This section of the G P Tromans Associates website aims to give visitors a very brief, but informative introduction to the range and capabilities of some of the additive manufacturing processes that are available today.

The group of manufacturing processes that are known as additive manufacturing (AM) consist primarily of four technologies. These are:

  • Selective Laser Sintering (SLS)
  • Fused Deposition Modelling (FDM)
  • Stereolithography (SL) and
  • 3Dimensional Printing (3DP).

This list is by no means exhaustive.

AM offers users a completely different way of manufacturing — and designing — compared with traditional techniques such as CNC machining, turning, milling etc.  These methods are classed as subtractive processes, where material is machined away, as opposed to AM, which builds geometries one layer at a time. Although all AM processes use the same data format as a basis to link with the systems, that is where the similarity ends.  Each process is different — both in the way that the system constructs the part and in the materials used.

Each technology starts with a CAD file of a specific geometry, the geometry then goes through a process of surface tessellation, which generates what is known as an .STL file.  This file is then transferred to the AM system for building.  Each of the systems will then require the geometry to be divided up into horizontal sections or slices.  The thickness of each slice is determined by what process is used and what the requirements of the final part will be.

Selective Laser Sintering (SLS) uses a material that has been granulated e.g. polymers and sand, building parts using a laser to sinter together the granulated particles one layer at a time, fusing together each 2-dimensional layer one on top of the other to form the final geometry. The sintering process is also used in the additive metal material processes, where granulated powders such as steel, titanium, aluminium, precious metals etc, can be used to grow metal parts.

Fused Deposition Modelling (FDM) utilises existing polymers that have been formed into a filament, wound onto a roll. The material is thermally melted by extruding it through a heated nozzle.  This molten polymer is then built up in 2-dimensional sections, with each section bonding to previous  section as it cools.

Stereolithography (SL) uses a combination of photochemistry and laser technology to build parts with photopolymer resins. Again, each part is built in layers, only with this process a UV laser traces the 2-dimensional section onto the surface of a vat of photopolymer resin.  This starts a chemical reaction, which causes the resin to solidify where it has been exposed to the laser.  The build surface is then lowered into the resin vat by the pre-determined thickness, and the resulting layer of resin is once again exposed to the laser.  This starts the solidification process off again with the new layer bonding to the one below.

3D Printing (3DP) uses two main techniques to form parts — the printing heads are broadly based on the standard type of heads used in any office printer.  One 3DP technique uses a binder to bond together a ceramic type powder in 2 dimensional sections.  This process also has the ability to build parts in full colour, the only process in the world with this capability.  The second technique prints a UV photopolymer resin on 2Dimensional sections, and the print head is followed closely by a UV lamp which flashes each layer as it passes over it,  starting a chemical reaction, which solidifies the resin, each layer bonding to the next.  This process allows for the blending of materials at the print head and can generate different material properties to suit the requirements of each part.  It can also use two different materials at the same time to produce parts to simulate two-shot moulding etc.