Rapid prototyping draws widening foundry interest.It is said that when Napoleon ordered cannons for his armies, foundries understood that his orders were to be filled immediately. Delivery delays often were corrected by guillotine guillotine Instrument for inflicting capital punishment by decapitation. A minimal wooden structure, it supported a heavy blade that, when released, slid down in vertical guides to sever the victim's head. , and that fact made French foundry managers especially eager to fill royal artillery “RGA” redirects here. For other uses, see RGA (disambiguation). The Royal Regiment of Artillery, generally known as the Royal Artillery (RA), is an Arm of the British Army. Despite its name, it is made up of a number of regiments. orders quickly. Their haste, however, resulted in some good cannons and some not so good. Frequently cannons burst when they were fired, resulting in the deaths of many cannoneers and shortening not a few foundry careers. The unfortunate failures were mostly caused by faulty cannon design or flawed castings. Had they existed back then, a good quality control system would have hepped immensely, and proper cannon design and testing would have proved to be lifesavers. Rapid prototyping Building a part one layer at a time using a method of additive fabrication such as 3D printing. Such parts are used for concept modeling to determine if the product design meets the customer's expectations. would have been an instant success. Rapid Prototyping The modern foundryman readily recognizes good casting design and product testing as necessary tools of his trade, but these take time. Thus, he is always alert to ways that can telescope the time between the design and molding of an acceptable casting. One new way to do just that is through rapid prototyping or stereolithography The first 3D printing technology, which was pioneered by Chuck Hull of 3D Systems. See 3D printing. . Rapid prototyping, or rapid modelling, is an extension of the patternmaker's traditional skills. It is a process used to create model parts directly from a computerized model without tooling or machining. It is a new concept that bears foundry investigation. It is important to note that none of the several rapid prototyping processes at this writing can produce metal parts directly. These processes create parts in plastic or wax materials. The parts created are nonfunctional, though this too is changing as the technology advances. A leader in this recently developed technology is the process called stereolithography. Stereolithography (STL (STereoLithography) A 3D printing file format created by 3D Systems for its stereolithography system. Also supported by many numerical control, rapid prototyping and rapid manufacturing machines, STL provides the surface geometry of the item in triangles. ), simply put, is a method of transforming, in a matter of hours, computer-aided design computer-aided design (CAD) or computer-aided design and drafting (CADD), form of automation that helps designers prepare drawings, specifications, parts lists, and other design-related elements using special graphics- and calculations-intensive (CAD) data (or 2-D engineering drawings converted to CAD by one of the new STL service bureaus) into solid models of virtually any geometry. Starting with the CAD model, STL uses proprietary software to horizontally slice the computerized representation of a part into very thin layers. The computerized data, representing each slice or layer, is used to control a laser or ultraviolet (UV) beam of light that traces the shape of each layer, starting from the bottom of the part, onto the surface of a photosensitive A material that changes when exposed to light. See photoelectric. resin. The resin changes from liquid to solid wherever the laser beam strikes it. The layers are drawn one on top of another until the object is complete. With a solid representation of an engineering concept in hand quickly and relatively inexpensively, the customer and the foundry together can work out design imperfections, accuracy, casting potential and the ultimate functional capability of the part before committing to any production tooling. Selective Laser Sintering sintering, process of forming objects from a metal powder by heating the powder at a temperature below its melting point. In the production of small metal objects it is often not practical to cast them. In addition to the photosensitive resin material used in STL, there are other processes available to make computer-generated prototype parts, one being a selective laser sintering See laser sintering and 3D printer. (SLS (Selective Laser Sintering) See laser sintering and 3D printing. ) process that uses any material that softens under heat and then resolidifies. This includes a wide variety of powdered materials that sinter sinter Mineral deposit with a porous or vesicular texture (having small cavities). Siliceous sinter is a deposit of opaline or amorphous silica that occurs as an incrustation around hot springs and geysers and sometimes forms conical mounds (geyser cones) or terraces. (soften and bond) such as polycarbonates polycarbonates, group of clear, thermoplastic polymers used mainly as molding compounds (see plastic). Polycarbonates are prepared by the reaction of an aromatic difunctional phenol with either phosgene or an aromatic or aliphatic carbonate. , nylon, ABS plastic, investment casting investment casting Precision casting for forming metal shapes with minutely precise details. Casting bronze or precious metals typically involves several steps, including forming a mold around the sculptured form; detaching the mold (in two or more sections); coating