Date of Award

Spring 5-5-2023

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Department

Mechanical Engineering

Advisor

Wilhelm Friess

Second Committee Member

Bashir Khoda

Third Committee Member

Steven Nolet

Abstract

In recent years, additive manufacturing (AM) has been successfully utilized for the production of large-scale composite tooling. Within these endeavors, however, limited research has focused on joining methods between printed sections. This work evaluates the feasibility of thermoplastic extrusion welding as a joining method for additively manufactured tooling structures. This joining method was assessed based on industry specifications of conventional thermoset tooling for wind blade manufacturing utilizing the vacuum-assisted resin transfer molding (VARTM) process. The specifications include requirements for the mechanical strength, vacuum integrity, roughness, and hardness of the tool surface. The feasibility of this welded polymer joint was demonstrated through subscale testing of 1” thick, welded, AM high-impact polystyrene (HIPS) plates. It was found that thermoplastic extrusion welds within AM components can maintain vacuum integrity at 20℃ with proper surface preparation and without a surface coating. This met the industry vacuum leakage specification of 10 millibar over 30 minutes with an average loss of 6.61 mbar over 30 minutes through the welded AM plate and bag system. Although beyond the industry specification, the vacuum leakage was further tested to evaluate performance at an infusion temperature of 80℃. At elevated temperature, the joint and plate lost approximately 26 mbar over 30 minutes. The surface finish was compared with hardness and roughness testing of the welded and machined AM surfaces, showing a decrease in hardness and roughness in the surface of the weld at both temperatures. Standardized ASTM mechanical testing of welded specimens showed an average comparative tensile strength of 80% of the base AM HIPS material. With the addition of undersurface reinforcement within the mold and a surface coating, extrusion welding shows promise for joining large-scale AM tool sections in a manufacturing environment.

Download

Share