UNDERSTANDING THE BASICS

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By Filippo Gilardi

The Metal 3D-printing method, wire-arc additive manufacturing (WAAM) is receiving increasing attention across multiple industries, where metal components are in use. To understand the use and capabilities of the technologies and their fields of application, this is a guide to provide a basic overview:

ADDITIVE MANUFACTURING

Wire arc additive manufacturing, in short WAAM, is a metal 3D printing technology in the subsection of direct energy deposition (DED). 3D printing, or Additive Manufacturing has found its way from prototyping into industrial application and final end products. In comparison to subtractive methods like milling and turning, material is added layer-by-layer such that only the material needed is used.

A large section in the Metal additive Manufacturing production is based on powder material. The usage of powder comes with certain drawbacks, as it is difficult to handle, a complex production process for uncommon alloys that requires substantial R&D, hardly recyclable and it is expensive. Powder based technologies can realise very refined sizes and geometrical details, but have a limitation in size, speed and come with significant investment and operational cost.

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HOW DOES IT ACTUALLY WORK?

The build plate and the welding torch are connected to a power source generating a high velocity. When both poles are close to each other, the electric arc is started. Argon or other inert gases are blown through the welding device to control this process, creating the arc with a local temperature of over 2000 degrees. This is necessary to meld the metal. To do this, a metal wire is fed through the welding torch into the arc where the wire material is melted. This area of liquid metal is referred to as a “melt pool”, which will harden when the arc is removed. Moving the torch over the substrate with a very defined wire speed, distance and feed rate creates the weld line.

All parameters have to be precisely defined and define the core complexities for a stable welding process. The used wire defines the material of the object. Therefore, in theory, all weldable wires can be used for WAAM. The most commonly used metals are low and high steel alloys, like stainless or carbon steel. Similarly, copper or nickel-based alloys such as bronze or high-performance metals like invar, inconel or duplex are very weldable. Also, lightweight metals with different variants of Aluminum alloys can be achieved with WAAM. Although it is difficult to investigate the mechanical properties of the print at times, most mechanical properties are conserved throughout the process.

PROCESS AND MATERIALS

WAAM is based on the traditional joining method of welding. Using a robotic controlled welding torch enables a precise deposition of a weld line onto a build plate (=substrate, base piece where the print begins). Continuing this process, the weld lines are stacked on top of each other and therefore create three dimensional objects.

APPLICATIONS, ADVANTAGES, USE CASES

The WAAM technology has evolved from a research-driven technology (TRL 2-4) in the early 2000s to an industry-ready 3D-printing alternative (TRL 8-9). Today’s applications of WAAM already make it a more economical production in certain use cases.

Due to its speed and size, WAAM is mostly considered with medium to large metal components that are difficult to produce conventionally.

On the one hand, this can be very specialised geometries like rudder blades, impellers or organic shapes. The main value is to make full use of the technology’s additive nature, enabling freeform or typology-optimised geometries that were impossible to produce efficiently. It also provides a geometry that is very close to the 3d-modelled design, giving new design freedoms for part construction.

On the other hand, WAAM has strong use cases for building parts that come with an intensive cost factor in producing them subtractively. Flanges, valves or moulds for tools can be very individual and diversified throughout their use in e.g. a power plant. The production of those parts is expensive due to high offcut materials or hardly available skilled labour, this comes with significant lead times or storing costs.
Hence, WAAM is a strong option to cut downtime and have new design freedoms also in large metal parts. This can be applied to multiple industries where these parts come into use.