Hızlı prototip üretim teknolojileri
Başlık çevirisi mevcut değil.
- Tez No: 66850
- Danışmanlar: YRD. DOÇ. DR. MUZAFFER ERTEN
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Makine Malzemesi ve İmalat Teknolojisi Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 107
Özet
ÖZET Bu çalışmada, Hızlı Prototip Üretim Teknolojileri (HPÜT) incelenerek, bir StereoLitografi (SL) uygulaması yapılmıştır. Sistemler, birbirleri ile karşılaştırmalı olarak ele alınarak, teknoloji seçimi için gerekli bilgilerin açığa çıkması hedeflenmiştir. Çalışmanın birinci bölümünde, ürün geliştirme aşamasında prototip ihtiyaçları incelenmiştir. Farklı ürün geliştirme aşamalarının tanımlanabilmesi için geometrik, fonksiyonel, teknik prototiplere ihtiyaç vardır. İkinci bölümde, en yaygın kullanılan beş HPÜT incelenmiştir. Tüm HPÜT, tabakalı imalat yöntemleri olarak bilinmektedir. Prototipler tabaka tabaka imal edilmektedir. Malzeme kullanımları yönüyle; fotopolimer malzeme kullanılan yöntemlerden SL yöntemi ve Solid Ground Curing (SGC) yöntemi ele alınmıştır. Termoplastik malzeme kullanılan yöntemler olarak; Selective Laser Sintering (SLS) ve Fused Deposition Modelling (FDM) sistemleri incelenmiştir. Son olarak ta Laminated Object Manufacturing (LOM) sistemi tanıtılmıştır. SL yönteminde, sıvı fotopolimer reçine üzerine gönderilen lazer ışını ile malzemenin katılaştırılması sağlanmaktadır. Lazer, parçanın Bilgisayar Destekli Model (BDT) verilerini kullanarak önce kesit sınırlarını daha sonra iç bölgeleri katılaştınr. Parçanın imal edildiği platform üzerinde, platform ile parça arasında destek yapılan oluşturulur. Daha sonra, parçanın ilk tabakasından başlanarak parça bitinceye kadar, tarama aynaları ile istenilen kesit formlarında katılaştırma yapılır. İmalatı tamamlanan parça platformdan alınarak, polimerizasyona uğramamış sıvı bölgelerin katılaştırılması için son ısıtma işlemi tabi tutulur. SGC yönteminde, önce bir cam levha üzerinde istenilen kesit formunda bir maske oluşturulur. Daha sonra, bir lazer ışığı bu maske üzerinden sıvı fotopolimer reçinenin yüzeyine gönderilerek maskede oluşturulan formda katılaşması sağlanır. SLS sisteminde, termoplastik malzeme tozlan bir lazer yardımıyla eritilip daha sonra sinterlenir. FDM yönteminde termoplastik malzeme, lif halinde bir ısıtılmış kafaya beslenir. Bu kafa bilgisayar kontrollü olarak istenilen kesit formlarını tabaka tabaka oluşturur. LOM sisteminde, kağıt türü malzeme ısıya ve basınca duyarlı bir yapıştırıcı ile kaplanmıştır. Bir rulodan beslenen malzeme istenilen formda lazerle kesilerek, ısıtılmış bir silindir yardımıyla bir önceki tabakaya yapıştırılır. İşlem parça bitinceye kadar devam eder. xıÜçüncü bölümde, BDT işlemleri hakkında bilgiler verilmiştir. Bu işlemler, bir Hızlı Prototip Üretim (HPÜ) sisteminde üretim öncesi işlemleri kapsar. Parçanın katı modelli uygun bir yazılımda yapılarak, HPÜT giriş formatı olan STL formatında kaydedilir. Ayrıca bu bölümde, parçanın üretimi sırasında ihtiyaç duyulan destek elemanlarından bahsedilmiştir. Çalışmanın dördüncü bölümünde, HPÜ sistemlerinde kullanılan formatlar ve firmalara göre yazılımlar incelenmiştir. Beşinci bölümde, HPÜ sistemlerinin kalıp imalatında kullanılmaları ele alınmıştır. Altıncı bölümde, yapılan SL uygulaması ve üretimde kullanılan parametreler verilmiştir. Sonuç bölümünde, parçanın üretimi sırasında önemli olan noktalar ele alınmıştır. Üretim süresini, parça kalitesini ve maliyetini etkileyen faktörler incelenmiştir. xıı
Özet (Çeviri)
SUMMARY RAPID PROTOTYPING MANUFACTURING (RP&M) TECHNOLOGIES Recent years ago, a new technology of rapid prototyping entered the market place to create a huge impression on industry, offering the opportunity to greatly reduce the lead times from conception to market of new products. This first generation system, using liquid baths of photopolymer and laser curing techniques, produced models directly from computer-aided design (CAD) files. After a couple of years, as new vendors introduced their products in this field, and customers have gained much experience and understanding of this new technology, a much more serious and demanding approach has been required. This is reflected in the thorough evaluations of the different systems and technologies available today by customers looking for a technology that will best fit their needs. Rapid Prototyping (RP) is just such a technology but one whose requirement for high integrity 3D product representation has a direct impact on the type of CAD system used. The current level of development of Solid Modelling system gives rise to the opportunity of radically changing the traditional way of designing. Many companies engaged in production processes have a requirement for a model or prototype component to be manufactured before commencing full scale volume production. Such models can be used for“form fit