Sphynx's Guide to Rapid-Prototyping

[Sphynx]

Sphynx's guide to Rapid-Prototyping
Converting your mesh models into real-world objects using STL and other rapid-proptyping techniques.

Introduction

This tutorial is being built over a period of time and will be running in conjunction with the 3D WIP thread 'Etherball: 3D mesh to real-world object'. This thread will contain all of the important information regarding what you need to know about rapid-prototyping techniques while the WIP thread is a major example of its implementation. Note however, that while that thread is using Blender to model, both threads are for the general membership and are not Blender tutorials. All of the points raised as of equal importance for all applications in use.

As this thread is being built gradually, it would be extremely useful for now if any comments, requests and questions should be placed in the accompanying WIP thread rather than disrupt the flow of this tutorial. Any posts placed here which are not by myself will be moved without warning to the WIP.

In the same way, I am fully aware that there are several members who have professionally produced items for rapid prototyping in the same way as myself. If any of those members see things that I've missed as I deal with each issue, please post comments in the WIP and I'll incorporate them into the main tutorial pages as we go.

The first major point to remember...

I've produced quite a few meshes for rapid-prototyping so far - in fact over the last year, while it is far from being my staple workload, I've produced twelve meshes, a quarter of them for a returning client. From that, it's clear that I have quite a bit of experience in producing meshes for production as real-world objects - I know the requirements, pitfalls, and great feeling that you get when you see items that you've created on-screen sitting on the desk as a real-world object.

The most major point to remember however, comes before all of that. Make no odds - rapid-prototyping is a commercial and industrial process. It is designed primarily for use in producing master items for reproduction, and prototypes for industry. It is not designed for a private individual to transfer their prize 3D mesh into a desktop model, and the best reason for this is cost.

Rapid prototyping is expensive.

The accompanying WIP thread is being run on a piece that I am producing for my company to produce commercially - I'll be lucky if after half of the pieces needed I have change out of £1000.

A simple 98mm high figurine produced by the 3D printing company that I'll be using comes in at just under £100 before tax - on average that's £1 per millimetre of height even for the cross-sectional surface area of a standing figure, so be warned. Saying that however, you don't need to go over the top. Meshes that I've produced have ranged from a 9mm high TIE fighter, to a 200mm tall figurine, and there are many ways to keep the costs down.

So read on.

REMEMBER - Post all of your comments and questions in the WIP thread.

[Sphynx]

Tutorial Contents
(links to be added as each part is completed)

What is Rapid-Prototyping

So many people get excited about rapid-prototyping and the potential of seeing their 3D meshes as a real-world object, but very few of them really know what Rapid-Prototyping really is. This is where we'll be doing the rounds of the various processes available, along with their limitations and possibilities.

Planning your mesh

Not everyone involved in 3D, and especially as a leisure activity, actually sits down and plans their mesh. At most, they may make a simple sketch of what they want to build. If you intend to produce your mesh for Rapid Prototyping however, and it is anything other than a small solid object, learn to plan. Plan well, and plan early.

Building your mesh

When your mesh is only intended to be on screen, you are building it for a forgiving audience - the human eye. Unintelligent Rapid-Prototyping machines however, are very unforgiving and a mistake here will either see your mesh not printed at all and rejected by the bureau or worse still, printed incorrectly and costing you money.

Preparing and verifying your mesh

This is where we'll be using one or two utilities that can doubly insure that you've got it right, and discussing some of the tactics involved in reducing the cost of printing and the risk of making some very costly mistakes. This is where we'll see that even the orientation of your mesh in the printer can have an impact on a good mesh being produced.

Bilbiography:
Note that various sources of industry information will be used in this tutorial in order to remain current with materials and methods available. Not least of which, are the public FAQ's available from Xpress3D.com, the Wikipedia and various rapid-prototyping manifacturers.

[Sphynx]

First off, lets get some of the basics out of the way before we actually look at the stuff that we need to do to produce something using Rapid Prototyping.

The Basics Concepts

The very basic idea of rapid-prototyping involves the use of a descending platform in a basin containing some form or media that will either form the object itself, or a support for the object as it is built. Above the platform is a 'gun' which, depending upon each of the various types of rapid-protoyping, either fires the material or some form of energy which converts the flexible, non-fixed material in the basin to the solid walls of the object.

The 3D object being built is sub-divided inside the computer into a series of thin layers that becomes a cross-sectional pattern for the 'gun'. The gun draws the cross-section into the basin, and the platform then descends by the thickness of that particular method's cross-section. Cross-sectional thickness can vary between methods, and the smoothness of the finished product usually directly correlates to the thickness of each cross-section. In the same way as a bitmap image onscreen, the larger the layer, the bigger the 'jaggies'.

Once the platform has fully descended into the basin and the 'gun' has finished drawing each layer, the gun retracts and the platform raises up again to let the remaining material drain away (if required by that process) and allow the object to be accessed.

Again depending on the individual process, the object may then need to be cleaned and then have a further process performed on it to finalise the material - some need a second curing process to fully harden the resins, while others may need to be sprayed with an additional finish.

The materials

There are a number of materials in general use within rapid prototyping, and what lies below is a simple summary and by no means meant to be complete. It is provided here as a general guide only as I'm guessing that most people from our fraternity will actually want a reasonably solid and smooth object rather than some of the special material properies that are available.

Somos
The various Somos resins provide a range of properties including general fast production, accuracy, water-resistance, transparency, pure and clear white, and even high temperature resistance suitable for prototype testing.

Accura and RenShape
Both durable and accurate materials mimicking ABS plastic.

Polycarbonate/ABS
A mix of polycarbonate and ABS plastic. It provides both strength and durability and is widely used in the production of parts in the automotive, electronics and toy industry. It has good thermal properties and while able to produce the same detailing as ordinary ABS, it is significantly stronger.

ABS / ABSi
Reasonably strong and durable it has become an industry standard plastic. Objects made from ABS in rapid-prototyping have about 3/4 the strength of moulded ABS used in other processes, such as injection moulding. ABSi is similar to ABS, but translucent and with a significantly higher resistance to impacts (hence the 'i' suffix).

Polycarbonate / Polycarbonate ISO
Probably the strongest material available for rapid-prototyping. Like ABS, it has about 3/4 the strength of the same material used in a process such as injection moulding. The ISO version of this material meets the highest of the six standards used in ISO grading and is also suitable for sterilisation using either gamma radiation or ethylene oxide.

Plaster Powder / Starch
A plaster based powder that is infused by cyanoacrylate or epoxy resin to produce a very high resolution cross-section. It probably has the thinnest cross-sectional width available, and allows the use of multiple colours within the same object. It is invariably only used with the ZCorp and other inkjet 'inkjet' processes. Starch provides the same type of powder based media but is really not used for permanent objects - probably just temporary items which may see destruction anyway, such as in a master mould making process.

Various PolyJet Resins
Various resins providing highly detailed and smooth finishes. These materials generally provide a good impact strength as well as a slight resiliance allowing 'snap fit' capabilities.

TangoGray and Black PolyJet Resin
These materials are very similar to rubber or silicone and objects made from these materials can therefore be made to stretch over other components.

Duraform PA and GF
Duraform is a polyamide based material providing high durability. The GF version of this product incorporated glass beads.

Next: The various types of Rapid Prototyping available