Endüstri Mühendisliği Bölümü / Department of Industrial Engineering

Permanent URI for this collectionhttps://hdl.handle.net/11413/6819

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A Cutting Sequencing Approach to Modular Manufacturing
(Emerald Group Publishing Limited, 2004) Özdemir, Rifat Gürcan; AKTİN, AYŞE TÜLİN; 109203
In this study, a two‐stage algorithm is developed for the cutting sequencing problem in a modular manufacturing system consisting of four basic workstations. Since the flexibility of the system is dependent upon the cutting stage of raw materials, the study focuses particularly on this workstation. In the first stage of the algorithm, an integer linear programming model is used to determine the number of hardboards that will be cut. The model is tested with two different objective functions. In the second stage, a heuristic which takes into account the due date of the products is developed to obtain the real‐time sequencing of these cutting patterns on the shop floor. The algorithm is further implemented in a furniture manufacturer that operates on a make‐to‐order basis. The results of the existing and proposed system are compared, and the proposed algorithm is found to provide a useful tool in such a real‐life planning problem.
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A Decision Support Model for Customer Value Assessment and Supply Quota Allocation
(TAYLOR & FRANCIS LTD, 11 NEW FETTER LANE, LONDON EC4P 4EE, ENGLAND, 2000-09) Barbarasoğlu, G; Yazgaç, Ayşe Tülin; AKTİN, AYŞE TÜLİN
The aim of this study is to develop a decision support tool for a supplier in a value-chain environment. The supplier under consideration is assumed to provide a strategic product to a number of customers and needs to allocate his capacity among them in a way to maximize his business value. First, an analytic hierarchy process (AHP) structure is designed to represent the criteria which are identified from the supplier's point of view to assess customer performance, and customer priorities are obtained by using the AHP composition principle. Then, these are deployed in numerical algorithms which aim to allocate the total supply capacity among customers as supply quotas. The approach is implemented in an electric motor manufacturer in Turkey, which possesses high competitive power with advanced manufacturing technology.
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A mathematical model for the delivery routing problem via drones
(Pamukkale Üniversitesi, 2019) Han, Sinem; Özer, Begüm; Alioğlu, Barış; POLAT, ÖZGÜR; AKTİN, AYŞE TÜLİN
Logistics sector aims to distribute merchandise to designated places on time, while focusing on the entire process that starts from storing the goods at warehouses. Transportation by land is the most common and preferred way in logistics in terms of cost and service. Studies have been going on for drone transportation with the purpose of reducing the service time and making the process automated. Advancement of this technology has led to an increase in transportation with drones. Traffic is a huge problem in land transportation causing delays in delivery time. Furthermore, nature and economy are affected because of the CO2 emission, which is a consequence of intense traffic. In this study, utilizing drones for delivery is proposed with the aim of increasing customer satisfaction and minimizing transportation cost per delivery in a green way. Istanbul's Bakirkoy district is selected as the implementation region, and daily drug delivery to pharmacies with drones is examined. In the first stage, a mathematical model that uses pharmacy coordinates as an input is developed for clustering analysis. In the second stage, one of these clusters is selected, and the location of the drone center that will serve pharmacies in the cluster is obtained by center of gravity method. Then, a vehicle routing model is proposed for finding the drone routes and calculating the total distance travelled within this cluster. Mathematical models are solved with GAMS/CPLEX solver. It is believed that this study will trigger new studies in "green delivery" literature in near future.
