AUT has a Dimension 3D Printer which allows the creation of plastic rapid prototypes and a Z-Corp 3D printer which makes parts from plaster, or Zcast material (for making direct metal casting molds). Each material and technology has different advantages depending on your intended use. As a very rough guide, plastic parts are much stronger than plaster parts but are much more expensive. Plastic parts are ideal for prototypes of functional engineering components. Plaster parts are quite fragile but are much faster and cheaper to print than plastic parts and are ideal for aesthetic models

We are offering this service to AUT staff and students, and industry research partners, who need models made.

The FDM system used as AUT University uses Fused Deposition Modeling (FDM) technology to produce parts in ABS plastic, with a resolution of 0.254mm per layer

The specifications of what the machine is capable of are as follows:

• Material: White ABS
• Maximum size 203 x 203 x 305 mm
• Layer Thickness: 0.254 mm or 0.33 mm.

The Z-Corp ZPrinter 310 Plus creates models out of plaster or ZCast material. The plaster material can be infiltrated with wax or epoxy as a secondary operation to add strength to the parts.

The specifications of what the machine is capable of are as follows:

• Material: Plaster
• Maximum size: 203mm x 254mm x 203mm
• Layer Thickness: 0.1 mm

GENERAL GUIDELINES

• Your parts need to be strong enough to print. As a general guideline, all parts of your model should be at least 2mm thick
• The material used in rapid prototyping is EXPENSIVE!!! Rapid prototyping is therefore too expensive to use because of laziness. If your component is a simple turned component, for example, then it may be much more cost effective for you to turn it on a lathe.
• By all means, do use rapid prototyping to test ideas, but this is no excuse for not having your idea as complete as possible from an engineering point of view. Remember that it will take you substantially more time to make changes to the prototype afterward than it would have taken you just to incorporate the changes in the CAD files in the first place.
• Try to avoid secondary operations whenever possible. If for example, your component will have a hole in it, then add it to the CAD model so it comes out as part of the prototype. If you have to drill it manually afterward, then you run the risk of it not being exactly where it should be.
• The only exception to this is tapping holes for screws, which should be done as a secondary operation (though a pilot hole should be inserted as part of the CAD model).
• In general, if your part could not be easily plastic injection molded, then it will probably cost a lot to prototype.

The following points about support material apply only to printing in Plastic.

• If your component has overhanging features, you must remember that the printer cannot print in thin air. It must therefore deposit a 'scaffolding' system made up of support material beneath the overhanging feature so that it has something to print onto when it gets to the feature.
• The support material is then removed after the part is built.
• If there are no other strength or finish specifications, we will generally try to print the part in the orientation that requires the least amount of support material.
• For solid components of large volume, we have the option of printing the part with a 'sparse' interior. This means that, instead of having a solid interior, the component will have a solid shell on the outside filled with 'scaffolding' in the inside.

TIPS AND TRICKS FOR OPTIMIZING YOUR MODEL

• Keep your wall thickness to between 1.5 and 3mm, unless there is a serious reason to go thinner or thicker. This thickness would also be a good representation of the thickness you would be likely to use if you were injection molding the part.
• If your parts are thin they need to be structurally sound. If, for example, on your part you have a long unsupported bit that is only 2mm tick it is more than likely to break when the part is removed from the machine.
• Avoid large solids as they weigh more and therefore will cost you more. They are probably also not easy to injection mold as they would result in 'sink marks' on the outside of your components.
• Parts are weaker in the layered direction. We have the option of building your parts by positioning them either horizontally or vertically. Let us know if you have any specific strength requirements in a particular direction, and we will try to optimize the build for you.
• Fillet the bottom of all screw posts or other thin protrusions to give them strength. This same rule should apply if you were injection molding the parts anyway.
• The models come out with a reasonably good finish, but exhibit something similar to a wood grain due to the layering process. This can easily be sanded down with a bit of wet and dry paper to give a nice, smooth finish
• The models can be painted using standard spray paints, resulting in extremely high quality finishes