If you are familiar with 3D printing, then you have a general idea of what additive manufacturing is. As inexpensive devices have become increasingly more accessible, you have likely seen 3D printing referenced in the news, TV shows or movies. This mainstream status is what the Harvard Business Review has called “the 3-D Printing Revolution.” It’s important to note, these depictions of 3D printing are oversimplified and too general. 

Although 3D printing and additive manufacturing are often used interchangeably, they are not synonymous. additive manufacturing is a broader term used to describe manufacturing techniques made in a similar layering fashion. These manufacturing techniques are used to create everything from toys to shoes to the parts on a jet engine.   


What is additive manufacturing?

Additive manufacturing is the process of building physical objects by layering materials like metal, plastic, or concrete. It is a process that uses special software and equipment.

The software will first create a design known as a Computer-Aided Design (CAD). The equipment will then take this CAD file and strategically layer material, creating a physical representation of the CAD.

There are seven types of additive manufacturing, each with its own processes, methods of layering, and equipment. 

What Are the Seven Types of Additive Manufacturing?

To clear up confusion on the different types of additive manufacturing, a set of standards were created that categorize the different processes. These categories were created by the International Organization for Standardization in 2010 and provided clear definitions for additive manufacturing processes. These definitions helped improve global communication between those who work in the industry. 

1. VAT Photopolymerisation

VAT Photopolymerisation is also known as stereolithography. This type of additive manufacturing uses a vat of liquid photopolymer resin—which is how VAT photopolymerization received its name.

A build platform is lowered from the resin’s top, moving downward, and a laser beam draws a shape in the resin, creating a layer. The average thickness of one layer is between 0.025 and 0.5mm. After each layer of resin, it must then be cured using ultraviolet (UV) light. 

This process of photopolymerization uses motor controlled mirrors to direct the UV across the resin surface, causing it to harden. These steps are repeated to add layers.

For increased accuracy and finish, most equipment uses blades that go over each layer to remove defects before applying and curing the next layer. Using a liquid creates a great deal of accuracy and detail in the finished project; however, it lacks the structural support provided by other types of additive manufacturing. This is corrected by adding support structures. Although the VAT photopolymerization process is quick to complete, the clean-up and post-processing time is lengthy. 

VAT Photopolymerisation is used in several industries to create parts and products ranging from hearing aids to Nike shoes. 

2. Material Jetting

With material jetting, the print head is above the platform, and material is deposited onto the surface in the form of droplets. Hundreds of micro-droplets are positioned with charged deflection plates, providing increased control and accuracy. These droplets then solidify, creating a layer. This is repeated, building up layers.

The droplets may be distributed continuously or individually using the Drop-on-Demand (DOD) method. This method is similar to an inkjet printer. Material jetting can be done with various materials, including polymers and waxes.

This type of additive manufacturing is precise, and you can use multiple materials for one project. Although accurate, it is not the most efficient method as time is spent re-filling the reservoir that depletes quickly. 

Material jetting is often used to create realistic models or prototypes.

3. Binder Jetting

This type of additive manufacturing uses a binder and a powder-based material. This powder-based material is applied to the build platform with a roller, and then the print head deposits the binder on top.

The binder adheres the layers together and is usually in liquid form. Following a layer, the product is lowered on the platform. This is repeated to create more layers until the product is finished. When using this process, you can use different materials, including polymers, ceramics, and metals.

Binder jetting is considered one of the speediest additive manufacturing methods and allows for customization. For example, if you require material of a specific quality, you can change the binder-powder ratio, or if you want to create a product that has color variation, you can do so.

One of the drawbacks of binder jetting is the increase in post-processing time, and it may not be the best choice for creating structural parts. 

Binder jetting is used in industrial applications, dental and medical devices, aerospace components, part casting, luxury applications, and more.

4. Material Extrusion

Material extrusion is a type of additive manufacturing process often used in inexpensive at-home 3D printers where the material is drawn through a nozzle, heated, and then deposited in a continuous stream. This nozzle moves along horizontally and the platform moves up, down, and vertically. This is how the layers are created. Because the material is heated (melted) when it is applied, it fuses to the previous layer. The bonding between layers can also be controlled through temperature and chemical agents.

Although material extrusion is often seen in inexpensive models, it has many capabilities. Polymers and plastics can be used, which provide strong structural support. However, there are also limitations to this additive manufacturing process. 

  • Accuracy is reduced because of the nozzle thickness. 

  • Material extrusion is also one of the slower types of additive manufacturing.

Many automotive companies use material jetting to create manufacturing devices used in assembly lines. 

5. Powder Bed Fusion

For powder bed fusion additive manufacturing, a layer of powder is applied to the platform. A thermal energy source like an electron beam or laser fuses the powder before a second layer is applied with a roller or blade. This layering process is then repeated.

There are slight variations within powder bed fusion, including:

  • Selective Laser Melting (SLM)

  • Selective Laser Sintering (SLS)

  • Electron Beam Melting (EBM)

  • Direct Metal Laser Sintering (DMLS)

Despite the differences between these variants, all powder bed fusion manufacturing occurs in a near-vacuum, pre-heated chamber with inert gas. Metals and polymer powder materials can be used, which act as a support structure, making it a suitable type for prototypes and visual models. 

There are some disadvantages to the powder bed fusion method as it requires more time to complete projects; however, this additive manufacturing process is still used in various industries, including aviation, to create parts of a jet engine. 

6. Sheet Lamination

Sheet lamination is a process that binds layers using ultrasonic welding or an adhesive.

There are two variations of sheet lamination; ultrasonic additive manufacturing (UAM) and laminated object manufacturing (LOM). The difference between the two is found in the material used and the bonding process.

  • UAM uses metal that is bound together with ultrasonic welding.

  • LOM uses paper that is bound together using an adhesive.

Sheet lamination is done by placing the material on a cutting bed. Layers are applied and bonded to that material. and the shape is cut with a knife or laser. This process can bind different materials and is relatively low cost and speedy.

Accuracy is sometimes lacking in sheet lamination and may projects that utilize this additive manufacturing process may require post-processing. Sheet lamination is often used for prototypes. 

7. Directed Energy Deposition

Directed Energy Deposition (DED) is one of the most complex types of additive manufacturing. A four- or five-axis arm will move around, depositing melted material around a fixed object. The material is melted by an electron beam or laser and will then solidify.

Metal powder or wires are the most common material used with DED, but ceramics and polymers may also be used. You can achieve a high degree of accuracy due to the ability to repair and control grain structure in DED.

The finish varies based on the material used. In the case of metal, a powder will provide a much better finish than wire; however, you can achieve your desired effect with wire through post-processing. 

Direct Energy Disposition is often used to repair or fabricate parts.

In summary, additive manufacturing is much more complex than the term “3D printing” suggests. Although these 7 types of additive manufacturing differ in many ways, they all play a vital role in countless manufacturing processes and have the revolutionary potential for future uses.

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