What Is 3D Printing
3D printing technology, also known as additive manufacturing technology, is a cutting-edge advanced manufacturing technology . It is praised by developed countries in Europe and the United States as the carrier of the third industrial revolution. Together with robotics, artificial intelligence and nanotechnology, it is called the key technical means to reshape the future manufacturing industry . It has been applied to the fields of automobiles, aerospace, consumer electronics, medical care, industrial design, culture and entertainment, and has broad development prospects. 3D printing technology not only has the characteristics of digital and intelligent manufacturing, but also has high material utilization, can achieve energy saving in the application process through lightweight structure, can realize complex structure manufacturing, personalized manufacturing and networked manufacturing, etc. It is a typical green intelligent manufacturing technology.
According to the definition of the American Society for Testing and Materials (ASTM): 3D printing is the use of three-dimensional digital model design, software layered discrete and CNC molding system, laser beam, electron beam and other methods to stack and bond special materials such as metal powder, ceramic powder, plastic, cell tissue layer by layer, and finally superimpose and shape to produce physical products .
Conceptually, 3D printing is synonymous with “additive manufacturing” in industrial terminology. The concept of “additive manufacturing” is different from traditional “removal-based” manufacturing. Traditional CNC manufacturing is generally based on raw materials, using cutting, grinding, corrosion, melting and other methods to remove excess parts to obtain parts, and then assembling, welding and other methods to combine into the final product. Its core is the “subtractive” or “equal material” manufacturing process. “3D printing” is completely different from it. It does not require original embryos and molds. It can directly generate objects of any shape based on computer graphics data by adding materials, simplifying the product manufacturing process, shortening the product development cycle, improving efficiency and reducing costs. Its core is the “additive” manufacturing process.
3D printing is usually achieved by using digital technology material printers. It is often used to make models in the fields of mold manufacturing, industrial design, etc., and then gradually used for direct manufacturing of some products. There are already parts printed using this technology. This technology is used in jewelry, footwear, industrial design, architecture, engineering and construction (AEC), automobiles, aerospace, dental and medical industries, education, geographic information systems, civil engineering, firearms and other fields.
3D printing materials and their classification
3D printing materials are an important material basis for the development of 3D printing technology. The performance and type of materials determine the quality and function of 3D printing products. At present, although all countries are vigorously carrying out research and development work on 3D printing materials, compared with the tens of thousands of materials with different performances and uses, the 3D printing materials that can be truly applied still have problems such as few types and varieties, and the performance cannot meet various application requirements. Therefore, breaking the bottleneck of materials restricting 3D printing technology is crucial to promoting the development of 3D printing technology.
At present, the main materials involved in 3D printing include polymer materials, metal materials, ceramic materials, composite materials and smart materials, etc., focusing on the structural properties, mechanical properties, biological properties and physical properties of macro and micro structure manufacturing. In addition, colored gypsum materials, artificial bone powder, cell biological raw materials and food materials such as sugar have also been used in the field of 3D printing.
Polymer materials
Thermoplastics
Thermoplastics refer to plastics that soften when heated and harden when cooled. Among them, thermoplastic engineering plastics are the most widely used. Thermoplastic engineering plastics refer to industrial plastics that are based on thermoplastic resins and added with various additives. They can be molded under certain temperature and pressure and are used as industrial parts or shell materials. They are plastics with excellent strength, impact resistance, heat resistance, hardness and aging resistance. Thermoplastic engineering plastics are currently the most widely used type of polymer 3D printing materials. Common ones include acrylonitrile-butadiene-styrene copolymer (ABS), polyamide (PA), polycarbonate (PC), polyetheretherketone (PEEK), polysulfone (PSU), etc.
ABS
It is a thermoplastic engineering plastic commonly used in rapid prototyping processes. It has the advantages of high strength, good toughness, and impact resistance. The normal deformation temperature exceeds 90°C. It can be machined (drilling, tapping), painted, and electroplated.
