A Rapid Prototyping machine by contrast adds material in a layeringprocess, to create the desired form, thus enabling complex forms to be manufactured in one piece that would otherwise be impossible.

The manner in which the layers are laid down, and the materials used to do so vary from method to method.

The whole subject area of RP is sometimes referred to as 3-D printing, but in fact that term refers to a specific form of machine which is the fastest of all RP methods currently available.

Definition:

Rapid Prototyping can be defined as a group of techniques used to quickly fabricate a scale model of a part or assembly using computer aided design (CAD) data.

In rapid prototyping, the machine reads in data from a CAD drawing, and lays down successive layers of liquid or powdered or semi solid material, and in this way builds up the model from a series of cross sections.

These layers, which correspond to the virtual cross section from the CAD model, are glued together or fused (often using a laser) automatically to create the final shape.

Several advantages (as well as limitations) are there with these techniques as compared to more traditional subtractive processes, such as milling or turning.

The primary advantage to this type of “additive” construction is its ability to create almost any geometry (excluding trapped negative volumes).

RP StepsRP Steps• CAD solid model• ‘.STL’ file• Slicing the file• Final build file• Fabrication of part• Post processing

CAD Solid ModelCAD Solid Model

• Solid model or closed surface model required

.STL File.STL File

• Software generates a tessellated object description

• File consists of the X, Y, Z coordinates of the three vertices of each surface triangle, with an index to describe the orientation of the surface normal

• Support generation to hold overhung surfaces during build

solid ascii facet normal 0.000000e+000 -1.018113e-001 -9.948037e-001

outer loop vertex 6.413766e+000 9.540946e+000 4.174942e-001 vertex 6.663766e+000 9.540946e+000 4.174942e-001 vertex 6.413766e+000 9.467294e+000 4.250320e-001

endloop endfacet

facet normal 1.587419e-015 -1.018113e-001 -9.948037e-001 outer loop

vertex 6.413766e+000 9.467294e+000 4.250320e-001 vertex 6.663766e+000 9.540946e+000 4.174942e-001 vertex 6.663766e+000 9.467294e+000 4.250320e-001

endloop endfacet

..

Slicing the FileSlicing the File

• Series of closely spaced horizontal planes are mathematically passed through the .stl file

• Generate a ‘.sli’ file : a series of closely spaced 2D cross-sections of the 3D object

• Typical Z thickness 0.006” (0.150 mm)• Other Parameters chosen

=fn(RP technology)

Part sliced Supports sliced RP technology parameters set

layer thickness, scan speed,... Send file to RP machine

Final Build FileFinal Build FilePart

Supports

Fabrication of PartFabrication of Part

Models built on stereolithography apparatus. Part and supports shown attached to platform.

Post-processingPost-processing• Removal of part from platform• Removal of supports from part• Cleaning of part (wiping, rinsing, ... )• Finishing part (curing, sanding, polishing, … )

Rapid Prototyping Rapid Prototyping TechnologiesTechnologies

• Several technologies Stereolithography (SL)

Laminated Object Manufacturing (LOM)

Selective Laser Sintering (SLS)Fused Deposition Modeling (FDM)Solid Ground Curing (SGC)3D Printing (3DP)Laser Engineered Net Shaping (LENS)

Classification of RP Process ( As per German standard of Production Processes)According to state of Aggregation of their original material

• The main enabling technology behind time compression engineering is 3-D computer-aided design modelling. If different design and manufacturing activities are carried out concurrently it is possible to compress the overall product development time.

• This can also allow engineers to be creative by providing more time for design iterations (Figure 1).

• Concurrent engineering environments have evolved considerably during the last few years to integrate 3-D modelling with computer-aided manufacturing (CAM), computer-aided engineering (CAE), rapid prototyping and manufacturing, and a number of other applications.

• The 3-D model becomes a central component of the whole product or project information base, so that in all design, analysis and manufacturing activities the same data are utilised.

• There is no duplication or possibility for misunderstanding. Product information captured in this way can be copied and re-used; it is readily available for different downstream applications.

• Three-dimensional models and virtual prototypes allow most problems with fitting to become obvious early in the product development process.

• Assemblies can be verified for interference. Structural and thermal analysis can be performed on the same models, employing CAE applications as well as simulating downstream manufacturing processes.

