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What Is 3D Printing?
Definition, Process, And Types
What Is 3D Printing?
3D printing is an additive technology used to manufacture parts. It is ‘additive’ in that it doesn’t require a block of material or a mold to manufacture physical objects, it simply stacks and fuses layers of material. It’s typically fast, with low fixed setup costs, and can create more complex geometries than ‘traditional’ technologies, with an ever-expanding list of materials. It is used extensively in the engineering industry, particularly for prototyping and creating lightweight geometries.
3D printing and additive manufacturing
‘3D printing’ is commonly associated with maker culture, hobbyists and amateurs, desktop printers, accessible printing technologies like FDM and low-cost materials such as ABS and PLA (we’ll explain all those acronyms below). This is largely attributable to the democratization of 3D printing through affordable desktop machines that sprung from the RepRap movement, like the original MakerBot and Ultimaker, which also led to the explosion of 3D printing in 2009.
Ultimaker FDM machine
By contrast, additive manufacturing (AM) is almost always associated with commercial and industrial applications
Commercial additive manufacturing
3D printing and rapid prototyping
‘Rapid prototyping’ is another phrase that’s sometimes used to refer to 3D printing technologies. This dates back to the early history of 3D printing when the technology first emerged. In the 1980s, when 3D printing techniques were first invented, they were referred to as rapid prototyping technologies because back then the technology was only suitable for prototypes, not production parts.
In recent years, 3D printing has matured into an excellent solution for many kinds of production parts, and other manufacturing technologies (like CNC machining) have become cheaper and more accessible for prototyping. So, while some people still use ‘rapid prototyping’ to refer to 3D printing, the phrase is evolving to refer to all forms of very fast prototyping.
How does 3D printing work?
Additive vs traditional manufacturing
Additive manufacturing has only been around since the 1980s, so the manufacturing methods developed before it are often referred to as traditional manufacturing. To understand the major differences between additive and traditional manufacturing, let's categorize all methods into 3 groups: additive, subtractive and formative manufacturing.
Additive manufacturing builds up 3D objects by depositing and fusing 2D layers of material.
This method has almost no startup time or costs, making it ideal for prototyping. Parts can be made rapidly and discarded after use. Parts can also be produced in almost any geometry, which is one of the core strengths of 3D printing.
One of the biggest limitations of 3D printing is that most parts are inherently anisotropic or not fully dense, meaning they usually lack the material and mechanical properties of parts made via subtractive or formative techniques. Due to fluctuations in cooling or curing conditions, different prints of the same part are also prone to slight variations, which puts limitations on consistency and repeatability.
Subtractive manufacturing, such as milling and turning, creates objects by removing (machining) material from a block of solid material that's also often referred to as a 'blank'.
Almost any material can be machined in some way, making it a widely used technique. Because of the amount of control over every aspect of the process this method is capable of producing incredibly accurate parts with high repeatability. Most designs require Computer Aided Manufacturing (CAM) to plot customized tool paths and efficient material removal, which adds setup time and costs, but for the majority of designs, it’s the most cost-effective method of production.
The major limitation of subtractive manufacturing is that the cutting tool must be able to reach all surfaces to remove material, which limits design complexity quite a lot. While machines like 5-axis machines eliminate some of these restrictions, complex parts still need to be re-orientated during the machining process, adding time and cost. Subtractive manufacturing is also a wasteful process due to the large amounts of material removed to produce the final part geometry.
Formative manufacturing, such as injection molding and stamping, creates objects by forming or molding materials into shape with heat and/or pressure.
Formative techniques are designed to reduce the marginal cost of producing individual parts, but the creation of unique molds or machines used in the production process means setup costs are very, very high. Regardless, these techniques can produce parts in a large range of materials (both metals and plastics) with close to flawless repeatability, so for high volume production, they’re almost always the most cost-efficient.
How these methods compare
Manufacturing is complex, and there are too many dimensions for comprehensively comparing each method against all others. It is near impossible to optimize all at once for cost, speed, geometric complexity, materials, mechanical properties, surface finish, tolerances, and repeatability.
In such complex situations heuristics and rules of thumb are more valuable:
⦁ Additive manufacturing is best for low volumes, complex designs, and when speed is essential.
⦁ Subtractive manufacturing is best for medium volumes, simple geometries, tight tolerances, and hard materials
⦁ Formative manufacturing is best for the high-volume production of identical parts.
Cost per part is usually the governing factor determining which manufacturing process is best. As a rough approximation the unit costs per method can be visualized like this:
3D printing technology
With so many different 3D printing technologies on the market, it can be hard to understand the whole landscape. The International Organization for Standardization created the ISO/ASTM standard 52900 to standardize the exploding terminology around 3D printing and we’ve pulled together the most-used language into this glossary of 3D printing terms.