At present, ABS is mainly used after being prefabricated into wire and powdered. The application range covers most daily necessities, engineering products, and some mechanical products. ABS materials have a full range of colors and are widely used in the fields of automobiles, home appliances, and consumer electronics. In recent years, ABS has not only gradually expanded its application range, but also continuously improved its performance. With strong adhesion and strength, through modification, ABS has further expanded its scope of application as a 3D printing material. In 2014, the International Space Station used ABS plastic as the material to print parts with a 3D printer. The latest ABS material ABS-M30 developed by Stratasys, the world’s largest 3D printer material company, is designed for 3D printing manufacturing. Its mechanical properties are 67% higher than those of traditional ABS materials, expanding the application range of ABS.
PA
It has both high strength and certain flexibility, and can be directly used to manufacture equipment parts using 3D printing. PA carbon fiber composite plastic resin parts manufactured using 3D printing have high toughness and can be used to replace metal tools. Solvay, a world-renowned company, uses PA engineering plastics to 3D print samples for engine peripheral parts, door handle kits, brake pedals, fuel filters, oil storage tanks, balanced rotating shaft gears, etc. Replacing traditional metal materials with PA materials ultimately solves the problem of lightweighting automobiles. In 2016, Guangdong Yinxi Technology Co., Ltd. fully launched PA powder and its composite materials.
PC
It is a true thermoplastic material with all the characteristics of engineering plastics: high strength, high temperature resistance, impact resistance, bending resistance, etc. PC is 60% stronger than ABS material and can be used as a final component. The three major application areas of PC engineering plastics are glass assembly industry, automobile industry and electronics and electrical industry, followed by industrial machinery parts, optical disks, packaging, office equipment such as computers, medical and health care, films, leisure and protective equipment, etc. PC can be used as door and window glass, PC laminates are widely used in protective windows of banks, embassies, detention centers and public places, for aircraft cabin covers, lighting equipment, industrial safety baffles and bulletproof glass. PC2605 developed by Bayer in Germany can be used for 3D printing of special-shaped components such as bulletproof glass, resin lenses, headlight covers, astronaut helmet masks, smartphone bodies, mechanical gears, etc. In addition, PC material is a white thermoplastic material that has passed medical hygiene certification and has high strength. It is widely used in the pharmaceutical and medical device industries and in professional fields such as surgical simulation, skull repair, and dentistry.
PEEK
It is a special engineering plastic with excellent properties such as high temperature resistance, self-lubrication, easy processing and high mechanical strength. It can be used to manufacture and process various mechanical parts, such as automobile gears, oil screens, shift starter discs; aircraft engine parts, automatic washing machine wheels, medical equipment parts, etc. In addition, PEEK has excellent wear resistance, biocompatibility, chemical stability and Young’s modulus closest to human bones. It is an ideal artificial bone replacement material and is suitable for long-term implantation in the human body. Therefore, combining 3D printing technology with PEEK materials to manufacture bionic artificial bones has important market prospects.
PSU
The melting point is 189℃. It is the strongest, most heat-resistant and most corrosion-resistant material among all thermoplastic materials. It is usually used as a final component and is widely used in the aerospace, transportation and medical industries. PSU materials can bring a direct digital manufacturing experience and have very stable performance. When used in conjunction with FORTUS equipment, amazing results can be achieved.
Thermosetting plastics
Thermosetting plastics are made of thermosetting resin as the main component, combined with various necessary additives to form plastic products through a cross-linking and curing process. Thermosetting plastics can soften and flow when heated for the first time. When heated to a certain temperature, chemical reactions and cross-linking reactions occur to solidify and harden. This change is irreversible. After that, it can no longer soften and flow when heated again. It is precisely with the help of this characteristic that molding is carried out. The plasticized flow during the first heating is used to fill the cavity under pressure and then solidify into a product of a certain shape and size. Thermosetting plastics, such as epoxy resins, unsaturated polyesters, phenolic resins, amino resins, polyurethane resins, silicone resins, aromatic heterocyclic resins, etc. , have the characteristics of high strength and good fire resistance, and are very suitable for powder laser sintering molding processes using 3D printing. Materials scientists at the Harvard School of Engineering and Applied Sciences and the Wyss Institute for Biologically Inspired Engineering have jointly developed a 3D printable epoxy-based thermosetting resin material. This epoxy resin can be 3D printed into building structural parts for use in lightweight buildings.
