[3D Printing Knowledge] Beginner's Guide: Comparison and Principles of Five Common 3D Printing Technologies (Updated Sep 2021)

Compared to traditional molding, 3D printing allows for significant cost reduction in internal manufacturing and offers greater freedom for rapid prototyping. Currently, the three most commonly used 3D printing technologies on the market are FDM (Fused Deposition Modeling), SLA/DLP/LCD (Resin 3D Printing), and SLS (Selective Laser Sintering). In addition, there are more advanced new types of 3D printing such as MJF (Multi Jet Fusion) and Polyjet (Color Inkjet). Beginners, don't worry, let us guide you through easy-to-understand explanations! A common principle for all 3D printing technologies is to horizontally slice a 3D CAD model into individual cross-sections, which are then stacked sequentially to form a three-dimensional object. However, the methods used by FDM, LCD, and SLS technologies are fundamentally different, and each will be explained individually below.

The formation method of 3D printing technology needs to consider the effect of gravity. Imagine an object suspended in mid-air would fall. Therefore, when 3D printing materials encounter unsupported structures during formation, additional auxiliary materials are needed to create the suspended main body to prevent the material from falling during formation. This structure is usually called support material, and its usage and materials vary depending on the printing method. Among them, SLS (Selective Laser Sintering) technology typically does not require such support structures, which will be explained below.
FDM is the most common 3D printing technology (also known as FFF). Its 3D printing material is typically a thermoplastic polymer delivered on a spool, commonly referred to as filament. The standard filament diameters are 1.75mm or 3mm (or 2.85mm), which are then extruded through a heated nozzle. The heated nozzle is mounted on a movable gantry, allowing the extruded material to be stacked layer by layer, cooled, and solidified on the build plate within the printing area to complete the object. 3DMart primarily carries FDM fused deposition 3D printers from brands such as Ultimaker, BCN3D, Prusa, Snapmaker, and more.
FDM is generally suitable for office environments, easy to operate and maintain, and requires no chemical post-processing. The available materials are diverse, relatively inexpensive, easy to use, and can be stored for long periods. FDM technology sometimes requires support structures, but careful CAD modeling design can effectively minimize support material. On the market, you can find two main types: the earliest single-nozzle and the latest dual-nozzle. With a dual-nozzle, two materials can be used simultaneously in a single print. By using two different types of compatible materials (e.g., water-soluble PVA support material), products with mechanical functions such as snap-fits and rotations can be printed directly. Alternatively, peel-away separation materials can be used to achieve a smoother surface, high quality, and reduced post-processing for the product.
Resin 3D printing technology uses liquid resin as the raw material. Resin is poured into a resin tank, and the print platform is immersed in it. A light panel or UV laser beam then irradiates the print platform. The irradiated resin hardens and forms a layer, and the platform rises from the resin tank to stack layers and form the object. This technology is often referred to by different abbreviations based on the light source used: SLA (laser), DLP (projector), LCD (LCD panel), etc., but the underlying principle is largely the same. In terms of industrial precision, SLA is superior to DLP and LCD, and its price is also significantly higher. The most affordable option is LCD technology, which can be purchased for under NT$8,000.
Resin 3D printing technology is suitable for complex parts with fine details or jewelry design. Support structures are almost always required. It can be used in well-ventilated small workshops or technical laboratories. Post-processing is more complex compared to FDM technology, usually requiring cleaning with alcohol or, depending on the requirements, placing in a UV chamber for additional curing. Resin materials can be pungent, flammable, and have a shorter shelf life. Old and new resins cannot be mixed, and material costs are relatively higher than the other two technologies. However, resin 3D printing produces the smoothest surface finishes, making it suitable for delicate models or prototypes of small parts.
SLS technology uses powder polymer as the 3D printing material. The powder is poured into the machine, which then lays down a thin layer of powder back and forth within the printing area. A laser beam then fuses the material, and the print is completed by stacking layers through slight vertical movements. Because the powder printing material fills the entire internal space, no support structures are needed for formation (as the entire volume is filled with compact powder before printing is complete, there is no issue of hollow material falling). Unused powder can be sieved using specialized equipment and then mixed with new powder for reuse.
SLS technology is suitable for designs with complex structures, high mobility, and many unsupported details. The finished product has a matte texture and is less prone to visible layer lines. In terms of initial setup and maintenance, SLS is the most expensive of the three 3D printing technologies, and the difficulty and complexity of operating the equipment are relatively higher than FFF and LCD technologies mentioned earlier. It is recommended to utilize the entire internal printing volume of the machine as much as possible for each 3D print to avoid wasting powder.
．FDM fused deposition modeling technology is the most common due to its affordability, small size, and ease of operation. Small and medium-sized enterprises can quickly get started, and it requires minimal post-processing and waste disposal. Because it is the most widely used, there are more related resources and instructional discussions; however, due to its relative ease of development, the market is flooded with brands of varying quality, so careful comparison is necessary when purchasing.

．SLA resin 3D printing technology is very suitable for printing small objects with complex details, figurines, artistic models, jewelry, etc. The finished surface is smooth and can display complex textures, but its physical and mechanical properties are less robust among the three technologies.

．SLS selective laser sintering offers the best mechanical and functional properties, emphasizing industrial prototyping applications. Its surface has a matte texture, requires no supports, and the finished product is relatively robust and durable; however, it is more difficult to operate and requires wearing a mask to clear powder.

Each of the three technologies has its strengths, and there is no distinction between good and bad. With proper design, all can 3D print movable structures and flexible materials. These desktop 3D printing machines are appropriately sized, allowing for rapid prototyping internally within companies, effectively shortening development time and costs.

With the basic concepts covered earlier, you should now understand the operating principles of resin 3D printing and SLS powder sintering. In recent years, these two technologies have also evolved into new 3D printing capabilities, namely PolyJet (Color Inkjet) and MJF (Multi Jet Fusion):

．PolyJet (Color Inkjet)
PolyJet directly uses resin as inkjet ink, and with the curing principle of resin 3D printing, it uses rapid light exposure to immediately cure after jetting, layer by layer, to complete the 3D print. Because the inkjet method allows for multi-color mixing, it can achieve full-color 3D printing, material simulation, and even replicate the appearance and texture of glass, acrylic, etc., by leveraging the resin's inherent transparency.
As technology advances, PolyJet can not only produce up to 500,000 color combinations based on Pantone color swatches but also print up to five resins simultaneously and adjust the hardness of the printed product, making PolyJet technology a new choice for design and development and product iteration. The full-color effect can be achieved directly in a single print!
PolyJet technology was primarily developed by the leading 3D printing manufacturer Stratasys. Currently, it is an industrial machine costing over a million. However, we also offer 3D printing services, allowing you to spend less and achieve more!
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．MJF (Multi Jet Fusion)
The one-piece movable structure and support-free nature of SLS powder printing are astonishing, but there's more than one way to do powder 3D printing. HP's MJF technology (Multi Jet Fusion) is another form based on powder printing: after laying powder flat on the print bed, a fusing agent is sprayed in the build area and a detailing agent is sprayed in non-build areas to prevent sintering. Then, infrared light is applied, and the areas sprayed with the fusing agent absorb heat, melt, and solidify. This process is repeatedly layered to complete the 3D print.
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