PHOTONICS INTERVIEW
Akad. Oberrat Dr.-Ing. Ingomar Kelbassa
Revolution in production

In work carried out by the Chair for Laser Technology LLT at RWTH Aachen University and Fraunhofer ILT over the last 20 years, additive manufacture has been developed from a niche application in the rapid prototyping area into a technology that will have a major influence on industrial production over the coming years. Senior Lecturer and Dr.-Ing. Ingomar Kelbassa is Deputy Chairman of the LLT at RWTH Aachen and Department Head at Fraunhofer ILT.

1. You won the Aviation Week Innovation Challenge 2012 in March with a team from Fraunhofer ILT. What achievement was the award for?
Dr.-Ing. Ingomar Kelbassa: For a start, we were the winners in one of eleven categories – the "Power & Propulsion" category.

We received the award in recognition of our work on developing an additive manufacturing process for BLISKs (Blade Integrated DiSKs). These integral, high-quality components are used in the jet engines of modern commercial aircraft. Until now, conventional methods such as 5-axis milling or linear friction welding have been used in the manufacturing of BLISKs. With both these methods, however, welding the individual blades onto the disk results in material losses of up to 80%, plus extremely long production times – 100 hours are required for milling alone when the 5-axis method is used. These manufacturing methods involve removing material in order to create the finished product (i.e. they are "subtractive" methods).

In additive processes, Laser Material Deposition in this particular case, the component is produced by building up material to create the individual blades on the disk. Compared to traditional 5-axis milling, this process results in materials savings of around 60% and lowers total production time by some 30%. Production is therefore faster as well as more efficient.

2. What are the basic principles behind additive manufacture, and what are the most important benefits?

Dr.-Ing. Ingomar Kelbassa: Two laser-based processes are known by the generic term "additive manufacture". On the one hand, there is the above-mentioned single-stage Laser Material Deposition (LMD), and, on the other hand, the two-stage powder-based Selective Laser Melting (SLM). With both processes, one or more filler materials in powder form are remelted in a melting bath using a heat source – laser radiation in this case. Tracks of metallurgically fused material are deposited. Tracks deposited next to each other form whole layers, and many layers on top of each other form whole components. The terms "single-stage" and "two-stage" merely indicate the stage when the powder-form filler material is added to the process. In the case of the single-stage LMD, it is placed directly into the melting bath, while with SLM it is deposited as a powder layer before the remelting (stage 2).

An important benefit of the additive process is, for example, that a component, or even a product, can be configured, designed and constructed with almost entirely functional considerations in mind, without having to worry about production-specific, geometric restrictions. In the past, it wasn't often possible to design optimum components due to limitations on milling, forging, welding or similar processes. These geometric restrictions are no longer relevant when a product is built up layer-by-layer during additive manufacture: any shape you can come up with can be manufactured (or "printed"). This is why the term "3D printing" is also used for this process. Another important benefit is being able to process 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.
 
3. What types of laser are used for this purpose?

Dr.-Ing. Ingomar Kelbassa: BFiber-coupled laser sources emitting beams with a wavelength of approx. 1 µm are generally used, i.e. solid-state lasers, diode lasers, fiber and disk lasers. For LMD, laser beams with a wavelength of approx. 10 µm (CO2 laser beam) can also be used.
 
4. What other areas can this production process be used in? Where has it been specifically employed already?

Dr.-Ing. Ingomar Kelbassa: For the past 12 years or so LMD has already been successfully used for maintenance and repairs in the aerospace and automotive industries and for tool and mold construction. The progression of LMD from a repairs process to an additive manufacturing technique is currently restricted to the turbomachine market (power generation as well as aerospace), where time and costs are crucial factors in product manufacture. It is already apparent, however, that LMD will come to be used for additive manufacture in the automotive sector and in tool and mold construction.

SLM was first used in a series additive manufacture application for producing customized dental implants, bridges and crowns, and this has been going on since 2002. Individual applications (not used for series production as yet) have also been implemented in other medical areas, in the automotive industry, in tool and mold construction, and in the aerospace sector. Generally speaking, additive manufacture is interesting for markets and application areas where high-quality products must be produced within strict time constraints, where optimum functional design is a critical advantage, and where individualized series products will be called for in the future.
 
5. Can additive manufacture also be integrated into automated process chains?
Dr.-Ing. Ingomar Kelbassa: Yes, it can. This was and remains the central theme of the "TurPro – Integrative Production Technology for Energy-Efficient Turbo-Engines" Fraunhofer innovation cluster developed in cooperation with the Fraunhofer Institute for Production Technology IPT. The additive BLISK manufacturing process has also been developed within the scope of this project. Because additive manufacture only replaces 5-axis milling, which is a single process step in the overall production chain – but all upstream and downstream steps remain practically unchanged – it was absolutely vital to integrate the new process step into the existing and proven CAx environment. And we were successful in this.

6. Will additive manufacture completely replace conventional machine tools in the long term?

Dr.-Ing. Ingomar Kelbassa: In niche areas yes, but not in large parts of the markets.

The areas in which additive manufacture could make conventional machine tools obsolete are mainly those where the products require no further work to enhance surface finish and quality. One example would be a ceramic-veneered dental bridge: the roughness after SLM is tolerable because the bridge is veneered in the next process step. A mechanical finishing, possibly including a heat treatment, is obligatory in markets where additive manufacture alone cannot yet guarantee the geometric and/or metallurgical specifications and/or the surface finish. "Near net shape" is a term used in this context and generally refers to a component produced using additive manufacture that is very close to the final (net) shape but needs to be finished in the final process step.

7. What are the latest trends in additive manufacture and what possibilities do they open up?
Dr.-Ing. Ingomar Kelbassa: Additive manufacturing processes have progressed significantly in recent years. Experts believe that the technique (also known as "3D Printing") could revolutionize industrial production. The possibilities it brings for developing new business models and value creation chains, together with the (practically) volume-independent nature of this method of manufacture, indicate a major potential. Keywords in this context are "mass customization", "open innovation" or "co-creation", where the end customers themselves can largely design the product they want.
 
Many companies are currently testing the use of additive manufacture for series production. In addition to being able to produce structural components of optimum functionality, these companies are also looking to significantly increase their resource and energy efficiency over the entire service life of a product.


More information
http://www.ilt.fraunhofer.de
http://www.lia.org/news/2011/12/19/lam-2012-21st-century-strides



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