CUWIP: A MODIFIED CONWIP APPROACH TO CONTROLLING WIP

Jules Comeau
Uday Venkatadri

Abstract: CONWIP (Constant Work In Process) is a production control method that puts an upper bound on the number of lots in a production line or individual work center in order to control the level of WIP.  In a make to order production environment with a first come, first serve sequencing rule, if customer demand varies greatly in terms of order size and product mix, the observed WIP level can fluctuate correspondingly.  In the proposed method, CUWIP, all customer orders are defined using Units of Equivalence (UE).  The proposed approach caps the number of UE’s for the entire production line.  The method is tested via an AweSim (SLAM based) simulation using actual data from a window plant production line.  Results show that production throughput is maintained (as compared to a push system) while reducing average WIP levels and average cycle times.  CUWIP also appears to give lower coefficients of variation for cycle times and WIP levels compared to those obtained with CONWIP.   Hence, CUWIP seems to retain the advantages of CONWIP, while being suited for a greater variety of environments.

Keywords: CONWIP, Pull production systems, variable demand, Little’s law

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