Additive manufacturing

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Rapid prototyping and additive manufacturing machines are like three dimensional printers that can turn virtual designs on a computer into solid objects, by building up extremely thin cross-sectional layers, using polymers and more recently metals, built one at a time on top of each other. This is known generically as additive fabrication or additive manufacturing in contrast to CNC milling which is a subtractive process, starting from a larger solid block of material.

Currently they are used mostly in industry to create accurate parts for developmental designs and prototypes. But they are increasingly being used in short manufacturing runs and is known in this circumstance as rapid manufacturing.

There are a variety of types currently in use:

  • Fused deposition modelling (FDM) which extrudes thin strands of molten material such as ABS
  • Selective laser sintering (SLS) which fuses nylon powder or metals with a laser
  • Electron-beam melting (EBM) which fuses metal powder using an electron beam in a vacuum
  • Stereolithography apparatus (SLA) which cures liquid resin in a tank with an ultra-violet laser. Parts are brittle but can be fully transparent and has a very high resolution
  • 3D printing which squirts out a UV curable resin from a matrix of nozzles. Recent machines can have variable colours and variable shore hardnesses, able to create a part that is has gradient of hardness along its length
  • Powder and glue plus inkjet colour printing on the surface
  • Paper cutting and lamination


  1. Intro
  2. Different types
  3. Materials
  4. Advantages
  5. Current limitations
  6. Rapid manufacturing
  7. Inevitability of 3D printers on home desktops (whether commercial or open-source)

There will likely be a convergence of multi-tool rapid-prototyping machines and the shrinking of multi-machine fablabs, allowing sopisticated digital manufacturing from a single desktop device.


RepRap version 1.0 'Darwin'
RepRap version 2.0 'Mendel'
Video introduction to 'Mendel'
Parts printed from a RepRap

RepRap is rather special rapid prototyping machine. The name is short for self-replicating rapid prototyper and the project was started at the University of Bath by Dr. Adrian Bowyer, a Senior Lecturer in mechanical engineering.

The idea is to create a rapid prototyping machine that, as well as being able to construct useful three dimensional objects to order, is also able to create most of the parts necessary to build another rapid prototyping machine. So for a very low cost, someone with a RepRap should be able to clone a new machine to give to someone else.

It uses the Fused Deposition Modelling 11px-Wikipedia_logo.jpg (FDM) system of additive construction where a thermoplastic material is extruded very thinly from a computer controlled nozzle to slowly build up a three dimensional shape layer by layer.

However there are various of its own component parts that it cannot currently reproduce such as the stepper motor, microcontroller, extrusion nozzle and lubricant. However over time as the design evolves and becomes more sophisticated it is envisioned that there will be fewer and fewer parts that cannot be made by the machine itself.


The RepRap team intend to include nozzles for applying different materials during the build process:

  1. A thermoplastic - generally used to create structure of the object being made.
  2. Wood's 11px-Wikipedia_logo.jpg or Field's metal 11px-Wikipedia_logo.jpg which are low melting point metal alloys used to create electrical circuits within three dimensions in the artefact being built
  3. Ceramic slurry for hard and strong cement-like structures
  4. Silicone polymer used for gaskets, seals and flexible parts
  5. Plaster/cellulose mixes, PVA or icing sugar for temporary support material to allow overhangs to exist as the object is being built up. After the object is created these supports can be dissolved away using warm water

Open design

This is an open collaborative design project in that everything relating to it – the schematics, 3D CAD models of the components and the software to run it – are being released under the GPL license 11px-Wikipedia_logo.jpg which enables anyone to use, customize and evolve it. The terms of the GPL also mean that any improvements will likewise be available under the same license for others to benefit from.

External links

Some RepRap variants:

Makerbot Ultimaker Printrbot 3D Touch
Makerbot's Cupcake
3D Touch
Makerbot's Cupcake CNC machine is an open-source 3D printer inpired by and partly based on RepRap. Kits are available to buy between $750 and $950 depending on how much assembly you want to do yourself Makerbot website. Thingyverse - an online repository of 3D objects you can print, started by the guys at Makerbot Kicker starter page for Printrbot


Fab@Home model 1

Fab@Home is an open-source rapid prototyping machine with a syringe-based extrusion system from Cornell University.

Solid metal objects

As well as CNC machines 11px-Wikipedia_logo.jpg which employs subtractive fabrication there are various additive fabrication techniques emerging to create fully dense and strong metal parts straight from a CAD model.

One is selective laser sintering 11px-Wikipedia_logo.jpg which more commonly uses nylon powder as its feedstock, but companies such as EOS now produce metal sintering machines which can produce high definition metal parts (or moould tools) directly. Another system, which is coarser but faster than M-SLS is electron-beam melting 11px-Wikipedia_logo.jpg, both of which fuse metal powder layer by layer to create a solid metal object.

Info on ARCAM electron-beam melting:

  • Parts are solid and void-free unlike some sintering techniques.
  • Layer thickness 0.05mm
  • Titanium powder stock. Parts are incredibly strong - even flight certifiable.
  • 3 - 5 times faster than SLS
  • Done in high vacuum to avoid imperfections caused by oxidation.

Example parts created from titanium powder using ARCAM electron-beam melting:

Images from

3D printed (DMLS) rocket motor

Stainless steel rocket motor chamber

Paul Breed from Unreasonable Rocket is attempting to create a Direct Metal Laser Sintered (DMLS) rocket motor with the aim of powering a real hydrogen peroxide fuelled rocket with it. See here and half-way down the page here for more images. Paul has form having previously flown a serious piece of hardware called 'Blue Ball' (a VTOL rocket-powered lander) in the Northrup Grumman Lunar Lander Challenge. Although they failed the competition rules, I would argue it was a pretty successful flight - judge for yourself Film_icon.png here.

The Future

two-photon polymerization/lithography employed to construct the word hair in 3D built upon a human hair
  • Higher and higher resolution parts (two-photon polymerization/lithography) [1] [2] Film_icon.png [3]
  • Multi-material (already here on some models)
  • Integrating circuitry into the build
  • Integrating off-the-shelf components into the build
  • Integrating subtracting and additive manufacturing processes into the same device. Multi-axis milling capability during an additive build giving very smooth surfaces inside and out during the build process
  • Human organs (already being done for simple organs like bladders) [4] Film_icon.png TED talk on printing organs
Printed human bladder

Handling parts

Current prototyping machines typically manufacture one part with one process, and then require a human to pull that part out, do any final finishing, and any further assembly. Some flexible manufacturing system 11px-Wikipedia_logo.jpg have a series of machines, each one optimized for a different process, often with a conveyor carrying parts from one machine to the next. "CubeSpawn" is an Open Source Free flexible manufacturing system. A few assembly lines use robotic automated assembly 11px-Wikipedia_logo.jpg.

Sometimes the parts themselves are designed in a modular way (modular design 11px-Wikipedia_logo.jpg) so they can be easily assembled and disassembled and re-used to assemble something else. Some open-source modular parts include MakerBeam Mini-T-slot (is this the same as MicroRAX  ?) and the Grid Beam [5][6] system.


Additive fabrication, 3D printing