Gefertec GmbH, Berlin, Germany, recently additively manufactured a 170 kg raw part made of stainless steel for the Institute of Fluid Mechanics and Hydraulic Machinery at the University of Stuttgart’s research into fluid flow machines for hydropower technology.
The increased use of hydropower is one of the building blocks on the path to greener energy, so increasing the efficiency of hydroelectric power plants can increase energy contribution explains Gefertec. This has led to a group at the University of Stuttgart’s research, which will include the investigation of the dynamic behaviour of fluid flow machines under extreme off-design operation conditions.
Erbud Group company IKR GmbH, Bitterfeld-Wolfen, was commissioned with the engineering and implementation of the test stand. In the procurement process, the company was confronted with prohibitive costs and long delivery times for the bellmouth intake which would have delayed the commissioning of the installation.
The diameter of the bellmouth intake that must be made of stainless steel increases from 650 mm on the flange side to 850 mm in a continuous curve. Manufacturing this component by machining would have required a high machining volume, even if a suitably thick-walled tube were available as the starting material. With stainless steel in particular, this would not only have been an expensive but also a very lengthy process in procuring and processing the raw material.
In the search for an alternative manufacturing option, the responsible staff at IKR investigated the possibility of having the component produced using Additive Manufacturing and approached Gefertec to utilise its wire-based Directed Energy Deposition (DED) process, which it refers to as Wire Arc Additive Manufacturing (WAAM), and take advantage of feasibility studies offered by the company’s Application Center. Here, the customers’ requirements are analysed in detail before the component production is implemented on the arc machines. The fulfilment of the material and application-specific requirements is also checked.
Gefertec has five WAAM machines in operation. With technological partners, such as Linde for the gas supply and voestalpine Böhler Welding Group as a supplier for the wire material, the company is well prepared for a wide range of applications. In addition to feasibility studies, clients can also order complete components; IKR selected this service for the bellmouth intake.
“The specialists from Gefertec provided us with competent support in all phases,” stated Tino Bock, who accompanied the project as a planner at IKR. “As a result, we were always sure that we would successfully complete the project.”
The benefits of the method were convincing to IKR: If the component had been machined from solid material, the semi-finished product would have weighed around 1.6 tons. With Additive Manufacturing, the near-net-shape blank weighs just 240 kg – a material savings of over 70%. The production was completed after forty-five hours.
The final challenge to overcome was the necessity to test the bellmouth according to Module G of the Pressure Equipment Directive 2014/68/EU, which includes a design review, strength & construction test and certification. As Wire Arc Additive Manufacturing isn’t regulated in the Pressure Equipment Directive, the testing itself was also new territory.
The Welding Institute for Training, Research and Services (SLV) Halle was commissioned with the test. The procedure test was conducted according to DIN EN ISO 15614-1:2012 and AD 2000 – HP 2/1:2017 and includes, among other things, visual inspection, tensile and bending tests as well as macro/micro sections. The component manufactured by Gefertec is reported to have completed the procedure tests without any problems.