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Analysis of global and local decision rules in a dual kanban job shop. Rafael Diaz, Ph.D. Student, Old Dominion University Ali Ardalan, Ph.D., Old Dominion University. Content. Introduction Background Push System versus Pull System Kanban system - Definitions Flow shop versus Job shop

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analysis of global and local decision rules in a dual kanban job shop

Analysis of global and local decision rules in a dual kanban job shop

Rafael Diaz, Ph.D. Student, Old Dominion University

Ali Ardalan, Ph.D., Old Dominion University

content
Content
  • Introduction
  • Background
    • Push System versus Pull System
    • Kanban system - Definitions
    • Flow shop versus Job shop
    • JIT
  • The model
  • Measures of performance
  • Results
    • Customer Waiting lines
    • Total inventory
    • Input stock point inventory
    • Output stock point inventory
  • Conclusions
introduction
Introduction
  • This study simulated the operation of four-station, dual-kanban controlled, pure job shop that manufactures four products.
  • Products went through the four stations in a different sequence.
  • Results demonstrated that considering information regarding the length of customer queues, improves performance measures of both customer waiting time and total inventory.
introduction1
Introduction
  • This work analyzes the effects of four kanban policy variables
    • number of kanbans
    • length of withdrawal cycle
    • priority rule
    • information regarding the length of the customer queues
  • on four performance criteria
    • average customer wait-time
    • total inventory
    • average of full containers in the input stock points of stations.
    • average of full containers in the output stock points of stations.
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Flow Shop

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Raw Material

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Job Shop

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just in time jit
Just In Time - JIT
  • JIT refers to a scheduling system that minimizes inventory by having material arrive just as it is about to be put in use.
  • To accomplish its goal, it is necessary to design production systems wherein required materials are made available on the production floor exactly when is needed.
  • JIT systems use containers and cards (kanbans).
  • A dual-kanban system has two types of cards: production and withdrawal card.
kanban system definitions
Kanban System – Definitions
  • The Pull System means that materials are drawn or sent for by the users of the material as needed. [Hall]
  • The Kanban System is an information system that harmoniously controls the production of the necessary products in the necessary quantities at the necessary time in every process of a factory and also among companies, which is known as the JIT production. [Monden]
  • A Kanban is a tool to achieve JIT production. It is simply a card which is usually put in a rectangular vinyl envelope. [Monden]
  • Two types of Kanban cards in general:
  • - Production-Ordering Kanban (or simply Production Kanban)
  • - Withdrawal Kanban (Conveyance or Transportation Kanban)
jit dual card kanban job shop

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JIT Dual-Card Kanban Job Shop

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Material inventories

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jit recent studies
JIT - Recent Studies
  • Bett et al (2005) - importance of replenishment in JIT and investment in capital.
  • Takahashi, (2004)- JIT that considered changes in the mean and variance of demand.
  • Chen et al (2004) methodology for integrating supplier and manufacturer capabilities.
  • Richter et al (2003) developedadynamic programming solution for a general non-linear alternate deterministic dynamic product recovery model - suppliers & customers considered.
  • Ardalan (1997) investigated the effects of local decision rules in a dual-kanban Flow Shop.
the model
The Model
  • Description:
    • The model system consists of:
      • Customer requirement arrivals
      • Four manufacturing Cells
      • Customer Departures
    • The system produces 4 parts, each visiting different sequence of station:
  • Exponential and Poisson distributions for interarrival and process times.
  • Interarrival time provided about 90% utilization level.
  • The study considered systems with one, two, and three kanbans.
description
Description
  • Description:
    • The time to move between any pair of cell is 1 minute, regardless of the distance.
    • Replication length 10,000 hours. Number of replication:100.
    • Cell producing a single-item class.
    • The inputs to the production process (raw material or labor) are always available.
    • Simulation Application: Arena.
    • Statistical Analysis: SAS.
the model continuation
The Model - Continuation
  • We considered two of the most accepted priority rules
    • First In, First Out (FIFO)
    • Shortest Processing Time (SPT).
  • Two levels of length of customer queues
    • use the information of the length of the customer
    • not use this information.
  • Five levels of Withdrawal Cycle, were 28, 36, 44, 52, and 60 periods.
measures of performance
Measures of performance
  • The policies were evaluated with respect to
    • Average customer wait time
    • The total of full containers in the system
    • The sum of the average number of full containers in the input and output stock points.
  • The first criterion is a measure of customer service, and the last two criteria are measures of WIP in the input and output stock point
results
Results
  • Using full factorial analysis of variance
  • Confidence levels of 95%.
  • Indicated significant interaction among the four components.
results customer waiting times

