Rapid prototyping
Rapid prototyping
is the name given to a host of related is the name given to a host of related technologies that are used to fabricate technologies that are used to fabricate physical objects directly from CAD data physical objects directly from CAD data sources. These methods are unique in that sources. These methods are unique in that they add and bond materials in layers to they add and bond materials in layers to form objects. Such systems are also known form objects. Such systems are also known by the names additive fabrication three by the names additive fabrication three
dimensional printing solid freeform dimensional printing solid freeform fabrication and layered manufacturing. fabrication and layered manufacturing. They offer advantages in many applications They offer advantages in many applications compared to classical subtractive
compared to classical subtractive fabrication methods such as milling or fabrication methods such as milling or turning!
turning!
"bjects can be formed with
"bjects can be formed with any geometricany geometric complexity
complexity or intricacy without the need or intricacy without the need for elaborate machine setup or final for elaborate machine setup or final assembly#
assembly#
"bjects can be made from
"bjects can be made from multiple materials,multiple materials, or as composites or materials can or as composites or materials can even be varied in a controlled fashion at any location in an object#
even be varied in a controlled fashion at any location in an object#
Additive fabrication systems reduce the construction of comple$ objects to a Additive fabrication systems reduce the construction of comple$ objects to a manageable
manageable straightforward, and relatively fast process.straightforward, and relatively fast process.
These properties have resulted in their wide use as a way to reduce time to market in These properties have resulted in their wide use as a way to reduce time to market in manufacturing. To
manufacturing. Today%s systems are day%s systems are heavily used by engineers heavily used by engineers to better understand andto better understand and communicate their product designs as well as to make rapid tooling to manufacture communicate their product designs as well as to make rapid tooling to manufacture those products. Surgeons architects artists and individuals from many other
those products. Surgeons architects artists and individuals from many other disciplines also routinely use
disciplines also routinely use the technology.the technology.
The names of specific processes themselves are also often used as synonyms for the The names of specific processes themselves are also often used as synonyms for the entire field of
entire field of rapid prototyping. Amrapid prototyping. Among these are ong these are stereolithography &S'A forstereolithography &S'A for stereolithography apparatus( selective laser sintering &S'S( fused deposition stereolithography apparatus( selective laser sintering &S'S( fused deposition
modeling &)D*( laminated object manufacturing &'"*( inkjet+based systems and modeling &)D*( laminated object manufacturing &'"*( inkjet+based systems and three dimensional printing &,D-(. ach of these technologies + and the many other three dimensional printing &,D-(. ach of these technologies + and the many other rapid prototyping processes + has its singular strengths and weaknesses.
rapid prototyping processes + has its singular strengths and weaknesses.
Reverse engineering (RE) used to be a
Reverse engineering (RE) used to be a nefarious term.
nefarious term.
/t formerly meant /t formerly meant making a copy of a product or the outright stealing of ideas from competitors. /n 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 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 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 thosemethods and technologies can still be used for negative purposes like those
mentioned but today there are numerous important legitimate applications for 0 as mentioned but today there are numerous important legitimate applications for 0 as well.
well.
This has come about over the last fifteen or more years due to the intense parallel 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 development of many different types of three dimensional digiti1ing devices and the
powerful reverse engineering software that allows the data they produce to be powerful reverse engineering software that allows the data they produce to be
manipulated into a useful form. manipulated into a useful form.
There are two parts to any reverse engineering application:
There are two parts to any reverse engineering application: scanning and data scanning and data manipulation. Scanning also called digiti1ing is the process of gathering the requisite 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 from an object. *any different technologies are used to collect three dimensional data. They range from mechanical
data. They range from mechanical and very slow to radiation+based and highly+and very slow to radiation+based and highly+ automated. ach technology has its advantages and disadvantages and their automated. ach technology has its advantages and disadvantages and their
applications and specifications overlap. 2hat eventually comes out of each of these 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+ data collection devices however is a description of the physical object in three+ dimensional space called a point cloud.
dimensional space called a point cloud.
-oint cloud data typically define numerous points on the surface of the object in terms -oint cloud data typically define numerous points on the surface of the object in terms of
of x,y, x,y, and and z z coordinates. At each coordinates. At each x,y, x,y,z z coordinate in the data where there is a point coordinate in the data where there is a point there is a surface coordinate of the original object. 3owever some scanners such as 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 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.
defines interior locations of the object and may also describe its density. Typical RE pplications
Typical RE pplications
Creating data to refurbish Creating data to refurbish or manufacture a part for or manufacture a part for which there is no CAD which there is no CAD data or for which the data data or for which the data has become obsolete or has become obsolete or lost.
lost.