• Ultimately, these very accurate and data-rich models can be taken directly to RP and CAM applications, speeding up process planning and in some cases eliminating the need for drawings.

• Currently, there are a number of RP machines available on the market but only three technologies have a significant commercial impact.

Typical application areas of RP parts

Stereolithography (SLA)Stereolithography (SLA)

Stereolithography (SLA)Stereolithography (SLA)

• 3D Systems, Valencia, CA• patent 1986, beginning of RP• photopolymerization using UV laser• epoxies, acrylates (brittle)• excellent accuracy < 50 mm• relatively slow• $179,000 (103 in3) to $799,000 (203 in3)

The computational steps in producing a Stereolithography file. (a) Three dimensionaldescription of part. (b) The part is divided intoslices (only one in 10 is shown).c) Support material isplanned. (d) A set of tooldirections is determined tomanufacture each slice. Shown is the extruder pathat section A-A from (c), for afused-deposition modelingoperation.

CAD package SLA-250

CAD Models SLA Build

Epoxy Back Fill

Injection Mould

Back Filled Inserts

Plastic Part

Injection Mold Making Process CAD SLA-250

Stereolithography (SLA) is the most widely used rapid prototyping technology. It can produce highly accurate and detailed polymer parts. It was the first rapid prototyping process, introduced in 1988 by 3D Systems, Inc., based on work by inventor Charles Hull.

It uses a low-power, highly focused UV laser to trace out successive cross-sections of a three-dimensional object in a vat of liquid photosensitive polymer.

As the laser traces the layer, the polymer solidifies and the excess areas are left as liquid.

When a layer is completed, a leveling blade is moved across the surface to smooth it before depositing the next layer.

The platform is lowered by a distance equal to the layer thickness (typically 0.003-0.002 in), and a subsequent layer is formed on top of the previously completed layers.

This process of tracing and smoothing is repeated until the build is complete.

Once complete, the part is elevated above the vat and drained. Excess polymer is swabbed or rinsed away from the surfaces. In many cases, a final cure is given by placing the part in a UV oven.

After the final cure, supports are cut off the part and surfaces are polished, sanded or otherwise finished.

How SLA process works:

Stereolithography process produces plastic parts directly from 3D CAD model; by solidifying the surface of a liquid photo polymer layer by layer with the help of a laser beam. When the laser beam hits the liquid, it solidifies the resin. When a layer is fully traced, the elevator is then lowered in the vat. The self-adhesive property of the material causes the layer to stick with each other and in this way a 3d part is formed in multi-layers. SLA process is very accurate and suitable for smooth surface finished parts. These parts are widely used for conceptual designs, Product verification, Pattern making, Form/Fit analysis and light functional testing.

Common Support Structures

Overhangs need support

Stereolithography Mould

Rapid Tooling – Quick Cast

Rapid Tooling - Quick Cast

Stereolithography Parts

1. A Moveable table initially is placed at a position just below the surface of a VAT filled with liquid photopolymer resin.

2. A laser beam is moved over the surface of the liquid photopolymer to trace the geometry of the cross section of the object.

3. This causes the liquid to harden in areas where the laser strikes.4. The laser beam is moved in X-Y directions by a scanner system.5. The resin exposed to laser will get hardened.6. The table is moved down or lowered by a distance equal to the thickness

of the layer.7. By doing so the liquid resin will spread over the hardened layer. To

speed up the process a knife edge or recaoter blade is drawn over the surface to smoothen it.

8. The tracing , lowering and recoating processes are repeated as per the total number of layers and till the object is completely formed.

9. Table containing the object is elevated and excess resin is drained out.10. Excess resin is swabbed manually from the surface.11. Object is given final cure in an post curing apparatus by bathing in

intense light

Procedure

All new SL machines now employ a method to supply the resin that is superior to deep dip process described above.

Because of the high resin viscosity after deep dip and recoating either too little or too much resin is left by the recoating blade, which affects part accuracy.

The new method involves spreading resin on the part as the blade traverses the vat.

Because the blade applies only the required amount of resin, good accuracy is achieved.

This method also provides a smooth surface finish and reduces non productive coating time.

Another important advantage is the elimination of trapped volumes.

A trapped volume is a volume of resin that cannot drain through the base of the part.