and function”trials or indeed for secondary manufacturing processes such as casting and moulding. Model-making is an integral of the design process behind almost any new product, either for“form, fit and function”testing, or“aesthetic visualisation”or as casting molds for actual production. Model-making has been considered a highly-skilled, time-intensive craft, involving considerable expense and weeks of work. And then, if a design flaw is uncovered, a new model often has to be made. There are several application for models.. Concept. Find out how a particular idea translates into a real- world project. Ensure that all members of the team understand the design.. Fit. Test the design dimensions of a part to check that it fits into the intended assembly.. Form. Check how a proposed design looks (aesthetics) and feels (ergonomics). Perform comparison tests on variations of a design using focus groups.. Function. Check that a product or part meets its specifications. Run wind tunnel, use cycle and harsh environment tests. (This application requires that the model be made in the design material). xni. Bid requests. Help prospective subcontractors understand the design they are bidding on, in order to get faster, more reliable and lower quotes.. Marketing presentations. Let the customer hold the proposed product in his hands, for better understanding of the proposal. Some secondary process which have been successfully used with patterns made by StereoLithography are :. Silicon rubber molds,. Spray metal molds,. Epoxy tooling, and. Direct investment casting. In response, rapid prototyping offers ways to make industrial-quality models and prototypes overnight, directly CAD files, essentially untouched by human hands. Unlike previous CNC technologies that create models by cutting away material from solid models, rapid prototyping systems are based on photo-reactive liquid polymers resins. In the first chapter, an introduction of the subject has been given. The necessity of prototypes in product development has been described. The designations used for the various forms of prototypes, models and specimen which are required in the course of product development vary considerably at generally valid identification of different product development phases and to classify the various forms of prototypes. In the second chapter, various systems of Rapid Prototyping have been described. These are StereoLithography (SL), Fused Deposition Method (FDM), Laminated Object Manufacturing (LOM), Selective Laser Sintering (SLS) and Solid Ground Curing (SGC). All of these are known that layering manufacturing technologies. Parts are built layer by layer. Therefore complex parts are manufacturing easily and quickly in a day. The time of the design process can be decreased by using Rapid Prototyping Technologies. In 1987 an entirely new application of CAD was developed. Stereolithography was the first commercially available layer-additive process to enable the rapid generation of physical objects directly from a CAD model of the desired object. In StereoLithography systems (Figure 1) photopolymer resins are used. In the system, a elevator is located at a distance from the surface of the liquid equal to the thickness of first, bottom-most layer. The laser beam will scan the surface following the contours of the slice. The interior of the contour is then hatched by using a hatch pattern (WEAVE, STAR-WEAVE, QuickCast, and ACES). The liquid is a photopolymer that when exposed the ultra-violet (UV) laser beam solidifies or is cured. The elevator is moved downwards, and the subsequent layers are produced analogously. Fortunately, the layers bind to each other. Finally, the oart is removed from the vat, and the that is still trapped in the interior is usually cured in a special oven (Postcuring Apparatus-PC A). xivRapid Prototyping is therefore very useful in this process, because it is not just a group of new model making techniques but also a new industrial philosophy. In the majority of industry, designers have become used to waiting weeks or months for their designs to be changed into prototypes which can then be checked and tested, manufacturing engineers also wait considerable periods for tooling to be produced before they can start full scale manufacture. With the advent of Rapid Prototyping designers can now have a prototype in a few days instead of waiting weeks or months. These models are used for checking the aesthetics of a design and to check form and fit. Some functional testing of these models is possible where there are no severe mechanical stresses and where the working temperatures are low. The major limitation with Rapid Prototyping at the moment is the limited number of materials available with the different systems and the generally poor mechanical properties of these. However, more