Major Assignment Sub – Production Engineering IITopic – Laser Sintering

Session – 2015 - 2016 Submitted To – Mr. Aditya MishraAsst. Proff.(Mech. Dept.)

Submitted By- Kanishka Gaur U.I.D.- K10805

B.tech, Civil Engg.Sem - VI, Year - III

Index Introduction Definition Principle Procedure Industrial Application Advantages/Disadvantages Recent trends Future Scope Conclusion

Introduction Selective laser sintering (SLS) is an intelligent manufacturing

process based on the use of powder coated metal additives, a process generally used for rapid prototyping and instrumentation. A continuous Laser beams are used or pulsating as heating source for scanning and aligning particles in predetermined sizes and shapes of the layers.

The geometry of the scanned layers corresponds to various sections of the models established by computer-aided design (CAD) or from files produced by stereo-lithography (STL). After scanning the first layer, the scanning continues with the second layer which is placed over the first, repeating the process from the bottom to the top until the product is complete.

SLS is known also as solid free and open shape manufacturing process, as a layer fabrication technology, rapid prototyping technology, a selective sintering of metal powders.

SLS is reactive when using a chemical reaction of mixing components in the presence of a laser and a selective laser melting (SLM), a direct metal laser sintering (DMLS) or direct metal laser re-melting, when the complete melting of powders is pervasive over the solid state dust sintering. This process was also used in manufacturing moulds, rapid handling of electrodes manufactured, polymer moulds, die casting, die casting of titanium zirconium, bio-medical applications, pieces of zirconium-titanium (PZT) and sheet metal parts.

Currently, the experiments in the laboratory of INCDMTM and dedicated magazines and articles draw attention to a new comprehensive, integrated approach, of the SLS process

Definition

One of the technologies used by today's 3D printers is called selective laser sintering (SLS). During SLS, tiny particles of plastic, ceramic or glass are fused together by heat from a high-power laser to form a solid, three-dimensional object.

The SLS process was developed and patented in the 1980s by Carl Deckard — then an undergraduate student at the University of Texas — and his mechanical engineering professor, Joe Beaman.

Additive manufacturing, or 3D printing, is the process of turning digital designs into three-dimensionalobjects. It is a convenient and affordable way to make prototypes as well as finished products, making it popular with businesses, hobbyists and inventors.

Principle An additive manufacturing layer technology, SLS involves the use

of a high power laser (for example, a carbon dioxide laser) to fuse small particles of plastic, metal, ceramic, or glass powders into a mass that has a desired three-dimensional shape. The laser selectively fuses powdered material by scanning cross-sections generated from a 3-D digital description of the part (for example from a CAD file or scan data) on the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed. 

Because finished part density depends on peak laser power, rather than laser duration, a SLS machine typically uses a pulsed laser. The SLS machine preheats the bulk powder material in the powder bed somewhat below its melting point, to make it easier for the laser to raise the temperature of the selected regions the rest of the way to the melting point.

In contrast with some other additive manufacturing processes, such as stereolithography (SLA) and fused deposition modeling (FDM), which most often require special support structures to fabricate overhanging designs, SLS does not need a separate feeder for support material because the part being constructed is surrounded by unsintered powder at all times, this allows for the construction of previously impossible geometries. Also, since the machine's chamber is always filled with powder material the fabrication of multiple parts has a far lower impact on the overall difficulty and price of the design because through a technique known as 'Nesting' multiple parts can be positioned to fit within the boundaries of the machine. One design aspect which should be observed however is that with SLS it is 'impossible' to fabricate a hollow but fully enclosed element. This is because the unsintered powder within the element can't be drained.

Since patents have started to expire, affordable home printers have become possible, but the heating process is still an obstacle, with a power consumption of up to 5 kW and temperatures having to be controlled within 2 °C for the three stages of preheating, melting and storing before removal.