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A Mathematical Programming Approach to Multi-Way Kidney Transplantation
(2015-07) Kutlu, Fatma; Girgin, S.; YÜKSEKTEPE, FADİME ÜNEY; AKTİN, AYŞE TÜLİN; 273471; 108243
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A mathematical programming approach to paired kidney exchange: the case of Turkey
(2018-08) Akın, Barış; YÜKSEKTEPE, FADİME ÜNEY; AKTİN, AYŞE TÜLİN; GÜNDOĞDU, FATMA KUTLU; 273471; 108243; 109203
Background: Kidney exchange has become a very common and important treatment alternative for patients suffering from serious kidney diseases with incompatible donors. Factors such as blood type, HLA matches and PRA existence are considered to determine compatibility. In a paired exchange, two incompatible patient-donor pairs switch their donors who are compatible with the other recipient. Currently, each hospital in Turkey operates individually in a decentralized manner using its own list. This list may contain patients having more than one incompatible donor, which differentiates the current work from those existing in literature. Methods: In this study, mathematical models are developed to propose an easy and practical approach for the paired kidney exchange problem in Turkey. Data are generated by employing a real data set provided by a hospital specialized in kidney transplantation. Results: The optimal solutions are obtained by using GAMS/CPLEX, and different scenario analyses are performed to measure the impact of "gender differences" and "age" on the solution. Furthermore, the original patient-donor list provided by the hospital is used to compare the model's solution with the planned transplantations. The study also evaluates a centralized approach which integrates all hospitals performing paired kidney exchange in Istanbul. Conclusions: As the optimal solution of the model is obtained in a basis of seconds, the developed approach offers an easy and applicable procedure for paired kidney exchange. Comparison of decentralized and centralized approaches reveals that the centralized approach is more favorable in terms of HLA compatibility and number of transplantations.
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A Reference Model for Competitive Power Assessment of Industrial Companies
(2000) Kaylan, Ali Rıza; AKTİN, AYŞE TÜLİN; 109203
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An analytical approach for analysing the impact of risks on production planning: Case of Öztiryakiler
(2020) Telatar, E.; Bekeç, T.; Başaran, A.; Balıkçı, N.; Bilgin, B.; İlbay, E.; AKTİN, AYŞE TÜLİN
Accurate and applicable production plans are a must for manufacturing companies. Although companies tend to prepare ideal production plans, some exogenous factors can affect their validity. These risks, which occur unexpectedly, will have a negative influence on the plan. This study aims to determine the exogenous factors affecting the success of production planning of square and rectangular food containers manufactured by Öztiryakiler, and analyse their impacts on the plans. The risk factors are evaluated using Failure Mode and Effects Analysis, and their risk priority numbers are calculated. A mixed-integer linear programming model with the objective of total cost minimisation is developed to obtain the production plan of containers. Initially, an ideal data set is used as input; hence, this model’s output displays a risk-free plan. Similarly, for each of the risk factor scenarios, mathematical models are solved with risk-related data. GAMS software and CPLEX solver is utilised in the solution of all models. Finally, for each of the selected high risk alternative, the expected total costs are calculated. This is achieved by multiplying the normalized risk priority number obtained from the Failure Mode and Effects Analysis with the corresponding optimal total cost of the risky plan. This analysis highlights the most critical risks, and comparison with the risk-free plan helps in proposing system improvements. © 2020, Springer Nature Switzerland AG.
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An Analytical Approach to the Inventory Management System of Turkish Technic
(2018) Karagöl, Belma Nüvit; Çöpürkaya, Derya; Kodaz, Kubilay; Ünek, Simge; AKTİN, AYŞE TÜLİN; 109203
Time, which constitutes an important limitation in a company’s operations, is a factor that affects the supply chain processes and cash flow. Another element that has an influence on cash flow is customer satisfaction. Sector leaders are mostly companies having high customer service levels. Moreover, there exists a strong bond between customer satisfaction and inventory. This study aims to propose an analytical approach to the inventory management policy of a company operating in the aviation industry. Founded in 2006, Turkish Technic has been established to support Turkish Airlines and other aviation companies in their maintenance, repair and overhaul (MRO) services. Aircraft are served in the hangars located at Istanbul Atatürk and Sabiha Gökçen Airports. As a result of their high safety and quality standards, Turkish Technic has become the leader MRO company in the region. Being an exemplary model in its sector, the company relies on the effective management of the diverse parts held in stock both as an indicator of the existence of a robust inventory system, and for a sustainable reputation. Since Turkish Technic holds a variety of parts, initially an ABC analysis will be performed in selecting the most critical ones. Using the past data acquired from the company and Arena Input Analyzer, demand distributions will be obtained and demand quantities for 2018 will be forecasted for each selected part. In the next step, optimum order sizes, safety stock levels, and reorder points of these parts will be calculated. Mathematical modelling and Excel will be used to determine these quantities. The aim is to minimize inventory holding costs, while meeting a preset cycle service level (CSL). The proposed model will be solved using GAMS/CPLEX software. Scenario analysis will be performed to observe and compare the effects of different CSLs on the behaviour of the company’s inventory system.
