Tasarımda kalite ve FMEA metodu

Bilgin, Mehmet
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Fen Bilimleri Enstitüsü
Geçmişte uzman bir servisin sorumluluğunda olan kaliteyi sağlama işlevi bugün işletmenin her düzeyine yaygınlaştırılmıştır. Artık amaç, ürettikten sonra kontrol ederek kaliteyi korumaktan çıkmış; daha tasanm ve planlama aşamasında kalite yaratmaya başlama ve bunu geliştirerek sürdürme işi haline gelmiştir. Bu amaç doğrultusunda ürünün ve prosesin tasarımı ve geliştirilmesinde kullanılan tekniklerden biri de "Hata Türü ve Etkisi Analizi (FMEA)B 'dir. Hata türü ve etkisi analizi (FMEA), potansiyel ürün veya proses hatalarını bu hataların emniyet ve fonksiyon açısından etkisini ve bu hatalara karşı korunmak için atılması gereken adımların neler olduğunu belirleyen sistematik bir yaklaşımdır. Bir proses FMEA; proses hata türüyle ilişkili ürünün, hata potansiyelini belirler, hataların müşteri üzerindeki etkilerinin potansiyelini ortaya çıkarır, potansiyel imalat ve montaj prosesi hata sebeplerini belirler ve hataları ortadan kaldırmaya yönelik bütün olasılıkları dener. Bir proses FMEA çalışması; proses geliştirilmesinde mühendislerin deneyim ve geçmişteki problemlere dayanarak, mantık örgüsü içerisinde, yanlış gidebilecek her birimin analizini içeren düşüncelerini özetler ve normal oalrak proses gereksinmelerini geliştirirken gözden geçireceği zihinsel disiplinle parallelik gösterir.
As recently as twenty years ago, most quality control departments were inspection operations. Today quality concept or quality assurance is much more inspection. Some companies have even delegated most of the inspection responsibilities to production workers, leaving the quality professionals free to concentrate on quality improvement activities. At other companies, quality control people still spend most of their time looking for defective products. This is a poor use of human resources. Quality control people should be helping to prevent problems rather than just reacting to them. What does a modern quality system look like? First of all, it is customer focused. Products are designed and produced and services provided to meet customer requirements. There is also a recognition of internal (to the company) as well as external customers. Everyone in the company identifies who their customers and suppliers are and what they require. The practice of each department optimizing its own operations, without regard to the needs of other departments in the company, is no longer acceptable. Another characteristic of a modem quality system is that the quality improvement process is led by top management. If the responsibility for quality in delegated to the quality department, then everyone in the company understands that quality is not a key management concern. There must be active, visible involvement by top management in the quality effort. It is important that everyone understand their specific responsibilities. for quality. Although it is true "Quality is everyone's job", it is also true that everyone has a different responsibility, depending on his or her position within the company. Product development is responsible for designing new products which meet customer requirements and which can be consistently and economically produced by manufacturing (manufacturing is a customer of product development). Purchasing must not buy materials on price and delivery alone. Top management - IX - must show by word and action that quality is of utmost importance to the companies survival. A fourth characteristic of a modern quality system is that it is defect prevention oriented rather than being focused on defect detection. Quality through inspection is not enough and is too expensive. Although it might be necessary to do some sort of inspection or audit of finished products, a company's quality efforts should be focused on preventing defects from occurring on doing the right thing right thing right the first time. A modem quality system works on controlling processes rather then focusing on finished products. If the process is right, the finished product will be right. Finally, quality must be way of life. Quality issues are discussed at every management meeting: there is no consideration given to shipping on unacceptable product in order to meet production schedules. Old technology is proven' to be dependable. All employees are given training in modem quality concepts and methods. Everyone in the company is allowed to participate in the quality improvement effort. A modem quality system can be divided into two parts: *quaiity of design,.quality of conformance. Quality of design refers to those activities which assure that new or modified products and services are designed to meet customer needs and expectations, and are economically achievable. Quality of design is primarily the responsibility of research and development (R&D), process engineering, market research, and related groups. Quality of conformance refers to manufacturing products or providing services meet previously determined and clearly defined specifications. Production, scheduling, purchasing, and shipping have primary responsibility for quality of conformance. Management has the responsibility to see that people have the training, tools and other resources to do their jobs, and have the opportunity to become involved in the quality improvement process. Quality In Engineering Design "Quality cannot be inspected out of a product, it must be built in". This statement is heard so often that we might start to think that everyone is busy doing just that designing and building quality into products, processes, and services. But the reality is that few people know how to "build quality". What passes for "building" in many companies is -X- problem solving. Problem solving