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What is 3D Printing and How Does it Work?


3D printing, also known as additive manufacturing, is a method of creating a three dimensional object layer-by-layer using a computer created design.

This article is one of a series of TWI frequently asked questions (FAQs).

3D printing is an additive process whereby layers of material are built up to create the 3d model. This is the opposite of subtractive manufacturing processes, where a final design is cut from a larger block of material. As a result, 3D printing creates less material wastage.

3D printing is also perfectly suited to the creation of complex, bespoke items, making it ideal for rapid prototyping.

What Materials can be used in 3D Printing?

There are a variety of 3D printing materials, including plastics, thermoplastics, metals (including powders), resins and ceramics.

History of 3D Printing

Who Invented 3D Printing?

The earliest 3D printing manufacturing equipment was developed by Hideo Kodama of the Nagoya Municipal Industrial Research Institute, when he invented two additive methods for fabricating three-dimensional plastic models.

When was 3D Printing Invented?

Hideo Kodama's early work was completed in 1981. His invention was expanded upon over the next three decades, with the introduction of stereolithography in 1984, and later developments such as selective laser sintering and laser melting, among others.

3D Printing Technologies

There are three broad types of 3D printing; sintering, melting, and stereolithography.

  • Sintering is a technology where the material is heated, but not to the point of liquidation, to create high resolution items. Metal powder is used for direct metal laser sintering while thermoplastic powders are stuck together for selective laser sintering.
  • Melting methods of 3D printing include direct laser sintering and electron beam melting, these use lasers and electron beams, respectively, to print objects by melting the materials together.
  • Stereolithography utilises photopolymerisation to create ceramic parts which can withstand high temperatures. This technology fires a ultraviolet (UV) light into a vat of photopolymer liquid resin to cure and solidify a cross-section of the object in thin layers.

Laser metal deposition manufacturing (LMD)

How Long Does 3D Printing Take?

The printing time depends on a number of factors, including the size of the model 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. 3D printing can take anything from a few minutes to several hours or days - speed, resolution and the amount of infill are all important factors here.

Advantages and Disadvantages

The advantages of 3D printing include:

  • Bespoke, cost-effective creation of complex geometries:
    This technology allows for the easy creation of bespoke geometric parts at no extra cost. In some instances, 3D printing is cheaper than subtractive production methods as no extra material is used.
  • Affordable start-up costs:
    Since no moulds are required, the costs associated with this manufacturing process are relatively low. The cost of a part is directly related to the amount of material used, the time taken to build the part and any post processing that may be required.
  • Completely customisable:
    Because the process is based upon computer aided designs (CAD), any product alterations are easy to make without impacting the manufacturing cost.
  • Ideal for rapid prototyping:
    Because the technology allows for small batches and in-house production, this process is ideal for prototyping, which means that products can be created faster than with more traditional manufacturing techniques.
  • Allows for the creation of parts with specific properties:
    Although plastics and metals are the most common materials used in 3D printing, there is also scope for creating parts from specially tailored materials with desired properties. So, for example, parts can be created with high heat resistance, water repellency or higher strengths for specific applications.

The disadvantages of 3D printing include:

  • Can have a lower strength than with traditional manufacture:
    While some parts, such as those made from metal, have excellent mechanical properties, many other 3D printed parts are more brittle than those created by traditional manufacturing techniques. This is because the parts are built up layer-by-layer, which reduces the strength by between 10 and 50%.
  • Increased cost at high volume:
    Large production runs are more expensive with 3D printing as economies of scale do not impact this process as they do with other traditional methods. This is because, costs do not reduce with each part produced. Estimates suggest that 3D printing is less cost effective than CNC machining or injection moulding in excess of 100 units.
  • Limitations in accuracy:
    The accuracy of your printed parts depend on the type of machine or process used. Some desktop printers have lower tolerances than other printers, meaning that the final parts may slightly differ from the designs. While this can be fixed with post-processing, it must be considered that 3D printed parts may not always be exact.
  • Post-processing requirements:
    Most 3D printed parts require some form of post-processing. This may be sanding or smoothing to create a required finish or the removal of support struts which allow the materials to be built up into the designated shape.

What is an STL File?

An STL file is a simple, portable format used by computer aided design (CAD) systems to define the solid geometry for 3D printable parts. An STL file provides the input information for 3D printing by modelling the surfaces of the object as triangles that share edges and vertices with other neighbouring triangles for the build platform. The resolution of the STL file impacts the quality of the 3D printed parts - if the file resolution is too high the triangle may overlap, if it is too low the model will have gaps, making it unprintable. All 3D printers require an STL file to print from, however these files can be created in most CAD programs.

3D Printing Industries

Due to the versatility of the process, 3D printing has applications across a range of industries, for example:


3D printing is used across the aerospace (and astrospace) industry due to the ability to create light, yet geometrically complex parts, such as blisks. Rather than building a part from several components, 3D printing allows for an item to be created as one whole component, reducing lead times and material wastage.


The automotive industry has embraced 3D printing due to the inherent weight and cost reductions. It also allows for rapid prototyping of new or bespoke parts for test or small-scale manufacture. So, for example, if a particular part is no longer available, it can be produced as part of a small, bespoke run. Alternatively, items or fixtures can be printed overnight and are ready for testing ahead of a larger manufacturing run.


The medical sector has found uses for 3D printing in the creation of made-to-measure implants and devices. For example, hearing aids can be created quickly form a digital file that is matched to a scan of the patient's body. 3D printing can also dramatically reduce costs and production times.


The rail industry has found a number of applications for 3D printing, including the creation of customised parts, such as arm rests for drivers and housing covers for train couplings. bespoke parts are just one application for the rail industry, which has also used the process to repair worn rails


The speed of manufacture, design freedom, and ease of design customisation make 3D printing perfectly suited to the robotics industry. This includes work to create bespoke exoskeletons and agile robots with improved agility and efficiency.

3D Printing Services

TWI has one of the most definitive ranges of 3D Printing services, including selective laser melting, laser deposition, small-scale prototyping, and more.


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