Optimising and simulating the assembly line balancing problem in a motorcycle manufacturing company : a case study

For Peer Review Only Optimizing and simulating the assembly line balancing problem in a motorcycle manufacturing company: a case study Journal: International Journal of Production Research Manuscript ID: TPRS-2009-IJPR-0059.R1 Manuscript Type: Original Manuscript Date Submitted by the Author: 10-Mar-2009 Complete List of Authors: Cortes, Pablo; University of Seville, Industrial Engineering Onieva, Luis; University of Seville, Industrial Engineering Guadix, Jose; University of Seville, Industrial Engineering Keywords: ASSEMBLY LINE BALANCING, LEAD-TIME REDUCTION, SIMULATION APPLICATIONS Keywords (user): motorcycle http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research peer-00583572, version 1 - 6 Apr 2011 Author manuscript, published in "International Journal of Production Research 48, 12 (2010) 3637-3656" DOI : 10.1080/00207540902926522 For Peer Review Only Optimizing and simulating the assembly line balancing problem in a motorcycle manufacturing company: a case study Pablo Cortés*, Luis Onieva, José Guadix Ingeniería Organización, University of Seville, Spain Escuela Superior Ingenieros, Camino de los Descubrimientos s/n. E-41092 / Sevilla SPAIN In this paper, we present a real life assembly line balancing problem for a motorcycle manufacturing company. Results from the initial situation in the company are compared to those provided by a heuristic method and by a novel neighbourhood search method. An ARENA simulation model is developed to test the different proposals. The model was validated by comparing the simulation results from the initial company scenario with the real operation results. Consequently, the extension to the developed proposals allows us to select an adequate assembly line for the company, resulting in a greater productivity level and a more balanced line with respect to the operation times in the stations and the activity of the workers. The company has subsequently implemented our proposed schedule, obtaining remarkable improvements in its productivity. Keywords: motorcycle, assembly line, lead time, simulation Introduction Automobile manufacturing is the industry sector that makes greatest use of assembly lines. The problem of design and balancing of assembly lines is difficult to be solved due to its combinatorial nature (Wee and Magazine, 1982) and also due to the large amount of constraints and tasks to be carried out in real life problems. An assembly line is a manufacturing process in which parts are added to a product in a sequential manner using optimally planned logistics to create a finished product much faster than with handcrafting-type methods. Essentially, the main aspects of assembly lines are the number of stations and the production rate. In the case we are dealing with in our paper, every worker is supposed to have the same amount of time for carrying out the operations that are associated to his/her post, C. Consequently, 1/C is the production rate better performance for the whole of experiments, which should be sufficient to meet the required demand. * Corresponding author: [email protected] / Tel. +34 954486134 Page 1 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Operations (or tasks) are assigned to the stations where the workers assemble the parts and subcomponents, depending on the precedence constraints between operations, the fixed stations constraints where an operation may have to be carried out, and the incompatible tasks constraints for operations that cannot be carried out in the same station. Assembly lines can also include many other specific constraints such as linked tasks, cumulated restrictions, excluded stations, station type, and minimal/maximum distance, amongst others. An interesting web page addressing most of the well-known problems in assembly lines can be accessed in the site www.assembly-line-balancing.de. This paper discusses manufacturing assembly line performance improvement of a company that produces motorcycles named MH, whose main factory is located in Spain. It is the most southern automobile industry company in Europe and the majority of its production (more than 75%) is destined for export. Currently, the most outstanding product of the company is the FURIA XP6 model (Figure 