Benefits of laser-based powder bed fusion technology

Among metal additive manufacturing processes, Selective Laser Melting (SLM) belongs to the powder bed fusion category. Also known as Direct Metal Laser Melting (DMLM), the technique is named after its fundamental mechanism. The process relies on a fine laser beam that is scanned across successive layers of a powder bed to selectively melt intricate tracks. The final components arise from solidification of the melted powder. When compared to other additive manufacturing technologies, this ability to produce high resolution features is one of the reasons why SLM tends to get selected to produce complex components with delicate features.

Practically, a SLM machine comprises

• a powder reservoir, filled with feedstock powder and positioned using fine vertical steps;
• an overflow reservoir, used to recover the redundant powder once a layer has been spread;
• a recoating/spreading system, used to cover each scanned layer with a new coat of powder. Various types of recoating blades exit. They are made of rubber, steel, fibre bush or ceramic;
• a building chamber, where the component is fabricated layer by layer. The building platform eases down after each layer is scanned;
• a laser source and its scan head, used for complex motion control and selective melting;
• a filtering system set up with inert gas, used to keep the building chamber under inert atmosphere and to suck up process fumes or spatter during machining.

Components have successfully been manufactured out of a wide range of common metallic alloys using DMLM industrial systems (or customisable R&D-focused systems). These materials include aerospace-grade titanium, high strength stainless steels, nickel-based superalloys, cobalt-chrome alloys, lightweight aluminum alloys, and others.

​The advantages of SLM over conventional substractive or formative methods are reflected in the following categories: 

Shape complexity: it is possible to manufacture virtually any shape. This means that fabricating small lot sizes is economically viable, customized and optimised geometries is possible.

High resolution: material is processed with a fine laser beam, point-by-point and one layer at a time.

Hierarchical complexity: resolution varies with machine capabilities, yet fabricating fines features means that complex hierarchical multi-scale structures can be designed and fabricated in one step with features size spanning the macro- and meso-scale (0.1-10 mm). For instance, lattices can be combined with macrostructures to vary mechanical properties and/or save weight.

Functional complexity: Geometrical flexibility makes it possible to integrate multiple functions in a single component traditionally made out of multiple parts.
 
Feedstock fluidity and re-usability: In DMLM, unused powder remains fluid and can easy be removed and recycled. Arguably, there still is some confusion about the impact of powder recycling on mechanical properties. Yet, it is a major advantage for parts that require inaccessible internal channels.