How to print with metal – on a big scale

3D printing has come a long way from producing small plastic prototypes. The selection of suitable materials and applications for additive manufacturing is constantly growing, and the most interesting current developments are in printing large objects in metal.

In the last few years, Wire Arc Additive Manufacturing technology, or WAAM, has taken giant leaps to make printing metal a viable solution for several use cases. In WAAM, computer-controlled machines weld together layers of metal to produce a larger object.

Obviously, robotic welding has been around for ages, so what has made WAAM such a hot topic recently? The main reason is that now the engineering and programming technologies have reached a stage of maturity where complex objects can be programmed and printed cost-efficiently.

There are now more opportunities for up-and-coming startups, which is bound to lower prices as new competitors enter the market. A great example of innovation in additive manufacturing is rocket startup Relativity Space. Whereas traditionally the number of different parts in a spacecraft is around 100,000, Relativity Space has cut this down to 1,000 through 3D printing.

According to the company, their rockets take only two months to manufacture. And when new technologies are developed, Relativity Space can produce new rocket model in significantly less time than the competitors.

The most apparent benefits of WAAM are the same as in any 3D printing. The production is location-independent, so there is no need for costly logistics. You can print bespoke replacement parts as the need arises without keeping an inventory of items that are rarely needed. Automated and computer-controlled processes reduce the risk of human error to the minimum.

One of the big advantages is that 3D printing facilitates completely new designs. There is greater freedom of form, which makes it possible to produce shapes that would be very costly or even impossible to make through traditional methods.

Digitized 3D engineering gives a chance to experiment and change plans flexibly. The process is much more effective than in traditional tooling-based production. Small changes and iterations can be made easily in the planning stage and the timeline from idea to finalized product is shorter than with other methods.

Another way WAAM is useful is that you can design metal parts that use less material. This is good for the carbon footprint as well as for the wallet.

In WAAM, the cooperation between the designer and manufacturer is crucial. A good example is the production of an engine bracket for power technology manufacturer Wärtsilä. The design was reviewed in Merinova energy cluster’s design sprint and executed by Etteplan. ANDRITZ  Savonlinna Works carried out the manufacturing.

The challenge was to design a part that would prevent the machine bed from vibrating. The original solution consisted of four thick metal sheets welded together with plane milling finalization. The bracket was fastened with 16 bolts and its total weight was over 31 kilograms.

During Merinova's design sprint it soon became apparent that 8 fastening bolts would be enough. As the project at this point existed only in digitized form, it was easy to change the course of planning on the fly.

In traditional design, it would have been tempting to ignore the change to avoid additional work and continue with 16 bolts – thus losing the chance to innovate with new kinds of solutions.

Figure 1. shows how the best features of three design software were utilized in one component design. The geometry changes can be quickly applied (16 to 8 bolt design in this case) thanks to right kind of 3d-data management.

Design software, such as Altair Inspire and nTopology used in the case of Wärtsilä’s engine bracket, can make suggestions for different solutions within the stated boundaries. This is a case of topology optimization – how to design a printable object that would use as little material as possible and still be sturdy enough to fulfill its intended purpose.

While software can open new avenues for thought, a human engineer is still needed to weed out impossible or unsensible suggestions and choose the ones to develop further.

The final design of the bracket weighed only about 21 kilograms, a significant drop from the original. As you can see in the image, the futuristic form is probably something that human planners wouldn’t have been able to envision.

Wärtsilä’s engine bracket

Can an object printed by joining several layers of metal be as sturdy and durable as a steel block? As it turns out, yes. ANDRITZ subjected another 3D-printed model which was comprised of 95 layers to rigorous tests. The welded block passed all tests, which included e.g. bending, corrosion, impact, and yield. In some cases, printed material was even way sturdier than data sheets demanded.

It takes courage and a future oriented mindset to try new approaches. In the project for Wärtsilä, a combination of expertise and out-of-the-box thinking were needed to carry out the project successfully. It required tight collaboration between the designer, manufacturer, and client.

The promise of additive manufacturing is huge. While the capabilities of WAAM are constantly growing, investments are still needed to be able to print with full capacity rather than dividing limited resources between traditional production and additive manufacturing projects.

WAAM has already proven to be a capable solution for production use. In addition to the engine bracket mentioned above, ANDRITZ has recently delivered and installed the first WAAM printed parts to pulp mill processing machinery. There is also an ongoing project to raise the size of printed parts from tens to hundreds of kilograms.

Additive manufacturing is part of the digitalization megatrend. It is also one important step on the road to connect virtual worlds with physical reality. Thanks to the developments in CAM capabilities, software, and manufacturing, we can make things in a way that would have been impossible only a few years ago. We cannot even imagine, what uses for WAAM can be dreamt up in the next years. It will be an exciting adventure to find out.

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