SPT – Using Info

FIFO – Using Info

SPT – Without Using Info

FIFO – Without Using Info

Results – Customer Waiting Times

W. Cycle = 60

results customer waiting time
Results - Customer waiting time
  • Statistically significant differences between the average wait times.
  • Overall, for those treatments that used information, results were up to 37 % shorter than those treatments that ignored this information.
  • Effects of withdrawal cycle for treatments with one kanban were observed more markedly.
  • With one kanban - using FIFO and information performed better than the ones that used SPT and ignored the information on the customer waiting line.
customer waiting time
Customer waiting time
  • A large number of kanbans increases the availability of WIP that stations use to produce end products.
  • It reduces the possibility of starvation and improves the availability of end products.
  • Short withdrawal cycle improves the station’s responsiveness to demand The result is short customer wait times.
  • Using the information increases the likelihood of producing the items that have real customer demand rather than producing items just to replenish inventory.
total inventory
Total inventory
  • There were interactions: number of kanbans, the withdrawal cycle, and the priority rule.
  • Treatments with 1, 2, and 3 kanbans and withdrawal cycles were significantly different.
  • There exist interactions between the number of kanbans, priority rule, and the status of the customer line length information.
  • With one kanban had significantly lower inventory levels than those with two and three kanbans.
  • Similar results for 2 and 3 kanbans.
  • There is no evidence of mean differences for a treatment with one kanban that used FIFO and those that used SPT.
  • The priority rule had a minor effect on total inventory
input stock point inventory
Input stock point inventory
  • Treatments with two kanbans using FIFO or SPT priority rule were not significantly different from each other.
  • Using the information regarding status of customer waiting line was significantly different.
  • Magnitude of the effects are number of kanbans, the status of customer waiting line, and priority rule.
output stock point inventory
Output stock point inventory
  • Those that used the information regarding the length of the customer queue had significantly smaller WIP than those that ignored such information.
  • Treatments with two kanbans that used the information, those with FIFO had significantly smaller WIP in output stock points than those with SPT.
  • The analysis of all pairwise comparisons of treatments means shows that:
    • One kanban and withdrawal cycle 60: lowest level of inventory
    • Three kanbans and withdrawal cycle of 28 : highest level of inventory.
output stock point inventory1
Output stock point inventory
  • Using the information results in assigning higher priority to production of products that have an immediate customer demand.
  • Using information reduces the inventory levels in the output stock point of station: As soon as these items are made, they will be moved to succeeding stations..
  • The priority rule FIFO results in low levels of inventory : since it may assign a higher priority to jobs that take a long time to be processed, therefore, it may replenish output stock point inventory at slower rate than Short Processing Time (SPT).
conclusions
Conclusions
  • Using the information regarding customer queue length in job shops:
    • It increases service levels, and
    • It reduces total inventory simultaneously.
  • Treatments that used the information of customer queue length result in shorter customer wait time.
  • It is more marked when smaller number of kanbans is used.
  • Whenever the information is used, finished and semi-finished products that have higher customer demand will be produced.
conclusions1
Conclusions
  • Priority rules and status of customer waiting line had a minor effect on total inventory, treatments with FIFO that used the information regarding the length of the customer queue, resulted in the lowest total inventory.
  • The experiments demonstrated that the input and output stock point inventory responded similarly to the number of kanbans and withdrawal cycle changes.
  • Increasing the number of kanbans from 1 to 2, and from 2 to 3, resulted in a similar increase in both input and outputs stock point inventories.
conclusions2
Conclusions
  • When the number of kanbans was reduced from two to one for treatments with cycle of 60, the inventory dropped significantly.
  • Although customer wait time increased, when the number of kanban was reduced from three to two, the decrease in total inventory was disproportionately larger.
  • It may be possible to decrease the number of kanbans and have a significant decrease in WIP inventory without severely increasing the average customer wait time.
references
References
  • Ardalan, Alireza, “Analysis of local decision rules in a dual-kanban Flow Shop,” Decision Sciences, Vol. 28, No. 1 (1997), pp. 195- 211.
  • Betts, John M., and Robert B. Johnston, “Just-in-time component replenishment decisions for assemble-to-order manufacturing under capital constraint and stochastic demand,” International Journal of Production Economics, Amsterdam: January 28, Vol. 95, (2005), pp. 51-70.
  • Chen, Chee-Cheng, Tsu-Ming Yeh, and Ching-Chow, Yang, “Customer-focused rating system of supplier quality performance,” Journal of Manufacturing Technology Management, Bradford, Vol. 15, Issue 7 (2004), pp. 599-617.
  • Richter Knut, and Barbara Gobsch, “The market-oriented dynamic product recovery model in the just-in-time framework International,” Journal of Production Economics, Amsterdam: January 11, Vol. 81/82 (2003), pp. 369-374.
references1
References
  • Stephe, Shmanske, “JIT and the complementarity of buffers and lot size,” American Business Review, West Haven: January, Vol. 21, Issue 1, (2003), pp. 100-106.
  • Takahashi, Katsuhiko, Katsumi Morikawa, and Nobuto Nakamura, “Reactive JIT ordering system for changes in the mean and variance of demand,” International Journal of Production Economics, Amsterdam, Vol. 92, Issue. 2 (2004),pp. 181-196.
  • White, Richard E, and John N. Pearson, “JIT system integration and customer service,” International Journal of Physical Distribution & Logistics Management, Bradford, Vol. 31, Issue 5, (2001), pp. 313-333.
  • Yang, Jiaqin, and Richard H. Deane, “A lotsize reduction model for just-in-time manufacturing systems,” Integrated Manufacturing Systems,Vol. 13, Issue 7, (2002), pp. 471-488.
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