The different types of 3D printing
3D printers can be categorized into one of several types of processes:
⦁ Vat Polymerization: liquid photopolymer is cured by light
⦁ Material Extrusion: molten thermoplastic is deposited through a heated nozzle
⦁ Powder Bed Fusion: powder particles are fused by a high-energy source
⦁ Material Jetting: droplets of liquid photosensitive fusing agent are deposited on a powder bed and cured by light
⦁ Binder Jetting: droplets of liquid binding agent are deposited on a bed of granulated materials, which are later sintered together
⦁ Direct Energy Deposition: molten metal simultaneously deposited and fused
⦁ Sheet Lamination: individual sheets of material are cut to shape and laminated together
3D printing processes
There are seven main 3D printing processes. Within each type of process there are unique technologies, and for every unique technology there are also many different brands selling similar printers.
Photopolymerization is the process of a photopolymer resin being exposed to certain wavelengths of light and becoming solid.
Stereolithography (SLA), direct light processing (DLP) and continuous direct light processing (CDLP) are additive manufacturing processes that fall under the category of vat photopolymerization. In SLA, an object is created by selectively curing a polymer resin layer-by-layer using an ultraviolet (UV) laser beam. DLP is similar to SLA but uses a digital light projector screen to flash a single image of each layer all at once. CDLP is a lot like DLP but relies on the continuous upward motion of the build plate. All vat photopolymerization processes are good for producing fine details and smooth surface finishes, making them ideal for jewelry and medical applications.
⦁ Smooth surface
⦁ Fine details
⦁ Good for prototyping of IM
⦁ Usually requires supports
⦁ UV sensitive
⦁ Extensive post processing required
Powder bed fusion
Powder bed fusion (PBF) technologies use a heat source to induce fusion (sintering or melting) between the particles of a plastic or metal powder one layer at a time. Selective Laser Sintering (SLS), electron beam melting (EBM) and multi jet fusion (MJF) all fall within this technology. The metal 3D printing processes selective laser melting (SLM) and direct metal laser sintering (DMLS) also use powder bed fusion to selectively bind metal powder particles.
⦁ Strong parts (nylon)
⦁ Complex geometry
⦁ Scalable (fits size)
⦁ No support
⦁ Longer production time
⦁ Higher cost (machines, material, operation)
Material extrusion technologies squeeze a material through a nozzle and onto a build plate, layer by layer. Fused deposition modeling (FDM) falls under this category and is the most widely used 3D printing technology.
⦁ Low cost
⦁ Common thermoplastics
⦁ Rough surface finish
⦁ Usually requires supports
⦁ Not scalable
⦁ Limited accuracy
Material jetting technologies use UV light or heat to harden photopolymers, metals or wax, building parts one layer at a time. Nano particle jetting (NPJ) and Drop-on-demand (DOD) are two other types of material jetting.
⦁ Realistic prototypes
⦁ Excellent details
⦁ High accuracy
⦁ Smooth surface finish
⦁ High cost
⦁ Brittle mechanical properties
Binder jetting uses an industrial printhead to deposit a binding adhesive agent onto thin layers of powder material. Unlike the other 3D printing technologies, binder jetting does not require heat.
⦁ Full-color options
⦁ Range of materials
⦁ No support
⦁ No warping or shrinking
⦁ Low part strength
⦁ Less accurate than material jetting
Direct energy deposition
Direct energy deposition (DED) creates 3D objects by melting powder material as it is deposited. It is mostly used with metal powders or wire and is often referred to as metal deposition. Laser engineered net shape (LENS) and Electron Beam Additive Manufacture (EBAM) also fall within this category.
⦁ Strong parts
⦁ Range of materials
⦁ Larger parts
⦁ High cost
⦁ Poor surface finish
This technology stacks and laminates thin sheets of material to make parts. There are a few different types of laminations to choose from: bonding, ultrasonic welding or brazing.
⦁ Low cost
⦁ No support structures necessary
⦁ Multi-material layers
⦁ Post processing is required
⦁ Limited materials
⦁ Finishing may vary
Selecting the right 3D printing processes
Selecting the optimal 3D printing process for a particular part can be difficult as there’s often more than one suitable process but each one will produce subtle variations in cost and output. Generally, there are three key aspects to consider:
⦁ The required material properties: strength, hardness, impact strength, etc.
⦁ The functional & visual design requirements: smooth surface, strength, heat resistance, etc.
⦁ The capabilities of the 3D printing process: accuracy, build size, etc.
