What is 3D Printing?

Tutorial

The world of 3D printing is at times a tangled web of technologies, materials, and new processes and capabilities and that can make navigating the 3D printing ecosystem difficult. 3D printing doesn’t refer to one kind of manufacturing or technological process and therefore a well-rounded understanding requires an in-depth look into all available 3D printing systems. While it’s not exactly easy to bundle 30+ years of manufacturing advancements into a succinct article, we’ve taken on the challenge because we want to help you make informed and grounded decisions on how, where and when to implement 3D printing into your own business operations or even daily life.

Index



3D Printing: Defined


3D printing refers to any manufacturing process which additively builds or forms 3D parts in layers from CAD data. The technology is significant because it offers direct manufacturing, meaning a design goes directly from you to physical product through a computer and a printer. Let’s break it down further.

3D printing starts with a digital file derived from computer aided design (CAD) software. Once a design is completed, it must then be exported as a standard tessellation language (STL) file, meaning the file is translated into triangulated surfaces and vertices. The STL file then has to be sliced into hundreds – sometimes thousands – of 2-D layers (Fig.1). A 3D printer then reads the 2-D layers as building blocks which it layers one atop the other, thus forming a three dimensional object. All design files, regardless of the 3D printing technology, are sliced into layers before printing. Layer thickness – the size of each individual layer of the sliced design – is determined partly by technology, partly by material, and partly by desired resolution and your project timeline; thicker layers equates to faster builds, thinner layers equate to finer resolution, less visible layer lines and therefore less intensive post-processing work (Fig.2). After a part is sliced, it is oriented for build.

CAD File Layers
Fig. 1
Video Game Controller With Layer Lines
Fig. 2

Orientation

Orientation refers to how and which direction a part is placed on the 3D printing build platform. For example, a part may be oriented at an angle, or lying flat/ standing vertical. Similar to CNC machining, orientation factors into the outcome of surfaces and details on a 3D printed part. Because 3D printing builds one 2-D layer at a time, the individual lines appear as ribbed surfaces on parts. Downward facing surfaces usually reveal more layer lines. Certain build orientations are better for curved or square features while delicate features require special consideration. Technologies with higher instances of warp (or material deformation) must account for large flat surfaces during build orientation. It is critical to consider these factors because how a part is oriented determines where supports are added – or needed – within the build. Supports are a huge factor for 3D printing, and can affect material finish and accuracy of a 3D printed part.

3D Printing With Support Structures Animation
Fig. 3

Supports

Most 3D printing processes require support structures to act as “scaffolding” for features that can’t be built above open air, such as overhangs, undercuts, holes, cavities, etc. Where supports are required largely depends on the material, build process (3D print technology) and build resolution (layer thickness), among other factors. Support structures are usually made using the same or similar material as the final build and are removed after the model cures. We will delve deeper into why technologies require supports – and which ones do not – once we break out into individual 3D printing processes.

3D Printing in a Nutshell

Let’s recap: 3D printing, regardless of process, takes a 3D CAD file, slices it into 2-D layers, and additively builds up a part 2-D layer by 2-D layer. 3D printing is significant because it changes the way we think about manufacturing.

We’ve detailed why 3D printing is viewed as a game-changer for manufacturing in the next section, including how 3D printing has changed prototyping and production through cost, lead time and design freedom.


Why 3D Printing is (Still) a Game-Changer


3D printing brings a revolutionary approach to manufacturing through three key advantages: Shorter lead time, design freedom, and lower costs.

Lead Time

In today’s on-demand ecosystem of Netflix and Amazon (and Starbucks online ordering, for that matter), it’s a little hard to appreciate manufacturing before 3D printing. The way we have approached prototyping for the past three decades might even be considered a luxury when compared with prototyping prior to 3D printing. Today, 3D printing an early phase design and re-printing it overnight is feasible and affordable thanks to rapid prototyping or 3D printing platforms like PolyJet and Stereolithography. 3D printing a final product in just one to two days is feasible with multiple 3D printing technologies, such as Laser Sintering, Fused Deposition Modeling and Direct Metal Laser Sintering. However, prior to these quick-turn prototyping and production manufacturing processes, bringing an idea into physicality was an involved and costly process and there often wasn’t room or time to re-prototype frequently or make multiple design adjustments. Let’s look at a fairly common example.

