Rapid Prototyping Notes

Rapid prototyping is the name given to a host of related technologies that are used to fabricate  physical objects directly from CAD data sources. These methods are unique in that they add and bond materials in layers to form objects. Such systems are also known  by the names additive fabrication three dimensional printing solid freeform fabrication and layered manufacturing. They offer advantages in many applications compared to classical subtractive fabrication methods such as milling or turning! "bjects can be formed with any geometric complexity  or intricacy without the need for elaborate machine setup or final assembly# "bjects can be made from multiple materials, or as composites or materials can even be varied in a controlled fashion at any location in an object# Additive fabrication systems reduce the construction of comple$ objects to a manageable straightforward, and relatively fast process. These properties have resulted in their wide use as a way to reduce time to market in manufacturing. Today%s Today%s systems are heavily used by engineers to better understand and communicate their product designs as well as to make rapid tooling to manufacture those products. Surgeons architects artists and individuals from many other disciplines also routinely use the technology. The names of specific processes themselves are also often used as synonyms for the entire field of rapid prototyping. Among Among these are stereolithography &S'A for stereolithography apparatus( selective laser sintering &S'S( fused deposition modeling &)D*( laminated object manufacturing &'"*( inkjet+based systems and three dimensional printing &,D-(. ach of these technologies + and the many other rapid prototyping processes + has its singular strengths and weaknesses.

Reverse engineering (RE) used to be a nefarious term.  /t formerly meant making a copy of a product or the outright stealing of ideas from competitors. /n current usage however 0 has taken on a more positive character and now simply refers to the process of creating a descriptive data set from a physical object. 0 methods and technologies can still be used for negative purposes like those mentioned but today there are numerous important legitimate applications for 0 as well. This has come about over the last fifteen or more years due to the intense parallel development of many different types of three dimensional digiti1ing devices and the

 powerful reverse engineering software that allows the data they produce to be manipulated into a useful form. There are two parts to any reverse engineering application:  scanning and data manipulation. Scanning also called digiti1ing is the process of gathering the requisite data from an object. *any different technologies are used to collect three dimensional data. They range from mechanical and very slow to radiation+based and highly+ automated. ach technology has its advantages and disadvantages and their applications and specifications overlap. 2hat eventually comes out of each of these data collection devices however is a description of the physical object in three+ dimensional space called a point cloud.

-oint cloud data typically define numerous points on the surface of the object in terms of x,y, of x,y, and  and z   z  coordinates.  coordinates. At each x,y, each x,y,z  z  coordinate  coordinate in the data where there is a point there is a surface coordinate of the original object. 3owever some scanners such as those based on 4+rays can see inside an object. /n that case the point cloud also defines interior locations of the object and may also describe its density. Typical RE pplications Creating data to refurbish or manufacture a part for which there is no CAD data or for which the data has become obsolete or lost. /nspection and5or 6uality Control + Comparing a fabricated part to its CAD description or to a standard item. Creating ,D data from a model or sculpture for animation in games and movies.

Creating ,D data from an individual model or sculpture for creating scaling or reproducing artwork.

7enerating data to create dental or surgical  prosthetics tissue+ engineered body parts or for surgical planning.

Documentation and5or measurement measurement of cultural objects or artifacts in archaeology archaeology paleontology and other scientific fields.

Documentation and reproduction of crime scenes.

Architectural Architectural and construction documentation )itting clothing or footwear and measurement. measurement. to individuals and determining the anthropometry of a  population

There is usually far too much data in the point cloud collected from the scanner or digiti1er and some of it may ma y be unwanted noise. 2ithout further processing the data isn8t in a form that can be used by downstream applications such as CAD5CA* software or in rapid prototyping. 0everse engineering software is used to edit the  point cloud data establish the interconnectedness of the points in the cloud and translate it into useful formats such as surface models or ST' files. /t also allows several different scans of an object to be melded together so that the data describing the object can be defined completely from all sides and directions. 9sually the shortest part of any 0 task is scanning or data collection. 2hile there are e$ceptions scanning might only require a few seconds or a few minutes. "n the other hand manipulating the data can be quite time+consuming and labor+intensive. /t

 powerful reverse engineering software that allows the data they produce to be manipulated into a useful form. There are two parts to any reverse engineering application:  scanning and data manipulation. Scanning also called digiti1ing is the process of gathering the requisite data from an object. *any different technologies are used to collect three dimensional data. They range from mechanical and very slow to radiation+based and highly+ automated. ach technology has its advantages and disadvantages and their applications and specifications overlap. 2hat eventually comes out of each of these data collection devices however is a description of the physical object in three+ dimensional space called a point cloud.