its waxes, ceramics, metals and advanced composites. In the SLS process, a thin layer of heat-fusible powder is deposited into a container and heated to just below its melting point melting point, temperature at which a substance changes its state from solid to liquid. Under standard atmospheric pressure different pure crystalline solids will each melt at a different specific temperature; thus melting point is a characteristic of a substance and . An initial cross section of the object under fabrication fabrication (fab´rikā´sh  n),n the construction or making of a restoration. is traced onto the layer of powder by a laser beam. The temperature of the powder impacted by the laser beam is raised to the point of "sintering" in a controlled atmosphere A controlled atmosphere is an agricultural storage method. An atmosphere in which oxygen, carbon dioxide and nitrogen concentrations are regulated, as well as temperature and humidity. Two major classes of commodity can be stored in controlled atmosphere. 1. to chemically or metallurgically bond the particles and form a solid mass. As the process is repeated, each layer fuses to the underlying layer, and successive layers of powder are deposited and sintered sin·ter n. 1. Geology A chemical sediment or crust, as of porous silica, deposited by a mineral spring. 2. A mass formed by sintering. v. sin·tered, sin·ter·ing, sin·ters v. until the object is complete. Metal Castings Metal casting A metal-forming process whereby molten metal is poured into a cavity or mold and, when cooled, solidifies and takes on the characteristic shape of the mold. Although rapid prototyping processes vary considerably, usually they will be used in similar ways to speed the creation of prototype metal castings. In most of the methods discussed, the rapid prototyping process chosen will not have a major effect on the prototype casting produced. Sand Casting Casting is the process of production of objects by pouring molten material into a cavity called a mold which is the negative, or mirror image of the object, and allowing it to cool and solidify. Vendors of rapid prototyping equipment have made vague statements about the use of rapid prototyping techniques to create patterns for sandcasting. Some have even hinted that the emergence of these technologies will speed the decline of the patternmaking patternmaking In materials processing, the first step in casting and molding processes, the making of an accurate model of the part, somewhat oversize to allow for shrinkage of the cast material as it cools. industry. To date, however, rapid prototyping has had little impact in either the sandcasting or patternmaking industries. It is doubtful that rapid prototyping will ever replace patternmakers, but it is very likely the technique will become an important tool for patternmakers. Loose Patterns Although STL-produced parts require careful handling (they are not as durable as a wood or aluminum patterns), most of the materials available for rapid prototyping processes are durable and stiff enough to be used as prototype loose patterns to create several sandcast parts as shown in Fig. 1. Rapid prototyping techniques provide an advantage to the patternmaker pat·tern·mak·er also pattern maker n. One who makes patterns, as for sewing, carpentry, or industrial machinery. pat in that they allow him to work directly from the CAD model of the finished part. Starting with the CAD model, he can scale up the entire model to compensate for shrinkage Shrinkage The amount by which inventory on hand is shorter than the amount of inventory recorded. Notes: The missing inventory could be due to theft, damage, or book keeping errors. . Machine stock and core prints can be added as necessary to the design. Draft can be checked and modified if required. Once the pattern design has been completed, the model can be conveyed to a rapid prototyping system to create the pattern. With little finishing, the pattern is complete. For complex parts, stereolithography patterns can often be made faster and less expensively than a conventional pattern. Simple designs, however, typically are less expensive to make by conventional means. Patterns created by many of the rapid prototyping processes currently available can meet or exceed the accuracy of conventionally produced patterns. To obtain more durability, copies of the pattern can be made in polyurethane polyurethane Any of a class of very versatile polymers that are made into flexible and rigid foams, fibres, elastomers (elastic polymers), surface coatings, and adhesives. or aluminum. Double Shrinkage can be incorporated easily into the stereolithography model to compensate for shrinkage if the durable patterns are to be from the rapid prototyping pattern. In the same manner that rapid prototyping techniques can be used to make loose patterns, they can also be used as an advantage in the creation of matchplates. The CAD model of the finished part can be split along the parting line before scaling up, adding machine stock, core prints, etc. The split pattern can then be mounted on a parting line block and used to cast production matchplates. Rapid prototyping techniques also be used to tie in the creation core tooling. Most CAD systems are capable of generating stereolithography models and will allow a CAD model of a cored area to be easily extracted from the model of the finished part, resulting in a rough model of the core print. Like the process for creating a loose pattern, the CAD model of the core print can quickly be scaled to compensate for shrinkage, and machining stock can be added to complete the design of the core. The core print then can be created from the finished