materials are being introduced, and the choice of StereoLithography resins for example has grown so that now we have resins which provide snap fit parts or elastomeric type parts. This change in expectation of the waiting time is now becoming more widespread amongst manufacturing engineers and so there is a demand to reduce the time from concept design to manufacture down to a few weeks. This has been possible for many years in some areas with the use of 'soft' tooling, using sprayed metal tooling, resin tooling, plaster cast moulds etc. Although 'soft' tooling can produce many thousands of parts using injection moulding, provided the moulds are plated and treated with respect, it is not suitable for more severe processes such as forging. It is therefore necessary to investigate how Rapid Prototyping can be used to produce hard tooling. Computers have profoundly affected the way of engineers to perform their function. Their introduction has simplified if not eliminated many of the repetitious tasks of the designer and manufacturing engineer. One of such example is the interface between computers and machine tools that has significantly shortened the manufacturing time of many designs and lead to reduced errors. Surface modelers, and more recently solid modelers provided the impetus for the development of manufacturing processes depending on computers. NC machining and now Rapid Prototyping are manufacturing technologies that emerged from the ability to represent objects in a three dimensional co-ordinate system on a computer. NC machining is a well established procedure which is based on material subtraction techniques under the control of a computer. Rapid Prototyping is a much more recent technology which is based on an additive process, but it is also controlled by a computer. Since computers are directly linked to machines and control the operations of these machines, an understanding of the way information is stored in the computers and of the needs of the processing equipment are needed to understand the related accuracy issues. In the early days of Solid Modelling systems all but a few observers were impressed by the notion of representing solid 3D objects within the“mind”of the computer. The xvuLaser r*L }-£3-% XY scanner Beam shaping optics Polymerized layered model Figure 1 Fused Deposition Modelling uses spools of thermoplastic filament as the basic material for part fabrication. The material is heated just beyond the melting point in a delivery head. The molten thermoplastic is then extruded through a nozzle in the form of a thin ribbon and deposited in computer controlled locations appropriate for the object geometry. The FDM system builds parts in multiple thin layers, as is the case with all current RP&M methods. LOM process builds objects in thin layers, but as the name implies, LOM parts are fabricated using laminated sheet materials. Consecutive layers are joined using an adhesive that is both temperature and pressure sensitive. The individual cross-sections are cut using a 25- or 50-watt corbon dioxide (CO2) laser, emitting in the infrared, at a wavelength of 10.6 microns. SLS technique is based on the selective fusing or sintering of small particles by means of a high power, 50-watt CO2 laser. SGC technique involves the use of photopolymer resins but, unlike SL, SGC does not utilize lasers. Rather, each layer is generated through a multi-step procedure. The black toner powder has formed an optical mask. A thin layer of resin is then prepared on a support carrige, which is moved to the exposure station. The glass plate, bearing the mask for that cross-section, is registered above the subsrate, and then exposed to flood UV radiation from a high power UV emitting lamb. The liquid photopolymer resin is then selectively cured wherever the mask is transparent. In the third chapter, CAD processes have been described. RP&M systems are highly depend on their electronic database input. Simply stated, they are three-dimensional duplicating machines. These systems take an electronic description of a three- dimensional object and reproduce that description into a solid object. The geometric description required for current RP&M equipment are provided by CAD systems. This chapter also involves support structure and its types using in RP&M xvRapid Prototyping is therefore very useful in this process, because it is not just a group of new model making techniques but also a new industrial philosophy. In the majority of industry, designers have become used to waiting weeks or months for their designs to be changed into prototypes which can then be checked and tested, manufacturing engineers also wait considerable periods for tooling to be produced before they can start full scale manufacture. With the advent of Rapid Prototyping designers can now have a prototype in