The presence of trapped volume in the deep dip process affects part accuracy and may leads to delamination or collision of the blade and part because of a build up of unwanted polymerized resin at the surface of the trapped volume.

Once the part is completed, it is removed from the vat and the excess resin is drained.

Due to resin viscosity this may take several hours.

The green part is then placed in an oven and post cured.

This ensures that no liquid or partially cured resin remains.

A SLA creates a solid or partially solid SL parts with either acrylic or epoxy resins in one of the several build styles.

The three most common being ACES, STARWEAVE and QUICK CAST.

Completely hollow parts are not normally constructed as they are fragile in the green state and deform with handling.

ACESInterior parts are cured wholly by Laser.

The hatch spacing is chosen so that all the solidified resin receives the same cumulative UV exposure and the downward facing surfaces are flat.

Used with epoxy resins that do not shrink much when polymerized.

Other wise the connected lines would cause warping in the prototype.

Most accurate of the three build styles for low distortion resins and employed when making high precision parts although the drawing time is the longest of the three styles.

STARWEAVE

Provides stability to a solid part by hatching interior with a series of solid grids which are off set by half of the hatch spacing every other layer.

The grids are drawn such that the ends are not attached to the part border to reduce the overall distortion.

Also to keep the distortion low the gridlines do not touch one another.

However they are located as close together as possible to improve the green strength of the part.

This build style should be employed with acrylic resins which shrink when polymerized.

It is some times used with epoxy resins in preference to ACES because the draw time is lower.

SLA Video http://www.acucast.com/video.htm

QUICK CASTIs usually adopted when the prototype is to serve as a pattern for investment casting as it produces almost hollow parts.

The outline of the layer is drawn before the interior is hatched.

Either squares or equilateral triangles are used to fill the part and these are offset after a specified vertical build distance to facilitate resin drainage.

The triangles are offset such that the vertices of one section are above the centroids of the triangles in the previous section.

The squares are offset by half of the hatch spacing. Since squares have larger interior angles than the triangles, the meniscus of the resin will be smaller so better drainage is achieved.

Horizontal sections that perform the outer surface of the part are completely solidified and are referred to as skinfull areas.

Three layers are drawn with skinfull areas corresponding to the part surface to avoid the formation of “pinholes”.

When the supports are removed and to prevent the upwards facing horizontal surfaces from sagging.

These skinfulls supports the surface which means that the hatch spacing must be larger. It also means that smaller percentage of the prototype is solid.

Vents and drains must be designed into these areas to allow the excess resins to bleed from the part.

These parts will collapse quickly upon firing so that little stress is developed on the ceramic investment shell, thus preventing it from being damaged.

Because quick cast parts have larger surface area and the resin is hygroscopic, they should be sued as quickly as possible or stored in an area with controlled to prevent later distortion from water absorption.

Several resin have been developed and the material properties of these resins are characterized by Density, Tensile strength, tensile modulus, elongation at break, Flexural Strength, Flexural Modulus, Impact Strength, Hardness, Glass Deflection Temperature And Heat Deflection Temperature

Factors to consider when ordering stereo lithography parts

1.Part size: Large parts can be built in pieces and then glued. This takes extra time and degrade accuracy2.Feature size: If the part has any features that are smaller then the layer thickness, then parts need to be built with thin layers.3.Type of resin: Selection depends on part geometry, complexity, surface finish.4.Support removal: Part supports must be easily removed after the part is built.5.Layer thickness: Thin layers eliminate need for hand finishing. But require more build time. This is costly6.Secondary processes: Silicon rubber or investment casting using 3D’s quick cast building style, will add to cost but will help build parts with good mechanical and chemical strength.

Stratasys, Eden Prarie, MN patent 1992 robotically guided fiber extrusion accuracy ± 0.005” casting and machinable waxes, polyolefin,

ABS water soluble or wax supports

Fused Deposition ModelingFused Deposition ModelingFDMFDM

Highlights

•Standard engineering thermoplastics, such as ABS, can be sued to produce structurally functional models.•Two build materials can be used and lattice work interiors are an option.•Parts up to 600 x 600 x 500 mm (24 x 24 x 20 inches) can be produced.

•Filament of heated thermoplastic polymer is squeezed our like toothpaste from a tube.

