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Selecting a Rapid Prototyping Method

Rapid prototyping has always been a sure-fire method to ensure your product reaches production faster than the competition, whilst also meeting the quality and expectations of the end consumer. However, how is it possible to discern which of the many types of production methods to choose and why are some more suitable than others? Below, we give you some information of each of the processes to help you decide:

Stereolithography SLA, also known as additive manufacturing, uses a cooling laser and photopolymer resin to produce parts. This is undertaken  by the laser sketching an imprint on the resin, which is slowly cured by every pass, adhering to the layer below until the process is completed and a finished part is produced. It is best for models and complex designs and is quite competitive in relation to cost, but the parts produced maybe fairly fragile and they may degrade when exposed to humidity and UV light.

Selective Laser Sintering SLS uses a laser which builds up a fused nylon-based powder into a solid material. The process uses either rigid nylon or TPU in order to create strong parts, albeit not incredibly cosmetically detailed, but complex in shape.

Direct Metal Laser Sintering DMLS is another additive manufacturing process that produced metal parts, with the laser being used to etch onto a metal powder surface, again welding the powder into a solid. Most types of metal can be utilised and it allows a full-strength, functional part to be made out of the same material and the final production parts. This can be a slow and expensive method of producing a prototype if you are looking to produce more than a small number of parts, with the surface finish also being slightly rough.

Fused Deposition Modelling FDM is an extrusion method of production, which involves the melting and re-solidification of layers of resin to produce a part. The resin used is mostly ABS, PC or a blend of the two and this allows a strong part to be produced at a reasonable cost. The downside is that the parts may not be a nicely finished as the production version.

Multi-Jet Fusion MJF uses an inkjet to fuse and detail across a bed of nylon powder, which then fuses into a solid layer. Residual powder is removed at the end of the process and the part is then heat-blasted and dyed black to improve the cosmetics of the finished part. The process is fast, although limited to certain materials, and does not have the accuracy to define small part tolerances as much as SLS.

Polyjet PJET also uses a print head spray to disperse layers of photopolymer resin onto a surface, which are then cured with an ultraviolet light. This produces strong parts at a relatively low cost and in multiple colours and in complex shapes. The parts produced are not exceptionally strong compared to other processes, such as SLA, and provide limited insight into the viability and longevity of the finished design.

Computer Numerically Controlled Machining  CNC uses a mill or lathe to work on a block of plastic or metal held in a clamp. The part produced is strong and accurately replicated from piece to piece in a variety of different colours and shapes. The part can be functionally tested and, with the latest 3 and 5 axis designs, very complex shapes can be produced straight from a CAD design file in a very short space of time. There can be a lot of wastage during the CNC process and it can be more expensive to produce a product using this method then 3D printing.

Injection Moulding  IM works by plastic resin from a hopper being heated and then forced into a mould under high pressure. The mould itself can be created from many different types of materials and can make many thousands of parts, depending on its composition. Many parts from many different materials can be made, with an excellent surface finish and high durability. The cost of the tool can be quite high initially and so prototypes may be produced by other methods prior to commencing the actual production run using injection moulding.

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