3D Printing: The Complete Guide
3D printing, also known as additive manufacturing, is the most agile and affordable option for manufacturing small- to medium-sized quantities of plastic and certain metal products—from industrial parts and consumer goods to functional prototypes and aesthetic models.
Additive manufacturing creates products layer by layer, unlike subtractive manufacturing (machining), which removes material from a solid block, or formative manufacturing (injection molding or thermoforming), which shapes products using molds. This makes 3D printing unique among manufacturing technologies in that it requires no tooling or other setup costs and can begin manufacturing right away.
As a result, 3D printing allows for accelerated product development cycles and unmatched economy for low-volume manufacturing. And because of the unique mechanisms of additive manufacturing, 3D printing can easily achieve designs that would be impossible with any other technology, opening the way for new product innovations to reduce part weight, eliminate assemblies and improve performance.
When correctly applied, 3D printing can save businesses hundreds of thousands of dollars and months of time, increasing their competitive advantage and allowing them to get better products to market faster.
What is 3D printing?
3D printing builds parts and products layer by layer using different methods to fuse and solidify those layers.
Before the 3D printing process can begin, digital 3D models must be broken down into 2D cross-sections that the printer can then use to build parts one layer at a time. This is accomplished in G-code, the machine language of 3D printers.
The technology for creating these layers varies by printer and includes fusing melted filaments, sintering with lasers, or curing with UV light or binding agents. Some 3D printers combine multiple methods.
These different 3D printing technologies offer a wide range of materials that is growing all the time. While plastics are the most common, new metal printing technologies like ExOne’s direct material printing have dramatically increased the affordability of 3D printed metals. 3D printed materials can be rigid or rubbery and offer many chemical, thermal and mechanical properties. It’s even possible to 3D print with sand to create sand molds and cores.
Unlike other technologies, the complexity of a design does not impact the cost of a 3D printed part. 3D printed parts can be used with their machine finish―which varies in quality by the type of machine―or can be finished manually. The cost of 3D printing is limited to materials, print speed, part size and any additional post-processing.
3D printing advantages
No expensive tooling or other start-up costs
Fast turnaround―as little as one day with Multi Jet Fusion or ColorJet
Easy design changes at no additional cost
Complex geometries
Combine multi-part assemblies into a single piece
Reduced inventory and overhead through just-in-time manufacturing
No material waste
When to use 3D printing
Although originally used primarily for prototyping, new developments have made 3D printing economical for small to medium production runs.
So when does it make sense to use 3D printing? As with most manufacturing questions, the answer must be determined on a case-by-case basis. However, the earlier in your product development process you start considering 3D printing, the more it can benefit your production.
Below are some qualities that may indicate that a project is a good candidate for 3D printing:
Smaller parts that would be difficult to machine
Production of less than 1000 units
Evolving designs or tooling for product development
Highly customized products like prosthetics or hearing aides where every unit is unique
Complex geometries, nested cores or single-piece parts with tubes that would be impossible to machine or mold
Lightweight parts with strong lattice interiors
Organic shapes
3D printing applications
While the advent of 3D printing inspired utopian visions of consumer manufacturing on-demand, the truth is that 3D printing is best suited to specific applications—complementing the capabilities of traditional manufacturing processes instead of supplanting them.
The idea that 3D printing will reduce jobs is one of the most persistent myths about the technology. In fact, the opposite is true! By expanding manufacturing capabilities for businesses of all sizes, 3D printing creates new jobs while expanding opportunities for existing technologies.
3D printing adds value throughout product life cycles, with common applications including:
Proof-of-concept and aesthetic models
Functional prototypes for product development
Transitioning to manufacturing
Small- to medium-sized production runs
Tooling and molds
Product support/replacement parts
Choosing the right 3D printer
Before we get into the different kinds of printers and materials available, there are a few key factors to consider when determining which 3D printer is best suited to a project:
The first and most important is the purpose of the project. Is this for a consumer product, industrial part, functional prototype, proof-of-concept or aesthetic model? The answer to this question will generally reduce your options to two or three printers.
