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What is Additive Manufacturing? Definition, Types and Processes


Additive manufacturing (AM) or additive layer manufacturing (ALM) is the industrial production name for 3D printing, a computer controlled process that creates three dimensional objects by depositing materials, usually in layers.

additive manufacture mesh structure


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How Does Additive Manufacturing Work?

Using computer aided design (CAD) or 3D object scanners, additive manufacturing allows for the creation of objects with precise geometric shapes. These are built layer by layer, as with a 3D printing process, which is in contrast to traditional manufacturing that often requires machining or other techniques to remove surplus material.

Additive Manufacturing Processes

There are number of distinct AM processes with their own standards, which include:

1. Binder Jetting

This technique uses a 3d printing style head moving on x, y and z axes to deposit alternating layers of powdered material and a liquid binder as an adhesive.

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2. Directed Energy Deposition

Direct energy deposition additive manufacturing can be used with a wide variety of materials including ceramics, metals and polymers. A laser, electric arc or an electron beam gun mounted on an arm moves horizontally melting wire, filament feedstock or powder to build up material as a bed moves vertically.

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3. Material Extrusion

This common AM process uses spooled polymers which are either extruded or drawn through a heated nozzle which is mounted on a movable arm. This builds melted material layer by layer as the nozzle moves horizontally and the bed moves vertically. The layers adhere through temperature control or chemical bonding agents.

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4. Powder Bed Fusion

Powder bed fusion encompasses a variety of AM techniques including direct metal laser melting (DMLM), direct metal laser sintering (DMLS), electron beam melting (EBM), selective laser sintering (SLS) and selective heat sintering (SHS). Electron beams, lasers or thermal print heads are used to melt or partially melt fine layers of material after which excess powder is blasted away.

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5. Sheet Lamination

Sheet lamination can be split into two technologies; laminated object manufacturing (LOM) and ultrasonic additive manufacturing (UAM). Laminated object manufacturing is suited to creating items with visual or aesthetic appeal and uses alternate layers of paper and adhesive. UAM uses ultrasonic welding to join thin metal sheets; a low energy, low temperature process, UAM can be used with various metals such as aluminium, stainless steel and titanium.

6. Vat Polymerisation

This process uses a vat of liquid resin photopolymer to create an object layer by layer. Mirrors are used to direct ultraviolet light which cures the successive layers of resin through photopolymerisation.

7. Wire Arc Additive Manufacturing (Now known as Directed Energy Deposition-Arc (DED-arc))

Wire arc additive manufacturing uses arc welding power sources and manipulators to build 3D shapes through arc deposition. This process commonly uses wire as a material source and follows a predetermined path to create the desired shape. This method of additive manufacture is usually performed using robotic welding equipment.

Additive Manufacturing Technologies

AM technologies can be broadly divided into three types.

The first of which is sintering whereby the material is heated without being liquified to create complex high resolution objects. Direct metal laser sintering uses metal powder whereas selective laser sintering uses a laser on thermoplastic powders so that the particles stick together.

The second AM technology fully melts the materials, this includes direct laser metal sintering which uses a laser to melt layers of metal powder and electron beam melting, which uses electron beams to melt the powders.

The third broad type of technology is stereolithography, which uses a process called photopolymerisation, whereby an ultraviolet laser is fired into a vat of photopolymer resin to create torque-resistant ceramic parts able to endure extreme temperatures.

What are the Advantages of using Additive Manufacturing?

Similar to standard 3D printing, AM allows for the creation of bespoke parts with complex geometries and little wastage. Ideal for rapid prototyping, the digital process means that design alterations can be done quickly and efficiently during the manufacturing process. Unlike with more traditional subtractive manufacturing techniques, the lack of material wastage provides cost reduction for high value parts, while AM has also been shown to reduce lead times.

In addition, parts that previously required assembly from multiple pieces can be fabricated as a single object which can provide improved strength and durability. AM can also be used to fabricate unique objects or replacement pieces where the original parts are no longer produced.

Additive Manufacturing Services

TWI has one of the most definitive ranges of AM services.


How Long Does the Process Take?

The printing time takes in a few factors, including the size of the part and the settings used for printing. The quality of the finished part is also important when determining printing time as higher quality items take longer to produce.

AM can take anything from a few minutes to several hours or days - speed, resolution and the volume of the material are all important factors here.

Arc based additive manufacturing

What Materials can be used in Additive Manufacturing?

There are a variety of materials used for AM, these include biochemicals, ceramics, metals and thermoplastics.

