What is 3D Printing Technology (3DP)?

Ⅰ. What is 3D printing technology?

3D printing technology, also known as additive manufacturing, is a technology that builds realistic three-dimensional objects by layering bondable materials layer by layer based on digital model files. As one of the "12 disruptive technologies that determine the future economy" and the engine of the third industrial revolution, 3D printing marks a huge industrial change from traditional manufacturing to intelligent manufacturing, triggering a new wave of technological revolution.

Compared with traditional manufacturing technology, 3D printing technology has the characteristics of "removing molds, reducing waste and reducing inventory". In production, it can optimize the structure, save materials and save energy, greatly improve manufacturing efficiency, and achieve "design-led manufacturing". Innovative idea.

Figure 2: General 3D printing process

Ⅱ. 3D printing development history

Throughout the development history of 3D printing technology, it can be traced back to the stereolithography appearance (SLA) invented by American scientist Charles Hull in 1984. Subsequently, technologies such as selective laser sintering (SLS), selective laser melting (SLM), and three-dimensional printing and gluing (3DP) were gradually developed.

Since the beginning of the 21st century, 3D printing technology has made a new breakthrough, and the world has officially entered the stage of rapid development of 3D printing, and various innovative sub-processes have gradually emerged under the subdivision of large-scale technologies to meet the needs of specific industries form an effective complement to traditional manufacturing.

Ⅲ. Classification of 3D printing methods

According to the  ISO /ASTM 52900: 2015 standard issued by the Additive Manufacturing Technical Committee under the International Organization for Standardization, 3D printing process solutions are mainly divided into seven categories.

Material extrusion

Material is selectively deposited through nozzles or orifices, etc. Fused deposition modeling (FDM) is one of the most intuitive and common printing methods. During printing, the equipment heats and melts the filamentous hot-melt material, extrudes and selectively deposits the material on the platform through a nozzle with fine nozzles, forms a layer of cross-section after cooling, and prints layer by layer until the entire entity is formed. . The printing materials are mainly polymers and plastics, including polylactic acid PLA, thermoplastic polyurethane elastomer TPU and acrylonitrile butadiene styrene ABS, etc.

Advantages: the low price of equipment and consumables, a wide range of materials, high strength of printed products.

Disadvantages: The printing accuracy is low, and the surface roughness of the printed sample is large.

Vat photopolymerization

Selective photocuring of liquid polymers using specific wavelengths of light. The materials used in this type of technology are photosensitive resins, which undergo a morphological transition from liquid to solid when exposed to light, thereby enabling the printing process. According to the type of light source, irradiation method, and molding method, it can be divided into stereolithography (Stereolithography appearance, SLA) and digital light processing (Digital light processing,  DLP ), etc., and their principles and printing processes are different. Among them, SLA  uses a laser to scan the liquid resin surface point by point, solidifies the point-line surface sequentially to complete the molding of one level, and then cooperates with the moving of the molding platform to superimpose layer by layer to form a three-dimensional entity.  DLP uses whole-surface exposure to form one layer. The light source is mostly an LED ultraviolet light source, and the exposure pattern of each layer is generated by spatial light modulators such as digital dynamic mask chips.

Advantages: high processing precision, smooth surface of printed products, high efficiency of whole surface exposure and forming.

Disadvantages: limited material range, weak material properties.

Directed energy deposition

The melt-and-deposit process uses focused thermal energy to melt materials. It mainly includes laser synchronous powder feeding (LENS, LBMD, LSF) and electron beam fuse deposition (Electron beam direct manufacturing, EBDM), etc., which are mostly used to build or repair existing structures. The process is that an energy source such as a laser beam generates a molten pool in the deposition area and moves at a high speed, and a nozzle sends filamentous or powdered materials (such as titanium and cobalt-chromium alloys) into a high-temperature area to be heated to the melting point and then deposited layer by layer after melting. The nozzle or table is mounted on a highly movable arm, enabling a high degree of flexibility in movement.

Advantages: no support, high processing flexibility, efficient preparation, and repair of components can be achieved.