Bioplastics
Biomedical materials refer to materials that can be implanted into organisms or bonded with biological tissues for medical purposes . They can be used for diagnosis, treatment, replacement of tissues and organs in biological organisms, or enhancement of their functions . Biomedical materials emerged in the 1960s, developed rapidly in the 1980s, and are widely used in clinical practice. The main 3D printing bioplastic materials are: polylactic acid (PLA), polyvinyl alcohol (PVA), polyhydroxyalkanoates (PHA), polyethylene terephthalate-1,4-cyclohexanedimethanol (PETG), polycaprolactone (PCL), and bio-based thermoplastic polyurethane products (bio-based TPU).
PLA
It is a new type of bio-based and biodegradable material with good biodegradability. After use, it can be completely degraded by microorganisms in nature under specific conditions, and finally produces carbon dioxide and water, which does not pollute the environment. It is a recognized environmentally friendly material. PLA can be biodegraded into active compost. It is extracted from corn starch and sugarcane, not fossil fuels. Tan.KH et al. of Nanyang Technological University in Singapore used degradable polymer materials to make high-porosity PLA tissue engineering scaffolds in their research on the application of PLA to manufacture tissue engineering scaffolds. Through tissue analysis of the scaffold, it was found that it has growth ability.
PVA
It is a biodegradable synthetic polymer, and its biggest feature is water solubility. As a new type of printing line used in FDM, PVA is a good support material in the printing process. After the printing process is completed, the support part composed of it can be completely dissolved in water and is non-toxic and odorless, and can be easily removed from the model. The PVC water-soluble support material launched by Esun has received unanimous praise both domestically and internationally. In the printing process, it is a perfect match with PLA filaments.
PHA
It is a bio-based material made from plants and has degradable properties. Because it is non-toxic and harmless, it is currently often used to make medical instruments, food packaging bags, children’s toys, electronic product casings, etc. When recycling, just bury it like food waste and it will naturally degrade in the soil. Not only that, it can degrade quietly in fresh water and salt water like in the soil, and will not leave any particles. In terms of 3D printing applications, PHA is similar to PLA and can be made into lines for 3D printers. Compared with PLA, it is more expensive and has a slightly narrower processing window.
PETG
It is a bio-based plastic synthesized from bio-based ethylene glycol produced from sugarcane ethylene. It is an amorphous copolyester. This material has good viscosity, transparency, color, chemical resistance and stress whitening resistance. As a new type of 3D printing material, PETG has the advantages of both PLA and ABS. During 3D printing, the shrinkage rate of the material is very small, and it has good hydrophobicity and does not need to be stored in a confined space. PETG has low shrinkage, low temperature, and almost no odor during the printing process. It has a broader development and application prospect in the field of 3D printing.
PCL (Polycaprolactone)
With good biodegradability, biocompatibility and non-toxicity, it is widely used as a medical biodegradable material and drug controlled release system. It can be used in tissue engineering and has been used as a drug sustained release system. PCL material is a degradable polyester with a low melting point of only about 60°C. Like most biomaterials, it is often used for special purposes – such as drug delivery equipment, sutures, etc. At the same time, PCL also has shape memory. Due to the low melting point, a very high printing temperature is not required in 3D printing, which can achieve the purpose of energy saving and effectively avoid burns during operation. At present, industry insiders are focusing on the excellent characteristics of PCL’s low melting point, and hope to use this characteristic to manufacture children’s printers. In addition, PCL material has the characteristics of shape memory, which makes the printed things have “memory” and can be restored to the original set shape under certain conditions.
Bio-based TPU
It is a new generation of renewable resources with a content of up to 60%. It has excellent mechanical properties, cold bending, hydrolysis resistance, good adhesion, wear resistance, pressure resistance, easy processing and recycling, and lower density than petroleum-based TPU. It is a lightweight and cost-effective raw material that can replace petroleum-based thermoplastic polyurethane and thermoplastic elastomer. In the field of 3D printing, as an elastic line material, it has a wide range of applications, such as printing shoes, bracelets, etc.
Photosensitive resin
Photosensitive resin is composed of polymer monomers and prepolymers, to which light (ultraviolet light) initiators (or photosensitizers) are added. When exposed to ultraviolet light of a certain wavelength (250 to 300nm), it can immediately cause a polymerization reaction and complete curing. Photosensitive resin is generally in liquid form. Its good liquid fluidity and instant photocuring characteristics make it the preferred material for 3D printing consumables for high-precision product printing. Photosensitive resin has a fast curing speed and excellent surface drying performance. After molding, the product has a smooth appearance and can be transparent or translucent frosted. Photosensitive resin has the characteristics of low odor and low irritating components, which is very suitable for personal desktop 3D printing systems. At present, the main companies researching photosensitive material 3D printing technology are 3D System in the United States and Object in Israel .
