Değer akış haritalama yöntemi kullanılarak tekstilsektöründe yalın üretim uygulaması

Abstract

Günümüzde rekabet ve pazar koşullarındaki değişim her geçen gün daha da artmaktadır. Şirketler gittikçe zorlaşan piyasa koşullarında değer yaratabilmek ve hayatta kalabilmek için faaliyet gösterdikleri sektörlere göre çözümlerüretmektedirler. Bu koşullara uyum sağlamak amacıyla üretim sistemleri, farklı stratejileri ve yenilikleri ortaya koyarak, geleneksel sistemlerden ayrılarak, her türlü israfı ve maliyeti düşürerek karlılığı arttırmak ve sürekliliğini korumak amacıyla yeniden şekillenmiştir.Bu üretim sistemlerinden biri olan Yalın üretim, üretim akışını en üst düzeye çıkarırken israfı en aza indirmeyi veya tamamen ortadan kaldırmayı amaçlar. İhtiyaç duyulan iyileştirme çalışmalarının başlayabilmesi için problemlerin ortaya çıkış sebeplerinin tanımlanması gerekir. Değer akış haritalama (VSM), mevcut sistemin performansını ortaya koymak ve analiz etmek için veri toplanmasını içeren ve üretim sürecini planlamaya yönelik bir yalın üretim aracıdır. Üretimde yer alan tüm malzeme, bilgi akışı ve nihai ürünlerin ortaya çıkması için gerçekleştirilmesi gereken prosesleri gösteren değer akış haritaları, firmaların kaynaklarını verimsiz kullanmalarına sebebiyet veren süreçlerin incelenmesinde ve iyileştirilmesi gereken istasyonların tespit edilmesinde önemli katkı sağlayan bir yalın üretim tekniğidir. VSM, analiz edilen üretim hattının toplam çevrim süresini, envanter seviyelerini ve mevcut teslim süresini belirlemek için kullanılan etkili bir yöntemdir. Bu değerler, nihai ürüne değer katmayan faaliyetleri tanımlamak ve ortadan kaldırmak için kullanılır. Bu çalışma, bir tekstil fabrikasında değer akış haritalama yöntemi kullanılarak belirlenen darboğazların yalın üretim uygulamalarıyla iyileştirme yapmayı amaçlamaktadır. Bunun için ilk olarak herbir istasyon arasında gereğinden fazla yarı mamul stoğu bulunması, hammaddenin temin süresinin uzunluğu, çalışan makinelerden istenilen verimin alınamaması, boyamave kukalama sürecinden karşılaşılan varyasyonlar ve hatalı üretim girişleri gibi birçok problem tespit edilmiştir. Daha sonrasında Hata Türü ve Etkileri Analizi (FMEA) yöntemi ile bulunan hatalar arasında değerlendirilme yapılmış olup en yüksek puana sahip olan üç hata mevcut durum üzerinde haritalandırılmıştır. Değer akışı yöntemi ile takt zamanlar ve çevrim zamanları ortaya çıkarıldıktan sonra firmanın rekabet gücünü artırmak için olası iyileştirmeler tartışılarak gelecek durum üzerinde tekrar FMEA yöntemi uygularak değerlendirmede bulunulmuştur.