Disadvantages: The precision of the machined surface is limited, the molding sample needs to be reprocessed (such as with a milling machine, etc.), and it is difficult to repair parts with complex structures.

Material jetting

A 3D evolution of the 2D inkjet printer. Material jetting can be divided into continuous material jetting (CMJ), nanoparticle jetting (NPJ), and drop-on-demand (DOD). The basic principle is to use a charged deflection plate and an electromagnetic field to precisely position the ejected material on the printing platform, and use an ultraviolet light source for curing and molding. Material jetting is very similar to Stereolithography (SLA) above, except that the former can jet hundreds of tiny droplets at a time, while SLA  is selectively cured point-by-point with a laser in a full vat of resin. The sprayed photosensitive droplet material contains polymers and plastics such as acrylonitrile butadiene styrene ABS and polypropylene PP.

Benefit: Enables high-accuracy full-color fast printing, increasing the aesthetic quality of prototypes and final parts.

Cons: Limited material range, expensive, requires post-processing to remove excess material.

Binder Jetting

Also known as three-dimensional printing and gluing (3DP), powder molding is achieved by spraying adhesives. The main process is to pack a powdered material such as ceramic or polymer into a container, use an inkjet printhead to spray a binder into the powder, just like sand mixed with water will create a stronger structure, a layer of powder will be in selected areas Bonding occurs inside, repeating this process, the next layer of powder will be integrated with the previous layer of powder through the penetration of the adhesive so that the layers are stacked and formed. When the materials used are metal and ceramic materials, it is necessary to remove the binder through high-temperature sintering and achieve metallurgical bonding between powder particles so that the finished product has a certain strength and density.

Advantages: high molding efficiency, different colors can be printed in the same batch, no support structure required.

Disadvantages: high toughness, low density of molded parts, and post-processing such as degreasing and sintering for metals and ceramics. For polymers, waxes may need to be added to increase structural strength.

Powder bed fusion

This is another powder bed-based method that is mainly used for the printed manufacturing of metal parts. Unlike the printing methods described above, powder bed melting does not involve depositing a binder to achieve printing, mainly represented by Selective laser sintering (SLS), Selective laser melting (SLM), and electronics Electron-beam selective melting (EBSM), etc. The process of powder bed melting is generally as follows: the powder material stored in the hopper and the material container is evenly coated on the surface of the printing platform using a powder spreading roller. The powder is melted and sintered to hold it together, and then a layer of powder is applied and the next layer is sintered until the entire body is formed. Among them, the electron beam selective melting will preheat the powder bed, and the temperature of the entire chamber can reach up to thousands of degrees, which greatly reduces the residual stress of the formed parts; SLS  needs to add additional binders, such as low melting point metals or resins materials, etc.

Advantages: High precision, can print metal (such as titanium, aluminum, copper, stainless steel and high-temperature alloys, etc.), ceramics and nylon, and other materials.

Disadvantages: high cost, easy to warp when printing large-sized objects, slow speed.

Sheet lamination

The material is laser cut and bonded together by adhesive or welding to form a solid. Unlike the other process methods listed above, the sheet lamination printing technology can be used for almost any other material that can be curled in addition to metal plates, or even paper. Sheet lamination mainly includes layered entity manufacturing (LOM) and ultrasonic additive manufacturing (Ultrasonic additive manufacturing,  UAM ).  LOM  is the use of glue to bond multiple layers of paper and cut with a sharp knife without heating or melting. Each sheet is cut slightly differently.  UAM is the use of ultrasonic welding machines to bond metal sheets or strips, each metal layer is rolled on the growing structure, the biggest technical advantage is low temperature, suitable for low melting point materials that are sensitive to temperature.

Advantages: fast forming speed, high precision, small warpage deformation.

Disadvantages: poor adhesion between layers, obvious anisotropy in the structural strength of the molded sample, the low utilization rate of materials, and only simple structural parts can be produced.

Ⅳ. What is 3D printing used for?