/nspection and5or 6uality /nspection and5or 6uality Control + Comparing a Control + Comparing a fabricated part to its fabricated part to its CADCAD description or to a standard description or to a standard item.
item.
Creating ,D data from a Creating ,D data from a model or sculpture for model or sculpture for animation in games and animation in games and movies.
movies.
Creating ,D data from an Creating ,D data from an individual model or individual model or sculpture for creating sculpture for creating scaling or reproducing scaling or reproducing artwork. artwork. Documentation and5or Documentation and5or measurem
measurement of ent of culturalcultural objects or artifacts in objects or artifacts in archaeology
archaeology paleontologypaleontology and other scientific fields. and other scientific fields.
)itting clothing or
)itting clothing or footwearfootwear to individuals and to individuals and determining the determining the anthropometry of a anthropometry of a population population
7enerating data to create 7enerating data to create dental or surgical
dental or surgical prosthetics tissue+ prosthetics tissue+
engineered body parts or engineered body parts or for surgical planning. for surgical planning. Documentation and Documentation and reproduction of crime reproduction of crime scenes. scenes. Architectur Architectural al andand
construction documentation construction documentation and
and measuremmeasurement.ent.
There is usually far too much data in the point cloud collected from the scanner or There is usually far too much data in the point cloud collected from the scanner or digiti1er and some of it ma
digiti1er and some of it may be unwanted noise. 2ithout further processing the datay be unwanted noise. 2ithout further processing the data isn8t in a form that can be used by downstream applications such as CAD5CA* 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 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 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 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 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.
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 9sually the shortest part of any 0 task is scanning or data collection. 2hile there are e$ceptions scanning might only require a few seconds or a few minutes. "n the are e$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 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 powerful reverse engineering software that allows the data they produce to be
manipulated into a useful form. manipulated into a useful form.
There are two parts to any reverse engineering application:
There are two parts to any reverse engineering application: scanning and data scanning and data manipulation. Scanning also called digiti1ing is the process of gathering the requisite 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 from an object. *any different technologies are used to collect three dimensional data. They range from mechanical
data. They range from mechanical and very slow to radiation+based and highly+and very slow to radiation+based and highly+ automated. ach technology has its advantages and disadvantages and their automated. ach technology has its advantages and disadvantages and their
applications and specifications overlap. 2hat eventually comes out of each of these 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+ data collection devices however is a description of the physical object in three+ dimensional space called a point cloud.
dimensional space called a point cloud.
-oint cloud data typically define numerous points on the surface of the object in terms -oint cloud data typically define numerous points on the surface of the object in terms of
of x,y, x,y, and and z z coordinates. At each coordinates. At each x,y, x,y,z z coordinate in the data where there is a point coordinate in the data where there is a point there is a surface coordinate of the original object. 3owever some scanners such as 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 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.
defines interior locations of the object and may also describe its density. Typical RE pplications
Typical RE pplications
Creating data to refurbish Creating data to refurbish or manufacture a part for or manufacture a part for which there is no CAD which there is no CAD data or for which the data data or for which the data has become obsolete or has become obsolete or lost.
lost.
/nspection and5or 6uality /nspection and5or 6uality Control + Comparing a Control + Comparing a fabricated part to its fabricated part to its CADCAD description or to a standard description or to a standard item.
item.
Creating ,D data from a Creating ,D data from a model or sculpture for model or sculpture for animation in games and animation in games and movies.
movies.
Creating ,D data from an Creating ,D data from an individual model or individual model or sculpture for creating sculpture for creating scaling or reproducing scaling or reproducing artwork. artwork. Documentation and5or Documentation and5or measurem
measurement of ent of culturalcultural objects or artifacts in objects or artifacts in archaeology
archaeology paleontologypaleontology and other scientific fields. and other scientific fields.
)itting clothing or
)itting clothing or footwearfootwear to individuals and to individuals and determining the determining the anthropometry of a anthropometry of a population population
7enerating data to create 7enerating data to create dental or surgical
dental or surgical prosthetics tissue+ prosthetics tissue+
engineered body parts or engineered body parts or for surgical planning. for surgical planning. Documentation and Documentation and reproduction of crime reproduction of crime scenes. scenes. Architectur Architectural al andand
construction documentation construction documentation and
and measuremmeasurement.ent.
