Open Journal of Social Sciences, 204, 2, 226-23 Published Online Septeber 204 in SciRes. http://www.scirp.org/journal/jss http://dx.doi.org/0.4236/jss.204.29038 Integration of Lean Approaches to Manage a Manual Assebly Syste Qian Wang, ick Bennett School of Engineering, University of Portsouth, UK Eail: qian.wang@port.ac.uk Received July 204 Abstract Today, iportance of flexibility and reconfigurability needs to be addressed when designing and ipleenting a cost-effective and responsive anufacturing syste. Such a syste should be able to accoodate dynaic changes of product varieties and production volues by axiizing its production capability and iniizing its production costs, this is particularly useful for a SME (sall and ediu-sized enterprises) to reain copetitive in the arket. For a anual assebly line, it is always a good practice using a highly skilled workforce that each assebly worker is capable of perforing ultiple tasks. Ideally, each worker is fully trained to coplete assigned tasks of a unit fro start to finish. This paper presents a case study of incorporating 5S anageent rules into an assebly syste using so-called skillful and dynaic walking workers as a cobination of lean anageent approaches to iprove productivity and efficiency of a shop floor production line at a local plant. Keywords Lean Manageent, Lean Production, Assebly Systes. Introduction It has been becoing a popular odel for any anufacturing copanies to introduce and ipleent lean approaches into every aspect of anufacturing-related activities. These activities include product design, anufacturing processes and systes planning and production anageent. One of lean production anageent techniques is called 5S, which is considered as a lean anageent ethod using visual identification and control anageent rules at a workplace. Major benefits of applying 5S techniques to a anufacturing plant were reported as such an iproveent of efficiency at a workplace, reduction of wastes, creation of a cleaner and well-organized working environent, and a prootion of eployee orale. These benefits can be enhanced by developing a ultiple skilled workforce that plays a key role in the success of operating a lean anufacturing syste, particularly when such a syste involves a great deal of huan-centered operations. Ballé et al. [] suggested that such a anpower production line should also be designed towards a reduction of the seven wastes, i.e., the waste of overproduction, the waste of waiting for parts to arrive, the waste of conveyance, the waste in processing, the waste of inventory, the waste of otion and the waste of rework. This paper presents a case How to cite this paper: Wang, Q. and Bennett,. (204) Integration of Lean Approaches to Manage a Manual Assebly Syste. Open Journal of Social Sciences, 2, 226-23. http://dx.doi.org/0.4236/jss.204.29038
Q. Wang,. Bennett study aied at iproving efficiency and productivity of a local anufacturing shop floor by integration of 5S anageent rules into a anual assebly line using highly skilled walking workers. These workers are capable of perforing ultiple and/or all the required tasks of a unit by traveling down between stations on the line. Such a syste can also be reconfigured easily and quickly as needed to accoodate the fluctuating change of production requireent on a daily basis. 2. A Lean Manageent of Using Walking Worker Assebly In anufacturing sectors, it is well-known that flexibility and reconfigurability of a anufacturing syste has increasingly becoe iportant as the syste needs to respond quickly to frequent changes of such as product ix and production volue due to a fluctuating deand of the copetitive arket today. Such a characteristic of flexible and reconfigurable anufacturing systes can also be helpful to axiize systes capability and iniize production costs to copete with other rivals that ake siilar products. It was reported that approxiately one third of all Geran copanies that have invested in highly advanced autoaton have recognized that these solutions were not flexible enough and have reduced again their level of autoation; 38% of these copanies have reduced autoation by taking advantage of a ore efficient use of their qualified workforce [2]. These workers can be trained to perfor ultiple or all the required tasks in a production area leading to a significant iproveent in ters of cost, tie, quality and capability when dealing with a variety of products over a traditional static allocation of worker(s) to a station in which each worker only perfors a single and repetitive task. Thus, capability in anufacturing products with high custoer custoization is relatively low. Figure illustrates a typical anufacturing syste using ultifunctional and dynaic walking workers. Within such a syste, each worker travels with a partially assebled product downstrea and stops at each station carrying out the essential assebly work as scheduled. Each worker