3D printing technology is an intelligent manufacturing technology that originated in the 1980s and integrates machinery, computer, numerical control and materials. The basic principle of this technology is that according to the two-dimensional section information obtained through layered processing of three-dimensional solid parts, points, lines or surfaces are used as basic units to stack and manufacture layer by layer, and finally the solid parts or prototypes are obtained. 3D printing is different from the traditional manufacturing methods of reducing materials (such as cutting) and equal materials (such as forging). It can realize the manufacturing of complex structural parts that are impossible or difficult to achieve by traditional methods, and greatly reduce the processing procedures and shorten the processing cycle. Therefore, it has received extensive attention from researchers around the world.
3D printing technology was first applied to rapid manufacturing of various prototypes, so it was also called Rapid Prototyping (RP) in the early days. Due to the limitation of material types, the early 3D printing technology mostly used organic polymer materials, and its mechanical and chemical properties were mostly difficult to meet the needs of practical applications. With the development of material technology and equipment technology, it is more and more urgent to apply this technology to the manufacturing of terminal components. Therefore, not only higher requirements are put forward for 3D printing equipment, but also the requirements for various properties of 3D printing materials are increasing.
3D printing material is an important material foundation of 3D printing technology, and its performance largely determines the comprehensive performance of formed parts. Up to now, its material categories have been very rich, mainly including polymer materials, metal materials, ceramic materials, etc. This paper first introduces the characteristics, performance requirements and related applications of polymer materials.
Thermoplastic polymer is one of the most common 3D printing materials. Common thermoplastic polymers for 3D printing include acrylonitrile butadiene styrene plastic (acrylonitrile butadiene), polylactic acid (PLA), polyamide (nylon) (PA), polycarbonate (PC), polystyrene (PS), polycaprolactone (PCL), polyphenylsulfone (PPSF), thermoplastic polyurethane (elastic rubber), polyetheretherketone (PEEK), etc.
PLA and acrylonitrile butadiene are the most commonly used consumables for FDM, which are very popular due to their low prices. Acrylonitrile butadiene is a common engineering plastic with good mechanical properties, but 3D printing conditions are demanding, which is prone to warping deformation and irritating smell during printing. PLA is a biodegradable and environment-friendly plastic with good printing performance. It is an ideal 3D printing thermoplastic polymer and has been widely used in education, medical treatment, architecture, mold design and other industries. In addition, PLA also has good biocompatibility, and PLA modified with hydroxyapatite can be used to manufacture tissue engineering scaffolds.
PA is a semi crystalline polymer, which can be formed by SLS to obtain high specific gravity and high strength components, and is one of the main consumables of SLS. PA used in SLS should have high sphericity and particle size uniformity, and is usually prepared by low-temperature pulverization. PA composite powder can be prepared by adding inorganic materials such as glass bead, clay, aluminum powder, carbon fiber, etc. The addition of these inorganic fillers can significantly improve the performance in some aspects, such as strength, heat resistance, conductivity, etc., to meet the application requirements in different fields.
PCL is a non-toxic, low melting point thermoplastic. PCL wire is mainly used as a consumer of 3D printing pens for children. Because of its low forming temperature (80~100 ° C), it has high safety. It is worth mentioning that PCL has excellent biocompatibility and degradability, which can be used as a scaffold material for tissue engineering in biomedicine. The mechanical properties and biocompatibility can also be improved by doping nano hydroxyapatite and other materials. In addition, PCL materials also have a certain shape memory effect, which has certain potential in 4D printing.
Elastomeric rubber is a thermoplastic polymer with good elasticity. Its hardness range is wide and adjustable, and it has certain wear resistance and oil resistance. It is suitable for the manufacturing of shoe materials, personal consumer goods, industrial components, etc. Combined with 3D printing technology, the complex porous structure that is difficult to manufacture by traditional forming technology can be manufactured, which makes the parts have unique and adjustable mechanical properties. The elastic performance and service strength of the porous elastic rubber insole printed with SLS technology have reached the market standard.
PEEK is a semi crystalline polymer with high melting point (343 ° C), excellent mechanical properties and excellent biocompatibility. It is currently a hot 3D printing material. The Young’s modulus of pure PEEK is 3.86 ± 0.72 GPa, and it can reach 21.1 ± 2.3 GPa after being reinforced by carbon fiber, which is the closest to the Young’s modulus of human bone. It can effectively avoid the stress shielding and looseness phenomenon with human bone after being implanted into the human body. It is an ideal orthopedic implant material. PEEK implants manufactured by 3D printing technology (Figure 1) can well meet the customized requirements of personalized implants for different patients with different conditions. At present, 3D printing PEEK implants in China have achieved good results in clinical practice.
Figure 1 Sternum prosthesis CAD model and real object
The next article will introduce metal materials for 3D printing.