Dövme ürünlerinin kalitesinin geliştirilmesinde olası hata türü ve etkisi analizi tekniğinin uygulanması
Başlık çevirisi mevcut değil.
- Tez No: 55998
- Danışmanlar: DOÇ.DR. TAPTIK YILMAZ
- Tez Türü: Yüksek Lisans
- Konular: Metalurji Mühendisliği, Metallurgical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1996
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 142
Özet
Günümüz serbest piyasa ekonomisi rekabet ortamı içersinde işletmelerin faaliyetlerini devam ettirip, diğer firmalarla arasındaki kalite düzeyini pozitif yönde devamlı arttırabilmeleri için çok sağlam bir Kalite Güvence Sistemine sahip olmaları gerekmektedir. Sağlam bir Kalite Güvence Sistemi de, sistemin çarklarını teşkil eden Kalite Araçlarının ve Kalite Tekniklerinin uzman kişiler tarafından işletmenin bütün bölümlerinde tam ve doğru uygulanması ile sağlanmaktadır. Bu tez çalışması kapsamında, otomotiv yan sanayi olarak dövme yöntemiyle çelik parçaların üretimini gerçekleştiren bir kuruluşa, kalite tekniklerinden Olası Hata Türü ve Etkileri Analizi (OHTEA) dövme prosesine ve bir parça üzerinde uygulamalı olarak yürütülmüştür. Bu çalışma, hem dövme teknolojisi ile ilgili kritik ve temel noktalan ortaya koymuştur, hem de OHTEA kalite tekniğinin dövme sektöründe karşılaşılan temel problemler üzerinde uygulamalı olarak tatbik edilmesi ile sektörün geneline dövme kalitesinin arttırılması için gerekli ipuçlarını vermesinden dolayı faydalı bir kaynak olacaktır, XI
Özet (Çeviri)
During the 20th century customer requirements, expectations and needs have been increasing extremely. Therefore, manufacturers do not only trying to meet them but also struggle with their competitors to live. Thus, many companies have to produce the products or services that bear on its ability to satisfy stated or implied needs. The quality of products depend on the production technology, production efforts of all workers, quality system of the company and the approach of Top Management. The most important concept of quality is that quality is not controlled but is produced in the production assembly by educated manpower. Consequently, quality is defined as satisfying the customer by consistently meeting and continuously improving on his requirements. A system is the way a process is designed and a process is the means by which a service or product is delivered to an internal and external customers. In a process, the consequence departments or operators in the production assembly are the suppliers and internal customers of each others. On the other hand, the final user, which is called customer is defined as external customer. Lack of the need of internal customer results in wasted time and has to spend time putting things right, which itself affect the external customer and lack of the need of external customer means the loss of future business. Total Quality Management (TQM) is a strategic approach for producing the best products and services through a process of continuous improvements of every aspect of a company's operation. TQM is an umbrella for a variety of improvement processs from Quality Control (QC) to Quality Function Deployment (QFD), from Statistical Process Control to Failure Mode and Effects Analysis, Taguchi and so on. Therefore, in TQM for providing the objective of finding root causes and selecting the best solutions thus preventing the problem from occuring again, companies have to use some simple data collection tools and techniques and more complex tools mentioned above. XIIThe most important concept of TQM is continuous improvement that companies have to adopt and must be involved in an ongoing effort to seek better levels of performance. Much of the problem in a company are due to inadequate processes. So, we have to trace the following steps to make improvements. a) Find the problem, b) Study the conditions or environment around the problem, c) Develop several solutions to solve the problem, d) Evaluate the solutions to find the best one, e) Implement the best solution, f) Compare the actual results against the expected results, g) Make adjustments for further improvement. The quality level of products and the cost of products are the main factors that affect the market share of companies. Cost of quality is identified as cost of activities to implement the expected quality, that are inspection, educated manpower, testing in a process and failure costs, and to get things wrong, that are waste time, scrap and rework in a manufacturing process. Quality cost is divided into following 4 categories.. Prevention costs: The amount spent to ensure that things are done right first time such as training, Quality Assurance System.. Appraisal costs: Amounts spent on inspection, testing, auditing and other checking of products & services of any stage.. Internal failure costs: Amounts spent putting things right while a product or service is still in the company's possession such as rework, scrap, waste, allowed, budgeted variance.. External failure costs: Amount spent of a product or service has passed into the customer's hand that are warranty claims, customer allowance, loss of customers. TQC is based on improving the quality of all the inputs to the business including material, labor, equipment and information. So, the success of process are directly proportional with the quality of inputs. Statistical Quality Control tools are used to understand the variation of quality. whether in specifications or out. The resultant trends may show that there is a set of problems causing the products to be close to specification. So, it may be possible to change the process and improve the specification. The main important tools are described below:. Brainstorming: This technique is a group of activity to develop an exhaustive list of ideas about a subject, that is a problem, failure, fault, for finding possible problems XIIIcausing a symptom, causes of problems, solution to problems and alternative manufacturing processes and test methods.. Cause-and-effect diagram: This technique is also known as the fishbone diagram or lshikawa diagram. The effect is the quality charecteristic that is under investigation; the problem that needs to be solved, the effect that needs to be improved or controlled. Improvements are made by the removal or prevention of the factors that cause the effect. This diagam consists of 6 main causes, manpower, machinery, materials, methods, media and measurements and subcauses of these main causes. Causes are found out by using brainstorming with asking the questions why and how?.. Check Sheets: Check sheets are used to collect data for confirming a thought about problem and monitoring the changes that occur as a result of actions taken to remedy a problem.. Histograms: Histograms are used to arrange and display data to see the variation easily..Also it shows the frequency of occurence of whatever is being measured compared with the frequency of another.. Pareto Charts: Pareto charts are means of