When we talk about additive manufacturing with metal, most people – even in the power generation industry – first think of ‘Selective Laser Melting’(SLM), which uses a laser to build components layer by layer from a bed of metal powder in a small chamber. This technology is proofing to be successful with respect to producing hard-to-come-by spare parts or improving upon existing designs such as we did with gas turbine burners recently.
But there is another by now established process in Additive Manufacturing which has revolutionized the way industrial steam turbines are being overhauled: Laser Metal Deposition (LMD), also referred to as Laser Deposition Welding. In this area, LMD can achieve what SLM couldn’t. LMD is not limited to small printing chambers that protect it from environmental disturbances.
With LMD, shielding gases emanate directly from the laser head, protecting the metal powder stream which together with the laser beam creates a melt pool. And since the laser head can move more flexibly, this also means additional freedom for refurbishing or even creating surfaces anew. Therefore, at Siemens we were not surprised at all that a current analysis by the American market research institute ‘Research and Markets‘ sees LMD as the technology with the highest growth rates in the 3D-printing industry).
Now, calling this a ‘revolution’ may be seen as accounting more for wishful thinking than real achievements. Still, it fits perfectly what we experienced at our ‘Laser Cladding Center’ (LCC) at our Siemens Power Generation Services Plant in Nuremberg, Germany, since we opened in June 2016.
It not only transformed how we repair, refurbish and upgrade components, it also allows us to avoid having to wait for weeks for till then sub-contracted production steps.
In the past years, conventional welding processes such as the Tungsten Inert Gas method (TIG) or Plasma Transferred Arc (PTA) or detonation spraying for coatings were used in order to repair and refurbish turbine rotors from all over the world. Today, at our factory these processes have been replaced by LMD-technology. It has essential advantages. Compared to traditional methods it works with lower overall heat input, allows reduced layer thickness and eliminates deformation of the components. This in turn leads to less post-processing, which additionally saves time. Using the virtual part, we simulate the whole motion-sequences offline with Siemens NX CAM software. Then the automated process starts.
Speed is of the essence for overhauling turbines, as time is money for our customers. For all type of repairs as well as part manufacturing the lead time has been tremendously reduced. This is partly thanks to two six-axis robot arms with a laser printing head at our LCC which execute automated programs that constantly monitor and adjust various parameters to ensure the highest welding quality. One of them is installed in a large chamber where we refurbish turbine rotors and a smaller one which has a flexible table on which smaller parts are handled. For more complicated parts, such as stator parts or casings, we scan these parts beforehand which allows us to create a digital twin. Using the virtual part, we simulate the whole motion-sequences offline with Siemens NX CAM software. Then the automated process starts.
I am happy to say that all our welding and coating results match our simulations perfectly. Without thorough digitalization of these processes, none of this would be possible.
Well, don’t take my word for it, but our customers’ response. They have reacted very favorably to the new technology. We are running at fully capacity. In addition, we have already either entered into cooperation with similar centers in India and Brazil, or we will introduce the application in the United States and in other areas in the near future. Additionally, we are developing mobile units which will show up at our customers’ doorstep, further shortening the time needed to react on findings and repair components on site.