selective laser sintering full report
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Selective laser sintering (SLS) is technique by which parts are building layer by layer. The SLS is a free form fabrication method to create components by precise thermal fusing of powdered materials.
This is durable, economical and fast. The SLS is another form of rapid prototyping. This selective laser sintering (SLS) is one among the rapid prototyping which include stereo lithography (SLA). This method has also been extended to provide direct fabrication of metal and ceramic objects and tools. With this method we can make required and different prototype. This SLS can be used as a mass production prototyping.
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 shapeÃ‚Â§" (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.
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WHY RAPID PROTOTYPING NECESSARY
The reasons of Rapid Prototyping are
Â¢ To decrease development time.
Â¢ To decrease costly mistakes
Â¢ To minimize sustaining engineering changes.
Â¢ 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
Â¢ Increasing number of variants of products.
Â¢ Increasing product complexity.
Â¢ Decreasing product lifetime before obsolescence.
Â¢ Decreasing delivery time.
Rapid Prototyping improves product development by enabling better communication in a concurrent engineering environment.
HIGHLIGHTS OF SLS
Â¢ It is patented in 1989.
Â¢ Considerably stronger than stereo lithography.
Â¢ Laser beam selectively fuses powder materials; nylon, elastomers and so on metals.
Â¢ Process is simple.
Â¢ There is no milling or masking steps required.
Â¢ Powdering, porous surface unless sealant is used. Sealant also strengthens the part.
Â¢ Uncured materials are easily removed after a build by brushing of. SELECTIVE LASER SINTERING
The selective laser sintering is a free form fabrication method to create components by precise thermal fusing (sintering) of powdered materials. Parts of complex geometries can build in successive layers that define subsequent cross sections of the component.
The sinter powder is powder fed to the process chamber from two cartridges flanking the partly built product. This allows for bidirectional powder feeding to the roller that lays powder across the top of the product, thus improving building speed. Unsintered powder is relumed to the powder feeding cartridges, to be/ recycled. The process is a C02 type ol'50watt power. The process chamber is Oiled with nitrogen to obtain safe materials sintering conditions.
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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.
Â¢ Working parts and assemblies with good detail and surface finishing
Â¢ Variety of material: rigid and flexible plastics, fully dense metal, rubber like elastomer, foundry friendly patterns
Â¢ Capable of living hinges,, high-flex snaps, high stress and heat tolerance and service as short-run tooling
Â¢ Can be finished and painted for presentation, demonstration and video reproduction
Â¢ Dimensional tolerancing with thousandths of a inch
Â¢ Delivery of most parts and patterns in just a few working days
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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.
The parts are built in polyamide (PA). The powder being a solid material has an attractive feature of being self supporting for the, generated product sections. This makes supports redundant. The polyamide material allows the production of fully functional prototypes with high mechanical and thermal resistance. The use of PA powder filled
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within glass particles (PA-GF) has a much higher thermal resistance and is typically used in functional test with high loads.
The polyamide SLS parts have excellent long term stability and are resistant, against most chemicals. They can be, made water tight by impregnation. The PA material is used as bio compatible, food safe and not harmful to health or environment.
EXPERIMENTAL SETUP OF SLS
Thermoplastic powder is spread by a roller over a surface of a build cylinder. The piston in the cylinder moves down one object layer thickness to accommodate the new
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layer of powder. The powder delivery system is similar in function to a build cylinder. Here a piston moves upwards incrementally to supply a measured quantity ofpowder for each layer.
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A layer beam is then traced over the surface of this tightly compacted powder to selectively melt and bond it to form a layer of the object. The fabrication chamber is maintained at a temperature just below the melting point of the powder so that heat from the laser need only elevate the temperature slightly to cause sintering. This greatly speeds up the process. The process is repeated until the entire object is fabricated.
After the object is fully formed the piston is raised to elevate it. Excess powder is simply brushed away and final manual finishing may be carried out. No supports are required with this method. Since overhangs and under cuts are supported by the solid power bed. It may take a considerable length of cool down time before the part can be
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removed from the machine. Large parts with thin sections may require as much as two days of cooling time.
