Tài liệu Time management practice 2

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TIME MEASUREMENT & PROCESS OPTIMIZATION DIGITAL LOCK ASSEMBLY LINE - FISCHER ASIA CO., LTD. WORK PROJECT Team B: Nguyen Thi Thu HIEN Ngo Phuoc LOC Huynh Truong LY Le Hoang NHAN Supervisor: Dr.-Ing. Marlene Helfert, Technical University of Darmstadt Binh Duong, 2016.11.20 2016-11-20 0 Abstract This project examined digital lock assembly processes at Fischer Asia Co. Ltd., a German company specializing in stamping and shaping processes for all kinds of metal products. REFA time study method is used to record and analyze time data of each working process, and line balancing and Lean management are applied to propose optimal improvement models. After analyzing actual processing time, time spent for waiting and additional activities of current workstations and line balancing, the assembly line has been optimized from ten to six workstations, the average percentage of waiting time, almost 14% reduces to 7.62% and we propose new short-term and future layouts after improvements. This project will contribute to future research into time studies on other processes in Fischer Asia Co., Ltd. in particular and manufacturing factories in general. 2016-11-20 1 Table of contents Abstract .........................................................................................................................1 Table of contents ...........................................................................................................2 List of figures .................................................................................................................3 List of tables ..................................................................................................................3 1. Introduction ............................................................................................................3 2. Measurement .........................................................................................................3 2.1. Method ............................................................................................................3 2.2. Result..............................................................................................................4 2.2.1. Workstation 3 ...........................................................................................4 2.2.2. Workstation 4 ...........................................................................................6 2.3. 2.3.1. Workstation 3 ...........................................................................................7 2.3.2. Workstation 4 ...........................................................................................7 2.4. 3. Discussion.......................................................................................................7 Conclusion ......................................................................................................8 2.4.1. Workstation 3 ...........................................................................................8 2.4.2. Workstation 4 ...........................................................................................8 Optimization ...........................................................................................................8 3.1. Method ............................................................................................................8 3.2. Current situation ..............................................................................................9 3.3. Improvement suggestions .............................................................................10 3.3.1. Combination of workstation 5 and workstation 6 ....................................10 3.3.2. Reduction of processing time of workstation 9 .......................................11 3.3.3. Assignment of more tasks to workstation 1 ............................................12 3.4. Result............................................................................................................13 3.5. Discussion.....................................................................................................13 3.6. Conclusion ....................................................................................................14 3.6.1. Short-term layout....................................................................................14 3.6.2. Long-term layout ....................................................................................15 4. Reference ............................................................................................................15 5. Appendix ..............................................................................................................16 2016-11-20 2 List of figures Figure 1. Current processing time of ten workstations Figure 2. Processing time of seven main workstations before improvement Figure 3. Processing time of production line after combining workstation 5 & 6 Figure 4. Current processing time of Workstation 