Step Up to the Plate
Article Published January 30th, 2018 in Shop Floor Lasers
When cutting thick metals, fiber lasers are the new MVP by Drew Schneider, product applications manager, and Troy Wilson, product manager, CNC table products, Cincinnati Inc.
Once mostly confined to the world of thinner sheet metal and aluminum processing, today’s fiber lasers are providing their owners with the opportunity to take on jobs requiring thick metal processing. As a result, OEMs and fabricators are getting even more mileage out of their fiber laser investments.
From stainless steel and aluminum through red metals and exotics, today’s lasers are extremely versatile in cutting a variety of materials. Fiber lasers, for example, are especially adept at the intricate thin material cutting often required for medical and aerospace applications.
But what about the other side of the coin? How well do fiber lasers perform when cutting thicker materials? And what should operators know to help ensure success?
Not long ago, if you wanted to process metal beyond 1/4 in. thick, your cutting machine options were pretty much limited to plasma or waterjet. Lasers weren’t even on the radar as they simply lacked the power and ability to produce quality edges. All of this changed, however, as laser technology advanced.
The laser evolution, along with an infusion of higher wattage, meant that lasers, especially CO2, had become a viable option to take on thicker metals. Fiber lasers were fast on the heels of their CO2 cousins, quickly reaching this same level of capability and performance. Today, no longer relegated to thin materials, fiber lasers are finding their way onto more and more shop floors providing parts for an ever widening variety of applications and industries.
Perhaps the key concern with regard to processing thick metals is the quality of the cut. Edge quality has far reaching ramifications going well beyond aesthetics and secondary processes. For manufacturers and fabricators alike, quality edges can have an impact that affects product quality and customer satisfaction, and it permeates all the way down to the company’s bottom line.
Manufacturers and fabricators throughout a number of industries routinely process mild steel ranging from 1/4 in. to 1 in. thick. Agricultural, off-highway, forestry, heavy and construction equipment are just a few examples of the industries whose finished products are constructed on the thicker end of that scale. For these and similar industries, edge quality is simply nonnegotiable.
Rough cut edges make welding difficult and unreliable, which has a direct impact on structural integrity. Because heavy machinery is subject to tremendous loads and forces on a daily basis, welds are under constant stress. There is a very real likelihood that weak welds will fail. Edge quality is, therefore, paramount for avoiding excessive warranty claims, product recalls, litigation or losing key supplier contracts – all of which take a tremendous toll on profitability.
For best results
While it has clearly come a long way with regard to processing ever thicker materials, fiber laser technology is still evolving. Because of this, some limits to its effectiveness remain. Just how thick you should attempt to venture depends on a number of factors, ranging from material type and grade to thickness, assist gas and more.
Unsurprisingly, there are a few things to keep in mind to increase your chances for quality fiber laser cuts when working with thick materials.
In the case of mild steel, the fiber laser cutting ceiling is generally about 1 1/4 in. thick. Grade here is important with A36 tight scale offering the best option.
Stainless steel can be safely processed up to about 1 in. thick. For best results, 300 Series stainless is recommended.
For best fiber laser processing results, aluminum 5052/6061 is recommended for material up to 1 in. thick.
Quality cuts with copper and other red metals are best achieved up to roughly 1/2 in. thick.
The choice of assist gas makes all of the difference with regard to fiber lasers and material thickness. A word of warning for the less experienced laser operator: Processing thick stainless or aluminum with nitrogen can present a challenge. This material/gas combination makes it difficult to obtain a consistent cut without some knowledge of proper programming techniques.
To aid in the process, there are a few basic guidelines to follow. If you have questions or concerns, it’s generally recommended to contact your laser cutting machine dealer.
When cutting thick mild steel, oxygen produces quality cuts from 3/16 in. to 1 in. Nitrogen can be effectively used when the job calls for processing mild steel from 22 gauge up to 3/8 in. On the other hand, air assist is not generally conducive for processing thick mild steel. It is not recommended to employ air assist when processing mild steel greater than 1/4 in.