a few days instead of waiting weeks or months. These models are used for checking the aesthetics of a design and to check form and fit. Some functional testing of these models is possible where there are no severe mechanical stresses and where the working temperatures are low. The major limitation with Rapid Prototyping at the moment is the limited number of materials available with the different systems and the generally poor mechanical properties of these. However, more materials are being introduced, and the choice of StereoLithography resins for example has grown so that now we have resins which provide snap fit parts or elastomeric type parts. This change in expectation of the waiting time is now becoming more widespread amongst manufacturing engineers and so there is a demand to reduce the time from concept design to manufacture down to a few weeks. This has been possible for many years in some areas with the use of 'soft' tooling, using sprayed metal tooling, resin tooling, plaster cast moulds etc. Although 'soft' tooling can produce many thousands of parts using injection moulding, provided the moulds are plated and treated with respect, it is not suitable for more severe processes such as forging. It is therefore necessary to investigate how Rapid Prototyping can be used to produce hard tooling. Computers have profoundly affected the way of engineers to perform their function. Their introduction has simplified if not eliminated many of the repetitious tasks of the designer and manufacturing engineer. One of such example is the interface between computers and machine tools that has significantly shortened the manufacturing time of many designs and lead to reduced errors. Surface modelers, and more recently solid modelers provided the impetus for the development of manufacturing processes depending on computers. NC machining and now Rapid Prototyping are manufacturing technologies that emerged from the ability to represent objects in a three dimensional co-ordinate system on a computer. NC machining is a well established procedure which is based on material subtraction techniques under the control of a computer. Rapid Prototyping is a much more recent technology which is based on an additive process, but it is also controlled by a computer. Since computers are directly linked to machines and control the operations of these machines, an understanding of the way information is stored in the computers and of the needs of the processing equipment are needed to understand the related accuracy issues. In the early days of Solid Modelling systems all but a few observers were impressed by the notion of representing solid 3D objects within the“mind”of the computer. The xvuLaser r*L }-£3-% XY scanner Beam shaping optics Polymerized layered model Figure 1 Fused Deposition Modelling uses spools of thermoplastic filament as the basic material for part fabrication. The material is heated just beyond the melting point in a delivery head. The molten thermoplastic is then extruded through a nozzle in the form of a thin ribbon and deposited in computer controlled locations appropriate for the object geometry. The FDM system builds parts in multiple thin layers, as is the case with all current RP&M methods. LOM process builds objects in thin layers, but as the name implies, LOM parts are fabricated using laminated sheet materials. Consecutive layers are joined using an adhesive that is both temperature and pressure sensitive. The individual cross-sections are cut using a 25- or 50-watt corbon dioxide (CO2) laser, emitting in the infrared, at a wavelength of 10.6 microns. SLS technique is based on the selective fusing or sintering of small particles by means of a high power, 50-watt CO2 laser. SGC technique involves the use of photopolymer resins but, unlike SL, SGC does not utilize lasers. Rather, each layer is generated through a multi-step procedure. The black toner powder has formed an optical mask. A thin layer of resin is then prepared on a support carrige, which is moved to the exposure station. The glass plate, bearing the mask for that cross-section, is registered above the subsrate, and then exposed to flood UV radiation from a high power UV emitting lamb. The liquid photopolymer resin is then selectively cured wherever the mask is transparent. In the third chapter, CAD processes have been described. RP&M systems are highly depend on their electronic database input. Simply stated, they are three-dimensional duplicating machines. These systems take an electronic description of a three- dimensional object and reproduce that description into a solid object. The geometric description required for current RP&M equipment are provided by CAD systems. This chapter also involves support structure and its types using in RP&M xv
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