1), which is the model we analyse in this paper. FIGURE 1 This paper focuses on the assignment of operations to the assembly line, comparing the previous scheduling in the company with diverse proposals. We address a method based on the traditional rank positional weight heuristic, which is adapted to the specific conditions of motorcycle assembly when two people must be always working on the vehicle at each station, and a neighbourhood search heuristic, which provided the better quality results. This neighbourhood search heuristic Page 2 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only algorithm has since been successfully implemented in the factory. Simulations are shown for all the cases, thus allowing the comparison between proposals. In a general scope the assembly line problem has been widely studied in scientific literature, being surveyed by several authors (Rekiek et al., 2002; Becker and Scholl, 2006; Scholl and Becker, 2006; or Boysen et al., 2007 as recent examples). Focusing on real case studies, an interesting paper (Lapierre and Ruiz, 2004) addresses a case study in the Canadian industry of appliances. The paper considers a two-sided conveyor with different speeds and grouping characteristics that make it different from other traditional cases. The problem was solved by implementing a priority-based heuristic developed in MsAccess. However, there are not many research papers dealing with the specific problem of motorcycle production. Pastor and Corominas (2000) studied the assembly line balancing problem with incompatibilities and bounded workstation loads in a motorcycle factory. They presented the case of a single-sided line with a given number of stations and different types of assignment restrictions: some tasks are required to be assigned to the same station and, thus, they may be combined to a single task; some tasks can only be performed at the left hand or the right hand side of a large, irremovable workpiece; and some tasks need to be executed at the top or at the bottom of the workpiece. The specific characteristics of the current assembly line imply a number of specific constraints that must be taken into account when considering their paper, differing from the case study we are addressing here. More recently, some of the same authors (Corominas et al., 2008) have presented the process of rebalancing in a motorcycle assembly line with the aim of reducing the number of temporary workers. This problem considers workers with different skills that must be correctly assigned to Page 3 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only stations in order to achieve the maximum productivity. Their paper differs in this respect from ours where all the workers are stable in the company staff. Additionally, we can assume that resources are homogeneous, and hence the task duration is not depending on its workstation allocation. Some of the same authors have continued researching on motorcycle assembly lines cases; it is the case of the alternative subgraphs assembly line balancing problem recently addressed in Capacho and Pastor (2008), or the papers by Andrés et al. (2008), and Pastor and Ferrer (2009). However, our paper relates more to Akagi et al. (1983) and Lutz et al. (1994) where the performance of workers on a specific task is the same. The difference from our work relies on the specific characteristic of a motorcycle assembly line where exactly two persons have to work at the same time at each station. The rest of the paper follows with the second section, which includes the description of the assembly line and the operations that are needed to produce a FURIA XP6 motorcycle model. The third section details the previous scheduling in the assembly line in the company, as well as the proposals that were considered. Expected results from a theoretical point of view are also shown. The fourth section is dedicated to the simulation model and the results that the simulation model provided using ARENA software. Finally, the main aspects are reviewed in the conclusion. 