The next consideration is whether there are any specific material requirements for the project—things like heat resistance, chemical resistance, corrosion resistance and biocompatibility.
Lastly, businesses should think about how many units they want to order and how large each piece is. Printers scale differently with part size and quantity, so these considerations will likely be the most important economic factor for any project.
Types of 3D printers
The term “3D printing” does not describe a single technology but instead refers to a variety of printers that use a few different methods to create products. Here, we’ll outline the seven main types of printing before going into some of the most common printers in detail.
Binder Jetting printers like Multi Jet Fusion, ColorJet, Voxeljet, and ExOne’s direct material printing selectively apply a binding agent to a bed of plastic or metal powder to solidify parts. Once completed, the parts must be cleaned of excess powder. Binder jetting does not require supports for parts.
Powder Bed Fusion uses lasers to sinter plastic or metal powders with a strong molecular bond. Historically, selective laser sintering (SLS) and direct metal laser sintering (DMLS) have produced the strongest 3D prints. However, newer technologies like MJF and direct material printing can now make comparable parts in a fraction of the time and cost.
Material Extrusion is the process used by most consumer 3D printers. Fused Deposition Modeling (FDM), also known as Fused Filament Fabrication (FFF), deposits heated plastic filaments in successive layers. These parts are durable and accurate but have a rough machine finish that is not suited to consumer products.
VAT Polymerization technologies like stereolithography (SLA) and digital light processing (DLP) use UV light to bond a vat of liquid photopolymers. These printers create the most detailed 3D prints and offer high-quality finishes but lack the mechanical strength of other technologies.
Material Jetting places drops of liquid material on the printer bed one layer at a time. PolyJet, the most common type of material jetting printer, uses a photopolymer which is then cured with UV light. Material jetting produces highly detailed prints that are ideal for aesthetic models but too brittle for functional parts.
Sheet Lamination stacks metal, plastic or paper sheets which are welded or glued together. Each layer is then milled to achieve the desired shape. This fast and inexpensive technology is used almost exclusively for aesthetic models.
Directed Energy Deposition (DED) is the oldest and least common metal 3D printing technology. It works similarly to FDM: a metal powder or wire is melted and applied in layers to build the print. DED can achieve larger builds than other metal 3D printers and is often used in conjunction with machining.
Plastic 3D printers
Multi Jet Fusion (MJF)
MJF is one of the newest and most powerful 3D printing technologies on the market. It uses a combination of binder jetting and powder bed fusion to produce nylon parts with nearly isotropic mechanical properties, making it an excellent choice for industrial-strength parts and consumer products alike.
And because of its large printing bed and fast turnaround, MJF 3D printing is viable for small to medium production runs in quantities up to or exceeding 1000 parts. As a result, MJF is the premier 3D printing option for general-purpose parts, products and prototypes.
Currently, MJF is compatible with nylon 12, nylon 11 and glass-filled nylon—allowing parts to be rigid, flexible or hard as needed. HP has announced plans to add rubbery TPU and flexible PP materials within the year.
Fused Deposition Modeling (FDM)
FDM printers extrude thermoplastic filament from a heated nozzle to be deposited and cured in successive layers. If you’re imagining something like a highly accurate computer-controlled hot glue gun, you’re on the right track.
One of the fastest and most affordable 3D printing technologies, FDM also offers the broadest material selection of any 3D printer.
Common applications include small runs of production parts for performance industries (like aerospace) and functional, non-load-bearing prototypes. However, because of its rough finish, limited fine detail, and reduced mechanical strength (due to its lack of isotropy), FDM is not generally used for consumer products.
Selective Laser Sintering (SLS)
SLS rolls out thin layers of powdered polymer that cover the entire bed of the printer. Once the polymer is in place, a laser sinters a cross-section of the design—a partial melt that occurs at a molecular level. Layers of polymer are added and sintered until the process is complete.
The variety of filled and unfilled nylons available for SLS prints allow parts to be stiff or flexible, hard or rubbery, and meet a range of thermal, mechanical, and chemical demands. And with nearly isotropic mechanical properties, SLS parts have excellent mechanical strength.