Polymer gel
Polymer gels have good intelligence. Polymer gel materials such as sodium alginate, cellulose, animal and plant glue, peptone, and polyacrylic acid are used for 3D printing . They polymerize under certain temperature and the action of initiators and cross-linking agents to form special mesh polymer gel products. When the ionic strength, temperature, electric field, and chemical substances change, the volume of the gel will also change accordingly, and it can be used for shape memory materials. The gel swells or shrinks to produce a volume change, which is used for sensing materials; the controllability of the gel mesh can be used for smart drug release materials.
Metal materials
In recent years, 3D printing technology has gradually been applied to the manufacture of actual products, among which 3D printing technology for metal materials has developed particularly rapidly. In the field of national defense, developed countries in Europe and the United States attach great importance to the development of 3D printing technology and have invested heavily in research, and 3D printing of metal parts has always been the focus of research and application. The metal powder used in 3D printing generally requires high purity, good sphericity, narrow particle size distribution, and low oxygen content. At present, the metal powder materials used in 3D printing mainly include aluminum alloys, mold steel, stainless steel, titanium and titanium alloys, cobalt-chromium alloys, nickel-based alloys, etc. In addition, there are precious metal powder materials such as gold and silver used to print jewelry.
Aluminum alloys (AlSi12, AlSi10Mg)
AlSi12 is a lightweight additive manufacturing metal powder with good thermal properties. Its typical application is to manufacture thin-walled parts such as heat exchangers or other automotive, aerospace and aviation industrial prototypes and production parts. The silicon/magnesium combination brings a significant increase in strength and hardness. AlSi10Mg aluminum alloy is suitable for manufacturing thin-walled, complex geometric parts and is an ideal application material for meeting the requirements of good thermal performance and low weight. Canon uses 3D printing technology to manufacture a special curved top cover of magnesium-aluminum alloy on the housing of its top-level SLR camera.
Mold steel (H13)
The suitability of tool steel comes from its excellent hardness, wear resistance and deformation resistance as well as its ability to maintain a cutting edge at high temperatures. High hardness and wear resistance make H13 suitable for many molds (injection molds, light metal alloy casting, stamping and extrusion), and also used in various high-performance industrial engineering parts (aerospace, high-strength fuselage parts and racing cars).
Stainless steel (316L)
Stainless steel powder is a type of metal powder material with high cost performance that is often used in metal 3D printing. It is suitable for printing larger objects. Austenitic stainless steel 316L is widely used for its resistance to corrosion by weak corrosive media such as air, steam, and water, and chemically corrosive media such as acids, alkalis, and salts. 316L can drop to low temperatures over a wide temperature range and can be used in a variety of projects such as aerospace, oil, and natural gas, as well as in food processing and medical fields. 3D printed stainless steel models have high strength.
Titanium Ti and titanium alloy Ti6Al4V
Titanium is an important structural metal. Titanium alloys are widely used in the manufacture of aircraft engine compressor components and various structural parts of rockets, missiles and aircraft due to their high strength, good corrosion resistance and high heat resistance. Titanium and titanium alloys are ideal for many high-performance projects such as aerospace and automotive transportation due to their excellent strength and toughness, corrosion resistance, low specific gravity and biocompatibility. They are also used to produce biomedical implants with high strength, low modulus and strong fatigue resistance. Titanium alloy parts manufactured using 3D printing technology have very high strength and precise dimensions. The minimum size that can be made can reach 1mm, and the mechanical properties of the parts are better than those produced by forging. Metalysis, a British company, successfully printed automotive parts such as impellers and turbochargers using titanium metal powder. In addition, titanium metal powder consumables will have broad application prospects in 3D printing automobiles, aerospace and defense industries.
