Why do nonlinearities matter? The repercussions of linear assumptions on the dynamic behaviour of assemble-to-order systems

The hybrid assembly-to-order (ATO) supply chain, combining make-to-stock and make-to-order (MTS-MTO) production, separated by a customer order decoupling point (CODP), is well recognised in many sectors. Based on the well-established Inventory and Order Based Production Control Systems (the IOBPCS family), we develop a hybrid ATO system dynamics model and analytically study the impact of nonlinearities on its dynamic performance. Nonlinearities play an important, sometimes even a dominant, role in influencing the dynamic performance of supply chain systems. However, most IOBPCS based analytical studies assume supply chain systems are completely linear and thereby greatly limit the applicability of published results, making it difficult to fully explain and describe oscillations caused by internal factors. We address this gap by analytically exploring the non-negative order and capacity constraint nonlinearities present in an ATO system. By adopting nonlinear control engineering and simulation approaches, we reveal that, depending on the mean and amplitude of the demand, the non-negative order and capacity constraints in the ATO system may occur and their significant impact on system dynamics performance should be carefully considered. Failing to monitor non-negative order constraints may underestimate the mean level of inventory and overestimate the inventory recovery speed. Sub-assemblers may suffer increased inventory cost (i.e. the consequence of varying inventory levels and recovery speed) if capacity and non-negative order constraints are not considered at their production site. Future research should consider the optimal trade-off design between CODP inventory and capacity and the exploration of delivery lead-time dynamics

Extending customer order penetration concepts to engineering designs

Purpose - The customer order decoupling point (CODP) concept addresses the issue of customer engagement in the manufacturing process. This has traditionally been applied to material flows, but has more recently been applied to engineering activities. This later subject becomes of particular importance to companies operating in ‘engineer-to-order’ (ETO) supply chains, where each order is potentially unique. Existing conceptualisations of ETO are too generic for practical purposes, so there is a need to better understand order penetration in the context of engineering activities, especially design. Hence, we address the question ‘how do customer penetration concepts apply to engineering design activities?’ Methodology - A collaborative form of inquiry is adopted, whereby academics and practitioners co-operated to develop a conceptual framework. Within this overarching research design, a focus group of senior practitioners and multiple case studies principally from complex civil and structural engineering as well as scientific equipment projects are used to explore the framework. Findings - The framework results in a classification of nine potential engineering subclasses, and insight is given into order penetration points, major uncertainties and enablers via the case studies. Focus group findings indicate that different managerial approaches are needed across subclasses. Implications –The findings give insight for companies that engage directly with customers on a one-to-one basis, outlining the extent of customer penetration in engineering activities, associated operational strategies and choices regarding the co-creation of products with customers. Care should be taken in generalising beyond the sectors addressed in the study. Originality - The paper refines the definition of the ETO concept, and gives a more complete understanding of customer penetration concepts. It provides a comprehensive reconceptualization of the ETO category, supported by exploratory empirical research

A systematic review of research into the management of manufacturing capabilities

Our study aims to explore the past and present knowledge related to the management of manufacturing capabilities and to assess the extent to which our knowledge of this field has developed. It places specific emphasis on the philosophical foundations of the field, while also providing a set of directions for future research. A systematic review is applied, covering 104 articles. The authors unfold a strong dominance of the positivist paradigm, and call for a more balanced and informed approach in philosophical and, more specifically, methodological selection by scholars. In terms of the research content, a strong bias exists towards measuring the impact that certain manufacturing capabilities, and various configurations of these, may have on key performance indicators, such as cost. Our review warns on the dangers of following a dominant paradigmatic stance and on the limitations of researching a limited area of the complex and dynamic manufacturing capabilities arena

The impact of product returns and remanufacturing uncertainties on the dynamic performance of a multi-echelon closed-loop supply chain

We investigate a three-echelon manufacturing and remanufacturing closed-loop supply chain (CLSC) constituting of a retailer, a manufacturer and a supplier. Each echelon, apart from its usual operations in the forward SC (FSC), has its own reverse logistics (RL) operations. We assume that RL information is transparent to the FSC, and the same replenishment policies are used throughout the supply chain. We focus on the impact on dynamic performance of uncertainties in the return yield, RL lead time and the product consumption lead time. Two outcomes are studied: order rate and serviceable inventory. The results suggest that higher return yield improves dynamic performance in terms of overshoot and risk of stock-out with a unit step response as input. However, when the return yield reaches a certain level, the classic bullwhip propagation normally associated with the FSC does not always hold. The longer remanufacturing and product consumption lead times result in a higher overshoot and a longer time to recover inventory, as well as more oscillation in the step response at the upstream echelons. We also study bullwhip and inventory variance when demand is a random variable. Our analysis suggests that higher return yield contributes to reduced bullwhip and inventory variance at the echelon level but for the CLSC as a whole the level of bullwhip may decrease as well as increase as it propagates along the supply chain. The reason for such behaviour is due to the interaction of the various model parameters and should be the subject of further analytical research. Furthermore, by studying the three-echelon CLSC, we produce a general equation for eliminating inventory offsets in an n-echelon CLSC. This is helpful to managers who wish to maintain inventory service levels in multi-echelon CLSCs

A hybrid multi-objective approach to capacitated facility location with flexible store allocation for green logistics modeling