2. Description of the assembly line for FURIA XP6 model The main parts of a motorcycle are: the chassis, which constitutes the backbone of the motorcycle and is where the rest of the components are assembled; the clutch-release yoke, which joins the handlebars to the front wheel and acts as front suspension; a tipping device to join the rear wheel and the rear muffler; the petrol deposit; the engine, which is joined to the dumper and to the rear wheel by a chain or belt with the Page 4 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only objective of propelling the whole vehicle; and the front and rear brakes to stop the motorcycle. The FURIA XP6 motorcycle assembly line is fed from manufacturing cells located near the corresponding station. Figure 2 depicts the layout of the manufacturing zone of the factory, where the assembly lines are located. Because Due to this model representing the largest part of the company’s sales, there is one specific line dedicated to the model: assembly line 1. The other line is used for the company’s remaining models. The assembly lines are operated in a discontinuous manner. The tasks are done with the chain stationary, and once the workers have finished their tasks the chain advances. FIGURE 2 Figure 2 depicts one individual characteristic of motorcycle assembly lines. The morphology of motorcycles allows two operators to work on a vehicle at the same time but on separate tasks, or while collaborating on a more complex task. 57 operations are carried out for the FURIA XP6 model and are described in Table 1, where the average time and standard deviation have been measured for each task. In our case, we need to consider precedence constraints between operations, some fixed stations constraints where an operation has to be carried out (e.g. the chassis assembly), and incompatible tasks constraints for operations that cannot be carried out at the same station. The table also indicates when an operation must be carried out by both operators (B), and when by the right (R) or left (L) one. The table states the operations as they were carried out in the initial scenario. TABLE 1 We have to note related to Table 1, that we carried out a checking analysis trying to identify which tasks were forced to be undertaken by “both” operators with Page 5 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only the objective to relax this restriction in an hypothetical re-assembly. We proposed to assign operation 7 (firstly assigned to B) to the left operator due to assembly reasons, and tasks 14, 22, 48, and 51 that were initially conditioned to both operators to one of them (indistinctively to the left or right operator). These proposals were checked during the Christmas planned maintenance stop and then approved by the General Manager after checking its feasibility. Once we have calculated the average times of each operation, ti , for N operations, we can calculate the total assembly time, T, and given a number of stations, K, and a lead time, C, we can calculate the inactivity time TCKI − ⋅ = . Thus, the objective of our problem is to minimize the lead time, C. Figure 3 depicts workers on the assembly line carrying out operations detailed in Table 1. FIGURE 3 3. Scheduling of operations on the assembly line: previous situation and proposals Let },.....,{ 21 N JJJ the set operations to be carried out on the assembly line. The execution time for the operations is known from Table 1, and is given by i t,Ni ,......1 = . The precedence constraints among operations are also known. As previously stated, the unique feature of motorcycle assembly lines is that two operators can carry out operations at the same time, or cooperate to carry out a more complex operation. The goal is to assign operations to stations with the objective of minimizing the lead time. 3.1. Previous situation The initial scheduling of the assembly line is described in Table 2. TABLE 2 Page 6 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only As can be seen, the initial situation depicts an assembly line that is poorly balanced, with two stations (1 and 2) much busier than the others (3 and 4). The expected lead time is 0:12:49. Additionally, Page 7 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Table 2 shows the operations that have to be carried out by two operators simultaneously, due to the special requirements of the task. The other operations can be interchangeable between the right and left operator. The table also includes waiting times. Idle times can result due to: (i) worker A is waiting for worker B to make a joint operation or (ii) worker A is waiting for worker B because worker A’s operation relies on worker B’s operation being completed. 