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Manufacturing Systems
Published in Richard L. Shell, Ernest L. Hall, Handbook of Industrial Automation, 2000
CONWIP (CONstant Work In Process) is a pull philosophy whose strategy is to limit the total amount of in-process inventory that is allowed into the manufacturing process. The mechanism for release of materials or components into the process is signaled by the customer withdrawing or “pulling” a unit from finished goods inventory. Once the unit is removed from finished goods, a signal is sent to the initial workcenter to release additional materials into the process (see Fig. 13). Once materials or components are released into the system they will progress all the way through the system until reaching finished goods inventory. If finished goods inventory is filled, there will be no mechanism to release materials into the system.
Pull Replenishment Systems
Published in Peter L. King, Lean for the Process Industries, 2019
ConWIP (Constant Work In Process) is a strategy for managing production that limits in-process inventory and can be used as an alternative to kanban. ConWIP can control an entire process, or several steps in the process. The fundamental idea is that nothing is allowed to enter the process segment being controlled by ConWIP, the ConWIP loop, until something leaves. This one-for-one relationship between lots leaving and lots entering maintains work in process within the loop to a fixed amount. Thus, overproduction is prevented, and ConWIP can be used as the control mechanism in a pull system.
CONWIP and Hybrid CONWIP Production Control Systems: A Literature Review
Published in Khojasteh Yacob, Production Management, 2017
Mehmet Bulent Durmusoglu, Canan Aglan
Studies about CONWIP control generally are applied to flow shop environment, and mainly rely on throughput time and WIP reduction. The majority of studies are based on performance comparison with other push/pull-based control mechanisms. Although there are control mechanisms which have better performance, CONWIP is generally superior to other control mechanisms in comparison studies.
A new methodological support for control and optimization of manufacturing systems in the context of product customization
Published in Journal of Industrial and Production Engineering, 2021
Yann Jaegler, Anicia Jaegler, Fatima Zahra Mhada, Damien Trentesaux, Patrick Burlat
This means that it would be a difficult problem for a manufacturer to calculate the best or even good parameters to size their ConWip. Indeed, even the simplest mathematical model to size ConWip is often NP-complete and therefore is difficult to optimize for a real-world problem, which deals with a large number of products and machines. Also, these models are usually in the form of a mixed integer linear program (MILP), in which some of the variables are continuous or integers (ConWip lot sizing, number of installations … .) and some are binary (position of the workshops, belonging to routings, …). The manufacturer would have no option but to use his own experience or to proceed by testing different parameters. This fact is demonstrated by [34], who explain that the literature highlights many challenging avenues that should be explored to effectively respond the PCS questions that have been raised relative to decision-making. Adapting ConWip to a specific environment, such as a highly complex industry characterized by MTO, high mix, job shops and high standard deviation between routings, constitutes a significant research challenge. In the case of a moving environment, this experience or testing driven optimization will take too much time to stand for a real solution. In this context, the question this paper will help to answer is the following: how can one decide which parameters to use to size a ConWip system in a moving product customization environment? To the aim, this paper designs a decision-making help tool in product customization environment ConWip for manufacturers.
On the meaning of ConWIP cards: an assessment by simulation
Published in Journal of Industrial and Production Engineering, 2019
Matthias Thürer, Nuno O. Fernandes, Nick Ziengs, Mark Stevenson
Constant Work-in-Process (ConWIP) [1, 2] is a simple card-based production control system. It is essentially a pull system [3] that uses a Work-In-Process (WIP) limit or WIP-cap (WIP-Cap) to realize input/output control [4]. In accordance with input/output control, the output of work from the shop floor determines the input of work to the shop floor. Jobs are only permitted to enter the shop floor if the WIP-Cap, which is pre-established by management, is not violated; otherwise, they have to wait in a so-called “backlog” [1] until a job on the shop floor has been completed. Cards circulate between the exit from the shop floor and the backlog or entry point. The return of a card signals that one job has been completed (output), and another can be released (input).
Comparison of pull management policies for a divergent process with DDMRP buffers: an industrial case study
Published in International Journal of Production Research, 2023
Guillaume Dessevre, Jacques Lamothe, Robert Pellerin, Maha Ben Ali, Pierre Baptiste, Vincent Pomponne
This paper proposes to delay allocation decisions until the last moment, where we have access to precise information about the quantities of FPs to bottle. One of the best ways to do that is to use a Constant Work-In-Process (ConWIP) system. The ConWIP is a control system using a single card type, called a ticket, to control the amount of WIP in a production loop (Spearman, Woodruff, and Hopp 1990). Based on Little’s Law (Little 1961), this method aims to control the amount of work by limiting it to control the cycle time in the ConWIP loop. The ConWIP tickets limit the waiting times in different queues in the loop by moving these times before the loop.