Assembling products that contain dissimilar materials has challenged engineers for decades. However, a new production process developed at the University of Missouri may change that.

The Freeform Multi-material Assembly Process can create complex devices with a single machine that combines additive manufacturing and laser technology.

According to Jian “Javen” Lin, Ph.D., an associate professor of mechanical and aerospace engineering at Mizzou, the new process can be used to mass-produce a variety of products, including multilayered sensors, printed circuit boards (PCBs) and textiles embedded with electronic components.

The process could also be used to produce different types of medical devices. Since it can use all thermoplastic materials as structure and carbon as conductive traces, it can create biocompatible products for task-specific applications.

“One of the main benefits is that innovators can focus on designing new products without worrying about how to prototype them,” explains Lin. “It will shorten fabrication time for device prototyping by allowing [engineers] to make prototypes in-house.

“This opens the possibility for entirely new markets,” claims Lin. “It will have broad impacts on wearable sensors, customizable robots, medical devices and [other products].”

“The advancement of 3D printing has already made it possible for designers to create products themselves at a significantly lower cost than outsourcing to a manufacturing company,” adds Bujingda Zheng, a doctoral student in mechanical engineering at Mizzou who worked on the project. “This democratization of manufacturing means that as long as you have the design, a printer can produce it for you.

“However, desktop 3D printers are currently limited in their ability to fabricate products that require multiple materials,” notes Zheng. “Our new process addresses this limitation by enabling low-cost, multimaterial 3D printing, thus expanding the capabilities and applications of additive manufacturing technology.

“This advancement not only reduces production costs, but also opens up new possibilities for complex, multifunctional product designs,” claims Zheng..

“By printing sensors embedded within a structure, [our] machine can make things that can sense environmental conditions, including temperature and pressure,” says Zheng. “That could lead to natural-looking objects such as a rock or seashell that could measure the movement of ocean water. Other potential applications include wearable devices that monitor vital signs such as blood pressure.

“The greatest benefit would be a reduction in the time required to create PCBs,” explains Zheng. “The existing process for producing PCBs is totally different from ours. It involves chemical etching and other complicated [steps].

“Currently, manufacturing a multilayered structure such as a PCB can be a cumbersome process that involves numerous steps and materials,” Zheng points out. “Those processes are costly, time consuming and can generate waste that harms the environment.

“[Our] new process is simple,” claims Zheng. “It produces PCBs on one station without any waste. So, it will replace the traditional PCB manufacturing process. And, it can be fully automated.”

Zheng and his colleagues built a machine that has three different nozzles. One adds ink-like material; another uses a laser to carve shapes and materials; and the third adds additional functional materials to enhance the product’s capabilities.

It starts by making a basic structure with a regular 3D printing filament, such as polycarbonate. Then, it switches to laser to convert some parts into a special material called laser-induced graphene, putting it exactly where it’s needed. Finally, more materials are added to enhance the functional abilities of the final product.

“Not only is the new technique better for the planet, [but] it’s inspired by systems found in nature,” says Zheng. “Everything in nature consists of structural and functional materials.

“For example, electrical eels have bones and muscles that enable them to move,” Zheng points out. “They also have specialized cells that can discharge up to 500 volts to deter predators. These biological observations inspired [us] to develop new methods for fabricating 3D structures with multifunctional applications.”

According to Zheng, other techniques fall short when it comes to how versatile the material can be and how precisely smaller components can be placed inside larger 3D structures.

“Previously, we developed a process called freeform laser induction (FLI), which enables the fabrication of 3D electronics on curved surfaces,” says Zheng. “However, this process is limited to the exterior of pre-existing objects.

“To enhance the capabilities of FLI, we integrated two additional processes: fused filament fabrication (FFF) and direct ink writing (DIW),” explains Zheng. “This integration is the rationale behind the project’s approach. This is the first time this type of process has been used, and it’s unlocking new possibilities.”

The new production process can use various types of thermoplastic filaments, such as polycarbonate, polylactic acid, polyethylene terephthalate glycol and thermoplastic polyurethane, as structural materials. Additionally, it employs laser-induced graphene, lignin, silver, zinc oxide and other extrudable materials as functional components.

“The laser converts the structural material into functional material and converts the precursor of extruded material into functional material, such as silver nitrate into silver,” says Zheng. “FFF constructs the structural material, while DIW deposits the precursor into the predesignated locations.”