3.2. Modified Rank Positional Weight Heuristic (MRPWH) First, we tried a new scheduling given by a heuristic based on the Rank Positional Weight Heuristic (RPWH) adapted to the unique situation of two operators working on the same vehicle on an assembly line. RPWH is an old reputed heuristic method (Helgeson and Birnie, 1961). We detail our modification of RPWH below in the following rules: • A weight is assigned to each operation i J according to ∑ ∈ += Di iii ttp . The weight is calculated as the operation i J time plus the time of all the operations that must follow operation i J, that are stated as set D in the formula. • Operations are ordered in decreasing order of weight, safeguarding the precedence relationship. This configures an assignment list. • An approximate lead time is estimated as the sum of the operations’ average time, divided by the number of stations and then multiplied by two due to the number of operators (in our case: 8). • Operations are assigned to operators following the order of the assignment list and according to the position requirements (left, right or both) up to satisfy the lead time (the nearest possible value to the lead time). First, in case of position requirement, the constraint is satisfied by assigning the operation to the specified operator. Second the rest of operations are assigned to left or right operator attending to his/her work load in the station and with the objective of minimizing the idle time. • The station’s total time is calculated for the four stations. • The lead time is calculated as the maximum of the four stations. Table 3 shows the scheduling proposal according to the MRPWH technique. TABLE 3 Page 8 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only We constructed a simulation model to test the different proposals. The simulations of the initial scenario permitted the validation of the simulation model. The results from the simulation were in fact in accordance with the factory plant’s current operation. Both MRPWH and MSNSH provided much better solutions than the model implemented in the initial scenario. Also, the MSNSH proposal was slightly better than the MRPWH proposal, creating a greater productivity level and a more balanced line, which affected the operation times in the stations as well as the activity of the workers. Furthermore, the MSNSH schedule was so balanced than the bottleneck varied from station 3 to station 4, depending on the simulation replication, although it was mainly located in station 4. The measurement of the tasks’ time by a statistical distribution allows a real representation of the current situation in the factory. MH is at present implementing the MSNSH schedule in its factory, obtaining a productivity level of between 55 and 59 motorcycles (most of the days it is 56). However, the efficiency of the workers is continuously improving, so the data in Table 1 is being revised. Additionally, new components are included in, or removed from, the motorcycle models each year. Due to all of these factors, the balancing of the assembly line must be continuously monitored and rebalanced in order to achieve better results and attain a state of continuous improvement. References Akagi, F., Osaki, H. and Kikuchi, S., 1983, A method for assembly line balancing with more than one worker in each station. International Journal of Production Research 21 (5): 755-770. Andrés, C., Miralles, C. and Pastor, R., 2008, Balancing and scheduling tasks in assembly lines with sequence-dependent setup times. European Journal of Operational Research, 187 (3): 1212-1223. Becker, C. and Scholl, A., 2006, A survey on problems and methods in generalized assembly line balancing. European Journal of Operational Research 168: 694-715. Page 15 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Boysen, N., Fliedner, M. and Scholl, A., 2007, A classification of assembly line balancing problems. European Journal of Operational Research, 183: 674- 693. Capacho, L. and Pastor, R., 2008, ASALBP: the alternative subgraphs assembly line balancing problem. International Journal of Production Research 46 (13): 3503–3516. Corominas, A., Pastor, R. and Plans, J., 2008, Balancing assembly line with skilled and unskilled workers. OMEGA, The International