A comparison of kitting and continuous supply in in-plant materials supply

In the context of in-plant materials supply, the materials feeding principle of kitting is often discussed as an alternative to the more common continuous supply (also known as line stocking). However, there are few detailed studies describing the relative effects of kitting and continuous supply. The current paper identifies the relative effects of kitting and continuous supply, and provides insight into how these effects arise. The paper draws on empirical data from two case studies in the Swedish automotive assembly industry. In each of the cases, continuous supply has been replaced by kitting, enabling comparison of kitting and continuous supply in the same production environment. The performance areas studied include man-hour consumption, product quality, flexibility, inventory levels, and space requirements. Interviews with production engineers, assemblers, and operators responsible for kit preparation at each company contribute to a broad yet detailed view of the relative effects of the two materials feeding principles.     

A classification of tactical assembly line feeding problems

Trends like mass-customisation and the increasing number of models produced and parts used on a single assembly line promote interest in the field of assembly line feeding. The assembly line feeding problem (ALFP) deals with the assignment of parts to line feeding policies such as line stocking, boxed-supply, sequencing and kitting (stationary and travelling), and emerged as a research field two and a half decades ago. In order to structure the increasing effort in this field, we provide an extensive review of the literature and organise it from various perspectives. Furthermore, we propose a classification for the ALFP and classify existing literature. The goal of this classification is threefold. Firstly, it should help the reader to get an overview of the problem and most of its related aspects. Secondly, the classification reveals blind spots in academic research. Finally, it enables practitioners to match real-world problems with existing research results. In order to encourage researchers to close the existing gaps, we finalise this paper by pointing out the most important open research fields.     

Selection of assembly lines feeding policies based on parts features and scenario conditions

This paper explores the impact of parts features, i.e. unit size and cost, as well as scenario variables on the total delivery cost of materials to assembly lines workstations, according to different materials feeding processes (kitting, line storage and just-in-time delivery). After building cost models based on parts features explicitation, a sensitivity and parametric analysis is carried out in order to justify the cost-effectiveness of each feeding policy and understand whether economic break-even points exist among available feeding alternatives on the basis of the values assumed by relevant attributes of parts. This allows to map areas where each feeding policy is more convenient and also allows a quick method to choose the best feeding policy for each part on an economic basis.     

Kitting in multi-echelon,multi-product assembly systems with parts substitutable

The kitting problem in multi-echelon, multi-product assembly systems with parts substitutable is to allocate on-hand stock and expected future deliveries to kits to minimize total cost including job earliness, job tardiness, and in-process holding cost while considering shop capacity and subassembly precedence restrictions, and parts being substitutable. This class of problem is NP-hard. When dealing with a large instance encountered in industry, in the worst case, it may not be possible to obtain an optimal solution in a reasonable time. In this paper, rules for using part substitutes along with heuristic procedure are presented. Computational results demonstrate that the proposed heuristic outperforms others tested. It is expected that the new heuristic can be applied in resolving largescale kitting problems encountered in industry to allocate available resources near optimality to enhance schedule performance and to lower the total cost of operating multi-echelon, multi-product assembly systems.     

Kitting optimisation in Just-in-Time mixed-model assembly lines: assigning parts to pickers in a hybrid robot–operator kitting system

With increasing components’ variety in mixed-model assembly lines, industrials show interest in kitting operations using robots. This paper deals with a hybrid kitting system that consists of a robot and an operator working in series to deliver parts to a Just-In-Time mixed-model assembly line. We develop a mathematical model that optimally assigns stock keeping units to either the robot or the operator so that the cycle time of the overall system is optimised. To test the model, a case study from the automotive sector is presented and a sensitivity analysis is carried out on relevant system parameters.     