CAD model by a rapid prototyping process and used as a pattern to make a corebox. Diecasting Applications Prototyping diecast parts has always been an expensive proposition. Parts can be machined from aluminum or zinc stock, but the machined prototype can be expensive and may not have the same mechanical properties as the diecast production part. Sandcast parts may come closer to the mechanical properties but may not have an acceptable surface finish. Single-cavity dies can be expensive to create and usually require long lead times. Rapid prototyping techniques in combination with plaster casting plaster casting, as a sculpture process, is of three kinds. One employs a waste mold, another a piece mold (both plaster of paris), and the third a gelatin mold; all reproduce the original clay or wax model executed by the sculptor. , a process that has been around a long time, offers a fast and inexpensive way to create prototypes of diecast parts as illustrated in Fig. 2. Plaster casting is similar to sandcasting except that the mold is made of plaster instead of sand. Wet plaster is poured into the flask flask (flask) 1. a laboratory vessel, usually of glass and with a constricted neck. 2. a metal case in which materials used in making artificial dentures are placed for processing. on top of the pattern and allowed to set. Once set, the pattern is removed and the mold is dried. The mold can then be used to case most common diecasting materials. Once the casting has solidified so·lid·i·fy v. so·lid·i·fied, so·lid·i·fy·ing, so·lid·i·fies v.tr. 1. To make solid, compact, or hard. 2. To make strong or united. v.intr. , the plaster is broken to extract the part. The surface finish is much better than sandcasting but not quite as good as a diecast part. There is more flash than would typically be obtained with a diecast part but that usually is not a significant drawback for prototype parts. The primary advantage of using rapid prototyping techniques along with plaster casting to prototype diecast parts is time; cast prototypes can usually be obtained within three weeks. In addition, for small runs, the cost is often significantly less than either machining prototypes or creating a prototype die. Finally, the material propeties of prototypes made in this manner more closely approximate the die casting die casting Forming metal objects by injecting molten metal under pressure into dies or molds. An early and important use of the technique was in the Linotype machine (1884), but the mass-production automobile assembly line gave die casting its real impetus. than a machined prototype. Investment Casting One area in which there has been much interest is in the use of rapid prototyping techniques to create investment cast parts. The benefits in creating the first few parts can be significant because tooling costs, especially for complex parts, can be very high. Lead times for tooling can be nearly as long as for the production of injection molds. The ability to create a functional casting for design verification before tooling is ordered is extremely attractive. Several of the rapid prototyping systems can create patterns for use in investment casting. Two systems in particular, those produced by Stratasys, Inc. and by DTM DTM dermatophyte test medium. Corporation, can create parts directly into investment casting wax. These parts can then be used by virtually any investment casting foundry to create metal parts. Stereolithography, the process developed by 3-D Systems, Inc., has also been used directly to create investment casting patterns, but mold cracking and burnout Burnout Depletion of a tax shelter's benefits. In the context of mortgage backed securities it refers to the percentage of the pool that has prepaid their mortgage. have presented problems. Most of the materials available for stereolithography tend to maintain strength at elevated temperatures. As a consequence, they tend to expand and crack thin shell molds. This can be overcome by using the older solid cast or flask casting technique that many investment casters casters the small rubber wheels on surgical trolleys, patient stretchers, mobile equipment. conductive casters the casters are impregnated with carbon to facilitate the dispersal of static electricity from equipment. are reluctant to use because of the difficulty in automating the process. Some of the newer stereolithography materials made specifically for investment casting applications contain a volatile component that evaporates when the part is heated, shrinking the part slightly so that it will not crack the mold. These patterns have been used successfully with thin shell molds. All of the materials available for stereolithography are thermoset A polymer-based liquid or powder that becomes solid when heated, placed under pressure, treated with a chemical or via radiation. The curing process creates a chemical bond that, unlike a thermoplastic, prevents the material from being remelted. See thermoplastic. materials, which means they will not melt out of the cavity like wax. Consequently, the pattern must be burned out, typically for several days in an oven. Another Approach A process under development at the Massachusetts Institute of Technology Massachusetts Institute of Technology, at Cambridge; coeducational; chartered 1861, opened 1865 in Boston, moved 1916. It has long been recognized as an outstanding technological institute and its Sloan School of Management has notable programs in business, takes a slightly different approach. Instead of making a pattern for investment casting, they have developed a process to make a ceramic shell. The process develops the shell in thin layers using inkjet