Journal of Management Science, 36(6): 1126-1132. Helgeson, W.B. and Birnie, D.P., 1961, Assembly Line Balancing Using Rank Positional Weight Technique. Journal of Industrial Engineering 12(6): 302- 310. Kelton, W.D., Sadowski, R.P. and Sturrock, D.T., 2007, Simulation with ARENA. McGraw-Hill International Edition. Lapierre, S. and Ruiz, A.B. (2004). Balancing assembly lines: an industrial case study. Journal of the Operational Research Society 55: 589-597. Lutz, C.M., Davis, K.R. and Turner, C.F., 1994, Development of operator assignment schedules: a DSS approach. Omega 22: 57-67. Pastor, R. and Corominas, A., 2000, Assembly line balancing with incompatibilities and bounded workstation loads. Ricerca Operativa 30: 23-45. Pastor, R. and Ferrer, L., 2009, An improved mathematical program to solve the simple assembly line balancing problem. International Journal of Production Research. doi: 10.1080/00207540701713832. Rekiek, B., Dolgui, A., Delchambre, A. and Bratcu, A., 2002, State of art of optimization methods for assembly line design. Annual Reviews in Control 26: 163-174. Scholl, A. and Becker, C., 2006, State-of-the-art exact and heuristic solution procedures for simple assembly line balancing. European Journal of Operational Research 168: 666-693. Scholl, A., Boysen, N., Fliedner, M., and Klein, R. Homepage for assembly line optimization research. Site: http://www.assembly-line-balancing.de/. Accessed in 2009, March. Wee, T.S. and Magazine, M.J., 1982, Assembly line balancing as generalized bin packing. Operations Research Letters 1: 56-8. Page 16 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only TABLES Table 1. Operations in the MH assembly line as they were carried out in the initial scenario Operation Precedence Position Average time Standard deviation Operation Precedence Position Average time Standard deviation 1 Front chassis B 0:00:10 0:00:04 31 Pinion cover 28 L 0:00:27 0:00:10 2 Clutch-release yoke 1 B 0:00:22 0:00:11 32 Left wire guidance 22 0:00:35 0:00:08 3 Tipping device 2 0:00:35 0:00:11 33 Right wire guidance 22 0:00:28 0:00:11 4 Rear fastening 3 0:00:34 0:00:03 34 Front mudguard 22,32,33 0:00:40 0:00:19 5 Snubber 4 0:00:37 0:00:09 35 Petrol tank flange 17,19,22,30,37,38,39,45 0:00:38 0:00:06 6 Handlebars 2 0:01:16 0:00:22 36 Petrol tank 35 0:00:14 0:00:02 7 Engine 2 B 0:01:22 0:00:09 37 Radiator antifreeze 24 R 0:00:41 0:00:08 8 Rear wheel shaft 5 0:00:09 0:00:04 38 Relief valve sleeve (right) 19,44 0:00:20 0:00:08 9 Rear wheel 10 0:01:00 0:00:16 39 Oil fill 23 R 0:00:20 0:00:08 10 Rear brake installation 8 0:00:06 0:00:02 40 Brake pedal 1 R 0:00:37 0:00:06 11 Front wheel shaft 2 0:00:06 0:00:04 41 Right rear cover 46 R 0:01:00 0:00:12 12 Front wheel 11 0:01:07 0:00:12 42 Right rear indicator 29 0:00:59 0:00:28 13 Mileometer 6,11 0:00:32 0:00:15 43 Right front cover 36 R 0:00:56 0:00:12 14 Front brake 6,12 B 0:01:04 0:00:23 44 Exhaust pipe 19,20,30 L 0:00:45 0:00:11 15 Rear chassis 5 0:02:15 0:00:34 45 Muffler 44 L 0:00:41 0:00:09 16 Rear brake connection 9 R 0:00:32 0:00:09 46 Rear mudguard 29 0:00:31 0:00:08 17 Electrical installation 15 R 0:02:20 0:00:30 47 Left rear cover 30,36,38,45,46 L 0:01:13 0:00:25 18 Crankcase oil 19 R 0:01:22 0:00:26 48 Connection mudguard-license plate 46,29 B 0:00:50 0:00:18 19 Engine connection 7,15 L 0:04:19 0:00:18 49 Left rear indicator 29 0:00:25 0:00:09 20 Left radiator grille 19 L 0:01:04 0:00:08 50 Left front cover 45,36 L 0:00:47 0:00:12 22 Electrical installation (handlebars) 7,13,14,17 B 0:03:14 0:00:29 51 Head lamp holder 22,19,32,33 B 0:02:05 0:00:53 23 Bolting oil tank 18 R 0:00:21 0:00:11 52 Seat 41,43,46,47,50 0:00:57 0:00:28 24 Radiator 17,19,,22 0:00:24 0:00:10 53 Carburettor connection 7,6 0:03:12 0:00:47 25 Right radiator 24 R 0:00:43 0:00:16 54 Oil filter sleeve 15,7 0:00:30 0:00:09 27 License plate holder framework 29 0:00:18 0:00:06 55 Clutch wire connection 57 0:00:23 0:00:08 28 Chain 9,7 L 0:03:02 0:00:35 56 Petrol plug vent 36 0:00:11 0:00:02 29 License plate holder 15,17 0:01:15 0:00:23 57 Clutch wire 6,7 0:00:52 0:00:07 30 Collector 19 0:00:50 0:00:15 Page 17 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Table 2. Initial scheduling in the assembly line Worker Worker Operation Right Both Left Operation Right Both Left 1 Front chassis 0:00:10 40 Brake pedal 0:00:37 2 Clutch-release yoke 