-oint cloud data typically define numerous points on the surface of the object in terms of x,y, of x,y, and  and z   z  coordinates.  coordinates. At each x,y, each x,y,z  z  coordinate  coordinate in the data where there is a point there is a surface coordinate of the original object. 3owever some scanners such as those based on 4+rays can see inside an object. /n that case the point cloud also defines interior locations of the object and may also describe its density. Typical RE pplications Creating data to refurbish or manufacture a part for which there is no CAD data or for which the data has become obsolete or lost. /nspection and5or 6uality Control + Comparing a fabricated part to its CAD description or to a standard item. Creating ,D data from a model or sculpture for animation in games and movies.

Creating ,D data from an individual model or sculpture for creating scaling or reproducing artwork.

7enerating data to create dental or surgical  prosthetics tissue+ engineered body parts or for surgical planning.

Documentation and5or measurement measurement of cultural objects or artifacts in archaeology archaeology paleontology and other scientific fields.

Documentation and reproduction of crime scenes.

Architectural Architectural and construction documentation )itting clothing or footwear and measurement. measurement. to individuals and determining the anthropometry of a  population

There is usually far too much data in the point cloud collected from the scanner or digiti1er and some of it may ma y be unwanted noise. 2ithout further processing the data isn8t in a form that can be used by downstream applications such as CAD5CA* software or in rapid prototyping. 0everse engineering software is used to edit the  point cloud data establish the interconnectedness of the points in the cloud and translate it into useful formats such as surface models or ST' files. /t also allows several different scans of an object to be melded together so that the data describing the object can be defined completely from all sides and directions. 9sually the shortest part of any 0 task is scanning or data collection. 2hile there are e$ceptions scanning might only require a few seconds or a few minutes. "n the other hand manipulating the data can be quite time+consuming and labor+intensive. /t

may even require days to complete this part of the job. The situation is analogous to scanning two+dimensional printed or photographic materials. /t doesn8t usually take very long to scan a picture or a diagram + but getting that picture into a presentable form can be quite a lot of work indeed.

!ot all applications are created e"ual.  ngineering is more e$acting than creating a ,D model for a movie for e$ample. /f you need to ascertain dimensions precisely more care and diligence must be used and measurement error quantified. :ut accuracy and fidelity requirements are not limited to engineering. *any artistic and architectural applications also have substantial accuracy requirements. After all would the data set that defines *ichaelangelo8s David be worth anything if it was inaccurate; /n some respects aesthetic applications can be more challenging than engineering. 2hile there may not be as great a need for absolute dimensional  precision requirements for the reproduction of surface qualities or acquiring data from difficult subjects such as hair represent a considerable challenge.

#o$ens of companies ma%e three dimensional digiti$ers and scanners, and it8s a frequently changing cast of characters. /nstruments are available to digiti1e objects from microscopic in si1e to entire construction projects or large portions of oil refineries. Data acquisition speeds range from a few points per minute using manual technologies to more than a million points per second. -rices range from a couple of thousand dollars to hundreds of thousands of dollars. To a great e$tent this situation reflects the wide range of applications that are presented to this class of devices. :ut the very e$uberance of engineering approaches may also be indicative of an immature market and technology base. 0apid prototyping is another field that e$hibits a similarly wide range of technologies and perhaps it is not a coincidence that reverse engineering may be considered reverse+rapid prototyping.

#igiti$ers have numerous specifications, but there are &ust three %ey ones: volume accuracy and a nd speed. evertheless an increasing number of applications are taking advantage of additive fabrication and now incorporate parts that are directly made by 0- processes. Today typically these requirements are for low+volume items with comple$ geometries used in high value added applications such as medicine or aerospace. As materials and technologies have improved and as the capabilities have become more widely understood direct manufacturing has  become a fast growing area in 0-. To address a wider range of applications sooner 0- is also often used as the starting  point for making conventional fabrication processes faster cheaper and better. 0apid  prototyping is used in two ways to accomplish this! *olds may be directly fabricated  by an 0- system or 0-+generated parts can be used as patterns for fabricating a mold through so+called indirect  or secondary processes . /ndirect or econdary -rocesses Typically a part made by the 0- system is used as a pattern or model in these

 processes. 2hile more than two do1en of them are in various stages of development  just a few are common and commercially important today. #irect -rocesses Speciali1ed rapid prototyping processes have been developed to meet specific application and material requirements for molding and casting. These may be forms of   basic 0- processes such as stereolithography or selective laser sintering or may be unique 0- methods developed for a specific application. As in the case of indirect or secondary processes there are a large number of technologies being e$plored but only a few are commercially important today.