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An Application of the Analytic Hierarchy Process to the Supplier Selection Problem
(1997) Barbarosoğlu, Gülay; AKTİN, AYŞE TÜLİN; 109203
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An integrated approach to the one-dimensional cutting stock problem in coronary stent manufacturing
(Elsevier Science Bv, Po Box 211, 1000 Ae Amsterdam, Netherlands, 2009-07-16) Özdemir, Rifat Gürcan; AKTİN, AYŞE TÜLİN; TR109203; TR141173
This paper presents a two-stage approach for pattern generation and cutting plan determination of the one-dimensional cutting stock problem. Calculation of the total number of patterns that will be cut and generation of the cutting patterns are performed in the first stage. On the other hand, the second stage determines the cutting plan. The proposed approach makes use of two separate integer linear programming models. One of these models is employed by the first stage to generate the cutting patterns through a heuristic procedure with the objective of minimizing trim loss. The cutting patterns obtained from Stage I are then fed into the second stage. In this stage, another integer linear programming model is solved to form a cutting plan. The objective of this model is to minimize a generalized total cost function consisting of material inputs, number of setups, labor hours and overdue time: subject to demand requirements, material availability, regular and overtime availability, and due date constraints. The study also demonstrates an implementation of the proposed approach in a coronary stent manufacturer. The case study focuses on the cutting phase of the manufacturing process followed by manual cleaning and quality control activities. The experiments show that the proposed approach is suitable to the conditions and requirements of the company. (C) 2008 Elsevier B.V. All rights reserved.
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An Analytical Approach to Machine Layout Design at a High-Pressure Die Casting Manufacturer
(Springer-Verlag Singapore Pte Ltd., 2022) EMİR, OĞUZ; AKTİN, AYŞE TÜLİN
Sahin Metal was founded in 1975 on a 7500 m(2) area in.Istanbul to supply high-pressure aluminum casting parts to a variety of industries, especially automotive manufacturers. 64 different products are produced with various routings through 14 workstations in the plant. Being a Tier 2 company, these products are then sent to Tier 1 firms and finally reach the leading vehicle manufacturers. Nowadays, increasing competition, changing customer demands, and quality targets bring the necessity of restructuring internal processes. In this regard, Sahin Metal plans to rearrange the existing machine layout to minimize the distance traveled between departments by taking into account the material flow. This study aims to determine an efficient machine layout design by implementing analytical approaches. The study is started by visiting the production facility and meeting with the company's engineers to determine the project roadmap. Following that, the data collection process is initiated, and ABC analysis is performed to define product classes. After this identification, two approaches are utilized simultaneously. The Hollier method is employed to find a logical machine arrangement. In addition, a mathematical model based on the Quadratic Assignment Problem (QAP) is developed to obtain the optimum machine layout. The developed integer nonlinear model is solved by CONOPT using GAMS software under various scenarios. Finally, these results are compared with the existing system, and a convenient layout design is proposed to the company.
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Analyzing the Operations at a Textile Manufacturer’s Logistics Center Using Lean Tools
(Springer Science and Business Media Deutschland GmbH, 2024) GÜNAY, AHMET CAN; ÖZBEK ,ONUR; MUTLU, FİLİZ; AKTİN, AYŞE TÜLİN
Compliance with delivery times is crucial for businesses in the logistics sector. Numerous research has been conducted to improve distribution performance. Many of these studies touch on lean production as well. The strategies used in lean manufacturing are often employed by businesses and have a positive impact on performance. This study focuses on the overseas shipping department of a textile company’s logistics center. Workflow starts with product acceptance from manufacturers and ends with shipment to customers abroad. After a thorough examination, some bottlenecks that increase delivery times are observed. Value Stream Mapping (VSM), which is a lean manufacturing technique, is chosen as the main method to be used. It aims to determine value added and non-value-added activities, resulting in minimizing or eliminating the non-value-added ones. Initially, necessary data are gathered through workshops and interviews, and observations on Current State VSM are made. During these workshops, various improvements are proposed and evaluated together with the company’s engineers. After takt time and cycle time calculations, label change station is identified as the bottleneck. In the next step, Kaizens are suggested for the stations, and some lean techniques are employed to solve different workflow problems. Finally, short-term applicability of proposed improvements is discussed, and Future State VSM is drawn. It can be concluded that significant improvements are achieved especially in lead time, changeover time, productivity rate and production speed. By reducing or eliminating non-value-added activities and identifying deficiencies that slow process flow, a standard, sustainable and developable process is proposed to the company. © 2024, The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.
