[3D Printing Knowledge] Beginner's Guide: Comparison and Mechanisms of 5 Common 3D Printing Technologies (Updated September 2021)

Compared to mold making, 3D printing allows for cost reduction through in-house manufacturing and enables highly flexible rapid prototyping. Currently, the most commonly used 3D printing technologies on the market are FDM (Fused Deposition Modeling), SLA/DLP/LCD (SLA/DLP/LCD), and SLS (Selective Laser Sintering). In addition, new 3D printing technologies such as the more advanced MJF (Multi Jet Fusion) and PolyJet (Color Inkjet) are also emerging. Beginners, don't worry! Let's explain them together in an easy-to-understand way! The fundamental principle common to all 3D printing technologies is to horizontally slice a 3D CAD model into individual cross-sectional data, and then stack them sequentially to create a three-dimensional object. However, there are essential differences in the manufacturing methods of FDM, LCD, and SLS technologies. The following provides a detailed explanation of each technology.

In 3D printing technology, the effects of gravity must be considered during manufacturing. Imagine an object floating in the air; it would fall downwards. Therefore, if 3D printing material reaches an overhang structure during printing, auxiliary material needs to be created to prevent the material from sagging and to form the airborne part. This structure is generally called support material, and its usage and material vary depending on the printing method. Among these, SLS (Selective Laser Sintering) technology typically does not require such support structures. More details will be explained later.
FDM is the most widely used 3D printing technology (also known as FFF). Its 3D printing material is typically a thermoplastic polymer supplied on a reel, commonly called filament. Standard filament diameters are 1.75mm or 3mm (or 2.85mm) and are extruded from a heated nozzle. The heated nozzle is attached to a motion mechanism, which extrudes the material layer by layer within the print area, stacking, cooling, and solidifying it to complete the object. 3DMart mainly handles FDM Fused Deposition 3D printers from brands such as Ultimaker, BCN3D, Prusa, and Snapmaker.
FDM is generally suitable for office environments, easy to operate and maintain, and does not require post-processing with chemicals. The variety of usable materials is very wide, and they are relatively inexpensive, easy to handle, and can be stored for long periods. FDM technology sometimes requires support structures, but careful CAD design can effectively reduce the amount of support material. The market ranges from early single-nozzle types to the latest dual-nozzle types, allowing two types of materials to be used simultaneously in a single print. By combining two different compatible materials (e.g., water-soluble PVA support material), products with mechanical functions such as snap-fit structures and moving parts can be directly printed. Additionally, using easily removable separation material can improve the smoothness and texture of the product surface, reducing post-processing.
Stereolithography technology uses liquid resin as material. Resin is poured into a resin tank, and with the build platform submerged in the resin, light is irradiated by a light exposure panel or a UV laser. The irradiated resin hardens to form a shape, and the platform rises from the resin tank, stacking layer by layer to create the object. Depending on the light exposure method used, it is called SLA (laser), DLP (projector), or LCD (LCD panel), but the basic technological principle is almost the same. In industrial applications, SLA has higher accuracy than DLP and LCD, and is therefore more expensive. On the other hand, the most accessible method is LCD, which can be purchased for less than approximately 8,000 New Taiwan Dollars.
Stereolithography technology is suitable for complex parts with fine details and jewelry designs. Support structures are required in almost all cases, but it can also be used in small workspaces or technical laboratories with adequate ventilation. Post-processing is more complex compared to FDM technology, typically requiring cleaning with alcohol. Also, depending on the application, additional irradiation may be performed in a UV curing box to enhance curing. Some resin materials have an irritating odor or are flammable, and their shelf life is relatively short. Additionally, new resin and used resin cannot be mixed. Material costs are higher than the other two types of technologies, but objects printed with stereolithography technology can achieve the smoothest surface quality and are suitable for producing precise objects and small part prototypes.
SLS technology uses powdered polymers as 3D printing material. When powdered material is loaded into the device, an internal mechanism evenly spreads a thin layer of powder across the entire build area, after which a laser fuses the material. By repeating the layering with slight height changes, the final object is completed. Since the powdered material fills the entire build area, no support structures are needed during printing (the entire object is supported by densely packed powder before printing is completed, preventing material from falling in hollow sections). Unused powder can be sieved with specialized equipment and then mixed with new powder for reuse.
SLS technology is suitable for creating complex structures, highly movable parts, and delicate airborne details. The finished product has a matte texture, and layer lines are less noticeable. In terms of initial setup and maintenance, SLS is relatively more expensive among the three 3D printing technologies, and the operational difficulty and complexity of the equipment are also higher than the previously mentioned FFF and LCD technologies. When 3D printing, it is recommended to maximize the build volume of the equipment as much as possible to reduce powder waste.
・FDM fused deposition modeling is the most popular method due to its economic efficiency. Its relatively small equipment size and easy operation allow even small and medium-sized enterprises to adopt it quickly. Furthermore, it minimizes the need for post-processing and waste disposal. Due to its large user base, there is an abundance of related information and tutorials. However, because it is relatively easy to enter the market, there are many brands with varying quality, requiring careful comparison before purchase.

・SLA stereolithography technology is highly suitable for printing small objects with complex details, figures, design models, and jewelry. The surface of the finished product is smooth, allowing for the expression of intricate patterns and shapes, but its physical strength and mechanical performance are relatively lower among the three technologies.

・SLS selective laser sintering technology offers excellent mechanical performance and functionality, making it suitable for industrial prototyping. The surface has a matte texture, requires no support structures, and the finished product typically boasts superior strength and durability. However, the operational difficulty is relatively high, and masks must be worn during powder removal.

The three technologies each have different characteristics, and there is no simple superior or inferior choice. With proper design, any of these technologies can be used for 3D printing movable structures or using flexible materials. These desktop 3D printers are sized perfectly for rapid in-house prototyping, significantly contributing to reduced product development time and costs.

Having understood these basic principles, you should now have a grasp of how stereolithography and SLS powder bed fusion technologies work. In recent years, new 3D printing technologies that have further developed from these two include PolyJet (Color Inkjet) and MJF (Multi Jet Fusion):

・PolyJet (Color Inkjet)
PolyJet is a technology that directly jets resin using an inkjet method and utilizes the principles of stereolithography to cure it instantly with high-speed light irradiation. By repeating the curing process layer by layer, the 3D print is completed. Since the inkjet method allows for mixing multiple colors, full-color 3D printing, texture simulation, and even the appearance of glass or acrylic using the inherent transparency of the resin are possible.
With further advancements in technology, PolyJet can now express up to 500,000 colors based on the Pantone color guide. Furthermore, it can simultaneously print up to five types of resin, allowing for adjustment of the hardness and softness of the printed object. This makes PolyJet technology a new option for product design and development and product renewal, enabling full-color expression in a single printing process.
PolyJet technology was primarily developed by the 3D printing giant Stratasys and is currently used as an industrial-grade device costing over 1 million Taiwan dollars. However, we also offer 3D printing services, enabling high-quality prototyping at a lower cost.
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・MJF (Multi Jet Fusion)
The features of SLS powder printing, such as integrated movable structures and no need for support, are very attractive. However, there is more than one type of powder 3D printing method. HP (Hewlett-Packard)'s MJF technology (Multi Jet Fusion), from a global leading manufacturer, is another additive manufacturing method using powdered materials. Powder is evenly spread on the print platform, then a fusing agent is jetted into the build area and a detailing agent to prevent sintering in non-build areas. Subsequently, infrared light is applied, causing the areas coated with the fusing agent to absorb heat, melt, and bond. This process is repeated layer by layer to complete the 3D print.
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