SELECTIVE LASER SINTERING

Rapid Prototyping (RP) can be defined as a group of techniques used to quickly fabricate a scale model of a part or assembly using three dimensional computer aided design (CAD) data. What is commonly considered to be the first RP technique, selective laser sintering was patented by CARL DECKARD A UNIVERSITY OF TEXAS GRADUATE STUDENT. The company was founded in 1989, and since then, a number of different RP techniques have become available. Rapid Prototyping has also been referred to as solid free-form manufacturing; computer automated manufacturing, and layered manufacturing. RP has obvious use as a vehicle for visualization. In addition RP models can be used for testing, such as wl Icrlan airfoil shape is put into a wind tunnel RP models can be used to create male models for tooling, such as silicone rubber molds and investment casts. In some cases, the RP part can be the final part, but typically the RP materia! is not strong or accurate enough. When the RP material is suitable, highly convoluted shape§" (including parts nested within parts) can be produced because of the nature of RP. There is a multitude of experimental RP methodologies either in development or used by small groups of individuals.

WHY RAPID PROTOTYPING NECESSARY?

The reasons of Rapid Prototyping are

To decrease development time.

To decrease costly mistakes

To minimize sustaining engineering changes.

To extend product lifetime by adding necessary features and eliminating redundant features early in the design.

Rapid Prototyping decreases development time by allowing corrections to a product to be made early in the process. By giving engineering, manufacturing, marketing, and purchasing a look at the product the design process, mistakes can be corrected and changes can be while they are still inexpensive. The trends in manufacturing industries to emphasize the following

Increasing number of variants of products.

Increasing product complexity.

Decreasing product lifetime before obsolescence.

Decreasing delivery time.

Rapid Prototyping improves product development by enabling better communication in a concurrent engineering environment.

HOW IT WORKS

The SLS technology uses a C02 laser to sinter (fuse) a variety of thermoplastic and metal powders to "grow" 3D objects layer-by-layer from 3D electronic data (STL files). Because this is an additive process, highly complex geometries can be built without issue; and, because the powder holds the parts, no support structures have to be added and removed. The key advantage of SLS is its ability to rapidly produce durable, functional objects for a wide variety of applications.

Working parts and assemblies with good detail and surface finishing

Variety of material: rigid and flexible plastics, fully dense metal, rubber like elastomer, foundry friendly patterns

Capable of living hinges,, high-flex snaps, high stress and heat tolerance and service as short-run tooling

Can  be  finished  and  painted  for presentation, demonstration  and  video reproduction

Dimensional tolerancing with thousandths of a inch

Delivery of most parts and patterns in just a few working days

THE PROCESS

Selective Laser Sintering (SLS) parts are built with successive layers' of powder selectively bound by a laser beam. SLS is also a technique by which parts are built layer by layer. The basic material consists of powder with particle sizes in the order of magnitude of 50 11m. Successive powder layers are spread on top of each other. After deposition, a computer controlled C02 laser beam scans the surface and selectively binds together the powder particles of the corresponding cross section of the product. During laser exposure, the powder temperature rises above the glass transition point after which adjacent particles How together. This process is called sintering.

ADVANTAGES OF SLS

It offers the key advantage ol'making functional parts in essentially final materials.

The system is mechanically more complex than SLA and most other technology

The method has extended to provide direct fabrication of metals and ceramic objects and tools.

Since the objects are sintered, they are porous.

LIMITATIONS OF SLS

Surface finish: The surface of an SLS part is powdery, like the base material whose particles are fused together without complete Melting. The smoother surface of an SLA part typically wins over SLS.

Dimensional accuracy: SLA is more accurate immediately after completion of the model, but SLS is prone to residual stresses that are caused by long term curing and environmental stresses. Both SLS and SLA suiler from inaccuracy, but SLS is less predictable because of the variety of materials and process parameters.

CONCLUSION

Selective laser sintering provides exact representations of yotir complex designs in just days. This means that without delay, you receive a superior design communication tool. Using the physical prototype, you can detect errors early and correct them before it's too late. It all adds up to hitting aggressive deadlines critical to time-to-market reductions.