9 and 10 Figure 5. Processing time of Workstation 9 and 10 after balanced work Figure 6. Compared processing time of workstation 1 before and after work assignment Figure 7. Processing time of production line after improvement Figure 8. Short-term layout after line balancing Figure 9. Long-term layout after improvement List of tables Table 1: Normal time of processing activity of workstation 3 Table 2: Total share of time spent for each activity of workstation 3 Table 3: Normal time of processing activity of workstation 4 Table 4: Total share of time spent for each activity of workstation 4 Table 5. Compared average percentage of waiting time and manpower 1. Introduction This report discusses work and time studies to analyze the types of time spent for operator’s activities of workstations in an assembly line of a digital lock product. The objective of the studies is to establish normal time used for increasing the efficient work facilities utilization as well as personnel performance, and to recommend optimization proposals for assembly processes. The report presents the method of work and time studies, the results, the analysis of those results and the process optimization. 2. Measurement 2.1. Method The digital lock assembly line currently includes ten workstations [Appendix 3], in which some workstations carry out same processes, for instance, workstation 2 and workstation 9, workstation 3 and workstation 8, workstation 4 and workstation 7. 2016-11-20 3 Our team focused on measuring time of workstation 3 and workstation 4, which were broken down into small processes, by using stopwatch time study method and data were recorded in REFA sheet Z2 [Appendix 1, Appendix 2]. Fifteen measurements of activities per each process were collected, and the measurements of interruption of activity, additional activities as well as unforeseen tasks were also observed and recorded during the studies.. 2.2. Result According to the measured actual time, normal time (ti) is calculated based on performance factor (L) and actual measured time (ti). In addition, total share of time spent for processing time, waiting time, additional activities and getting and/or searching parts are counted. 2.2.1. Workstation 3 Table 1: Normal time of processing activity of workstation 3 Process name Process description Normal Relative time - ti confidence (second) level Put motor Reach for motor, fold into shaft wire, put motor into shaft Min real Max real value value (second) (second) 12.84 10.16% 11.54 14.15 6.23 28.37% 4.46 8.00 5.32 9.78% 4.80 5.84 8.84 15.98% 7.43 10.25 Release motor Add sprocket Reach for sprocket and put it on motor Release sprocket Grease Reach for brush, grease locking block holder Release brush Add locking Reach for prepared block locking block, add it on locking block holder Release block 2016-11-20 locking 4 Add slider Reach for slider, add it on sprocket 5.50 15.41% 4.65 6.35 8.79 17.88% 7.22 10.36 Release for slider Fold board Reach board, fold it Release board Total processing time per cycle 47.53 Table 2: Total share of time spent for each activity of workstation 3 Activity Put motor in shaft Normal time Time share - ti (second) of activity 192.60 23.11% Add sprocket 93.45 11.21% Grease lubricant 79.80 9.57% Add locking block 132.60 15.91% Add slider 82.50 9.90% Fold board 131.10 15.82% Total share of processing time 712.95 85.52% - - 46.20 5.54% - - 74.50 8.94% - - Total share of waiting time Total share of time spent for getting/searching parts Total share of time spent for personal allowances Total share of time spent for additional activities Others 2016-11-20 5 2.2.2. Workstation 4 Table 3: Normal time of processing activity of workstation 4 Process name Process description Normal Relative time - ti confidence (second) level Put housing Reach for housing in assembly from box, put it on box assembly box, check position Min real Max real value value (second) (second) 3.31 14.32% 2.84 3.78 23.74 10.73% 21.19 26.29 3.51 13.31% 3.04 3.98 3.62 13.95% 3.11 4.13 3.31 17.55% 2.73 3.89 Release housing Add buttons Reach for 7 buttons from the box, add them on housing Release buttons Add support Reach for support grid grid from box, add on 7 buttons in the rights side Release grid support Add main Reach for main board and board from box, fix it add on support grid with the right side for led operation Release board Add battery Reach for battery holder holder from box, add on board. Release holder battery Total processing time per cycle 2016-11-20 37.49 6 Table 4: Total share of time spent for each activity of workstation 4 Activity Put housing in assembly box Normal time - Time share of ti (second) activity 49.65 6.81% 356.10 48.86% Add support grid 52.65 7.22% Add board and fix it 54.30 7.45% Add battery holder 49.65 6.81% 562.35 77.15% 40.00 5.49% - - 52.50 7.20% 74.50 10.15% - - Add all buttons Total share of processing time Total share of waiting time Total share of time spent for getting/searching parts Total share of time spent for personal allowances Total share of time additional activities Others spent for 2.3. Discussion 2.3.1. Workstation 3 Table 1 shows the processing time of 47.53 seconds which was slightly greater than the number of workstation 8 which implemented same processes (38.80 seconds) [Appendix 3]. Because the operator was quite new with these processes, so she spent quite long time in readjusting parts after each process [Appendix 1]. The operator spent 5.54% total share of time spent for getting parts from store and 8.94% total share of time spent for rework and transfer of products from workstation 4 to workstation 2 [Appendix 1]. 