from the 12/18/14 patent (one I hadn't seen before)
reducing the pressure in the vacuum chamber from a first pressure level to a second pressure level between the providing of said first powder layer and said second powder layer, preheating the powder bed at least partially with said first pressure level, wherein a mean pressure level during the preheating is higher than a mean pressure level during the fusion of the selected locations.
The invention is not limited to the above-described embodiments and many modifications are possible within the scope of the following claims. Such modifications may, for example, involve using a different source of energy beam than the exemplified electron beam such as laser beam. Other materials than metallic powder may be used such as powder of polymers or powder of ceramics.
The control unit may control the vacuum pump(s) and one or a plurality of gas supply valves. A supplementary gas may be let into the vacuum chamber during preheating. Said supplementary gas may for instance be a gas which is capable of providing ions when irradiated by the electron beam during said preheating. Said supplementary gas may be Helium, Argon, Carbon dioxide, Nitrogen, Neon, Krypton, Xenon, Radon.
note that some of the recently posted papers show a problem with oxides in the melt/\. Presumably due to traces of eater or air left after the vacuum pump out. adding non reactive gases then pumping most of them out should purge the system of oxygen, and provide ions to alloy the metal. And as the recent patents has done, these apply to any energy beam, not just electrons. And to polymers and ceramics, not just metal.
Most analysts don't seem to realize the huge patent moat around Arcam.
