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How does a 3D Printer work?

Forget everything you think you know about printing, manufacturing, assembling and designing objects. The world of 3D printing has developed in such a way that it disrupts every aspect of conventional product manufacturing. The underlying principles of 3D printing and the printers themselves are moving towards a unified state of turn-key manufacturing limited only by our imagination.

HOW DOES A 3D PRINTER WORK?

While 3D Printing isn’t quite as simple as laying down an A4 sheet and clicking ‘Print’, the concept is not that difficult to grasp once you understand the basic principles, printing process and types of 3D printers.

Basic principles of a 3D printer 

Forget everything you think you know about printing, manufacturing, assembling and designing objects. The world of 3D printing has developed in such a way that it disrupts every aspect of conventional product manufacturing. The underlying principles of 3D printing and the printers themselves are moving towards a unified state of turn-key manufacturing limited only by our imagination.

The most essential aspect that needs to be understood about 3D printing or ‘additive printing’ as a personal user tool, is its process. Although there are different ways by which the varied models of 3D printers operate, they’re all based on a simple premise. As the term ‘additive printing’ suggests, 3D printers work by “adding” layers of print material together to create an object. Converting a software-based design into distinct 2D layers or slices, which are “printed” and bonded to each other in order to create a 3D product is the primary method of operation of any 3D printer.

A simple workflow. It doesn’t look that complicated, does it?

Imagine placing a dot of glue on a piece of paper. Now imagine adding layer upon layer of glue on that dot in a precise and adhesive manner. That dot would grow off the two dimensional page into the third dimension and become a cylinder with the diameter of the original dot. Another example: a single sheet of paper would be two-dimensional but a stack of sheets would make it three-dimensional. In the exact same way, 3D printers create 3D objects by printing layer upon layer of a variety of materials to achieve a three-dimensional product.

The overall workflow of any 3D printer is oriented towards achieving the goal of converting a 3D design created using software into a hardcopy version. While the methods used by different printer models vary, they’re all based on the same type of workflow. Let’s look at this workflow and then delve deeper into the world of 3D printing by exploring the different types of 3D printers available in the market.

From inception to actualisation

The 3D printing process of any printer can be simplified into a series of basic steps. These steps are independent of the printer’s size, scale, material or design, and are closely adhered to by nearly all printer manufacturers.

Step 1: Just as any 2D digital printing begins as a file in a word processing software or page layout software, 3D printing begins in computer-aided design (CAD) software. The version or degree of the software’s complexity may vary but they all share the same basic attribute of being able to design a three-dimensional object inside the computer’s memory. Depending on the type of software, users can exert various degrees of control over the physical and structural integrity of the final product within the simulated environment of the computer. Data relevant to the product’s real world attributes, such as material’s property or mensuration can also be accurately depicted using computer-aided design software. The scientific data available to this software is also instrumental in giving users an accurate virtual prototype of their design, allowing them to test how the conceptualised object will behave under a variety of real world settings.

The complexity of any product is limited only by your imagination and CAD skills

Another highly useful means of obtaining a virtually simulated design of an object is through the use of a 3D scanner. A 3D scanner will allow you to virtually “copy” a physical real world object into a computer by collecting detailed data regarding the object’s size, scale, design and composition. This collected data is then exported into CAD software where digital 3D models are created for augmentation, virtual analysis or simple replication using a 3D printer. These virtual simulations, either manually designed through CAD or acquired using scanners, are the necessary first step towards beginning any 3D printing project.

Step 2: The next step on the 3D printing journey is the conversion of the CAD-based models and designs into a language format that’s compatible with that of 3D printers - the STL format. The STL format, or ‘standard tessellation language’ format, is the current industry standard that was developed for the use of 3D printers. It was originally created in 1987 for use on stereo lithography apparatus machines (We’ll come back to this and other types of 3D printers at the end of this chapter). Although STL format files are the primary standard for 3D printers, a small group of other assorted proprietary file formats such as ZPR and ObjDF which require specialised software can also do the job. However, the significant majority of professional as well as Open Source software support STL, so new users don’t need to worry about multiple conversions.

As with any machine a little hands-on adjustment is always necessary

Step 3: The next step will determine how the 3D printer will interpret the STL file design. This is where “Print Properties” comes into the picture. In the same way that we adjust printer properties such as horizontal or vertical orientation when we print a 2D document, we can adjust properties such as size and print orientation of an STL file when printing a 3D design.

