Crafting items manually at the manufacturing plant does not require any energy and is almost instantaneous because it interfaces with your suit & build tool to perform the work. If you would like to continuously manufacture an item while you are away this can be done using just the facilities within the manufacturing plant but at the cost of both time and energy. Select the item to manufacture, enter the number of items required, or select 'Repeat' to continue forever, and press the Automate button. The materials needed must be in a adjacent storage hopper with I/O permissions set to either 'Add/Remove' or 'Remove only' (recommended), the manufactured items will also be placed into a storage hopper, which should have I/O status of 'Add Only'.