While more expensive than MJF and consumer-grade FDM products, SLS scales well and is generally cheaper than FDM for production-grade parts. SLS parts have a textured finish and can be susceptible to warping on large surfaces or small details.
Large Format Printing (Voxeljet)
Another binder-jetting technology, Voxeljet’s large format 3D printers selectively apply binding agents to successive layers of powdered material. As each layer solidifies, the printing bed moves down, a new coat of powder covers the bed, and more binding agent fuses the part.
Large format printing is unique among technologies for the bed size it offers—up to 1000 mm x 600 mm x 500 mm—and the materials available to it. In addition to the acrylic-based PMMA, Voxeljet can use sand to make cores and molds.
Voxeljet prints can also be infused with wax to create low-ash burnout patterns for investment casting, one of its most common applications. Because of its bed size and material selection, Voxeljet is a great option for industrial tooling.
ColorJet
ColorJet printing (CJP), the oldest binder-jetting technology, forms prints from two elements: the core and the binder. The powdered white core forms the body of each part and is spread over the printing bed. Then, the printer selectively applies a thin coat of colored binder to solidify the core before moving on to the next layer.
The results are detailed, full-color prints that are quick and inexpensive to produce—great for aesthetic models and interactive marketing. However, ColorJet prints should not be used for functional parts.
PolyJet
One of the highest detail 3D printing technologies available, PolyJet places many small droplets of polymer in a single layer. The printer then cures the polymer droplets with UV light before adding the next layer.
PolyJet parts have superior fine detail, surface finish, and accuracy. Moreover, they can be printed in an array of colors, a unique property among 3D printers.
While PolyJet prints can be brittle and are not suited to functional parts, they are the best option when aesthetics and fine details are a priority.
Stereolithography (SLA)
The oldest 3D printing technology, SLA uses UV light to selectively cure layers of an object within a vat of photopolymer resin. Prints can be made with rigid polymers as well as some rubbers. Like polyjet SLA provides the highest detail and best surface finish.
SLA accurately achieves a very high level of fine detail and surface finish that rivals injection molding. However, because of its slow print speed and expensive resins, SLA does not scale well. Additionally, SLA parts can be brittle and are not recommended for functional parts or outdoor use―it is primarily used for aesthetic prototypes and proofs of concept.
Metal 3D printers
Direct Metal Printing
Although binder jetting is a common technique for plastic and nylon prints, ExOne’s direct material printing was the first to bring the technology to metal 3D printing. Like its plastic counterparts, direct metal printing applies a binding agent to a bed of metal powder, typically stainless steel. Then, parts are cured and sintered for improved strength.
Direct metal printing is up to 10 times faster than other metal printing technologies and offers superior value for part quantities up to 1000 parts. While other metal printers are prohibitively expensive and only used for prototypes or very small quantities of parts, direct metal unlocks the power of 3D printing for production runs of metal prints that rival machined parts in quality and performance. Moreover, the stainless steel parts produced by direct metal printing are easy to machine for improved tolerances or appearance.
Direct Metal Laser Sintering (DMLS)
DMLS works on the same principle as SLS―a laser sinters powdered metal in successive layers. DMLS parts are very expensive but can achieve greater mechanical strength than just about any other technology. Plus, DMLS is compatible with specialty metals that can be difficult or impossible to use with traditional manufacturing.
Because of the extreme cost of DMLS, it is typically only used for specialty parts that cannot be produced with any other technology or when a project demands small runs on a faster turnaround than machining can deliver. Performance applications like those in the aerospace industry are some of the most common uses for DMLS parts.
Selective Laser Melting (SLM)
Selective laser melting differs from DMLS in that it uses a laser to fully melt layers of metal powder as opposed to the partial melt of sintering. As a result, parts made with SLM are denser than DMLS parts but can be subject to internal defects and stresses.
Because of the need for materials to melt completely, SLM is more limited than DMLS when it comes to compatible metals. Materials include stainless steel, titanium, aluminum and cobalt chrome.
