Veronique Limère

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.

Determination of standard times of nursing activities based on a Nursing Minimum Dataset

AIM This paper is a report of a study conducted to determine the standard time per nursing activity and the proportion of nursing time covered by the nursing activities of the Belgian Nursing Minimum Dataset compared to the total time of a nurse shift, and to evaluate the correlation between hospital size and standard times of nursing activities. BACKGROUND Because of a shrinking workforce and rising workload, nursing managers need tools that help them to allocate their staff to the wards. Such tools should be based on objective time measurements. METHODS The study was performed in surgical, internal medicine and elder care wards in an acute hospital care setting. In the first phase, a two-round Delphi-procedure was used to operationalize the definitions of nursing activities. In the second phase, the standard time for each nursing activity was determined, based on data collected over a 6-month period during 2006-2007. A combination of 13,292 work sampling observations by external observers, 3000 recordings of direct time measurement by self-recording and subjective time assessments yielded times that were used to analyse the duration of the nursing activities. RESULTS A standard time for 102 nursing activities was established. The coverage of the Belgian Nursing Minimum Dataset in the surgical, internal medicine and elder care wards was 47.5%, 46.4% and 51.0% respectively. The Belgian Nursing Minimum Dataset was found to cover almost 70% of direct and indirect nursing care. CONCLUSION Further research is needed to assess the impact on the standard times of nursing activities of inefficient organizational structures and different cultural interpretations of the way an activity is conducted.

A decision model for kitting and line stocking with variable operator walking distances

Purpose – The purpose of this paper is to propose a decision model to choose between kitting and line stocking at the level of single parts, while taking into account the variable operator walking distances. Different ways of feeding assembly lines, such as kitting and line stocking not only have an impact on in-plant logistics flows but also determine the amount of stock that is available at the line. This, in turn, has an impact on operator walking distances during assembly. Design/methodology/approach – A mixed integer linear programming model is developed for the assignment of parts to one of both methods, and to be able to extensively test the model, an algorithm is created for the construction of representative datasets. Findings – Parts are often kitted because of a space constraint at the line, but even without a space constraint, the shorter walking distances might give preference to kitting. An analysis is presented that demonstrates how specific part characteristics influence the chances of a p...

Comparing quantifiable methods to measure complexity in assembly

In order to measure complexity and stay competitive, manufacturing companies need to be able to quantify production complexity. For this reason, two methods were developed within the context of two concurrent research projects are compared: the Belgian Complexity Calculator, CXC, measures objective complexity and the Swedish Complexity Index, CXI, focuses on subjective complexity, as experienced by operators in the stations. This paper presents a comparative analysis of the two methods by comparing them to seven relevant existing quantitative methods and by examining results from case studies. It is observed that the two methods can be used as a compliment to one another, where CXC can be used for scanning data automatically CXI can be used for in-depth analysis. In addition, the comparison of existing methods provides insight on how to measure complexity depending on need and scope.

Workload balancing and manufacturing complexity levelling in mixed-model assembly lines

To effectively react and meet the current ever growing demand for individualised motor vehicles, built to customer specific requirements, automotive industry has accelerated its transition towards mass-customisation. As a result, the number of new model introductions has drastically increased over the past three decades. To cope with this intensified customisation, the current automotive assembly platforms are designed to assemble a wide range of relatively different models, and are turned into mixed-model assembly lines (MMALs). This implies that the set of tasks to be performed on each workstation is no longer stable but varies highly with the model-mix. As a consequence, the manufacturing complexity increases at the workstations and throughout the whole assembly system. This paper proposes a method to monitor manufacturing complexity at each workstation while the MMAL is being balanced. An entropy-based quantitative measure of complexity, which incorporates the variability of each task duration, is developed. This measure is used to monitor the manufacturing complexity level at each workstation. An integrated mixed-line balancing and complexity monitoring heuristic is proposed, to determine workload balance solutions, in which manufacturing complexity is levelled throughout the workstations composing the line. This procedure is tested on a real data-set provided by an automotive manufacturer. The results are reported and thoroughly discussed.

