Additive 101: A General Purpose User's Guide

By Tim Shinbara, Technical Director, AMT-The Association For Manufacturing Technology

What is additive manufacturing? Sometimes known as “3-D printing,” additive manufacturing uses emerging technologies to fabricate parts by building them up layer-by-layer. It allows rapid transformation from "art" (CAD model) to "part" (manufactured product), and shows great promise for applications as diverse as lightweight aerospace structures and custom biomedical implants.

Additive 101*

What is additive manufacturing?
How does it work?

Basic Definitions

Additive Manufacturing
Additive Systems

Additive Manufacturing Processes

Directed Energy Deposition
Material Extrusion
Powder Bed Fusion
Jetting
Sheet Lamination
Vat Photopolymerization
Multi-functional


What is additive manufacturing?

Sometimes known as “3-D printing,” additive manufacturing uses emerging technologies to fabricate parts by building them up layer-by-layer. It allows rapid transformation from "art" (CAD model) to "part" (manufactured product), and shows great promise for applications as diverse as lightweight aerospace structures and custom biomedical implants.

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How does it work?

Metallic, plastic, ceramic, or composite materials are laid down one thin layer at a time and placed precisely as directed from a digital file. Frequently, the raw materials used are in the form of powders or wires that can be melted and shaped by a laser, in a fashion somewhat akin to welding. An example application for the medical industry would be the creation of an artificial jawbone. A 3-D computer model of a jawbone is created based on a person’s bone structure, and this model is sliced into many layers. The computer then feeds the information into the additive machine, which could generate the complex bone structure substitute out of metal.

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Additive Manufacturing (AM)

A process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies. The AM layer upon layer methodology is generally followed without relying on molds, casts or patterns, as opposed to subtractive manufacturing methodologies whereby material is removed from a pre-existing workpiece. Synonyms: additive fabrication, additive processes, additive techniques, additive layer manufacturing, layer manufacturing, and freeform fabrication.1

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Additive Systems

Machines used for additive manufacturing.

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Additive Manufacturing Processes 2

Directed Energy Deposition

Simultaneous introductions of material and focused thermal energy fuse material by melting, during the process of deposition. "Focused thermal energy” means that an energy source (e.g., laser, electron beam, or plasma arc) is focused to melt the materials being deposited.

Advantages: Increased degrees of freedom for material deposition; can be applied to pre-existing part features (example: depot, re-work) or to create the 3D object itself; high level of interoperability with automation.

Disadvantages: For pre-existing parts and features, there may not be a complete phase change at the interface of the pre-existing material and the newly deposited material. This may create a bond line that may have dissimilar (and usually reduced) material properties even if the two materials are the same. May still require heat treatments (for metals) even if a single-build 3D object is fabricated.

Usage: Primarily use this process for re-work of articles that can accommodate post-machining and heat treating (e.g. stress relief for metals) or for 3D objects / end-use parts that may not have high structural property requirements.

Examples: Tooling, feature refurbishments (e.g. bosses), fracture fill and fair, preform structures (post-machining necessary with heat treatments).

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Material Extrusion

A continuous filament material is heated (usually to a semi-molten state) and then selectively dispensed through a nozzle or orifice.

Advantages: Increased degrees of freedom for material deposition; can be applied to pre-existing part features (requires similar polymer base materials), high level of interoperability with automation; material is typically an industrial-friendly spool.

Disadvantages: Typically very high in-plane (X,Y) material properties, but larger area parts that require longer extrusion times on a given layer may drastically reduce out-of-plane (Z) properties as extrusions have a distinct build line between layers (prone to fatigue failures at bond line).

Usage: Primarily use this process for 3D objects that may not have high structural property requirements; some offerings have higher temperature and material strengths, but typically this process is for nylon or ABS-like materials.

Examples: Tooling, light/modular structures (e.g. mini-vehicles, hollow spheres).

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Powder Bed Fusion

Thermal energy selectively fuses regions of a powder bed.

Advantages: The required chamber enclosure provides a more consistent work environment resulting in more consistent material properties through the work volume; high level of material coalescence resulting in higher mechanical properties out-of-plane (Z) than extrusion or deposition; can achieve very high detail resolution.

Disadvantages: Limited volume for single-piece part fabrication, higher cost for industrial applications, some materials and fusion processes require very high chamber temperatures with low-tolerances for temperature variation that increases the need for higher process control capabilities. May require heat treatment depending on fusion technology and material (currently only electron beam melting does not require heat treating for metals).

