Basınçlı döküm yöntemiyle üretimde OTHEA ve HAA teknikleri uygulaması ile ürün ve proses optimizasyonu
Ooptimising product and process by fmea and fta techniques on die casting production
- Tez No: 66597
- Danışmanlar: PROF. DR. YILMAZ TAPTIK
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Metalurji Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Malzeme Bilim Dalı
- Sayfa Sayısı: 236
Özet
ÖZET Bu çalışmada orta ölçekli bir basınçlı döküm fabrikasında, kalite güvence çalışmaları kapsamında kalite tekniklerinden OHTEA (Olası hata türleri ve etkileri analizi) ve HAA (Hata ağacı analizi) tekniklerinin uygulamaları gerçekleştirilmiştir. Kalite tekniklerinin başarılı bir şekilde uygulanabilmesi öncelikle o prosesin çok iyi bir şekilde bilinmesiyle sağlanabilmektedir. Bu sebepten dolayı çalışmada ilk olarak basınçlı döküm prosesi hakkında gereken bilgiler verilmiş, basınçlı döküm makinaları ve kalıpları birçok şekille birlikte tanıtılmış, basınçlı döküm alaşımları tablolar yardımıyla tüm özellikleriyle anlatılmış bununla birlikte bitirme işlemleri gibi önemli kademeler de ifade edilmiştir. Ayrıca bu bölümde döküm sırasında ki, döküm şartlan, kalıp ve faz ayarlan ve hata oluşumunda ki etkin parametreler değerlendirilerek uygun döküm şartlan izah edilmeye çalışılmıştır. Kalite güvencesi ve kalite anlayışının ifadesi kalite teknikleri veya tüm geliştirici faaliyetlerin de uygulanmasının gerekliliğini ortaya koyacaktır. Bununla birlikte ülkemizde kalite yaklaşımının kısmende olsa gözardı edilişi veya hakettiği önemin verilmeyişi, kalite güvence yaklaşımının bu çalışmada verilmesi gerekliliğini doğurmuş ve bu şekilde kalite tekniklerinin ifadesi kolaylaşmıştır. Uygulanan kalite teknikleri tümüyle aynı amaca hizmet etmektedir. Genel olarak hatayı oluşturan parametrelerin durumu işaret edilerek sebeplerin dikkate alınması sağlanır ve bu etkiler doğrultusunda bir çalışma programı geliştirilerek proseste üretim bu anlayış çerçevesinde gerçekleştirilir. Kalite teknikleriyle bu faaliyet gerçekleştirilirken, kalite tekniklerinden herhangi bir tanesinin tek başına kullanılması söz konusu değildir. Herbir kalite tekniği, bir diğerinden elde edilebilecek veriye ihtiyaç duymaktadır veya bu şekilde daha etkili bir sonuç verir. Bu yaklaşım doğrultusunda tüm kalite teknikleri anlatılmış olmakla birlikte uygulaması yapılacak olan OHTEA ve HAA teknikleri oldukça geniş bir kapsam çerçevesinde değerlendirilmiştir. Bu iki tekniğin temel anlayıştan ortaya konarak, kalite faaliyetleri çalışmalarında ki gereklilikleri ifade edilmiştir. Bu tez çalışmasında son olarak OHTEA ve HAA tekniklerinin orta ölçekli bir basınçlı döküm fabrikasında ki uygulama çalışmalarına yer verilmiştir. Bu tekniklerin uygulanmasında öncelikle proses geliştirme faaliyetleri arasında ilk olarak düşünülmesi gereken kılçık diyagramı, prosesten haberdar kişilerin katılımıyla bir beyin fırtınası şeklinde oluşturulmuştur. Bununla birlikte fabrikada ki prosesin tanımlanması ve üretim kalitesinin anlaşılması amacıyla geçmiş üretimler incelenmiş ve bu doğrultuda pareto analizleri yapılarak hata değerleri grafiklere dökülmüştür. OHTEA tekniğinin uygulanması düşünüldüğü parçalar incelenmiş ve bu parçalara ait ürün sinoptikleri, kontgamlar ve talimatlar formlar halinde verilmiştir. Bununla birlikte OHTEA tekniğinin uygulanmasıyla OHTEA formları düzenlenmiş ve bu formlara çalışmada yer verilmiştir. HAA tekniği proses bazında en çok problem yaratan hatalar üzerinde denenmiş ve bu hatalara ait HAA diyagramları oluşturulmuştur. Oluşturulan bu diyagramlar, tez çalışmasında uygulama çalışmaların gerçekleştiği son bölümünde yer almıştır.