We propose an efficient evolutionary multi-objective optimization approach to the capacitated facility location–allocation problem (CFLP) for solving large instances that considers flexibility at the allocation level, where financial costs and CO2 emissions are considered simultaneously. Our approach utilizes suitably adapted Lagrangian Relaxation models for dealing with costs and CO2 emissions at the allocation level, within a multi-objective evolutionary framework at the location level. Thus our method assesses the robustness of each location solution with respect to our two objectives for customer allocation. We extend our exploration of selected solutions by considering a range of trade-offs for customer allocation

The value of regulating returns for enhancing the dynamic behaviour of hybrid manufacturing-remanufacturing systems

Several studies have determined that product returns positively impact on the dynamics of hybrid manufacturing-remanufacturing systems, provided that they are perfectly correlated with demand. By considering imperfect correlation, we observe that intrinsic variations of returns may dramatically deteriorate the operational performance of these closed-loop supply chains. To cope with such added complexity, we propose a structure for controlling the reverse flow through the recoverable stock. The developed mechanism, in the form of a prefilter, is designed to leverage the known positive consequences of the deterministic component of the returns and to buffer the harmful impact of their stochastic component. We show that this outperforms both the benchmark push system and a baseline solution consisting of regulating all the returns. Consequently, we demonstrate that the operation of the production system is greatly smoothed and inventory is better managed. By developing a new framework for measuring the dynamics of closed-loop supply chains, we show that a significant reduction in the net stock, manufacturing, and remanufacturing variances can be achieved, which undoubtedly has implications both for stock reduction and production stabilization. Thus, the known benefits of circular economy models are strengthened, both economically and environmentally

The effect of returns volume uncertainty on the dynamic performance of closed-loop supply chains

We investigate the dynamics of a hybrid manufacturing/remanufacturing system (HMRS) by exploring the impact of the average return yield and uncertainty in returns volume. Through modelling and simulation techniques, we measure the long-term variability of end-product inventories and orders issued, given its negative impact on the operational performance of supply chains, as well as the average net stock and the average backlog, in order to consider the key trade-off between service level and holding requirements. In this regard, prior studies have observed that returns may positively impact the dynamic behaviour of the HMRS. We demonstrate that this occurs as long as the intrinsic uncertainty in the volume of returns is low —increasing the return yield results in decreased fluctuations in production, which enhances the operation of the closed-loop system. Interestingly, we observe a U-shaped relationship between the inventory performance and the return yield. However, the dynamics of the supply chain may significantly suffer from returns volume uncertainty through the damaging Bullwhip phenomenon. Under this scenario, the relationship between the average return yield and the intrinsic returns volume variability determines the operational performance of closed-loop supply chains in comparison with traditional (open-loop) systems. In this sense, this research adds to the still very limited literature on the dynamic behaviour of closed-loop supply chains, whose importance is enormously growing in the current production model evolving from a linear to a circular architecture

Investigating sustained oscillations in nonlinear production and inventory control models

Even in a deterministic setting, nonlinearities can yield unexpected dynamic behaviours in a production and inventory control system, such as sustained oscillations or limit cycles. Describing function in combination with simulation is used to analyse the effect of discontinuous nonlinearities on the system responses. Utilising a nonlinear production and inventory control model, we investigate the occurrence of limit cycles and propose a technique to predict their amplitude, frequency and stability and to control such oscillations. Findings suggest that, even for an autonomous production and inventory control system, limit cycles do occur and this periodic behaviour occurs due to non-negativity constraint in the ordering rule. Moreover, we demonstrate the potential of the describing function method to provide insight into the impact of system constraints and therefore facilitate a more effective system design. This paper fills a gap in the literature on nonlinear supply chain dynamics by expanding and complementing the sparse recent research in this area. Most previous studies have either focused on linear mathematical models or relied on simulation, which greatly limit the relevancy and/or rigour of the published results

The dynamics of emergency transhipment supply chains

Considers the dynamical effect of lateral emergency transhipments within a supply chain. It tests various different strategies for improving customer service via the MIT Beer Game. Four distinct strategies are considered. “Electronic point of sales (EPOS)”, where marketplace information is forwarded to all players throughout the supply chain; “Excel”, where the stock levels in all echelons are controlled by the factory; “Emergency transhipments”, where an express transportation route bypassing an echelon in the supply chain is permitted; “Eliminate”, where an echelon is removed from the supply chain. The Beer Game strategies are also studied via a simulation exercise. Results show that the Excel strategy is flawed, whereas the EPOS strategy has a strong impact on inventory cost, Emergency transhipments has a strong impact on customer service level and Eliminate results in less stock for an improved customer service level. Combinations of the three viable strategies are also tested. This paper concludes that the three strategies can be integrated to significantly improve supply chain performance

Rethinking infrastructure supply chain management – a manifesto for change

Infrastructure projects exemplify engineer-to-order supply chains, where there is a high degree of complexity and uncertainty associated with developing a ‘unique’ product. While there is much advocacy of translating operational excellence techniques from high volume manufacturing sectors, we argue that such an approach is based on a mis-presumption of order and structure at all systems levels. We suggest an alternative ‘travel of an idea’ from the knowledge management discipline, a phenomenological framework describing contexts in terms of ordered and un-ordered, which directs us towards the need for diverse management approaches if we are to minimise the risk of project underperformance and failure. We contemplate the value of the framework and reflect on the contribution it can make to the construction industry specifically and to engineer-to-order production systems more generally; we provide a basis to bring a healthy challenge when ‘travelling ideas’ and expose how unthinking choices can be expected to fail