What is Wire Arc Additive Manufacturing (WAAM)?

Printing is only one stage of the process. A WAAM component goes from CAD file to certified part in five stages:

1. Design for additive manufacturing (DfAM). Engineers review the design for printability, set the build orientation and add a machining allowance of a few millimetres to functional faces. Existing designs can also be optimised for additive manufacturing.
2. Build strategy and parameters. The toolpath is programmed and parameters such as wire feed speed, travel speed, heat input and interpass temperature are set. For production parts, these come from qualified parameter sets.
3. Robotic deposition. A robot-mounted welding torch melts the wire with an electric arc while shielding gas protects the molten metal. Each layer fuses to the one below. In-process monitoring uses infrared cameras to control interpass temperature and surface scanning to compare each layer against the digital model.
4. Heat treatment and machining. Stress relief heat treatment is applied where required, and the near-net-shape part is finished to tolerance by five-axis CNC machining.
5. Inspection and certification. Parts undergo dimensional inspection, non-destructive testing (NDT) and destructive testing (DT) of material samples, and are supplied with a full documentation pack for third-party approval, where required.

What happens at the arc?

The deposition process is too bright to see with the naked eye but high-speed imaging lets us see the melt pool as the wire melts into it and solidifies, layer by layer:

The welding processes behind WAAM

WAAM is the manufacturing method; welding is the process it uses. Gas metal arc welding (GMAW, or MIG) is a welding process. WAAM uses it, or a related arc process, under robot control to build a whole component rather than join two parts. The main options are:

• GMAW (MIG): the wire is the electrode, giving high deposition rates. It is widely used for steels, nickel alloys and bronzes.
• Cold metal transfer (CMT): a lower heat-input variant of GMAW that reduces distortion and spatter, and is useful for thinner walls and aluminium.
• TIG (GTAW) and plasma: the wire is fed separately into the arc, giving finer control at lower deposition rates. These are often used for titanium.

What materials can be used in WAAM?

As a general rule, if an alloy is available as a qualified welding wire, it can usually be deposited using WAAM. This includes carbon and low-alloy steels, stainless steels, nickel superalloys, copper alloys, aluminium and titanium.

Materials we work with at DEEP Manufacturing:

• Carbon and low-alloy steels: ER70S-6 and ER80S-D2. These are high-strength, cost-effective steels with good toughness and weldability, used for structural and pressure-bearing parts.
• Stainless steels: 316LSi and super duplex, which are corrosion resistant for harsh environments.
• Nickel superalloys: Inconel 625 (ERNiCrMo-3), which offers high strength and corrosion and oxidation resistance at elevated temperatures.
• Copper alloys: nickel aluminium bronze (ERCuNiAl) and CuNi30, used in marine applications such as propellers.
• Aluminium alloys: 2319, a lightweight alloy for aerospace and subsea applications.

Our DNV Approval of Manufacture currently covers carbon steel and Inconel 625 grades.

How new materials are qualified

Our in-house metallurgy team qualifies each new material in stages:

1. Review the material specification.
2. Run bead-on-plate trials to establish a stable process window.
3. Progress to single-layer and multi-layer builds.
4. Carry out full mechanical and microstructural testing, followed by external validation.

The results are documented in an engineering material specification, and the process is proven on a demonstration production part. Mechanical properties are quoted as ranges because they vary with build strategy, part geometry, orientation and heat treatment.

See the full list of materials qualified for WAAM.

What size of component can be created using WAAM?

In WAAM, part size is set by the reach of the robot and the design of the system holding the part, not by the process itself. At DEEP Manufacturing, single-arm systems build parts up to 3 m × 3 m × 3 m, and multi-robot systems can build larger components. Parts can weigh up to 20 tonnes, depending on the system.

Robotic WAAM systems

We run several robotic WAAM system configurations, matched to the size and geometry of the part, including:

Enclosed and open cells: a single robot builds onto a fixed table. Build volumes are up to 3.0 m × 1.5 m × 2.4 m, for parts up to 20 tonnes.

Single-axis manipulator: the part rotates as it is built, allowing builds up to 3 m × 3 m × 3 m and 10 tonnes.

Two-axis manipulator: the part tilts as well as rotates, so complex geometries such as hemispheres and nozzles can be built without support structures.

Multi-robot systems: several robots deposit onto one part at the same time, for components larger than a single arm can reach. They can also build several parts at once, or one part in more than one material.

Rollerbot: a gantry-mounted robot that travels up to 13 m. It welds and prints inside long structures such as hulls and pressure vessels up to 3 m in diameter, and can add features to existing components as part of hybrid manufacturing.

Read more about our robotic WAAM systems, or download our multi-robot WAAM whitepaper to see how multiple robots work together on a single build.

What are the limitations of WAAM?

WAAM produces near-net-shape parts with a rough, wavy surface, so most components need machining to reach final tolerances. The process also brings heat into the part, which has to be managed to control residual stress and distortion. Each limitation is well understood and can be managed through process control, testing and post-processing.

Common limitations and how they are managed:

• Surface waviness. As-deposited surfaces show the weld bead profile. A machining allowance is built into the design, and functional faces are finished by CNC machining.
• Residual stress and distortion. Repeated heating and cooling can build stress into the part. This is managed through build strategy, interpass temperature control, fixturing and stress relief heat treatment.
• Resolution and feature size. Each bead is several millimetres wide, so very fine features and thin walls can’t be printed directly. They are added by machining.
• Porosity. Some alloys, particularly aluminium, are prone to porosity. Shielding gas, parameter control and non-destructive testing keep it within acceptance limits.
• Anisotropy. Properties can vary with build direction. Build strategies are developed to minimise this, and material is tested in multiple orientations.
• Qualification effort. Safety-critical parts need a qualified process and documented testing before they go into service. This takes time up front, but once a process is qualified it can be repeated.

