Charged particle beam control during additive layer manufacture

An additive layer manufacturing apparatus comprising:

• a charged particle source;
• beam forming apparatus operable to form a beam of charged particles from the charged particles provided by the charged particle source;
• beam steering apparatus;
• at least one hopper operable to dispense powder;
• a table positioned to receive the powder dispensed by the at least one hopper in a volume defining a powder bed, and wherein the beam steering apparatus is operable to scan the beam over the powder bed;
• and
• a processor and associated memory,
• the memory having stored therein a computer readable file;
• wherein the file comprises:
• a layer description for each layer of the shape of the product that describes the shape of the layer;
• for each layer, the shape of the layer is decomposed into one or more hatch areas to be scanned by the beam, each hatch area having a shape description that describes the shape of the hatch area;
• for each hatch area, the shape of the hatch area is decomposed into one or more lines to be scanned by the beam, each line having a line description;
• a beam acceleration voltage to be used when forming the product;
• for each hatch area, a respective beam current to be used when forming the hatch area;
• for each line,
• (i) a respective beam spot size to be used when scanning the beam along the line,
• (ii) a respective series of beam position values, beam step sizes and beam step dwell times to be used when scanning the beam along the line, wherein the beam step size is the size of the step the beam is moved from the current beam position on the powder bed to the next beam position on the powder bed and the beam dwell time is the time the beam is held at each position on the powder bed;
• and
• the processor being configured to access the file and to control the additive layer manufacture apparatus to form the product according to the file by forming the product as a series of layers, each layer being formed by fusing powder deposited as a powder bed by scanning a powder bed using a charged particle beam to form a desired layer shape;
• wherein, for each layer, the powder is fused by scanning the charged particle beam from beam position to beam position as specified by the beam position values in the line descriptions and holding the beam at each position according to the beam dwell times in the line descriptions thereby scanning the beam along each line and, in turn, scanning the beam over each hatch area to complete the layer;
• wherein the processor is configured to dynamically adjust at least one of the beam spot size, beam step size and beam dwell time from the beam spot size, beam step size and beam dwell time specified in the file in response to assessing energy deposited to the powder.