technology to spray a binder on ceramic powder particles. The powder is added in thin layers and the process repeated for each layer. When the part is completed, the shel is removed from the tank of powder, any excess powder is poured out and the shell is fired to completely bind the ceramic powder. The shell is then ready for pouring. There are two primary benefits from using a rapid prototyping technique to directly create patterns for investment casting. First, because they create parts in thin layers, it is possible to construct geometries that cannot be molded or machined in a single piece. Thus, these techniques can be used to quickly create patterns that would be difficult to build by other means. Second, because rapid prototyping techniques can create patterns without tooling, small numbers of castings can be created faster at less cost than machined molds. Rapid prototyping is, therefore, effectively used to create a few castings to test the design. However, it is not yet practical to use them to create patterns for even low-volume production. The cost of a pattern created by a rapid prototyping process is typically many times the cost of molding a was pattern. Also, the rate at which patterns can be produced by a rapid prototyping process is usually limited to a few per day, compared to the hundreds per day that can be molded. Even though it may not be practical to directly create patterns for investment casting using rapid prototyping techniques, there are ways that rapid prototyping techniques can be used in combination with other techniques. Rubber Pattern Molds One successful technique is to use the rapid prototype as a pattern to create a silicon rubber mold in which wax patterns can be cast. The prototype is scaled to compensate both for wax and metal shrinkage. A parting line block (used to define the partine line in the mold, similar to a follow board in sandcasting) is created and used to make a silicon rubber mold. Molten wax can then be poured into the mold to cast wax patterns for investment casting. Although the mold costs a few hundred dollars, the cost of the wax patterns is so much lower that this process can significantly reduce the cost of creating more than a few parts. The molds are typically good for 20 -- 40 pours before the silicon rubber is unusable. Spray Metal Pattern Molds When many parts are required, a spray metal tool can be created from the stereolithography part rather than a silicon rubber mold. In the spray metal process, an electric gun feeds two wires through an arc. The arc melts the wires into tiny droplets in the form of a spray. Compressed air compressed air, air whose volume has been decreased by the application of pressure. Air is compressed by various devices, including the simple hand pump and the reciprocating, rotary, centrifugal, and axial-flow compressors. drives the droplets onto the part where the metal collects and hardens to form the mold as in Fig. 3. To create a mold for wax patterns, a rapid prototyping model of the part, scaled to compensate for wax and cast metal shrinkage is made. As in creating the silicon rubber mold, a parting line block is required to define the parting on the mold. Metal is slowly sprayed (about 0.002 in. per pass) onto the rapid prototyping pattern positioned in the parting line block until a metal layer approximately 0.080 in. thick is created. The metal face is then backed with an aluminum-filled epoxy epoxy Any of a class of thermosetting polymers, polyethers built up from monomers with an ether group that takes the form of a three-membered epoxide ring. The familiar two-part epoxy adhesives consist of a resin with epoxide rings at the ends of its molecules and a curing to provide a strong, rigid backing for the mold face. Once the epoxy has cured, the entire assembly is inverted inverted reverse in position, direction or order. inverted L block a pattern of local filtration anesthesia commonly used in laparotomy in the ox. , and the parting line block is removed, exposing the spray metal parting line and the pattern surface previously hidden by the parting line block. The process is repeated to create the other half of the mold. When the second half is completed, the rapid prototyping pattern can be removed, leaving a cavity and core, which is the starting point Noun 1. starting point - earliest limiting point terminus a quo commencement, get-go, offset, outset, showtime, starting time, beginning, start, kickoff, first - the time at which something is supposed to begin; "they got an early start"; "she knew from the for the mold. Such molds are typically gated at the parting line and can be used for several hundred to several thousand pours. Spray metal tools offer an attractive alternative of low-to-medium volume parts. EPC (1) (Entertainment PC) See HTPC. (2) (Electronic Product Code) A standard code for RFID tags administered by EPCglobal Inc. (www.epcglobalinc.org). Applications Although there has been no investigation into the use of rapid prototyping parts in expendable pattern casting (EPC), rapid prototyping processes have been used to create tooling for expandable polystyrene polystyrene (pŏl'ēstī`rēn), widely used plastic; it is a polymer of styrene. Polystyrene is a colorless, transparent thermoplastic that softens slightly above 100°C; (212°F;) and becomes a viscous liquid at around 185°C; patterns. Tooling to create EPC patterns must withstand extreme conditions. After the polystyrene beads have been blown into the cavity, steam is introduced into the cavity through vents. The steam expands the beads and causes them to bond. Water is then sprayed on the back side of the mold surface to cool the pattern, allowing into to be easily extracted from the mold when opened. In the last year and a half, several EPC molds have been made using rapid prototyping parts as patterns and the spray metal process to create the mold itself. The construction process is slightly different from an injection mold. The spray metal layer is approximately 0.375 in. thick rather than 0.080 in., and there is no epoxy backing. The spray metal component of the mold is made as an insert to be bolted on a fabricated fab·ri·cate tr.v. fab·ri·cat·ed, fab·ri·cat·ing, fab·ri·cates 1. To make; create. 