Effective material flow at an assembly facility

Effective material flow in an assembly facility leads to reduced material handling costs and increased productivity. This research focuses on improving the flow of materials for an assembly facility that receives supplied parts through receiving docks and transfers the parts to material storage locations and then to part usage locations. The locations of the receiving docks, storage locations, and line locations are predetermined, but the assignment of parts to dock locations and storage locations and the material flow paths through the facility are decision variables. Furthermore, design decisions such as the dock strategy employed and the configuration of the storage areas lead to additional decision variables. The goal is to reduce overall material handling costs by effectively receiving, storing and transferring the material from loading docks to line locations. The contribution of this research is in applying multi-commodity network flow models that integrate many of the sub-problems that are assumed to be solved a priori in many existing models. This integrated approach was used to evaluate configuration changes for a collaborating facility. One of the scenarios analysed showed an improvement in the material handling costs of nearly 10% as compared to current practices.     

Man-hour efficiency of manual kit preparation in the materials supply to mass-customised assembly

Addressing the materials feeding principle of kitting, commonly applied in the materials supply to mass-customised assembly, the current paper has the purpose of exploring how the man-hour efficiency of kit preparation is affected by the design and the context of the kit preparation. The study presented in the paper is based on a comprehensive methodology, comprising several steps and considering a large set of qualitative as well as quantitative data from 15 case studies. It also utilises the expertise of practitioners from the industry. The paper provides a valuable addition to the existing literature where empirical evidence is scarce. From a practical perspective, it offers support to the design of man-hour efficient kit preparation systems. The findings show that the design and the context of the kit preparation system can have a decisive, yet complex, impact on the man-hour efficiency and, thereby, on an assessment of the applicability of kitting. The paper identifies several important aspects of both design and context and indicates how these aspects are linked to the man-hour efficiency of kit preparation.     

Making IT fit: the design of integrated manufacturing systems

One of the important implications of information technology (IT) is that it has made possible widespread automation in manufacturing industry. However, the bulk of this has involved discrete automation of single plant items or process elements rather than the total production system. Although the capital cost of such total system automation is a significant factor in slowing the rate of change in this direction, there are also a number of problem issues related to the integration of machines, computers and human systems within manufacture and design. Arguably the types of issue involved are not fully understood and in many cases the technological change is demanding totally new approaches and responses to the design of production systems and the traditional manufacture/design connections.The paper explores some of the issues raised in advanced manufacturing systems, drawing on case study research into the adoption of flexible manufacturing systems as an example of computer-integrated manufacture. It comments on the experience of case study firms and presents some comments on the design problems facing those responsible for integrated manufacturing systems.     

A comprehensive literature review and analysis of the design,balancing and scheduling of assembly systems

This paper reports the results of a comprehensive review and analysis of the assembly line balancing literature. Quantitative developments and qualitative issues are addressed at both the strategic and tactical levels. The numerous quantitative and qualitative factors which the literature mentions could impact the design, balancing and scheduling of assembly systems are organized into an eight-level hierarchical, factor/decision taxomony. This comprehensive taxonomy is used to assess our progress in assembly system design and operation. Finally, from the results of the literature review and progress assessment, suggestions for future research on socio-technical assembly systems are offered.     

Optimising part feeding in the automotive assembly industry: deciding between kitting and line stocking

In a synchronous and fast-paced assembly line operation, it is crucial that the right parts are being supplied at the right time and at the right place. In automotive assembly, the need for efficient material handling part delivery is particularly great because of extensive product customisation and the lack of space to stock all the required parts at the assembly line. This paper introduces a mathematical cost model for evaluating the assignment of parts to one of two possible material supply systems: kitting or line stocking. Case data from an automotive company in Belgium is used to test the model. The results demonstrate that hybrid policies, where some parts will be kitted while others will be stocked in bulk at the line, are preferred to the exclusive use of either material delivery system. The factors influencing the preferred delivery method for individual parts are explored. Numerical results are presented.     

Optimisation of the transmission of disruptions in assembly systems

The dynamic analysis of disruption transmission in networks of closed loops formed by machines and intermediate buffers is of vital importance in most production systems. Nevertheless, little research has been done on optimisation in this field. This study analyses the disruption time transmission in a generic assembly system, which has been modelled as a network of closed loops of machines and intermediate buffers. In addition, this modelling has been used to analyse a real automobile assembly line, taking into account variables that have not previously been considered in the literature, such as working regimes of machines, their cycle times, capacities of the intermediate buffers and their minimum contents. The optimal configuration of the intermediate buffers is analysed. Dynamic outlines of these kinds of assembly systems are proposed in order to maximise the transmission of disruption times and, hence, their availability. For this purpose, an algorithm for analysing and optimising availability in this kind of manufacturing system has also been developed.     