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Capacity Driven Due Date Settings in Make-to-Order Production Systems
(1997-03-14) Özdamar, Linet; AKTİN, AYŞE TÜLİN; 57877; 109203
Due date setting is a difficult task for make-to-order companies and requires efficient capacity and lead time management. In the job-shop literature, production planning for make-to-order companies is tackled by using shop floor scheduling algorithms coupled with simulation. However, capacity management cannot be realized in the most detailed phase of planning and should be carried out at a higher decision level so that work loads are smoothed over time. A linear capacity planning model is proposed for dealing with problems of load leveling in bottleneck departments over a planning horizon. In this model, end items in each order are conveniently grouped into product families so that the proposed model becomes tractable in terms of practical problem sizes. Capacity constraints are included in the model and covers a number of future periods with known firm orders. The objective is to minimize total backorder and overtime costs. In this context, an order is assumed to be backordered if it is delivered some weeks later than that of its arrival. Actually, the time during which an order is backordered represents the production lead time for that order. Furthermore, the production lead time of each order is constrained by an order specific maximum lead time determined as a company policy. The output of the model conveys weekly order release and delivery times which serve as order due dates. Hence, lead time management and due date setting as well as load leveling are achieved by the proposed model. Since the model does not take family set-up times into consideration, an iterative algorithm which balances over time, the additional capacity demanded by set-up times, is proposed. The production plan developed for the bottleneck department is propagated to the other stages of the production system through a binary LP model whose binary variables are reduced at every stage. The proposed multi-stage planning system is applied for planning production in a manufacturing company which makes/assembles custom kitchen cupboards. The case study demonstrates the advantages of the system.
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Drone ile Teslimat Rotalaması için Bir Matematiksel Model
(2017) Han, Sinem; Özer, Begüm; Alioğlu, Barış; POLAT, ÖZGÜR; AKTİN, AYŞE TÜLİN; 109203
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An Excel-Based Stock Management System for a Leather Label Manufacturer
(Springer Science and Business Media Deutschland GmbH, 2024) UÇUCU, EMİNE; ERASLAN, FATMA BEYZA; KAYMAKLI, ZEYNEB NUR; EMİR, OĞUZ; AKTİN, AYŞE TÜLİN
This paper presents a proposal for an Excel-based digital inventory tracking system to address the operational challenges faced by a leather label manufacturer located in Istanbul, Turkey. The company is currently reliant on manual stock keeping and tracking methods for its leather labels and raw materials, resulting in significant functional difficulties due to the absence of a systematic and efficient inventory tracking system. The proposed system aims to enhance overall productivity and decision-making processes within the company. By implementing the new tracking system, the company can overcome the limitations of manual stock management, leading to improved efficiency and organization in inventory control. Furthermore, the installation of a barcode system is suggested to augment the tracking system’s capabilities, and the profitability of the proposed system is evaluated using three different financial analysis methods. This research contributes to the advancement of inventory management practices and provides valuable insights into the potential benefits of adopting digital solutions for stock control in the leather label industry. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2024.