1. Biochemicals

Biochemicals used in AM include silicon, calcium phosphate and zinc while bio-inks fabricated from stem cells are also being explored. These materials are generally used for healthcare applications.

2. Ceramics

A range of ceramics are used in AM, including alumina, tricalcium phosphate and zirconia as well as powdered glass which can be baked together with adhesives to create new types of glass product.

3. Metals

A wide variety of metals and metal alloys are used for additive manufacturing, including gold and silver, stainless steels and titanium amongst others. These can be made to create a variety of different metal parts, ranging from jewellery to aerospace components.

4. Thermoplastics

Thermoplastic polymers are the most commonly used of AM materials and include a variety of types with their own advantages and applications. These include acrylonitrile butadiene styrene (ABS), polylactic acid (PLA) and polycarbonate (PC) as well as water-soluble polyvinyl alcohol (PVA) which can provide temporary support before being dissolved.

Where is AM used?

AM is used to create a wide range of products across a growing number of industries, including:

1. Aerospace

AM is particularly suited to aerospace applications due to its weight saving capability and ability to produce complex geometric parts such as blisks.

2. Automotive

A variety of materials are widely additive manufactured for the automotive industry as they can be rapidly prototyped while offering weight and cost reductions.

3. Medical

The medical sector is finding an increasing number of applications for additively manufactured parts, especially for bespoke custom-fitted implants and devices.




Visit our press release section to find out how TWI is helping industry with additive manufacturing.

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Find out about TWI's case studies in AM and how we have helped our members with this technology over the years.

See TWI additive insights


Who Invented AM?

Although the concept had been around since the 1940s, Hideo Kodama of the Nagoya Municipal Industrial Research Institute developed the earliest 3D printing manufacturing equipment in 1980, when he invented two additive methods for fabricating 3D models.

When was Additive Manufacturing Invented?

The concept of additive manufacturing dates back to 1945 and the publication of Murray Leinster’s short story, ‘Things Pass By.’ However, this early idea was not really developed until 1971 when Johannes F Gottwald patented the Liquid Metal Recorder, a continuous inkjet metal material device that could form a removable metal fabrication on a reusable surface.

This was developed further with Hideo Kodama’s invention of 3D printing equipment in 1980, although even then the funding and interest for the technology was limited. Further patents quickly followed, including for stereolithography process and Bill Masters’ Computer Automated Manufacturing Process and System in 1984.

Which is the Oldest Additive Manufacturing Technique?

The oldest fully realised additive manufacturing technique is stereolithography, which was developed in 1987 by 3D Systems. The system works with a lithograph printer that uses UV light and a laser to solidify thin layers of liquid polymer to create three-dimensional objects.

Is Additive Manufacturing the same as 3d Printing?

3D printing is a synonym for additive manufacturing, they are two terms for the same process which both mean the same thing. However, ‘additive manufacturing’ is generally the term used by industry.

Are Companies using Additive Manufacturing?

Yes, lots of different companies across a range of industries use additive manufacturing, including the medical industry, aerospace and more. Additive manufacturing is particularly useful for making complex or bespoke parts – whether for a new application or to replace an old part that may no longer be available.

How is Additive Manufacturing different from Traditional Manufacturing?

Additive manufacturing is different from traditional manufacturing as it allows a part to be built layer-by-layer, whereas traditional manufacturing often requires a part to be made by joining separate components or by machining away unwanted material to produce the part.

Will Additive Manufacturing Replace Conventional Manufacturing?

Additive manufacturing is unlikely to fully replace conventional manufacturing due to the time taken to manufacture parts. Conventional manufacturing is still preferable for simple and easy to produce items, but additive manufacturing is becoming the chosen method for manufacturing smaller batches of more complex parts. 

Why is AM Important?

AM is important for the creation of lighter, complex designs that may be too difficult or expensive to produce using traditional manufacturing techniques. Removing the need for moulds, milling or machining, AM offers a range of advantages for both prototyping and production.

How will Additive Manufacturing Change the World?

It may be something of a stretch to say that AM will ‘change the world,’ but it is already having a positive impact. It allows for the creation of complex design with less material wastage when compared to parts that require machining, as well as allowing for the creation of lighter structures. When these lighter structures are applied to aerospace or automotive applications, for example, they lead to fuel savings and the related environmental (and financial) benefits. AM also allows for the replacement of parts that may otherwise be impossible to replace, meaning that machines can be repaired rather than scrapped. In addition to these benefits, AM has also seen a level of democratisation in manufacturing, as more people set up domestic 3D printing stations to produce their own bespoke items.

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