The principal ways of using R- to generate in&ection molds  today are  presented below in appro$imately increasing order of cost and part quantity. /f only a few parts are needed 0T< silicone rubber tooling is often the best choice. :eyond about ?@ parts or to study the operation of a production mold or for other reasons it will probably be advantageous to choose one of the other 0- injection mold fabrication methods. 0hy 1se Rapid -rototyping to a%e /n&ection olds2 Skilled craftspeople are in short supply product comple$ity is increasing and product cycles are growing ever shorter. This means that an ever larger number of more  precise tools have to be created by a declining population of toolmakers. There is therefore a great deal to gain from a process which provides both great time and labor savings and addresses these limitations head+on. /n addition 0- offers the tantali1ing  prospect for improvement in mold performance beyond anything that can be accomplished with subtractive technologies. The ability to fabricate comple$ conformal cooling channels to provide better thermal performance or to use multiple or gradient materials to optimi1e each portion of a mold for performance and cost may ultimately lead to a revolution across the entire field. 0hat are the 'imitations2 0apid prototyping injection mold fabrication methods should be considered for  projects in which the reduction of time to market is important for prototype and short to medium volume production runs and for parts which may be very hard to machine  because of their geometry. The general limitations of 0- methods compared to C>C today are! • • • •

they produce somewhat less accurate and less durable tools they may have part si1e and geometry limitations they don%t necessarily produce identical parts to hard tooling and 0-+generated tools may not easily be modified or corrected using typical toolmaking techniques.

These limitations vary both as function of the specific 0- technology used and for each individual case. electing a -rocess. Selection of the optimum 0-+based process for each case is comple$. Among the

factors to consider are the final application production volume part si1e accuracy and material requirements.

anual -art 3abrication ethods RT4 ilicone Rubber Tooling. This is a popular method of making small quantities of polymer parts. Any rapid  prototyping+generated part can be used as a pattern to make silicone rubber tooling. These tools can be used to mold small to medium quantities of parts in a large variety of urethane epo$y or other polymers. /f quantities greater than about @ to ?@ are needed an injection mold may be the way to go. There are many suppliers for this  process as well as the very similar aluminum+filled epo$y sprayed metal and kirksite tooling methods.

/n&ection old 3abrication ethods  Indirect or Secondary Processes that Utilize RP-generated Patterns. luminum*filled Epoxy Tooling. Aluminum+filled epo$y tooling is a good choice for short prototype or production runs for applications that require a final engineering thermoplastic. These tools are fabricated much like 0T< silicone rubber tooling. Aluminum+filled epo$y tools work  best for relatively simple shapes with tool life adequate for anywhere from ?@ to @@@ parts depending on requirements. &*any suppliers.( pray etal Tooling. These tools and the methods for making them are very similar to aluminum+filled epo$y tooling. Tool life is about the same as well but the method can accommodate larger parts. &*any suppliers.( 5ir%site Tooling. Similar to but less accurate than aluminum+filled epo$y or spray metal but a good choice for more comple$ parts in quantities up to about @@@. &*any suppliers.(

 Direct Fabrication of Injection Molds oft Tooling 3rom etals The "S 7mb3  Direct Metal Laser Sintering M  &D*'S( S'S process can use a  bron1e alloy which offers a step up in soft tooling over epo$y+based stereolithography

methods. As many as several thousand relatively simple parts have been produced from such D*'S molds. 6ard Tooling 3rom etals ,D Systems% selective laser sintering process for metals uses polymer+coated steel  powders. The resultant green part is burned out sintered and infiltrated with bron1e in secondary furnace operations to produce a fully+dense mold with about B@ steel content. "S%s D*'S process for bron1e alloys and steel powders doesn%t require secondary sintering and burnout cycles in a furnace because the parts produced are already at ? density. These steel+based processes offer the greatest benefit for small comple$ geometry parts that would be difficult to machine.

A process from -ro*etal a division of $"ne Company competes with these methods. /t%s based on Three Dimensional -rinting technology developed at */T. -rocesses based on laser powder forming technologies are in early commerciali1ation stages. "ptomec Design Corp. -"*+7roup and other companies offer methods that create fully+dense hard tools in multiple materials and with conformal cooling.

