What is Rapid Prototyping?
Rapid Prototyping (RP) is defined as a group of technologies used to quickly produce a scale model of a component or group of components using 3-dimensional computer aided design (CAD) data. It can also be referred to as additive manufacturing and/or 3D printing.
What this actually means is that a computer generated virtual design from 3D design software is translated into thin horizontal cross-sections. These layers are created one at a time to create a real physical model where the layers are joined together or fused automatically to create the final model. This is where the names additive manufacture and 3D printing are derived. It is a ‘what you see is what you get’ process where the virtual model is almost identical to the physical model. This gives the technology a fundamental advantage over traditional techniques as it can create almost any geometric feature or shape.
Why would you use Rapid Prototyping?
- To decrease product development time (time compression technology)
- To minimise engineering changes
- To increase effective communication between engineers, product designers and marketing departments
- To extend the product life cycle
By letting the design department, manufacturing/production engineering and marketing departments see the model at an early stage allows costly errors to be eliminated. Any mistakes can be rectified before expensive tooling has been made for full production whilst the models at this stage are relatively inexpensive.
The word Rapid is relative as some models can take only a few hours to build whereas others may take several days. The time taken to build is dependant on the size, complexity and the technique being used.
The standard file format that is used between the CAD software and the rapid prototyping machines is the STL file format. Although for colour models such as those produced on the Z Corporation machines the VRML format is used, as there is no colour information in the STL file format. Both formats create an approximation of the shape of a component or assembly by using triangular facets. The smaller the triangles the smoother the surface, however, there is a point where there will be no further improvement because of the limitations of the technology. In order to see how the rapid prototype machines will see your model you need to turn off smooth shading in the 3D CAD software.
There are a variety of methods that can be used to deposit the material and which one is best for your project will depend on what you want from your models. They are:
- Stereolithography (SLA)
- Selective Layer Sintering (SLS)
- 3D Printing (3DP)
- Fused Deposition modelling (FDM)
All of these techniques require a second material that is known as the support material, which allows tapered surfaces and overhangs to be produced as the component is ‘grown’. These come in a variety of forms that can be powder, liquid, wax or even the model material that has to be cleaned or removed from the model afterwards. Some machines generate the support structure for you so you have no control over where it goes, whereas other machines you have to manually generate the support material using specialist software.
As materials and techniques develop, increasingly Rapid Prototyping technologies are being used for production parts rather than just prototypes. Currently RP models aren’t as accurate or the material isn’t as good as CNC machined parts for instance, but, some of the most accurate 3D printers are generally creating parts to a tolerance of +/- 0.125mm. This does not mean that they cannot do better but this is what service providers generally quote. Traditional techniques such as injection molding will be cheaper for higher quantity parts but additive manufacture can be faster and less expensive for smaller batch quantities, especially for hard to manufacture parts.
Some of the other advantages to Rapid manufacture are:
- Low material waste
- Speed
- Complex Geometries
- Energy Efficiency
Rapid Manufacturng is widely regarded by experts as the next stage for Rapid Prototyping technologies.