There is usually far too much data in the point cloud collected from the scanner or There is usually far too much data in the point cloud collected from the scanner or digiti1er and some of it ma
digiti1er and some of it may be unwanted noise. 2ithout further processing the datay be unwanted noise. 2ithout further processing the data isn8t in a form that can be used by downstream applications such as CAD5CA* 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 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 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 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 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.
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 9sually the shortest part of any 0 task is scanning or data collection. 2hile there are e$ceptions scanning might only require a few seconds or a few minutes. "n the are e$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 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 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 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 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.
form can be quite a lot of work indeed.
!ot all applications are created e"ual.
!ot all applications are created e"ual. ngineering is more e$acting than creating ngineering is more e$acting than creating a ,D model for a movie for e$ample. /f you need to ascertain dimensions precisely a ,D model for a movie for e$ample. /f you need to ascertain dimensions precisely more care and diligence must be used and measurement error quantified. :ut accuracy more care and diligence must be used and measurement error quantified. :ut accuracy and fidelity requirements are not limited to engineering. *any artistic and
and fidelity requirements are not limited to engineering. *any artistic and
architectural applications also have substantial accuracy requirements. After all architectural applications also have substantial accuracy requirements. After all would the data set that defines *ichaelangelo8s David be worth anything if it was 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 inaccurate; /n some respects aesthetic applications can be more challenging than engineering. 2hile there may not be as great a need for absolute dimensional engineering. 2hile there may not be as great a need for absolute dimensional precision requirements for the reproduction of surface qualities or acquiring data precision requirements for the reproduction of surface qualities or acquiring data
from difficult subjects such as hair represent a considerable challenge. from difficult subjects such as hair represent a considerable challenge.
#o$ens of companies ma%e three dimensional digiti$ers and scanners,
#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 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 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 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 technologies to more than a million points per second. -rices range from a couple of thousand dollars to hundreds of
thousand dollars to hundreds of thousands of dollars. To a great e$tent this situationthousands of dollars. To a great e$tent this situation reflects the wide range of applications that are presented to this class of devices. :ut reflects the wide range of applications that are presented to this class of devices. :ut the very e$uberance of engineering approaches may also be indicative of an immature the very e$uberance of engineering approaches may also be indicative of an immature market and technology base. 0apid prototyping is another field that e$hibits a
market and technology base. 0apid prototyping is another field that e$hibits a
similarly wide range of technologies and perhaps it is not a coincidence that reverse similarly wide range of technologies and perhaps it is not a coincidence that reverse engineering may be considered reverse+rapid prototyping.
engineering may be considered reverse+rapid prototyping.
#igiti$ers have numerous specifications, but there are &ust three %ey ones: #igiti$ers have numerous specifications, but there are &ust three %ey ones: volume accuracy a
volume accuracy and speed. <ond speed. <olume is lume is self+e$planatory but it should be self+e$planatory but it should be noted thatnoted that for most technologies it8s not actually
for most technologies it8s not actually much of a limitation. That8s because it8smuch of a limitation. That8s because it8s
possible to stitch together numerous scans using 0 software to accommodate objects possible to stitch together numerous scans using 0 software to accommodate objects
that are much larger than the available scanning volume. The tradeoff is time and that are much larger than the available scanning volume. The tradeoff is time and accuracy however.
accuracy however.
Accuracy and resolution are related but not the same. Accuracy refers Accuracy and resolution are related but not the same. Accuracy refers to how precisely the measurements correspond to dimensional
to how precisely the measurements correspond to dimensional
standards. 0esolution specifies the smallest increment of distance or standards. 0esolution specifies the smallest increment of distance or volume that the instrument can measure. /t8s possible for an instrument volume that the instrument can measure. /t8s possible for an instrument to have high resolution and be inaccurate and vice versa. Some
to have high resolution and be inaccurate and vice versa. Some manufacturers specify one value and not the other and each uses its manufacturers specify one value and not the other and each uses its own terminology and conditions. Different specifications can apply to own terminology and conditions. Different specifications can apply to each a$is of measurement as well. Accuracy and resolution are the each a$is of measurement as well. Accuracy and resolution are the main =weasel clauses= in most digiti1er specs. /f they are critical to main =weasel clauses= in most digiti1er specs. /f they are critical to
your application it may be necessary to get further data from the manufacturer or perform certification testing.
