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Rapid Prototyping and Manufacturing:AMRCC member practitioner of this technology Rapid Prototyping Concepts
Rapid Tooling Concepts
Rapid Prototyping (RP) is the automated fabrication technologies of seamlessly and rapidly creating accurate representative physical models of mechanical parts directly from 3-dimensional Computer Aided Design (CAD) data without the use of tooling and with minimal human intervention. Developed in the mid-'80s, RP uses state-of-the-art laser technology, positioning systems, materials and computer technologies in the various processes. There are many RP processes that are widely used, each one using different methods and materials to produce the final part. This report will briefly describe these RP processes along with others of interest, materials, uses and services available. As always, if additional information is needed, please contact the AMRCC. Some of the many potential benefits of Rapid Prototyping include:
The process common among all modeling systems begins with the creation of a CAD solid model of the part to be prototyped. Virtually any shape that can be made by the CAD software can be prototyped with no size limitations on the part. Multiple part assemblies may be prototyped, including moving parts and parts within parts. An industry standard, STL file of the part is created and then sent electronically to a service provider to generate the prototype part. The .STL file defines the part as a grouping of triangular facets, which describe the surfaces of the part. If the CAD software does not support .STL files, other file types such as IGES and STEP are usable but may be subject to software compatibility between the customer and service provider. The service provider reviews the CAD part for various design criteria, designs support structures if needed and then sends it to the modeling system. Support structures to hold the part in place while building, are not necessary for some systems while other systems software automatically design their own. The part Designer does not need to be concerned with these support structures. The modeling system software then automatically slices the CAD part into layers (stacked in the Z dimension) .001 to .020 inch thick, dependent upon the parts geometry and the RP systems capabilities. This slicing is done on the fly as the model part is created. A Laser or machine head traces the profile of the part in the X and Y directions on a build platform forming the first layer. The build platform lowers in the Z direction one layer thickness and the next part layer is traced, including any necessary support structure. Layers are added successively to create the part from the bottom up. After the part is removed from the modeling system, the support structure is removed and the part is cleaned and a finish applied if needed. It is then sent on to the customer for various uses or to the toolmaker for fabricating molds. It is important to note that until the model is removed from the modeling system, it has existed as only electronic data. Generation of the .STL file and sending the data to the service provider takes only a few minutes of time. There is no need to make time consuming dimensioned drawings or sketches, as all part data is transferred electronically. Preparation, .STL file creation and sending of the file to the service provider takes a very short time. Most service providers will be able to return completed parts in typically three to five days after the receipt of valid files plus shipping time of approximately one day. There are too many variables to predict actual RP system run time but all systems run 24 hours a day, unattended. Unfortunately, a service provider's workload will delay delivery but they make a very good effort to meet deadlines. Additional part finishing and molding or casting will also add time to the schedule, but a 10 to 14 day turnaround is possible for small quantities. 3D Systems manufactures the Stereolithography Apparatus (SLA) which uses the process commonly known as Stereolithography. First to market a commercial Rapid Prototyping system in 1988, they have the most systems in operation and therefore have the most experience. The name "Stereolithography" is occasionally misused to refer to the entire Rapid Prototyping process (similar to the misuse of "Xerox" and "Coke"). 3D Systems process uses a laser-generated beam of ultraviolet radiation focused onto the surface of a bath of photosensitive resin. The laser traces the profile of the slice onto the liquid resin and then fills in the solid areas using an open crosshatching pattern. This solidifies the resin into a mostly solid layer of the part profile, which is then lowered into the bath to expose material for the next layer. The process is repeated for each slice until the 3-dimensional object is completely built. The part is then post-cured in an UV oven to solidify the material not solidified by the crosshatching pattern. Many formulations of acrylic resin are available to match various applications and needs. The parts produced can be machined and finished but are not strong enough to replace production plastic parts. Part detail and quality are excellent, especially the ability to model small details. The ability to hold tolerances across the entire part is in the range of +/-.003. Slice thickness may be as thin as .001 inch. These parts may also be used as masters to produce various types of secondary molds and dies (see the "Rapid Tooling" section). 