The 7 Types of Additive Manufacturing: An Engineer’s Guide

If you’ve ever tried to navigate the world of 3D printing, you’ve likely been hit by a tidal wave of acronyms: FDM, SLA, SLS, DMLS, MEX, VPP, PBF… it’s a confusing landscape where marketing terms and technical standards collide. What do they all mean? How do they relate? And which one is right for your project?

Here’s the quick answer you’re looking for. According to the official ASTM F42 / ISO 17296 standard, there are exactly seven categories of Additive Manufacturing (AM). Every 3D printing technology on the market fits into one of these families:

1. Vat Photopolymerization (VPP)
2. Material Extrusion (MEX)
3. Powder Bed Fusion (PBF)
4. Material Jetting (MJT)
5. Binder Jetting (BJT)
6. Directed Energy Deposition (DED)
7. Sheet Lamination (SHL)

The problem is that simply listing them doesn’t explain the profound differences in how they work, the materials they use, or the problems they solve. Understanding these seven families is the key to moving from a hobbyist to a professional who can strategically select the right tool for the job.

At RM (Rapid Manufacturing), we work with these technologies every single day. This isn’t just a list for us; it’s our toolbox. In this definitive guide, we will demystify the entire landscape. We will explain each of the seven AM types, explore the common technologies within them, and give you the practical knowledge to understand why a part might be printed with a laser curing resin versus another built by welding metal powder.

Why 7 Types? The Official ASTM Framework

Before we dive in, it’s important to understand why this framework exists. For years, the 3D printing industry was like the Wild West. Companies invented their own marketing terms for their processes, leading to massive confusion. To bring order to the chaos, ASTM International, a globally respected standards organization, formed Committee F42 on Additive Manufacturing Technologies.

They created a system that ignores brand names and focuses on the fundamental physics of the process—how the material is joined together to form a part. This is why it’s the gold standard for engineers. It groups technologies that work in similar ways, which means they often share similar strengths and weaknesses.

Let’s begin our deep dive.

Vat Photopolymerization (VPP): Curing Liquid into Solids

Vat Photopolymerization is one of the oldest and most precise forms of 3D printing. If your primary goal is achieving razor-sharp details and a surface finish that looks almost injection-molded, VPP is where you start.

The Core Concept: Light as a Chisel

Imagine a shallow pool (a “vat”) filled with a special liquid plastic called a photopolymer resin. This resin has a unique property: it remains a liquid until it’s exposed to a specific wavelength of ultraviolet (UV) light, at which point it instantly hardens, or “cures.” VPP technologies use this principle, employing a highly precise light source to “draw” the shape of a layer onto the surface of the resin, solidifying it. The process is repeated, layer by painstaking layer, to build a solid object from the liquid.

The Process Step-by-Step

While different VPP machines exist, they all follow a similar workflow:

1. Initialization: A build platform lowers into the vat of photopolymer resin, leaving a tiny, precise gap between the platform and the bottom of the vat—the thickness of a single layer.
2. Curing: A controlled UV light source selectively illuminates the resin in the shape of the first cross-section of the part. The exposed resin solidifies.
3. Layer Change: The build platform moves up (or down, in some machines) by one layer height, allowing a fresh layer of liquid resin to flow into the gap.
4. Repetition: The process repeats, with the light source curing each subsequent layer and fusing it to the one below until the entire part is complete.
5. Post-Processing: Once printing is finished, the part is lifted from the vat, dripping with excess resin. It must be chemically washed (typically in isopropyl alcohol) and then fully cured in a UV chamber to achieve its final material properties.

Key Technologies Within VPP

• Stereolithography (SLA): This is the original VPP technology. It uses a single UV laser beam, directed by mirrors (galvanometers), to trace the geometry of each layer. It’s incredibly precise but can be slower as the laser has to draw every single line.
• Digital Light Processing (DLP): Instead of a laser, DLP uses a digital projector to flash an image of the entire layer all at once, like a slide in a slideshow. This is much faster than SLA, especially for large, solid parts, as the complexity of the layer doesn’t affect the cure time.
• Masked SLA (MSLA or LCD): This is the technology that brought high-resolution resin printing to the masses. It uses a powerful UV LED array as a backlight, which is “masked” by an LCD screen that displays the shape of the layer. The LCD acts as a stencil, only allowing light to pass through where the part should be. It’s cost-effective and very fast.