OVERVIEW OF SLS
X & Y AXIS CONTROL
MATERIAL BED BUILD LEVEL
This overview bypasses many intricacies of the processes involved. Selective laser sintering is very similar to Stereo Lithography (SLA) with the exception of using powdered raw material rather than photo-sensitive liquid as the build material. The system consists of an X-Y axis controlled laser, a Z axis controlled table, and a bed of powdered raw material that is maintained at a constant level. Prototypes are created with the table initially positioned below the surface of the powder a distance equal to (he thickness resolution (or the part. The laser traces a two dimensional cross-section of the item at that level, fusing the powder touched by the laser. The table then descends a distance equal to the thickness resolution and powdered media is replenished over the solidified layer. This process continues until the entire prototype has been solidified.. At
this time the model is lifted out of the media bed. cleaned of loose material and smoothed to remove the Z axis stair-steps created by the process. "Trapped volumes" are not a problem for SLS models. Support structures arc generally not required. A good selection of materials is available for this process, ranging from a rubber-like polymer to hard plastic.
PROTOTYPES MANUFACTURED BY SLS
AIRFOIL PAINTBALL - MASK MPELLER
GARDEN TRIMMER VALVE BODY DIESEL ENGINE
ADVANTAGES OF SLS
Â¢ It offers the key advantage ol'making functional parts in essentially final materials.
Â¢ The system is mechanically more complex than SLA and most other technology
Â¢ The method has extended to provide direct fabrication of metals and ceramic objects and tools.
Â¢ Since the objects are sintered, they are porous.
Durable and functional parts Large and complex parts Small series, produced in one building process No support structure' necessary
All kinds of finishing degrees can be made water light
LIMITATIONS OF SLS
1. 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.
2. 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.
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3. Accuracy: the accuracy of a rapid prototype is dependent on many factors. Upon completion of the prototype the SLA provides greater accuracy than SLS.
Selective Laser Sintering is the ideal solution for Fully functional prototypes and series. Rapid Manufacturing.
Fully functional prototypes and series
1. Parts for mechanical and thermal tests
The polynmide material allows the production of strong, durable parts that can be used tor extensive functional testing. Sintered products have mechanical properties comparable to those of injection moulded PA 12 parts, typical applications are snap fits but it is also possible to produce working hinges.
Polyamide parts with glass filling have a much higher thermal resistance and are perfectly suited for lighting elements and ventilation systems or products that require high thermal loads. Apart from their use as test products, the functional SLS parts often also need to be used at the same time for a visual/csthetical control or dimensional check.
2. Scries of small plastic parts
SLS is an interesting and cost-effective alternative to injection moulding (Rapid Tooling). With the P 700 machine which has a large build area, a series of small pieces can be built in one single laser sintering process. This dramatically decreases the price, as the cost of an SLS part depends on its volume. Or in other words, the cost is defined by the amount of powder it takes to build it and not by an initial investment in an injection moulding tool. Moreover, series of SLS parts are available in a few days. So no need for
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high start-up investments, no long lead times to produce a mould and injection mould the parts, no difficulties in case the parts are complex.
Component of a vacuum cleaner, buiii on the EOSINT P700 with a build volume of700x380x580mm
3, Large and complex functional parts
The EOSINT P 700 machine can build large, complex geometries in one piece, up to 700x380x580mm. The number of layers to be built is significantly reduced as large parts can be built horizontally, which considerably shortens the building process. Parts exceeding the P 700' maximum dimensions .can be built in multiple pieces and put together afterwards. The process of gluing sub-parts and assembling components can be done in the most accurate and secure way using the Rapid Fit system. Rapid Fit allows to firmly position the parts on a unique support system with individualized fixtures, supporting the part on well positioned points.
l)enl. Of M cchanical Engineering
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.
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SELECTIVE LASER SINTERING
4. K. Murali e t al. / Journal of Materials Processing Technology 136 (2003) 179-185
5. Selective laser sintering of metals and ceramics, Int. J. Powder Me tall.
6. Laser sintering, J. Mater. Process. Technol. 111 (2001)210-213
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13-12-2010, 07:04 PM
send full seminar and presentation report on selective laser sintering...
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you should download the seminar and presentation report from the above post. The ppt of the topic is available at:
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selective laser sintering
Pravara Rural Education Society.doc (Size: 647.5 KB / Downloads: 49)
Bonding common surface of adjacent particles touching each other in a mass of powder or compact by using heating is called sintering. Sintering is always necessary operation to impart the required strength and density to product. Sintering is related with powder metallurgy in which finely metal particle used to get finished or semi finished objects.
