6.3.5 How to use rapid prototyping?

At least six different rapid prototyping techniques are commercially available, each with unique strengths. Because RP technologies are being increasingly used in non-prototyping applications, the techniques are often collectively referred to as solid free-form fabrication, computer automated manufacturing, or layered manufacturing.

Rapid prototyping is an "additive" process, combining layers of paper, wax, or plastic to create a solid object. In contrast, most machining processes (milling, drilling, grind-ing, etc.) are "subtractive" processes that remove material from a solid block. RP’s ad-ditive nature allows it to create objects with complicated internal features that cannot be manufactured by other means.1

The Basic Process

The following statements in this chapter are based on a Method for automatically cre-ating a denture using laser altimetry to create a digital 3-D oral cavity model and using a digital internet connection to a rapid stereolithographic modeling machine.2

Although several rapid prototyping techniques exist, all employ the same basic five-step process. The steps are:
1. Create a CAD model of the design
2. Convert the CAD model to STL format
3. Slice the STL file into thin cross-sectional layers
4. Construct the model one layer atop another
5. Clean and finish the model

CAD Model Creation: First, the object to be built is modelled using a Computer-Aided Design (CAD) software package. Solid modellers, such as Pro/ENGINEER, tend to represent 3-D objects more accurately than wire-frame modellers such as AutoCAD, and will therefore yield better results. The designer can use a pre-existing CAD file or may wish to create one expressly for prototyping purposes. This process is identical for all of the RP build techniques.3
For an example of CAD modelling and making use of virtual reality, have a look at the following video made at Volkswagen’s Design Center in Potsdam (Germany): www.youtube.com/watch?v=ckuh1ZfIYrw.

Conversion to STL Format: The various CAD packages use a number of different al-gorithms to represent solid objects. To establish consistency, the STL (stereolithogra-phy, the first RP technique) format has been adopted as the standard of the rapid pro-totyping industry. The second step, therefore, is to convert the CAD file into STL for-mat. This format represents a three-dimensional surface as an assembly of planar tri-angles, "like the facets of a cut jewel."4 (Figure 2)

Slice the STL File: In the third step, a pre-processing programme prepares the STL file to be built. Several programmes are available, and most allow the user to adjust the size, location and orientation of the model.5 

Layer by Layer Construction: The fourth step is the actual construction of the part. Using one of several techniques, RP machines build one layer at a time from poly-mers, paper, or powdered metal. Most machines are fairly autonomous, needing little human intervention.6

Clean and Finish: The final step is post-processing. This involves removing the proto-type from the machine and detaching any supports. Some photosensitive materials need to be fully cured before use. Prototypes may also require minor cleaning and sur-face treatment. Sanding, sealing, and/or painting the model will improve its appear-ance and durability.7 
An example of a complete rapid prototyping process at Motorola can be seen in the following video: www.youtube.com/watch?v=s3gHHeD6cv8

The investment need of a rapid prototyping technology:
Computer-Aided Design (CAD) software package is used for rapid prototyping. The process supported by CAD file is ideal for all of the RP build techniques.
Companies can buy AutoCAD software via the Internet, or an expert It is relatively ex-pensive however, it can increase your productivity as well as efficiency with customis-able and extendible user interface enhancements that increase overall drafting produc-tivity by reducing the number of steps involved. Additionally, AutoCAD software has several other features that make it worth investing in. The newly developed software packages have easy-to-use navigation tools that make finding your way around 3D models a snap.

Why don’t you take half a day to look through rapid prototyping at your organisation? Involve experts and your colleagues in the brainstorming session. Ask them how diffi-cult it would be for them to follow the above mentioned steps and what kind of difficulties do they have at present! Prepare a checklist according to the above mentioned five-step process technique in order to check if rapid prototyping in your organisation meets the basic requirements.

1 William Palm (May 1998) Rapid Prototyping Primer: www.me.psu.edu/lamancusa/rapidpro/primer/chapter2.htm
2 Thomas, Richard J.: Method for automatically creating a denture using laser altimetry to create a digi-tal 3-D oral cavity model and using a digital internet connection to a rapid stereolithographic modeling machine,   www.patentstorm.us/patents/7153135/fulltext.html
3 William Palm (May 1998) Rapid Prototyping Primer: www.me.psu.edu/lamancusa/rapidpro/primer/chapter2.htm
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7 What is Rapid Prototyping? http://www.rapid-prototyping.us/BasicProcess.php