•Thermoplastic is cooled rapidly since the platform is maintained at a lower temperature.

•Milling step not included and layer deposition is sometimes is non-uniform as “plane” can become skewed.

•Not as prevalent as SLA and SLS, but gaining ground because of desirable material properties. At present has become a very popular process.

Fused Deposition ModelingFused Deposition Modeling

Fused Deposition Modeling (FDM) was developed by Stratasys in Eden Prairie, Minnesota. In this process, a plastic or wax material is extruded through a nozzle that traces the part's cross sectional geometry layer by layer. The build material is usually supplied in filament form, but some setups utilize plastic pellets fed from a hopper instead. The nozzle contains resistive heaters that keep the plastic at a temperature just above its melting point so that it flows easily through the nozzle and forms the layer. The plastic hardens immediately after flowing from the nozzle and bonds to the layer below. Once a layer is built, the platform lowers, and the extrusion nozzle deposits another layer.

The layer thickness and vertical dimensional accuracy is determined by the extruder die diameter, which ranges from 0.013 to 0.005 inches. In the X-Y plane, 0.001 inch resolution is achievable.

A range of materials are available including ABS, polyamide, polycarbonate, polyethylene, polypropylene, and investment casting wax.

The FDM rapid prototyping process is akin to using a hot glue gun to make parts. An FDM machine consists of the following parts a build platform, filament feed devices, heated extrusion nozzles and a nozzle control apparatus. The whole system is contained within a heated environment to reduce the amount of energy needed to melt the filament at the nozzle. The FDM process feeds filaments of build material and support material to heated nozzles. These nozzles are used to lay down molten filaments of build and support materials in the desired cross sectional geometries. Once the first cross section is completed the build platform is lowered one layer thickness and the next cross section is printed. This process is continued until the part is completed. Once complete, the part can be taken out and any support structures can be removed.

The main advantage to using FDM is the very durable parts that can be made using waxes and various engineering plastics.

The drawback to using the FDM method is that the parts generally take much longer to build and the layering is clearly visible because of the extrusion type process.

FDM is the second most widely used rapid prototyping technology, after stereolithography. A plastic filament, approximately 1/16 inch in diameter, is unwound from a coil (A) and supplies material to an extrusion nozzle (B). Some configurations of the machinery have used plastic pellets fed from a hopper rather than a filament. The nozzle is heated to melt the plastic and has a mechanism which allows the flow of the melted plastic to be controlled. The nozzle is mounted to a mechanical stage (C) which can be moved in horizontal and vertical directions. As the nozzle is moved over the table (D) in the required geometry, it deposits a thin bead of extruded plastic to form each layer. The plastic hardens immediately after being squirted from the nozzle and bonds to the layer below. The entire system is contained within an oven chamber which is held at a temperature just below the melting point of the plastic. Thus, only a small amount of additional thermal energy needs to be supplied by the extrusion nozzle to cause the plastic to melt. This provides much better control of the process.

FDM begins with a software process, developed by Stratasys, which processes an STL file (stereolithography file format) in minutes, mathematically slicing and orienting the model for the build process. If required, support structures are automatically generated. The machine dispenses two materials – one for the model and one for a disposable support structure.

The thermoplastics are liquefied and deposited by an extrusion head, which follows a tool-path defined by the CAD file.

The materials are deposited in layers as fine as 0.04 mm (0.0016") thick, and the part is built from the bottom up – one layer at a time. FDM works on an "additive" principle by laying down material in layers.

A plastic filament or metal wire is unwound from a coil and supplies material to an extrusion nozzle which can turn the flow on and off.

The nozzle is heated to melt the material and can be moved in both horizontal and vertical directions by a numerically controlled mechanism, directly controlled by a computer-aided manufacturing (CAM) software package.

The model or part is produced by extruding small beads of thermoplastic material to form layers as the material hardens immediately after extrusion from the nozzle. Stepper motors or servo motors are typically employed to move the extrusion head.Several materials are available with different trade-offs between strength and temperature properties. As well as acrylonitrile butadiene styrene (ABS) polymer, polycarbonates, polycaprolactone, polyphenylsulfones and waxes. In addition, these materials are available in several standard colors. A "water-soluble" material can be used for making temporary supports while manufacturing is in progress, this soluble support material is quickly dissolved with specialized mechanical agitation equipment utilizing a precisely heated sodium hydroxide solution.The term fused deposition modeling and its abbreviation to FDM are trademarked by Stratasys Inc. The exactly equivalent term, fused filament fabrication (FFF), was coined by the members of the RepRap project to give a phrase that would be legally unconstrained in its use. It is a new model.