With stainless steel, one can safely use nitrogen or air assist from 3/16 in. up to 1 in. Oxygen is not a recommended assist gas for processing stainless steel.
With copper measuring between 0.020 in. and 1/2 in., best results are achieved with high-pressure oxygen.
When processing brass or bronze from 0.020 in. up to 1/2 in., best results are achieved with nitrogen.
Cutting thick aluminum offers the greatest flexibility with regard to assist gasses, and all are relatively interchangeable. Nitrogen, air and oxygen are all suitable for processing this metal anywhere from 0.020 in. up to 1 in. For optimum results, it’s recommended to use high-pressure air or oxygen.
In addition to material type, thickness and assist gas, there are other factors to consider. Don’t be intimidated by piercing and lead-ins, and don’t overthink cutting speed. Pierce techniques and lead-ins are handled just as you would with any other thickness or just as you would with a CO2 laser. Programming techniques that have routinely been used on a CO2 laser can also be used on a fiber laser.
Fiber laser cutting speed has always been an advantage, and thick metals are no exception. You may be tempted to slow cutting operations. When it comes to machine performance and cut quality, however, faster is better.
Finally, remember that aluminum re-solidifies quickly. This can have a detrimental impact on edge quality. When cutting aluminum, keep the power density up and expand the kerf width.
For many years, light reflectivity has been an inherent issue with the fiber laser light source. As the laser beam bounces off of red metals and similar reflective materials, the energy reflects back up through the laser head, along the fiber optics and into the circuit board. This burst of energy melts circuit board polymers and damages pump diodes and other key components.
As a result, the damaged units must be taken out of service and returned to the manufacturer for repair. This downtime results in significant revenue lost that cannot be recouped.
To help combat this, many light source manufacturers have adopted a kill switch approach. As sensors detect reflected light, an action is triggered to automatically shut down the laser. While this approach does help prevent machine damage, the downside is that the laser must be restarted. In addition, the abrupt shutdown may also damage parts being processed.
While light source technology has progressed steadily since the 1990s in terms of quality, reliability and safety, perhaps the biggest breakthrough to date comes from light source provider, nLight Corp.
The company offers a revolutionary methodology that, in essence, makes the system immune to back reflection – even with copper, brass and other highly reflective metals. The nLight system absorbs and neutralizes reflected energy before it can cause damage. This allows cutting operations to continue cutting without skipping a beat.
Today, Cincinnati Inc. (CI) and nLight are partnering to provide this light source on the CL-900 fiber laser series. The capability was demonstrated late last year at Fabtech 2017 by cutting ½-in. copper without fear of reflectivity issues.
Fiber laser technology continues to break down the barriers, offering new levels of functionality and performance. As the industry continues its quest for processing thicker materials, laser OEMs and component providers will work to advance their individual and collective expertise. In the near term, nozzle tip design and machine power will be key enablers toward taking that next step.
At the recent Fabtech show, CI showcased its CL 900 8-kW fiber laser. Complete with 5-ft.-by-10-ft. dual pallets, this laser features the nLight optical configuration. With this new offering, CI still continues to invest in research and development, and new fiber lasers will be introduced to further expand cutting capabilities. In fact, the company plans to unveil its latest fiber laser breakthrough at Fabtech 2018 in Atlanta.
Driven by advancements in power, cut quality and light source technology, today’s fiber lasers are well-suited to process an ever-widening array of material types and thicknesses. Even novice operators can achieve good results by broadening their understanding of machines and materials and by adhering to a few simple rules.
If you’re processing only thinner materials with that fiber laser on the shop floor, you’re missing out on a real opportunity. Should you have questions or run in to problems, remember to utilize the applications department where you purchased your laser. They should be happy to assist and help you to more fully optimize your laser cutting capabilities and investment.