In-situ evaluation of surface roughness for internal channels by ultrasound


Additively manufactured (AM) of metals has attracted much attention in wide range of industries. However, rough surface is an inherent characteristic of AM process, which significantly limit industrial applications of AM components. Post-processing surface finish is therefore necessary to improve surface quality and quantitative measurement of surface is required to ensure the surface meets high level of accuracy requirement. For external surface, a number of methods can be applied to measure the roughness, such as contact stylus profilometer and non-contact optical microscope. However, it is challenging for these conventional methods to measure internal surface because of limited access. Different from conventional methods, ultrasonic wave may overcome the limited access and provide an advanced measurement to evaluate the quality of the internal surface. In this paper, we present a methodology to evaluate the roughness of internal surface by placing an ultrasonic transducer on the external surface. An ultrasonic wave can be excited by the transducer, interact with the internal surface, then go back to the external surface and be received by the transducer. The information of the internal surface can be encoded into the ultrasonic wave during the wave interaction with the surface. The useful information can thus be decoded from the received signal with appropriate inverse algorithm. This methodology can be used for off-line measurements as well as on-line monitoring.
