Views: 0 Author: Seasoned Engineer Chole Publish Time: 2024-06-12 Origin: Tianchen Laser
By Chloe Wong, Tianchen Laser Engineer
While fiber laser cutting machines are incredibly versatile and capable of processing a wide range of metals, some metals do pose unique challenges. As an engineer at Tianchen Laser, a top manufacturer of fiber laser cutters in China, I have extensive experience with the capabilities and limitations of these powerful machines. In this article, I'll discuss the metals that can be tricky to cut with a fiber laser and provide tips for overcoming those difficulties.
Fiber lasers use a seed laser and amplifier to generate an extremely focused, high-energy beam of light. This laser beam is directed by a cutting head with focusing optics to cut through metal workpieces. The material is melted, burned, vaporized, or blown away by a jet of gas, separating the metal sheet into parts.
Fiber lasers offer advantages like high cutting speeds, precision, small kerf widths, energy efficiency, and low maintenance compared to other industrial cutting methods. They are well-suited for cutting reflective metals like aluminum, brass and copper as well as steel, stainless steel, and exotic metals.
However, certain metal properties and types of alloys can make laser cutting more challenging. Understanding these special cases is key to achieving the best cutting results.
The primary difficulties metals can pose to fiber laser cutting are:
High reflectivity
Thermal conductivity
Low melting point
Hardness and thickness
Let's examine each of these factors and the metals that exhibit them.
Highly reflective metals like aluminum, copper, and brass pose a challenge because they reflect a significant portion of the laser light rather than absorbing it. This reflected light can potentially damage the cutting head optics.
Pure copper is especially problematic due to its extremely high reflectance of over 90% at fiber laser wavelengths around 1 micron. Polished or plated surfaces increase reflectivity even further.
To cut highly reflective metals, the peak laser power density at the workpiece surface must be high enough to overcome reflectivity and initiate cutting. Specialized cutting heads use a conical nozzle to avoid back reflections. Alloying elements, surface coatings, and textures that increase absorptivity also help.
Metals with high thermal conductivity like aluminum and copper rapidly dissipate heat away from the cutting area. This "heat sink" effect makes it harder to reach the melting point for cutting. More laser power is required to overcome thermal conductivity.
Slowing down the cutting speed and using compressed gas like nitrogen to blow away molten metal can counteract high thermal conductivity to an extent. Pulsing the laser rather than using continuous wave output also helps by allowing heat to build up with each pulse.
Metals and alloys with relatively low melting points tend to melt and re-solidify very quickly during laser cutting. This rapid phase change can cause rough cut edges, burrs, and spatter.
Aluminum alloys are prone to this issue. Their low melting point and viscosity means the metal tends to melt into a blob rather than vaporizing cleanly. Pulsed lasers and specialized gas nozzles that provide extremely localized shielding gas coverage help with this issue.
The thickness and hardness of the metal workpiece affects the laser power and cutting time required. Thicker sheets need more power or a slower feed rate to cut through. Some very hard metals like certain tool steels also need more power to initiate and sustain cutting.
Fiber lasers are more effective at cutting metal up to about 20mm thick. They can cut thicker metals over 25mm, but it may be at a slower rate. The laser power, focusing optics, assist gas pressure, and nozzle standoff distance all need to be optimized based on the specific metal thickness and type.
Stainless steel, while generally easy to cut with a fiber laser, can pose some challenges depending on the specific alloy grades. The high chromium content in stainless steel creates an oxide layer that has much higher melting and vaporization temperatures than the underlying metal.
During laser cutting, this refractory chromium oxide layer impedes the cutting process. Fiber lasers can generally handle this, but some grades of stainless pose greater difficulty:
303 stainless steel contains added sulfur and phosphorus for improved machinability. But these additives make laser cutting more difficult by reducing the alloy's surface tension and viscosity.
416 and 420 stainless steel have high carbon content which reduces their ductility. Laser cutting these grades produces more dross and can cause micro cracking at the cut edge.
Super austenitic grades like 904L have such high nickel content that they have thermal conductivities approaching pure copper. This makes more laser power necessary to cut.
Martensitic grades like 410 and 440C are also challenging due to their extremely high hardness and strength. They have higher reflectivity and less inclination to melt compared to austenitic stainless steels.
Based on my experience cutting a wide range of metals with Tianchen fiber lasers, I recommend the following for processing the most challenging metals:
Use the highest peak laser power available to overcome reflectivity and thermal conductivity. Our 20kW T-20000 fiber laser has the highest cutting power in the industry.
Utilize high pressure cutting gas, typically pure nitrogen or shop air. High gas pressure provides extra cooling and blows molten metal out of the kerf.
Decrease the nozzle standoff distance to 0.5-1.0mm, half the typical distance. This puts the focal point of the beam at the top surface of the metal for the fastest heating.
Slow down the cutting speed to give the laser more time to melt and vaporize metal. Speeds for difficult metals may be 50-80% slower than for mild steel.
Experiment with using frequency-doubled green or UV wavelengths instead of the typical 1064nm infrared. Green and UV light is absorbed more readily by reflective metals like copper and aluminum.
Apply anti-reflective coatings or surface textures to the metal workpiece to increase laser absorptivity. Coatings like black oxide or roughened surfaces absorb more laser light.
Use a specialized cutting head with a conical nozzle to reduce back reflections and a large diameter focus lens to handle high laser powers. Tianchen offers customized "bright metal" cutting heads for our fiber lasers.
If possible, choose an alloy that is more amenable to laser cutting. For example, 6061 aluminum is easier to cut than 2024 aluminum. 304 stainless cuts more readily than 303.
At Tianchen Laser, we have been at the forefront of fiber laser cutting technology for over a decade. Our fiber lasers are used to cut both easy and difficult metals by manufacturers in a wide range of industries around the world.
We offer fiber lasers with powers from 1kW to 20kW and beyond to handle everything from thin-gauge foils to thick plate. Our cutting heads, gas delivery systems, focusing optics, and control software are optimized for the challenges of difficult-to-cut metals.
If you are struggling to cut reflective, conductive, thick, or hard metals with your current laser, contact Tianchen today. Our expert applications engineers can assess your needs and recommend the ideal fiber laser solution.
With the right Tianchen fiber laser and optimal cutting parameters, even the most challenging metals can be cut cleanly, quickly, and reliably. Discover the Tianchen difference and take your metal cutting capabilities to the next level.
