, cutting speed and throughput are the most critical elements of an automotive production process. While automotive parts also require quality and precision, they are more often secondary to processing speed. Edge quality and feature size do not have the same impact on the performance of an automotive component as they do on an aerospace component. Cycle time often determines process viability for automotive components.

For laser processing to be deemed acceptable in automotive applications, it has to perform quickly and produce quality parts. That’s why as Prima Power Laserdyne worked to commercialize this technology for the automotive industry it set aggressive goals for 5- to 10-mm-thick sections of low-carbon steel.

The cut quality required rapid pierce without spatter. Cuts had to be dross-free with minimum taper. Features such as slots and holes had to be located within the required precision, despite the fact that the formed blanks could vary significantly from the design shape. Part-to-part cycle time was the key goal, while minimizing the cost of optics, assist gases, and other utilities.

Piercing and Processing

Laser cutting thick-section carbon steel traditionally is a gas-assisted process using either oxygen or an inert gas such as nitrogen. Variables related to the assist gas, such as pressure, nozzle design, and standoff distance, have a big influence on the cut quality. All play important roles in governing the gas dynamics and significantly influence the cut quality and cycle time.

Figure 2
Prima Power Laserdyne’s dual gas process uses compressed air for piercing and oxygen for cutting to provide consistent cut quality.

One of the benefits of using an oxygen assist gas instead of air for automotive applications is its ability to clear the cut of molten material and produce a dross-free cut. The pressure of the gas is important. With too little pressure the molten material may adhere to the parent material, forming dross and sometimes sealing and ruining the cut. Too much oxygen can burn and significantly degrade the cut quality. To avoid failures in these applications, manufacturers prefer to use oxygen assist gas to achieve a clean cut.

Most important, oxygen assist gas results in faster cutting speeds. Also, the consumption of oxygen is much lower in these applications than the consumption of compressed air or nitrogen, thus reducing costs.

Regardless of material type and thickness, the laser cutting operation begins with a piercing process that governs the overall cut quality. In other words, if the pierce is clean, the stage has been set for a clean cut. However, if the pierce is poor or incomplete, the part may have poor cut quality and, in some cases, be set aside for rework.

Naeem said Prima Power Laserdyne’s cutting tests using a 20-kW QCW fiber laser and oxygen assist gas revealed that cut quality of the 5- to 10-mm-thick steel was acceptable in terms of dross, taper, and cut speed. However, piercing with oxygen proved to be very difficult and unsuitable for this application because faster pierce times and spatter-free pierces were required. Repeatable oxygen pierces were possible using low peak power. However, the pierce time of 0.8 seconds for 7.5-mm-thick steel plate was far too high, and the spatter accumulated at low gas pressure, which required the process to be stopped and the nozzle to be cleaned after only 15 pierces.

Naeem said that the application of the SmartPierce process, which used compressed air for piercing and oxygen for cutting, optimized the piercing process. The high-powered QCW fiber laser was used as the power source. (SmartPierce is a technique that involves pulse-by-pulse changes in any or all of peak power, pulse width, and pulse frequency, Naeem explained. Direct control of the laser with the Laserdyne control provides this capability.)

When SmartPierce was used, the cycle time to provide consistent pierces in 7.5-mm steel plate using compressed air was reduced to just 0.4 seconds.

Of course, after compressed air is used for piercing, a purge of the nozzle is needed to switch to the low-pressure oxygen flow for laser cutting. A minimum dwell time of 2 seconds was required to purge the assist gas delivery lines for consistent cutting. With modification to the assist gas hardware, the changeover dwell time between the two assist gases was reduced to 0.7 seconds. While this may not seem like a major time savings, the total time savings is quite significant and can add up to hours per day when multiplied by hundreds of cut features required in multiple automotive components.

To achieve the stated goals by minimizing changeover time between the two assist gases (compressed air and oxygen), the equipment manufacturer developed and tested extensively its new Dual Gas Delivery Cutting Nozzle (see Figure 2). The nozzle is designed to deliver both coaxial and directional noncoaxial assist gas for piercing thick steel sections followed by fast laser cutting of the material. The directional noncoaxial gas acts as an assist gas for piercing and simultaneously protects the laser optics and nozzle assembly during piercing. The coaxial gas is used for the cutting process. When both gases are used, piercing is accomplished quickly and cleanly through the thick sections, and the need to purge gases when transitioning from piercing to cutting is eliminated.

VanderWert said the final innovation in this new laser process was to create a routine for mapping selected surfaces of the actual 3-D blank to adjust for its imperfect shape before piercing and cutting the various features. This mapping process was required to meet the feature location tolerances for the part.

SmartSense is a laser-based, noncontact measurement tool that operates coaxial with the cutting laser beam. It collects and analyzes measurement data from the surface. The mapping results are used to adjust the planes of processing to reflect the real part location and shape to achieve laser processed feature precision. This technique provides the proper location of holes and other cut features within the component despite a less-than-perfect shape of the blank.

Prima Power Laserdyne, 763-433-3700, lds.sales@primapower.com, www.primapower.com