Step 4: This step varies according to the type of the printer. Once the STL file is ready for printing, the machines need to be checked for the required materials and placement configurations, just as a paper printer needs to be checked for ink and tray alignment. In the case of 3D printing, the types of machines vary greatly based on their printing techniques, and accordingly require different types of materials to work with. This includes polymers, binders, adhesives and powders. In addition to this, the placement of the base tray or chemical solution base also needs to be adjusted.

Step 5: The next step is very easy - the machine proceeds to process the STL file and fabricate the object that’s been designed. For most consumer grade 3D printing machines and most designs, the entire printing process is automated. Only in certain rare cases, manual intervention may be called for; E.g. If the printing process requires large material quantities and reloading is necessary or if parts of the design need. The printer creates layers measuring 0.1mm in average thickness. Based on the material, this can be thicker or thinner. Printing objects can take a variable amount of time - from minutes to hours to even days. You may sometimes be required to keep checking in on the printer’s progress to ensure that there are no errors or misalignments.

The printer apparatus moves in all dimensions to fabricate the CAD-based object

Step 6: Once the object has been printed, its removal from the printer is an extremely delicate and critical step. In many cases, the printing process leaves the object’s surface hot and malleable, and in certain cases requires additional time to clear off fumes and particulates. Users are advised to take special precautions such as wearing gloves and glasses when removing the object from the printer.

Step 7: The next stage involves processing the item. With most 3D printers, the final object is usually found covered with the remains of the additive materials, or a layer of powder or coarse material. The processing stage requires either dusting off the physical particulates or bathing the object in water to remove water soluble elements. It’s important to note that not all objects taken from a 3D printer are immediately ready for processing. Depending on the material and design configuration used, sometime may be required for the additive material to “cure” and harden completely before it can be processed without risk to the physical integrity of the object. If this is ignored, there’s a significant risk that certain parts of the object will fall apart, dissolve or weaken the overall structure of the object.

The above stated workflow of 3D Printing is common to all models. Once the process is complete, you can use the final object for its intended purpose. Many printers are capable of printing multiple objects allowing users to carry out simultaneous manufacturing tasks for maximum efficiency.

The printing process

As you can see, the generic workflow of a 3D printing process is divided into a series of stages. The most important of which is obviously the printing stage where the actual magic of 3D printing happens. The system that governs how 3D printers take a digitally created computer-aided design or a scanned object file, and convert it into a layer-based printing protocol is worth understanding so that users can maximise the utility of their workflow.

The slice-based layering of objects is similar to the deconstruction of a loaf of bread

The 3D printer has been created to interpret the STL file format of an object’s design and deconstruct it into layered segments. Imagine a loaf of bread that has been sliced into hundreds and thousands of thin layers. The ability to craft layer upon layer of this bread in perfect alignment and fusing them into one single object gives you the loaf of bread that those slices were a part of originally. Similarly, a 3D printer digitally dismantles an object into numerous layers and prints them in perfect alignment.

Depending on the type of printer and the object being printed, the material used can be liquid, powder, paper, metal or even food based. The printer uses the cross-sections of the object to create the final item. Since almost every object can be physically broken down into layers, the reverse process of joining together the layers is made simple by the printer. The printer takes the virtual crosssections from the computer- aided design model and replicates its geometric shape in layered stages.

3D printers are capable of extremely small layers providing detailed resolutions

The degree of complexity and finesse with which a printer can create objects is based on the resolution of the printer. Just as high resolution paper printers give us a clearer and crisper final image, higher resolution 3D printers are able to craft objects of great precision and accuracy. A 3D printer’s resolution is calculated on the horizontal two-dimensional X-Y axis in dots per inch (DPI). The thickness of each layer is generally 250 DPI which is about 0.1 millimeter (100 µm), but can also be as little as 16µm or 0.00016 millimeter. The individual particle or dot size produced by these printers is on average between 50µm to 100µm in diameter.

Additive printing methodologies rely heavily on the accuracy and detailing of the particulate size chosen to achieve perfect fabrication. The time and effort taken by a 3D printer is therefore based entirely on the scale, size and complexity of the object being created and the specific printer being used. Some printers are about the size of a microwave oven while others can take up a whole room.