Support structures must be designed and fabricated for any overhanging geometries and are later removed in secondary operations. Several materials are available for the process including a nylon-like polymer and both machinable and investment casting waxes. The introduction of ABS plastic material led to much greater commercial acceptance of the method. It provided better layer to layer bonding than previous materials and consequently much more robust fabricated objects. Also a companion support material was introduced at that time which was easily removable by simply breaking it away from the object. Water-soluble support materials have also become available which can be removed simply by washing them away. The recent introduction of polycarbonate and poly(phenyl)sulfone modeling materials have further extended the capabilities of the method in terms of strength and temperature range. Several other polymer systems as well as ceramic and metallic materials are under development.

The method is office-friendly and quiet. FDM is fairly fast for small parts on the order of a few cubic inches, or those that have tall, thin form-factors. However, it can be very slow for parts with wide cross sections.

The finish of parts produced with the method have been greatly improved over the years, but aren't quite on a par with stereolithography. The closest competitor to the FDM process is probably three dimensional printing.

However, FDM offers greater strength and a wider range of materials than at least the implementations of 3DP from Z Corp. which are most closely comparable.

FDM material

FDM PARTS

• Helisys, Torrance, CA (out of business in 2000, serviced by a successor organization, Cubic Technologies)

• patent 1988• cross-sectional cutouts fused together• paper, plastic (new)• accuracy ±0.005”

Laminated Object ManufacturingLaminated Object Manufacturing(LOM)(LOM)

Highlights of Laminated Object Manufacturing

• Layers of glue-backed paper form the model.• Low cost: Raw material is readily available.• Large parts: Because there is no chemical reaction involved, parts

can be made quite large. • Accuracy in z is less than that for SLA and SLS®. No milling step. • Outside of model, cross-hatching removes material • Models should be sealed in order to prohibit moisture. • Before sealing, models have a wood-like texture. • Not as prevalent as SLA and SLS®.

Laminated Object ManufacturingLaminated Object ManufacturingLOMLOM

• The first commercial Laminated Object Manufacturing (LOM) system was shipped in 1991.

• LOM was developed by Helisys of Torrance, CA. • The main components of the system are a feed mechanism that

advances a sheet over a build platform, a heated roller to apply pressure to bond the sheet to the layer below, and a laser to cut the outline of the part in each sheet layer.

• Parts are produced by stacking, bonding, and cutting layers of adhesive-coated sheet material on top of the previous one.

• A laser cuts the outline of the part into each layer. • After each cut is completed, the platform lowers by a depth equal to the

sheet thickness (typically 0.002-0.020 in), and another sheet is advanced on top of the previously deposited layers.

• The platform then rises slightly and the heated roller applies pressure to bond the new layer.

• The laser cuts the outline and the process is repeated until the part is completed.

• After a layer is cut, the extra material remains in place to support the part during build.

Laminated Object Manufacturing (LOM) - (Helisys)

The figure below shows the general arrangement of a Laminated Object Manufacturing (LOM™, registered trademark by Helisys of Torrance, California, USA) cell:

• Material is usually a paper sheet laminated with adhesive on one side, but plastic and metal laminates are appearing.

• Layer fabrication starts with sheet being adhered to substrate with the heated roller.

• The laser then traces out the outline of the layer. • Non-part areas are cross-hatched to facilitate removal of waste material. • Once the laser cutting is complete, the platform moves down and out of the way so that fresh sheet material can be rolled into position.

• Once new material is in position, the platform moves back up to one layer below its previous position.

• The process can now be repeated. The excess material supports overhangs and other weak areas of the part during fabrication. The cross-hatching facilitates removal of the excess material. Once completed, the part has a wood-like texture composed of the paper layers. Moisture can be absorbed by the paper, which tends to expand and compromise the dimensional stability. Therefore, most models are sealed with a paint or lacquer to block moisture ingress.

