POROSITY DETECTION AND ANALYSIS USING MATLAB OF THIN-WALLED STRUCTURES FABRICATED USING POWDER BED FUSION AT DIFFERENT ANGLES WITH RESPECT TO THE RECOATER BLADE

Open Access
Author:
Dolack, Matthew Edward
Area of Honors:
Mechanical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Timothy W. Simpson, Thesis Supervisor
  • Sean Brennan, Honors Advisor
Keywords:
  • Additive Manufacturing
  • Powder Bed Fusion
  • Porosity
  • Defect Detection
  • Part Fabrication Angle
  • Recoater Blade
Abstract:
The additive manufacturing industry has undergone significant innovation and advancement in the field of selective laser melting technology during the past decade. A common concern when fabricating parts using powder bed fusion, which is a form of selective laser melting, is unintentional internal porosity. Unintentional porosity in a fabricated part can be problematic because it can negatively impact both its mechanical and heat transfer properties. When fabricating components using powder bed fusion there are many alterable process parameters that can affect internal porosity. A Ti-6Al-4V pad with 25 rectangular fins ranging in thickness from 300 to 60 microns was printed using powder bed fusion to test whether build angle with respect to the recoater blade affects internal porosity. The laser scan pattern for each unique fin thickness was not changed when printed at angles of 0°, 30°, 60°, and 90° with respect to the recoater blade. Data on laser spot size and corresponding melt pool size were also analyzed for possible effects on internal porosity. Using computerized tomography scanning, each fin pad’s internal structure was digitized. The internal structure of each built fin was then analyzed for internal defects using a custom-built MATLAB program. Analysis of the collected defect data indicates that internal porosity of thin-walled structures can be decreased substantially if fabricated using a laser scan pattern and spacing that causes melt pool overlap to occur. Internal porosity of thin-walled structures is independent of fabrication angle with respect to the recoater blade when melt pool overlap occurs during part construction and is dependent on fabrication angle with respect to the recoater blade when melt pool overlap does not occur during part construction. Furthermore, when melt pool overlap does not occur during part fabrication internal porosity is most significant in parts printed at 0° with respect to the recoater blade and is least significant in parts printed at 90° with respect to the recoater blade.