Additive manufacturing is often referred to as 3D printing, as it works in a similar way to a laser printer. The technique builds a solid object from a series of layers - each one printed directly on top of the previous one.

The raw material for ALM is a powder, which can be a thermopolymer or a metal; aluminium, stainless steel and titanium 6,4 are common. The printing chamber is generally heated to 10ºC below the melting point of the material - this ensures that the laser used to heat the powder can melt it quickly. For metals, this preheating eliminates residual stress from their processing, which can make them warp when welded.

The machines’ operating software cuts the CAD model of the workpiece into slices, whose thickness depends on the type of material used; CALM uses 0.1mm for polymers and 30 microns for metals. A blade mounted on a moving arm sweeps an even layer of the powder on top of the work surface inside the chamber, then a laser - generally around 200W - scans back and forth over the surface, melting the powder in the shape of the first layer. The work surface then drops by the thickness of the layer and another layer of powder is distributed over the surface.

Other ALM machines use electron beams rather than lasers, as they are capable of transmitting more energy and therefore melt the powder faster. These machines work at room temperature, again speeding up the process. However, they produce pieces with a rougher surface finish that requires further machining and residual stress isn’t eliminated.

Read more: http://www.theengineer.co.uk/in-depth/the-big-story/the-rise-of-additive-manufacturing/1002560.article#ixzz2zfx2No00