is previously trained to be capable of building a product copletely fro start to end along the line. Under such a pull syste, a new ite of assebled products enters the line whenever a walking worker is available after a product assebly is copleted by this walking worker at the end of the line and this worker then releases the assebled product and oves back to the first station ready to start a new ite. Because each ite can only travel with one walking worker who works on it by visiting all the stations along the line, the nuber of ites in the syste is therefore deterinistic and theoretically it cannot be greater than the total nuber of workers eployed on the line. Thus, this type of syste inherently prevents unnecessary in-process inventory thereby decreasing the buffer requireent. Moreover, each walking worker on the line cannot be starved because each worker is attached to one ite all the tie and it is their responsibility for copletely assebling a product within an expected cycle tie through training, this decreases the loss of labor efficiency and axiizes individual labor utilization in practice. However, the loss of labor efficiency can be ade by the idle tie, which includes a cobination of a possible in-process waiting tie on the line and a travel tie fro each walking worker. evertheless, a U-shaped cell as show in Figure can iniize the travel tie along the line. 3. Matheatical Analysis The following notations are used: -: the total nuber of stations (or achines) on the line. -: the total nuber of walking workers in operating the syste. - PTi: the processing tie (fixed) at achine i. - PTi, j: the processing tie at achine i for walking worker j ( j ). Figure. A linear walking worker U-shaped line 227
Q. Wang,. Bennett -IPWTj: the in-process waiting tie for worker j ( j ). -TTj: the average travelling tie for walking worker j ( j ), who travels fro the first station to the last station along the line. -ITj: the total idle tie for walking worker j ( j ) during a copletion of a product. 3.. Workers with Equal Perforance In the first case study, we assue that each walking worker has equal efficiency; this is an ideal situation. Shown in Figure, we note that achine b (Mb), where b refers to the bottleneck, has the longest processing tie. After a period of syste war-up to reach a steady state, fro the oent that a walking worker j leaves the bottleneck Mb to the oent that this worker is about oving into the bottleneck Mb again (but not in Mb yet), a total aount of processing (operation) tie this walking worker spends in a circuit is given by: i b i PTb () Meanwhile, a total aount of tie that other walking workers (except walking worker j) spend in ters of processing (operation) ties at Mb is given by: ( ) PTb (2) If () (2): there is no in-process waiting tie. If () < (2): the in-process waiting tie for this walking worker j is given by: IPWTj (2) () [( ) PTb] PTb], i.e., IPWTj PTb Thus, the total idle tie for this worker j during the copletion of a product is given by: ITj IPWTj + 2TTj PTb PTi PTi + 2TTj, i.e., ITj PTb PTi + 2TTj (4) Therefore, the aount of tie this walking worker needs for producing a unit in a circuit is given below: ITj + or PTb + 2TTj (5) Based on this, the output worker j produces after a period of run Tp is given by: Tp/[ PTb + 2TTj] (6) Because we assue that each walking worker has equal efficiency in this case; for a syste with walking workers, the overall output after a period of run Tp is given by: {Tp/[ PTb PTi +2TTj + 3.2. Workers with Unequal Perforance ]}, i.e., {Tp/[ PTb + 2TTj]} (7) In practice, it is ipossible that each walking worker has equal efficiency. In this case, the slowest worker ay deterine the overall output of the line. After a war-up period, the slowest worker will only possibly encounter the in-process waiting tie in front of the bottleneck achine Mb. Fro the oent that the slowest worker s leaves the bottleneck, this worker needs the following aount of tie to arrive to it again in a circuit: i b s) s) PTb, s (8) (3) 228
Q. Wang,. Bennett Meanwhile, a total aount of tie that other walking workers spend at Mb is given by: j s ( PTb, j) (9) If (8) (9): there is no in-process waiting tie. If (8) < (9): the in-process waiting tie for the slowest walking worker s is given by: IPWTs (9) (8) [ PTb, j] ( PTi, s) PTb, s], i.e., j s IPWTs [ PTb, j] s)] (0) Thus, the total idle tie for this slowest worker s during the copletion of a product is given by: ITs IPWTs + 2TTs [ PTb, j] s)] + 2TTs, i.e., ITs [ PTb, j] s)] + 2TTs () Knowing that a faster worker cannot overtake the slowest worker, therefore, each walking worker will have the sae output as the slowest worker can produce. We define T to be the aount of tie each walking worker needs for producing a unit, two cases are possible: If the slowest walking worker does not encounter any in-process waiting tie: T Because IPWTs is 0, based on equation 0, T can also be given by: T PTi, s + 2TTs (2) PTb, j + 2TTs (3) If the slowest worker encounters an in-process waiting tie before oving into the achine b: T IPWTs + or, T PTi j s, + 2TTs (4) s PTb, j + 2TTj (5) Finally, a total aount of in-process waiting tie a walking worker j spends for producing one unit is given by: IPWTj T PTi, j 2TTj (6) 4. Ipleenting 5Ss into Lean Walking Workers Production Lines i In a anufacturing copany, 5Ss are considered as a lean anageent technique aiing to eliinate anufacturing-related wastes that ay obstruct the syste perforance in ters of line efficiency and productivity, and iniize unnecessary production costs. This is particularly useful for huan-centred assebly systes where 229