3D Systems is also the manufacturer of a 3-D printing system (see the following section on "3-D Printers"). SELECTIVE LASER SINTERING (SLS) 3D Systems also manufactures the Selective Laser Sintering (SLS) system (formerly manufactured by DTM Corporation, which has merged with 3D System). This process is also well established with many machines in operation. The process is very similar in operation to Stereolithography but differs in that the material used is in powered form. The SLS process uses a thin layer of heat-fusible powdered material deposited onto a movable build platform, which is then sintered by exposure to a laser beam. The laser traces the profile of the slice onto the powdered material and then fills in the solid areas using a crosshatching pattern. This heats the material to just above its melting point which solidifies after the laser beam has passed. The part is then lowered into the chamber and covered with fresh material to allow for the next layer to be added. The process is repeated for each slice until the 3-dimensional object is completely built. Because the materials used are in a solid form, supports for the model are not required. Materials include: "DuraForm" Polyamide and "DuraForm GF" for producing parts; "Polycarbonate" and "CastForm" for investment casting patterns; "SandForm Si" and "SandForm ZR" for sandcasting molds and cores; "Copper Polyamide" for short-run tooling and parts; "LaserForm" for injection molding tooling inserts and parts; and "DSM Somos" for flexible/soft parts. Where applicable, the parts produced are quite strong and may be used in pre-production marketing units. Part detail and quality are very good, but fine details and sharp edges loose some definition. The ability to hold tolerances across the entire part is in the range of +/-.005. The parts produced are somewhat porous and require a small amount of work to apply a smooth painted finish, although a dipped coating of resin or "superglue" helps to fill the voids. FUSED DEPOSITION MODELING (FDM) Stratasys, Inc. manufactures the Fused Deposition Modeling (FDM) systems. This process is rather simple in concept and does not cure its material with a light source. The systems offered are the first truly office environment and desktop machines available. The Stratasys FDM system uses a reel or cassette of plastic filament that is fed into a heated extruding head, melting it to a temperature just above its solidification state prior to deposition. Within a heated build chamber, the machine head fills in the 2-dimensional profile of each slice in the X and Y directions on a movable build platform to form each layer. The material solidifies as it is placed, creating a laminate of each slice, but is kept at an optimal temperature within the build chamber to allow for fusing with the next layer. A second material, which forms the support structure for overhanging features, is also traced onto the same layer if needed. The part is then lowered by the platform to allow for the next layer to be added; repeating the process for each slice until the 3-dimensional object is completely built. Materials include ABS and medical grade ABSi; Elastomer E20 for flexible parts; and investment casting wax. Parts produced can be machined and finished and the ABS materials are quite strong and may be used in pre-production marketing units. Part detail and quality are very good, but fine details and sharp edges loose some definition. The ability to hold tolerances across the entire part is in the range of +/-.005. DIRECT SHELL PRODUCTION CASTING (DSPC) Soligen manufactures the Direct Shell Production Casting System (DSPC). This system directly fabricates the ceramic molds (negative) for investment casting of metals, bypassing the steps of creating the cores used to fabricate the ceramic mold (see the "Rapid Tooling" section). This system jets a resinous binder onto sequential layers of ceramic powder, in a process somewhat similar to the SLS process, until the 3-dimensional object is completely built. The unbound powder is removed and the resulting mold is fired. A new shell is required for each metal part that is cast. This mold is a direct replacement for those made by the traditional methods and the investment casting process continues unchanged. The cast parts themselves have a slightly rougher surface finish overall and tolerances across the entire part are also slightly more. This process is an excellent choice to use for obtaining castings for prototype testing, marketing samples or small quantity production runs. Cost for small quantity runs is competitive with traditional methods but delivery of parts is substantially faster. Another sector of Rapid Prototyping is 3-D Printer technologies, which address the need for low cost, easy to use conceptual modelers located in an office environment. The 3-D Printers quickly produce smaller, detailed parts that are mainly used for visualization and concept verification. Stratasys, Inc. offers the "Prodigy" desktop modeler, which uses an extrusion head to deposit beads of nylon polymer in layers to produce parts. They also offer the "Dimension" 3-D printer that produces parts in ABS. These systems are capable of creating durable parts with good dimensional accuracy, detail and surface finish that may also be used for soft tooling masters. 3D Systems, Inc. produces the "ThermoJet" office modeler which uses a print head of multiple jets to deposit layers of material in a process called "Multi- Jet Modeling" (MJM). This high-speed system produces parts in an organic thermopolymer material with excellent detail that may also be used for investment casting masters. Z Corporation manufactures the "Z" series of three-dimensional printing systems, based upon technology originally developed by the Massachusetts Institute of Technology. This process uses a print head with 125 jets to selectively spray drops of binder onto successive layers of powder to create "appearance models". This same technology is also licensed to Soligen Technologies to create ceramic investment casting shells. A proprietary water-based solution binder that glues the grains of binder together activates the powdered raw material. The resultant part is porous and not very strong, but can be "quick dipped" into a bath of molten wax or a low-viscosity epoxy to obtain greater durability. The systems main strength is its ability to create parts very