Laser additive manufacturing: A revolution in production

Senior lecturer Dr. Ingomar Kelbassa, deputy chairman of the LLT at RWTH Aachen and department head at Fraunhofer ILT, discusses the evolution of "generative production" using laser technology.

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Aachen, Germany -- The Chair for Laser Technology (Lasertechnik LLT) at RWTH Aachen University and Fraunhofer ILT have developed generative production over the last 20 years from a niche application in the rapid prototyping area into a technology that will substantially influence industrial production in the coming years. Senior lecturer Dr. Ingomar Kelbassa, deputy chairman of the LLT at RWTH Aachen and department head at Fraunhofer ILT, discussed the technology in an interview with Hermann Straubinger of World of Photonics News, shared with Industrial Laser Solutions with permission of Laser World of Photonics.

What Fraunhofer ILT achievement won the Aviation Week Innovation Challenge 2012?

Dr. Ingomar Kelbassa: For a start, we were the winners in one of eleven categories -- the "Power & Propulsion" category. This award was for our process development for generative production, known as BLISKs -- blade integrated disks, i.e. compressor disks with integrated blading. These top-quality integral components are used in the modern jet engines of commercial aircraft, and until now have been produced, for example, with 5-axis milling or linear friction welding. With both 5-axis milling and linear friction, welding the individual blades on the disk results in very high material losses of up to 80% and long production times -- 100 hours of mere milling time with the 5-axis method. It is produced subtractively, that is, by material removal.

In the generative process, laser build-up welding in this specific case, the component is produced by material build-up of the individual blades on the disk. Compared to traditional 5-axis milling, approximately 60% of materials and 30% in total production time are saved here. Production is faster and more efficient.

How does this generative production process work?

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Dr. Ingomar Kelbassa, RWTH Aachen and Fraunhofer ILT

Kelbassa: The two laser-based processes bundled under the generic term, "generative production process are: the single-stage "laser material deposition" (LMD), and the two-stage powder-based "selective laser melting" (SLM). With both processes, one or more powder-form filler materials are remelted in a melting bath using a heat source, laser radiation in this case. This produces built-up tracks with a melting metallurgy compound, including whole layers with tracks built up beside one another, and whole components with layers built up over one another. The difference between single- and two-stage is merely when the powder-form filler material is added to the process. With the single-stage LMD it is placed directly into the melting bath, while with the SLM it is deposited as a powder layer before the remelting (stage 2).

An important benefit of the generative process is, for example, that a component, or even a product, can be configured, designed, and constructed practically as function-optimized, without having to consider production-specific geometric restrictions. Consequently, in the past, optimum components could for the most part not be produced, as they could not be milled, forged, or welded, etc. These geometric restrictions disappear with the product's layer-by-layer build-up in the generative process: what you can conceive you can produce, or "print". This is where the term "3D printing" for this process comes from.

Another important benefit is the processability of series-relevant (mostly metallic) materials. The earlier rapid prototyping on a polymer basis has now become a rapid manufacturing process on a polymer, metallic and ceramic basis.

What types of laser are used for this purpose?

Kelbassa: Beam sources that emit a fiber-coupled laser beam with a wavelength of approximately 1 μm are generally used -- i.e. solid-state lasers, diode lasers, fiber, and disk lasers. For LMD, laser radiation with a wavelength of approx. 10 μm (CO2 laser beam) can also be used.

What other areas can this process be used in and where has it been employed?

Kelbassa: LMD has been used for approximately 12 years for maintenance and repairs in aviation, car manufacturing, and tool and mold construction. The further development of LMD from a repairs process to a generative production is first used in the turbo engine market (power generation as well as aviation and aerospace), where manufacture of these products is time and cost-intensive. However, we can now see that LMD will also be used for generative production in car manufacturing and tool and mold construction.

SLM's first production application for generative production is the patient-specific production of dental implants, bridges and crowns, in use since 2002. Generally speaking, generative production is interesting for markets and application areas where high-quality products must be produced time-critically, which can be configured function-optimized where possible, and where individualized series products can be requested in the future.

Can generative production also be integrated into automated process chains?

Kelbassa: Yes, it can. This was and is the subject matter of the Fraunhofer innovation cluster "TurPro -- Integrative Production Technology for Energy-Efficient Turbo-Engines," developed in cooperation with the Fraunhofer Institute for Production Technology (IPT). The generative BLISK production process has also been developed within the scope of this project. As generative production exclusively replaces the 5-axis milling process step within the entire production chain, but all upstream and downstream processes remain practically unchanged, the integration of the new process step into the already existing and established CAx environment is absolutely necessary. And we have achieved this.

Will generative production put conventional machine tools out of work in the long term?

Kelbassa: In niche areas yes, but not in large parts of the markets. The areas in which, for example, generative production processes could make a conventional machine tool obsolete, are mostly product manufacturing areas where the product no longer has to be finished with regard to the surface finish and quality. An example here would be a ceramic-veneered dental crown, with which, for instance, the roughness after SLM is already tolerable, as it is veneered in the next process step.

A mechanical finishing, possibly including a heat treatment, is obligatory in markets where, product-dependent, generative production alone cannot yet guarantee either the geometric and/or metallurgical specifications and/or the surface finish. Near net-shape in this context mostly means a generative produced component with corresponding measurements, which must then be finished in the last process step.

What are the latest trends and possibilities of generative production processes?

Kelbassa: Generative production processes have advanced significantly in recent years. Experts believe that the process known as "additive manufacturing" or "3D printing" could revolutionize industrial production. The ability to develop new business models and value creation chains and the (almost) quantity-independent production costs of these production processes appear to have major potential. Keywords here are "mass customization," "open-innovation," or "co-creation," whereby the end customers can largely design the product they want themselves.

Many companies are currently testing the use of generative production processes in series production. In addition to the production of functionally optimized structural components, these companies in particular pledge a significant increase in resource and energy efficiency over the entire service life of a product.

For more information: http://www.ilt.fraunhofer.de.

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