prioritizing that action, since all problems cannot be tackled simultaneously and shows data classifications in the scending order from left to right.. Process Flow Charts: Process flow charts shows the steps of operations to understanding a process and it defines the starting and stopping points of the process.. Control Charts. Control charts are used to monitor a process to rapidly identify when the process is out of control and therefore to prevent nonconformities from the process on time. The most important Quality Management Techniques are Quality Function Deployment (QFD), Fault Tree Analysis (FTA), Design of Experiment (DoE) and Failure Mode & Effect Analysis (FMEA). QFD is a cross-functional planing tool which ensures that the quality charecteristics, requirements or wishes important to the customer and can then deploy them from initial research and product design to distribution after sales service. QFD uses a series of matrix diagrams to link the needs of external customers to internal process by asking the following questions. What is the requirement9, Which is the most important9, How can we achieve it?. QFD not only sets the requirements, but brings the voice of the customer impact the pocesses, subprocesses and activities, while deploying quality, capabilities, costs and reliability. The benefits of QFD are:. Reduced development time, XIV. Fewer late changes,. Greater customer satisfaction,. Reduced start-up problems,. Reduced start-up costs. The primary tool of QFD is the“house of quality”. House of quality is a correlation matrix used to define relationships between objectives and strategies. The general steps of QFD approach are:. Translating customer needs into design requirements such as important functions and features.. Changing the design requirements into critical charecteristics and specific parts required.. Finding the manufacturing operations and critical process features for the critical charecteristics and specific parts.. Developing production requirements for the manufacturing operations. DoE concepts can be used to plan experiments for the least number of test runs in the product development phase. Using DoE, we can find the nominal values and tolerances that will achieve design goals. The Taguchi Method, is a popular technique for identifiying the design needs which really affect the overall performance of a system and then to establish those parameters which control the factors. FMEA is a methodology to maximize the satisfaction of the customer by eliminating and/or reducing known or potential problems by the team, forms by- experienced and talented people. Also, it evaluates and identifies a system, design, process or service for possible ways in which failures (problems, risks, errors) can occur and after that corrective actions are identified to prevent the failures from occuring. The benefits of FMEA are: Improves the quality, reliability and safety of the products or service. Helps define the corrective action. Helps identify critical and / or significant charecteristics. Helps error identification and preventation. Helps increase customer satisfaction. Reduces product development time and costs. Lists potential failure and identifies their affects. Develops early criteria for manufacturing process, assembly and service. XVAn FMEA program should start:. When new systems, designs, products, processes or services are designed.. When existing systems, designs, products, processes or services are about to change regardless of reason.. When new applications are found for the existing conditions of the systems, designs, products, processes or services.. When improvements are considered for the existing systems, designs, products, processes or services. There are 4 types of FMEA to apply. These are:. System FMEA ; is used to analyse systems and subsystems in the early concept and design stage that focuses on potential failure modes between the functions of the system caused by system deficiencies.. Design FMEA ; is used to analyze products before they are releassed the manufacturing that focuses on failure modes caused by design deficiencies.. Process FMEA ; is used to analyze manufacturing and assembly processes that focuse on failure modes caused by process or assembly deficiencies.. Service FMEA ; is used to analyze service before they reach the customer that focuses on failure modes ( mistakes, errors ) caused by system or process deficiencies. There are 3 components in FMEA which help us to define the priority of failures:. Occurence (O): Frequency of the failure. Severity (S): Seriousness of the failure. Detection (D): Ability to detect the failure before it reaches the customer. The priority of problems is articulated via the Risk Priority Number (RPN) RPN is a product of the O, S, D. Even it is neither a standard nor a universal number for the problems which has RPN equal or greater than 50 means, problems needs to take corrective actions. Forging is defined as manufacture by means of deformation in conjunction with heating, separating, (and joinig) of a workpiece without permanent work hardening, Forging is divided into three main groups that are open-die forging, closed-die forging and rough forging. In the open-die forging, material is allowed to flow freely but in the closed-die forging material flow is constrained. Forging is usually carried out after heating to a temperature range at which recoverv and recrystallization operations occur. Before forging operations, forging XVIproducts may be heated in the following different places: * Heating in a furnace, * Induction heating, * Conduction heating ( resistance heating ). Although open-die forged parts tend to require a considerable amount of mechanical machining, closed-die forged parts are often only partly machined. Open-die forging is mainly concerned with single-item or small batch production of workpieces between 1 kg and 386 tons, while closed-die forging of steel is on medium and large batch production of parts betweeen 50gr and 1.65 tons. Generally forging defects are divided into following categories: 2 Surface marks or cracks; Caused by mistakes during formation of the initial or intermediate shapes. 2. 1 Marks on the finished forging due to defects in the surface of the initial or intermediate shapes, 2 2 Overlaps resulting from bending of intermediate flash, 2.3 Marks due to cracks in dies, 2.4 Cracks caused by : 2.4.1 sharp edges of the forging, 2.4.2 sharp concernss of the forging, 2.4.3 too much material, 3 Inadequately filled forging due to an insufficient volume of material, inexact positioning or high lubricant gas pressures. 4 Mistakes in the material structure, such as defects in the grain flow. Advanced forging techniques are; * Precision and high-precision forging, * Hot impact extrusion, * Warm forging, * Hot-die forging of powder -metal preform, * Hot-die, isothermal and superplastic forging. XVII
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