3unctional -arts and Tools 3rom Rapid -rototyping

Rapid anufacturing7  8rief /ntroduction -arts made by rapid prototyping systems may be used directly in many final applications today. This was not true just a short a while ago and reflects great strides in materials and systems that have been spurred by insistent market forces. 0apid  prototyping+generated parts may well offer a direct solution to application problems having material requirements ranging from plastics or ceramics to steel or titanium. 0- is making its greatest headway in direct manufacturing applications that take advantage of the unique benefits of additive fabrication. /t has long been accepted that 0- is a solution for fabricating geometrically+comple$ low+volume or customi1ed  parts. 0- is now also being increasingly recogni1ed as a means to produce materials in forms and combinations not otherwise possible. 2hile still mostly in the development stage the range of potential applications is very broad. /t e$tends from the microscopic scale of nano+devices and integrated circuits to the construction of entire buildings boat hulls and the like. /n some cases 0-%s nominal liabilities are  being turned into advantages. )or e$ample the capability of some 0- technologies to create porous parts is being found useful in fabricating comple$ filters gas storage devices and similar products. Descriptions of many of the 0- technologies available for direct manufacturing are provided in the sections under in&ection molds. Also see the RTR Technology +omparison tables.

See the rapid manufacturing section for an e$tensive e$ploration of the enormous potential of this application of additive fabrication.

#irect fabrication of plastic parts -lastic parts are most often directly fabricated for end use using selective laser sintering &S'S( fused deposition modeling &)D*( or stereolithography. "ther technologies are also used but these are the main ones that are of commercial importance at present. The choice of a technology is most greatly influenced by the end+use material requirements.

The development of photopolymers for use in stereolithography and similar light+  based technologies has led to materials that e$hibit a wide range of properties. *aterials are available that mimic the mechanical properties of polypropylene and other plastics e$hibit fle$ibility for snap+fits and have optical properties such as high transparency. fforts are ongoing to develop speciali1ed photopolymers to widen their  applications. *aterials with properties such as low shrinkage rubber+like fle$ibility and thermal conductivity or to address speciali1ed applications such as the construction of scaffolds for tissue engineering are in development. 2hile today%s materials can solve many problems and the future looks very promising  photopolymers are analogs of engineering plastics. They may not possess all of the  properties required for a particular application. :oth selective laser sintering and fused deposition modeling can produce parts in final engineering polymers. They may offer solutions when photopolymer+based technologies cannot. S'S can be used to fabricate parts in several types of engineering  plastics including glass+filled nylon. )D* can fabricate parts in A:S  polyphenylsulfone polycarbonate polyester and a few other materials. These technologies may offer parts with additional strength or other properties not currently available from photopolymers. "ne thing to note is that the properties will not be the same as a part fabricated in an injection molding process of the same material however.

#irect fabrication of metal parts *etal parts are most often directly fabricated with selective laser sintering or laser  powder forming processes. 3ere again other technologies can be used but these are the most commercially important ones at the moment. S'S can be used to fabricate steel stainless steel and bron1e parts. -orosity is eliminated by secondary metal infiltration. -arts usually need final machining and their properties will not be quite the same as parts formed entirely of the intrinsic material. 'aser powder forming  processes can produce parts in steels titanium and other metals at full density. 3owever this desirable characteristic may have to be traded+off against somewhat higher finish machining requirements compared to S'S. Direct fabrication of metal  parts is finding its greatest application in high value+added applications such as aerospace and medicine.

Rapid Tooling 2hile there is much progress in direct part fabrication even the fastest 0- systems are still far too slow and are limited in other ways! They simply can%t produce parts in a wide enough range of materials at a fast enough rate to match the enormous spectrum of requirements of industry. Conventional processes such as molding and cast ing are still the only means available to do that. 3owever 0- is often t he starting point for making these manufacturing processes faster cheaper and better. /ndeed the fabrication of tooling is perhaps at present the most important application of direct manufacturing. 0apid prototyping is used in two ways to make tooling! *olds may be directly fabricated by an 0- system or 0-+generated parts can be used as patterns for fabricating a mold through so+called indirect  or secondary processes. #irect 3abrication -rocesses

Speciali1ed rapid prototyping processes have been developed to meet specific application and material requirements for molding and casting. These may be forms of basic 0 processes such as stereolithography or selective laser sinter ing or may be unique 0methods developed for a specific application. There ar e a large number of technologies  being e$plored but only a few are commercially important at present.

