Powder supply in additive layer manufacturing apparatus

Additive layer manufacturing apparatus 10 for fusing powder with an electron beam 15 comprising layer forming means 14 and a housing 11 bounding a vacuum chamber 12. Powder supply 17, which is located outside vacuum chamber 12, may be detachable and can be placed in an evacuated state. Vacuum chamber 12 is communicable with the evacuated supply means 17, perhaps by a door, for the transfer of stored powder to the layer forming means 17. Between the powder supply 17 and the vacuum chamber 12, there may be chutes 27 and 28 and/or a transfer chamber 22 that acts as an air lock. The chutes may be positioned automatically when the doors 25 and 29 are opened. The supply means may have a valve comprising a rotary drum 26 and the amount powder in the power supply may be measured, monitored and communicated. The layer forming device 14 may comprise levelling blades 31 and a powder reservoir 30 with capacity for enough powder to form many layers. Included is a method for replenishing powder in a vacuum chamber without disrupting the vacuum environment.