Driven by a large amount of R&D investment in scientific research and the industry, 3D printing's ability to upgrade the manufacturing industry is aimed at innovation, starting from the depth and breadth of the introduction of the application side, enabling value and creating revolutions for various downstream industries, covering areas including aerospace Military industry, automobiles and ships, energy and power, life and medical care, cultural creativity and architecture, etc.

Figure 3: Deep Blue Rocket Test Flight

In the fields of aviation and energy, recently, Arris Composites of the United States and Airbus have cooperated with the 3D printing carbon fiber composite material market to make mass production to create lightweight cabin brackets; Solvay has cooperated with OEM 9T Labs to 3D print carbon fiber reinforced plastic parts. Introduce mass production for the production of small and medium-sized components required by industries such as aerospace, automation, and oil and gas.

Looking back at China, the 3D printing industry has ushered in an opportunity for rapid development under the guidance of "Made in China 2025", which is helping the rapid development of domestic commercial rockets. In February 2021, Chongqing One Zero Space used 3D printing attitude control power system products to fly for the first time, and in July 2021, the low-altitude vertical recovery flight test of the deep blue aerospace liquid rocket manufactured by 3D printing was successful. It can be seen that 3D printing has spawned a new track for rocket manufacturing, and has gradually become an important supporting technology in the rocket manufacturing process.

The development in the manufacture of medical prostheses is not limited to orthopedics, artificial ears, etc., but also includes eye prostheses. In November 2021, the Fraunhofer Institute in Germany made a breakthrough in the clinical application of 3D printed artificial eyes Indicates the commercialization trend of 3D printing to manufacture medical prostheses.

It is believed that with the continuous exploration of demand, the continuous guidance of policies, and the gradual standardization of industry standards, the breadth, and depth of 3D printing applications will be further accelerated.

Figure 4: 3D Printed Bionic Eyeball

3D printing technology has only been in existence for more than 30 years since its birth in the 1980s, but it is leading the world's manufacturing revolution. As a representative of "Internet + intelligent manufacturing", it almost perfectly meets the requirements of customization and mass production and shows infinite creativity in many fields. The 3D printing industry is entering a growth stage. It is estimated that the global 3D printing output value is expected to reach 37.2 billion US dollars by 2026, and the global competition has kicked off. However, how to achieve precision, intelligence, generalization, and convenience is an important issue in front of 3D printing technology. It is expected that on the road of continuous improvement and refinement, it will bring milestone changes to future intelligent manufacturing.

Frequently Asked Questions about 3D Printing Technology:

1. What is 3D printing？

3D printing (3DP), a type of rapid prototyping technology, first appeared in the mid-1990s. It is a technique of constructing objects by layer-by-layer printing using bondable materials such as powdered metal or plastic, based on digital model files. 

2. When was 3D printing invented?

3D printing technology was invented in the mid-1990s.

3. What can 3D printing print?

Different 3D printers print different things. 3D printers can print metal materials, some models with low precision requirements, and high-precision models Can even print human organs.

4. What is 3D printing material?

3D printing materials are generally divided into two categories: metal and non-metal, including polylactic acid, ABS, aluminum dioxide, nylon, ceramics, high temperature, high toughness, high strength photosensitive resin, translucent photosensitive resin, soft 3D printing, DLP imported red wax, DLP imported blue wax, all-cobalt color 3D printing, CNC ABS processing, desktop ABS plastic and other dozens of materials. Metal 3D printing materials: gold, silver, aluminum alloy, stainless steel, titanium alloy, and other materials. The popular materials today are plastics (ABS&PLA), high detail resins,

High strength flexible nylon, colored sand, and casting waxes and resins

5. What is the difference between 3D printing and ordinary printing?

1. The computer templates are different. Ordinary printing requires templates that can construct various plane graphics, such as word, PowerPoint, PDF, photoshop, etc. as the basic template; 3D printing design is based on 3-dimensional graphics.

2. The printing materials are different. The common printing material is ink; while 3D printing materials are various, such as thermoplastics, titanium alloys, gypsum, photopolymers, and liquid resins. What these materials have in common is their ease of molding.

3. The printing time is different. Typing a document with dozens of pages can take at most a few minutes, while 3D printing can take days.