Understanding the 7 types of additive manufacturing processes

Additive manufacturing is redefining what’s possible for product and part design, and businesses are increasingly using it in production.

Overall additive manufacturing products and services worldwide grew by 19.5% to $15.244 billion in 2021, according to the 2022 Wohlers report. This is compared to a growth of 7.5% to $12.759 billion in 2020. An impressive rate, especially at a time when a global pandemic caused a considerable slowdown in many manufacturing operations.

While it is often hailed as the technology of future factories, in fact, additive manufacturing isn’t a single method. There are various techniques that fall under this umbrella term, and they have different applications. And some of them can be difficult to scale as they require skilled technicians and operators that are a rarity in today's job market.

In this blog we’ll take a look at the basics of additive manufacturing, including its advantages, the techniques it involves, and a few of the common use cases.

What is additive manufacturing? 

Additive manufacturing, also known as 3D printing, refers to a variety of processes that create a three-dimensional object by adding material together layer by layer. Additive manufacturing is an automated process guided by a digital model and controlled by computer. 

There is a long list of materials that can be deposited, joined, or solidified with additive manufacturing, and these materials can be plastics, liquids, ceramics, or powdered metals. As you can imagine, these materials can be combined in many ways with a variety of technologies. (We’ll cover the most common options shortly.) 

Regardless of the material or technique, what makes additive manufacturing unique is its inversion of conventional “outside in” manufacturing processes, such as CNC machining, that subtract material from a solid block. This also includes casting and injection molding, both of which typically create molds using subtractive methods. 

Because additive processes build up objects in layers in an “inside out” manner, they can create complex, intricate designs that would be impossible to make with any other approach. And they can do this just as easily for one product as they can for a big batch. This creates exciting opportunities for manufacturers. 

What are the advantages of additive manufacturing? 

Product design often runs into two big problems: a design that is not manufacturable with traditional equipment, or one that is technically possible but too expensive to make. Additive manufacturing addresses both challenges, enabling shops to produce parts that are highly complex but do not require any special setup, extra steps, or additional tooling. 

So, not only can additive manufacturing build intricately latticed and organic-looking structures, it can do so in a way that supports mass customization. Parts and components can effectively be printed on demand, making additive much less expensive than traditional methods for low-volume and medium-volume runs.  

Additive manufacturing also helps accomplish two critical goals of manufacturing: lightweighting and part consolidation. 

Because it builds elegant cellular designs and other complex geometries, additive is ideal for designs that use less material (and therefore weigh less) while still meeting specifications for strength and durability. In automotive and aerospace, for example, small reductions in weight can lead to significant fuel savings. 

Part consolidation allows manufacturers to replace multiple complex parts with a single component, simultaneously simplifying the supply chain and minimizing potential points of failure.  

The most well-known example is a 3D printed fuel injector nozzle from GE, which had previously required the production of 20 separate components that were welded together. The additive version was not only easier to make but also 25% lighter and resulted in 15% more fuel efficiency. 

This example highlights another advantage of additive manufacturing: time savings. By reducing the amount of material and the number of parts involved, additive manufacturing can produce parts much faster than traditional means. 

GE successfully produced 100,000 parts in 2021, a major milestone not just for the company, but for additive manufacturing in general as it proved that industrial-scale production was possible. 

Types of additive manufacturing

Here are seven of the most common types of additive manufacturing: 

1. Binder jetting

This method precisely deposits adhesive (liquid binding agent) onto a bed of powdered material. The printer head moves over the bed, depositing the binder layer by layer to build an object that is then post-processed (sintered) to harden it. The powdered material can be chalk, plastic, ceramic, metal, or glass, among others. This process is relatively inexpensive and runs faster than other methods but does require the additional post-processing. 

2. Material jetting

In this process, tiny droplets of liquid polymer are sprayed on the build platform. The droplets are then cured, typically with ultraviolet light. One printer can have separate jets for different materials, creating opportunities to combine materials in one product. The process is similar to binder jetting, but what’s jetted is the actual build material rather than the binding agent. Like binder jetting, this method is inexpensive and highly accurate but limited to certain materials and is also slower than other approaches, going drop by drop. 

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Application spotlight: Making a statuette model with MultiJet printing  

If you need to quickly make smooth, high-resolution objects with complex geometries, MultiJet Printing (MJP) is an ideal option. This is a type of material jetting that UK firm Impossible Creations used to create a replica of an iconic British statuette, the Britannia-upon-Globe. 