Materials, Pros, Cons, and Applications

• Materials: Liquid photopolymer resins. These come in a huge variety, including standard resins, tough/durable resins (mimicking ABS), flexible resins (mimicking rubber), and castable resins for jewelry making.
• Pros: Unmatched detail and accuracy; incredibly smooth surface finish; ideal for complex and intricate geometries.
• Cons: Parts can be brittle; requires messy post-processing (washing and curing); material properties can degrade with prolonged UV exposure.
• Best Applications: High-fidelity prototyping, dental and medical models, jewelry casting patterns, tabletop miniatures, and any application where fine features are the top priority.

Material Extrusion (MEX): Building with Filaments

This is, by far, the most common and recognizable form of 3D printing. If you’ve seen a desktop 3D printer in a school, library, or a friend’s workshop, it almost certainly uses Material Extrusion.

The Core Concept: A High-Tech Hot Glue Gun

The principle behind MEX is incredibly simple. A long, thin strand of solid plastic (a “filament”) is fed from a spool into a heated print head (an “extruder”). The print head melts the plastic to a semi-liquid state and then forces it out through a tiny nozzle. The machine moves this nozzle around in a precise path, laying down a thin bead of molten plastic that cools and solidifies almost instantly. This process is repeated layer by layer, with each new layer fusing to the one below it.

The Process Step-by-Step

1. Loading: A spool of thermoplastic filament is loaded onto the printer. The end of the filament is fed into the extruder mechanism.
2. Heating: The extruder’s “hot end” heats up to the specific melting temperature of the plastic being used (e.g., ~210°C for PLA, ~245°C for ABS).
3. Extrusion: The machine’s gantry system moves the print head along the X and Y axes while the extruder pushes the filament through the hot nozzle, depositing the first layer onto a build plate.
4. Layering: Once the layer is complete, the build plate moves down (or the gantry moves up) along the Z-axis by one layer height.
5. Repetition: The process repeats until hundreds or thousands of layers have been stacked to form the final object.

Key Technologies Within MEX

• Fused Deposition Modeling (FDM): This is the term trademarked by Stratasys, the company that invented the technology in the 1980s. It is often used to refer to industrial-grade MEX machines.
• Fused Filament Fabrication (FFF): When the FDM patents began to expire in the 2000s, the open-source RepRap movement adopted the term FFF to describe the same process. Today, “FFF” is generally used for desktop and prosumer printers, while “FDM” is often associated with the high-end industrial systems, but they are functionally the same process.

Materials, Pros, Cons, and Applications

• Materials: A vast and ever-growing library of thermoplastic filaments. This is a major strength of MEX. Common materials include PLA (easy to print, biodegradable), ABS (strong, temperature resistant), PETG (durable, food-safe), and TPU (flexible). Industrial machines can print with high-performance engineering polymers like PEEK, PEKK, and Ultem, which have incredible strength and chemical resistance.
• Pros: Very low cost of entry; wide range of materials with diverse properties; machines are simple, reliable, and easy to operate; produces strong, functional parts.
• Cons: Visible layer lines are always present, resulting in a rougher surface finish; lower resolution and dimensional accuracy compared to VPP; part strength is anisotropic (weaker in the Z-axis, between layers).
• Best Applications: Rapid prototyping, manufacturing aids (jigs, fixtures, and tools), architectural models, end-use functional parts that don’t require a perfect surface finish, and hobbyist projects.

In the first part of our guide, we explored the foundational technologies of 3D printing: curing liquid resins with light (Vat Photopolymerization) and extruding molten filaments (Material Extrusion). Now, we move away from liquids and strands and into the world of powders. The next two families, Powder Bed Fusion and Binder Jetting, are the workhorses of industrial 3D printing, capable of creating everything from complex nylon prototypes to flight-ready titanium components.

