May 8, 2018

“Then this technology will literally take off”

					Prof. Reinhart Poprawe

Prof. Reinhart Poprawe is in charge of the Fraunhofer Institute for Laser Technology (ILT) in Aachen. He also heads the Chair of Laser Technology (LLT) at RWTH Aachen University, is a member of the board of the Laser Institute of America and is an honorary professor at Tsinghua University Beijing. In the interview, he talks about laser processes in Industry 4.0, the technological outlook for additive manufacturing and the progress made with ultrashort pulse lasers and extreme UV lithography.

Prof. Poprawe, one of the key activities at your institute is laser material processing. What role can and will it play in Industry 4.0?

Lasers offer top-quality energy. The entropy, in other words, the degree of disorder in the system, is virtually zero. As a result, we can bundle and focus the energy very precisely in terms of space and time. This is what makes lasers ideal for material processing. And the costs which were always an obstacle are falling: Fiber lasers nowadays cost around EUR 50,000 per kilowatt—five years ago, this figure was eight times higher! The better we can adapt this versatile form of energy to the particular application, the wider the range of applications will be. Because this energy is massless and therefore faster than any mechanical tool, lasers are increasingly being used as tools for electronically controlled manufacturing processes in Industry 4.0.

What are the key advantages?

Digital Photonic Production can individualize components at no extra cost and create even the most complex structures. And because lasers can also be used as sensors, digital twins can also be created at the same time. Nowadays, however, we tend to rely on “digital shadows”: We use a projection of the digital twin in order to obtain the key data actually required. These end-to-end process chains in Industry 4.0 require data to be transferred precisely from station to station. This too is easier with laser processes than with mechanical processes since all the process data is available digitally. Laser material processing is predestined for Industry 4.0.

Many corporations and medium-sized companies are involved at the Aachen Center for Additive Manufacturing. Will additive manufacturing (AM) become an industrial serial process?

It is already a serial process in a number of sectors. In medical technology, aircraft manufacturing or pump construction, manufacturers rely on industrial 3D printing for small-scale production. Automotive manufacturers are also looking closely at the processes. At our campus in May, BMW will present the first mass-produced component produced using selective laser melting (SLM). It will be used in an electrically driven cabriolet, in other words, in a small-scale application. In projects like these, the sector checks whether and to what extent the reliability and robustness of the components are adequate for broader use. Overall, production quantities are constantly increasing—a result of the growing productivity of additive processes.

What are the perspectives?

The Fraunhofer Group has launched the “future-AM” focus project in order to increase productivity 20-fold within three to five years. Although the process costs are rising, high productivity and the speed of production will easily compensate for this. Our aim is to reduce costs by a factor of ten. Even today, additive manufacturing of complex components makes economic sense. What we need to do now is to push the break-even point toward mass production where more than 100,000 components are produced. The potential is also by no means exhausted when it comes to plastics. We are working on new processes such as “thiol-ene click chemistry”, a photo-induced polymerization process whose quality approaches that of injection molding.

What will the typical AM process for metal components look like in 2030?

The powder will go in at the front and the finished components will come out at the back. The process will be fully automated, from powder handling to post-processing. If everything goes well, the systems will have far more lasers than they do at the moment. Instead of using diode-pumped solid-state lasers, with numerous beam sources combined to create a single beam that is moved across the powder bed extremely quickly, we can use the numerous beam sources directly in order to expose the powder to the laser energy. Concepts involving fiber-coupled diode lasers promise much greater productivity since much better use is made of the lasers’ output and the powder can be exposed to the laser energy in parallel. The process will also become freely scalable. Segmented spaces measuring 1.5 x 3 m—the usual size for metal processing—will then be normal.

Change of topic: Semiconductor manufacturers are hoping to use extreme UV lithography soon. As an EUV expert, where do you see the biggest hurdles when it comes to using the process for large-scale production?

From 2019, three semiconductor manufacturers, including Intel and Samsung, will launch large-scale EUV production. The developers of conventional exposure processes, however, are fighting tooth and nail. Using excimer lasers, they have achieved figures of 15 nanometers (nm) in mass production processes—something we never believed possible. What is more, they did this with 193 nm beam sources! That is very impressive indeed. EUV technology will initially use CO² lasers with single-figure nm wavelengths. The biggest obstacles were always the complexity, the costs and the successful resistance of manufacturers of classic technologies.

In which areas other than the semiconductor sector does EUV technology have potential?

Incoherent EUV radiation with a wavelength of 2.5 nm could allow extremely high-resolution transmission microscopy. Biologists could gain an even better understanding of living cells, even if the cells die when the image is taken owing to the extreme UV light. Coherent EUV beam generation is also an option. This would make laser radiation with wavelengths of 10 nm available and this could be focused in a single-figure nm range. This would make it a very attractive proposition for quantum technology since we could address qubits individually. Wavelengths in this range are also highly attractive for measuring systems. Given the demand on the semiconductor market, a new enabler technology is developing for important photonics fields of the future.

Ultrashort pulse lasers are undergoing rapid development at the moment. What do you believe are the most important areas of use for USP technology—in the context of the international markets too?

Have you noticed that aircraft wings look different from how they did ten years ago? They now have curved tips. These so-called winglets minimize lateral movement and hence turbulence, which increased kerosene consumption by several percent. Aircraft manufacturers are now focusing on other turbulence: An enormous downward vortex results where the faster stream of air on the wing surfaces meets the slower stream beneath the wing. This reduces efficiency. Why am I telling you this? With ultrashort pulse lasers, it is now possible to adapt the boundary areas on the upper side of the wing so that part of the air stream is sucked away. Using USP technology, around 10 billion holes are made in the second skin of the wing. As a result of these holes, a negative pressure sucks in air and diverts it.

With what effect?

According to NASA, minimizing these vortexes behind the wings could reduce kerosene consumption by ten to 15 percent! This is motivating us to develop USP lasers with an average power of 10 kW. We have set up a Fraunhofer cluster to pursue this goal. 100 watt systems are currently typical. These will soon be replaced by 2 kW systems and 10 kW systems could be standard in three to five years. Users need productive systems like these so that USP processes take just hours and minutes rather than weeks and days. The technology will literally take off wherever surfaces need to be structured and optimized from a flow point of view. However, surface technology applications for wind power or corrosion protection are also in the pipeline. They offer extreme precision—in the order of 100 nm—and should offer advantages over familiar microprocesses such as eye correction with femtosecond lasers on a macro scale.