Usage: Primarily use this process for 3D objects of either polymers or metals. Many end-use parts will require further surface finishing efforts as most metal surface roughness averages will range between 350 Ra – 700 Ra.

Examples: Tooling, secondary/tertiary structures, orthopedic and dental implants/replacements, mechanical joints/sub-components/ducting.

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Binder and Material Jetting

Materials are selectively deposited for joining. Binder Jetting is when a liquid bonding agent is selectively deposited to join powder materials. Material Jetting is when droplets of build material are selectively deposited. Example materials include photopolymer and wax.

Advantages: Increased area for work envelope; some jetting processes do not require an enclosed, controlled work environment at the point of jetting (allows for open gantry-type work). May use multiple build materials for varying material properties (including color). Trends with the technical advancements and cost competitiveness of the computer printing industry as most jetting processes utilize those components for their additive solutions.

Disadvantages: Some binding and build materials typically used may not have as high structural properties as some other processes (requirements-dependent); such lower mechanical properties may be due to the combination of inherent base materials used and the binding material and process not yielding as complete adherence or coalescence to particulates as other processes.

Usage: Binding material jetting applications have realized tremendous value in casting operations (e.g. sand castings) as well as some metal end-use parts with metallic build materials; typical build material jetting with enclosed chambers are well-positioned for intricate multi-color detailed fabrication, multi-property structures (varying hardness in single build) with very affordable ABS-like materials.

Examples: Castings and non-structural metallic parts (binding agent processes), marketing prototypes (with color),  tooling (including castings), automotive covers/trim kits/dashboards, consumer electronics.

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Sheet Lamination

Sheets of material are bonded to form an object.

Advantages: Does not require an enclosed chamber, though management of some environmental conditions are necessary; most materials are reasonably consistent, understood and readily available; provides one of the largest temperature operating windows (resin-dependent).

Disadvantages: Limited 3D geometries as compared to other AM processes; mechanical properties highly dependent upon base resin systems and bond line curing processes; curing process can be highly technical and sensitive (less of a processing window in some cases as compared to other process like extrusion, jetting or deposition) .

Usage: Large parts; accessible, machinable features.

Examples: Tooling, non-structural parts.

"Bonded” could also include any permanently assembled objects by means of joining mechanically (e.g. fasteners), adhesively (e.g. paste, gel adhesives) or with appropriately timed exposure to heat or pressure.       

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Vat Photopolymerization 

Liquid photopolymer in a vat is selectively cured by light-activated polymerization.

Advantages: One of the highest resolution processes for additive manufacturing; highly mature process with well-understood system parameters; with beginnings in rapid prototyping and wind tunnel modeling most designers understand this process’ constraints for an optimal solution.

Disadvantages: Liquid vat does require an enclosed chamber and has a significantly smaller work envelope than most other systems. UV-curable resins typically have some of the lowest mechanical properties of other available resins; usually a monochromatic solution.

Usage: Primarily for prototypes (fit, form and limited function) and wind tunnel models; also used in many consumer toy and electronic offerings; some guides/jigs/fixtures.

Examples: Tooling, templates/patterns, plastic enclosures, demonstration products.

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Multi-functional

More than one methodology is included within a single machine solution. Multi-functional could refer to more than one additive process, as well as an additive process that includes another non-additive process for the purposes of object fabrication.

Examples: Additive metal deposition with a secondary milling operation all within the same additive manufacturing system. Examples of additional processes not included would be: inspection or validation processes within a single machine solution.

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*The fundamental definitions have been developed by the ASTM F42.91 Terminology Subcommittee and have been adopted by the ASTM F42 Committee on Additive Technology and ISO Technical Committee (TC) 61 on Additive Technology. Supplemental information has been provided as an “AMT Discernment” point of clarity. These points of clarity are not to supersede, substitute or otherwise make irrelevant the currently approved definitions. This is not intended to be an exhaustive nor all-inclusive discriminator, but rather is intended to offer interested parties information to proceed with educated questions.

1 From the ASTM F42 Terminology subcommittee (F42.91)(ASTM F2792.1549323-1).

AMT recognizes these additive processes as defined by ASTM Designation F2792 − 12a, and includes an additional process to cover hybrid offerings designated as “Multi-Functional.”

For more information regarding Additive Manufacturing, email Tim Shinbara, AMT Technical Director or call him at at 703-827-5243.


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