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Additive Manufacturing

Contrary to subtractive manufacturing, where materials are constantly reduced, additive manufacturing refers to continuously adding materials. Additive manufacturing here specifically refers to the processing method of manufacturing objects like 3D printers. In the 1990s, the term for additive printing was called rapid prototyping.

Similar to the ancient printing method of engraving, the engraved image is printed by applying ink to the engraving. 3D printing is based on 2D printing, continuously printing layer by layer because each layer has a thickness, thus forming a three-dimensional object. A 3D printer is also a CNC-controlled machine, printing by way of dots forming lines and lines forming surfaces. Of course, it can also print a slice directly and then cover it layer by layer.

3D printers usually add material by layer until all the layers have been printed. Then, the thickness of each layer is fixed. A typical 3D printer for home use has an accuracy of 0.1 mm per layer, while commercial printers can achieve 0.01 mm or even higher accuracy.

Figure 2-30  is a prototype of a 3D printer using FDM (Fused Deposition Method ) printing.

Figure 2-31 are the samples of the FDM printer.

From the 1990s, limited to materials and processes, 3D printing has been used as prototyping and has not been used for production. The 3D printing process can meet industrial production requirements regardless of accuracy, repeatability, and material variety since 2019, so the term additive manufacturing can be equated with 3D printing.

Figure 2-30 Open source 3D printer                         Figure 2-31-1 Printer sample an animal

Figure 2-31-2 Printer Sample II – Small Table

One of the main advantages of 3D printing is producing very complex shapes or geometries, especially shapes and structures that cannot be achieved by subtractive manufacturing, such as hollow structures. However, just as subtractive manufacturing is limited by the processing method, additive manufacturing is the opposite, limited by the variety of materials. For example, it is currently impossible to print textured materials such as wood and leather.

The prerequisite for producing any 3D printed parts is a digital 3D model file, usually an STL format file. The 3D model file can be obtained from a prototype scanned by a 3D scanner or designed with 3D modeling software. After obtaining the 3D model file, the data required by the 3D printer should be generated according to the process requirements of the printer. Generally speaking, first, obtain the slice from the prototype and then generate the required data from the slice according to the printing process. For example, a light-curing printer only needs to provide sliced image data, while a 3D printer using a fusion method needs to generate a path file similar to a tool milling bottom.

A 3D printer using the FDM method, see F2-30. The mechanical architecture of the printer uses a Cartesian coordinate system, where XY is the horizontal plane. After the 3D print head prints a layer, the print head rises with the Z-axis to a fixed height (typically 0.05 mm or 0.1 mm) until all the slices are printed.

A light-cured SLA printer uses a photosensitive resin. In contrast to FDM, the light-cured printer is not at the highest but the lowest point. One slice at a time is projected completely on the bottom, and the gap between the bottom of the workpiece and the light-curing base plate is around 0.05. The resin in the interlayer, rapidly cured by light irradiation, is raised again by one layer height and continues to cure until all the slices are printed.

There is also an initial 3D printing method that uses the principle of inkjet printers to print on a powder with a binder ink, which is deposited on the powder. After printing one layer in this way, the printed workpiece is lowered by one layer (usually 0.05 mm, depending on the process requirements and the accuracy of the machinery), and another layer of powder is spread once more with a foam similar to a pancake, and then printed once more until the end.

Additive manufacturing is also based on the electron beam and additive manufacturing with laser sintering[1], similar to the laser marking principle.

3D printing is a buzzword, in the broad sense of the term “additive manufacturing” being used as the official term in the US and global technology standards. This is because additive manufacturing has a broader scope and does not necessarily use 3D printing to do additive manufacturing. 3D printing is strictly a major form of additive manufacturing, not the whole thing.

The relationship between subtractive and additive manufacturing

Whether animals or humans, additive and subtractive manufacturing coexisted from ancient times to the present. Each has its own merits. The concept of additive and subtractive manufacturing has become popular only after the continuous commercialization of 3D printer applications in recent years. Of course, subtractive manufacturing here refers explicitly to machine tools instead of manual manufacturing.

There are both subtractive and additive manufacturing in smart machines in smart manufacturing applications, both of which are the most important processing methods in smart factories. The combination of the two can realize many products that could not be manufactured in the past.

As additive manufacturing technologies continue to grow, traditional machining has been re-categorized in terms of ideas and language as a subtractive manufacturing method. In a courteous conceptual sense, additive and subtractive manufacturing may compete with each other. Still, in a broad sense, in the context of the industry, their relationship is complementary, with each method having its strengths. While additive manufacturing methods can produce very complex prototype designs, which subtractive manufacturing cannot do, additive manufacturing can be limited in material selection and strength.

In the manufacturing industry, additive manufacturing and subtractive manufacturing have been integrated into the manufacturing process of a workpiece. For example, in the process of processing metal parts, the processing is completed with subtractive manufacturing first. Then the parts that cannot be processed in subtractive manufacturing are processed with laser sintering technology so that the advantages of the two can be brought into play to meet the needs of intelligent manufacturing.

There is another common method to make good slices of the 3D prototype design and then use a CNC cutting machine for subtractive manufacturing to do the cutting. After the cutting is done, these slices can be glued together to form a 3D solid. Usually, we can use paper, steel, wood, etc., to achieve this. The specific choice of sheet mainly depends on the accuracy needed for the specific application scenario.

For example, to make fine art sculptures, you can use laser cutting to do the cutting of the plates, and then glue these slices together in sequence to form a 3D prototype entity, and then do the surface treatment so that the sculpted fine artworks can save time and materials substantially.

Just as addition and subtraction form the basis of mathematics, additive and subtractive manufacturing form the basis of manufacturing, and when the two are integrated, better products can be made.

[1] Laser sintering is an additive manufacturing technique that uses a laser as the power source to sinter powdered material (typically nylon or polyamide).

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