WAAM Process Series Production With Wire Arc Additive Manufacturing

Related Vendors

Gefertec GmbH

Taiwan Machine Tool & Accessory Builders' Association (TMBA)

Wuxi InfiMotion Technology Co., Ltd.

SIMTOS (Seoul International Machine Tool Show)

3D printing has long been established as a manufacturing process for prototypes or small series. However, with Wire Arc Additive Manufacturing (WAAM), there is also a process suitable for series production, as demonstrated by the example of a leading steam turbine manufacturer.

The fundamental principles of steam turbine manufacturing have been established for decades: rotor and stator blades play the central role in converting thermal energy into electrical energy. Depending on the application, turbines vary significantly in size and complexity. While smaller units do not surpass the dimensions of a car, large turbines can reach lengths of up to 66 feet, consist of up to 70 stages, and weigh several hundred tons. Their fields of application range from combined heat and power plants to biomass power plants and large-scale solar thermal power plants. Due to the specific requirements, each turbine is designed individually.

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Production Planning Under Complex Conditions

This variety of configurations made production planning increasingly challenging for a leading turbine manufacturer. Stockpiling was only feasible to a limited extent. The production manager always had to balance between delivery times and costs. A typical example is the turbine blades for the rotor and stator. The flat material from which the turbine blades are milled is sourced from China. Due to global supply chain issues, lead times can take several months. At the same time, customers are demanding ever shorter delivery times, which are then difficult to meet. To address market cost pressures, the company is also constantly looking for ways to reduce costs to remain competitive in the international market.

Under these conditions, the idea emerged to manufacture the stator blades, which range from 12 to 28 inches in length, additively. Due to the twisted shape of the blades, the machining volume is relatively high at 70 percent when milled from flat material. This results not only in high material costs but also in costly machine times on milling centers as well as tool wear. Initial considerations by the project team to invest in a powder bed additive manufacturing process quickly showed that this method would not only be too slow but also would not achieve the required cost savings.

The Berlin-based (Germany) company Gefertec made a name for itself with its WAAM process. As early as 2015, the company developed machines for 3D printing using WAAM, making the proven method of arc welding usable in a machine tool.

WAAM As An Economical Alternative to Machining

The arc machine used by the turbine manufacturer utilizes wire as the base material and prints a near-net-shape workpiece layer by layer. The WAAM process runs fully automatically within the machine. This is followed by a milling finish. A high-alloy, high-temperature-resistant solid wire with a thickness of 0.05 inches is used as the material—a standard steel that is easy to source in wire form. Long lead times, which are a problem with the flat material used for milling, are now a thing of the past.

One of the main tasks before starting the series production of turbine blades was the qualification of the process. Since no standards existed, a great deal of foundational work was initially required. For the first produced batches, CT examinations were conducted on all turbine blades to detect any potential pores. Additionally, destructive testing methods were used to determine hardness and bending strength, as well as to conduct metallurgical examinations and chemical analyses. Based on the results, the parameters of the 3D printing process in the arc machine were continuously optimized.

In the end, there was a stable and qualified manufacturing process suitable for series production. These extensive quality controls during the qualification phase were necessary to ultimately achieve a process where only a few random sample tests are conducted during quality control, similar to cast parts.

Already Well Over 1,500 Pieces in Series Production

The advantages of the process now used in series production are clear. Instead of 70 percent machining volume, it is now only about 20 percent. Due to lower material costs and reduced machine times on the milling centers, the manufacturer achieved cost savings of around 15 percent. Additionally, delivery times were shortened by up to 75 percent. In series production, nine or 16 turbine blades are always manufactured in parallel in the machine. This optimally utilizes the capacity of the arc machine, and cooling wait times for the top layer are also eliminated.

Even though it was a long journey from the initial idea through qualification to series production, the turbine manufacturer is fully convinced of the WAAM process for series production. The WAAM machine leads to significantly more flexible production, particularly as the time-consuming procurement process for the base material is eliminated. In the meantime, well over 1,500 turbine blades have already been produced on the machine. Production operates in three shifts, running almost fully automatically around the clock.

The turbine manufacturer is working closely with Gefertec to further optimize the machines. One goal is the complete automation of contact tube replacement without operator intervention. The integration of additional sensors for in-situ quality assurance is also a current focus. Furthermore, WAAM opens up new design possibilities that cannot be achieved with conventional milling processes—a potential that is to be further explored and translated into new products in the future.

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