Q. Wang,. Bennett intensive operational tasks are carried out anually and huan-errors are often ade during an assebly of a unit. The key ethod of ipleenting 5S anageent rules into a anual assebly working environent is to ake a workplace readable and visible. This can be achieved by arranging visual boards or tags at a workplace with 5S concepts ebedded into each anufacturing process or anufacturing-related activity. Figure 2 deonstrates a road ap as an exaple for iplanting 5S at a workstation using walking workers as part of a 5S-enabled shop floor flow line at a local anufacturing plant. Figure 3 illustrates a 3D siulation odel of the 5S-enabled shop floor. The siulation odel was used for onitoring various scenarios with perforance easures based on siulation results before and after the ipleentation of 5S anageent rules into the production line using walking workers. 5. Siulation Outputs A feasibility study of applying highly skilled walking workers to a shop floor environent was investigated based at a local plant. The copany is a sall edia sized enterprise (SME). In its shop floor, anufacturing processes were perfored anually by individual workers who were trained coplete a unit by travelling fro one workbench station to next workbench station along the line. The siulation result shown in Figure 4 indicates that the original production syste has a axiu output of between three and four units per day and the proposed lean production syste has a axiu output of five units per day providing a significant increase of productivity. Based on the siulation result shown in Figure 4, it can be seen that the original syste requires six walking workers operating on the line siultaneously when the axiu output (three or four units per day) of the line reaches stable, whilst the reconfigured lean syste requires four walking workers to achieve the axiu output (i.e., five units per day). This iplies that the proposed lean syste is ore efficient than that of the old syste in ters of output per worker per day. For both siulation results shown in Figure 4, it can be seen that the output can be increased or decreased by siply adjusting the nuber of walking workers on the line, i.e., such a syste is very adaptable to the change of a daily or weekly deand of products to be anufactured. evertheless, when the line reaches the axiu output, any further increase of the nuber of workers on the line will not increase but will gradually decrease the overall output. Figure 5 illustrates a trend of the drop of output per worker per day versus the nuber of additional workers to be put on the line after the line reaches the axiu output. Figure 2. Ipleentation of 5S anageent rules into a shop floor environent. Figure 3. The 5S-enabled walking worker assebly line. 230
Q. Wang,. Bennett Figure 4. Output vs nuber of walking workers before and after the ipleention of 5 S. 6. Suary Figure 5. Output per walking worker before and after the ipleention of 5S rules. The paper reports a feasibility study of incorporating 5S anageent rules into a production syste using wellskilled, flexible and dynaic walking workers at a local anufacturing plant. Both 5S and walking workers techniques were applied to the shop floor production as an integrated lean approach aied at iproving efficiency and productivity of the existing syste and reducing unnecessary production wastes (costs). The ipleentation of 5S anageent rules also iproves the visibility and visual control for production as well as safety issues in the shop floor environent. The application of walking workers on the line leads to a significant increase of daily output as well as output per worker per day. Acknowledgeents The authors thank Laura Arias, Alexander Bearne and Saleh Alyahya for their contributions to this project; the Director and Production Manager of Wessex Doors for providing valuable inforation and assistance. References [] Balle, F. and Balle, M. (2005) Feel the Force of Flexible Manpower. IET Manufacturing Engineer, 84, 20-5. [2] Bley, H., Reninhart, G., Seliger, G., Bernardi, M. and Korne, T. (2004) Appropriate Huan Involveent in Assebly and Disassebly. CIRP Annals, 53, 487-509. http://dx.doi.org/0.06/s0007-8506(07)60026-2 23