Özet (Çeviri)
One of the oldest methods of casting molten metal is by gravity pouring into sand molds. That method, with many refinements, is still practiced in our present so called sand foundries. In the course of time, the jewellery trade by its requirements for sharper outlines and smoother castings developed a process utilising plaster or gypsum molds. This method resulted in parts having a finer surface finish than sand castings, but the disadvantage that, as in sand casting, the mold had to be destroyed to remove the cast part. The effects of these factors caused the using of iron molds in casting. Producing of sharper, better and smoother cast parts provided by using iron molds. The next logical step was to improve accuracy and appearance of cast parts further by applying pressure to force the molten metal into strong steel molds, instead of merely relying on gravity pressure. Therefore the die casting was begun to use in 1950's. The basic die casting alloys are zinc, magnesium, aluminium. The other die casting alloys are tin, lead and copper. Zinc base alloys, having a slightly higher melting point than tin and lead. Zinc alloys are used for approximately 60 per cent by weight of all die cast parts, chiefly because of economies resulting from the ease and speed with which they can be cast. In many instances, speeds of up to 500 cycles/hr can be obtained. In addition, the low casting temperature of these alloys results in low fuel cost, low die cost, and low die maintenance. They have good mechanical properties and can be readily machined and economically finished. Aluminium has increased 30 per cent in die casting. The properties of aluminium; 1. are light in weight, 2. have excellent creep resistance, electrical and thermal conductivity, and tarnish resistance, 3. are competitive in cost with cast iron and steel casting, formed steel parts, and many other types of castings, 4. can be commercially and economically finished. Magnesium die castings are used mostly for applications where lightness, the principal advantage of the metal, is a main requirement. Such equipment as portable typewriters, stenotype and other business machine cases and housings, cameras, optical instruments, portable tools, and similar devices utilize magnesium die castings. Magnesium die castings are also used in reciprocating and moving parts in textile, conveying, and packaging machinery. The salient properties of high strength, toughness, and corrosion and wear resistance of copper alloy die castings particularly brass make them suitable for many varied uses and open to industry a source of engineering parts having the accuracy, intricacy, stability, and economy of the die casting process. The applications of brass die castings are far too varied to give in detail, but the following partial list may suffice to indicate their potentialities: automotive gears, transmission forks, clutch xvparts, shock absorber parts, pumps, bearings, electrical switch board parts, contactor parts, brush holders, refrigerator parts, steam fittings, valves, trunnion bearings, oil burner parts, general engineering fittings, and household hardware. Tin die castings were extensively used in the past for antifriction bearings, especially for automotive use. This use, however, has greatly dwindled, and today tin alloy die castings are not being used for bearings because of the substation of other materials and better methods for producing bearings. Tin die castings are used particularly for their corrosion resistance in such parts as soda fountain equipment, milking machines, syrup pumps, dental appliances, and surgical instruments. Finally, lead alloys are usually applied where low cost, noncorrodible metal is required and when strength, hardness, and other mechanical properties are unimportant. Parts that must withstand the action of strong mineral acids, such as fire extinguisher parts, batteries, and chemical apparatus, are produced as lead die castings. They are used in X-ray equipment because of their resistance. The mechanical properties of both lead and tin alloys are very low, and die casting of them therefore represent only a very small percentage of the total die casting consumption. In order to make successful die casting, there are some requirements which must be done. These requirements; 1. A smoothly working casting mechanism, properly designed to hold and operate a die under pressure. 