Rapid Prototyping / History / Prototyping Technologies

History of Rapid Prototyping

Rapid prototyping is quite a recent invention. The first machine of rapid prototyping hit the markets in the late 1980s. The early rapid prototyping process derived its name from the activities and the purpose for which the earlier machines were utilized.

What is Rapid Prototyping?

Rapid prototyping refers to physical objects that are automatically constructed with the aid of additive manufacturing technology.

Rapid prototyping in its earlier days was applied to production of models and prototype parts. But nowadays with the advancement in technology, rapid prototyping is used widely for many applications that include manufacturing production-quality parts. The manufacturing of these quality parts however are very small in numbers. Apart from industrial applications, rapid prototyping is also used in sculpting. The application of rapid prototyping in sculpting is to generate fine arts exhibitions.

Rapid prototyping as mentioned earlier, involves the use of additive manufacturing technology which actually takes the virtual designs from computer aided design (CAD) or animation modeling software (AMS).

These designs are further transformed into thin, virtual, horizontal cross sections and then the process of creating successive layers continues till the model in complete. On completion of the model, one may find that the virtual model is almost same as the physical model. Over here a process called WYSIWYG (What You See Is What You Get) takes place wherein the final product is same as the image created. Once the layers which correspond to the virtual cross section from CAD are formed, they are either joined or fused automatically to yield the final shape. Additive fabrication has the benefit of creating any shape or geometric feature.

Working of Rapid Prototyping Machines

CAD software and the rapid prototyping machine are connected with a data interface that is called as the STL file format.

This STL file format enables the approximation of a shape of a part or the entire assembly using triangular facets. Smaller the facet, higher is the quality surface. One should consider the meaning of the word rapid as ‘relative’, as the construction process of a model with the contemporary methods can take up a long time which can be several hours to several days. It actually depends upon the complexity and size of the model. The method used over here also plays an important role. Sometimes the type of machine being used also influences the time taken for the creation of a new model though the additive systems are applied. Even here the size and the number of models to be created play an equally important role.

There are some other techniques that are used in the construction of parts. The technique used in solid free-form fabrication involves the use of two materials in the construction of parts. One of it is the building material of that part and the other is the support material. The use of support material is to provide support to the projecting features during construction.

In case of manufacturing polymer products in higher quantities, a process called traditional injection molding is more feasible in terms of cost, but when it comes to manufacturing parts in smaller volumes, the application of additive fabrication is recommended more and is cost effective.

Prototyping Technologies

Some of the prototyping technologies used in various rapid prototyping machines are as follows:

Selective Laser Sintering (SLS):

This technology involves the use of high power laser for the fusion of tiny particles of plastic, metal etc, into a mass that represents a desired 3D object, through the help of a SLS machine. This is an additive manufacturing technique. Materials used in this technique are metal powders and thermoplastics.

Fused Deposition Modeling (FDM):

This additive manufacturing technology was invented in the late 1980s by S. Scott Crump and is used for applications like modeling, prototyping and production. This technology involves the use of eutectic metals and thermoplastics.

Stereo lithography (SLA):

This also is an additive manufacturing technology and is used for production of models, patterns etc through the Stereo lithography machine. Photo-polymer is the principle material used in this technique.

Laminated object manufacturing (LOM):

Paper material is the base material used in this technology. In this method layers of adhesive-coated plastic, paper or metal laminates are fused together and cut into shape with the aid of a knife or a laser cutter.

3D Printing:

This too is an additive manufacturing technology and involves the use of various materials. In this technology successive layers of material create a 3D object. 3D printing technology actually is said to be more affordable, easy to use and speedy than the additive manufacturing technologies. Though production applications are actually dominated by the additive manufacturing technologies, 3D has a great potential to prove useful in the production applications.

Rapid prototyping, is now entering into rapid manufacturing which is more advanced as compared to rapid prototyping machines as it can be used for large products. This is an additive fabrication technique, that would be applied to the manufacturing of solid objects. This process involves the sequential delivery of energy, material (material sometimes may not be used) to the specified points in space, in order to produce a particular part. Rapid manufacturing is an advanced form of this technology.