The finishing process

The finishing process, as we discussed in the steps, is a careful and delicate process, but usually the fastest in the entire workflow. What’s more, some basic finishing techniques allow for greater quality in the final product. Though 3D printers that can print in high resolution are available, it’s possible to achieve even higher quality through a post-printing subtractive process.
While additive printing is about adding materials together, subtractive printing is the exact opposite. This process is similar to photographers shooting an image at the highest resolution, then cropping out the desired part and rescaling it to fit a smaller frame. This allows for greater clarity and quality in the image. In 3D printing, a slightly larger or oversized version of the item is printed at normal resolution and then subjected to a high resolution subtractive process, which makes it possible to craft a more accurately sized final object. This is akin to scaling down a larger sized model proportionally to achieve greater precision in detail.

Object finishing is critical if you want a smooth surface

This finishing technique is especially useful when working with 3D printers that use multiple materials in their process. Subtractive printing allows users to flesh out the variances in composition and style – especially handy when multiple colour components or parts are printed together. Another aspect of the finishing process is erasing or removing “supports” that are used while printing. In certain designs, it’s necessary to use small components that hold up the orientation or structure of the object during the printing process, after which they’re no longer useful and need to be removed. During the finishing process, these supports are removed either manually or by dissolving them once the object has been printed.

Additives used

We’ve said it before and we’ll say it again: 3D printing is essentially additive printing where materials are added in layers to achieve the final object. These materials that are used by 3D printers are called additives, which are available in a variety of types contingent on the type of printer used and the object designed. Addictives are essentially the “ink” with which three-dimensional objects are printed. A significantly large variety of materials – ranging from plastic to chocolate - can be used as additives, if the printer supports them of course.

The most common and affordable additive material is plastic of various properties. The plastic used to make LEGO toys is one of the top used additives and is called acrylonitrile butadiene styrene or ABS. It is cheaply available and easy to work with, in addition to being found in a variety of colours. The other types of plastics being used in 3D printing are as follows:-

1. Polylactic acid-based plastics (PLA): Available in a range of grades, from soft to hard. It’s gradually gaining favour as the more preferred additive type in comparison to ABS.

2. Polyvinyl alcohol (PVA): It’s an essential additive agent used as a dissolvable material, most commonly used to make supports in 3D objects.

3. Polycarbonate (PC): Polycarbonate is a currently experimental additive material being tested with certain types of 3D printers. It’s ejected in liquid state from high temperature ejectors or printer nozzles, similar to inkjet printers.

4. Soft poly-lactic acid (Soft PLA): This plastic is the extreme version of PLAs and has the unique property of being very flexible. However, it’s currently still in limited use due to its basic range of colours and production. And then you have the more resilient and traditional manufacturing materials such as metals and complex polymer. Sturdier additives such as different types of steels, titanium, precious metals such as gold and silver, and other metals are currently not easily available or used in consumer level 3D printers.

Polymers will continue being the top choice amongst the types of additives used

However, research and interest in their use are helping them slowly work their way outside of scientific grade 3D printers into consumer grade printers. The potential of a variety of other materials such as nylon, glass-based polyamide, epoxy, wax and photopolymers has not gone unnoticed either and they’re also finding root in the world of 3D printing. In fact, just about any material (besides a few exceptions) can be used as an additive. It’s just a matter of incorporating the materials into existing or emerging printer designs.

•    A few examples of ways in which exotic and unique materials are being used in 3D printing:
•    Chocolate additives used to make custom designed desserts using CAD applications
•    Bio-ink or stem cells to print human tissues such as blood vessels, bladders and kidney parts for surgery
•    Silicon, calcium and zinc as additives to make an artificial bone structure on which real bone tissue could grow

Types of 3D printer technologies

Now that you know about the process of printing and materials used, it’s time for an overview of the different types of 3D printer technologies and ways in which they differ. The methods they all use are of an ever-evolving nature and as newer techniques are perfected, they’re bound to undergo change. For now, 3D printers are broadly based on four operational methods.

1. Traditional 3D Printers

Traditional 3D printers employ the simplest method of them all. The addictive’s are layered in a basic two-dimensional way across an X-Y axis, similar to an inkjet printer’s functioning. This basic style is typically known as ‘3D printing’, with more specialised names for other versions of this technique. An advanced version of this technique is known as ‘PolyJet photopolymer’ 3D printing which employs the traditional inkjet method of applying ink but uses a photopolymer liquid that solidifies when struck by UV light. The use of photopolymer allows for a variety of materials to be used in an assortment of colours and very high resolution prints.