Speed is frequently given in points5second. 3ere again there is great variation among manufacturers in terminology and
conditions. Some manufacturers supply essentially anecdotal specifications or no information at all. >evertheless it8s usually possible to at least get an idea of the regimen the instrument falls
into.
n important basic distinction
among digiti1ing technologies is betweencontacting and non+contacting instruments. Contacting digiti1ers or touch+probes are often very accurate over a wide measurement volume and some instruments in this class are among the most affordable devices available. There are contact digiti1ers that are positioned manually to yield a single measurement at a time or may be scanned across a surface to produce a series of measurements. There are also touch probe instruments available which can automatically scan an object using a variety of
mechanical drive means. Contact instruments are often in the form of an articulated arm that allows for multiple degrees of freedom of movement. The position of each section of the arm is determined by encoders glass scales or in the case of the more ine$pensive devices by potentiometers mounted in each joint. "ther mechanical arrangements besides arms are also used.
"n the down+side contacting devices can distort soft objects such as auto upholstery and are too slow to digiti1e parts of human bodies or may require much labor to scan comple$ curved surfaces. "n the other hand they are not affected by the color of a surface or if it is transparent or reflective the way laser and other light+based systems may be. And while slow they may actually be the fastes t way to digiti1e simple
surfaces where just a few data points need be gathered. *anually positioned devices can also make it easier to get at hard to digiti1e areas of an object such as narrow slots or pockets
'aser+based Systems
'ine and pot canners Triangulation
The two major classes of non+contact scanners are those based on laser technology and those based on some form of non+coherent white or broadband light source. 'aser scanners most often use straightforward geometric triangulation to determine the surface coordinates of objects. A laser line is scanned on the target object and individual sensors image the line usually simultaneously from each side of the line. 2here the laser line%s image falls on each sensor most often a CCD array is easily determined and the rules of trigonometry are then applied to calculate the position of the target surface at each point on the laser line. The simplicity of the technique and its ability to fairly quickly digiti1e a substantial volume with good accuracy and
resolution have made laser line scanners a popular choice. -roducts are supplied both as complete systems and as self+contained measuring heads for mounting to standard touch+probe arms or in other ways including customi1ed mechanical fi$tures for speciali1ed applications.
'aser and other light+based systems may be affected by the color of a surface or if it is transparent or reflective. As more e$perience has been gained over the years
however users have become adept at work+arounds for surface problems which may cause errors. "ne must also be appropriately safety conscious when using any laser source. ven though most lasers used for scanning are rated well below any harmful threshold reflections on curved surfaces and other inadvertent events can result in a potentially harmful focused beam.
#ual*+apability ystems
*any companies that make contact digiti1ing instruments as well as many of those that make laser scanners provide turnkey products that have both of these quite complementary capabilities. :road areas can be quickly scanned using a laser device mounted on the arm and features which might be geometrically problematic for the laser can be contact+probed. Some companies provide instruments which can carry both a contact probe and a laser head simultaneously.
A few companies provide color laser scanning technology. Arius ,D uses a
multiple$ed arrangement of red green and blue lasers to simultaneously gather color and geometric data. The company mainly offers scanning services however rather than selling equipment. "ther companies such as *inolta and Cyberware use laser scanning to gather surface measurements and combine that data with color video information gathered separately. *ost color scanners use structured white light or broadband sources. See that section.
ther Types of 'aser ystems
Several additional laser technologies are also utili1ed including time of flight optical radar and laser tracking. /n general these methods offer good accuracy combined with the capability of making measurements from a long distance away from the subject + in some cases tens of meters. This so+called =stand+off= distance is important for applications such as digiti1ing large machinery buildings and the like which represent a large fraction of the applications for these technologies.
Time of flight systems measure how long it takes for light emitted by a laser to return to a sensor located near its source. "ptical radar systems are similar in operation and both are analogous to standard radar systems which measure the return+time of a radio
wave. Time of flight and radar systems don%t usually require retroreflectors mounted on the object to be measured and can operate at very high rates to quickly capture entire scenes or objects. /n contrast laser trackers look for a signal in their field of view from a retroreflector placed or held on the object. The main advantage these systems offer is high precision over a large working volume and a frequent use is for aligning large pieces of machinery or verifying as+built dimensions of large objects.