POISSON’S RATIO

When an element is stretched in one direction, it tends to get thinner in the other two directions. Hence, the change in longitudinal and lateral strains are opposite in nature (generally). Poisson’s ratio ν, named after Simeon Poisson, is a measure of this tendency. It is defined as the ratio of the contraction strain normal to the applied load divided by the extension strain in the direction of the applied load. Since most common materials become thinner in cross section when stretched, Poisson’s ratio for them is positive.

For a perfectly incompressible material, the Poisson’s ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. A Poisson’s ratio greater than 0.5 cannot be maintained for large amounts of strain because at a certain strain the material would reach zero volume, and any further strain would give the material negative volume.

Some materials, mostly polymer foams, have a negative Poisson’s ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.Foams with negative Poisson’s ratios were produced from conventional low density open-cell polymer foams by causing the ribs of each cell to permanently protrude inward, resulting in a re-entrant structure.

An example of the practical application of a particular value of Poisson’s ratio is the cork of a wine bottle. The cork must be easily inserted and removed, yet it also must withstand the pressure from within the bottle. Rubber, with a Poisson’s ratio of 0.5, could not be used for this purpose because it would expand when compressed into the neck of the bottle and would jam. Cork, by contrast, with a Poisson’s ratio of nearly zero, is ideal in this application.

It is anticipated that re-entrant foams may be used in such applications as sponges, robust shock absorbing material, air filters and fasteners. Negative Poisson’s ratio effects can result from non-affine deformation, from certain chiral microstructures, on an atomic scale, or from structural hierarchy. Negative Poisson’s ratio materials can exhibit slow decay of stress according to Saint-Venant’s principle. Later writers have called such materials anti-rubber, auxetic (auxetics), or dilatational. These materials are an example of extreme materials.

POISSON'S RATIO

When an element is stretched in one direction, it tends to get thinner in the other two directions. Hence, the change in longitudinal and lateral strains are opposite in nature (generally). Poisson’s ratio ν, named after Simeon Poisson, is a measure of this tendency. It is defined as the ratio of the contraction strain normal to the applied load divided by the extension strain in the direction of the applied load. Since most common materials become thinner in cross section when stretched, Poisson’s ratio for them is positive.

For a perfectly incompressible material, the Poisson’s ratio would be exactly 0.5. Most practical engineering materials have ν between 0.0 and 0.5. Cork is close to 0.0, most steels are around 0.3, and rubber is almost 0.5. A Poisson’s ratio greater than 0.5 cannot be maintained for large amounts of strain because at a certain strain the material would reach zero volume, and any further strain would give the material negative volume.

Some materials, mostly polymer foams, have a negative Poisson’s ratio; if these auxetic materials are stretched in one direction, they become thicker in perpendicular directions.Foams with negative Poisson’s ratios were produced from conventional low density open-cell polymer foams by causing the ribs of each cell to permanently protrude inward, resulting in a re-entrant structure.

An example of the practical application of a particular value of Poisson’s ratio is the cork of a wine bottle. The cork must be easily inserted and removed, yet it also must withstand the pressure from within the bottle. Rubber, with a Poisson’s ratio of 0.5, could not be used for this purpose because it would expand when compressed into the neck of the bottle and would jam. Cork, by contrast, with a Poisson’s ratio of nearly zero, is ideal in this application.

It is anticipated that re-entrant foams may be used in such applications as sponges, robust shock absorbing material, air filters and fasteners. Negative Poisson’s ratio effects can result from non-affine deformation, from certain chiral microstructures, on an atomic scale, or from structural hierarchy. Negative Poisson’s ratio materials can exhibit slow decay of stress according to Saint-Venant’s principle. Later writers have called such materials anti-rubber, auxetic (auxetics), or dilatational. These materials are an example of extreme materials.