Selective Laser Sintering

Selective laser sintering is an additive rapid prototyping technique that uses a high power laser to fuse small particles of thermoplastic, metal, polyamide (nylon), ceramic, or glass filled nylon. SLS offers the key advantage of making functional parts in essentially final materials, depending on use of the part.

• SLS prototypes like many rapid prototyping processes are constructed from a .STL file. A .STL file is is simply a mesh of triangles wrapped around a CAD model (this was defined by 3D CAD systems in 1980s).

• .STL’s name is derived from a rapid prototyping process, StereoLithography, also known as abbreviation of Standard Triangulation Language. • This very simple format has become an industry standard for the Rapid Prototyping sector.

The Solid Models as a: (a) Solid Model,

(b) an STL file, and (c) in Sliced Layers.

•The process of Selective Laser Sintering (SLS) is somewhat similar to sterolithography, in that a prototype is produced rapidly through layering of material.

•From thermoplastic powders mostly, although SLS is useful in that many different materials can be used.

A thermoplastic is a plastic that melts to a liquid when heated and freezes to a brittle, very glassy state when cooled sufficiently.

•Such as, polyamide (Nylon), material allows the production of fully functional prototypes with high strength.

•Glass Filled Nylon is suitable for high thermal resistance and high impact strength prototypes.

•SLS Somos 201 is used for functional rubber like parts.

•Depending on the use of the part being constructed these parts may be functional, a capability which is exceptionally useful.

•Price - Multiple pieces of the same part are much cheaper than ordering a single piece. Even various SLS models ordered at the same time as a single batch are much cheaper to make than ordering separately.

•Speed - It could be few hours or a day it really depends upon the build size, shape, and accuracy needed.

•Size of SLS single-made parts are generally 13.3” x 13.3” x 2’. Although larger parts can be constructed by making many smaller parts to assemble, and form a larger part. The thickness of an individual SLS layer is 0.15 to 0.2 mm layer thickness, depending upon the material used.

The process of Selective Laser Sintering is actually quite simple. The entire internal system is heated to below the melting point of whatever substance is being used. So that when heat is applied by the high energy CO2 laser melts and fuses (sinters) the substance.

To do this two piston-like platforms, a roller, an optical sensor, and whatever material is being used to form a part are used in co-ordination with the laser.

The first piston contains most of the substance. When this piston is raised it makes the substance available to the roller. The roller moves the material over the second piston to cover the part being constructed. The material which has been moved to the second piston will then be sintered by the laser, to form an additional layer on the part.

SLS Material

• variety of different types of materials available for use in the selective laser sintering (SLS) process.

• The most beneficial characteristic of selective laser sintering (SLS) is how durable and functional the materials are.

• DuraForm and DuraForm glass-filled (GF) which are nylon based materials that create plastic prototypes.

• Other selective laser sintering (SLS) materials are CastForm used for investment casting patterns, selective laser sintering (SLS) Flex for elastomeric, rubber-like parts, and selective laser sintering (SLS) LaserForm which makes metal prototypes.

SLS Processing• Each of selective laser sintering (SLS) materials requires little to

no post build processing to be ready to use which cuts out several steps in post processing of selective laser sintering (SLS) parts as compared to stereolithography (SLA).

• However, all of the selective laser sintering (SLS) materials can be finished in multiple ways to meet the desire or needs of selective laser sintering (SLS) users. Among other types of post processing, selective laser sintering (SLS) parts can be sanded, painted, plated, tapped, or even machined. This allows for a higher grade of smoothness and appearance to selective laser sintering (SLS) parts and assemblies and also gives users an unlimited number of ways to use selective laser sintering (SLS) parts.

MERITS OF SLSMERITS OF SLS

SLS can produce parts from a relatively wide range of commercially

available powder materials, including polymers (nylon, also glass-filled

or with other fillers, and polystyrene), metals (steel, titanium, alloy

mixtures, and composites) and green sand.

SLS is a direct tool for Rapid Tooling

Injection mould tooling (inserts).

Die casting mould inserts.

Other tooling, e.g. sheet metal forming, blow moulding etc.

Tooling fixtures etc.

Applications of SLS

• Concept model: Physical representation of design ideas, form and style.

• Functional model and working prototype: Parts that can withstand limited functional testing, or fit and operate within an assembly.

• Polycarbonate (RapidCasting) patterns: Patterns produced using polycarbonate, then cast in to metal of choice through investment casting process. Faster than wax process, ideal for thin and fine features. Durable and heat resistant.

• Metal Tools(Rapid Tool): Direct RP of tool of molds for small or short production runs

Laser Engineered Net Shaping

• Sandia National Laboratories • new technology to fabricate 3-dimensional metallic

components directly from CAD solid models.• LENS exhibits enormous potential to revolutionize the way in

which metal parts, such as complex prototypes, tooling, and small-lot production items, are produced.

• metal parts directly from the CAD solid models using a metal powder injected into a molten pool created by a focused, high-powered laser beam.

LENS Process• Additive process• Nd-YAG laser used• Free-form metal fabrication • Deposition head supplies the

metal powder• Focus of laser beam on area to

be melted• Laser focusing by fibre optics or

precision angled mirrors• Laser focused on a particular

spot by series of lens

LENS Process Continuation..• A motion system underneath the platform

moves horizontally and laterally as the laser beam traces cross section of the part.

• Fabrication in low pressure argon chamber for oxygen free operation in melting zone to ensure good adhesion.

• When a layer is complete, the deposition head moves up and continues with next layer.

• Process is continued till part is complete.

LENS Materials• Wide variety of metals are

used in this technique.• Wide variety of materials

that, at minimum,include: stainless steel alloys (316, 304L, 309, 17-4), maraging steel (M300), nickel-based superalloys(Inco designations 625, 600, 718, 690), tool steel alloys (H13), titanium alloy (6Al- 4V), and other specialty materials.

Impeller

H13 tool steel

Fixtures

Housing

Principle of LENS

• High powered Nd-YAG laser focused onto a metal substrate creates a molten puddle on substrate surface.

• Powder is then injected in to molten puddle to increase material volume.

• A “printing “ motion system moves platform horizontally and laterally as laser beam traces the cross-section of part.

• After a layer formation,the machine powder delivery nozzle moves upwards proir to building next layer.

Applications of LENS

• Build mold and die inserts• Producing titanium parts in racing

industry• Fabricate titanium components for

biological implants • Produce functionally gradient structures

Merits and Demerits

Merits of LENS

• Superior material properties

• Complex parts • Reduced post-

processing requirements

Demerits of LENS

• Limited materials: narrow focus only on metal parts

• Large physical unit size: large area to house the unit

• High power consumption: requires very high wattage

Bibliography

• http://www.conceptual-reality.com/sls.htm• http://home.att.net/~castleisland/sls_int.htm• http://www.arptech.com.au/slshelp.htm• http://www.me.utexas.edu/~rbarr/rapid/

Types_Of_RPS.html• http://www.3drg.com/our_process.php