Minimization of material waste in SLS processes

One of the main advantages of additive manufacturing processes over traditional machining is the reduction of material waste generated during the production process. This not only leads to noticeable cost savings, but also contributes to the use of additive manufacturing as a sustainable and cost-effective technology. Selective laser sintering (SLS) processes are particularly attractive in this respect, as only a small amount of material cannot be reused at the end of a manufacturing process - an opportunity to drastically reduce material costs. When the printing process is complete, much of the material remaining in the powder bed can simply be collected and reused in the next project, which in theory should avoid material waste altogether. In practice, however, the upcycling process is not quite so simple.

It is important to note that the collection and reuse of powder residues (at the time of writing) is not possible with certain materials. For example, the wood-polymer composites (WPC) currently available for printing are limited by their material quality and purity and are not suitable for recycling until material separation technology becomes available. Similar issues arise with a number of widely used metal powders, where the by-products of the SLS process can potentially affect the chemical quality of the remaining powder. Even with the highest precision during the sintering process, there will inevitably be additional particles in the powder bed that fuse together without attaching to the part, affecting the size distribution of the material and leading to inconsistencies when reused.

There are also concerns about whether the recycling process can affect the mechanical properties of materials (both metals and plastics) and thus affect their usability in subsequent productions, especially if AM is used for production rather than prototyping. Academic research is constantly being conducted in this area to determine the potential impact on sustainability and a reduction in the cost of additive manufacturing. Particularly in industries such as aerospace, where the raw materials used for additive manufacturing are quite expensive and additively manufactured parts need to be delivered with precision, the ability to recycle unused raw material without affecting its mechanical properties would lead to a wider application for AM as a production tool.

With this in mind, some companies have been looking for ways to solve these problems for SLS and other processes to ensure that as much powder residue as possible can be recycled. For example, a gas stream can be incorporated into the printer to filter out by-products created during the sintering process. After the printing process is complete, the remaining material can be automatically sieved so that any fused particles are removed and the particle size distribution remains consistent. Similarly, certain SLS machines such as the Renishaw AM400 have a sealed build platform where moisture, nitrogen and oxygen are removed during printing to minimize chemical changes in the powder bed. The challenge here is that the actual volume of remaining material that can be reused after printing varies greatly depending on material selection, printer model and specific AM technique.

In extreme cases (e.g. when using machines for which the measures described above are missing), it is possible that no material is recyclable. This should be considered before investing in a new 3D printer, especially if the ongoing material costs are the main point of the calculation. Combined with thoughtful volume and production planning, an effective approach to minimizing material waste can help reduce the overall cost of additive manufacturing and encourage more forward-thinking companies to explore its use as a production tool.