Speeding up 3D printing
Multi-laser technology speeds up additive manufacturing processes. Embedded in automated process chains, the technology is increasingly being used in serial production.
SLM Solutions GmbH, from Lübeck in Germany, is setting the trend with its SLM 500 HL model. In the system, four fiber lasers build up metal powder on components. Multi-laser technology such as this is seen as the ideal way to speed up additive manufacturing, to print larger components, and to increase productivity. The objective is clear: Serial industrial production.
Aircraft manufacturers, such as Airbus and Boeing, are already using printed serial parts. NASA and ESA have reported that their designers are merging assemblies made from dozens of individual parts into components that can be printed in one piece. Complete process chains, from design to ready-to-install components, can be handled in-house. The advantages are also encouraging machine and plant engineers, the automotive industry, medical engineers and sports equipment manufacturers to rethink their processes. 3D printing is booming.
SLM sets the pace with its multi-beam technology. With four times 700 watts laser power, the SLM 500 HL builds up metal parts at a rate of up to 105 cm³ per hour, although the individual layers are only about 20 to 75 µm thick and at the exposure point the light is focused to less than 100 µm. The scan speed is several meters per second. The transition between the lasers is the particular challenge. “The working ranges of the four lasers overlap,” explains Dr. Dieter Schwarze, SLM Development Manager Additive Processes. The system controller ensures that the melting areas of the speeding light beam intermesh and that there is absolutely no porosity in the overlapping areas.
More lasers—but not more power per laser
“Of course, we are considering whether we could also use eight or more lasers. And not only in simulation games,” says Schwarze. He believes that in the medium term, build-up rates of 500 cm³ per hour are feasible. Multi-laser technology is needed, as the layer thicknesses cannot increase by very much and the inertial force of the mirrors puts limits on further acceleration of the light beam. “The power cannot be increased by much, as an increase in energy results in more tension and deformation in the components,” he explains. The energy input is always based on the specific material. With aluminum and copper-based alloy, powers in the kW range are certainly required.
The expert also expects to see new process strategies. Such as faster build-up with higher laser power on the component core and even finer surface structures towards the outside with less power. The process strategy could also be used to influence microstructures. “We are able to introduce single crystal microstructures with no particle size limits whose lattice is aligned uniformly in the load direction,” he explains. This makes additive manufactured components ideal for use in high-temperature areas, such as turbine blades, for example. Especially as wear and tear can also be repaired additively.
Scanner systems and fiber lasers will remain the means of choice for the time being
Scientists at the Fraunhofer Society have implemented a system concept in which five diode lasers are guided over the processing area. Schwarze is rather skeptical about this approach. The problem with most lasers was rapid, precise process control. Another issue was the capacity utilization of the individual lasers. At present, there was no real alternative to the current combination of fiber lasers and mirror scanner systems.
The decision-makers at Concept Laser GmbH from Lichtenfels, Germany have similar opinions; the company was nominated for the 2015 German Future Prize along with Airbus and Laser Zentrum Nord. They also use fiber lasers. The current top system is the X line 2000-R with two 1-kW lasers. During 2016, the company plans to introduce a four-laser-system with the option of 4 x 400 watt or 4 x 1,000 watt laser power.
The overall process
Concept Laser sees multi-laser technology as part of an overall strategy with which it can increase the productivity of its systems. “We are working on a complete modular, automated process chain,” says Daniel Hund, Head of Marketing and Communication. The goal is the “AM Factory of Tomorrow”, a digital, networked factory in the style of Industry 4.0. In this, any number of systems can be combined and processes that are now carried out manually will be automated. Immediately after the print process, installation spaces that are designed as independent modules go to post-processing where robots receive the produced components and subject them to heat treatment and post-processing. “Productivity depends not only on the number of lasers and their power, but also on minimizing idle time in the process chains, which, in some cases, have not been fully automated,” he says.
With this factory of the future, Concept Laser believes that it can decrease the space required for additive manufacturing by up to 85 percent. In addition, the productivity of multi-laser technology will no longer be eroded by manual work. But the company also wants to optimize the actual 3D process. For example, the planned 4-laser system will be able to complete construction jobs even if one of the lasers breaks down, which will be done by automatically enlarging the working area of the other three lasers. Processing the powder bed is another innovative idea that the company has announced. “We want to leverage efficiency potentials in the process before we address the next stages of multi-laser technology,” says Hund. After all, sturdy, automated production chains are needed for serial industrial production.