Advances in cutting with ultrahigh-power fiber lasers
Ultrahigh-power (UHP) fiber lasers in the range of 10 to 40 kW have seen rapid adoption for cutting during the past few years, and the maximum laser power used for cutting is expected to continue to climb. We present cutting application results within this range and discuss the main factors driving the use of UHP fiber lasers, namely their remarkable productivity advantages, cut quality gains, and increased thickness capability (e.g., 230-mm-thick steel cutting shown in this article at 40 kW).
UHP lasers are defined here as greater than 10 kW of power, and they enable new process regimes to facilitate the expansion of laser cutting into new markets (e.g., by cutting up to 50 mm steels 4x faster than high-power plasma using air-assist gas). Application results show UHP lasers are changing the way steel is cut by replacing nitrogen and oxygen cutting processes with the air-assist process for high-quality and high-speed economical cutting.
Laser cutting has been marked by periods of intense technological advancements since its inception about 50 years ago, namely the introduction of commercial laser cutting machine tools in the 1970s and their use in mass production by early adopters. This was followed by the expanded adoption of carbon dioxide (CO2) laser cutting systems in 1980s, and the introduction of high-power fiber lasers in the late 1990s and early 2000s. During the late 2000s, the development of kilowatt-level fiber laser cutting tools enabled laser cutting to migrate away from specialized niche applications to become a mainstream fabrication process. Fiber laser cutters dominated the market for laser cutting of sheet metals, mainly due to their ease of integration, reliability, low maintenance, relatively low capital and running costs, high cutting throughput, and the feasibility of scaling their power.
In the late 2010s and early 2020s, the path for market growth of laser cutting took two directions. One trend is across the low-power end of the market, with surging demand for 1–3 kW cutters, driven by a lowered equipment capital cost. The second trend is in the high-power end of the market, which has also seen increasing demand for UHP lasers. This is being driven by their high productivity and technological capabilities offered at an economical price, and the laser cutting field has experienced a remarkable power transformation that is unparalleled among other sheet metal manufacturing processes during the same period. Maximum laser power offered on cutting machine tools at fabrication tradeshows has risen from 6 kW in 2015 to an expected 40 kW in 2022, a nearly 7X increase (see Fig. 1 at top of this page). In the last three years alone, the available system power has climbed from 15 kW to 40 kW—a 2.5X surge.
Why now?
Reliable high-power fiber lasers were available several years before the UHP cutting trend started, with 100 kW industrial fiber lasers available as early as 2013.1 But it was only after the rapidly declining price per kilowatt of lasers within the past few years that the barrier to entry into UHP laser cutting was reduced. Cutting heads to reliably handle such high optical power levels within the harsh cutting environment also became available, as well as cutting libraries for UHP cutting systems.
Test setup
For the tests presented here, IPG YLS-40000 40 kW and IPG YLS-30000-ECO2 30-kW high-wall-plug efficiency fiber lasers were used, set up with 100 µm fiber core diameter and the IPGCut-HP cutting head to assess the cutting speed and quality in different metals. To the extent of the authors’ knowledge, 40 kW laser power in 100 µm fiber core diameter is the highest level of laser source intensity ever used to date for industrial laser cutting. We selected a 100 µm fiber core diameter because of the additional 10–25% increase gained in cutting speed compared to 150 µm diameter.
Higher cutting speeds
Our experiments show laser cutting speed increases with increasing average power up to 40 kW for all metals tested, including stainless steel, carbon steel, and aluminum. Figure 2 shows the increase of cutting speed vs. laser power within the range of 12 to 40 kW, for 6–40 mm carbon steel with air-assist gas. The percentage gain in speed increases with increasing metal thickness. For example, a 280% increase in cutting speed for 12-mm-thick carbon steel from 15 to 40 kW (a 270% increase in power) is observed, while a 420% increase is observed for 20-mm-thick carbon steel. For 30 mm carbon steel, going from 30 to 40 kW (a 33% power increase) leads to 66% faster cuts. This suggests that UHP lasers with even higher power may lead to further productivity gains in thick cutting.