The LOM™ developer continues to improve the process with sheets of stronger materials such as plastic and metal. Now available are sheets of powder metal (bound with adhesive) that can produce a "green" part. The part is then heat treated to sinter the material to its final state.

Laminated Object Manufacturing

Working :Special type of paper with an adhesive backing is laid down on the machine’s table.

A heated roller passes over the paper and the adhesive bonds it to the surface beneath.

The laser head then traces the outline of the required layer. Waste areas are cross-hatched, and then the table drops by the thickness of the paper.

Another layer is laid down, rolled and cut and so on until the model is complete.

The cross-hatched areas can be easily broken off afterwards, and the surface smoothed down.

The laser cutting process produces smoke, and the models are notespecially accurate.

Profiles of object cross sections are cut from paper using a CO2 laser as shown in Fig. 3. The paper is unwound from a feed roll (A) onto the stack and bonded to the previous layer using a heated roller (B). The roller melts a plastic coating on the bottom side of the paper to create the bond. The profiles are traced by an optics system that is mounted to an X-Y stage (C). The process generates considerable smoke. Either a chimney or a charcoal filtration system is required (E) and the build chamber must be sealed. After cutting the geometric features of a layer is completed, the excess paper is cut away to separate the layer from the web. The extra paper of the web is wound on a take-up roll (D).The method is self-supporting for overhangs and undercuts. Areas of cross sections which are to be removed in the final object are heavily cross-hatched with the laser to facilitate removal. It can be time consuming to remove extra material for some geometries.

In general, the finish, accuracy and stability of paper objects are not as good as for materials used with other RP methods.However, material costs are very low, and objects have the look and feel of wood and can be worked and finished in the same manner. This has fostered applications such as patterns for sand castings. While there are limitations on materials, work has been done with plastics, composites, ceramics and metals. Some of these materials are available on a limited commercial basis. Variations on this method have been developed by many companies and research groups.For example, Kira's Paper Lamination Technology (PLT) uses a knife to cut each layer instead of a laser and applies adhesive to bond layers using the xerographic process. Solido 3D Ltd. also uses a knife, but instead bonds layers of plastic film with a solvent. There are also variations which seek to increase speed and/or material versatility by cutting the edges of thick layers diagonally to avoid stair stepping.

While the technology has been successful in certain applications, it hasn't fared well as a general solution. Several producers have come and gone.

The principal US commercial provider of laser-based LOM systems, Helisys, ceased operation in 2000.

However the company's products are still sold and serviced by a successor organization, Cubic Technologies.

Solido 3D closed its doors in January, 2011, and Kira has had limited sales success. Mcor Technologies is the most recent entrant.

It emphasizes the low cost of materials in its marketing.

Material: paper Envelope: 800 x 550 x 500 mm (largest available at present.)

SpeedRelatively fast, especially considering possible size of model.

Surface finish and accuracyBecause it is in effect a built up piece of wood, it is accurate to the thickness of the layers, and stepping is visible.

Practicality and durability of modelThe models are strong and easily worked on afterwards. They can easilybe painted, and are durable.

UsesSuitable for use as patterns for production of castings.

CostsMaterial costs for the paper that builds up the layers is very low.Machines cost £80,000 to £160,000.

Selective Laser SinteringSelective Laser Sintering

• DTM, Austin, TX, now 3D systems• patent 1989, Carl Deckard’s master’s thesis• fusing polymeric powders with CO2 laser• accuracy 160 mm• no supports• polycarbonate, nylon, wax, glass-filled nylon,

powder coated metals or ceramics• can be end-use parts

Selective Laser Sintering (SLS)Selective Laser Sintering (SLS)

SLS Video http://www.acucast.com/multimedia

Solid Ground Curing

http://home.att.net/~castleisland/sgc.htm

Solid Ground Curing (SGC)

• Devleoped by Cubital Ltd. of Israel• High capital and operational cost• Large heavy equipment• Good dimensional accuaracy

SGC (from Efunda)

http://www.efunda.com/processes/rapid_prototyping/sgc.cfm

Instead of using a laser to expose and harden photopolymer element by element within a layer as is done in stereolithography, SGC uses a mask to expose the entire object layer at once with a burst of intense UV light. The method of generating the masks is based on electrophotography (xerography). This is a two cycle process having a mask generation cycle and a layer fabrication cycle. It takes about 2 minutes to complete all operations to make a layer:

1. First the object under construction (A) is given a coating of photopolymer resin as it passes the resin applicator station (B) on its way to the exposure cell (C).