ther Types of Trac%ing ystems
#irectory of +ommercial -roviders of this Technology .../n addition to laser+based tracking systems a number of companies make 'E#*based and other types of tracking systems such as magnetic trackers. These technologies generally have smaller working envelopes than laser+based systems and may not be quite as accurate. They%re most frequently used in human and other types of motion studies but are also useful for reverse engineering. A probe with one or more 'D%s is touched or attached to the object to be digiti1ed. Sensors most often utili1ing CCD chips in a dual camera arrangement image the 'D%s in their field of view. As with laser scanners trigonometry is then used to calculate the position of the probe on the surface of the object. ncoding schemes based on high+speed modulation of the light emitted by the 'D%s allow some instruments to simultaneously track the position of hundreds of 'D%s.
agnetic trac%ers offer the added benefit of being able to digiti1e points on objects that are not within a direct line of sight. /nstead of an 'D probe these systems use a small wire coil as a target. "ne company that makes magnetic trackers -olhemus combines this technology with laser scanning. The result is a system that has many of the same features as laser scanners mounted on mechanical arms while providing very great freedom of movement.
/n 0 applications these systems provide good accuracy over a substantial volume and moderate speeds. They aren%t affected by surface quality or color. "n the down+ side they require a contacting probe or marker and can be slow to digiti1e comple$ surfaces.
Rapid prototyping
systems can%t yet produce parts in a wide enough range of materials at a fast enough rate to match anywhere near the entire spectrum of requirements of industry and science. >evertheless an increasing number ofapplications 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
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 afew 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.
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
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 RTR 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
Rapid Tooling
/ndirect or econdary -rocesses
Although the properties of 0- materials improve and e$pand continuously a limitless array of applications means that there will always be a need to transfer parts fabricated in a material used in an 0- process into yet another material. /n addition it%s usually necessary to use very specific materials to make most tools. Consequently numerous material transfer technologies have been developed. Typically a part made by the 0- system is used as a pattern or
model in these processes. As in the case of the direct fabrication processes discussed above there are many secondary processes in various stages of development. 3owever of the more than two do1en such methods available just a few are common and commercially important today. +hoosing /sn9t Easy
The net result is that there are a bewildering number of routes to get to a final functional part or tool starting from a CAD definition. The choice depends on!
bout R-*generated
-atterns
0-+generated patterns must undergo finishing operations before they can be used in any
indirect or secondary process. >o rapid prototyping technology
today delivers surface finishes that are adequate for accurate applications such as injection mold tooling. 0emoval of the stair+stepping inherent in the process and other surface
artifacts is necessary before parts will eject from a mold and
may lead to additional errors being introduced. The accuracy
of most secondary processes is ultimately limited by the
precision of the pattern after finishing. 0apid prototyping patterns are best for applications
with just a few critical dimensions! /f many tight tolerances must be held it%s
generally still faster and cheaper to use C>C.
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 processes such as stereolithography or selective laser sinter ing or may be unique
0-methods 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.
• 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 &0T<( molding compound is then poured around the pattern. /t may be necessary to apply a vacuum to the assembly to pull air bubbles out of the rubber and insure fidelity to the pattern. "nce the rubber has solidified the pattern is removed and the mold is ready to be used.
Silicone rubber tooling is most often used in manual casting processes but in recent years more automated technologies have appeared. So+called reaction injection
molding &0/*( systems can produce several parts per hour from rubber molds. *olds also last longer because of the lower e$posure time to chemical processes. A number of other variants of the process are also available from particular vendors such as rubber plaster molding. 0-* allows the technique to be e$tended to other materials such as metals.
/n&ection olds etal -arts
The intent is frequently to fabricate injection molds faster and at lower cost than
possible with subtractive technology. 0- is also sometimes used to get an idea of how production tools will perform. 0apid tooling molds are used to make thermoplastic parts in quantities of few do1en for testing or prototyping to production quantities
ranging to a million or more. /n addition these same technologies are being used more for the direct fabrication of metal parts. ven though many of these technologies arose
initially as solutions for tooling it%s a good bet that the majority of parts fabricated with them today are end+use items.
0hy 1se Rapid -rototyping2
/nterest in the development of injection molds by rapid prototyping technology has been strong. *aking injection molds by subtractive C>C or spark erosion methods is
e$tremely slow and e$pensive. Skilled craftspeople are in short supply product
comple$ity is increasing and product cycles are growing ever shorter. This means that an ever larger number of more precise tools have to be created by a declining
population of toolmakers. There is therefore a good deal to gain from a process which provides both great time and labor savings and addresses these limitations. /n addition
0- offers the prospect for improvement in mold performance beyond anything that can be accomplished with subtractive technologies. The ability to fabricate comple$
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. Decreases in cycle times of E@ to ,@ or more in e$perimental molds have been achieved for e$ample. Consequently this application has been a major driving force in the development of rapid prototyping technologies that produce metal parts as well as in material transfer processes that use 0-+generated patterns.
