WP-305 WAAM (Wire plus Arc Additive Manufacturing) for Marine Propellers and Aircraft Structures

HFT PHO 02A Industrial Pipelines 123rf

Since 3D printing was introduced over 30 years ago there have been a number of significant developments. Various melting techniques have been used to achieve this aim including electron beams and lasers. but one being most actively pursued currently is Wire and Arc Additive Manufacture (WAAM) using a GTAW (TIG) power source. To be specific, additive manufacturing is not the same as 3D printing! 

The recent use of fusion welding as a deposition source has opened up wide ranging possibilities in manufacturing. The process is one in which metal is deposited layer-by-layer under computer control to form a three dimensional shape.

No longer is it necessary to keep an inventory of high value generic stock: parts can be customised and manufactured on demand. A recognition that components can be fabricated using WAAM technology has spawned a new industry to exploit a wide range of exciting opportunities.

Two outstanding examples showing how engineers have exploited the potential of WAAM to achieve major cost savings are the production of ship propellers and the fabrication of airframe components. 

The Damen Shipyards Group entered a cooperative consortium with RAMLAB, Promarin, Autodesk and Bureau Veritas to develop first class approved marine propellers. Damen’s involvement in the project began as a result of one of its in-house student research programmes. Three students from Delft Technical University were investigating the potential of WAAM technology and they introduced Damen to the other members of the consortium. Kees Custers, Project Engineer in Damen’s Research & Development department commented, “What is quite unique about this group of five companies is that, while we have joint interests, we also have individual aims. This leads to a very productive and cooperative atmosphere in what is a very exciting project.”

The early work terminated in the production of the world’s first WAAM manufactured propeller in 2017. It is based on a Promarin design typically found on a Damen Stan Tug type 1606 (Fig 1).

Damen Shipyard 3D

Fig 1. 1300mm diameter propeller produced by Damen Shipyards Group.
It weighs approximately 180kg.
The WAAM product has been fabricated from a bronze alloy using the GTAW process.


Researchers at Cranfield University in the UK have developed the WAAM process to examine the use of Inconel, titanium, aluminium and various nickel alloys. The focus is currently directed towards airframe components.

Although “laser and powder methods” are useful for certain applications such as rapid prototyping or for small highly complex parts, this technology is limited by its speed and the size of component it can accurately manufacture. In contrast, the processes being developed at Cranfield are designed for high deposition rates.

The programme began in 2007 with funding from both the University’s Innovative Manufacturing Research Centre and 15 industry partners. The idea is to simplify the process of complete product within a single one-hit additive manufacturing system incorporating a fully integrated robot. The Centre is currently targeting a deposition rate of 10kg an hour for titanium, compared with a typical 0.1 kg using laser + powder methods. WAAM systems are also capable of producing parts several metres in size and simplify the process of producing single piece linear intersections.

Additive Manufacturing WAAM titanium part

Fig 2. This main structural element of an aircraft wing was produced using WAAM technology.
Traditionally this type of component would be manufactured by machining from a solid block of metal.
Over 50% of the original stock is lost as swar.


A common problem facing any arc welding fabricator, particularly when welding stainless steels, nickel alloys and titanium, is the need to protect the weld and immediate metal from oxidation during the welding process. For sheet and plate applications the hot zone can be protected to some extent, by the inert gas from the welding torch. With complex weld geometry and three dimensional structures such as those witnessed in WAAM applications this becomes much more difficult. Inert gas coverage is likely to be disrupted by the variations in profile and changes from the laminar flow in the torch to a more turbulent flow at the joint. This leads directly to entrapment of air and subsequent oxidation of the weld.

Overcoming the problem of oxygen contamination during WAAM

One solution is to undertake operations inside a steel chamber filled with inert gas. With the electron beam process for example, protection is assured since operations are carried out in a vacuum. Nevertheless this is an expensive alternative to arc welding.

Huntingdon Fusion Techniques, HFT® in the UK has resolved the issue of adequate protection by providing some WAAM users, such as teams at Cranfield and the Welding Institute, with Flexible Enclosures®.

The company has been developing these enclosures for many years by exploiting the opportunities offered by advanced engineering polymers. The innovative products offer significant attractions over both vacuum and glove box alternatives; a significant reduction in cost, very small floor footprint and availability of a range of sizes up to 27 cu m. Since that time the HFT® product has been developed and is rapidly becoming the preferred alternative enclosure.

18W FlexibleWeldingEnclosures

Fig 3. Flexible Enclosure manufactured for a sports car manufacturer.
It illustrates some singular features of flexible enclosures such as multiple operator and equipment access points
and the available size range: this model is 4.0 x 1.6 x 1.6 metres.

Small Enclosure

Fig 4. Low volume enclosure coupled with robot operating through a flexible uper seal for demonstration work and the production of small components.
For larger scale manufacture flexible enlosures can be made large enough to accomodate the entire work, welding equipment and robot.


The largest facility supplied to Cranfield has a volume of 27 cu m, adequate to accommodate all work pieces, welding equipment and even a programmable robotic system.

Oxygen content of the enclosure gas can be monitored continuously with instruments developed specifically for the welding industry. These are capable of measuring residual oxygen down to 10 ppm, well below the acceptance level required for high quality deposits of sensitive materials such as titanium alloys.

Software is available for data acquisition and logging where traceability is vital. A high/low feature allows the operator to control deposition between set oxygen levels. Relay contacts can be used to operate warning lights, alarms or even switch welding power supplies on and off if levels exceed set limits.

Nano with AFE front
Fig 5. Advanced Weld Purge Monitor® in use for measurement of residual oxygen content.


Flexible Enclosure® concept

Technical Specification

Ultra violet stabilised translucent or optically clear engineering polymers are used with a material thickness typically 0.5 mm.

Principle large access zips are fitted and additional entry points can be provided for operators’ gloves, welding torches and for electrical leads and cooling water supplies. A purge gas entry port and an exhaust valve to vent displaced gas to atmosphere are incorporated. A port is also provided for gas sampling with a weld purge monitor.

Cost

Size for size the HFT® range costs less than 10% of a metal glove box and only 2% that of a vacuum system.

Flexibility

Size and shape can be made to meet customer requirements. Standard models from 0.3 to 3.0 cubic metres are available. Weight is very low and the enclosures occupy little space – the collapsed volume of a 1.25 metre diameter system is less than 0.2 cubic metres and weighs only 8 kg. They can thus be moved easily and stored efficiently so floor footprint is minimised.

Welding sources

The enclosures are suitable for use with Tig/GTAW welding and plasma/Paw arc welding techniques and laser beam welding.

24W FlexibleWeldingEnclosures

Fig 6. Special Cranfield WAAM Robot in Flexible Enclosure®. 


REFERENCES

  1. Zelinski P. Additive Manufacturing April 2017
  2. Design for Wire and Arc Additive Layer Manufacture. J. Mehnen et al. 20th CIRP Design Conference, Nantes April 2010
  3. RAMLAB focuses on accelerating 3D printing. Bridget Butler Millsaps. Nov 30, 2016. 3D Printing, Business, Robotics
  4. World’s first class approved 3D printed propeller. International Institute of Marine Surveying May 2017 

 

By Dr. Michael J. Fletcher M.Sc. Metallurgy

Loughborough University
Delta Consultants  

 

Download White Paper Number 305 - WAAM (Wire Plus Arc additive manufacturing) for marine propellers and aircraft structures  



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