bout R-*generated -atterns

/ndirect or econdary -rocesses Although the properties of 0- materials improve 0-+generated patterns must and e$pand continuously a limitless array of  undergo finishing operations applications means that there will always be a  before they can be used in any need to transfer parts fabricated in a material used indirect or secondary process. in an 0- process into yet another material. /n  >o rapid prototyping technology addition it%s usually necessary to use very today delivers surface finishes specific materials to make most tools. that are adequate for accurate Consequently numerous material transfer  applications such as injection technologies have been developed. Typically a mold tooling. 0emoval of the  part made by the 0- system is used as a pattern or  stair+stepping inherent in the model in these processes. As in the case of the  process and other surface direct fabrication processes discussed above artifacts is necessary before there are many secondary processes in various  parts will eject from a mold and stages of development. 3owever of the more may lead to additional errors than two do1en such methods available just a few  being introduced. The accuracy are common and commercially important today. of most secondary processes is ultimately limited by the +hoosing /sn9t Easy  precision of the pattern after The net result is that there are a bewildering finishing. 0apid prototyping number of routes to get to a final functional part  patterns are best for applications or tool starting from a CAD definition. The with just a few critical choice depends on! dimensions! /f many tight tolerances must be held it%s generally still faster and cheaper  to use C>C.

• • • •

the application volume of parts to be produced final material and accuracy requirements rapid prototyping process used

and numerous other factors. Choosing isn%t easy since most technologies are immature have significant limitations and there are usually several competing alternatives. The tables accompanying this section provide basic selection information.

-lastic or -olymer -arts Silicone tools can typically be used to mold several parts before it becomes necessary to replace them. The number depends on accuracy and finish requirements and the specific geometry of the item produced. /t may be possible to make many do1ens of simple or non+critical parts from a single silicone rubber mold but ten to twenty is typical if the parts are more comple$. 2ear of the mold occurs due to the e$othermic and reactive nature of the polymers and because of the necessity to mechanically deform the mold to remove the part. /t may often be necessary to replace the 0-+ generated pattern as well depending on the number of molds to be made and similar accuracy and geometric considerations. The process is carried out by placing the 0-+generated pattern in a frame usually made of wood. The pattern itself usually must undergo secondary operations to bring it to the desired state of accuracy and finish before it can be used. See the section on 0-+generated patterns. Silicone rubber room temperature vulcani1ing &0TC technology and part using 0methods. The most economic and appropriate process must be selected for each  portion of a tool and not necessarily for the tool as a whole. ther Technologies This is not an all+inclusive listing. *any other technologies are being e$plored in corporate university and government laboratories. /ndeed several companies  particularly in urope are developing proprietary rapid tooling methods for their e$clusive internal use in the hopes of obtaining a competitive advantage. There are also a number of methods which have not succeeded commercially over the course of several years but are still being pursued on an e$perimental or limited commercial  basis. The great ma&ority of molds today are still made using subtractive fabrication. *arket acceptance for 0-+based methods will continue to increase as business demands faster time to market more individuali1ed and shorter run products and e$isting technical limitations are overcome.

etal +astings /nvestment +astings  >umerous 0- technologies are appropriate for use as investment casting patterns. These material displacement casting methods are among the first industrial processes ever developed and are thousands of years old. The castings produced can be e$quisitely detailed and intricate. :eeswa$ was the first material used for patterns but the process is so adaptable that bees themselves have been used as patterns to produce stunningly detailed gold jewelry. *ore environmentally and socially conscious  jewelry is a significant application of rapid prototyping+generated casting patterns even today. There are numerous applications in industry where parts are produced in a variety of metals with castings weighing up to several hundred pounds. These processes typically involve thickly coating or investing a pattern which is made of a material that melts or burns out easily with a material such as ceramic which doesn%t. The pattern may be e$tended to provide a gate into which metal in a hot liquid state is poured. -assageways are also provided to allow melted or burned  pattern material and air to escape. The invested pattern is then fired in a furnace to  burn out or melt the pattern and fuse the ceramic into a strong hollow mold. *olten metal is then poured into the ceramic mold. After the metal cools and hardens the mold is broken away to reveal the final object. $tra gate material is cut off and usually the part will require substantial finish machining and clean+up.

