On the meaning of ‘Waste’: review and definition

Waste reduction is one of the main principles of lean, but it has been taken for granted that we have a common understanding of what waste means. We first present a critical, qualitative discussion that identifies four distinct waste concepts. We then conduct a systematic review of the literature that examines the different uses of these concepts. We find that only the classic concept of the seven wastes and the concept of waste as non-value-adding activity are widely applied. However, both concepts are, at times, not only incompatible but used in a way that leads to open contradiction. A new definition, centred on an efficient, timely transformation process seeks to consolidate the literature. We outline two distinct waste types: (i) obvious waste, to refer to any waste that can be reduced without creating another form of waste; and, (ii) buffer waste, to refer to any waste that cannot be reduced without creating another waste. The paper has important implications for practice. To reduce waste, managers must undertake three interlinked tasks: the elimination of obvious waste; the reduction of variability to transform buffers into obvious waste; and, the balancing of remaining buffers to best achieve performance targets. The paper supports managers in their endeavours to identify waste, which is an important precursor to waste reduction/elimination.     

Well-being of mid- and later-life mothers of children with developmental disabilities

This study examined the well-being of mid- and later-life mothers of developmentally disabled (DD) children. Mothers of DD children (n = 33) and mothers in a comparison group (n = 27) responded to a series of quantitative measures of well-being and open-ended questions. In general, quantitative results indicated lower levels of well-being for mothers of DD children. However, we examined these results within the contexts of educational and financial realities and access to adequate social support. Analysis of the qualitative data resulted in the themes of enhancements to well-being, challenges to well-being and normative experiences of being a parent. Results point to the need to further understand reciprocity in the mother-child relationships and the influence of severity of the developmental disability on mother's well-being.     

Concerning Workload Control and Order Release: The Pre‐Shop Pool Sequencing Decision

Every production planning concept that incorporates controlled order release will initially withhold jobs from the shop floor and create a pre‐shop pool. Order release is a key component of the Workload Control concept that aims to maintain work‐in‐process within limits while ensuring due dates are met. Order release includes two decisions: (i) a sequencing decision that establishes the order in which jobs are considered for release; and, (ii) a selection decision that determines the criteria for choosing jobs for release. While selection has received much research attention, sequencing has been largely neglected. Using simulation, this study uncovers the potential for performance improvement in the sequencing decision and improves our understanding of how order release methods should be designed. Although most prior studies apply time‐oriented sequencing rules and load‐oriented selection rules, analysis reveals that load balancing considerations should also be incorporated in the sequencing decision. But an exclusive focus on load balancing is shown to increase mean tardiness and, paradoxically, require high workloads. A new sequencing rule is developed that only balances loads when multiple orders become urgent. It avoids high mean tardiness and allows the shop to operate at a low workload level. At the same time, the percentage tardy is reduced by up to 50% compared to a purely time‐oriented rule. The findings have implications not only for Workload Control but for any concept that features order release control, such as ConWIP and Drum‐Buffer‐Rope.     

Lean Control for Make‐to‐Order Companies: Integrating Customer Enquiry Management and Order Release

A lead time that is short, predictable, and reliable is an increasingly important criterion in supplier selection. Although many companies may achieve this through lean implementation, high‐variety manufacturers, for example, small and medium‐sized make‐to‐order companies, have found that lean's planning and control techniques do not apply. This article outlines a planning and control concept known as workload control (WLC) that integrates customer enquiry management, including a due‐date setting rule, with order release control. Simulation is then used to assess its impact on shop performance. Results demonstrate that an integrated WLC concept can reduce the percentage of tardy jobs—so short lead times can be realistically quoted—while also reducing and stabilizing workloads. WLC can level demand and production over time when work is not standardized and it is not possible to synchronize flows on the shop floor. Results are shown to be robust to changes in routing characteristics, the mix of orders with due dates specified by the customer and proposed internally, and the strike rate (or order‐winning probability). Hence, an integrated approach to WLC represents an important step toward achieving lean in make‐to‐order companies.     

Card-based production control: a review of the control mechanisms underpinning Kanban,ConWIP, POLCA and COBACABANA systems

Since the emergence of Kanban, there has been much research into card-based control systems. This has included attempts to improve Kanban and/or develop alternative systems, particularly ConWIP (i.e. Constant Work-In-Process), POLCA (i.e. Paired-cell Overlapping Loops of Cards with Authorisation) and COBACABANA (i.e. Control of Balance by Card-Based Navigation). Yet, to date, no unifying review of the mechanisms underpinning these systems has been presented. As a consequence, managers are not provided with sufficient support for choosing an appropriate system for their shop; and researchers lack a clear picture of how the mechanisms compare, leading to several misconceptions. This paper reviews the control mechanisms underpinning the Kanban, ConWIP, POLCA and COBACABANA systems. By comparing the ‘control mechanism’ (i.e. the loop structure and card properties) and ‘contextual factors’ (i.e. routing variability, processing time variability, and whether stations are decoupled by inventory or the flow of jobs is controlled), we provide managers with guidance on which system to choose. For research, we show for example that most criticisms put forward against Kanban systems, e.g. to justify the development of ConWIP, POLCA or COBACABANA, only apply to work-in-process Kanban systems and not to production Kanban systems. Future research directions for each control system are outlined.