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Additive manufacturing
Additive manufacturing

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4.2 Metallic materials

Powder-bed systems are designed to be used with metallic materials. Figure 19 shows a powder-bed system. Powder is added to the workpiece in a thin layer using a roller or rake. The layer is then consolidated. A metal is usually fully melted but sometimes it is only sintered (compacted and heated). Lasers are the most common choice for an energy source because of the powers and wavelengths available, but electron beams have also been used. Electron beams require a high vacuum though and are therefore less popular.

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Figure 19 Powder-bed system

The powder-feed system shown in Figures 20 and 21 delivers material through a powder nozzle directing a stream of powder into the path of a laser or electron beam. A wire can be used instead of the powder stream.

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Figure 20 Powder-feed system
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Figure 21 A powder-feed system in operation. The powdered metal feedstream, confined and protected against oxidation with a surrounding jet of inert shielding gas, is fused by a laser focused through a central bore in the head.

Both powder-bed and powder-feed systems have benefits and drawbacks (Table 1).

Table 1 Benefits and drawbacks of powder-bed and powder-feed systems
SystemBenefitsDrawbackPotential applications
Powder bed

No powder is lost

Precise layer thickness

Constrained to the three-axis system

Semibulk production

Production line integration

Powder feed

Freedom to change z direction

System can be taken to existing components – deposition in situ

Powder usage efficiency is low

As component grows, variations in layer height may occur

Repair of damaged components

Addition of detail to large structures