Procedure Just like the Stereolithography (SLA) technology, Selective

Laser Sintering is an additive manufacturing technique which can be used to turn digital CAD designs into 3-Dimensional objects.

The printing process in Selective Laser Sintering (SLS) is however not quite the same as that used in Stereolithography.

In SLA, an ultraviolet curable photopolyme resin is used instead of powder and an ultraviolet laser is used to cure the liquid into a solid object.

When it comes to SLS on the other hand, powdered is heated by a high powered laser at just below its melting point. This causes the powders to sinter together forming the solid 3D model which was intended to be made.

Industrial Application Digital ManufacturingProduce models directly from digital files. Any deviations form the ideal model can be easily corrected and applied to your next SLS prototype. High-Temperature ResistanceHigh temperatures often ruin prototypes. They are typically unable to withstand the additional stress, causing issues in testing as well as R&D. With SLS prototypes, high temperatures can be tolerated to enhance the realness of your prototype.  Complex, Thin-Wall Ductwork SLS prototyping technologies can produce large, durable models. They are also capable of delivering miniscule, intricate prototypes, with no deviation in quality or durability.

Rapid Manufacturing The material selection of SLS technology provide a whole array of rapid manufacturing possibilities, including aerospace hardware, medical and healthcare products, military hardware, and consumer goods. Concept Models A concept model is used when time and cost effectiveness constraints are more important than cosmetics and accuracy. We can develop CAD files. Production Parts Without Tooling The durability of the materials, as well as the ability to prototype metal mean the tooling step can be skipped with an SLS production process. 

Advantages/Disadvantages First of all, there is no need for supports when printing

overhanging, unsupported structures (e.g. the horizontal parts of a capital letter F). The powder itself provides the necessary support. Second, parts can be created out of a wide selection of materials. And lastly, complexity isn’t an issue as long as you can remove the not sintered powder.

Next are some of the disadvantages of SLS. The biggest problem of the technology is that the fabricated parts can be porous and/or have a rough surface depending on the used materials. Another problem, mainly for polymer parts, is thermal distortion. This can cause shrinking and warping of fabricated parts. These are two things to keep in mind when designing products to be fabricated using SLS printers.

Recent trends 3D printing is an additive technology in which objects are built

up in a great many very thin layers. The first commercial 3D printer was based on a technique called stereolithography. This was invented by Charles Hull in 1984. Stereo lithographic 3D printers (known as SLAs or stereolithography apparatus) position a perforated platform just below the surface of a vat of liquid photopolymer. A UV laser beam then traces the first slice of an object on the surface of this liquid, causing a very thin layer of photopolymer to harden. The perforated platform is then lowered very slightly and another slice is traced out and hardened by the laser. Another slice is then created, and then another, until a complete object has been printed and can be removed from the vat of photopolymer, drained of excess liquid, and cured. Stereo lithographic printers remain one of the most accurate types of hardware for fabricating 3D output, with a minimum build layer thickness of only 0.06mm (0.0025 of an inch).

Future Scope Imagine a future in which a device connected to a computer can

print a solid object. A future in which we can have tangible goods as well as intangible services delivered to our desktops or high-street shops over the Internet. And a future in which the everyday "atomization" of virtual objects into hard reality has turned the mass pre-production and stock-holding of a wide range of goods and spare parts into no more than an historical legacy.

Such a future may sound like it is being plucked from the worlds of Star Trek. However, while transporter devices that can instantaneously deliver us to remote locations may remain a fantasy, 3D printers capable of outputting physical objects have been in both development and application for over three decades, and are now starting to present a whole host of new digital manufacturing capabilities. 3D printing may therefore soon do for manufacturing what computers and the Internet have already done for the creation, processing and storage of information.

Conclusion Since its emergence, the SLS has attracted attention from

both researchers and users. As a result, various aspects of the processes and materials used for SLS sintering have been studied and there have been established that this is a modern and at the same time also a rapid means for prototyping and manufacturing.

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