When WAAM is not the right choice

We’ll tell you if another process suits your part better. WAAM is usually not the best route for:

• small parts, where powder bed fusion or machining is more precise and economical
• high production volumes, where casting or forging tooling pays for itself
• simple geometries that are quick and cheap to make conventionally
• fine features or tight tolerances that can’t be machined afterwards
• alloys that aren’t available as welding wire
• parts already available as a stocked casting or forging with an acceptable lead time

How fast can you produce a part using WAAM?

WAAM is one of the fastest metal additive manufacturing processes, capable of depositing several kilograms of metal per hour. However, the speed that matters to a customer is how long it takes to deliver a finished, inspected part. That's why it's important to understand the difference between deposition rate and production rate.

What is the difference between deposition rate and production rate?

Deposition rate is the speed at which the torch lays down metal while the arc is running, usually measured in kilograms per hour. It is the figure most often quoted on equipment datasheets, sometimes as high as 10 to 15 kg per hour.

Production rate is the speed a part is actually built at once everything else is accounted for. That includes cooling time between layers to keep the interpass temperature in range, surface preparation, in-process inspection, torch cleaning and recalibration. On a large part, these steps can take as long as the deposition itself.

As a result, production rate is typically lower than deposition rate but provides a more accurate indicator of total manufacturing time, as it is influenced by part size, geometry, and quality requirements.

At DEEP Manufacturing, carbon steel deposition rates typically range from 2 kg to 8 kg per hour, with production rates averaging around 50% of the deposition rate, depending on component complexity and process requirements. That’s why we plan lead times around production rate, not peak deposition rate.

Lead time: a real example

For a pressure vessel built at our Bristol facility, the cylindrical section (1.75 m in diameter and 1.5 m high) was printed in 22 days, and each of the two hemispherical end caps in 10 days. Similarly, a 413 kg nickel aluminium bronze propeller blade section was printed in 13 days.

Large castings and forgings can take several months to arrive once tooling and foundry queues are included. Depending on the application, WAAM can deliver a component in around a third of the time of conventional casting or forging, because it builds directly from a digital design with no tooling stage.

Can WAAM parts be certified?

Yes. WAAM parts can be certified for safety-critical service, provided they are made using a qualified process and tested against the relevant standard. DEEP Manufacturing was the first company in the world to achieve DNV Approval of Manufacture for WAAM, covering high-strength steels for hull structures, pressure equipment, boilers and pressure vessels for human occupancy (PVHOs).

What qualification involves

Certification isn’t something that happens at the end of a build. It is designed into the manufacturing process from the start. To achieve approval, we qualified our build process in line with DNV-ST-B203, the DNV standard for additively manufactured metallic parts. That meant producing a build process qualification record, building test pieces under controlled conditions, and carrying out destructive and non-destructive testing to prove that material properties are consistent and repeatable.

It’s also an iterative process. The results of process qualification shape how we approach new component geometries, and the demands of those geometries in turn inform how we develop the process. For customers, this means an approved manufacturing route is already in place. We take on the burden of qualification and certification, so they don’t have to build that capability in-house.

Standards and approvals

The standards a client is most likely to come across are ISO/ASTM 52900, which defines DED-Arc terminology; DNV-ST-B203, for additive manufacturing of metallic parts; and API 20S, the American Petroleum Institute’s standard for additively manufactured components in oil and gas. Our quality management system is aligned with API Q1 requirements.

Our Bristol WAAM facility holds DNV Approval of Manufacture, ISO 9001, ISO 14001, ISO 45001, JOSCAR registration and Cyber Essentials Plus. Our WAAM facility in Houston, Texas holds DNV Approval in Principle for DED-Arc manufacture of steels for pressure hulls and PVHOs, along with ISO 9001, ITAR registration and Cyber Essentials Plus.

See all our certifications and accreditations.

Why certification matters for WAAM adoption

In sectors such as oil and gas, defence, maritime and subsea, every component must be proven to perform before it goes into service. These industries rely on recognised standards and independent approvals to give engineers, operators and regulators a consistent way to assess any manufacturing route, including WAAM.

Standards such as DNV-ST-B203 and API 20S now give additively manufactured parts a clear, established framework within that system. Each qualified component that enters service adds to the track record that helps WAAM become a routinely specified manufacturing method, alongside casting and forging.

“We need to see parts in service. That’s the bottom line.”

Harry Thompson, Engineering and Manufacturing Operations Director

WAAM at DEEP Manufacturing

At DEEP Manufacturing, WAAM is delivered as part of a fully integrated manufacturing route, combining additive deposition with design for DED-Arc, material development, machining, testing and certification. This allows us to produce large, high-integrity metal components at speed for the energy, maritime, defence, subsea and aerospace sectors, while meeting the quality and assurance requirements of safety-critical applications.

Our Bristol WAAM facility in Avonmouth is home to our multi-robot systems, in-house metallurgy lab and five-axis machining. Our WAAM facility in Houston, Texas, set in the heart of the US energy corridor, gives US operators, OEMs and defence customers direct access to WAAM production, backed by the experience developed in Bristol.

To find out whether WAAM is right for your component, explore our WAAM capabilities or speak to one of our engineers.