Rewind to 1985: You’re a design engineer bidding on a new product. It’s a dream project; you already have an idea of the design. Where do you start? First, you head to the drafting room (AutoCAD, the earliest computer aided design software (CAD), has only been out two years – too early for your company to have fully adopted it just yet). You develop a design, hand drawing details and carefully measuring out dimensions via ruler and pencil. Once the design is finalized, you meet with your model shop or an outside modeling firm. The shop can machine the model manually – adding in features and details, with painstaking hand labor and fabrication – or the shop can create a prototype tool and cast a plastic or metal part, which will add another 2-4 weeks to your project.

You choose CNC machining. Machine drafters help translate your design into instructions a machinist can use to build the part and your design is manually translated into a lengthy program (known as RS-274 or simply g-code) for the machine to read and execute code line by line. The design undergoes further configurations as you figure out what can and can’t be built given your timeframe and the constraints of the manufacturing process. By now, more than a month has passed and your model is still in early production stages.

Fast forward to 2005. You are offered the chance to bid on a new product. It’s a dream project; you’ve had a rough idea of the design for years. You draft out a rough sketch before moving to 3D CAD, easily plugging in dimensions and executing the design in the 3D software (you’re a CAD modeling pro!). You finalize your design with your project leader, upload your 3D CAD file to Stratasys Direct Manufacturing and select PolyJet prototyping. The next afternoon, you’re showing your physical model to your team. They immediately point out a flaw – hey, nobody’s perfect – and you head back to the 3D drawing board. A few prototypes later and you and your team land on it, the perfect model. You order a new print – this time, you need it to be functional and cosmetically finished. Your trusted 3D printing partner, Stratasys Direct Manufacturing, prints up your part in Fused Deposition Modeling, hand sands it down and ships it back to you all in the span of five business days. It’s only been four weeks since you started prototyping. It only took you roughly one month to get your finalized idea into the bidding room.

That’s the difference 3D printing has made—from weeks to days. From “no, we can’t make that” to “yes, we can build it”. And today, 3D printing isn’t just used for prototypes and models. 3D printing includes:

  • Prototyping
  • Manufacturing large entertainment models used in everything from movies to training personnel in new practices
  • Low volume production and tooling
  • Aerospace manufacturing
  • Medical device solutions
  • And much more

It’s a matter of knowing which technology is good for what application, and when to use one over the other. But lead time is just one small piece of the 3D printing solutions puzzle. Perhaps the most revolutionary advantage 3D printing offers are its inherent design freedom.

Design Freedom

Traditionally, designers and engineers have relied heavily on the manufacturing process to dictate the end design. Involved conventional manufacturing processes like CNC machining have inherent strict limitations on assembly rules, manufacturability and overall feasibility. Stepping outside of design practices for these conventional manufacturing processes directly results in increased cost and labor. However, sticking to the design rules of the past inevitably results in stunted innovation growth. Additive manufacturing, or 3D printing, has opened doors previously unimaginable to designers and engineers because it doesn’t rely on the same design and manufacturing constraints as conventional manufacturing. Through 3D printing, free-flowing, organic and intricate designs are seamlessly executed while maintaining strength in ways impossible via any other manufacturing process.

In the images below, we’ve laid out some of the more beautifully complicated designs built using a 3D printing process called Laser Sintering. These 3D printed designs are involved, and yet the part can be built in a consolidated unit. Attempting to machine parts like these would be either very expensive or even impossible. There are designs only 3D printing can execute, and without 3D printing they simply wouldn’t be feasible.

Part Produced By Laser Sintering
Fig. 4
Part Produced By Laser Sintering
Fig. 5
Part Produced By Laser Sintering
Fig. 6

An excellent case example of the design freedom of 3D printing comes straight from NASA. NASA’s Marshall Space Flight Center was able to transform a part that previously contained 150+ parts and, through 3D printing, consolidated the whole design into one continuous unit!

NASA DMLS Injector
Fig. 7

Design freedom in 3D printing is considered “zero-cost” because of the layering process. Design features are seamlessly integrated within each cross-section as the part builds, eliminating the need for tooling, labor intensive assembly, and reducing time and part count to result in significant cost savings.

Cost

3D printing reduces manufacturing / production costs through a variety of advances that can be boiled down to three key advantages: Zero tooling, zero-cost complexity, reduced labor. These three advantages ultimately result in shorter lead times, which additionally relates to cost savings. We’ve defined these three cost savers below and how 3D printing accomplishes them.