Cobalt-chromium alloy (Co28Cr6Mo)
Cobalt-chromium alloy is a high-temperature alloy with cobalt and chromium as the main components. This type of alloy has high strength, excellent corrosion resistance, good biocompatibility, and non-magnetic properties. High wear resistance, good biocompatibility, and nickel-free (nickel content < 0.1%) make it commonly used in surgical implants including alloy artificial joints, knee joints and hip joints. It can also be used in engine parts, wind turbines and many other industrial parts, as well as the fashion industry, jewelry, etc. Titanium alloy and cobalt-chromium alloy parts manufactured using 3D printing technology have very high strength and precise dimensions. The minimum size that can be made can reach 1mm, and the mechanical properties of the parts are better than those produced by forging technology.
Nickel-based alloys (In625, In713, In718)
In625 maintains excellent load-bearing performance and corrosion resistance at temperatures as high as 815°C, and is widely used in industries requiring high pitting, crevice corrosion and high temperature resistance, such as aerospace, chemical and power industries. In713 has excellent thermal fatigue resistance and special fracture strength at 927°C, making it ideal for jet engine gas turbine blades. In718 is an iron-nickel hardened superalloy with excellent corrosion resistance and good heat resistance and tensile, fatigue and creep properties, meeting a variety of high-end applications including aircraft turbine engines and land-based turbines (blades, rings, casings, fasteners and instrument parts).
Rare and precious metals
3D printed products are becoming more and more influential in the fashion industry. Jewelry designers around the world benefit the most from using 3D printing rapid prototyping technology as a powerful and convenient alternative to other manufacturing methods. In the field of jewelry 3D printing materials, commonly used materials include gold, sterling silver, brass, etc.
Ceramic materials
Ceramic materials have excellent properties such as high strength, high hardness, high temperature resistance, low density, good chemical stability, and corrosion resistance. They are widely used in aerospace, automotive, and biological industries. The hard and brittle characteristics of ceramic materials make it particularly difficult to process and shape, especially complex ceramic parts that need to be formed through molds. The mold processing cost is high and the development cycle is long, which makes it difficult to meet the needs of continuous product updates.
The ceramic powder used for 3D printing is a mixture of ceramic powder and a certain binder powder. Due to the low melting point of the binder powder, laser sintering only melts the binder powder to bond the ceramic powder together. After laser sintering, the ceramic product needs to be placed in a temperature-controlled furnace for post-processing at a higher temperature. The ratio of ceramic powder to binder powder will affect the performance of ceramic parts. If the binder is high, sintering is easier, but the parts shrink more during post-processing, which will affect the dimensional accuracy of the parts; if the binder is low, it is not easy to sinter. The surface morphology and original size of the particles are very important for the sintering performance of ceramic materials. The smaller the ceramic particles, the closer the surface is to a sphere, and the better the sintering quality of the ceramic layer. The liquid phase surface tension of ceramic powder is large during laser direct rapid sintering, and large thermal stress will be generated during the rapid solidification process, thereby forming more microcracks. At present, the direct rapid prototyping process of ceramics is not yet mature, and it is still in the research stage at home and abroad, and has not yet been commercialized.
Composite materials
Arevo Laboratory in Silicon Valley, USA, 3D prints high-strength carbon fiber reinforced composite materials. Compared with traditional extrusion or injection molding methods, 3D printing optimizes specific mechanical properties, electrical properties and thermal properties by precisely controlling the orientation of carbon fibers, and strictly sets their comprehensive properties. Since 3D-printed composite parts can only be manufactured one layer at a time, each layer can achieve any desired fiber orientation. Complex-shaped parts printed in combination with reinforced polymer materials have excellent high temperature and chemical resistance. Arevo uses this material to print lighter, stronger and more durable parts for aerospace, defense and medical applications. Solvay will use three grades of KetaSpire PEEK resin qualified by Airbus for the manufacture of aircraft interiors. In addition to carbon fiber, glass fiber can also be used as the reinforcing phase in the composite material. Solvay’s Radel R-7000 PPSU resin, which was previously qualified by Airbus, is a material specifically designed for aircraft interiors.
Smart Materials
Smart material structures, also known as smart/intelligent materials and structures, can integrate the three functions of sensing, control and driving to complete the corresponding response under the stimulation of external environment, such as electromagnetic field, temperature field, humidity, light, pH value, etc. Smart material structures have the self-value-added, self-repairing, self-diagnosis, self-learning and environmental adaptability that imitate organisms.