With a 3D scan to CAD workflow and the Geomagic software suite, Impossible Creations produced a digital model of the original statuette. The next step was to 3D print a plastic model that would serve as the pattern for metal casting.  

The printing process had to hold the extremely small details created in Freeform while creating a surface so smooth that it did not require secondary finishing. The Impossible Creations team addressed this challenge by printing the master pattern using MJP technology from 3D Systems. 

Restoring a miniature version of the Britannia-upon-Globe with MultiJet Printing

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3. Directed energy deposition (DED)

This process uses a “directed” energy source like a laser to melt powdered material (or metal wire), like conventional welding. The melted material is then deposited onto the build platform, forming a layer as it hardens. Layers are repeated to build the final part. DED is unique in that it can be used to repair parts as well as make them. 

4. Material extrusion

This technique feeds thermoplastic material into the 3D printer from a coil or spool, and the tip of the nozzle on the print head heats the material until it melts. As with DED, the melted material is deposited on the build platform in layers to cool and harden. Material extrusion is the least expensive method of additive manufacturing. Plastics are the most common material to use, but other options include metallic materials, ceramics, and even chocolate. 

5. Powder bed fusion (PBF)

This is an additive manufacturing process that uses a bed of powdered plastic, metal, or ceramic that is fused with a laser, layer by layer. In some applications, the powder solidifies without first liquefying (sintering), and in others the material melts first. PBF is the most common additive manufacturing method for complex metal parts. There are several types of PBF, including selective laser sintering (SLS), selective laser melting (SLM), direct metal laser sintering (DMLS), electronic beam melting (EBM), and high-speed sintering (HSS). 

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Application spotlight: Pump impeller made with SLM 

Manufacturers often order industrial parts in big numbers to ensure that, if a part breaks, a substitute is always readily available. But that comes at great expense. For one, there’s the upfront cost of a big order, and then there’s the price of keeping those parts safely stored.  

To reduce this spending, Finnish technology giant Wärtsilä explored the possibility of using SLM technology to produce pump impellers. With the help of Amphyon, simulation-driven build preparation software, they created an additively manufactured pump impeller that’s lighter than the standard but equally as robust. 

As a result of replacing traditional manufacturing methods with additive, Wärtsilä could produce parts on-premises, as the need arises, making long lead times, and spending on casting and storage part of the past. 

Using additive manufacturing to make pump impellers like this one would result in huge cost savings 

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6. Sheet lamination

With sheet lamination, thin stacked sheets of material are bonded together with ultrasonic welding or brazing. After the sheets are bonded, excess material is removed with a CNC machine or laser cutter. Sheet lamination lets you mix materials at a lower cost, but it does require post-processing and involves more waste than other methods. This approach is also known as ultrasonic additive manufacturing (UAM) or laminated object manufacturing (LOM). 

7. Vat polymerization

In this technique, a vat of liquid photopolymer resin is exposed to certain wavelengths of light which make it solidify quickly. Depending on the process, the light may be from the visible spectrum (commonly the case with DLP), a laser (SLA), or ultraviolet. After one layer is complete, more resin is added to build the next layer. The resin can be costly, but the process runs more quickly than others. And it does require some post-processing to remove excess resin and clean the final product. 

Dental labs use vat polymerization to print models

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Application spotlight: Resin 3D printing in the dental industry

Different industries have adopted additive manufacturing at varying degrees. If there’s one area where additive made significant inroads, it's undoubtedly the dental industry. Today various additive manufacturing processes are used to create a wide range of applications, from metal printing of crowns, bridges and RPD frames, to resin printing for dental models or dentures.  

Prosthetics company Crown Ceram adopted 3D printing in their production centre in France over 10 years ago. With an ever-growing number of machines and software solutions, they were struggling to efficiently manage production. Oqton’s Manufacturing OS gave them a single platform for all their machines and software. With its AI-driven automation, they increased the productivity of resin printing machines, which use vat polymerization, by 30 percent. 

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Moving forward with additive manufacturing 

Choosing an additive manufacturing method ultimately comes down to which variables are most important to your application. The good news? No matter the process, software can help you get the most out of this technology.  

AI-driven automation and end-to-end solutions are making it easier to scale additive manufacturing, ensure repeatability and keep costs down. If you’re looking for a solution that can help you track, trace and analyse your additive manufacturing workflow, learn more about Oqton’s Manufacturing OS.