• Journal of the Korean Operations Research and Management Science Society
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• v.36 no.2
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• pp.51-65
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• 2011

We compared a CONWIP(constant work-in-process) system with a kanban system in a production line with constant processing times. Based on the observation that a WIP-controlled line production system such as CONWIP and kanban is equivalent to a m-node tandem queue with finite buffer, we applied a max-plus algebra based solution method for the tandem queue to evaluate the performance of two systems. Numerical examples with 6 workstations were used to demonstrate the proposed analysis. The numerical results support the previous studies that CONWIP outperforms kanban in terms of expected waiting time and WIP. Unlike the kanban case, sequencing workstations in a CONWIP does not affect the performance of the system.

• 제어로봇시스템학회:학술대회논문집
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• 1990.10b
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• pp.1250-1255
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• 1990

This paper discusses an optimal cyclic scheduling problem for a FMC (Flexible Manufacturing Cell) modeled by a two-machine flowshop with two machining centers with APC's (Automated Pallet Changers), an AGV (Automated Guided Vehicle) and loading and unloading stations. Cyclic production in which similar patterns of production is repeated can significantly reduce the production lead-time and WIP (Work-In-Process) in such flexible, automated system. Thus we want to find an optimal cyclic schedule that minimizes the cycle time in each cycle. However, the existence of APC's as buffer storage for WIP makes the problem intractable (i.e., NP-complete). We propose an practical approximation algorithm that minimizes, instead of each cycle time, its upper bound. Performances of this algorithm are validated by the way of computer simulations.

• Proceedings of the Korean Institute Of Construction Engineering and Management
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• autumn
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• pp.416-421
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• 2001

The domestic reinforcement concrete works have mainly worked the process of re-bar fabrication/assembly on site and re-bar works affected by structural safety, durability, and schedule with form work. Accordingly, This study analyzes the process of re-bar fabrication/assembly on site to apply lean production principles to construction Value Stream Analysis(VSA) is analyzed into value-adding activity and non-value-adding activity on construction process through value analysis and Value Stream Mapping(VSM). In the results, non-value-adding activity generates waste such as the activity steps, labors, equipments, materials, time, and so on. Additionally, push-driven production is investigated making low productivity from the overproduction and so on. To resolve the problems in the process, The purpose of this paper eliminates waste factor through maximizing the value-adding activity generating value added and minimizing non-value adding activity. Particularly, it makes flow production and pull-driven production through minimizing work-in-process(WIP ).

• Journal of the Korea Society for Simulation
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• v.17 no.4
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• pp.51-60
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• 2008

The purpose of this study is the use of simulation modelling to enhance productivity. In this paper, the optimal buffer allocation of small and medium size industries which produce solenoid valves for automobiles, is performed using simulations. The simulation model was developed under considerations of production layout, process & operation, process time, total work time, WIP, utilization, failure rate, and operation efficiency as inputs, and it was validated with careful comparisons between real behaviors and simulation outputs of the production line. Therefore, we can evaluate effects and changes in productivity when some strategies and/or crucial factors are changed. Although too large buffer could decrease productivity, the solenoid production line in this paper has been maintained large buffer. It is because reducing the size of buffer could result in the termination of the process. We determined the optimal number of buffers that could not cause any interrupt in productions using simulations. This simulation model considers diverse input variables which could influence productivity, and it is very useful not only for the production line of solenoid valves, but also for other production lines with various purposes, especially, small and medium size industries.

• Proceedings of the Safety Management and Science Conference
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• 2005.11a
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• pp.505-510
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• 2005

The manufacturing industries which played a major role in the rapid economic growth and industrialization of Korea in the late 20th century had considerable difficulties changing their manufacturing conditions from producer-oriented conditions to customer-oriented ones according to market changes. In this study, increase plant efficiency because grafts together modular system to plant layout and analyzes Work In Process(WIP) between product's cycle time and each process, family efficient plan wishes to choose opposite bank. Simulation approach used for presented methodology The effect will not gain the results for other reasons the inherent conditions of companies, people, and culture which have been hitherto described, but will be expected to help the direction for a new Lay-out production system to reflect on the native conditions rather than fixed technological means and methods in way of an analysis of fundamental problems which small and medium companies in Korea face.