There are many ways to classify smart materials. According to their functions and components, they can be roughly divided into: electroactive polymers, shape memory materials, piezoelectric materials, electromagnetic rheological materials, magnetostrictive materials, etc. Smart material structures have important applications in many fields, such as aerospace vehicles, intelligent robots, biomedical devices, energy recovery, structural health monitoring, vibration and noise reduction, etc.
However, due to the complexity of smart material manufacturing process, traditional smart material manufacturing methods can only manufacture smart materials of simple shapes, and it is difficult to manufacture smart material structures of complex shapes. The traditional preparation methods of smart materials have severely restricted the development and application of smart material structures. The recently developed smart material 3D printing technology makes it possible to manufacture smart material structures of arbitrary complex shapes. The newly proposed 4D printing technology combines 3D printing technology with smart material structures. Based on 3D printing, smart material structures can realize their own structural changes over time under the stimulation of the external environment.
3D Printing Electroactive Polymer Materials
Electroactive polymer materials (EAP) are a new type of flexible functional materials that can produce large changes in size or shape under electric field stimulation, and are an important branch of smart materials. Ionic polymer-metal composites (IPMC), Bucky Gel and dielectric elastic materials (DE) are typical representatives of EAP . Fabricating three-dimensional complex-shaped electroactive polymer structures is an important research topic in this field.
Bucky Gel is a newly developed ionic electroactive polymer smart material. The composition and driving sensing principle of Bucky Gel are similar to IPMC. Bucky Gel consists of a three-layer structure. The middle matrix material is an electrolyte layer composed of polymer and ionic liquid. The two sides of the matrix material are electrode materials composed of carbon nanotubes, polymer and ionic liquid. When voltage is applied to the electrodes on both sides, the anions and cations in the ionic liquid move toward the two electrodes, causing the Bucky Gel to bend. The traditional preparation of Bucky Gel often adopts the solution casting method, and the electrode and matrix layer are solidified separately in layers. The prepared Bucky Gel is mostly in the form of sheets, and it is difficult to prepare Bucky Gel with complex shapes. In 2008, N. Kamamichi proposed to use 3D printing technology to manufacture Bucky Gel. Using 3D printing technology, the electrode-matrix material-electrode can be solidified point by point, and Bucky Gel with any complex shape can be prepared. The use of 3D printing technology can overcome the defects of traditional preparation methods and manufacture Bucky Gel smart material structures with any shape. The research team used 3D printing technology to create hand-shaped Bucky Gel.
Shape memory materials
Including shape memory alloy (SMA), shape memory colloid (SMG), shape memory polymer (SMP) , etc. The biggest feature of shape memory material is the shape memory effect. It is shaped at high temperature and plastically deformed at low temperature or room temperature. When the ambient temperature rises to the critical temperature, the deformation disappears and returns to the original state of the shape. This phenomenon of recovery after heating is called shape memory effect.
Other 3D printing materials
In addition to the 3D printing materials introduced above, other materials currently used include colored plaster materials, artificial bone powder, cell biological raw materials, and sugar.
Colored gypsum material is a full-color 3D printing material that is based on gypsum, brittle, strong and clear in color. Based on the molding principle of layer-by-layer printing on powder media, after the 3D printed product is processed, a subtle granular effect may appear on the surface, which looks very much like rock, and a subtle annual ring-like texture may appear on the curved surface. Therefore, it is mostly used in fields such as anime dolls.
3D printing technology, combined with medicine and tissue engineering, can produce drugs, artificial organs, etc. for treating diseases.
The ” bone printer ” being developed in Canada uses technology similar to that of an inkjet printer to transform artificial bone powder into precise bone tissue. The printer sprays an acidic agent on a film made of bone powder to make it harder.
The fresh meat printed by the University of Pennsylvania in the United States is made by first using a cell medium cultured in the laboratory to generate a substitute substance similar to fresh meat, using a water-based sol as a binder and then combining it with special sugar molecules.
There is also bio-ink made from human cells , which is still in the conceptual stage, and equally special bio-paper. When printing, the bio-ink is sprayed onto the bio-paper under computer control, eventually forming various organs.
In terms of food materials, the sugar 3D printer CandyFab4000 can currently make beautiful and delicious desserts in various shapes by spraying heated sugar.
