Defining accurate delivery dates in make to order job-shops managed by workload control

Abstract

Workload control (WLC) is a lean oriented system that reduces queues and waiting times, by imposing a cap to the workload released to the shop floor. Unfortunately, WLC performance does not systematically outperform that of push operating systems, with undersaturated utilizations levels and optimized dispatching rules. To address this issue, many scientific works made use of complex job-release mechanisms and sophisticated dispatching rules, but this makes WLC too complicated for industrial applications. So, in this study, we propose a complementary approach. At first, to reduce queuing time variability, we introduce a simple WLC system; next we integrate it with a predictive tool that, based on the system state, can accurately forecast the total time needed to manufacture and deliver a job. Due to the non-linearity among dependent and independent variables, forecasts are made using a multi-layer-perceptron; yet, to have a comparison, the effectiveness of both linear and non-linear multi regression model has been tested too. Anyhow, if due dates are endogenous (i.e. set by the manufacturer), they can be directly bound to this internal estimate. Conversely, if they are exogenous (i.e. set by the customer), this approach may not be enough to minimize the percentage of tardy jobs. So, we also propose a negotiation scheme, which can be used to extend exogenous due dates considered too tight, with respect to the internal estimate. This is the main contribution of the paper, as it makes the forecasting approach truly useful in many industrial applications. To test our approach, we simulated a 6-machines job-shop controlled with WLC and equipped with the proposed forecasting system. Obtained performances, namely WIP levels, percentage of tardy jobs and negotiated due dates, were compared with those of a set classical benchmark, and demonstrated the robustness and the quality of our approach, which ensures minimal delays.

A new perspective on Workload Control by measuring operating performances through an economic valorization

“…We also note that, if a single norm is used to constrain the cumulative workload of the system , the release phase is named ‘total shop load’ control. Conversely, if multiple norms are used to limit the cumulative workload of individual machines, the release phase is labelled as ‘bottleneck load’ or ‘load at each machine’, if control is limited to the supposed bottlenecks or extended to all machines, respectively (for more details, see 39 – 41 ).…”

“…Like the ‘aggregated approach’, the load is rescaled as soon as job is released and, next, the value of will no longer be changed. The use of the corrected aggregate approach is generally preferable, as it assures high performance, and it also simplifies the fine-tuning of the norms, as described in greater details by 15 , 41 .…”

Modeling and data analytics in manufacturing and supply chain operations

“…The fourth paper, by Mezzogori et al (2021), considers the workload control in lean production systems with the goal of reducing tardinesses and ensuring ontime deliveries. Existing research often handles this task by making use of sophisticated dispatching rules and complex job-release mechanisms, but it can make the workload control too complicated for real applications.…”

“…Two papers focus on supply chain problems, one on information sharing by Dominguez et al (2021) and one on leasing and selling strategies by Li et al (2021)). Two papers consider scheduling and dispatching problems in manufacturing, one in flexible manufacturing by Zanchettin (2021) and one on lean manufacturing by Mezzogori et al (2021). The fifth and last paper, by Guo et al (2021), considers a scheduling problem in the services industry, namely a medical staff scheduling problem.…”

Balancing earliness and tardiness within workload control order release: an assessment by simulation

“…Workload Control is a production planning and control concept which was developed for high-variety make-to-order contexts, but can also be applied to make-to-stock contexts (Zaepfel and Missbauer 1993b;Stevenson et al 2005;Hutter et al 2018). A key production control function of Workload Control is order release, which reduces queues and waiting times by imposing a cap on the workload released to the shop floor (Mezzogori et al 2021). When order release control is applied, jobs do not enter the shop floor directly.…”