Direct laser sintering (DLS) is an advanced, rapid tooling and manufacturing process that enables production of near net-shape metal parts. A high power laser sinters special non-shrinking steel-based or bronze-based metal powders, layer by layer, from a three-dimensional (3D) computer aided design (CAD) model.
The 3D CAD model of the component is converted into to a series of triangulated surface slices which is then used to control movement of the laser head. A powder layer of predetermined thickness is first spread on the surface of the building plate using a powder feeding system. The laser scans the slice file geometry on the powder layer and lightly bonds it (metallurgically) to the building plate. After the layer is completed, the building plate moves downward exactly the distance of the deposited layer thickness. The powder spreading system then moves over the plate and spreads a new layer of powder on the previously sintered layer. The next slice is then built up by the next laser traverse. This process continues until the part is finished. At this point the building plate is removed for re-use.
The key factors that affect the quality of laser sintered metal parts are powder characteristics and control of accuracy. The powders are carefully selected so that shrinkage is balanced by the expansion of the powder particles. The powder mixtures contain either pure metal or metal alloy powders. Polymer binders can also be used. Bronze powders and steel powders suitable for laser sintering have been developed for different applications. With the optimised powder mixture and accurate control of laser parameters, each scanned powder layer maintains its dimensional accuracy and a near net-shape metal component can be manufactured.
DLS can be used to produce tool inserts for injection molding tools, pressure casting dies and forging tools. The process can also be used for direct component manufacturing and difficult-to-manufacture components such as complex geometries and parts with an internal hollow space which are difficult to manufacture by other methods. The main advantages of DLS are:
- Very fast, irrespective of component complexity
- Produces one or more parts at the same time
- Near net-shape capability
- Sintered parts have good mechanical and thermal properties. Metal parts with functional properties can be produced with tailored powder feeding
- Minimal tooling required - even for components with holes and other features which usually demand complex, special tooling
- A range of different materials can be processed
The main drawbacks of the DLS process are that the precision of the sintered part depends on the size and composition of the powder. The process has to be carefully controlled to avoid defects such as porosity, and hollow spaces inside the part can be difficult to clean. Currently, DLS is limited to the manufacture of small components.