/ndirect or econdary -rocesses that 1tili$e R-*generated -atterns 0-+generated patterns can be obtained from fused deposition modeling &)D*( in wa$ selective laser sintering &S'S( in polystyrene or other plastics and inkjet technology in wa$+like plastics. These materials may be melted or burned out of the investment very cleanly. The patterns from these processes tend to be small to medium in si1e and especially for inkjets offer the highest resolution and detail. Stereolithography is also used to produce patterns for investment casting but the  photopolymer materials used in that process are more difficult to burn out than the materials used in others mentioned above and also have a tendency to e$pand and crack the mold. To get around these problems ,D Systems has produced a special  build style for this application with the trade name !"ic#$ast M . The 0-+generated  pattern is built in hollow thin sections which tend to crumple during burn out rather than e$pand and also results in a smaller mass of pattern material to remove. The

 process has been developed over a number of years in partnership with large foundry companies and customers. 'aminated object manufacturing &'"*( has also been used for investment casting although a more typical application is for sand casting. See below. The paper material used in the '"* process is said to sometimes be difficult to remove completely from the mold although this is probably a strong function of the particular geometry being  produced.

#irect 3abrication of /nvestment -atterns Soligen is a licensee of */T%s ,D -rinting process and uses it to produce investments directly without patterns at all. :inder is deposited to bond a bed of ceramic powder in layerwise cross sections to sequentially build up the investment. $tra powder is  brushed and vacuumed from the green part which is fired to consolidate it in a process similar to a conventional burn out. Soligen is vertically integrated to produce the final  parts in its own foundry. Another */T ,D- licensee F Corp. introduced the FCastT* process in E@@E which is very similar in concept to Soligen%s technology. The process uses slightly modified versions of the company%s FG@H and FI@ printers and was developed in conjunction with 7riffin /ndustries. F Corp. is first introducing the ability to cast low temperature materials such as aluminum 1inc and magnesium but has a long+term goal of casting high temperature ferrous materials. )inishes are said to be similar to those available from sand casting and parts can be finish+machined normally.

and +astings The sand casting process starts by tightly compacting fine moist foundry sand in a  bo$+like frame around a pattern which is typically made of wood. The pattern is removed from the sand to leave a cavity into which the molten metal is poured. "nce the metal cools and hardens it%s removed from the sand which is then recycled. As with investment casting it may be necessary to remove e$tra material and perform finish machining and clean+up.

/ndirect or econdary -rocesses that 1tili$e R-*generated -atterns

'aminated object manufacturing &'"*( has been a popular way to produce patterns for sand castings. The large si1e of parts that can be produced and their similarity to wood patterns historically used in the process have been important factors. /t may be necessary to seal the '"*+generated pattern against moisture to guarantee dimensional stability. -arts made using other methods of 0- such as stereolithography are also used in the  process and may have some advantages compared to laminated object manufacturing in terms of tolerances finish and dimensional stability. 3owever sand casting is often used for very large parts and '"* has an advantage there.

#irect 3abrication of and +asting -atterns

/t%s possible to skip the step of building a pattern for a sand casting mold altogether. This may be advantageous in the early stages of a project before final dimensions and other parameters may have been determined or if very few castings are required making the cost of producing a pattern prohibitive. Selective laser sintering &S'S( systems are available that fuse polymer coated sand layer by layer to form sand casting molds. :oth manufacturers of S'S systems ,D Systems &products inherited from DT*( and "S 7mb3 produce systems with this capability. "S%s method has been dubbed Direct$roning M . "ne limitation these methods have is in the si1e of molds they can produce. A solution for much larger parts is offered by -ro*etal 0CT 7mb3 of 7ermany. )ormerly 7eneris 7mb3 -ro*etal 0CT &0apid Casting Technology( is commerciali1ing the S? System. This machine uses a wide area inkjet to bond layers of sand into sand casting and core patterns and has a build volume of ? $ E $ E inches. The method is reminiscent of the , Dimensional -rinting process developed  by */T. A build chamber full of sand weighs several tons. Clinkenbeard J Associates offers a process that avoids the use of additive fabrication altogether. )airly robust blocks of sand are formed using a polymer binder. The blocks are subsequently machined using diamond tools and standard C>C techniques to fabricate a hollow mold in which metal is directly cast.

#ie*+astings The processes that are used to make metal die casting molds are similar those used to fabricate metal injection molds. -lease see that section. 3owever low+cost prototype  plaster die casting molds have also been fabricated using 0- generated patterns. This is accomplished by casting plaster material against an 0-+generated pattern in a  process similar to making an 0T< rubber mold.

