4D printing of composite materials more efficient, economical than curved moulds for composite structures

In the race to provide faster, less expensive manufacturing techniques for things like satellites, there’s a new player in the game: 4D printing of composite materials.

Essentially, 4D printing is creating objects with a 3D printer that change shape over time once they’re removed from the printer (in this instance the fourth dimension is an activation mechanism like heat, light, magnetic field, or absorption of moisture).

“4D printing allows us to make curved composite structures without the need to make curved moulds,” says Suong Van Hoa, professor in the Department of Mechanical, Industrial and Aerospace Engineering in Concordia’s Faculty of Engineering and Computer Science.

“My main finding is that one can make curved composite pieces — long continuous fibres that have high mechanical properties — more quickly and economically.”

Last fall, Hoa became the first Canadian to be named a fellow of the American Society for Composites for his “outstanding contributions to the composites community through research, practice, education and service.”

He announced his latest discovery in the journal Advanced Manufacturing: Polymer & Composites Science.

How it works

Imagine what it takes to manufacture a composite leaf spring, a lightweight shock absorber in vehicles. For example, to make an s-shaped piece, an s-shaped mould would need to be made out of a solid material like metal. Then, a reinforcing fabric that is pre-impregnated with a resin system would be laid up on the mould to make the composite piece.

But that first step – building a complex mould – could be skipped to save time and money, says Hoa, who’s the founding director of Concordia’s Centre for Composites (CONCOM). His findings show how the manufacturing process can be significantly streamlined.

“4D printing of composites utilizes the shrinkage of the matrix resin, and the difference in coefficients of thermal contraction of layers with different fibre orientations to activate the change in shape upon curing and cooling,” he says.

“This behaviour can be used to make parts with curved geometries without the need for a complex mould. As such, manufacturing of pieces of curved shapes can be fast and economical. However, the degree of shape-changing depends on the material properties, the fibre orientation, the lay-up sequence and the manufacturing process.”

A new approach

To arrive at his results, Hoa reconsidered the anisotropic properties of composite layers.

Anisotropy can be defined as how a material acts while bearing loads along different axes; a material's anisotropic properties are a measure of how it can change in relationship to other factors.

In his paper for Advanced Manufacturing: Polymer & Composites Science, Hoa outlines the anisotropic properties at play in building a composite structure.

For example, resin shrinkage can cause materials to be deformed. Or, temperature changes can cause fibres to expand or contract. Understanding and controlling for these changes is key to making curved laminates without curved moulds, Hoa argues.

“Anisotropic properties have been looked at as a liability in the past,” he says. “Now I look at them as an asset.”

Taking innovation off the ground

Eventually, this technology could be applied to the aerospace industry, among other areas, Hoa says.

“Another application is for space structures like satellites, where the structures are subjected to extreme temperature fluctuation,” he says. “The structure can open up during the day (when the temperature is high) to collect the solar energy, and close up at night to provide protection for its interiors.”

Read the published paper, “Factors affecting the properties of composites made by 4D printing (mouldless composites manufacturing).”

Learn more about Concordia's Department of Mechanical, Industrial and Aerospace Engineering (MIAE).