Ultimately, as DMLS has evolved to use more powerful lasers with more complete melts, the two technologies have become very similar—the terms “DMLS” and “SLM” are often used interchangeably.
Electron Beam Melting (EBM)
EBM is very similar to SLM, with the main difference being that EBM uses a powerful electron beam instead of a laser to fully melt metal powders. The use of the electron beam requires that EBM parts be built in a vacuum.
EBM materials are even more limited than SLM and consist primarily of titanium and cobalt chrome. EBM parts offer improved precision and surface finish than DMLS and SLM but with slightly lower accuracy.
3D printing materials
Choosing the right material for a given project is every bit as important as choosing the right 3D printer. In fact, the 3D printer to be used is often determined by material requirements.
Whether a product needs to be rigid, flexible, mechanically strong, medical grade, food grade, chemical resistant, heat resistant, flame retardant, colorful or clear will all determine which material is the best fit.
Below is a list of some of the most popular plastics and metals for 3D printing. Check out our 3D printed materials page for even more information on materials.
Plastic
Nylon 12 (PA)—The go-to choice for industrial-strength parts. Used by MJF and SLS. High heat and chemical resistance, low water absorption. Quality gray (MJF) or white (SLS) matte finish that can be dyed black.
Nylon 11 (PA)—Another SLS and MJF nylon with more flexibility than nylon 12. Frequently used for tubing, fuel lines and hoses as well as living hinges. Available in white (SLS) or gray (MJF) with black dye options.
Ultem 9085 and Ultem 1010—Flame-retardant, high-performance thermoplastics with very high heat resistance and strength-to-weight ratio. Often used in aerospace applications.
PMMA—Dyeable plastic used for large format printing. Good tensile strength and high heat resistance. Large surfaces can warp.
Filled Nylons—Filled nylons offer many options for strength, rigidity, aesthetics and chemical and heat resistance. Glass-filled nylon is available for both MJF and SLS, while other filled nylons are exclusive to SLS.
Thermoplastic Elastomer (TPE)—Flexible thermoplastic elastomers for creating rubber-like parts with SLS.
Polycarbonate (PC)—A durable, biocompatible polycarbonate used by FDM for medical applications. Highly sterilizable. Comes in white.
ASA—UV-resistant FDM material, great for outdoor applications with lots of sun exposure.
Polypropylene (PP)—Semi-rigid, extremely flexible thermoplastic polymer with high heat and corrosion resistance. Often used in the food industry and for piping. Available for FDM and soon to be available for MJF.
Thermoplastic Polyurethane (TPU)—Elastic, rubber-like plastic with high resistance to oil and grease. Used in a wide range of consumer and industrial applications. Currently only available for FDM, but slated to be introduced for MJF in the next year.
PPSF/PPSU—FDM plastic with very high heath and chemical resistance. Used for testing performance industrial prototypes and small runs of parts.
Metal
Stainless Steel—The workhorse of 3D printed metals. High strength and corrosion resistance, sterilizable and easy to machine. Very economical in small to medium quantities when using direct metal printing. Varietie include 304, 316, 17-4 and more.
Tungsten-Bronze—High-density shielding material with a high melting point for direct metal printing. Used for radiation shielding and in applications for aerospace, medical and nuclear industries.
Titanium Ti64—Strong, corrosion-resistant and biocompatible metal for DMLS. Commonly used for medical devices and applications in the transportation industry.
Cobalt Chrome MP1—Another biocompatible DMLS metal with even greater corrosion resistance and strength, often used for replacement joints and dental implants.
Aluminum ALSi10Mg—Lightweight and strong DMLS metal, used for parts with thin walls or complex geometry.
Inconel 625 and Inconel 718—DMLS nickel alloys with superior mechanical strength as well as corrosion and thermal resistance. Often used in high-heat, high-corrosion performance applications, especially in aerospace.
Maraging Steel—Hard and durable tool steel, used to produce molds, tooling, and other industrial fixtures with DMLS.
