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3D printing is any of a number of processes in which a digital model is used to create a physical three-dimensional object by adding one layer at a time.
You might think it sounds like science fiction, but 3D printing technology has been widely used in manufacturing industries for years.
HOW DOES 3D PRINTING WORK?
3D begins with modeling. 3D printable models are created with a computer-aided design (CAD) package using a 3D scanner or using a plain digital camera and photogrammetry software (software which takes data from digital photographs and creates measurements for a 3D model).
This manual modeling process of converting geometric data for 3D computer graphics is similar to sculpting. 3D scanning collects digital data about the shape and appearance of a physical object and creates a digital model based on it.
The CAD model is saved in a file which is then processed by a piece of software known as a “slicer.” The slicer converts the model into a series of thin layers and produces a file with instructions (G-code) tailored to a specific type of 3D printer.
Following directions from the computer program, 3D printing enables the creation of physical 3D objects using a series of layered development - or additive - framework. What that means is materials (such as liquid molecules or powder grains) are added together layer by layer to create a complete 3D object.
For example, desktop FDM (Fused Deposition Modeling) printers melt plastic filaments and lay it down onto the print platform through a nozzle, kind of like a high-precision, computer-controlled glue gun. Large industrial SLS (Selective Laser Sintering) machines, use a laser to melt, or sinter, thin layers of metal or plastic powders.
The materials used vary by process. Plastics are the most common, but metals can also be 3D printed. Depending on the size of the object being printed and the type of printer used, a print can take about 4-18 hours to complete. The 3D printed part is, however, not yet ready to use. It often will require some post-processing to get the desired level of surface finish. These steps take more time and usually manual effort.
3D printing, no matter which process is involved, takes place in stages. First, as mentioned, a 3D CAD file is created which is then sliced or segmented into 2-dimensional layered graphical data - 2D layers.
The 3D printer applies the required combination of raw material and then builds an object or part 2D layer by 2D layer - that is, additively - until it is completely designed and finished according to the design criteria from the original CAD file.
This is why 3D printing is also known as additive manufacturing.
3D printing is an alternative to traditional, subtractive manufacturing processes, where objects are designed and constructed by cutting and machining raw materials - or formative manufacturing processes - through the use of molds and dies (injection molding).
Printed layer thickness and X-Y resolution in dots per inch or micrometers are referred to as printer resolution. Layer thickness is typically around 250 DPI although some machines can print layers as thin as 1,600 DPI. The particles or 3D dots are about 510 - 250 DPI in diameter.
Traditional subtractive or formative construction of a model can take from several hours to several days, depending on the method used and the complexity of the model.
3D printing reduces this production time to a few hours.
The printer - produced end product is often sufficient as is, depending on the application. Greater accuracy is achieved by printing a slightly oversized version of the object and then finishing the product by removing material using a subtractive process such as cutting.
Some printable polymers must be finished by having the surface smoothed and improved using chemical vapors based on acetone or similar solvents.
Certain 3D printing techniques allow the use of multiple materials while constructing parts. They’re able to print in multiple colors and color combinations at the same time, eliminating the need for painting.
Depending on the object being printed and the printing techniques used, some processes need internal supports to be built for overhanging features during construction. These supports have to be removed or dissolved after the product is completed.
As noted, some 3D printing allows the printing of objects using different and diverse materials. Though difficult, multi-material 3D printing systems is are a key element in developing future technologies. It is already being used in various industries to make toys, shoes, furniture, phone cases, instruments, and even works of art.
Using a BAAM (Big Area Additive Manufacturing) machine, large products like 3D printed houses and cars are in the works. Researchers are producing high-temperature tools for aerospace applications with BAAM.
In medicine, 3D printing of multiple medications can be united, decreasing risks and side effects for patients.
In education, 3D printing can bring a textbook to life, allowing students to create the actual 3-dimensional object of their study.
With the number of applications for 3D printing increasing, the costs of high technology development and use will most certainly go down.
Advantages of 3D Printing
In manufacturing, 3D printing is a game-changer, because of three key advantages...
Shorter Lead Times
In the early 1980s, a design engineer would develop a design for a new product by first hand-drawing the details, carefully measuring out dimensions using a pencil and ruler (remember those?).