  1. Zero Tooling: Tooling is required in a variety of production processes, from lost wax tooling for investment casting to steel tooling for injection molding. Tooling typically involves machining an A and B side of a design. Tool designs must take into account design features such as release points, to actually get the molded part out of the tool; holes and angles, which can become difficult to execute given that the tool can’t have floating interior features unattached to the tool itself and features can’t inhibit the release of the molded part; and typical features like wall thickness, which usually can’t vary because varying wall thicknesses can harden at different times which even on a small scale effects the accuracy of the part. There are many design and manufacturability constraints inherent to tooling, which is why 3D printing is such a game changer. 3D printing builds parts from the bottom up and doesn’t require any tooling to execute complicated designs. By eliminating tooling, 3D printing removes the cost and labor of building tools. Plus, 3D printing frees up designs for a much broader range of geometric capabilities – like interior floating parts!
    Example of Interior Floating Parts
    Fig. 8
  2. Zero-Cost Complexity: We covered this idea in the above section, but it’s worth reiterating. With tooling or machining, achieving an interior floating part, for example, would require a lot of extra labor. It would require pins and manual pin extraction, in terms of tooling and molding, or multiple coding and re-orienting of a part in terms of machining. Overall, such an interior feature would be so cost prohibitive to produce, it would most likely not be considered for a final design. Thanks to 3D printing, interior, no access features are seamlessly executed without increased labor, time or design finagling.
  3. Reduced Labor: While 3D printing requires manual labor to remove build supports or smooth surfaces, it reduces manual labor in many ways when compared to conventional processes. As we mentioned above, because 3D printing doesn’t require tooling, it is able to significantly reduce labor associated with tooling production. 3D printing also reduces labor by consolidating multiple part assemblies into one single unit. Eliminating assembly is a huge cost saver. 3D printing further reduces labor through automation. Preparing a part for a build is largely automated with some manual interaction to perfect part orientation or support creation. Unlike machining, which typically requires 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.

It’s a Good Day to 3D Print

While some may disagree on whether or not 3D printing is truly revolutionary for manufacturing, its cost, time and labor reductions positively transform the production landscape in a way not seen since the industrial revolution. It’s a great time to be in the industry, as further materials developments and process controls evolve to further automate and perfect 3D printing for use in thousands more applications. To see where businesses are implementing 3D printing in their practices today and in the future, download our industry report of 700 professionals.


3D Printing Processes, Technology and Materials


PolyJet

Monikers: Material jetting, photocuring, inkjet printing

How it Works: Think of PolyJet like your home 2-D paper printer. Your 2-D color printer lays out minuscule droplets of color onto your paper, forming words and images. In a similar fashion, PolyJet uses fine print head nozzles to deposit droplets of photocurable material in layers as fine as 16 microns to form detailed 3-D parts. Material is simultaneously cured as it is deposited via UV light.

 

PolyJet parts require support structures to build overhanging features and holes. Without support structures, the material can escape its intended form resulting in inaccurate walls, features and other details. PolyJet support material is a separate composition formulated to release from the part when blasted with water. Other material jetting technologies like PolyJet use wax supports which require an oven to melt off and remove.

PolyJet Printer Building a Part
Fig. 9 – Supports (white) fill in the design to keep the features of the part (blue) from shifting.

Materials: PolyJet relies on photopolymer resins. Photopolymers or photocurable materials come in many different kinds of compositions, from flexible to rigid, transparent to opaque. PolyJet is one of two 3D printing technologies to print color directly into a part and it is the only technology capable of printing multiple materials simultaneously, offering gradations from stiff to flexible in one part.

PolyJet Anatomical Model 3D Printed With Multiple Materials
Fig. 10 – This model demonstrates PolyJet’s ability to print in multiple materials. The opaque organs and transparent body were built simultaneously, creating a unique effect.

Applications: Because PolyJet uses UV energy to cure liquid resins, parts can warp and change color with prolonged exposure to heat and light which means PolyJet parts are not used for stressful applications involving rugged use. Ideal PolyJet applications include: Master patterns for cold or low temperature molds; show models; detailed prototypes, and form, fit and feel models.

Why it’s Significant: PolyJet 3D printing is the fastest 3D printing technology commercially available. Parts within a 5” cube can print within as little as 2 hours. Outside of a 5” cube, PolyJet becomes slower (remember, the nozzle is moving back and forth across the platform depositing a thin layer of material, therefore, the farther the nozzle travels, the slower the process becomes). PolyJet prints in the thinnest layers of any 3D print process and that means less visible layer lines for smooth, detailed parts. Its speed, resolution and affordability make it ideal for quick-turn applications, from master patterns to show models to early design prototypes.

