On process and parameters development for Selective Laser Melting

Aeromat 15, the conference dealing with materials and processing methods focused on aerospace applications, was held last week in Long Beach, California. As additive manufacturing technologies mature, numerous presenters discussed aspects such as materials properties of SLMed components, successful industrial applications by world-leading institutes such as TWI, MCAM or remaining challenges being addressed.

As the number of successful aerospace applications increases, it’s easy to overlook the challenges involved in producing flight-ready components.

Yet, even as the technology matures, a disparity grows between leading organisations and new comers setting out to build profitable businesses. SLM is not the easy plug-and-play technology portrayed by the media to the general public – at least not for industrial metallic components anyway. And being unaware of that can be costly.

Parameters development is one step of the manufacturing process. It is also essential but unfortunately overlooked. The argument goes that not every company can afford its own processing development activities or expertise. As such, companies are driven to rely exclusively on standard parameters supplied by the manufacturers of the SLM production machines they acquire to build high-value components.

True, some machine suppliers are excellent. These SLM machines must have reliable high-precision motion systems, vacuum systems, powder collection systems, laser systems, software controls. This encompasses topics of high-precision engineering, computer software engineering, system engineering, mechanical and laser, awareness of powder health and safety to name a few!

Yet this is still a very different expertise skill-set than that involved in finding suitable laser processing parameters to create usable aerospace components. An exhaustive knowledge and understanding of the machine operation must be coupled with fundamentals scientific knowledge.

To highlight the importance and challenges of process and parameters development, it is important to emphasize the extent and range of expertise required to achieve high-yield production of reliable sound parts.

Engineering suitable mechanical properties via processing parameters demands to ensure high density, knowledge of microstructure evolution, understanding of thermal treatments influence, control of surface roughness, to arrive (in the best case scenario) to isotropic properties. This is an intensive effort that spans a wide range of specialised skills: material sciences (metallurgy, mechanical properties, powder metallurgy), laser/material interactions as well as a sound manufacturing acumen to juggle build rate, manufacturing efficiency and reliability with component quality. That does not take into account the SLM-specific CAD re-design for improved yield.

Thankfully, more and more proofs emerge that prove that not only slm can produce reliable components, but that the mechanical properties can also equal or exceed those achieved with conventional manufacturing methods.

Preliminary results show that you can’t fix everything with ‘conventional’ heat treatment, ie heat treatment applied to parts built using conventional methods such as casting, etc… This is certainly the case of isotropy. SLM-specific heat treatment conditions may be required.

The good news is that instead of spending money on non-optimal heat post treatment, you can probably spend this money on processing parameters developments and end up with superior properties.

Of course if your application doesn’t require any stringent mechanical characteristics (jewellery, etc…), you’re off the hook. For the rest of us, process parameters and understanding of their impact on metallurgy and mechanical properties is still a critical research area.

References
Cpam2015