Additive Manufacture (AM) is a recent fabrication technology, which consists of building parts by consecutively depositing layers of material, onto a substrate. Wire + arc additive manufacture (WAAM) is a variant of AM, which is based on welding processes such as metal inert gas and plasma welding.

When producing a part, the main geometrical parameters to control are the effective wall width and the layer height. They result from the interaction between power from the arc, travel speed, deposition rate, inter-pass temperature and material properties. Utilising in-process layer height measurements a closed loop can be formed in order to control the parameters and subsequently the finished part.

The layer height measurement system is composed of 3 main components: the fibre optics, the data capture electronics, and the embedded processing unit i.e. a Field Programmable Gate Array (FPGA).  This FPGA device is responsible for generating the appropriate signals to drive the electronics, as well as to process the acquired signals and calculate the distance of the wall from the sensor and thus determine the layer height. The depth information is captured using a technique known as Range Resolved Interferometry (RRI).