Post-processing is an often-overlooked part of additive manufacturing. Rarely does a part meet the customer’s expectations when it pops off the printer. Large-format additive manufacturing makes big parts fast, but it also uses large beads, so the surface has very noticeable layers. Post-processing is the key to many LFAM applications, from cars to tooling.
One of the first methods used on a large part was sanding. It took a team of technicians a week to sand the ORNL Shelby Cobra to get the surface they wanted. Sanding carbon-reinforced ABS is a little like sanding concrete.
It is much easier to spray on and sand a filler. Subsequent vehicles were filled and sanded for a class-A finish. Some early tooling projects even applied fillers in a large thickness and machined.
Machining is the most common method used for post-processing. Machining can provide both the accuracy and the surface condition demanded by customers. We can see that the machining time often exceeds the printing time for some high-tolerance parts. We will explore machining, tooling, fixturing, speed, and surface condition tradeoffs.
Heat treating can reduce internal stresses and provide a more accurate final part.
Gelcoat can be applied to machined tools or molds to provide a smooth surface and protect the thermoplastic from the resins and solvents used in the fiberglass layup process. Gelcoat thickness can vary, usually between 0.02 to 0.03”, affecting the accuracy of the final mold.
Several off-the-shelf coatings can be applied to smooth the tool surface, filling micropores and improving vacuum integrity. When combined with a release agent, these fillers make it so that the resin from a composite part does not bond the part to the tool.
Post-processing can provide parts that meet expectations of surface condition and accuracy.
Learning Objectives:
- Upon completion, participants will be able to understand the post-processes needed to get a class-A finish on parts fabricated using large-format additive manufacturing.
- Upon completion, participants will be able to understand the post-processes needed to make aerospace tooling using large-format additive manufacturing.
- Upon completion, participants will be able to better understand the machining of thermoplastic composite parts made with additive manufacturing.