Powder Bed Fusion (PBF): Fusing Powders with Lasers and Beams

If Material Extrusion is the most common form of 3D printing, Powder Bed Fusion is arguably the most transformative for professional applications. This family of technologies unlocks the ability to create highly complex, support-free parts from robust engineering plastics and high-performance metals.

The Core Concept: High-Energy Precision Welding

Imagine a build chamber filled with a perfectly smooth, flat bed of microscopic powder—either a polymer or a metal. A powerful energy source, either a laser or an electron beam, is then directed onto the powder bed with pinpoint accuracy. This energy selectively scans the shape of the part’s first layer, melting or sintering the powder particles and fusing them together into a solid mass. The bed then lowers slightly, a fresh layer of powder is swept across the surface, and the process repeats, building the object layer by layer within the powder bed.

A key advantage emerges from this method: the surrounding, unfused powder acts as a natural support structure. This allows for the creation of incredibly complex, free-form geometries and interlocking parts that would be impossible to produce with VPP or MEX without a dense network of support structures that would need to be removed later.

The Process Step-by-Step

1. Preparation: The build chamber is heated to a temperature just below the material’s melting point. This reduces thermal stress and makes it easier for the energy source to fuse the powder. For reactive metals like titanium, the chamber is also filled with an inert gas (like argon) to prevent oxidation.
2. Powder Deposition: A recoating blade or roller sweeps a thin, precise layer of powder from a reservoir onto the build platform.
3. Fusing: The energy source (laser or electron beam) selectively scans the cross-section of the part, fusing the powder particles into a solid layer.
4. Lowering: The build platform lowers by the height of a single layer.
5. Repetition: The recoater deposits a new layer of powder, and the process repeats until the parts are fully formed, encased within the powder bed.
6. Cooldown and Breakout: The entire build chamber must cool down slowly (sometimes for many hours) to prevent warping. Once cool, the build platform is removed, and the parts are excavated from the surrounding powder cake in a process called “breakout.”
7. Post-Processing: The parts are cleaned of excess powder (which is often recycled) using brushes and compressed air or media blasting. Metal parts are typically still attached to the build plate and must be cut off and may require further heat treatment or surface finishing.

Key Technologies Within PBF

• Selective Laser Sintering (SLS): This is the primary PBF process for plastics. It uses a CO2 laser to sinter (heat particles until their surfaces bond without fully melting) polymer powders, most commonly Nylon (PA11, PA12). At RM, we use SLS to produce durable, functional prototypes and end-use parts, like enclosures and snap-fit assemblies, that have properties similar to injection-molded parts.
• Direct Metal Laser Sintering (DMLS) / Selective Laser Melting (SLM): These two terms describe the process for metals and are often used interchangeably, though a subtle technical difference exists. Both use a high-powered fiber laser to fuse metal powders. DMLS technically sinters the particles, while SLM fully melts them into a homogenous liquid pool. In practice, modern machines achieve a full melt, creating parts with densities over 99.9%. This technology is a game-changer for creating lightweight, optimized metal parts for aerospace, medical implants, and high-performance automotive applications.
• Electron Beam Melting (EBM): Invented by Arcam (now a part of GE Additive), EBM uses an electron beam instead of a laser. This has several key differences: the process must happen in a vacuum, and it operates at much higher temperatures. The result is metal parts that are almost completely free of the internal stresses found in DMLS/SLM parts, making it ideal for medical-grade titanium and aerospace components.

Materials, Pros, Cons, and Applications

• Materials: A wide range of engineering materials. For plastics: primarily Nylons (PA11, PA12), often filled with glass or carbon fiber for added strength. For metals: Aluminum alloys, Stainless Steels, Titanium alloys, Inconel (a superalloy), and Cobalt Chrome.
• Pros: Excellent mechanical properties; ability to create highly complex, support-free geometries; high productivity, as the entire build area can be packed with parts (“nesting”).
• Cons: High machine and material costs; rougher surface finish than VPP; extensive post-processing and cooling time required.
• Best Applications: Functional prototypes, complex ducting, jigs and fixtures, medical implants, lightweight aerospace brackets, and low-volume production of complex end-use parts.