2. To construct by combining or assembling diverse, typically standardized parts: aluminum steam chest. Spray metal EPC tools have been used to make several hundred patterns. Mold life is estimated to be 1000 pieces, but none have yet run to failure. Accessing the Technology Some larger foundries and pattern-makers have installed several varieties of rapid prototyping equipment in their operations. Equipment cost currently ranges from slightly less than $100,000 to nearly $400,000 depending on the manufacturer and size capability of the system. However, the equipment costs is only part of the cost of an installation. A CAD system, finishing equipment, specialized facilities and training are contributing factors that may increase the cost. Service Bureaus Even companies who could easily afford the cost of installing a system may be reluctant to invest in the first-generation equipment currently available. Future generations of equipment are likely to be substantially more productive, use better materials and obsolete current equipment. Some companies have chosen to wait until the direction of the technology has become more certain before investing in equipment. A small industry has emerged to serve the rapid prototyping needs of companies who can benefit from the use of the techniques, but who have chosen not to purchase equipment. For them, working with a service bureau may be a cost-effective alternative. Working with a service bureau can give a foundry access to rapid prototyping, providing them with the ability to add another service for their customers. Making castings better, faster and more accurately are three of the important benefits of this new technology. Some Guidelines To minimize the possibility of problems when working with service bureaus, here are some guidelines: [TABULAR DATA OMITTED] * Make sure that the bureau understands what the part is intended to accomplish. A part to be used as a direct pattern for investment casting will have a very different set of requirements from one to be used as a loose pattern for a sandcasting (surface finish, accuracy and applied scale factor). * Make sure the design is complete. All of the rapid prototyping techniques require a complete definition of the geometry, including such details as fillet fillet /fil·let/ (fil´et) 1. a loop, as of cord or tape, for making traction on the fetus. 2. in the nervous system, a long band of nerve fibers. fil·let n. 1. radii ra·di·i n. A plural of radius. radii Noun a plural of radius , definition of blended surfaces, etc. Additional time will be required to define the CAD model before the part can be built. * All expectations concerning surface finish, accuracy and delivery should be in writing. Specifications will vary widely depending on the prototyping process used and the skill of the operator. Service bureaus have a wide variety of capabilities. Each specializes in a specific type of rapid prototyping process, CAD system and application. To ensure that a specific bureau can meet your needs, some of the following information is useful. What kind of process does the bureau use, and what materials does it use? There are a variety of both available, some more appropriate for some applications than others. Determine the bureau's level of experience. Although manufacturers of the equipment will minimize its importance, the skill and experience of the operator is the single biggest determinant determinant, a polynomial expression that is inherent in the entries of a square matrix. The size n of the square matrix, as determined from the number of entries in any row or column, is called the order of the determinant. of the quality and accuracy of the parts created on most rapid prototyping systems. Can the bureau accept your CAD data easily, or must it regenerate re·gen·er·ate v. re·gen·er·at·ed, re·gen·er·at·ing, re·gen·er·ates v.tr. 1. To reform spiritually or morally. 2. To form, construct, or create anew, especially in an improved state. the data on another system? Service bureaus should be able to take your blueprints and generate CAD files adequate for rapid prototyping. If you have already generated a CAD model, however, it may be less expensive and faster to work with a service bureau that can handle your data directly. What experience does the bureau have in your specific interest areas? If a bureau has never done a particular applications before, you may not want to risk a critical project with it. Will the bureau supply customer references for similar work? If the bureau subcontractors part of the process, how reliable are the subcontractors capabilities? Especially in the area of metalcasting, no service bureau provides everything in-house. It is important to establish that the bureau has a good relationship with the subcontractor One who takes a portion of a contract from the principal contractor or from another subcontractor. When an individual or a company is involved in a large-scale project, a contractor is often hired to see that the work is done. and that the subcontractor is competent and reliable. |
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