• Journal of the Korea Safety Management & Science
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• v.5 no.4
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• pp.209-217
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• 2003

The traditional Kanban needs a lot of preconditions for fitting conditions of dynamic production processing environment. The traditional Kanban isn't suitable conditions of dynamic production processing environment. Therefore conditions of dynamic production processing environment is needed more stable system. This study is describe CONWIP system such as suitable in dynamic production processing environment. Most Pull system is a Kanban system than use Kanban cards or signal for production management and inventory control. The object of Kanban system is reducing inventory between shop-floor that can reduce inventiry cost. If the system reduce the number of Kanban cards would be reduce the working process WIP, can be reduced and can be found all potential problem of production between shop-floors. This study apply to CONWIP system model for Korean industrial companies.

• Korean Management Science Review
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• v.5 no.2
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• pp.57-70
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• 1988

This paper examines both MRP and JIT for reducing WIP(Work In Process). The MRP/JIT system is suitable for multi-model, small-production manufacturing comparies in Korea because of the short delivery distance and low risk of accident during delivery. The objective of this paper is to manage vendors effectively by informing supply points and quantity of parts of vendors with MRP and JIT.

• Proceedings of the Korea Society for Simulation Conference
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• 2000.04a
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• pp.131-136
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• 2000

FMS(Flexible Manufacturing System, 유연생산 시스템)는 1960년대 최초로 소개된 이후, 뛰어난 Throughput과 Flexibility로 지금까지 다양한 생산 현장에서 널리 활용되고 있다. 하지만 복잡한 Part의 흐름, 충분하지 못한 AGV(Automated Guided Vehicle) 등으로 인한 성능 저하는 가장 큰 장애물이라 할 수 있다. 이에 대한 대비책으로 시스템 내에 설치하는 버버는 일시적인 WIP(Work In Process, 재공재고)의 저장공간으로써 Blocking, Starving 등의 발생을 최소화하는 역할을 수행한다. 따라서 이러한 버퍼의 적절한 배치는 시스템 성능에 큰 영향을 미치게 되며, 이에 본 연구에서는 각 Workstation의 Workload를 고려해 각 버퍼의 적절한 Capacity를 결정하는 과정을 소개하며, 제시된 방법론의 실효성을 시뮬레이션을 통해 검증하고자 한다.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.9
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• pp.1330-1335
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• 2012

This paper proposes an automatic measurement sampling method for the semiconductor manufacturing process. The method recommends sampling rates using information of process capability indexes and production scheduling plan within the restricted metrology capacity. In addition, it automatically controls the measurement WIP (Work In Process) using measurement priority values to minimize the measurement risks and optimize the measurement capacity. The proposed sampling method minimizes measurement controls in the semiconductor manufacturing process and improves the fabrication productivity via reducing measurement TAT (Turn Around Time), while guaranteeing the level of process quality.

• Journal of the Korea Society for Simulation
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• v.11 no.4
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• pp.69-80
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• 2002

This study deals with the productivity improvement on a flow production system with the consideration of line-balancing. In a flow production system, similar product models are produced on a same assembly line, the predefined process order and the limitation of total worker number. The system can be increased the work-in -process(WIP) inventory and the worker's idle time. In this study, the worker assignment model is developed to assign evenly workload of process to each product model in such a manner that each process has the different number of worker. This worker assignment model is the mathematical model that determines worker number in each process such that the idle time of processes is reduced and the utilization of worker is improved. We use a simulation technique to simulate the production line proposed by the mathematical model and apply real production line. With the result of simulation, this study analyzes the propriety of production line and proposes the alternatives of new production line