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Implementation of a Recycling System in PG Turkey Using a Two-Stage Approach for Network Design and Vehicle Routing
(2018) Yavaş, Burçay; Keskin, Beril; Kulunçkıran, Duhan; AKTİN, AYŞE TÜLİN; 109203
Sustainability has become an inevitable concept for companies in the modem world. Consequently, converting used products to secondary raw materials and incorporating them into the recycling process is becoming important for fast-moving consumer goods (FMCG) companies. These products constitute an indispensable part of our daily lives and have high consumption rates. Procter and Gamble (P&G) is a worldwide FMCG corporation, specialized in different product categories. Sustainability is a crucial component in P&G’s success in this highly competitive sector, and environmental concerns include recycling of materials. This study aims to design a recycling system for P&G’s used product packages, and a pilot study will be implemented in Istanbul’s European side. The two-stage approach will cover network design of recycling bin locations and vehicle routing problem of recycling trucks. The first stage will start with a survey for collecting quantitative data on consumers’ recycling habits. This intends to identify the consumers’ main reasons behind participating in such a recycling activity, and to support the motivation of the study. Analytical Hierarchy Process will be employed to select the primary location types (Migros, CarrefourSA, municipalities, etc.) at which the recycling containers will be placed. Coordinates of location types above a certain priority value will then be input to a clustering model to determine the design of the recycling bin network. The second stage will handle the vehicle routing problem within one of the clusters obtained from stage 1. Its objective is to find routes that minimize total distance travelled while collecting recycled products from container locations. Both stages incorporate mixed-integer linear programming models, which will be solved using GAMS/CPLEX. Finally, scenarios having different recycling rates will be analyzed. It is worthwhile to note that, the proposed methodology can be implemented in all of the clusters, as well as, in the Asian side of Istanbul.
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Industry 4.0 Scorecard for SMEs
(Springer, 2018-09) Gergin, Zeynep; Gençyılmaz, Mehmet Güney; İlhan, Doğan Aybars; Dündar, Uğurcan; Cebeci, Özay; Çavdarlı, Ali İhsan; YÜKSEKTEPE, FADİME ÜNEY; AKTİN, AYŞE TÜLİN; 141772; 30141; 109203; 274545; 275477
Today the industry is revolutionizing into a new era with the total integration of all elements of the production through digitalization and establishing communication between each other. This new revolution is named as “Industry 4.0”. Turkey is categorized as a developing country in terms of economy and Turkish economy is ranked at 17th place in world Gross Domestic Product (GDP) ranking. The country’s economy met the expectations and reached 7.4% GDP growth in 2017 while worldwide average growth was 3.6%, and developing countries had the average of 4.6%. Turkish government encourages enterprises to keep up with industry 4.0, and KOSGEB (Small and Medium Sized Enterprises Development Organization) is supporting the SMEs with various programs. This can be seen as an opportunity for Turkish industry to catch the trend and increase its growth rapidly. And at this point the exact knowledge of the current situation is crucial. Small and Medium Sized Enter- prises (SME) has the 99.8% of the total according to Turkish Statistical Institute (TÜİK). Hence, this project is initiated to identify the current situation of SMEs of Turkish industry. A comprehensive questionnaire is prepared to find out the readiness and requirements of the SMEs for Industry 4.0 transformation. This questionnaire is applied to SMEs operating in Marmara Region of Turkey. The outcome of the research shows a scorecard for the SMEs in terms of technology usage, readiness to Industry 4.0, and also increased their awareness on the concept and the importance of the new era. The future studies are continuing as a second phase of this research in order widen the research to all regions of the country, and to develop the transformation capabilities of the selected enterprises.