Binder Jetting (BJT): Gluing Powders for Mass Production

Binder Jetting operates on a similar principle to PBF—building parts within a bed of powder—but it uses a completely different fusing mechanism. Instead of heat, Binder Jetting uses a liquid binding agent, essentially a high-tech glue, to join the powder particles together. This distinction is the key to understanding why BJT is poised to become a true mass-production technology.

The Core Concept: A 3D Inkjet Printer for Powders

Imagine replacing the paper in a 2D inkjet printer with a bed of ultra-fine metal or sand powder. An industrial printhead, very similar to an inkjet printhead, sweeps across the powder bed, selectively depositing micro-droplets of a liquid binder onto the areas that will form the part. The binder soaks into the powder, binding the particles together. The bed lowers, a new layer of powder is spread, and the process repeats.

The parts produced at this stage are in a fragile, “green” state. They have the shape of the final object but are held together only by the binder. They must undergo a significant post-processing step (sintering) to become strong, functional parts.

The Process Step-by-Step

1. Powder Deposition: A recoating roller spreads a thin layer of powder onto the build platform.
2. Binder Deposition: An inkjet-style printhead moves across the bed, precisely depositing droplets of the binding agent to form the layer.
3. Layering: The build platform lowers, and a new layer of powder is applied.
4. Repetition: The process continues until the parts are finished, encased in unbound powder.
5. De-powdering: The “green” parts are carefully excavated from the powder bed.
6. Sintering: This is the crucial step. The green parts are placed in a high-temperature furnace. The binder is burned out, and the powder particles are heated to just below their melting point, causing them to fuse together into a dense, solid object. During this process, the parts shrink significantly and predictably.

Materials, Pros, Cons, and Applications

• Materials: Metals (Stainless Steel is very common), sand (for creating casting molds), and ceramics.
• Pros: Extremely fast printing process (no heat involved); lower cost compared to PBF; capable of very high-volume production, competing with traditional methods like Metal Injection Molding (MIM).
• Cons: Requires a significant, multi-step post-processing workflow; final parts have lower density and mechanical properties than PBF parts; managing part shrinkage during sintering can be complex.
• Best Applications: High-volume production of small, complex metal parts; creating large sand molds and cores for the foundry industry; decorative hardware and consumer products.

In the first two parts of our definitive guide, we have journeyed through the core technologies that define modern 3D printing. We started with the precision of light-cured resins (Vat Photopolymerization) and the ubiquity of filament-based printing (Material Extrusion). We then delved into the industrial powerhouses that build parts from powder beds: the high-strength capabilities of Powder Bed Fusion and the mass-production potential of Binder Jetting.

Now, we complete our exploration by examining the final three official categories. These are often more specialized technologies, each solving unique engineering challenges, from creating hyper-realistic, full-color models to repairing multi-million-dollar aerospace components.

Material Jetting (MJT): The Ultra-Realistic Prototyping Powerhouse

Material Jetting is to 3D printing what a high-end inkjet color printer is to 2D printing. It is a technology built for one primary purpose: producing parts with stunning visual realism, ultra-fine detail, and an exceptionally smooth surface finish. It is also the only technology that can easily print with multiple materials and a full spectrum of colors in a single build.

The Core Concept: Jetted Droplets and Instant Curing

Imagine an industrial printhead with hundreds of tiny nozzles, similar to a 2D printer. Instead of ink, this printhead jets microscopic droplets of a liquid photopolymer (a light-sensitive resin) onto a build platform. As these droplets are deposited, a UV light source, which is integrated into the printhead assembly, passes over them and instantly cures them, turning the liquid into a solid plastic layer.

