CONWIP versus POLCA: A comparative analysis in a high-mix, low-volume (HMLV) manufacturing environment
Abstract: Few studies
comparing manufacturing control systems as they relate to high-mix, low-volume
applications have been reported. This paper compares two strategies, constant
work in process (CONWIP) and Paired-cell Overlapping Loops of Cards with Authorization
(POLCA), for controlling work in process (WIP) in such a manufacturing
environment. Characteristics of each control method are explained in regards to
lead time impact and thus, why one may be advantageous over the other.
Design/methodology/approach: An industrial system in the Photonics
industry is studied. Discrete event simulation is used as the primary tool to
compare performance of CONWIP and POLCA controls for the same WIP level with
respect to lead time. Model verification and validation are accomplished by
comparing historic data to simulation generated data including utilizations.
Both deterministic and Poisson distributed order arrivals are considered.
Findings: For the system considered in this case study, including order
arrival patterns, a POLCA control can outperform a CONWIP parameter in terms of
average lead time for a given level of WIP. At higher levels of WIP, the
performance of POLCA and CONWIP is equivalent.
Practical Implications: The POLCA control helps limit WIP in specific áreas
of the system where the CONWIP control only limits the overall WIP in the
system. Thus, POLCA can generate acceptably low lead times at lower levels of
WIP for conditions equivalent to the HMLV manufacturing systems studied.
Originality/value: The study compliments and extends previous studies
of CONWIP and POLCA performance to a
HMLV manufacturing environment. It demonstrates the utility of discrete event
simulation in that regard. It shows that proper inventory controls in
bottleneck áreas of a system can reduce average lead time.
Author: Todd Frazee, Charles
Standridge
Journal Code: jptindustrigg160006
