A case study of a principally new way of materials kitting—an evaluation of time consumption and physical workload
Introduction
The car industry's customers demand a wide variety of models and variants. Manufacturers thus compete by for example offering customised cars. This demand and the manufacturing strategy result in the handling of a large number of components in production systems. The problem of keeping many and varied components is met in many companies by materials kitting. A materials kit consists of all the components needed to assemble an individual product or a complete part of a product. Materials kitting is the process of producing the materials kit (Cox et al., 1995) and is often needed when parallel production flows are used to enable material feeding of workstations (i.e. to reduce costs of stocks and space for materials in progress). Kitting is also introduced in traditional line assembly as an alternative to line stocking, foremost for reasons of accuracy and less work in progress (Bozer and McGinnis, 1992).
Traditionally, materials picking is done according to a picker-to-material principle: kitting is done in a storage area where a material picker moves him/herself between material containers (storage packages) and picks materials to so-called picking packages. Such systems are generally time consuming as pickers are forced to transport themselves a great deal in the storage area. Some companies have attempted to improve picking systems by using a material-to-picker principle: storage packages are moved to material pickers who pick materials to picking packages, reducing the need for transportation. However, there is a great need to improve present picking systems in terms of their efficiency.
The physical exposure of workers must be considered when improvements are made in picking systems since work-related musculoskeletal disorders are common in manual materials handling. Manual materials handling generally involves repetitive movements and work postures with the arms abducted and elevated. These work conditions are known risk factors, especially for neck and upper limb disorders (Kourinka and Forcier, 1995).
To this time, ergonomic interventions have generally showed little success in improving musculoskeletal health (Westgaard and Winkel, 1997). One reason might be that the actions taken have been inadequate owing to a lack of quantitative data on physical/mechanical exposure (Winkel and Westgaard, 1992), although methods for assessing exposure are now available (Hansson et al., 1996; Åkesson et al., 1997; Hansson and Mikkelsen, 1997; Nordander et al., 2000).
However, in the few studies in which exposure data have been registered, it has most often been done without considering detailed levels of the production systems, e.g. tasks and work activities. In an intervention perspective, it is essential to gain knowledge on the exposure imposed by different tasks. Thus exposure data and information on work content must be registered synchronously and analysed in an integrated manner.
This paper presents a case study carried out in a production plant at a car manufacturer. The aim of the study was to make an integrated evaluation of a new kitting system in terms of time consumption and physical exposure.
Section snippets
The case study
The case study focused on warehouse operations in a production system for materials kitting. Two types of material kits were made in the warehouse: (1) sets of plastic containers with material and (2) material on specially designed material carts. The total work was divided into nine work tasks (picking different types of material, material transportation, quality work, etc.) that the workers rotated between on daily basis (1 day/work task). In total, 29 employees worked in the warehouse.
The
Analyses of work activities
Analyses of work activities were made for the four material pickers. The analysis comprised a total of 858 min of work time and included 5509 picking operations. Table 2 shows the mean time/picking operation of each work activity group for each material picker. Results of the zero-based analyses are reported in Fig. 3.
Time consumption can be related to different measures such as picking operation, work cycle (i.e. one for each part number), batch of picking packages of a similar type or total
Discussion
The results of the case study show that the kitting system's productivity, in comparison with similar kitting systems, is high and has a potential for further improvement. A major reason for the high level of productivity was the material-to-picker principle used, which involved larger batch sizes and less need for transportation. The level of losses is rather high, however. This is partly explained by the fact that the kitting system was in a run-in phase at the time of the study. Results of a
Conclusions
The results of the case study show that the kitting system's productivity, in comparison with similar kitting systems, is high and has a potential for further improvement. As a consequence of the system design, the materials picking work was highly repetitive. The workers experienced also the work as repetitive and as containing some physically stressful work situations. The results indicate that an improved productivity, i.e. reduced time for losses, should not automatically result in higher
Acknowledgments
This study was carried out under a Swedish industrial research program called Co-operative for Optimisation of industrial production systems regarding Productivity and Ergonomics, COPE, funded by the Swedish National Institute for Working Life.
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