Kitting and time efficiency in manual assembly

The present paper focuses on parts presentation in manual assembly. Its aim is to determine how kitting affects the time spent by the assembler fetching parts and, more specifically, what is the impact of the proportion of parts included in the kit. The present paper is based on four case studies of automobile assembly, in which parts presentation by kitting is compared with parts presentation in component racks. In the case studies, kitting enabled shorter distances between parts presentation and assembly object and thereby a potential reduction in the time spent fetching parts. However, when only a proportion of parts were kitted, the time spent fetching parts was not always reduced, in spite of this potential. The present paper finds that when deciding which parts should be kitted, attention should be paid to how and in what order assembly operations are performed.     

Impact of work teams: a comparison study of assembly cells and assembly line for a variety of operating environments

This research compares assembly lines with different cellular, team working environments. Organization of an assembly system using cells requires worker flexibility where each worker is allowed to help his or her co-workers in the same cell and often to undertake a number of different tasks within the cell. We compare two different cellular systems with an unpaced, serial assembly line. The manufacturing systems are initially compared through an exploratory Markovian approach. Subsequently, the relative performance levels of the systems are examined across a variety of operating environments using simulation models. Operating environments vary based on shop size, setup times and processing time variances. The results indicate the general superiority of the cellular systems over the assembly line. However, some interesting observations are drawn for cases where the assembly line outperforms the cells. One of the cases is where workers realize substantial benefits in terms of performing their tasks in less time due to specialization on the tasks. The other scenario is where working in teams make the overall completion of the tasks more inefficient compared to working individually. Specific cross-over points are analyzed where the assembly lines start performing better than the assembly cells under these scenarios. The conclusions highlight guidelines for practicing managers on the most appropriate system under a given set of operating conditions.     

Meeting demand variation using flexible U-shaped assembly lines

Nowadays, companies must be able to provide a higher degree of product customisation to fulfil the needs of the increasingly sophisticated customer demand. This can only be achieved by having flexible production systems, able to cope with extended product ranges and with the uncertainty and variability of demand in the current market environment. The purpose of this paper is to present a contribution related to facilities design that accounts for this issue, by presenting flexible U-shaped line configurations for an assembly system. In this type of line, whenever the production volume or product mix changes, the only modification in the line will be the number of operators working in the line, as the physical workstations remain fixed. The relevance of the problem is stated and a heuristic procedure, based on ant colony algorithms, developed to address this problem is described. The results of the application of the proposed procedure to an assembly line of a major manufacturer of electronic security systems are reported.     

Labour productivity in modular assembly: a study of automotive module suppliers

Modular assembly is being applied to an increasing number of vehicles and part manufacturers to manage the ever-changing demands of the automotive industry. In spite of many researches performed on the supply chain management and logistics aspects of modular production, there is no research discussing modular production line concepts used by module suppliers. In this paper, labour productivity of two assembly line concepts including the conveyor line and box assembly line is studied under modular production environment. Both line concepts and respective assembly processes are described in detail. Mathematical models showing the total work faced by these two assembly line concepts are developed and compared. Two productivity scales are defined: the maximum achievable productivity and the actual productivity. The labour productivity rates of these assembly line concepts on above productivity scales obtained from calculations and a simulation are compared as a performance measure.     

Computational modelling of manufacturing choice complexity in a mixed-model assembly line

Manufacturing systems have evolved to adopt a mixed-model assembly line enabling the production of high product variety. Although the mixed-model assembly system with semi-automation (i.e. human involvement) can offer a wide range of advantages, the system becomes very complex as variety increases. Further, while the complexity from different options can worsen the system performance, there is a lack of quantifiable models for manufacturing complexity in the literature. Thus, in this paper, we propose a novel method to quantify manufacturing choice complexity for the effective management of semi-automated systems in a mixed-model assembly line. Based on the concept of information entropy, our model considers both the options mix and the similarities between options. The proposed model, along with an illustrative case study, not only serves as a tool to quantitatively assess the impact of choice complexity on total system performance, but also provides an insight into how complexity can be mitigated without affecting the overall manufacturing throughput.     