2. Stereolithography (SLA)
The next method is known as stereolithography. It is chemical based and relies on the combination of light sensitive chemicals and lasers. These chemicals are oriented in such a manner that when they’re exposed to UV laser light they turn from liquid to solid. The 3D printers that use this method are designed to maneuver the UV laser across a thin surface of the chemical liquid in the design of the required object. As each layer solidifies, it is lowered and thinly submerged in the chemical liquid. The UV laser then creates another solid layer by moving across the liquid and so on until the final product is solidified and complete.

The stereolithography method has proven to provide a very high level of detailing and finishing on the surface of the objects created. The entire printing process takes places in the chemical liquid and the finishing involves separating the solidified 3D object from the pool of chemicals in a single flow. This was the first ever method of 3D printing that was invented in 1983 by Charles Hull.

3. Fused Deposition Modeling (FDM)

The third technique, known as ‘Fused Deposition Modelling’, is based on the use of molten material that becomes solid as it’s layered on to the print surface. As the molten material is injected from the printer head, it creates the successive layers of the 3D design. This process continues until the product is fully created. This technique also uses food-based molten material such as cheese and chocolate to create complex-shaped food items. This is one of the most affordable types of 3D printers available in the market.

These types of printers use ABS and PLA plastics as well as biodegradable polymers which are organic in nature. The plastic additives used can also be dispensed as filaments from spools in a slightly augmented type of this printer. This technique is called ‘Fused Filament Fabrication’ since the additive source is in the form of spooled filaments of plastic.

Printers of this design are capable of employing nearly any material that has a creamy viscosity, including materials such as clay, silicone, chocolate, cheese, frosting, cement and certain metals. The heating necessary for different additives is either done through the ejection nozzle or the additive storage unit based on the required melting point.

4. Selective Laser Sintering (SLS)

The fourth method uses powdered materials that are fused together using either heat or adhesives between layers to achieve the desired 3D shape. This method is called ‘Selective Laser Sintering’ (SLS) and is actually a combination of traditional 3D printing and powered lasers, (instead of UV light). By augmenting the stereolithographic method, SLS replaces the chemical pool with powdered base material and the UV light with a powered laser.

Combining both the methods makes it possible for SLS printers to use not only all plastics but also ceramics and metals to fabricate objects. It has proven to be a cost-effective alternative to other 3D printers in specialised cases which call for the use of materials such as polystyrene, nylon, glass, metals and other exotic additives. The powdered material from these sources is easy to fuse using a laser and once the 3D printing project is completed, the surplus material is left available for reuse. It also removes the need for the use of supports and makes the overall process much more efficient.

Developing technologies

Even as we discuss the world of 3D printer technologies progress is being made in more versatile and innovative methods. Three of the most promising technologies that are likely to find acceptance in the near future are Selective Laser Melting, Electron Beam Melting and Laminated Object Manufacturing.

1.  Selective Laser Melting: is similar to Selective Laser Sintering but far more advanced as it uses the power of lasers to fully melt the powder granules into a fixed solid layer instead of simply fusing the powder together. This results in stronger and longer lasting objects that can be intensively used. It is similar to the Electron Beam Melting method as well where electron beams are used instead of a UV laser.

2.  The Electron Beam Melting method: is used for extremely high precision object printing, which is required to make biological grade implants, such as those used in orthopedic surgery.

LOM techniques almost make it seem like the object was inside the materials block just waiting to be released

The complete freedom in choice of materials and extremely high grade of manufacturing bring it the closest in terms of quality to traditional manufacturing methods.

3.    Laminated Object Manufacturing: is the name given to a printing methodology herein the layers of paper, polymers or metal laminates are coated in adhesive and bound together. After this step, a high-precision laser cutter or blade carves out the desired object. This process uses thousands of adhesive layers from which an object is extracted, similar to sculpting from a marble block in the olden days.

The diversity and variety in the world of 3D printing may seem overwhelming but it isn’t that dissimilar from 2D printing; just as choosing between inkjet, laser, all-in-one and photography grade printers is based on the user’s need, so is the choice between the different types of 3D printers. Whatever be your need - professional prototyping or simple craftsmanship - there’s a 3D printer out there that will suit your need.