The process repeats, building the object one razor-thin layer of cured droplets at a time. The true magic of MJT lies in its ability to use multiple printheads, each jetting a different material. This allows it to deposit different base resins (e.g., a rigid opaque material and a flexible transparent material) in specific locations within the same layer. By mixing these droplets before they are cured, the machine can create “digital materials” with a spectrum of intermediate properties, like varying shades of color, gradients of transparency, or different Shore hardness values, all within a single, monolithic part.

The Process Step-by-Step

1. File Preparation: A 3D model is prepared, assigning specific materials or colors to different bodies or faces within the CAD file.
2. Material Jetting & Curing: The printhead assembly sweeps across the build platform, jetting droplets of photopolymer according to the digital file’s instructions.
3. Instant Solidification: The integrated UV lamp cures the jetted material almost instantly.
4. Layering: The build platform lowers, and the process repeats for the next layer.
5. Support Generation: Because the parts are built from a liquid, MJT requires a support structure. This is typically a gel-like, dissolvable material that is jetted alongside the primary model material and is easily removed in post-processing.
6. Support Removal: Once the print is complete, the part is placed in a cleaning station where the gel-like support material is removed with water-jetting or by dissolving it in a solution, leaving a perfectly smooth surface behind.

Materials, Pros, Cons, and Applications

• Materials: A wide variety of UV-curable photopolymers (acrylic-based resins). These are formulated to mimic different engineering plastics (e.g., ABS-like, polypropylene-like) and elastomers (rubber-like), and are available in a full spectrum of colors and transparencies.
• Pros: Unmatched surface finish and realism; ability to print in full color and with multiple materials; extremely high dimensional accuracy; easy support removal.
• Cons: Parts are often brittle and have lower mechanical properties than those made with PBF or MEX; materials can be sensitive to UV light and may degrade over time; high machine and material cost.
• Best Applications: Ultra-realistic appearance models for consumer products; anatomical models for surgical planning; jigs and fixtures requiring soft-touch surfaces; low-run injection molds for prototyping.

Directed Energy Deposition (DED): Additive for Repair and Large Structures

Directed Energy Deposition is a fundamentally different approach to additive manufacturing. While the previous technologies build parts from scratch within a contained build volume, DED is an “open-air” process often used to add material to existing components or to build very large structures. Think of it less like a printer and more like a highly precise, robotically controlled welding or cladding process.

The Core Concept: Fusing Material at the Point of Deposition

In a DED system, a multi-axis robotic arm aims a nozzle at a target surface. This nozzle simultaneously deposits a stream of material—either metal powder or wire—and directs a powerful energy source—typically a laser, electron beam, or plasma arc—at the same point. The energy source creates a small molten pool on the target surface, and the feedstock material is fed into this pool, melting and fusing with the substrate. The robotic arm moves along a programmed path, building up a bead of material. By layering these beads, it can create complex shapes, add features, or repair worn-out surfaces.

Because the process is not confined to a powder bed, DED machines can create very large parts, limited only by the reach of the robotic arm.

Materials, Pros, Cons, and Applications

• Materials: Almost exclusively metals, often in wire or powder form. Common materials include Titanium alloys, Inconel, stainless steels, and various tool steels.
• Pros: Can create very large parts; high material deposition rates; excellent for repairing or adding features to existing high-value parts; can create functionally graded materials by changing the feedstock mid-process.
• Cons: Very low resolution and poor surface finish, almost always requiring significant post-machining; high capital equipment cost; process control can be complex.
• Best Applications: At RM, we recognize DED’s power for high-value applications like repairing worn turbine blades for the aerospace industry, adding custom features to large metal forgings, and manufacturing large-scale structural components for defense and maritime use.

7. Sheet Lamination (SHL): The Niche Technology of Layers

Sheet Lamination is one of the oldest and least common forms of AM. It is a family of processes that builds objects by stacking, bonding, and cutting thin sheets of material. While it has niche applications, its limitations in geometry and material properties mean it is not widely used for functional parts.

The Core Concept: Stacking and Cutting Sheets

The process starts with a roll or sheet of material (paper, plastic, or metal foil). This sheet is placed on the build platform and bonded to the layer below it using either an adhesive or, in more advanced systems, ultrasonic energy. Once bonded, a laser or a physical blade cuts the outline of the part for that specific layer. The waste material remains in place to serve as a support structure. The platform then lowers, a new sheet is fed and bonded, and the process repeats. When the build is finished, the part is encased in a block of laminated, diced material and must be excavated.

