The term “Rapid Prototyping” refers to a class of technologies that can automatically construct physical models from Computer-Aided Design (CAD) data. The construction of the part is usually done using “3D printing“. It is also called “Desktop Manufacturing or Free-form Fabrication”. These technologies enable us to make even complex prototypes that act as an excellent visual aid to communicate with co-workers and customers. These prototypes are also used for design testing. Rapid Prototyping (RP) has been used to provide a physical representation of a product in relatively short time. RP is performed by either material removal or addition.
Why Rapid Prototyping?
- Objects can be formed with any geometric complexity or intricacy without the need for elaborate machine setup or final assembly.
- Free-form Fabrication systems reduce the construction of complex objects to a manageable, straightforward, and relatively fast process.
- These techniques are currently being advanced further to such an extent that they can be used for low volume economical production of parts.
- It significantly cut costs as well as development times.
The Basic Processes
RP is basically a five-step process.
- Create a CAD model of the design
- Convert the CAD model to STL format
- Slice the STL file into thin cross-sectional layers
- Construct the model one layer atop another
- Clean and finish the model
Rapid Prototyping Techniques
RP Techniques have proven to be more convenient in building complex prototypes. This is because these processes are additive in nature, unlike conventional subtractive processes. At least six different rapid prototyping techniques are commercially available, each with unique strengths.
However recent advance in rapid prototyping technology has allowed the use of production type polymers that can be used to access the functional behavior of these materials. One of the shortcomings of testing prototyped products made of production type material is that the prototyped parts may not match those resulting from conventional processing that is used to fabricate the actual product. This is the main difference between conventional processing and rapid prototyping
Stereolithography
Stereolithography was the first RPT (Rapid Prototyping Technology) developed in the United States in 1986. It uses a photosensitive polymer that solidifies when exposed to UV light. The model is built upon a platform situated just below the surface in a vat of liquid epoxy or acrylate resin. The object is built layer by layer. A low power highly focussed UV laser is used to solidify the first layer leaving the excess area’s liquid. This process is repeated until the desired shape according to the CAD model is obtained.
Laminated Object Manufacturing
In LOM (Laminated Object Manufacturing) layers of adhesive-coated sheet material are bonded together to form a prototype. The model material consists of paper laminated with heat-activated glue. The paper is pressed onto the base using a heated roller. A focused laser cuts the outline of the first layer into the paper and then crosshatches the excess area. The next layer is built on top of the first layer in the same manner. The hatched parts (excess area) are removed after the final layer is bonded. The final model has a wood-like texture and since it is made of paper the model has to be varnished to prevent moisture damage.
Solid Ground Curing
Solid Ground Curing (SGC) is nearly similar to stereolithography (SLA). It uses ultraviolet light to selectively harden photosensitive polymers. First, a photosensitive resin is sprayed on the build platform. Next, the machine develops a photo mask (like a stencil) of the layer to be built. The mask is exposed to UV light and the exposed parts are solidified. After the layer is cured, the machine vacuums up the excess liquid resin and sprays wax in its place to support the model during the build. The top surface is milled flat, and then the process repeats to build the next layer.
Fused Deposition Modeling
In this technique, the heated thermoplastic is sent through an extrusion mold. The thin beads thus obtained are deposited on the build platform to form the first layer. The platform is maintained at the lower temperature for the thermoplastic to harden quickly. After the first layer is formed the platform lowers and the extrusion head deposits the next layer on top of the first layer.
Applications of Rapid Prototyping
- Prototyping
- Rapid Tooling
- Rapid Manufacturing
- Heterogeneous Modelling
Advantages of Rapid Prototyping
- Objects having Complex geometry can be easily manufactured.
- Better surface finish.
- Materials used are cheaper.
- Considerable reduction in production time.
- Less wastage of build materials.
- RP manufacturers are dramatically reducing build time.
Disadvantages of Rapid Prototyping
- The polymer material has to be in a special form to be used for prototyping.
- Less tensile strength
- Not economical for the manufacture of simple designs.
- Not suitable for small-scale production.
- Physical properties of the part change with the method of manufacture.
- Since the objects are made layer by layer there is a Stair Stepping Effect.
CONCLUSION
Rapid prototyping is starting to change the way companies design and build products. Today’s commercially available machines are accurate to ~0.08 millimeters in the x-y plane, but less in the z (vertical) direction. Improvements in laser optics and motor control should increase accuracy in all three directions. In addition, RP companies are developing new polymers that will be less prone to curing and temperature-induced warpage.
The introduction of non-polymeric materials, including metals, ceramics, and composites, represents another much-anticipated development. These materials would allow RP users to produce functional parts. Today’s plastic prototypes work well for visualization and fit tests, but they are often too weak for function testing. More rugged materials would yield prototypes that could be subjected to actual service conditions. In addition, metal and composite materials will greatly expand the range of products that can be made by rapid manufacturing.
The United States currently dominates the field, but Germany, Japan, and Israel are making inroads. In time RP will spread to less technologically developed countries as well. With more people and countries in the field, RPs growth will accelerate further.