3D Printing (Introduction, Principles and Technology)3D Printing (Introduction, Principles and Technology)

3D printing is a kind of rapid prototyping technology. It is a digital model file based on the use of powdery metal or plastic and other bondable materials. Techniques for constructing objects (ie, the “layering method”). In the past, it was often used to make models in the fields of mold manufacturing and industrial design, but now it is gradually used in the direct manufacturing of some products. In particular, some high-value applications (such as hip joints or teeth, or some aircraft parts) already have parts printed using this technology, which means the popularity of “3D printing” technology.

The technology has applications in jewelry, footwear, industrial design, architecture, engineering and construction (AEC), automotive, aerospace, dental and medical industries, education, geographic information systems, civil engineering, guns, and other fields.

Three-dimensional design

The design process of 3D printing is: first modeling by computer-aided design (CAD) or computer animation modeling software, and then “splitting” the built three-dimensional model into layer-by-layer sections to guide the printer to print layer by layer.

The standard file format for collaboration between design software and printers is the STL file format. An STL file uses triangular faces to roughly simulate the surface of an object. The smaller the triangle, the higher the surface resolution it produces. PLY is a scanner that generates three-dimensional files by scanning. The VRML or WRL files generated by them are often used as input files for full-color printing.

2. The printing process

The printer reads the cross-section information in the file, prints these sections layer by layer with liquid, powder or sheet materials, and then glues the layers’ sections in various ways to create an entity. The feature of this technology is that it can make almost any shape of an object.

The thickness of the cross-section printed by the printer (ie, the Z direction) and the resolution in the plane direction (ie, the X-Y direction) are calculated in dpi (pixels per inch) or micrometers. The typical thickness is 100 microns, or 0.1 mm. Some printers, such as the Objet Connex series and 3D Systems’ ProJet series, can print a thin layer of 16 microns. The plane direction can print a resolution close to that of a laser printer. Printed “ink droplets” are typically 50 to 100 microns in diameter. It usually takes hours to days to make a model using traditional methods, depending on the size and complexity of the model. The 3D printing technology can shorten the time to several hours, of course, it is determined by the performance of the printer and the size and complexity of the model.

Traditional manufacturing techniques such as injection molding can mass-produce polymer products at a lower cost, while 3D printing technology can produce a relatively small number of products faster, more flexibly, and at a lower cost. A desktop-sized 3D printer can meet the needs of designers or concept development teams to make models.


At present, the resolution of 3D printers is sufficient for most applications (the curved surface may be rough, like jagged on the image). To obtain higher resolution items, you can use the following methods: first use the current 3D The printer hits a larger object, and then grinds it slightly to get a “high-resolution” item with a smooth surface.

Some technologies can print on multiple materials at the same time. Some technologies also use a support during the printing process. For example, when printing some objects with an upside down shape, it is necessary to use something that is easy to remove (such as soluble things) as a support.

Fused deposition modeling (FDM): Some 3D printers use the “jet” method. The entire process is to melt plastic in the nozzle and then form a thin layer by depositing plastic fibers.

Advantages: higher molding accuracy, higher strength of the molded object, color molding, but rough surface after molding.


2. Stereolithography (SLA): Netizens can imagine cutting a cucumber into thin slices and then forming a whole root. The software first cuts the 3D digital model into several planes, which forms many sections. When working, there is a platform that can be lifted. There is a liquid tank around this platform, and the tank is filled with The solidified liquid can be irradiated with ultraviolet rays. The ultraviolet laser will start from the bottom layer, solidify the bottom layer, and then move the platform down to solidify the next layer, and so on until it is finally formed.

Advantages: high precision, can show accurate surface and smooth effect, precision can reach 0.05mm to 0.15mm per layer thickness. The disadvantage is that the materials that can be used are limited and multi-color molding is not possible.


3. Selective laser sintering (SLS): formed using powdery materials. Spread the material powder on the upper surface of the formed part and scrape it flat; use a high-intensity CO2 laser to scan the section of the part on the new layer just laid; the material powder is sintered together under high-intensity laser irradiation to obtain The cross section of the part is bonded to the formed part below; when the cross section of one layer is sintered, a new layer of material powder is placed and the lower section is selectively sintered.

Advantages: It is much stronger than SLA, and can usually be used to make structural and functional parts. Laser beam selectively fuses powder materials: nylon, elastomers, and metals in the future. Advantages of SLA: materials are diverse and performance is close to ordinary engineering. Plastic material; no rolling step, so Z-direction accuracy is not easy to guarantee; simple process, no rolling and masking steps are needed; using thermoplastic materials can be used to make parts such as living hinges; the surface of the molding is powdery and porous. Sealants can improve and strengthen parts; brush or blow can be used to easily remove unsintered powder material from the prototype.

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