ASRS sizing for recreating automotive assembly sequences

Since a mixed model assembly line's efficiency depends on the sequence of jobs moving down the line, manufacturers spend considerable effort optimizing the sequence of jobs entering the plant. In automotive assembly plants however, repair loops and parallel stations scramble the sequence before it reaches the final assembly stage. Many automotive assembly plants use an automatic storage and retrieval system to revamp the scrambled sequence before final assembly. One plant even goes so far as to reconstruct the original sequence by completely undoing the sequence scrambling. We derive a relationship between the sequence scrambling information, the variety of model-colour configurations, and the size of the automatic storage and retrieval system needed to reconstruct the initial sequence. We enunciate this new ASRS sizing problem actually facing industry, show how to model it, present a solution approach, and demonstrate the approach on actual sequence scrambling data from an automotive assembly plant.     

An End-to-End Authentication Scheme for Healthcare IoT Systems Using WMSN

The healthcare internet of things (IoT) system has dramatically reshaped this important industry sector. This system employs the latest technology of IoT and wireless medical sensor networks to support the reliable connection of patients and healthcare providers. The goal is the remote monitoring of a patient’s physiological data by physicians. Moreover, this system can reduce the number and expenses of healthcare centers, make up for the shortage of healthcare centers in remote areas, enable consultation with expert physicians around the world, and increase the health awareness of communities. The major challenges that affect the rapid deployment and widespread acceptance of such a system are the weaknesses in the authentication process, which should maintain the privacy of patients, and the integrity of remote medical instructions. Current research results indicate the need of a flexible authentication scheme. This study proposes a scheme with enhanced security for healthcare IoT systems, called an end-to-end authentication scheme for healthcare IoT systems, that is, an E2EA. The proposed scheme supports security services such as a strong and flexible authentication process, simultaneous anonymity of the patient and physician, and perfect forward secrecy services. A security analysis based on formal and informal methods demonstrates that the proposed scheme can resist numerous security-related attacks. A comparison with related authentication schemes shows that the proposed scheme is efficient in terms of communication, computation, and storage, and therefore cannot only offer attractive security services but can reasonably be applied to healthcare IoT systems.     

Clusters and filling-curve-based storage assignment in a circuit board assembly kitting area

Kitting is the process that gathers all of the components necessary to assemble a batch of circuit boards on production machines. An objective in kitting storage design is to minimize the travel involved in collecting the components in the storage area so as to decrease labor costs. From outward appearances, the kitting process is similar to order picking in a warehouse. Closer observation, however, reveals that its unique characteristics favor a cluster-based allocation over the storage strategies usually adopted in warehouses. We present a clustering and cluster assignment method. In the clustering method we develop a new objective function and incorporate it into a genetic algorithm. In the cluster assignment method we first develop a new index for cluster assignment priorities. We then prove optimum assignments of clusters under restrictive conditions and extend the result to realistic storage configurations using filling curves. We analyze the properties affecting the quality of filling curves and develop a class of filling curves with good performance characteristics. Finally, we perform numerical analyses to show that the cluster and filling-curve-based assignment in the kitting area can reduce travel distances.     

Analysis of the type II robotic mixed-model assembly line balancing problem

In recent years, there has been an increasing trend towards using robots in production systems. Robots are used in different areas such as packaging, transportation, loading/unloading and especially assembly lines. One important step in taking advantage of robots on the assembly line is considering them while balancing the line. On the other hand, market conditions have increased the importance of mixed-model assembly lines. Therefore, in this article, the robotic mixed-model assembly line balancing problem is studied. The aim of this study is to develop a new efficient heuristic algorithm based on beam search in order to minimize the sum of cycle times over all models. In addition, mathematical models of the problem are presented for comparison. The proposed heuristic is tested on benchmark problems and compared with the optimal solutions. The results show that the algorithm is very competitive and is a promising tool for further research.