2. A properly designed and constructed die. 3. A suitable alloy All three of these factors must be considered together not individually. Good castings cannot be produced if one of them is not up to standard. For instance, if a perfectly designed and constructed die is mounted on a well operating casting machine, a poor die casting will result if the alloy is inferior or not in accordance with standard specifications. Similarly good casting cannot be produced from a perfectly balanced alloy if either the die or the machine is not up to standard. The successful production of die casting also requires, in some cases, the setup of low cost, high production, gang machining equipment; facilities for mechanical, chemical, or organic or metallic finishing of the castings; facilities for rapid but accurate inspection, both during and following the casting, machining, and finishing operations; and last but not least, a staff of trained engineers, metallurgists, and technicians to effect the coordination of all factors. Parts must first be suitably designed before they can be produced as the castings; dies must be properly designed and constructed; and alloys must be designated to meet the service requirements of the part and must be carefully prepared and rigidly controlled within the limits set by standard specifications. Quality assurance activities are very important and have some difficulties. However it must be applied in die casting industry. In order to assure quality, it is therefore necessary first to ensure that all the requirements for the total presentation are known. In other words, the customer's requirements must be sufficiently detailed to be fully understood by the supplier so that there are no areas of doubt as to the service requirements. Quality assurance requires the total integration and control off all elements within a particular area of operation so that none is subservient to the other. These elements cover such aspects as administration, finance, sales, marketing, design, xviprocurement, manufacture, installation, commissioning and even, as we have seen, decommissioning. Quality assurance is a management function which cannot be delegated and quality assurance is;. Cost effective. An aid to productivity. A means of getting it right first time every time. The responsibility of everyone The background to quality assurance is the customer-supplier relationship. The ultimate purpose of any quality system is to ensure complete satisfaction by the customer with the goods or services provided by the supplier. Thus, the customer- supplier relationship is an active rather than a passive one. The first step in this relationship is to determine the customer. Depending on the nature of the product or service, either the customer will, or should, provide a full specification of requirements, or the supplier, by the market research and feedback from the market place, will produce services or goods to a presumed customer requirement. Any quality system must, therefore, involve the customer, either directly or indirectly. Although this customer-supplier relationship may be regarded, at least partly, as external to the supplier's activities, the same philosophy applies internally within a supplier's workplace at each stage of the operation. The customer becomes the user or consumer of the next stage in the operational process and so a quality system applies through the whole complex of activities within any organisation. Figure 1 typifies this internal customer-supplier relationship. SALES & MARKETING, ADMINISTRATION, ACCOUNTS, PUBLIC RELATIONS, PERSONNEL, TRAINING Figure 1: Internal customer-supplier relationship Quality tools and techniques are usually applied in quality assurance activities. The quality tools; 1. Pareto analysis, 2. Cause and effect diagram, 3. Histogram, 4. Check sheet, 5. Stratification, 6. Control chart, 7. Scatter diagram. Quality techniques, which are used in quality assurance activities, are XVH1. Quality Function Development (QFD) 2. Failure Modes and Effect Analysis (FMEA) 3. Faulty Tree Analysis (FT A) 4. Statistical Quality Control (SPC) 5. Design of Experiment (DoE) Failure Modes and Effect Analysis (FMEA) and Faulty Tree Analysis (FT A) are important quality techniques. A Failure Mode and Effect Analysis is an engineering technique used to define, identify and eliminate known and potential failures, problems, or errors, from the system, design, process and service before they reach the customer. The analysis of the evolution may take two courses of action. One, using historical data, similar data for similar products and or services, warranty data, customer complaints and any other appropriate information available, to define failures. Two, using inferential statistics, mathematical modeling, simulations, concurrent engineering, reliability engineering to identify and define the failures. Using an FMEA, doesn't mean that one approach is better than the other, or that one is more accurate than the other, Both can be efficient, accurate, and correct