0:00:22 55 Carburettor connection 0:03:12 3 Tipping device 0:00:35 19 Engine connection 0:04:19 4 Rear grip 0:00:34 20 Left radiator grille 0:01:04 5 Snubber 0:00:37 idle time 0:01:34 6 Handlebars 0:01:16 22 Electrical installation (handlebars) 0:03:14 idle time 0:00:31 57 Clutch wire 0:00:52 7 Engine installation 0:01:22 24 Radiator 0:00:24 8 Rear wheel shaft 0:00:09 25 Right radiator grille 0:00:43 10 Rear brake installation 0:00:06 18 Crankcase oil installation 0:01:22 9 Rear wheel 0:01:00 23 Bolting oil tank 0:00:21 11 Front wheel shaft 0:00:06 54 Oil filter sleeve 0:00:30 13 Mileometer wire 0:00:32 STATION 2 28 Chain 0:03:02 12 Front wheel 0:01:07 Station total time 0:09:35 0:03:14 0:08:25 idle time 0:00:30 0:12:49 15 Rear chassis 0:02:15 14 Front brake caliper 0:01:04 16 Rear brake connection 0:00:32 STATION 1 17 Electrical installation (wire) 0:02:20 Worker Station total time 0:06:24 0:04:08 0:04:36 Operation Right Both Left 0:10:32 idle time 0:01:15 Worker 46 Rear mudguard 0:00:31 Operation Right Both Left 29 License holder 0:01:15 39 Oil fill 0:00:20 idle time 0:00:31 37 Radiator antifreeze 0:00:41 48 Connect mudguard to license plate holder 0:00:50 33 Right wire guidance 0:00:28 idle time 0:00:52 34 Front mudguard 0:00:40 47 Left rear cover 0:01:13 idle time 0:00:14 50 Left front cover 0:00:47 38 Relief valve sleeve (right) 0:00:20 52 Seat 0:00:57 30 Collector 0:00:50 49 Left rear indicator 0:00:25 55 Clutch wire connection 0:00:23 35 Petrol tank flange 0:00:38 31 Pinion cover 0:00:27 36 Petrol tank 0:00:14 44 Exhaust pipe 0:00:45 41 Right rear cover 0:01:00 45 Muffler 0:00:41 43 Right front cover 0:00:56 32 Left wire guidance 0:00:35 42 Right rear indicator 0:00:59 idle time 0:00:57 27 License plate holder framework 0:00:18 STATION 3 51 Head lamp holder 0:02:05 STATION 4 56 Petrol plug vent 0:00:11 Station total time 0:03:40 0:02:05 0:03:40 Station total time 0:06:04 0:00:50 0:06:01 0:05:45 0:06:54 Page 18 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Table 3. MRPWH scheduling proposal Worker Worker Operation Right Both Left Operation Right Both Left 1 Front chassis 0:00:10 17 Electrical installation (wire) 0:02:20 2 Clutch-release yoke 0:00:22 53 Carburettor connection 0:03:12 7 Engine installation 0:01:22 54 Oil filter sleeve 0:00:30 3 Tipping device 0:00:35 19 Engine connection 0:04:19 4 Rear fastening 0:00:34 29 License plate holder 0:01:15 5 Snubber 0:00:37 18 Crankcase oil installation 0:01:22 6 Handlebars 0:01:16 STATION 2 Station total time 0:06:54 0:00:00 0:06:04 57 Clutch wire 0:00:52 0:06:54 11 Front wheel shaft 0:00:06 Worker 13 Mileometer wire 0:00:32 Operation Right Both Left 12 Front wheel 0:01:07 42 Right rear indicator 0:00:59 14 Front brake caliper 0:01:04 37 Radiator antifreeze 0:00:41 15 Rear chassis 0:02:15 23 Bolting oil tank 0:00:21 8 Rear wheel shaft 0:00:09 39 Oil fill 0:00:20 10 Rear brake installation 0:00:06 38 Relief valve sleeve (right) 0:00:20 9 Rear wheel 0:01:00 34 Front mudguard 0:00:40 40 Brake pedal 0:00:37 25 Right radiator grille 0:00:43 STATION 1 Station total time 0:05:53 0:00:32 0:06:19 16 Rear brake connection 0:00:32 0:06:51 31 Pinion cover 0:00:27 Worker 27 License plate holder framework 0:00:18 Operation Right Both Left 49 Left rear indicator 0:00:25 55 Clutch wire connection 0:00:23 44 Exhaust pipe 0:00:45 22 Electrical installation (handlebars) 0:03:14 45 Muffler 0:00:41 46 Rear mudguard 0:00:31 idle time 0:00:05 28 Chain 0:03:02 idle time 0:00:04 35 Petrol tank flange 0:00:38 32 Left wire guidance 0:00:35 48 Connect mudguard and license plate holder 0:00:50 36 Petrol tank 0:00:14 idle time 0:00:07 56 Petrol plug vent 0:00:11 33 Right wire guidance 0:00:28 47 Left rear cover 0:01:13 51 Head lamp holder 0:02:05 41 Right rear cover 0:01:00 20 Left radiator grille 0:01:04 43 Right front cover 0:00:56 30 Collector 0:00:50 50 Left front cover 0:00:47 24 Radiator 0:00:24 idle time 0:00:48 STATION 3 Station total time 0:06:41 0:00:00 0:06:56 52 Seat 0:00:57 0:06:56 STATION 4 Station total time 0:06:32 0:00:00 0:07:29 0:07:29 Page 19 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Table 4. MSNSH algorithm pseudocode w=1 Do Do Do Do If w=1 Random selection in ( ) E i V x  ( ) i i V x Else Random selection in ( ) i V x  ( ) i i V x While neighbour feasibility test fails Calculate ( ) ( ) i i f V x If ( ) ( ) i i f V x < f(Best_V(xi)) Best_V(xi) ( ) i i V x While [f(Best_V(xi))> ( ) ( ) i i f V x ] OR Iterations < Nloop If f(Best_V(xi))< ( ) ( ) i i f V x xi Best_V(xi) If w=1 Calculate New_bottleneck_station  E While Iterations < Nw w=0 While Iterations < NH Page 20 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Table 5. MSNSH scheduling proposal Worker Worker Operation Right Both Left Operation Right Both Left 1 Front chassis 0:00:10 17 Electrical installation (wire) 0:02:20 2 Clutch-release yoke 0:00:22 53 Carburettor connection 0:03:12 7 Engine installation 0:01:22 54 Oil filter sleeve 0:00:30 3 Tipping device 0:00:35 19 Engine connection 0:04:19 4 Rear fastening 0:00:34 29 License plate holder 0:01:15 5 Snubber 0:00:37 18 Crankcase oil installation 0:01:22 6 Handlebars 0:01:16 STATION 2 Station total time 0:06:54 0:00:00 0:06:04 57 Clutch wire 0:00:52 0:06:54 11 Front wheel shaft 0:00:06 Worker 13 Mileometer wire 0:00:32 Operation Right Both Left 12 Front wheel 0:01:07 42 Right rear indicator 0:00:59 14 Front brake caliper 0:01:04 37 Radiator antifreeze 0:00:41 15 Rear chassis 0:02:15 23 Bolting oil tank 0:00:21 8 Rear wheel shaft 0:00:09 39 Oil fill 0:00:20 10 Rear brake installation 0:00:06 38 Relief valve sleeve (right) 0:00:20 9 Rear wheel 0:01:00 35 Petrol tank flange 0:00:38 40 Brake pedal 0:00:37 25 Right radiator grille 0:00:43 STATION 1 Station total time 0:05:53 0:00:32 0:06:19 43 Right front cover 0:00:56 0:06:51 31 Pinion cover 0:00:27 Worker 27 License plate holder framework 0:00:18 Operation Right Both Left 49 Left rear indicator 0:00:25 55 Clutch wire connection 0:00:23 44 Exhaust pipe 0:00:45 22 Electrical installation (handlebars) 0:03:14 45 Muffler 0:00:41 46 Rear mudguard 0:00:31 34 Front mudguard 0:00:40 28 Chain 0:03:02 idle time 0:00:04 idle time 0:00:03 32 Left wire guidance 0:00:35 36 Petrol tank 0:00:14 24 Radiator 0:00:24 56 Petrol plug vent 0:00:11 48 Connect mudguard to license plate holder 0:00:50 47 Left rear cover 0:01:13 33 Right wire guidance 0:00:28 41 Right rear cover 0:01:00 51 Head lamp holder 0:02:05 16 Rear brake connection 0:00:32 20 Left radiator grille 0:01:04 50 Left front cover 0:00:47 30 Collector 0:00:50 idle time 0:00:14 STATION 3 Station total time 0:06:45 0:00:00 0:06:45 52 Seat 0:00:57 0:06:45 STATION 4 Station total time 0:06:30 0:00:00 0:06:55 0:06:55 Page 21 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Table 6. Daily productivity results Daily average productivity Standard deviation Interval MH initial scenario 35.20 0.51 (34,36) MRPWH heuristic 56.25 0.70 (55,57) MSNSH heuristic 57.05 0.44 (56,58) Page 22 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only LIST OF FIGURE CAPTIONS Figure 1. FURIA XP6 motorcycle model Figure 2. Layout of the manufacturing plant Figure 3. Workers on the assembly line carrying out operations Figure 4. Solutions encoding Figure 5. Station performance modules Figure 6. Operation modules in Stations 1, 2 and 3. MSNSH heuristic solution Figure 7. Operation modules in Station 4. MSNSH heuristic solution Figure 8. Animation module of the simulation model Figure 9. Operation time in the stations. Figure 10. Waiting times in the assembly line Figure 11. Comparison of workers’ activity for the proposals Figure 12. Analysis of the productivity with respect to the replications Page 23 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Figure 1. FURIA XP6 motorcycle model 254x190mm (96 x 96 DPI) Page 24 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Figure 8. Animation module of the simulation model 254x190mm (96 x 96 DPI) Page 31 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Figure 9. Operation time in the stations. 254x190mm (96 x 96 DPI) Page 32 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Figure 10. Waiting times in the assembly line 254x190mm (96 x 96 DPI) Page 33 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Figure 11. Comparison of workers' activity for the proposals 254x190mm (96 x 96 DPI) Page 34 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011 For Peer Review Only Figure 12. Analysis of the productivity with respect to the replications 254x190mm (96 x 96 DPI) Page 35 of 35 http://mc.manuscriptcentral.com/tprs Email: [email protected] International Journal of Production Research 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 peer-00583572, version 1 - 6 Apr 2011