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3D printing from scratch

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Theory

Core principle

The traditional machining process, whether it is cutting, cutting, drilling, planing, or milling and grinding, is a “subtraction” method for materials, that is, to remove part of the material to shape the object. This is not the case with 3D printing, which uses the “additive” method—a three-dimensional object is made by adding materials layer by layer. Therefore, “layered manufacturing, layer by layer” is the core principle of 3D printing.

work process

The working principle determines the working process. The 3D printing process can generally be divided into such several steps.

1. Use computer-aided design (CAD) or computer animation modeling software to model, and “slice” and layer the built three-dimensional model to form a layer-by-layer cross-section, and then connect it through the network, U disk or local Wait to send the file to the 3D printer.

The standard file format for collaboration between design software and printer is usually STL. STL files use triangular faces to simulate the surface of an object. The smaller the triangular faces, the higher the resolution of the generated surface.

2. The 3D printer uses liquid, powder, sheet, or linear consumables to print out the “cut” cross-sections layer by layer, and bond them in various ways to form the desired shape.

The thickness of the cross-section printed by 3D printing is usually calculated in microns, and the general thickness is 100 microns, that is, 0.1 mm. Some printers can even print a layer of only 16 microns thick. As for the resolution in the plane direction, it can be close to the accuracy of a plane laser printer. The diameter of the “ink drop” is only 50 to 100 microns.

3. Take out the typed objects for further processing.

The resolution of the 3D printer is sufficient for most applications, but the curved surface may be rougher, just like the jaggedness on the image with insufficient sharpness, you want higher “resolution” or anti-aliasing , It is necessary to reprocess the finished parts. You can use a 3D printer to print out a slightly larger item, and then polish the surface to get a “high-resolution” item with a clear and beautiful outline.

In addition, some items will use supports in the printing process, so the finished piece must be carefully processed to remove the supports.

Molding

According to different forming mechanisms, 3D printing processes can be divided into many types. Different processes have their own advantages and disadvantages, and have different requirements for materials and equipment. At present, there are mainly 5 technologies with more mature technology and more common applications.

1. FDM: Fused deposition molding.

FDM is widely used, and the forming principle is relatively simple: use high temperature to melt the linear consumables into a liquid state, extrude it from the nozzle, and then cool and solidify; this cycle repeats and builds layer by layer.

There are many types of printing materials available for FDM. The industrial use is mainly filamentous and linear hot-melt plastics; desktop FDM printers have more choices, including nylon, wood, certain metals, and even food materials. To print.

The advantages of FDM are high molding accuracy, good hardness of the finished parts, various colors, and low cost. The disadvantage is the rough surface of the article.

2. SLA: Three-dimensional light curing molding.

As the name implies, this technology uses a laser to harden and solidify a liquid photosensitive material (usually a photosensitive resin) to form a shape.

SLA molding speed is fast, the accuracy is high, and the surface of the finished part is smooth, but the disadvantage is that the printing material is not so popular.

3. SLS: Selective laser sintering.

Like SLA, SLS technology also uses lasers, but the difference is that SLS uses the high temperature of the laser to sinter powdered consumables together.

The consumables used in SLS mainly include metal powder, ceramic powder, etc. Its advantage lies in the manufacture of metal products with higher strength.

4. 3DP: Three-dimensional powder bonding.

3DP can be said to be true 3D “printing”, because this technology is very similar to flat printing, and even the nozzles are directly used by flat printers. And like the toner used in flat printing, 3DP also uses powder materials.

But unlike the high temperature sintering of SLS, 3DP uses a binder (such as silica gel) to bond the powder. When printing, the powder storage tank of the 3DP printer will first spread a layer of material powder about 0.1 mm thick, and then the nozzle will spray the adhesive on the powder according to the designed slice shape; repeat the above process until the final shape. Of course, the articles made in this way have low strength and need to be processed to increase the strength. The specific method is to burn off the adhesive first, and then penetrate the metal at high temperature to densify the article.

The cost of 3DP equipment and materials is low, and multiple nozzles can be used, which is suitable for printing small items; the disadvantage is that the surface of the items is not smooth enough.

5. LOM: Layered solid manufacturing.

LOM uses film materials, such as paper, metal film, plastic film, etc., and works in a special way: the contours of layered objects are printed on the film, cut off, and then glued layer by layer.

The LOM molding speed is fast, and it is suitable for larger objects; the disadvantage is that it is a little weak for complex objects.

A 3D printer is generally composed of a control board, a nozzle (also called a hot head), a hot bed, a screw rod, and a stepping motor.

The control board is equivalent to the “brain” of the 3D printer, used to process information and send instructions to the stepper motor.

The nozzle is composed of heater, nozzle, stepping motor and fan. The heater heats the nozzle; the stepper motor rotates to squeeze the consumables onto the nozzle, and the nozzle sticks the melted consumables on the hot bed or the upper layer of material; the fan is used to dissipate heat for the stepper motor.

The hot bed is mainly used to heat the material, stick the material on it, and prevent edge warping.

The sprinkler head and the hot bed are fixed on the slider of the screw rod. When the screw rod rotates, the slider will move in a certain direction, driving the sprinkler head and the hot bed to move together.

Both the nozzle and the screw rod use a stepping motor, which feeds the nozzle or drives the screw rod to rotate.

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