quickly in an office atmosphere. Objet Geometries Ltd. offers the "Quadra" and "QuadraTempo" three-dimensional printing systems which use 1536 nozzles to deposit a proprietary acrylic photopolymer that is cured by UV lights and requires no post-cure or post-processing. The parts support structure is made of the same material as the part, except that the last layer that is attached to the part is a weaker material. This allows the supports to be separated easily from the part without leaving any contact points or blemishes that require post-process finishing. The part strength is excellent for a conceptual modeler as well as accuracy and build speed. A major goal of many Rapid Prototyping researchers is to develop a process that can directly create a metal part without any secondary operations. That goal has been accomplished in theory although there are problems with the parts themselves. These problems include density, weight, warping and not the required material. Two of the manufacturers above offer this technology along with an additional two others that offer only that capability. Many other research organizations and manufacturers are feverishly working on developing direct-to-metal prototyping as well as ceramics and other materials. 3D Systems currently offers a metal process that is produced on its Selective Laser Sintering (SLS) systems. "LaserForm", is an Stainless Steel based metal which is intended to be used to produce injection molding inserts (see the "Rapid Tooling" section) and parts. The SLS part fabrication process is the same as that of its other materials. Once completed, the "LaserForm" part must be cycled through a furnace process to remove the particle binders and infiltrating it with bronze to bring it to full density. The PROMETAL Rapid Tooling System is a purpose built system that produces only metal molding inserts. The system is a combination of the Selective Laser Sintering (SLS) process with the laser being replaced by an inkjet printer head. The printer head sprays a binder onto a layer of powdered metal. Once completed, the part is cycled through a furnace process to remove the binder and infiltrate it with another, lower melting temperature material. Any metal that is available in powdered form can be used and the system is capable of producing functional parts as well as molding inserts that can be machined and finished. Laser Engineered Net Shaping (LENS) is a process developed by Sandia National Laboratories, that uses a laser to focus its beam on a substrate which creates a weld pool. Powdered metal is "injected" into this weld pool and is melted. As the laser moves to trace the profile and filled areas of the part, the metal solidifies. This is repeated layer by layer until the part is finished. The metals currently being examined are stainless steel, inconel, H13 tool steel and titanium. Aluminum does not work well with this process. The process is holding tolerances of .005 in the X & Y and .015 in the Z-axis. Two companies. Optomec and Precision Optical Manufacturing (POM) are currently offering systems featuring this technology. This article includes only the major systems available in the U.S. market and most of them happen to be produced by U.S. companies. The information provided here is open knowledge that may be obtained through the manufacturer's web site, promotional literature or trade publications. Please see the manufacturer's web site for current product descriptions and other technical information. There are a number of systems produced or under development in the U.S., Europe and Japan, but they are not marketed in this country. Many of these systems operate very similarly to those included here. When these systems become available, they will be included in this section. Also not included here are a number of systems under development that target larger parts. Rapid Prototyping produces dimensionally accurate and highly detailed parts in durable materials that have many valuable uses to reduce product development time and costs. There are many potential applications for these parts regardless of the material and process that they are made from. The only limitations are in the mindset of the person searching for the application. Some sample applications are as follows:
Rapid Tooling is the result of combining Rapid Prototyping (RP) techniques with conventional tooling practices to produce parts of a functional nature from electronic CAD data in less time and at a lower cost relative to traditional machining methods. Rapid Tooling is also known as Secondary Tooling, Bridge Tooling or Soft Tooling consisting of processes that, in many cases, existed long before Rapid Prototyping techniques. Many of the Rapid Tooling processes have the ability to create production quality parts in the intended production material in less time and at considerably less expense than conventional hard tooling. This report will briefly describe these RP processes along with others of interest, materials, uses and services available. As always, if additional information is needed, please contact the AMRCC. The main intent of Rapid Tooling is to "bridge" the gap between the product design phase and actual production of the end product, hence the name "Bridge Tooling". Many times in the product design cycle, there is a need to produce relatively small quantities of parts for market testing, environmental testing, production set-up and many other reasons. Rapid Prototyping can quickly generate one or two parts but becomes inefficient in larger quantities. Fabricating hard tooling to create parts and mold masters for a small quantity of parts with a high probability of geometry changes is not time and cost effective. There may also exist a situation where the total production run quantity of parts is in the hundreds or even a few thousand. In these situations, Rapid Tooling can be a valuable resource to provide a temporary solution until the design is proven and permanent hard