0hat are the 'imitations2
The long+term prospect is for the direct additive fabrication of injection molds with the same level of precision and durability as C>C methods. 2hile great strides have been made in that direction and important time and labor savings are being reali1ed today by 0- methods the technology is still immature. This means that the benefits reali1ed are not universal and must be evaluated for each case. 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 • may have part si1e and geometry limitations
• don%t necessarily produce identical parts to hardened tooling and
• 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. The inability to modify many tools fabricated by 0- technology means that making such a tool is frequently a one+shot deal# if it%s not right the first time it may be necessary to scrap the tool and start over. 0apid tooling may lose its advantage compared to conventional tooling methods under those circumstances.
electing a -rocess
Selection of the optimum 0-+based process for each case is comple$. Among the factors to consider are the final application production volume part si1e accuracy and material requirements. The descriptions of the available technologies here provide a general guide for selection as well as places to learn more. "ne important thing to keep in mind at the present state of the art is that while direct 0- tool generation
methods may actually offer faster turn+around one of the indirect processes may offer lower costs and higher accuracy. Another thing to keep in mind is that it%s sometimes appropriate to fabricate part of a tool with C>C technology and part using
0-methods. The most economic and appropriate process must be selected for each portion of a tool and not necessarily for the tool as a whole.
ther Technologies
This is not an all+inclusive listing. *any other technologies are being e$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.
/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.
/!TR#1+T/!
#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$isting 0-systems to specific 0* applications are underway on a proprietary basis. As technology materials and other barriers are overcome additive fabrication will find its way into the mainstream across a broad spectrum of applications. 0* will be the branch of the technology that has the most direct impact on people%s lives.
Some observers have likened it to a second industrial revolution. That may be going a little too far but it%s a good long+term bet that nearly all facets of life will be impacted in some way by 0* + and many in ways which may not be apparent at present.
dvantages and #isadvantages
The fundamental advantages and disadvantages of rapid prototyping carry over to rapid manufacturing. The benefits of 0* must be balanced against its substantial limitations today. 9nless there is an overwhelming need for a specific advantage that 0* provides the balance most frequently favors a conventional approach. 3owever as technical problems on many fronts are solved the balance can be e$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 KL. 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
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$tended to provide direct
fabrication of metal and ceramic objects and tools.
Since the objects are sintered they are porous. /t may be necessary to infiltrate the part especially metals with another material to improve mechanical characteristics.
'aminated b&ect anufacturing
% &rief "torial
Back Next
-rofiles of ob&ect cross
sections
are cut from paper or other web material using a laser. The paper is unwound from a feed roll onto the stack and first bonded to the previous layer using a heated roller which melts a plastic coating on the bottom side of the paper. The profiles are then traced by an optics system that is mounted to an 4+N stage.After cutting of the layer is complete e$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$tra material for some geometries however.
as for materials used with other 0- methods. 3owever material costs are very low and objects have the look and feel of wood and can be worked and
finished in the same manner. This has fostered applications such as patterns for sand castings. 2hile there are limitations on materials work has been done with plastics composites ceramics and metals. Some of these materials are available on a limited commercial basis.
<ariations on this method have been developed by many companies and research groups. )or e$ample Oira%s -aper 'amination Technology &-'T( uses a knife to cut each layer instead of a laser and applies adhesive to bond layers using the $erographic process. Solidimension of /srael also uses a knife but instead bonds layers of plastic film with a solvent. This technology is sold
in the 9S by ,D Systems as the /n<isionT* 'D. There are also variations
which seek to increase speed and5or material versatility by cutting the edges of thick layers diagonally to avoid stair stepping.
The principal 9S commercial provider of laser+based '"* systems 3elisys ceased operation in E@@@. 3owever the company%s products are still sold and serviced by a successor organi1ation Cubic Technologies.
'aser Engineered !et haping
T% &rief "torial
Back
'aser ngineered >et ShapingT*
&'>S P(Q and similar laser powder forming technologies are
gaining in importance and are in early stages of commerciali1ation. A high power laser is used to melt metal powder supplied coa$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.
