Interest in additive manufacturing has been high for at least the past 15 years. Many companies have been experimenting with the technology, with aerospace being one of the sectors that is leading the way with its adoption.
But, even after 15 years, experts estimate that there are only between 500 and 700 big industrial additive machines printing in metal worldwide. It’s a high- value business, but it’s far from being mainstream. Many believe the technology is far from realising its full potential.
What excites Pete Baxter, vice-president of digital manufacturing sales for Autodesk, isn’t so much improvements to additive manufacturing technology as the impact it can have on design: “Additive manufacturing allows us to make parts and components that can’t be made in any other way, effectively any shape of any complexity"
“This has massive implications where weight is important. You’re reducing parts and improving air flow while maintaining integrity. It allows us to think very differently about design.”
Equally important is that additive manufacturing lets engineers turn multi-part assemblies into whole individual parts, says Baxter, enabling companies to cut down on the amount of assembly that needs to be done on the shop floor. There are caveats, though, he says: “Engineers must understand the benefits of the new methods of manufacturing and think fundamentally differently about how they design.
“If the new advances are used as an alternative way to produce stuff we’ve already designed, we’ve kind of missed the opportunity.”
Also, if additive manufacturing is to become mainstream, its processes need to become repeatable and reliable – to enable production of tens of thousands of identical components. “That’s the acid test,” he says. “You have to get the unit cost down and be clear on quality.”
Part of the challenge is realising that additive and subtractive methods need not be exclusive – they can and, some would say, should be part of the same process. Additive technology might be used first, and then a subtractive machine employed to finish the parts, which would require specialised software.
Baxter says: “You take a 3D printed part and use metrology software, such as Power Inspect, to probe it and compare it to the design and CAD model. From that the machine figures out where the supports are, where the part is out of tolerance, and where it needs to be finished. You’re finishing a complex part.”
This finishing could be done manually, by another machine or by new hybrid additive and subtractive machines. Several of these hybrid machines, which add material then take it away to form a closer-to-finished part, are already available, from firms such as DMG Mori and Mazak.
Part of the remit of Sheffield’s Advanced Manufacturing Research Centre (AMRC) is to look at the machinability of materials and consider the improvements that can be made. This applies to metal additive layer manufacturing processes such as powder bed, blown powder and bulk additive.
James Hunt, technical leader for near-net shape processes at the AMRC, says that additive manufacturing’s biggest challenge is dealing with the “inherent variability” in its processes. The centre’s researchers are looking at how to reduce this variability, in the metal powder feedstock and in downstream finishing processes. This is an attempt to mitigate the quirks and foibles of additive manufacturing, by introducing new techniques before and after the process.
Areas the researchers are looking at include the feedstock, examining and evaluating the metal powder as it comes into the machine, as well as newer materials and the additive manufacture of thin-wall structures.
Compared to having two separate machines, one for additive and then one for subtractive technology, the main benefit of hybrid machines is that they reduce the number of processing steps. There is also a reduction in the number of problems with the datum, because only one base plate is used. A further benefit is the ability to finish internal surfaces of a part that otherwise would be impossible or very expensive to finish.
Hunt says: “Toolmakers and people in the aerospace sector are using them to make inserts for things, like when you want conformal cooling channels running through cavities and you are using plastic injection moulding.”
However, hybrid machines are far from a cure-all for additive manufacturing’s many challenges. Hunt says: “They can address some of the issues around variability but there are still challenges, such as the variation from machine to machine, operator variability, process variability and residual stresses in some parts.
“There is also a lot of work to do with the datum and how you transfer that into the final CAD geometry for downstream processing. In terms of design for manufacture, you may need to add stock to places where you are going to have to take it away from in post-processing.”
When designing components for additive processes such as powder bed, this means not only accounting for support structures, but adding to areas where you know a subtractive finishing process is going to be applied. There is still a fair amount of design and operator “craft” required to achieve this, but work is ongoing to automate the processes. The focus for the development isn’t in the control software – Hunt says current offerings are able to deal and plan with the tool paths adequately – but in process monitoring for quality assurance. He says: “There is work going on to detect defects as they are generated in the parts. The goal is to have a feedback system so it can re-melt an area or add more powder to mitigate. They would use infrared cameras and X-ray detectors to look at the melt pool or the soundness of the layer you’ve just deposited.”
Hunt says that additive manufacturing and hybrid machines are enabling technologies for Industry 4.0, in particular for the mass personalisation of products in sectors such as medical and sports. They are also enabling the decentralisation of manufacturing – eliminating logistics by having manufacturing at the point of use.
“The machines are always getting bigger, better and faster,” says Hunt. “But we need to lock down the repeatability and robustness of these processes. Part of that is the feedstock and part of that is making them simpler to set and use, and more robust for production readiness.
“I don’t know if we will get to the same point as rapid prototyping machines with the metals machines – it would be a step too far in terms of liability.”
Baxter from Autodesk shares the same vision – of a machine with a robot arm that is discovering the part and making adjustments to get to the finished part. “The machine isn’t just thinking subtractive – you can start changing tool paths, changing the operation on the part, according to what’s needed,” he says.
“That means that every component that comes off could be personalised.”