Among the different kinds of turbines currently used in hydropower production, the Pelton turbine is one of the most complex and fascinating in terms of design. (Photo 1: Pelton turbine).
The buckets are facing a lot of stress and their intricate shape is a key factor to ensure optimal efficiency of the power plant.
Common methods of manufacturing a Pelton turbine
There are several ways to manufacture a Pelton turbine. In most cases, this type of turbine is entirely machined, starting from a giant forged disc of stainless steel CA6NM, which involves a lot of material loss.
For larger turbines, bucket heads can be added by welding them to the pre-machined forged disc. This manufacturing process reduces the raw material loss, but increases the complexity of the production process because of the precision needed during the joining application.
Additive manufacturing brings opportunities to improve production methods.
3D metal printing is becoming more and more widespread in the industry. This new technology was established thanks to, not only a continuous evolution of the welding processes (laser, arc, etc.), but also the welding consumables. It allows for the fabrication of parts by adding material as close as possible to the final expected dimensions, even for very complex geometries.
This new method of production is a game-changer. Manufacturers can be more competitive by drastically reducing production costs and lead-times, resulting in increased opportunities for new business.
The use of wire arc additive manufacturing (WAAM) has already been successfully used for the production of a Pelton turbine. In 2019, the ANDRITZ Hydro manufacturing plant, based in Ravensburg, successfully constructed the buckets of a 5020mm Pelton turbine, using their MicroGuss™ technology, but the use of wire laser additive manufacturing is a world first.
World first Wire Laser Additive Manufactured Pelton bucket
IREPA LASER and Welding Alloys combined their knowledge and skills to manufacture a Pelton bucket using the AMFREE laser-wire technology. (Photo 2: Overview of the WLAM Pelton bucket).
Unique manufacturing technology
The wire laser additive manufacturing was carried out by IREPA LASER, using a dedicated robotic cell. This production tool integrates the AMFREE laser-multi-wire technology, which allows several wires to melt simultaneously leading to a significant increase in the deposition rate, while ensuring optimal stability of the process.
To manufacture the Pelton bucket, each of the layers was produced according to a special methodology. Starting with the outline of the shape (to guarantee a smooth outer surface), followed by the filling of the shape (to guarantee excellent compactness).
(Photo 3: Pelton bucket being manufactured using multi-wire-laser welding head)
The final manufactured bucket measures 360mm high, 340mm wide and has a depth of 170mm.
14 hours were needed to produce this 61 kg bucket with an average deposition rate of 5-6 kg/h, using a 1.2mm diameter metal cored wire. Recent developments already indicate that it would be possible to achieve up to 8 kg/h.
Advanced cored wire
Welding Alloys has a full range of soft martensitic stainless steel cored wires (13%Cr-4%Ni) dedicated to the hydropower industry. In this case example, we used our CHROMECORE M 410NiMo-G ø1.2mm wire.
The use of cored wires offers numerous advantages for additive manufacturing:
- A cored wire is composed of a tubular sheath filled with metal powders, making it possible to adjust its chemistry according to the customer requirements.
- There is a lot of flexibility in the manufacturing of cored wires; it is possible to supply just 15 kg of wire on a single spool, right up to several tons.
- Using a cored wire increases productivity because the cross-sectional area is small and so the cored wire melts faster than a solid wire.
- The soft fusion of this wire means there is a very low amount of spatter and optimal wire feeding.
In cases of extreme stress and therefore premature wear, it is also possible to deposit a special wire into the internal surface of the bucket to offer superior cavitation wear resistance, using our CAVITALLOY wire.
This hardfacing wire deposits an austenitic alloy with chrome, cobalt, manganese, silicon, with the addition of nitrogen, especially developed to resist extreme cavitation and erosion.
The use of advanced Welding Alloys cored wires combined with AMFREE laser-wire manufacturing solutions, offers exciting new opportunities and possibilities to the hydropower industry.
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