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İstanbul’da Drone ile Trafik Kontrolüne Bir Matematiksel Yaklaşım
(2018) Baştürk, Ceren; Acar, Elif Nur; Çakır, Ahmet Cemil; Culha, Uğur Deniz; AKTİN, AYŞE TÜLİN; 109203
Büyük şehirlerdeki iş ve yaşam olanaklarının çekiciliği, bu şehirlerdeki nüfus yoğunluğunun sürekli artmasına neden olmaktadır. Bu durumdan en fazla etkilenen şehirlerin başında gelen İstanbul’da, yolların kapasiteleri taşıt yoğunluğu karşısında yetersiz kalmakta ve kent içi ulaşım gittikçe zorlaşarak, belirli saatlerde durma noktasına gelmektedir. Kısacası trafik sorunu, İstanbul’da yaşayanların gündelik hayatını olumsuz etkileyen faktörler arasında ilk sıralarda yerini alarak, işgücü ve zaman kaybına yol açmaktadır. Mevcut trafik kontrol sistemleri, kör noktalardaki hız aşımı, kaza gibi vakaları tespit etmede etkin değildir. Polis devriye araçları ise, trafik tıkanıklığı durumunda görevlerini yerine getirmede zorlanmadadırlar. İnsansız hava aracı olan drone’ların yukarıda belirtilen problemlerin çözümüne katkı sağlayacak teknik donanıma sahip olmaları, diğer kullanım alanlarında olduğu gibi, gelecek için ümit vadetmektedir. Bu çalışmada, İstanbul’da trafiğin en yoğun olduğu noktaların minimum sayıda drone ile kontrolünün yapılarak, anlık veri toplanması amaçlanmaktadır. Devriye gezen drone’lar tarafından sisteme aktarılacak veriler sayesinde, karayolunda meydana gelen olumsuz vakaların anında saptanarak hızlı bir şekilde olaya müdahale edilmesi ve tıkanıklık durumlarında hemen yönlendirme yapılması mümkün olabilecektir. Pilot bölge olarak, yoğunluğun en fazla yaşandığı yerlerden olan E-5 ve E-80 karayolları seçilmiştir. Önerilen yöntem iki aşamadan oluşmaktadır. Birinci aşamada, trafiğin en yoğun olduğu yollarda devriye gezecek olan drone’lar için en iyi rotanın bulunması hedeflenmektedir. Bu amaçla, öncelikle harita ve trafik verileri yardımıyla bir yönsüz çizge oluşturulacaktır. Drone ile trafik kontrolü problemi, Yönsüz Çinli Postacı Problemi olarak ele alınacak ve en kısa mesafeli eşleştirme yöntemi kullanılarak çözülecektir. İkinci aşamada ise, ilk aşamada tespit edilen rota boyunca devriye gezecek drone sayısını enküçüklemeyi amaçlayan bir matematiksel model geliştirilecektir. Bu model, GAMS/CPLEX programı yardımıyla çözülecektir. Çalışmanın sonunda, mevcut trafik kontrol sistemi ve drone kullanımı, çeşitli faktörler açısından karşılaştırılacaktır. Bakım maliyetinin daha düşük olması, geniş tarama alanı kapasitesi, anlık veri toplama kabiliyeti ve deprem, sel, vb. doğal afetlerde etkin olarak faaliyet gösterebilmesi gibi özelliklerinin, trafik kontrolünde drone kullanımına avantaj sağlayacağı düşünülmektedir.
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Joint Decision Making for Production and Marketing
(1995) Ulusoy, Gündüz; AKTİN, AYŞE TÜLİN; 109203
The prosperity of a firm depends highly on the functional integration of its various departments, and in particular the cooperation between the production and the marketing departments appears to have a large impact on the well-being of a firm. The aim of this study is to model an aggregate production planning problem that considers the production and marketing functions in a simultaneous manner. The developed multi-period, multi-product model with the objective of profit maximization reflects the characteristics of both departments. Demand for each product in each period is generated through the use of demand functions. The advertising efficiency and price of the products are determined within the model. The cash outflow for advertising expenditures is approximated by a quadratic cost function, and the production cost exhibits economies of scale. Also, stockouts are taken into consideration in the form of backlogging. A solution methodology consisting of two phases is developed, and cases displaying some important characteristics are generated and solved in order to test the performance of the proposed model. This methodology incorporates linear mixed integer programming which is embedded in two different search techniques, along with a dynamic programming-based heuristic procedure.
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Kalıtsal Meme Kanseri Tahmini için Bir Karar Destek Sistemi
(2016) Kartal, Büşra; Fettahoğlu, Emine; Edalı, Özcan; Akdeniz Ödemiş, Demet; Kılıç, Seda; Şükrüoğlu, Özge; Tuncer, Buğra; Avşar, Mukaddes; Yazıcı, Hülya; YÜKSEKTEPE, FADİME ÜNEY; AKTİN, AYŞE TÜLİN; 108243; 109203; 140724; 1292

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