if done properly and appropriately. Any FMEA conducted properly and appropriately will provide the user useful information that can reduce the risk load in the system, design, process and service. This is so, because it is logical and progressive potential failure analysis method which allows the task to be performed more effectively. FMEA is one of the most important early preventive action in system, design, process or service which will prevent failures and errors from occurring and reaching the customer. Generally, it is accepted that there are four types of FMEA. The four types are; 1. System FMEA: is used to analyse system and subsystems in the early concept and design stage. A system FMEA focuses on potential failure modes between the functions of the system caused by system deficiencies. It includes the interactions between system and elements of the system. 2. Design FMEA: is used to analyse products before they are released to manufacturing. A design FMEA focuses on failure modes caused by design deficiencies. 3. Process FMEA: is used to analyse manufacturing and assembly processes. A process FMEA focuses on failure modes caused by process or assembly deficiencies. 4. Service FMEA: is used to analyse services before they reach the customer. A service FMEA focuses on failure modes (tasks, errors, mistakes) caused by process or system deficiencies. The FMEA will identify corrective actions required to prevent failures from reaching the customer, thereby assuring the highest durability, quality and reliability possible in a product or service. A good FMEA is one which;. Identifies known and potential failure modes. Identifies the causes and effects of each failure mode. Priorities the identified failure modes according to the Risk Priority Number (RPN) the product of frequency of occurrence, severity and detection. Provides for problem follow up and corrective action xviiiThere is a FMEA flowchart in Figure 2. Identify the system/ unit/ company, which will be analyzed Seperate the system elements Collect the element's references and design informations Choose a element for analysing The work is finished Figure 2: FMEA flowchart xixFaulty tree analysis is a systematic way of identifying all possible faults that could lead to system fail danger failure. It is a top down method starting from the fail danger failure as the top event, a logic diagram is constructed showing all possible combinations of faults and conditions that could cause the top event. This logic diagram is built up from a number of AND and OR gates. Tree diagrams are extremely useful in helping visualise and analyse more complex systems or problem situations. Tree diagrams can be used as either reactive or prospective analysis tools. When used reactively to investigate accidents and events, they are called fault or root cause trees. Tree diagrams may also be used prospectively to systematically plan and organise requirements for organisations, programs and projects, or future improvements to current plant operations. Used for goal attainment, they are called positive trees. Tree diagrams can also be used to analyse the probability of an event happening, used in this fashion, they are termed risk or probability trees. Figure 3 shows the use of AND and OR gate symbols to represent two different ways of combining probabilities. TOP EVENT AND P(Top Event)=P(A or B)=P(A)+P(B) P(Top Event)=P(A and B)=P(A)xP(B) Figure 3: The Basic FTA diagrams Finally, those results were gained in this thesis. 1) These techniques can not be used alone. All of them need the others. Primarily fishbone diagram was prepared by brainstorming in this work. The fishbone diagram has the basic information about process. Therefore making of fishbone diagram before FMEA and FTA is very useful. 2) FMEA and FTA are applied before process. These techniques determine the probable failures and search reasons of these failures. xx3) During the using of FMEA and FT A in this work, old productions were considered and by making of pareto analysis, results of old productions were utilized. Than which failures were serious was decided. 4) Another important problem is selection of quality techniques. Quality techniques have some advantages and disadvantages. For instance one of them can be useful in die casting process, but another one may have disadvantages in the same process. Therefore selection of quality techniques is very important. 5) The quality techniques are practiced successfully. The pareto analysis and the fishbone diagram supported FMEA and FTA techniques. FMEA and FTA techniques were started, after the selection of failure had been made by considering of their results. XXI
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