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#efinition 0apid manufacturing &0*( is the use of additive fabrication technology to directly produce useable products or parts. As is the case with rapid  prototyping the field is also known by several other names such as direct manufacturing direct fabrication and digital manufacturing. /t may also be referred to by the names of one or more of the several technologies utili1ed# a number which is continuously growing.

0* is one of the three major blossoming outgrowths of rapid prototyping. The others are three+dimensional printing + a lower+cost flavor of 0- and rapid tooling + actually a special case of rapid manufacturing. Today the

distinctions among the trunk and branches of the 0- tree are not very clear. *oreover these differences can be e$pected to continue to blur as the technologies mature and applications specifications and capabilities of the  branches overlap more and more. -resent tatus 2hat we see today is only a pale outline of the future. A few 0- systems specifically aimed at rapid manufacturing applications are just beginning to appear commercially. 0* is not yet being practiced at present at least  publicly in any large way. 3owever many e$periments that adapt e$isting 0systems to specific 0* applications are underway on a proprietary basis. As technology materials and other barriers are overcome additive fabrication will find its way into the mainstream across a broad spectrum of applications. 0* will be the branch of the technology that has the most direct impact on  people%s lives.

Some observers have likened it to a second industrial revolution. That may be going a little too far but it%s a good long+term bet that nearly all facets of life will be impacted in some way by 0* + and many in ways which may not be apparent at present.

dvantages and #isadvantages The fundamental advantages and disadvantages  of rapid prototyping carry over to rapid manufacturing. The benefits of 0* must be balanced against its substantial limitations today. 9nless there is an overwhelming need for a specific advantage that 0* provides the balance most frequently favors a conventional approach. 3owever as technical problems on many fronts are solved the balance can be e$pected to tip in favor of 0* with greater frequency.

The driving force to solve these problems comes from the early adopters whose present applications already possess an overwhelming balance in favor of additive fabrication. These individuals and companies are providing the foundation upon which further improvements will be based. ;eometric freedom. ssentially all additive fabrication technologies provide the ability to fabricate with unbounded geometric freedom. /t%s their most important advantage over subtractive methods and main reason to e$ist. 7eometric freedom comes with several limitations using today%s technology however. The speed of fabrication compared to standard manufacturing methods is much slower. :y some estimates e$isting mass production methods are @ to @@@ times faster  KL. The finishes and accuracy are also not on a par with conventional technology. Secondary operations are also required such as support removal and hand+finishing. /n a production situation where multiple parts are fabricated secondary operations can add up and become time+consuming.

There are also part si1e limitations at present which are more restrictive than those of standard methods. aterials. Additive fabrication offers the potential to use multiple materials as well as to control the local geometric meso+ and micro+structure of a part. This means that the functionality of a part can be optimi1ed in ways that are impossible with previously e$isting manufacturing methods. *aterials can be selected for  their mechanical thermal optical or other properties and then can be  physically deposited in a manner that optimi1es or changes those properties  beyond the capability of the intrinsic material itself.

"n the other hand the reality today is that the key word here is =potential.= /t will be a long time before the choice of materials available to rapid manufacturing is even remotely comparable to those available to standard manufacturing technologies. There are just a few do1en 0-50* materials commercially available today spread out over all classes of materials such as  plastics metals and ceramics. /n contrast plastic selection databases e$ist t hat list a mind+boggling G@@@@M active grades of plastic alone KEL. /n addition recycling comple$ materials may be difficult or impossible. Elimination of tooling. CAD directly drives all additive fabrication processes making it theoretically  possible to avoid the use of tooling altogether. /n practice it may often still not be possible to do that because of process and materials limitations of one kind or another but complementary rapid tooling technology might offer a  beneficial compromise. 2hen feasible however the complete elimination of tooling results in enormous savings in time and money. /t makes it possible to fabricate parts and products in small quantities or using materials and design  parameters that might not otherwise be conceivable. 'owered costs. The ability to fabricate products more economically arises from several links in the 0* process chain! "ne of the largest savings as mentioned is doing away with the need for tooling. Additional savings arise from lowered or 1ero inventory requirements and eventually can be e$pected to also arise from the ability to fabricate complete operational assemblies. The latter further lowers inventory costs and also does away with assembly labor. "f course the economic potential described here requires substantial technological development to fully reali1e.