Developing products for 3D printing with design for additive manufacturing (DfAM)
Additive manufacturing has rewritten the rules for design, which means engineers and designers need to rethink products and supply lines from the ground up if they want to get the most out of 3D printing for their businesses. As a general rule, the sooner in product development that you start thinking about 3D printing, the more it will benefit your business.
Businesses often compare 3D printing to other technologies on a purely economic basis using the exact same part design. While 3D printing may offer significant savings, this is only a fraction of the technology’s potential.
To understand why this is the case, let’s take a look at some of the unique capabilities of 3D printing:
Organic shapes, internal geometries and uneven wall thicknesses that are difficult or impossible to achieve with injection molding or machining are easy with 3D printing. This allows designers to reinforce high-stress areas of the part while reducing mass in non-load-bearing sections, dramatically reduce weight by substituting lattices for solid sections and streamline designs by replacing multi-piece assemblies with single parts.
3D printing can print single units of custom parts at no additional cost. Unlike traditional manufacturing, where each setup is used to produce many versions of the same part, 3D printing can just as easily print one copy of each part, creating unprecedented possibilities for highly customized parts like medical prosthetics. This same quality even allows businesses to produce every part for an entire assembly in a single run.
And with no start-up time or setup costs, 3D printing is ideal for just-in-time manufacturing and creating limited quantities of replacement parts—allowing businesses to dramatically reduce inventory and overhead by only producing exactly what they need at any given time.
Maximizing printer space is one of the best ways to reduce costs, because the cost per part of 3D printing is almost entirely determined by how many parts can be printed in a single cycle of the printer. This can be achieved through any number of techniques, including tesselating or stacking parts.
As 3D printing technologies continue to develop along with our understanding of them, it’s exciting to imagine the possibilities for the future of manufacturing. To learn more about designing for additive manufacturing, check out our Design for Additive Manufacturing guide.
For home printers, rigid.ink has an excellent troubleshooting guide for common 3D printing problems.
3D printed tooling for thermoforming, urethane casting and more
3D printing can benefit products made with other technologies as well. 3D printed molds and tools are durable—good for hundreds or even thousands of uses—and are much faster and less expensive to produce than machined tooling. 3D printed burnout patterns for investment casting are faster and less expensive to produce than any other technology. These advantages can provide cost-effective options for technologies that would otherwise be too expensive at a given production volume or schedule.
By using 3D printed tooling for casting, thermoforming or injection molding, businesses can accelerate product development and save tens of thousands of dollars. Going through more iterations in less time makes better products that get to market sooner. And for some technologies, 3D printed tooling is just as viable for full production runs!
It’s not just molds, either. 3D printing is a great option for industrial tools like robotic-arm-end effectors and injection nozzles, where parts can be printed with integrated ports for wiring and tubes. These streamlined designs improve functionality, create smaller part profiles and reduce the need for assembly.
So even if a final product needs to be produced with another technology, businesses can still take advantage of the unique strengths of 3D printing.
3D printed replacement parts
As 3D printing has come to rival machining in part strength and quality, 3D printed replacement parts have become a great option for extending product life cycles, both for consumer products and industrial equipment.
Maintaining customer support for old equipment requires major investments from businesses. At the same time, customers don’t want to be left with a dead product! 3D printing makes it possible to supply replacement parts without expensive supply chains and inventory space.
Similarly, anyone who has ever owned major industrial equipment has probably experienced the dread that occurs when an original equipment manufacturer (OEM) discontinues support for its product. Businesses are often faced with the difficult choice of trying to maintain unsupported equipment with increasingly expensive and hard-to-find replacement parts or purchasing pricey new equipment that they might not otherwise need. With 3D printing and 3D scanning, it’s easy to reverse engineer long-lasting replacement parts to keep industrial equipment running even after the OEM has discontinued support.
3D printing vs. machining
3D printing is most commonly compared with machining. While 3D printing is more affordable for very low quantities, both offer good value for medium quantities—each with its own advantages and disadvantages.