These correspond to the three most common methods for selecting the right process:
⦁ By required material
⦁ By required functionality or visual appearance
⦁ By required accuracy or build size
3D printing materials
A complete 3D printing material overview
The number of available 3D printing materials grows rapidly every year as market demand for specific material and mechanical properties spurs advancements in material science. This makes it impossible to give a complete overview of all 3D printing materials, but each 3D printing process is only compatible with certain materials so there are some easy generalizations to make.
Thermoplastic and thermoset polymers are by far the most common 3D printing materials, but metals, composites and ceramics can also be 3D printed.
Another way of categorizing materials is by their properties: cheap, chemically resistant, dissolvable, flexible, durable, heat resistant, rigid, water resistant, UV resistant. Many industrial applications require durable plastics such as Nylon 12, and most hobbyist applications use either PLA or ABS, which are the most common materials used in FDM 3D printing.
3D printing design guidelines
The exact best practices and rules of thumb vary between the different 3D printing technologies, but there are certain features you always need to pay attention to:
⦁ Supported wall thickness
⦁ Unsupported wall thickness
⦁ Supports and overhangs
⦁ Embossed and engraved details
⦁ Horizontal bridges
⦁ Connecting or moving parts
⦁ Escape holes
⦁ Minimum feature size
⦁ Minimum pin diameter
⦁ Maximum tolerance
Applications of 3D printing
3D printing is exceptionally useful for prototyping. Speed is everything in prototyping, and the ability to move from CAD to print with close to zero set up costs means 3D printers can produce parts fast and have great unit economics for single-part and small runs.
For printing production parts, speed and price are also important, but the characteristics most commonly exploited are design freedom and ease of customization. In aerospace and automotive, topology optimized structures with a high strength-to-weight ratio are used for high-performance parts, and components that previously required assembly can be consolidated into a single part. In healthcare, customization is critical - most hearing aids manufactured in the US are made almost exclusively using 3D printing. In manufacturing, low-run injection molds can be 3D printed from stiff, heat-resistant plastics instead of machined from metal, making them much cheaper and faster to produce.
Medical 3D printing
There are many applications for 3D printing in the medical industry, and each year doctors and scientists come up with new and creative ways to use this fast-growing technology. The speed and versatility of 3D printing makes it perfect for developing customized prosthetics and implants and patient-specific replicas of bones, organs and blood vessels. It is also used for 3D printing surgical tools, anatomical models, personalized medical equipment and a range of other life-saving innovations.
Automotive 3D printing
In the automotive industry, automakers use 3D printing to test form and fit, to experiment with aesthetic finishes and make sure that all parts operate and interact as intended. It also provides a flexible solution for the quick turnaround of jigs, fixtures and grips; creating bellows; engineering complex ducting; and rapidly manufacturing complex, lightweight mounting brackets.
3D printing jewelery
There are a few reasons that so many designers use 3D printing to create jewelry. The technology allows jewelers to produce very complex, highly customizable designs, sidestepping some of the limitations of previously popular jewelry making techniques such as CNC machining, handcrafting and lost-wax casting. Today, precious metals can be 3D printed in a variety of patterns and designs quickly and cost effectively.
What are the benefits of 3D printing?
3D printing is an exceptional tool for custom parts and rapid prototyping with a unique set of advantages but also lags behind traditional manufacturing in some ways. The key benefits and limitations can be summarized as follows:
Benefits - Very low start-up costs - Very quick turnaround - Large range of available materials - Design freedom at no extra cost - Each and every part can easily be customized
Limitations - Less cost-competitive at higher volumes - Limited accuracy & tolerances - Lower strength & anisotropic material properties - Requires post-processing & support removal
How to get something 3D printed
3D printing has come a long way since its inception and it’s now very easy to get something 3D printed quickly and affordably.
Buy a printer or use a 3D printing service?
3D printing has come a long way since its inception and it’s now very easy to get something 3D printed very fast for pretty cheap.
Should you buy your own 3D printer or use an online service? It’s an important decision to make, so we’ve collected arguments for both sides to help you make the right choice.
Buy a 3D printer if…
You need to print regularly, but not in huge volumes (10-25 times a week)
You have one specific application in mind for the printer
You are ready to make a sizeable investment You want to access the latest technologies at all times
You are prepared to set up, tinker and optimize your machine
You have the necessary space and time to install and operate the printer You want to test and learn first before deciding what printer to buy
Use an online service if...
You will need only a few (less than 10) or large volumes (25+) of parts printed per week
You want to print using multiple processes and materials, including industrial printers
You want to access the latest technologies at all times
You prefer to focus your time on designing and perfecting your models
You want to test and learn first before deciding what printer to buy
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