The establishment of distributed manufacturing is simplified once tooling and inventory requirements are done away with. -arts and products can be fabricated at the point of use and in the e$act quantity required. )or e$ample  parts may be manufactured at the location of the final assembly line or at a replacement part distribution site or on a ship at sea or in outer space. /t will only be necessary to inventory the requisite materials rather than many parts or sub+assemblies or even the final product itself.

ass customi$ation. Taking distributed manufacturing to its logical e$treme one of the major reasons that some pundits are e$cited by the possibilities of 0* is that it holds  promise to lead to an era of products designed directly by consumers. /f it%s  possible to economically make as few as a single unit of an item then it%s hypothesi1ed that there will develop a significant demand for products created  by and for individual consumers. Such products might be e$pected to satisfy consumers% needs more precisely than mass+produced goods.

This scenario is predicated at least to some e$tent by e$trapolating on the many e$amples of semi+custom designed products available in the marketplace today. Automobiles personal computers and houses are all built with significant customer input. Cell phone covers watch face designs and other fashion items over the last several years have also become products that offer consumers personali1ed choice. The trend can be e$pected to continue especially for some items and for certain consumer groups. 3owever these are all products that are either based on a limited but nevertheless large mi$ and match menu or for which functionality is not seriously impacted. The question remains will we all be designing our own sneakers automobiles toys and toasters in the not too distant future; The answer is that that%s not likely to happen.

Thermoplastic powder is spread by a roller over the surface of a build cylinder. The piston in the cylinder moves down one object layer thickness to accommodate the new layer of powder. The powder delivery system is similar in function to the build cylinder. 3ere a piston moves upward incrementally to supply a measured quantity of  powder for each layer. A laser 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. $cess powder is simply brushed away and final manual finishing may be carried out. >o supports are required with this method since overhangs and undercuts are supported by the solid  powder bed. That%s not the complete story though. /t may take a considerable length of  cool+down time before the part can be removed from the machine. 'arge parts with thin sections may require as much as two days of cooling time. S'S offers the key advantage of making functional parts in essentially final materials. 3owever the system is mechanically more comple$ than stereolithography and most other technologies. A variety of thermoplastic materials such as nylon glass filled nylon and polystyrene are available. Surface finishes and accuracy are not quite as good as with stereolithography but material properties can be quite close to those of the intrinsic materials. The method has also been e$tended to provide direct fabrication of metal and ceramic objects and tools. Since the objects are sintered they are porous. /t may be necessary to infiltrate the  part especially metals with another material to improve mechanical characteristics.

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-rofiles of ob&ect cross sections are cut from paper or other web material using a laser. The paper is unwound from a feed roll onto the stack and first bonded to the previous layer using a heated roller which melts a plastic coating on the bottom side of the paper. The  profiles are then traced by an optics system that is mounted to an 4+N stage. After cutting of the layer is complete e$cess paper is cut away to separate the layer from the web. 2aste paper is wound on a take+up roll. The method is self+supporting for overhangs and undercuts. Areas of cross sections which are to be removed in the final object are heavily cross+hatched with the laser to facilitate removal. /t can be time consuming to remove e$tra material for some geometries however. /n general the finish accuracy and stability of paper objects are not as good

as for materials used with other 0- methods. 3owever 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. 2hile 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. S P(Q and similar laser  powder forming technologies are gaining in importance and are in early stages of commerciali1ation. A high power laser is used to melt metal powder supplied coa$ially to the focus of the laser beam through a deposition head. The laser beam typically travels through the center of the head and is focused to a small spot by one or more lenses. The 4+N table is moved in raster fashion to fabricate each layer of the object. The head is moved up vertically as each layer is completed. *etal powders are delivered and distributed around the circumference of the head either by gravity or by using a pressuri1ed carrier gas. An inert shroud gas is often used to shield the melt pool from atmospheric o$ygen for better control of  properties and to promote layer to layer adhesion by providing better surface wetting. A variety of materials can be used such as stainless steel /nconel copper

aluminum etc. "f particular interest are reactive materials such as titanium. *aterials composition can be changed dynamically and continuously leading to objects with properties that might be mutually e$clusive using classical fabrication methods. The strength of the technology lies in the ability to fabricate fully+dense metal  parts with good metallurgical properties at reasonable speeds. "bjects fabricated are near net shape but generally will require finish machining. They have good grain structure and have properties similar to or even better than the intrinsic materials. Selective laser sintering is at present the only other commerciali1ed 0- process that can produce metal parts directly. 3owever laser powder forming methods have fewer material limitations than S'S don%t require secondary firing operations as some of those processes do and can also be used to repair parts as well as fabricate them.

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