Machining is extremely accurate—as it does not have any of the shrinking of 3D printing or injection molding—and it offers unmatched surface finish. The wide selection of solid materials used in machining yields parts that are stronger than most 3D prints, with the exception of some printed metals. On top of that, machining can create larger parts than most 3D printers at significantly lower cost. Parts with greater material mass and simpler designs are ideal for machining.
Like all manufacturing technologies, however, machining has its drawbacks. Tools must be calibrated for each new design before manufacturing can begin and require manual intervention throughout the production, increasing lead times, lengthening production schedules and raising labor costs. Many projects even require custom tools.
Because machining subtracts material from the outside in, it is usually not possible to render interior geometries—something which is easy to do with 3D printing. Similarly, since parts must be affixed to the machine, those that need to be machined on all four sides require additional manual intervention. Small parts (smaller than 5”) can be difficult to secure and can take even more labor.
Machining requires somewhat larger volumes than 3D printing to achieve economical manufacturing and is more expensive at lower volumes. Both stop providing reduced costs after a few hundred units, however, as machining’s setup costs amortize relatively quickly.
Each technology has its place, and they’re not mutually exclusive: 3D printed parts can be machined to achieve tighter tolerances and improve their finish, allowing manufacturers to get the best of both worlds.
In summary, if your parts are smaller than 5”, have complex geometries or would require machining on all four sides, 3D printing is probably the better choice. For larger parts with simpler designs and solid mass, machining may offer better value.
3D printing vs. injection molding
When it comes to comparing 3D printing and injection molding, the determining factor will almost always be the scale of your production.
Injection molding is the undisputed king for most high-volume manufacturing and has been for centuries (literally). It offers excellent surface finish and, while not as accurate as machining due to shrinkage, is highly repeatable at scale. At the same time, injection molding cannot create hollow tubes, varying wall thicknesses or internal geometries in a single piece―all of which are easy to 3D print.
If you’re making plastic parts in runs greater than 1000 units, you’ll want to use injection molding unless your parts are very small. Metal part options are a little more complex, as they vary by the metal being used. There’s die casting, metal injection molding, metal stamping and more—but at the end of the day, these are all exclusively high-volume manufacturing technologies.
Injection molding’s applications are limited by the expensive and time-consuming tooling they require. Molds for plastic injection molding take 4–8 weeks to produce and cost anywhere from tens to hundreds of thousands of dollars. Metal injection molds cost even more. If you decide you want to change your design, then you have to pay and wait all over again.
Once made, however, these molds last practically forever. The tooling costs can be amortized over tens of thousands of units, making injection molding extremely economical at high volumes but prohibitively expensive at low volumes.
In many ways, injection molding is the opposite of 3D printing. While the cost curve of injection molding is long and asymptotic, the cost curve of 3D printing is basically flat and is almost entirely unaffected by economies of scale. If you’re looking at an order of less than 500 units, you probably won’t even consider injection molding. Unlike injection molding, however, the cost per part of 3D printing effectively stops scaling once your order is big enough to fill up an entire printer.
The benefits of using a 3D printing service bureau
Years ago, when people imagined the future of 3D printing, they often pictured home appliances that could materialize any object a consumer needed—Star Trek-style.
The reality of modern 3D printing is a bit different. While there are many consumer 3D printers that can be a lot of fun for hobbyists, they pale in effectiveness to their industrial cousins.
Like all industrial equipment, however, high-end 3D printers are expensive. The cost is hard to justify if they won’t be running continuously. And because different types of printers perform different functions, there is no one-size-fits-all printing solution. Even for large businesses, it rarely makes sense to purchase industrial 3D printers for in-house use.
Instead, 3D printing service bureaus allow businesses to order high-quality 3D printed parts and products made with the latest technology and backed by knowledgeable 3D printing engineers. Running the machines may sound easy, but it requires specialized knowledge to get the best results. And as the technology advances, a service bureau will always stay on top of the latest and greatest so businesses don’t have to.
When you use a service bureau like RapidMade, our expert engineers become your expert engineers. We have experience with thousands of projects to help you get the most from your project and optimize your product designs. Plus, since 3D printing runs on 3D files, communication and design changes are easy―no flying out to visit factories or coordinating long supply chains.
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