2. A mask is generated by electrostatically transferring toner in the required object cross sectional image pattern to a glass plate (D) An electron gun writes a charge pattern on the plate which is developed with toner. The glass plate then moves to the exposure cell where it is positioned above the object under construction.

3. A shutter is opened allowing the exposure light to pass through the mask and quickly cure the photopolymer layer in the required pattern. Because the light is so intense the layer is fully cured and no secondary curing operation is necessary as is the case with stereolithography.

http://home.att.net/~castleisland/sgc.htm

4. The mask and object under fabrication then part company. The glass mask is cleaned of toner and discharged. A new mask is electrophotographically generated on the plate to repeat the cycle.

5. The object moves to the aerodynamic wiper (E) where any resin that wasn't hardened is vacuumed off and discarded.

6. It then passes under a wax applicator (F) where the voids created by the removal of the unhardened resin are filled with wax. The wax is hardened by moving the object to the cooling station (G) where a cold plate is pressed against it.

7. The final step involves running the object under the milling head (H). Both the wax and photopolymer are milled to a uniform thickness and the cycle is repeated until the object is completely formed within a wax matrix.

Secondary operations are required to remove the wax. It can either be melted away or dissolved using a dish-washing-like machine. The object is then sanded or otherwise finished as is done in stereolithography. The wax matrix makes it unnecessary to generate extra support structures for overhangs or undercuts. This, and the large volume capacity of the system, also makes it easy to nest many different objects within the build volume for high throughput.

http://home.att.net/~castleisland/sgc.htm

3D Printing3D Printing

Inkjets

http://home.att.net/~castleisland/sgc.htm

• ZCorpSanders Prototype Inc., NH• ink jet technology• dual heads deposit part material

(thermoplastic) and support material (wax)• build layers as thin as .0005”• very fast and cheap process

3D Printing3D Printing

Laser Engineered Net Shaping TM

http://home.att.net/~castleisland/sgc.htm

Laser Engineered Net Shaping TM

• In development (Sandia Labs, Optomec)• Fully Dense Metal parts with good

metallurgical properties• Laser melts metal powder• Powder delivered coaxially with laser• Inert gas protects weld pool• Near net shape with some finish machining

http://home.att.net/~castleisland/sgc.htm

Laser

Powder delivery tube

A process that can create metal tools directly from a CAD file. This process is capable of using multiple materials, stainless steel, HSS, tungsten carbide as well as others. A laser beam melts the top layer of the part in areas where material is to be added until the part is complete. Unlike sintering, LENS does produce a solid metal part since the metal as melted.

The Laser engineering net shaping (LENS) process involves feeding powder through a nozzle on to the part bed while simultaneously fusing it with a laser (Fig. 6) .

The powder nozzle may be on one side of the bed or coaxial with the laser beam.

If it is to a side, a constant orientation to the part creation direction must be maintained to prevent solidied sections from shadowing areas to be built.

When the powder feeder is coaxial, there may be inaccuracies in the geometry of the part and the layer thickness if the beam and the powder feeder move out of alignment.

Because the stream of powder is heated by the laser, fusion to the previous layer is facilitated.

Other systems have also been developed based on the same principle, in particular direct metal deposition (DMD) and AeroMet laser additive manufacturing .

LENS PROCESS

This process is in the early stages of development and is not widely available yet.

The process uses metal powder, and works by feeding the powder to a nozzle where it is melted by a laser.

The process is similar to building layer upon layer of weld, only much more accurate.

The metal powders can be varied and even mixed in ways that are not possible using conventional processes, and as well as being used for making prototypes, the process can also be used to repair parts.

Material: metal powders, for example: aluminium, stainless steel, copper, titanium

SpeedReasonably fast.

Surface finish and accuracyVery good finish and accuracy. Objects may need some machining butdo not require infiltration.

Practicality and durability of modelVery good.

UsesProduction of metal prototypes that are strong and accurate. Can beused for tooling up.

Light Engineered Net Shaping Parts

http://www.xpress3d.com/