When the design was finalized, the company’s model shop or an outside modeling firm machined the model manually, adding features and details using painstaking hand labor and fabrication, or it created a prototype tool and cast a plastic or metal part, which would take 2-4 weeks.
Machine drafters translated the design into instructions a machinist would use to build the part. The design would then go through more configurations as the constraints of the manufacturing process dictated what could and could not be built given a particular timeframe. By this time, more than a month had passed and the model would still be in the early production stages.
Fast forward to the present day. The design engineer drafts a rough sketch then moves into 3D CAD, easily entering in dimensions and executing the design in 3D software. The project leader finalizes the design, the 3D CAD file is uploaded to the 3D printer and the next day the physical model is presented to the project team.
Designers and engineers have traditionally depended on the manufacturing process to dictate the end design. Assembly rules, manufacturability, and overall feasibility have created inherently strict limitations on design practices. Going outside of these practices typically results in increased cost and labor, leading to stunted innovation growth.
Because additive manufacturing, or 3D printing, does not rely on these same design and manufacturing constraints, it has opened doors previously thought closed to designers and engineers. Because of 3D printing, free-flowing, organic, and intricate designs are executed seamlessly in ways that are unachievable by any other manufacturing process.
3D printing lowers manufacturing/production costs in several key ways:
- Zero Tooling: Tooling is required for many production processes, such as casting and molding, where each part requires a unique mold. Also, tool designs must account for release points - how to actually get the molded part out of the tool, and features like wall thickness, which usually cannot vary because different thicknesses can harden at different times which can affect the accuracy of the part.
By contrast, 3D printing allows easy fabrication of complex shapes, many of which would not be able to be produced using any other manufacturing method. 3D printing builds parts from the bottom up and requires no specialized tooling to execute complicated designs. By eliminating the need for tooling, 3D printing removes the cost and labor of building tools.
- Reduced Labor: While 3D printing does require manual labor to remove build supports or for smoothing surfaces, it reduces manual labor in many ways when compared to conventional manufacturing processes. Because 3D printing doesn’t require tooling, it significantly reduces the labor associated with tooling production. It reduces labor by consolidating multiple part assemblies into a single unit.
Also, unlike machining, which usually needs a manual programmer to execute the lines of code necessary to machine a part, 3D printing software automates the creation of line by line information to build a part one layer at a time.
- Low-cost Prototyping: One of 3D printing’s main uses is prototyping, for both form and function. Using 3D printing, creating a prototype is done at a fraction of the cost and at speeds other manufacturing processes cannot compete with. Parts printed on a desktop 3D printer are usually ready overnight. Orders placed with professional services that have large industrial machines are ready for delivery in 2-5 days. This speed of prototyping greatly accelerates the design cycle (designing, testing, improving, redesigning). A product that used to take months is now ready in a few weeks.
LIMITATIONS OF 3D PRINTING
Because 3D printed parts are built layer-by-layer, they’re weaker and more brittle in one direction by about 10%-15%. This is why they’re most often used for non-critical functional applications. On the other hand, 3D printers using high-power laser melting (sintering) can produce metal parts with excellent mechanical properties, often better than the bulk material.
Less cost-competitive at higher volumes
3D printing has lower startup costs because there is no need for customized tooling which means prototypes and identical parts needed in small numbers can be manufactured economically. It also means the unit price decreases only slightly at higher quantities, therefore economies of scale do not enter in. 3D printing cannot compete with traditional manufacturing processes when a large production run is needed.
Limited accuracy and tolerances
3D printed parts depend on the process and the calibration of the machine for accuracy. Parts from a desktop machine have much lower accuracy than those that come from a laser 3D printer used for printing metal parts or metal alloys for critical applications.
Post-processing and support removal
3D printers cannot print a part out of thin air. They require support structures for the part being built. These supports then are printed with the part so material can be added under an overhang or to anchor the printed part on the build platform. When they’re removed, they leave marks or blemishes that require sanding, smoothing and painting to achieve a high-quality surface finish.
Overall, 3D printing, like anything else, has its benefits and limitations. One thing is sure, 3D printing is transforming industry and society in ways not seen since the start of the industrial revolution.