A modern, more advanced form is Ultrasonic Additive Manufacturing (UAM), which uses ultrasonic vibrations to create a solid-state metallurgical bond between layers of metal foil, all without significant heat. This low-temperature process allows for the embedding of electronics and sensors directly into solid metal parts.

Materials, Pros, Cons, and Applications

• Materials: Paper, plastics, and metal foils (aluminum, copper, titanium).
• Pros: Very fast for large, bulky objects; low material cost (for paper-based systems); UAM can embed electronics and bond dissimilar metals.
• Cons: Very wasteful process; limited geometric complexity (no internal voids); final parts can be prone to delamination; poor surface finish.
• Best Applications: Early-stage, low-cost concept models (especially with paper); creating parts with embedded sensors or electronics (UAM); producing custom metal-matrix composites.

Making the Choice: A Summary of the 7 AM Technologies

Choosing the right additive manufacturing process is a critical engineering decision that depends entirely on your application’s requirements for speed, cost, material properties, and geometric complexity. As we’ve seen, there is no single “best” method—only the right tool for the job.

The team at RM (Rapid Manufacturing) lives these trade-offs every day, guiding our clients to the optimal solution. To simplify your decision, here is a summary of the seven official technologies:

Frequently Asked Questions (FAQ)

Q1: How many types of additive manufacturing are there?

According to the official ISO/ASTM 52900 standard, there are seven main types or families of additive manufacturing processes. While there are dozens of different machine brands and trademarked process names (like FDM®, SLA®, DMLS®), they all fall under one of these seven core categories based on their fundamental operating principle.

Q2: What is the difference between additive manufacturing and 3D printing?

For all practical purposes, the terms “additive manufacturing” and “3D printing” are used interchangeably. “3D printing” is the more popular and widely understood term, especially in consumer contexts. Additive manufacturing” is the more formal, industrial term that emphasizes the technology’s use in professional production environments, distinguishing it from traditional “subtractive” manufacturing (like CNC machining) or “formative” manufacturing (like injection molding).

Q3: What are the 8 steps in a typical additive manufacturing workflow?

While each of the seven technologies has its own nuances, the general workflow from idea to part can be broken down into eight key steps:

1. 3D Modeling (CAD): Create a digital 3D design using CAD software.
2. File Export (STL/3MF): Convert the CAD model into a printable file format like STL or 3MF.
3. Slicing: Use slicer software to digitally cut the model into thin horizontal layers and generate the G-code instructions for the machine.
4. Machine Setup: Prepare the additive manufacturing machine by loading the material, cleaning the build platform, and performing calibrations.
5. The Build Process: The machine builds the part layer by layer, an automated process that can take hours or even days.
6. Part Removal: Carefully remove the finished part(s) from the machine. This may involve letting the chamber cool or detaching the part from the build plate.
7. Post-Processing: This is a crucial stage that includes support removal, cleaning (e.g., removing excess powder), and curing (e.g., UV post-curing for resins).
8. Finishing/Inspection (Optional): The part may undergo further steps like sanding, polishing, painting, or heat treatment, followed by quality inspection to ensure it meets specifications.

References

1. ISO/ASTM International. (2021). ISO/ASTM 52900:2021: Additive manufacturing — General principles — Fundamentals and vocabulary. https://www.astm.org/standards/iso-astm52900
2. Gibson, I., Rosen, D. W., & Stucker, B. (2015). Additive Manufacturing Technologies: 3D Printing, Rapid Prototyping, and Direct Digital Manufacturing (2nd ed.). Springer. https://link.springer.com/book/10.1007/978-1-4939-2113-3
3. Wohlers Associates. (2023). Wohlers Report 2023: Additive Manufacturing and 3D Printing State of the Industry. https://wohlersassociates.com/product/2023-wohlers-report/

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