Embedding Optical Sensors in Additively Manufactured Parts for In-Situ Performance Measurement

Abstract

The aim of this project is to explore the potential of embedding sensors in additively manufactured metal parts towards smart product development. Smart product development is desirable due to its ability to detect product stress in-situ. There are challenges both in the construction of appropriate channels (for sensor embedding) in metal Additive Manufacturing (AM) and in packaging the sensor in an AM part for application-specific specimen measurands. Thus, this project investigates the feasibility of incorporating specific channels into AM parts for sensor embedding, packaging of the sensor in the parts, and the characterization of the sensor for sensing a given measurement. Primarily, Fiber Bragg Grating (FBG) sensors have been chosen for their compact size, ability to operate in hazardous environments, and their immunity to electromagnetic radiation. By creating such fiber-embedded smart products, it is possible to take preventive action for part failure by monitoring key areas of the product.

To see the feasibility of such development, stainless steel coupons were fabricated via laser powder-bed fusion (LPBF) and its fabrication parameters were optimized. LPBF uses lasers to melt layers of metal powder layer by layer for its fabrication. LPBF allows diverse material choices while giving more dense parts compared to traditional casting methods and has high part accuracy due to the small laser spot size utilized. Parameters such as laser power, hatch offset, and print orientation were optimized to yield a channel best suited for embedding FBG sensor within the bulk of the material. Thermal epoxy was injected into the channel after the FBG sensors were embedded to package the sensors and effectively translate the stress from the AM-created part to the FBG sensors.

With the fabricated proof-of-concept coupons, various tests and simulations were conducted to characterize the property and performance of the coupons. This was done to compile a guideline for designing such a part in the future and to understand the overall feasibility of the design. Tensile tests such as cyclic and fracture tests were conducted to understand the accuracy of the sensors during deformation. A thermal test was conducted to understand the temperature sensitivity of the product. COMSOL simulation was utilized to explore the geometry limitations of the sensor when packaged inside of the AM part.

The obtained results and characterizations show that it is indeed feasible to embed FBG sensors in metal AM parts for its monitoring and enhanced functionality. 500 micron diameter channel was able to be fabricated via LPBF. Recurring trends were observed from the dataset and results corresponded with hypothesized theoretical results. FBG readings were able to accurately monitor cyclic test until 240 cycles and its plastic deformation. The condition of the AM parts can be predicted using the sensors and established guidelines from this experiment. This guideline is to be utilized as a foundation for future fabrication of smart products of varying applications.