tooling is completed, or in some instances, be the production tooling itself. Rapid Tooling is usually acquired through an engineering services provider which has Rapid Prototyping capabilities. It has become difficult to evaluate the best process and compare Service Bureaus as each company has added their own twist and there are hundreds of providers to go to. Therefore, when considering the use of Rapid Tooling, the part should be reviewed by a cross-section of providers before a specific process/provider is selected. There are a number of items to consider before applying Rapid Tooling as a solution. Most Rapid Tooling processes work well with difficult and complex geometries that would take a considerable amount of time to machine into hard tooling. Examples of this would be fine and "busy" details, compound curved surfaces, surfaces with changing radii and sculpted surfaces. This works best with tooling that requires only the core and cavity halves with no ejectors, inserts or multiple pulls. If the tooling requires a great deal of machining to put in additional details and tight tolerance features along with mold related details, the time and cost savings over traditional methods are reduced. The part must be right for the process and a general rule of thumb is: the simpler the part, the better the result. Other problem areas for some processes include limitations on part size, accuracy and detail with some types of geometry, unsophisticated tooling and short tool life. Rapid Tooling does however, offer many advantages. Tooling can be created in some instances in a matter of days with potential cost savings of up to 70% over traditional methods. As stated before, complicated geometry is usually not a problem and the molds offer excellent accuracy. While many of the processes are capable of molding only 25 to a few hundred parts, there are a few that can produce many thousands. The features common among all Rapid Tooling processes begins with the creation of a CAD solid model of the part to be molded. That part is then Rapid Prototyped by one of the many systems available to create either the positive or negative master as required by the tooling process. Fits, shrinks, part sectioning and other mold considerations may need to be allowed for at this step. In most cases, the core and cavity halves will be created as injection molding inserts. Many mold parameters and details must be determined at this time including parting lines, gates, risers, runners, ejector pins, inserts, slides, cooling lines, etc. Many processes allow some of these parameters and details to be incorporated in the initial fabrication steps, or they may be machined in later. Not all of these parameters and details are applicable to each type of mold or part. One must realize that Rapid Prototyping has limitations that are inherent to the process and parts produced should not be compared one-to-one with production parts. Of primary consideration is the speed in which the part is in-hand and ready for whatever analysis or purpose that the engineer intends. The biggest limitation to the Rapid Prototyping process is the engineers' imagination. Following are some of the more common traits that can be expected. PROTOTYPE PARTS
As with any technology, the system manufacturers are constantly working on process improvement, cost reduction, materials and new processes. Many private research institutions as well as colleges and universities also support the Rapid Prototyping and Manufacturing industry. Listed below are some of the many areas that enjoy on-going research. METALS
Please note that the following examples are general guidelines that will apply to most Rapid Prototyping (RP) systems capabilities. Each RP system will have slightly different characteristics in the materials used and how the part is produced. Most RP systems are also capable of producing part geometry that cannot be machined in one piece. Therefore, it is best to design parts to the desired end product without consideration to the RP process that will be used. The goal is, after all, to produce a model of the part to be manufactured. If there is any doubt or questions, contact the RP service provider for assistance.
SERVICES AVAILABLE There are many Engineering Service Providers that offer a wide range of engineering services. These companies major purpose is to aid other companies in "Rapid Product Development" with the goal of reducing the cycle time from product development through production. A wide variety of services are offered either individually or as a whole, from concept to reality. The vast majority of these providers use Stereolithography (SLA) or Selective Laser Sintering (SLS) systems as their tool of choice due to their speed and accuracy. In addition to producing prototype parts, many providers offer various extended services, including: RAPID TOOLING PROCESSES
AMRCC member practitioner of this technologyThe companies listed below, are willing to discuss their hands-on Rapid Prototyping and Manufacturing experiences with you. Please feel free to use the email contact feature below to notify them of your interest. You will be contacted by the company's expert with that software to address your questions at their first convenience. Company: HON INDUSTRIES, Muscatine, IA Rapid Prototyping equipment: One SLS 2500plus modeler by 3D Systems, Inc. Materials/processes used:
Secondary Processes used:
For additional information from this current user, contact: HNI Corporation Company: Rockwell Collins, Inc. Cedar Rapids, IA Rapid Prototyping equipment: Previous in-house operations used the Stratasys FDM technology. Currently use external service providers. Materials/process experience:
For additional information from this current user, contact: Rockwell Collins, Inc. Click Service Providers to search Iowa companies by solution Search Useful Links to find manufacturers and suppliers of this technology. |
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