Rapid prototyping is a tool that can be utilized by industrial designers to stem the gap between sketches on a notepad or a CAD model to making the huge commitment of mass producing parts. Traditionally designers have used materials like modelling clay or foam to construct prototypes or presentation models. But let’s face it, these techniques require lots and lots of time, and as they say time is money. Even though these prototype materials have the advantage of being highly malleable and inexpensive, they lack the accuracy that rapid prototyping can deliver, which is so pivotal for user testing. In this tutorial we are going to explore the advantages and processes of rapid prototyping and how to actually get your CAD model into a 3 dimensional reality.

Article by Martin Gibson – Twitter – 18.03.2010

An Introduction to Rapid Prototyping

Ever since the introduction of rapid prototyping in the late 1980’s rapid prototyping has been the default prototype method for design studios around the world. Rapid prototyping has served a variety of purposes including the development of the 3D sculpture industry and even as a way to manufacture short runs of products. But for most intensive purposes rapid prototyping is used as a way of testing and visualising 3d models before they go into mass production.

The machines themselves are like a highly sophisticated desktop printer, but instead  they print 3D material and usually cost upwards of $50 000US. However unlike desktop printers which may print a sheet in a few seconds, to print a model it can take hours and even days for highly intricate and large models.

How Does Rapid Prototyping Work?

There are a number of technologies that drive different 3D printing machines some of which include:

• Selective Laser Sintering
• Fused Deposition Modeling
• Stereolithography
• Laminated Object Manufacturing
• Electron Beam Melting
• 3D Printing

However the process of rapid prototyping is relatively the same. The rapid prototyping machine collates and analyses the data received from a CAD model and using successive layers of fluid, powder or sheet material the machine beginds to create the model. The machine then continuously builds the model up from this series of cross sections. These layers are then fused to one another automatically to create the final model shape. The advantages of this additive building method is that any shape, even shapes that are manufacturing-wise are impossible can be created. For example one could create a sphere with no injection holes, or shapes that have differing draft angles which an injection moulding machine could never comprehend.

But one must consider the printing time of shapes created. The building time very much depends on the total volume of the shape and the amount of support material required, as well as the intricacy of the model. Rapid prototyping is fantastic at replicating an injection moulded component which might have bosses, snap fits, shadow/part lines and other interlocking wall sections that could never be envisaged by clay or foam.

Constructing Your Model in CAD

Ensure that your CAD program can export models into an STL or STEP file. It is very difficult to find a CAD program that can’t do this; I can tell you with certainty that Solidworks and Rhinoceros work a treat. When you export your model into an STL file, the program turns your model into hundreds, thousands or even millions of tiny triangles. This triangulation tolerance can usually be specified during the export process (the more triangles the more accuracy). Generally speaking however the tolerance of the rapid prototyping machine will never be able to facilitate every little triangle so even if you have poor quality triangulation your resulting model is likely to be the same, that and you wont clog up the rapid prototyping companies email box.

If your model is particularly large like an aeroplane or a car, consider making a scaled version rather than a full blown print job, your bank account will be extremely thankful. If your model can fit within a cube that is between 250mm(3) – 300mm(3) you will save money and the model can be printed as one piece, so no gluing!

To retain structural integrity of your model, and because the tolerance limitations of the 3D machine, make sure your wall sections are no smaller than 2mm. There is no harm in aiming for 3mm this would be optimal. Some companies may be able to print to a tolerance of  0.5mm but definitely seek their output recommendations.

As mentioned previously there doesn’t need to be a draft angle or strict guidelines as if the product had to be manufactured, but in the sake of modeling your product correctly you should treat your CAD model as a manufacturing considered product. So if your product ever does get to the manufacturing stage the tooling will be seamless and your product testing will be extremely accurate.

How Do I Find a Good Rapid Prototyper?

There are many 3D printers around, a quick Google search or a search in a directory should find a comprehensive list of different businesses. You need to look for a business that delivers high quality models and utilises strong materials like ABS as their raw material. Make sure you enquire about the finish quality of the printing as if you plan on painting the material it might take hours and hours of extra sanding to get a satisfactory grain. Like any product you purchase request a quote beforehand as sometimes rapid prototyping can be expensive.

If you are living in Australia there is one company I couldn’t talk more highly about when it comes to rapid prototyping, which is 3D Prototyping. I have scoured the country looking for the best value for money printer and no-one has been able to match the price and the smoothness of finish of 3D Prototyping. They are based in Queensland but they can deliver anywhere in Australia and they just provide fantastic service as well with same day quotes.

A few months ago I had to design a large tool box and I can honestly say that they saved me at least $200-$300 from what others had quoted me. They would have easily saved me days in sanding and finishing, the resulting model was ridiculously smooth compared to models I have got rapid prototyped in the past.

3D Prototyping also offers Stereolithography, Rapid CNC, Low volume moulding in vacuum casting and even 3D Scanning solutions so pelase check them out if you need any work done.

www.3dprototyping.com.au

Below are some images of other rapid prototyping jobs completed by 3D Prototyping.

I Have the Rapid Prototyping Complete, Now What?

Once you have picked up your rapid prototyped model there are a couple of options open depending on what you want to achieve. If you want to create a beautiful painted presentation model I highly recommend purchasing some spray putty as this will cover up the thousands of layer lines in your model and it will prevent you from sanding away the actual material loosing its form. Spray putty can be purchased from car accessory shops like Super Cheap Auto or Auto One and normally costs $10-$20 a can. Once you have applied the spray putty wait a few hours for it to dry and begin sanding it down with around a 600 coarse sand paper. Then respray your model again, wait a few hours and then sand the model with higher course paper and so on until you get a silky smooth finish.

You can then purchase paint spray cans to paint the model yourself or if you’re worried about blobs perhaps get a professional spray painter to do it for you (often nice auto detailers can help you out).

Alternatively if you just need the model to do some user testing, well you don’t have to do a thing!