is, of course, an important activity, but wouldn't it be better if we could design products and process so that the problems never occurred in the first place. There are companies where problems are prevented at the design phase, where product quality is addressed before the specifications are issued. At these companies some or all of the following six methods are used by design and development engineers: Concurrent Engineering, *Quality Function Deployment (QFD),.Reliability Analysis,.FAILURE MODE AND EFFECT ANALYSIS ( FMEA) *Taguchi Methods,.Statistically designed experiments. Concurrent Engineering refers to the integrated development of products, their manufacturing processes, and support system. Rather than have research and development design a new product, pass the new design on to manufacturing engineers to develop manufacturing procedures. The result is reduced development and manufacturing cost, and a product that meets customer expectations. Concurrent engineering is more an engineering philosophy than a method. Quality Function Deployment (QFD) is a highly structured technique for assuring that the "voice of the customer" is not lost in the noise of product development. It is described the following four basic components: Planning Matrix _ The rows of this matrix represent customer requirements, and the columns list final product control characteristics. Deployment matrix _ Customer requirements and product control characteristics are listed in this matrix, so that critical component characteristics can be identified. Process plan and Quality Carts _ The process plan chart shows the relationship between manufacturing processes and critical component characteristics. Operation instructions _ This document describes operations which plant personnel must perform to assure that critical product requirements are met. -XI- Reliability Analysis addresses the quality of a product over time. Will the product operate properly during the required or anticipated time of use? Statistical analysis of failure data, life testing, probability models of survival, and FMEA are all important tools in reliability engineering. FAILURE MODE AND EFFECT ANALYSIS ( FMEA ) is tool used by design engineers and design review committees to protect against potential problems in processes and products. FMEA is a systematic approach to identifying potential product or processes failures (failure modes), their effects in terms of functionality and safety, and what steps need to be taken to protect against these failures. FMEA should be done during product development, and again when unanticipated failures occur or there are design changes. Timely use of FMEA can avoid expensive modifications by revealing potential design deficiencies or hazards prior to actual production. Usually an FMEA is carried out from the bottom up, starting at the component level and working up through subsystems to the complete system. FMEA should examine performance under extreme environmental conditions and should try to anticipate possible misuse or misapplication by customers. An FMEA is conducted prior to production and involves the listing of potential failure modes and causes. FMEA 's identify actions required to prevent defects and thus keep products which may fail or not fit from reaching the customer. Its purpose is to analyze a product's design characteristics relative to the planned manufacturing or assembly process to ensure the resultant product meets customer needs and expectations. When potential failure modes are identified, corrective action can be initiated to eliminate them or continuously reduce their potential occurrence. The FMEA also documents the rationale for the manufacturing or assembly process developed. Because of rapidly changing customer expectations, especially the automotive industry's need for disciplined use of a technique to identify and prevent potential problems is more important than ever before. FMEA was originally used in the aerospace industry to prevent potentially catastrophic equipment failures. The technique is now applied to production processes and service operations as well. Food and drug industries use FMEA under the name Hazard Analysis and Critical Control Points (HACCP) as a way of preventing contamination of products during production and handling. A process FMEA is an analytical technique which identifies potentials product related process failure modes, assesses the potential customer effects of the failures, identifies the potential manufacturing or assembly process causes and identifies significant process variables to - XII, focus controls for prevention detection of the failure conditions. It utilizes occurrence and detection probability in conjunction with severity criteria to develop a Risk Priority Number (RPN) for prioritisation of corrective action considerations. A disciplined review and analysis of a new or revised process is promoted to anticipate, resolve or monitor potential process problems during the manufacturing planning stages of a new model or component program. Process FMEA 's can also assist in developing new machine or equipment processes. The methodology is the same, however, the machine or equipment being designed would be considered the product. An FMEA summarizes the engineers' thought (including analysis of every item that could conceivably go wrong based on experience and past problems) in developing a process. This systematic approach parallels and formalizes the mental discipline that an engineer normally goes through to develop processing requirements.
Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 1994
Anahtar kelimeler
Hata türleri ve etkileri analizi, Kalite, Tasarım, Toplam kalite kontrol, Failure mode and effect analysis, Quality, Design, Total quality control