PolyJet Velociraptor Dinosaur
Fig. 11 – Check out those wrinkles on this (oddly featherless) velociraptor! These wrinkles are easy details for PolyJet.

Stereolithography

Monikers: Vat photopolymerization, photocuring, SLA, SL

How it Works: Stereolithography relies on a precise UV laser to cure liquid plastic layer by layer. Its build platform sits atop a bath of liquid plastic. The build platform is coated with a thin layer of liquid plastic. A UV laser hits dynamic mirrors which direct the UV energy downwards across the build platform, curing the liquid plastic in precise patterns one cross-section at a time. After each layer is cured, the build platform retracts into the bath of liquid while a recoater blade evenly distributes the plastic across each new layer.

 

As with PolyJet, Stereolithography also requires build supports. Stereolithography support material is the same material as the final part. Unlike PolyJet, Stereolithography parts do not fully cure during build. During printing, the resin within the chamber can become trapped within the part or pool in certain part features. If leftover resin is not removed, it reabsorbs into the part causing bloating and design distortion. Therefore, after a build is complete, excess resin is drained and supports are removed. The part then enters a UV oven to complete curing.

Stereolithography Animation
Fig. 12

Materials: Stereolithography uses photocurable plastics to form rigid, opaque and transparent parts in white, grey and clear. Stereolithography materials, which can warp or change color with prolonged exposure to light and heat, aren’t ideal for stressful applications.

SL Investment Casting Pattern
Fig. 13

Applications: Stereolithography is perhaps best known for its ability to build mostly hollow parts with a thicker outer shell and a honeycomb interior. The most common application for hollow Stereolithography parts is investment casting patterns. Additional common applications for Stereolithography include: large entertainment models, prototypes, and master patterns for cold or low temperature molds.

Why it’s Significant: While Stereolithography is a staple in prototyping and modeling for clear, large and lightweight patterns and parts, it’s most significant contribution to production applications might be its ability to print mostly hollow, lightweight investment casting patterns. Stereolithography is an alternative to conventional investment cast patterns. Traditional lost wax patterns for investment casting can take weeks to build and, should an error or design modification arise, the tool must be scraped and re-built. In contrast, Stereolithography does not require tooling and is built all in one piece eliminating the need for multi-part assembly work. Investment cast pattern designs can go directly from designer to printer to foundry without the significant investment of time and money associated with lost wax tooling.


Fused Deposition Modeling

Monikers: Fused Filament Fabrication (FFF), filament extrusion, fused filament deposition, material deposition, FDM

How it Works: FDM extrudes heated thermoplastic through a nozzle layer by layer to form parts. FDM uses multiple nozzles for final part and support material. After each layer is extruded, the build platform moves down making room for the following layer. FDM can deposit thicker or thinner layers which in turn can speed up a build (thicker layers) or decrease hand finishing time (thinner layers) due to the smoother surface. FDM requires support material to build angles, overhangs and holes that can’t be built on thin air.

 

Materials: FDM materials can be opaque to semi-transparent in multiple colors including blue, red, yellow, white, black, and tan. FDM thermoplastics include FAR-rated and biocompatible thermoplastics, and many thermoplastics common to injection molding such as ABS and ASA.

Applications: FDM is commonly used to build aircraft interior components and ducting, and medical, consumer, industrial, and transportation prototypes and products.

FDM Aircraft Ducting
Fig. 14

Why it’s Significant: FDM uses the same materials aerospace, medical and industrial sectors have relied on from injection molding with the ability to build complex geometries and the lower material consumption associated with 3D printing. Because FDM builds layer by layer, features and multiple components can be combined into one design, minimizing assembly. Undercuts, interior features, attachment fittings are seamlessly incorporated into one part. FDM has become invaluable to sectors requiring lightweight, strong and affordable plastic parts – without the need for hard tooling or machining.


Laser Sintering

Monikers: Powder bed fusion, Selective Laser Sintering, LS, SLS

How it Works: Laser Sintering requires an enclosed build chamber to heat and fuse parts layer by layer. Laser Sintering begins by heating its internal build chamber to just below the melting point of the powdered plastic. A CO2 laser hits the powder in determined design patterns, thus bringing specific areas to full melting point to form parts one layer at a time. Laser Sintering is the only 3D printing process that is completely free from added support structures. The unsintered powder within the chamber is dense enough to support the part as it builds.