To kit or not to kit: optimizing part feeding in the automotive assembly industry

This is a summary of the author’s PhD thesis supervised by Hendrik Van Landeghem and defended on 22 December 2011 at the Universiteit Gent. The thesis is written in English and is available from the author upon request at veronique.limere@ugent.be and from https://biblio.ugent.be/publication/1985447. This work deals with the materials supply of automotive assembly lines. Mathematical optimization models are proposed for the tactical choice between two opposite materials supply systems, i.e. line stocking and kitting, and a theoretical basis for hybrid materials feeding policies is developed. The automotive industry is characterized by mass customization. Customers are very demanding and want products tailored to their needs. As a consequence, production in the automotive industry takes place on mixed-model assembly lines and a lot of different variant parts need to be supplied to the line. Because of the high number of transactions, efficient material handling is of great importance. An additional distinguishing feature of the automotive industry is the diversity of parts being assembled at the line, ranging from small (e.g. bolts and nuts) to large and voluminous (e.g. wheel well liners and truck side mirrors). This diversity of parts suggests that different methods of line feeding might be appropriate. In industry, different materials supply systems are found. Two opposites in the spectrum of materials supply systems are line stocking and kitting. Both systems have been studied separately, but no general purpose model that would facilitate the selection process—between kitting, partial kitting, and line stocking (i.e. no kitting)—has been reported in literature. This is the topic of this PhD study. A first mixed integer linear programming model (MILP) is developed to assign individual parts to one of both materials supply system alternatives to minimize total costs. The costs considered are the average yearly labor costs for operator picking at the line, internal transport, the kit assembly operation and replenishment of the supermarket. Based on some initial results, a second improved model is obtained taking into

Analysing the effectiveness of vendor-managed inventory in a single-warehouse, multiple-retailer system

This paper considers a two-stage supply chain, consisting of a single warehouse and multiple retailers facing deterministic demands, under a vendor-managed inventory (VMI) policy. It presents a two-phase optimisation approach for coordinating the shipments in this VMI system. The first phase uses direct shipping from the supplier to all retailers to minimise the overall inventory costs. Then, in the second phase, the retailers are clustered using a construction heuristic in order to optimise the transportation costs while satisfying some additional restrictions. The improvement of the systems performance through coordinated VMI replenishments against the system with direct shipping only is shown and discussed in the comparative analysis section.

Warehousing efficiency in a small warehouse

Small warehouses generally have different needs than large warehouses. They usually do not have warehouse management systems that are data intensive and involve high capital investment. Operational procedures are more nebulous and management control is less rigid. Because of the difference in operational approach, different measures are needed in order to enhance productivity. This paper describes the results and insights gained from a study of the inventory control and warehouse operations at an industrial distributor of maintenance and repair items. The accuracy of the inventory and the efficiency of order picking are studied and appropriate measures are proposed in order to improve operations. Improvements are in the areas of process organization, inventory accuracy, inventory control, and order picking. Implementations and results are reported. Major improvements include lowering inventory levels and more efficient order picking.

Simulation modeling for end-of-Aisle automated storage and retrieval system

This paper presents a simulation study of an End-of-Aisle automated storage and retrieval system. Various elements of AS/RS control policies are combined to compare and analyze the performance of an End-of-Aisle automated storage and retrieval system. The extensive simulation study shows the isolated effects of various policies, as well as compares several combinations of policies and rules. This comparison provides a base for selecting the most suitable policy in the evaluated system.

Simulation based Performance Analysis of an End-of-Aisle Automated Storage and Retrieval System

This paper presents and discusses simulation of an end-of-aisle automated storage and retrieval system, using FLEXSIM 6. The objective of the simulation model is to analyze and compare results of different control policies and physical designs. The performance measures considered for the evaluation of each control policy and layout combination are the total travel time of the crane and the number of storage and retrieval operations performed. The experiments set up and the corresponding results are discussed.