Tarek I. Zohdi - Modeling and Simulation of Functionalized Materials for Additive Manufacturing and 3D Printing: Continuous and Discrete Media

Heated filament-based materials (historically for prototyping) are comprised of thermoplastics. To extend the materials to applications beyond prototyping, second-phase particles are added to the heated mixture which solidify (cure) to form the overall material properties comprised of particles in a binding matrix when deposited onto a substrate. The particles are used to tune the binding matrix properties to the desired overall state. Specifically, much of the commercial additive manufacturing processes are polymer-based, with second-phase particles added to enhance the properties of the binder, which is typically either (1) polylactic acid or polylactide (PLA), which is a biodegradable thermoplastic aliphatic polyester or (2) acrylonitrile butadiene styrene (ABS) which is a common thermoplastic polymer. In 2015, PLA had the second highest consumption volume of any bioplastic of the world. PLA is derived from renewable resources, such as plants (corn starch, sugarcane, etc.). ABS is a terpolymer that is significantly stronger than PLA. It is made by polymerizing styrene and acrylonitrile in the presence of polybutadiene. The styrene gives the plastic a reflective surface, while the rubbery polybutadiene endows toughness. The overall properties are created by rubber toughening, where fine particles of elastomer are distributed throughout the rigid matrix. Typically, metal and ceramic particles are also added to endow specific mechanical, thermal, electrical, and magnetic effective overall properties.

Functionalized ink materials (primarily for printed electronics) are comprised of particles in a solvent/lubricant which cure when deposited. Oftentimes, these inks are used to lay down electric circuit lines or to have some other specific electromagnetic function on a surface. One application where such functionalized inks are important is printed electronics on flexible foundational substrates, such as flexible solar cells and smart electronics. One important technological obstacle is to develop inexpensive, durable electronic material units that reside on flexible platforms or substrates which can be easily deployed onto large surface areas. Ink-based printing methods involving particles are, in theory, ideal for large-scale electronic applications and provide a framework for assembling electronic circuits by mounting printed electronic devices on flexible plastic substrates, such as polyimide and PEEK (polyether ether ketone, a flexible thermoplastic polymer) film. There are many variants of this type of technology, which is sometimes referred to as flexible electronics or flex circuits. Flex circuits can be, for example, screen-printed silver circuits on polyester. For an early history of the printed electronics field, see Gamota []).

Dry powder-based materials (primarily for sintered load-bearing structures) are deposited onto a surface and then heated by a laser, e-beam, or other external source, in order to fuse them into place. These types of applications and associated technology are closely related to those in the area of spray coatings, and we refer the reader to the extensive works of Sevostianov and Kachanov [ Because of the monochromatic and collimated nature of lasers, they are a highly controllable way to process powdered materials, in particular with pulsing, via continuous beam chopping or modulation of the voltage. Carbon dioxide ( ) and yttrium aluminum garnet ( YAG ) lasers are commonly used. The range of power of a typical industrial laser is relatively wide, ranging from approximately 10010000 W. Typically, the initial beam produced is in the form of collimated (parallel) rays, which are then focused with a lens onto a small focal point as fine as 0.00001 m in diameter. However, a chief concern of manufacturers are residual stresses and the microstructural defects generated in additively manufactured products, created by imprecisely controlled heat-affected zones, brought on by miscalibration of the laser power needed for a specific goal. In particular, because many substrates can become thermally damaged, for example, from thermal stresses, ascertaining the appropriate amount of laser input is critical.