Today, the competition and the change in the market conditions increase everyday. Companies create solutions based on the sector in which they operate to be able to create value and survive in the market conditions which get more and more difficult. Competition and change in market conditions is increasing every day. Companies,regarding the sector they are operating in, develop solutions in order to create value and survive in the harsh market conditions. In pursuit of adapting themselves to these conditions, production systems have been reshaped to reduce any waste and cost, and increase profitability and maintain sustainability, by discarding traditional systems and developing different and innovative strategies. Being one of these production systems, lean manufacturing was developed following Eiji Toyoda and Taichni Ohno's research trip to the U.S. in order to visit the production sites and analyze the production systems of Ford in 1950. The Toyoda family became much more successful after 1970 compared to their competitors through their innovative methods. Lean manufacturing systems are practiced all over the globe and are discussed in numerous academic studies. Regardless of being large or small scaled, every company operates among a vast number of competitors to serve customers who become more conscious every day. Within this context, lean manufacturing provides competitive advantage by identifying the problems in our business and offering more efficient ways of operating. Being concerned with every step of a process from design to transportation, lean manufacturing comprises five principles; Identify value Map the value stream Create flow Establish pull Seek perfectionWhen applied in compliance with the above mentioned principles, lean manufacturing provides customer satisfaction, regular cash flow, continuous profitability and continuous improvement. The main principle of lean manufacturing is to eliminate everything that does not add value for the customer. This perspective considers everything as waste which the customer does not believe adds value and is unwilling to pay for. There are seven types of waste; Defects OverproductionExcess Inventory Inappropriate Processing Unnecessary Transportation Unnecessary/Excess Motion WaitingThe aim of this system is to eliminate waste at each step of production from design to delivery in order to reduce cost, increase customer satisfaction, accelerate cash flow and maximize company profitability. Lean manufacturing system incorporates main performance criteria. These criteria are key indicators of providing process standardization along with continuous improvement. Major performance criteria analyzed in this study are as follows; Productivity Process Quality Throughput Overall Equipment Effectiveness Work in Process HeijunkaThere are various tools to create leanness by steady elimination of waste; Just in time (JIT) Kaizen Kanban Jidoka Poke Yoke SMED 5S Total quality management Value stream mappingValue Stream Mapping (VSM) is one of lean manufacturing techniques aiming to eliminate or reduce non-value adding operations in the process where input is transformed into output. In order to begin with necessary improvement actions, origins of problems need to be addressed. VSM is a lean manufacturing method to analyze the performance of the current system by gathering data and to redesign the production process. Identifying necessary processes required for all materials, data flow and end products, VSM is a lean manufacturing technique providing significant contributions to analyzing processes leading to inefficient use of sources, and determining stationsthat require improvement. VSM has proven to be quite efficient in terms of determining total cycle time, inventory levels and lead time of the analyzed production line. Analysis results are employed to define and eliminate non-value adding activities regarding the end product. VSM technique starts with selecting a product family within a process. The next step is to determine necessary improvement by analyzing the current system and to makea future state analysis. Eventually the future state plan is carried into practice. Failure Mode and Effects Analysis (FMEA), another technique analyzed in this study, is a total quality management technique initially developed by the U.S.military. This method targets to identify all potential failure modes with their causesand effects, and to eliminate them. It has become one of the most important risk analysis methods due to its easyapplicability. While analyzing failures within the process, FMEA becomes more effective when applied with methods such as fishbone or Pareto analysis.FMEA incorporates a number of activities; Assessment of failure types in the production process of a product or service Determining potential causes of the failures Prioritizing failures connected to probability, severity and detection accordingto RPN value Monitoring problems and taking correcting actionsAccording to RPN value, in order to eliminate potential failures and their causes, or to minimize their negative effects, change in various elements, such as design, production process, material or production method, is recommended. This requires reduction in probability, severity and detection values. Recommended correctiveactions should be applied, following results should be evaluated. Application of corrective measures is quite important. At this level, results are periodically analyzed and evaluated until the critical RPN values are eliminated. The purpose of this study is to offer solutions to the problems encountered during production to increase customer satisfaction and improve production processes of a textile company which is manufacturing hand knitting yarn for almost 60 countries in its 2 production facilities with over 1200 employees. The company incorporates several major processes such as preparation, ring-spinning, specialty yarn spinning, skeining, dyeing and swa print. This study consists of 2 main parts. In order to prioritize problems, initially, FMEA method was applied, involving all processes from arrival of raw material to delivery of end product. Then, VSM technique was employed to improve processes in which failures occur. Firstly a team in charge of conducting FMEA technique was formed; secondly, together with this team, 6 most frequently encountered failures were determined. The team, then, examined the whole process from demand forecasting to delivery to the customer so as to identify failures taking both domestic and international customer feedback into consideration. Fishbone method was utilized to better examine failures by intensifying the analysis. Potential causes of the failures were identified by this method facilitating solution propositions throughout the whole process. When designing the fishbone, the criteria listed below were taken into consideration; Method Manpower Machine Environment MeasurementFishbone method encompasses benefits such as; Detecting the causes of the problem more clearly, Creating an open discussion environment, Strengthening communication within the team.Detailed failures are listed from higher to lower in the fishbone diagram according to the RPN value calculated by multiplication of severity, probability and detection degrees of the failures. The study, then, aimed to improve work in process and bottlenecks identified with VSM method by lean manufacturing practices. Applying these methods served to determine various problems such as excess work in process, long material lead time, low productivity of equipment, variations encountered during dyeing and skeining processes, manufacturing defects, and the current state map was constructed. After identifying takt time and cycle time through VSM, possible improvements to increase competitiveness of the company were discussed. The difference between takt time and cycle time were reduced as much as possible with suggested improvements, and work in process and bottleneck problems wereminimized. Moreover, total lead was improved by 48% and total cycle time by 57%. Future state map was constructed. Then, with this new map FMEA was applied again and it was observed that RPN values of initial failures had decreased. In addition, the employees have become more conscious, more educated and more environmentallyaware through the improvements. Considering these applications and their results, it is striking what a significant system lean manufacturing is.