Selective laser Sintering can be consider an advance manufacturing. The selective laser sintering is rapid prototype which can create three dimensional parts by using laser as selective sinter (heat& fuse). Rapid prototype means use of group of techniques used to fabricate scale model of part or assembly by using three dimensional designs. Selective laser sintering is the first rapid prototype which is patented in 1989 by CARL DEKARD UNIVERCITY OF TEXAS STUDENT. After which company give wide range of RP
Selective laser sintering Process
Diagram for SELECTIVE LASER SINTERING process is shown in figure.SLS process start with 3D computer aided design which is converted to 2D manufacturing drawing. It consists of center processing computer with newly developed CAD software in which model of part can be constructed with detailing .this computer also used to control the laser beam intensity, and path. Laser unit provided with optics & galvanometer to get focused intense laser beam. A process chamber is provided in which roller mechanism is used to distribute powder evenly on chamber process platform. Powder filled cylinder is provided with motor by using which powder can be filled in process chamber. Another cylinder is provided which is used to support part which build already.
Before starting of any process its input parameter should be studied. For SLS it can be distinguish in following ways
2.2.1.Direct Input Parameter: - direct input parameter are used directly according to Standard. Some of the input parameter discussed below.
a) for laser: i) laser focus diameter ii) laser wave length iii) beam profile
iv) laser power v) Scanning velocity
b) For machine: i) platform temperature ii) hatch distance iii) type of material
c) Powder characteristics: - i) powder size ii) particle size iii) particle roughness
iv) Particle size distribution
Chemical Induced Bonding :-
In chemically induced binding to binder element is used. As interaction time for material is less the diffusion can not occur. In chemical induced binding the part of same material is used as binder by partial disintegration. For example for laser sintering of SiC material the SiC is disintegrated in Si & C so obtained Si will react with oxygen and forms SiO2.this SiO2 can utilized to binder material for SiC product.
APPLICATIONS of SELECTIVE LASER SINTERING
1. It can be used for making parts in aerospace industry where reduced weight &good strength are necessary.
2. It can be used in automobile industry to produce different concept cars. In automobile also weight and strength have equal importance both can be obtained using SLS
ADVANTAGES AND DISADVANTAGES OF SELECTIVE LASER SINTERING
1. Use of newly developed software.
2. The Z’th dimension which is difficult to give on ‘PM’ can be given easily in SLS.
3. By using laser beam we can focus on certain area.
4. Decreased development time for model of part or assembly.
5. More flexibility in design process by the use of computer programming.
6. Material saving can be done up to 7% to 10%.
7. Different material can be mixed to get required strength.
8. Functional part is durable, heat &chemical heat resistant.
9. Surface finishes from 500to 32 micro inches.
1. High power is required because of use of laser
2. Shrinkage may affect dimensional accuracy.
3. Skilled computer operator required.
4. Set up cost is high
From this we can conclude that Selective laser sintering supported by advance software is powerful tool for manufacturing complex part. The energy density given for product will decide the mechanical properties obtain for given part. The energy density should not cross its optimum level beyond optimal level the mechanical properties are strongly reduced. The accuracy of part obtain from selective laser sintering are affected by wrong building strategies result in the form of shrinkage.
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23-04-2012, 05:03 PM
SELECTIVE LASER SINTERING
SEMINAR ON.pptx (Size: 295.54 KB / Downloads: 54)
Sintering is the process by which bonding between common particle can be obtained.
Selective Laser Sintering a Rapid Prototype
SLS is advance manufacturing process with use of powerful software
SLS process capable of producing complex parts
result to compensate shrinkage
Laser exposure should be along hatching
Part should be oriented along with X axis of chamber
Select beam compensation factor properly
Shrinkage along direction is more than across scanning
Effect of laser sintering parameter
Mechanical properties obtained depends on energy density given.
Laser power and scan speed does affect the properties.
If the energy density constant for different laser power and scan speed the mechanical properties obtained are constant.
If energy density is different mechanical properties are also different.
SLS is advance manufacturing process capable of producing complex parts with accuracy
SLS allows to use different combination of materials.
The mechanical properties obtain depends only on energy density not on laser parameter.
Shrinkage affect the accuracy of parts to compensate use the different building strategies
We should use liquid state sintering with coated grain to bind the particle properly.