To harness the high cutting speed that UHP lasers provide to achieve a significant reduction in cycle time, it is important to cut parts at high accelerations, especially for thinner materials. In recent years, the acceleration limit on typical machines has shifted from 1 g to 3 g to cope with higher laser powers. On the high end, UHP laser cutters with accelerations as high as 6 g were introduced, along with mechanical designs to support such forces without significant path deviations.
Lowering cost per part for fast return on investment
UHP laser cutting (vs. lower power) significantly reduces the cost per part and leads to a fast return on investment and higher profitability. In laser cutting, a major contributor to the operating cost is gas consumption, and gas costs tend to increase significantly with part’s thickness.
UHP laser cutting requires the same or less gas pressure and nozzle size as lower-power cutting. But the cutting speed increases dramatically, which reduces the cutting time per part and substantially reduces gas consumption. For example, a 30 kW laser can cut a typical 16-mm-thick stainless steel part in half the cycle time compared to a 15 kW laser—cutting gas consumption in half.
The electricity consumption of the laser and chiller typically grows linearly with power. Despite that, the electricity consumption of the rest of the cutting machine tool remains about the same. Therefore, with half the cycle time per part in the previous example, we lower the overall electricity costs per part with increased laser power. With continuous developments, high-power fiber lasers’ energy efficiency exceeds 50% and further contributes to electricity savings.2
Factors other than faster cutting also contribute to gas savings with UHP lasers. UHP lasers allow for fast, dross-free cutting of thick carbon steel with high-pressure air, compared to the use of more expensive nitrogen or much slower oxygen cutting. In both nitrogen and air cutting, UHP allows for reduction of gas pressure needed for dross-free cuts. For example, for dross-free cuts in 20-mm-thick carbon steel at 15 kW, air pressure higher than 16 bar is needed, while 10–12 bar will be sufficient at 20 kW or higher. Since gas usage roughly varies linearly with pressure (at the same nozzle size), significant pressure reduction contributes to gas savings and eases the specification of gas generation equipment.
A high-power laser cutting system with twice the productivity vs. lower power is not twice as expensive. This is because the cost per kilowatt decreases with increasing laser power. In addition, the higher laser cost is absorbed in the total machine tool cost, which can have a marginal increase vs. a lower power laser tool. Therefore, it is not surprising to see a UHP laser cutter with 2x productivity gained by higher laser power with only 30–40% higher capital cost.
With significantly higher productivity, one UHP system can replace multiple lower-power systems, requiring a proportionally smaller footprint, fewer operators, and fewer facility preparations. On the other hand, the reliability requirements for UHP fiber laser sources and cutting heads are higher to maintain productivity. Namely, for the fiber laser source, stable power output and beam quality over the long term is required, driven by the quality of diodes, components, and optical integration. As for the UHP cutting head, it should handle high optical power, high-pressure gas, dust, process heat, and high acceleration for reliable operation.
New process options for cutting steel
Carbon steels can be cut with oxygen, nitrogen, or air-assist gas. Figure 3 summarizes the pros and cons of using each assist gas. While oxygen cutting excels at cutting thick carbon steel with lower laser power due to additional oxidation energy, it can become a productivity hindrance, because its speed does not scale well with laser power. On the contrary, air cutting of carbon steel scales well with power (see Fig. 2). For example, for 16-mm carbon steel, oxygen cutting speed remains flat from 10 to 30 kW, around 2 m/min, while the air cutting speed at 30 kW rises to higher than 9 m/min, which is 4.5x faster than with oxygen.
Thicknesses exclusively cut with oxygen at lower power and lower speed can now be processed several times faster and with good quality using UHP lasers and air. For low-power lasers, air cutting results in hard-to-remove dross and an undesirable surface quality. Development of this new high-productivity UHP fabrication option has been enthusiastically accepted by industries that heavily rely on thick steels, such as manufacturing construction equipment and heavy industry applications.
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