Professor Ronald Daggett first introduced plastics engineering into the mechanical engineering curriculum at the University of Wisconsin-Madison in 1946—and for the next seven decades, he and his predecessors remained at the forefront of plastics research and education. That tradition continues to this day, as UW-Madison engineers are conducting cutting-edge research that will take 3D printing to the next level.
3D printing, or “additive manufacturing,” is the process of using a machine to “print” layers of material to ultimately create a 3D object. It’s an emerging interdisciplinary area with stakeholders from diverse backgrounds—only a handful of whom have expertise in plastics.
Natalie Rudolph and Tim Osswald are among the experts in plastics engineering and additive manufacturing at UW-Madison, and they seek to share their knowledge to enhance the additive manufacturing community.
Rudolph, an assistant professor in the Department of Mechanical Engineering, and Osswald, the Consolidated Papers Foundation Chair in the same department, focus on a 3D printing process known as fused filament fabrication, a technology that feeds polymer filament from a spool through a heated nozzle, which melts the filament in layers onto the final product. Think something like a space-age, computer-driven hot glue gun.
Additive manufacturing could revolutionize the manufacturing industry by allowing manufacturers to quickly and efficiently create custom products using a single manufacturing infrastructure of 3D printers, but it’s still in its infancy. “A lot of research in additive manufacturing is done with materials that weren’t developed for additive manufacturing,” says Osswald. “Therefore, the properties are not necessarily tailored for the printing process.”
For example, the composition of the polymer filaments available today can vary between batches and shipments, leaving consumers, manufacturers and researchers in the dark about key properties like strength, elasticity and melting temperatures. “Right now, there is no reliability, which makes it hard to do reproducible research,” says Rudolph.
Aside from an undependable polymer composition, most 3D printers today operate within a strict range of manufacturer-dictated printer settings—and that creates a barrier to robust research efforts.
At UW-Madison, Rudolph and Osswald co-direct the UW-Madison Polymer Engineering Center, one of few university research facilities in the country that has full control of the additive manufacturing process—from creating its own filament through printing final products.
In the lab, the researchers create their own polymer filaments for 3D printing from polymer pellets with known properties. This gives them control over the raw material with which they conduct their research.
They and their students also are investigating “highly filled” polymers, which they create by adding fillers such as carbon fiber and copper to the plastic filament to impart various functional properties. This allows them to print components that, for example, conduct heat or electricity, or are magnetic. “Once you start thinking of filled plastics, it opens up a whole bunch of potential applications,” says Rudolph.
They create these polymer filaments using single- or twin-screw extruders, which consists of screws in a heated barrel that conveys the polymer mixture along the screws until they are eventually squeezed out as a uniform strand.
Then, the researchers run the spools of filled polymer filament through a laser micrometer, a machine that shoots three 60-degree-offset lasers at the polymer strand to measure its diameter and circularity. This allows them to fine tune the dimensions of the filament so that it feeds through the nozzle of the 3D printer consistently.
To control the printing process itself, they use an open-source software program called SciSlice developed by Luke van Hulle, a graduate student under Rudolph. SciSlice allows researchers to create custom designs for fused filament fabrication 3D printers and provides them better control over all aspects of the printing process. By supporting various adjustable printing parameters such as nozzle diameter and flow rate, SciSlice enables the researchers to characterize each parameter’s effect on the overall composition of the end product.
“All the activities at the Polymer Engineering Center are focusing on a very fundamental approach to understand the underlying principles of additive manufacturing,” says Osswald. “We can then transfer this knowledge to other materials, processes and process conditions that the industry needs.”
Author: Pat DeFlorin