 

Materials: Laser Sintering utilizes Nylon 11 and 12, raw and filled, to deliver FAR-rated and biocompatible plastics. A filled nylon used with Laser Sintering is a composite of one or two more materials, including glass, carbon or aluminum. Filled nylons can increase rigidity, strength, heat deflection or as-built surface finish.

LS: Composite Part
Fig. 15

Applications: Laser Sintering is one of the most widely used 3D printing plastic technologies for aerospace ducting and similar rugged, high temperature uses. It is also used in the automotive, medical, consumer, art, and architecture sectors for thousands of products.

Why it’s Significant: Laser sintering was one of the earliest 3D printing processes to be adopted into end-use part production. It was one of the first 3D printing technologies to take to the skies through aerospace ducting production. Laser Sintering doesn’t require labor to remove support structures; powder is simply shaken out of interior areas. Therefore Laser Sintering is able to produce truly zero-cost complexities. It is used to consolidate tricky ducting applications because it can build interior, no-access features seamlessly while using high-temperature, chemical-resistant materials. It uses lightweight material with exception strength to deliver fuel tanks, ailerons, control surfaces, and many other critical UAV features.


Direct Metal Laser Sintering

Monikers: Metal 3D printing, additive metal manufacturing, metal powder bed fusion

How it Works: DMLS requires a completely enclosed build chamber. The chamber is heated to a degree just below the melting point of the metal. A thin layer of powdered metal is deposited across a clean build platform and a powerful heat laser sinters, or melts, the design into the powder. The process repeats, sintering layer by layer.

 

While plastic laser sintering does not require supports, DMLS requires support structures for angles, holes and over-hanging features. DMLS requires support structures because the temperature used to melt metal is exponentially higher than the temperature used to melt plastic, and once the metal powder melts it becomes denser than the unsintered powder and can therefore simply fall through the powder or break off from the design if left unsupported. During post-processing, supports are machined off and sanding, bead blasting or other surface treatments are implemented to remove support residue. To avoid the need for support structures with DMLS, there are many design tricks which we’ve outlined in our DMLS white paper: Getting the Most out of Metal 3D printing.

Materials: Creating powdered metals compatible with DMLS is a huge market, and therefore new metals are popping up every few years. Currently, DMLS offers titanium, aluminum, Inconel, cobalt chrome and stainless steel alloys.

DMLS Part
Fig. 16

Applications: DMLS is an alternative to manufacturing metal parts and components impossible or cost-prohibitive to produce using conventional methods such as machining or casting. DMLS is a staple for complex parts requiring involved geometries and for parts that have difficult to access features or would require labor-intensive assembly to complete. DMLS builds consolidated, lightweight units that remove the intensive assembly processes and don’t require a tool or mold to achieve. Common applications for DMLS include medical device prototypes and products, aerospace and energy units and parts, and metal manufacturing of custom parts.

Why it’s Significant: DMLS produces fully dense, smartly designed metal parts without tooling. Inner features that would be impossible to machine are possible with DMLS. This metal printing process takes an engine, underhood, or medical component and gives it a direct manufacturing solution. In some applications, DMLS has consolidated over 150 parts into 2 complicated units that ultimately simplify production, reduce manufacturing time and labor, and increase overall business efficiencies.


Additional Resources


These staple 3D printing technologies comprise a foundation for understanding the many variations of 3D printing based on these core processes. If you’re ready to look into starting a new project, we recommend checking out these additional sources for further knowledge on how best to implement 3D printing into your business practices and product development:

BLOG: 7 Questions to Ask Yourself When Choosing a 3D Printing Technology and Material

  • We’re sharing the 7 fundamental questions every design engineer should ask themselves when determining how best to produce their new idea.

WEBINAR: Where Additive Meets Traditional Manufacturing

  • Discover the best kept industry secrets on how veteran machinists use 3D printing to complement traditional manufacturing.

WHITE PAPER: Choosing the Right Material for Your Application

  • Our exclusive white paper takes an in-depth look at each technology and the available materials that can put your project on the road to success.

INDUSTRY REPORT: State of 3D Printing

  • We interviewed 700 industry professionals on current and future trends for 3D printing including how businesses plan to implement 3D printing and where they look for advancements.

WOHLERS REPORT: 2015

  • The Wohlers report has a guide to all 3D printing systems and platforms currently available and is a key resource for any beginner.
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