An Overview

3D Printing is a technology used for printing three dimensional objects. It is a part of Rapid Prototyping technology. A three dimensional object is created by layering and connecting various successive cross sections of materials. It can create parts of any material like polymers, ceramic or metals of any geometry. 3D printers are faster, affordable and easier to use than other similar technologies. It works by building parts in layers; previously it was done with traditional old machines which were high in cost thus providing their limited usage.

However with the introduction of Stereolithography (SLI) it has been made commercially available. In SLI a laser is used to harden a liquid resin which is held in a movable tray. The tray is lowered after creation of every object till the object is created. Then came the Fused Deposition Method (FDS) in which the object was created by melting and forcing each layer of the object through small nozzles. This method was followed by Selective Layer Sintering (SLS) in which a laser was used to fuse powder instead of resin.

Usage of 3D Printing

The development of these methods has made 3D printing easier these days. The growth of its use in various fields to create parts of products has fairly good chances. Recently the need for 3D printers was also felt by NASA to create spaceship parts .Then in medical science through its use the surgeons can have a preview of a bone, limb or any other organ to study the case details prior to making any surgeries. It can also be used for implantation of human parts and replacement of dental crown. Army is also looking at it as an option for reproducing broken parts of tanks and other army equipment that is used in the warfare. It also gives options to the architects to design multiple design concepts efficiently. 3D printers enable one to find the drawbacks in the initial stages leading to the perfect design and saving the time of the users.

Future

It is the fastest growing part of prototyping industry which had revenues of $809 million in 2005 which was considerably higher than $705 which was an estimated figure in 2004. It is an ideal way for producing complex, multi dimensional objects and the cost estimation depends on the size of the object. Roughly it can be taken from $2 to $3 per cubic inch of material used. The usage of 3D printing is rapidly taking pace with the fall in the cost and acknowledgment of the multiple benefits being derived from its use. They will no longer be large, costly machines found only in big corporations.

I would like to give a brief idea about the rapid prototyping process in general before discussing types of rapid prototyping. The virtual design for rapid prototyping is generated from animation modeling software or computer aided design (CAD). Then using this rapid application development technique the virtual design is converted into thin, horizontal, virtual cross-sections and then the process proceeds step by step. These virtual cross sections are transformed into physical cross sections that are grouped to form the complete model or prototype. This is possible because of the process of synchronization of virtual and physical model. Computer bifurcates the 3D drawing created by CAD software into layers and forwards the segmentation layer information to rapid prototyping machine and this machine using the software information creates physical layers using materials like wax, metals, etc. to build the whole part. Additive fabrication imparts flexibility to have varying geometric features and shapes. The machine reads the drawing from CAD and lays down material or the fabrication substance in successive layers. The created cross section in the physical space corresponds to virtual sections of the CAD model.

There are several factors accountable for the construction of a model or a prototype - machine type used for construction, size of the model to be developed and most important complexity of the model to be constructed. Using different technologies the layers are built to create the final parts. Example: For 3D Printing various materials are used; for Selective laser sintering (SLS) thermoplast metal powders are used. Stereolithography uses liquid acrylic polymer to form parts. The methods to create the layers and also the base material used for constructing these model parts differentiate these prototype models.Basic Types of Rapid Prototyping are:

Stereolithography - Liquid polymer is the material used on Stereolithography and ultra violet rays are used to harden the material in the desired shape. This liquid polymer is a combination of liquid acrylic monomers and photo initiator. The UV rays are thrown on liquid acrylic polymer filled in the platform raised to highest height, to trace the base shape. Gradually height of platform is reduced to obtain layer and then next layer by submerging the cured layer. The process is continued to obtain desired shape of the model.

Tolerance around 0.0125mm is found in parts formed by Stereolithography and this depends on the layers formed. Parts formation time varies depending on the complexity of the part. For parts whose geometry and fine detail make machining difficult, this process is most useful.

Selective Laser Sintering - This procedure involves sintering of non-metallic powders into the required shape of prototype. With the help of piston and roller the powder is sinter to produce the layer as per CAD design pattern and this cycle continues to build the prototype part.

Polymers, wax and ceramics are most commonly used materials and this type of prototyping is used for making materials and parts of higher resistance.

Laminated Object Manufacturing - With its own limitation (size limited) and exception; in this method raw material is used in solid form. Papers or plastic are laid at once with heat activated adhesive between the layers. With laser, layer is cut to produce model and prototype parts with softwood feel.

Tolerances are similar to those in Stereolithography (0.0125mm); raw materials used are paper and plastics and due to their small size and strength limitation they are used as visualization aids only. At the same, this type of rapid prototype machines are cheaper to buy.

Three Dimensional Printing (3D Printing) - This procedure gives maximum adaptability and accuracy in producing parts. It is a cheap process and produce parts quickly and also easily. A print head ejects a binding material onto the powder spread on the piston to produce the base layer as per the specified CAD design pattern and repeatedly this is done to produce the required part.

Aluminium oxide, silicon carbide, silica and zirconia are common materials used in parts production. This procedure can be used for producing prototypes which can be used as visualization aids and also design development because of the advance machinery.

Fused Deposition Modeling - Wax or plastic is the base material used in this modeling technique. One by one each layer is extruded so that it forms a strong base before the part can be built over it. The Prototype part is produced by moving the head of the rapid prototyping machine over the path defined by CAD design.

0.5-0.25mm is the tolerance defined for vertical dimensions and approximately 0.025mm for horizontal dimension. Depending on the material (Thermoplastics and wax) used the part production time varies.

Other types of rapid prototypes are: ballistic particle manufacturing, photochemical machining, optical fabrication, solid base curing.

Rapid prototyping is the automatic fabrication of physical objects directly from CAD data sources using solid freeform fabrication. According to Wikipedia, the first techniques for rapid prototyping became available in the late 1980s and were used to produce models and prototype parts. Rapid prototyping techniques put in and tie materials in layers to form objects.

Rapid prototyping takes virtual designs from computer aided design (CAD) or animation modeling software, transforms them into thin, virtual, horizontal cross-sections and then creates each cross-section in physical space, one after the next until the model is finished.

Technologies Available for Rapid Prototyping:

There are many contending technologies that are accessible in the market. As all are additive technologies, their main differences are found in the way layers are built to create parts. Some of the technologies available for Rapid Prototyping are:

Selective Laser Sintering (SLS)
Fused Deposition Modeling (FDM)
Stereolithography (SLA)
Laminated Object Manufacturing (LOM)
Electron Beam Melting (EBM)
3D Printing (3DP)

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