2.3.2. Workstation 4 Workstation 4 spent 37.49 seconds of processing time as compared to 44.23 seconds of workstation 7 because workstation 4 didn’t implement the removal of battery holders out of plastic cover (8.60 seconds) [Appendix 3]. However, if the time for that process could be added to workstation 4, the estimated processing time of workstation 4, 46.09 2016-11-20 7 seconds, would be a little bit higher than that of workstation 7 (44.23 seconds). It would be because the operator was not experienced with all processes. At the beginning of the task, the operator had to wait in 40 seconds for getting housing from workstation 7. The operator usually spent approximately 2 seconds for adjusting the position of assembled housing after every completion of the last process. The operator spent 52.50 seconds for her small break during her task. 2.4. Conclusion Due to long processing time and much time spent for additional and waiting activities, some recommendations have been provided as followings. 2.4.1. Workstation 3 The operator should be given more training in order to increase her performance, reduce processing time of each process, and eliminate additional activity of reworking defective products Due to current bad layout [Appendix 4], the operator spent much time to transfer preassembled main housings from workstation 4 to workstation 2 which was her additional activity, so the working position of this operator must be re-located to cut down this additional activity. Material supply system should be established so that this operator’s time spent for getting raw materials are completely rejected. 2.4.2. Workstation 4 The operator should be trained to minimize her additional activities of adjusting holder position after finishing the final process as much as possible and to get performance as good as the operator who worked at workstation 7. 3. Optimization 3.1. Method Line balancing method was used to analyze activities of ten workstations. Re-designing layout of assembly line by process layout method and Lean management to cut down wastes in production line. 2016-11-20 8 Workflow between every workstation was recorded and drawn in current layout [Appendix 4]. 3.2. Current situation Figure 1. Current processing time of ten workstations Workstation 2, 3, and 4 are temporary in production line during observation time. The processes of those workstations are similar to workstation 9, 7 and 8 respectively [Appendix 3]. In order to ensure line balancing, these three momentary workstations are not be considered and are cut down in production line, therefore, the assembly line consists of seven main workstations [Figure 2]. 2016-11-20 9 Figure 2. Processing time of seven main workstations before improvement From Figure 2, workstation 9 has the highest processing time, 45.41 seconds, while the lowest processing times are at workstation 1 and 5, 12.40 and 14.32 respectively. The next section will focus on these workstations in order to balance processing time. 3.3. Improvement suggestions 3.3.1. Combination of workstation 5 and workstation 6 Figure 3. Processing time of production line after combining workstation 5 & 6 2016-11-20 10 Workstation 5 soldered wires on motor and workstation 6 carried out soldering board on motor while both workstations used same work facilities. For this reason, we suggest that they should be merged into one workstation which is implemented by only one operator. It reduces one workstation and one operator. The estimated total processing time after improvement is 36.71 seconds. 3.3.2. Reduction of processing time of workstation 9 Figure 4. Current processing time of Workstation 9 and 10 Figure 4 shows processing time of each process in workstation 9 and 10. Workstation 9 included “Check buttons” process which utilized 7.03 seconds while workstation 10 spent waiting time of 13.24 seconds during laser marking machine was operated. We propose the process of checking buttons should be transferred to the waiting process of laser marking at workstation 10. That means while the laser marking machine is doing coding, the operator does checking buttons by using battery. Thus, the estimated processing time of workstation 9 reduces from 45.41 seconds to 38.38 seconds while the total share of processing time of workstation 10 still remains unchanged (30.57 second) [Figure 5]. 