A dissertation submitted to the graduate faculty in partial fulfillment of the requirements for the degree of doctor of philosophy by Farzaneh Ahmadi, electrical and computer engineering major
Program of Study Committee:
- Reza Zoughi, Major Professor
- Mohammad Tayeb Al Qaseer
- Jiming Song
- Peter Collins
- Qing Li
Abstract
Additive manufacturing (AM), commonly known as 3D printing, involves the layer-by-layer addition of material based on patterns designed in slicer software. This method is favored for its speed and cost-effectiveness while minimizing waste. However, AM presents several challenges; objects produced often exhibit weaker mechanical strength and higher defect rates compared to those made using conventional methods like computer numerical control (CNC). These issues can arise from both the manufacturing process and the quality of raw materials, highlighting the need for effective monitoring techniques, which is the focus of this study.
This research investigates two commonly used additive manufacturing techniques for polymers and metals: fused deposition modeling (FDM) and laser powder bed fusion (LPBF). Literature indicates that small voids or moisture in the raw polymers used in FDM can significantly impact the quality and mechanical strength of the final printed parts. In this study, the efficacy of three near-field millimeter-wave probes was compared. Results showed that the proposed optimized structure can detect hemispherical voids as small as 1 mm in diameter and moisture content of about 0.5% in polylactic acid, the most commonly used material in polymer-based additive manufacturing.
The second part of the research focused on developing a monitoring method for the laser powder bed fusion (LPBF) process. The results indicated a correlation between changes in the radar cross-section of the cloud of metallic particles ejected during the process and variations in the processing parameters. Specifically, these parameter changes resulted in either the creation of a keyhole defect or the deepening of an existing keyhole. Additionally, measurements demonstrated that the packing density of the particles is effectively detectable using microwave and millimeter-wave methods.