2016-11-20 11 Figure 5. Processing time of Workstation 9 and 10 after balanced work 3.3.3. Assignment of more tasks to workstation 1 Figure 6. Compared processing time of workstation 1 before and after work assignment Workstation 1 implemented putting spring into locking block which has used the lowest processing time, 12.40 seconds. Thus, we recommend this workstation should be assigned more tasks such as doing reworks of defective products or supplying materials to other workstations during her waiting time. We assume the time spent for doing reworks and for supplying materials is 23.00 seconds, on average, so the estimated 2016-11-20 12 processing time of this workstation after improvement is 35.40 seconds which is utilized effectively. 3.4. Result Figure 7. Processing time of production line after improvement Table 5. Compared average percentage of waiting time and manpower [Appendix 6, 7] Item Before improvement Average waiting time (%) Manpower After improvement 13.99% 7.62% 10 6 3.5. Discussion Workstation 1 and new workstation are considered as pre-assembly line, so the main assembly line has four remaining workstations. After improvement, the processing time of each workstation is more balanced. There are very small fluctuations in time values among workstations, from nearly 30 seconds at least to almost 39 seconds [Figure 7]. With the tact time of 38.80 seconds, the mean percentage of waiting time in main production line after balancing is 7.62% as opposed to before improvement of approximately 14%, on average [Table 5]. Before improvement, ten operators take part in ten workstations [Appendix 3], but after line balancing, the assembly line has only six workers working at six workstations [Appendix 5]. 2016-11-20 13 3.6. Conclusion From six workstations in Figure 7, we suggest that the layout of assembly line should be re-arranged so that worker’s tasks are much easier to be done, and the distance of moving materials and semi-products are shortened as much as possible. We propose two layouts which can be used in short term and in future, and we analyze the benefits and drawbacks of both layouts for virtual application. 3.6.1. Short-term layout Figure 8. Short-term layout after line balancing In short-term layout, the pre-assembly area is established including two workstations. The first workstation, which carries out putting spring into locking block, is located next to new soldering workstation. The main assembly line is unchanged as compared with the current layout [Appendix 4]. However, each operator in this line must follow new arranged works as line balancing [Appendix 5]. Advantage: ● Pre-assembly processes is moved to separated area ● Simple improvement and able to apply immediately Disadvantage: ● Long distance of movement between pre-assembly area and main assembly area. 2016-11-20 14 3.6.2. Long-term layout Figure 9. Long-term layout after improvement The purpose of long-term layout is to provide permanent solutions for the manufacturing process of digital lock. Two tables are rearranged closely in the middle of room. Operators sit face-to-face and transfer semi-product directly to others on surface’s table. Advantages: ● Shorter distance of movement between pre-assembly line and main production line. ● Workflow is smoother and easier to control. Disadvantage: ● Need more time to set-up facilities: pneumatic system, electricity, vacuum machine. ● Design new table of production line and tray to keep components don’t fall out ● Need to consider flexibility of changeover ability between different products. 4. Reference http://p7883.mittwaldserver.info/en/home/ Dr.-Ing. Marlene Helfert (2016), Work and Time studies, Technical University of Darmstadt Liker, Jeffrey K. (2004). The Toyota Way: 14 Management Principles from the World's Greatest Manufacturer. McGraw-Hill. ISBN 978-0-07-139231-0. 2016-11-20 15 5. Appendix Appendix 1: REFA sheet Z2-Workstation 3 Nr. 1 Workstation 3 Ref. quant. Zy mz Unforeseen task (Transfer products from workstation 4 to workstation 2) 1 L ti Release pre-assembly board Put motor in shaft 2 main F Release motor & shaft Add sprocket Release sprocket Grease lubricant Release brush Add locking block Release locking block Add slider 2016-11-20 19.0 6 7 8 9 10 11 12 13 14 15 23.5 19 ∑L/n ∑ ti / n L ti t= L 100 ti 42.50 42.50 42.50 328 L ti F 100 100 100 105 105 90 100 115 60 80 100 110 90 100 100 15 13.0 12.6 12.8 11.9 11.3 14.5 12.2 9.1 20.1 16.9 13.6 10.1 14.6 12.6 13.3 198.59 32 116 175 230 276 343 412 449 500 601 648 690 736 784 831 15 L ti F 70 80 60 90 100 30 100 105 105 105 90 100 70 105 100 15 8.0 7.1 10.8 6.9 5.8 20.1 5.4 4.4 4.8 4.4 6.4 5.0 8.2 4.3 5.6 107.01 40 123 186 237 282 363 417 453 505 606 654 695 744 789 836 15 L ti F 95 100 100 95 100 95 105 90 105 105 100 100 105 90 100 15 6.0 5.0 4.9 6.2 4.6 6.7 4.2 7.2 4.4 4.9 5.3 4.9 4.2 7.3 5.0 80.61 46 128 191 243 287 370 421 460 509 611 659 700 748 796 841 15 L ti F 100 60 80 100 105 80 100 105 105 90 105 110 100 105 100 15 9.0 17.8 11.5 8.5 7.7 12.1 8.4 7.2 7.5 10.5 7.3 6.0 8.3 7.1 8.9 137.66 55 145 203 251 294 382 430 467 517 621 667 706 756 803 850 15 L ti F 100 60 105 100 100 105 110 100 105 105 105 100 105 70 105 15 6.0 10.6 4.6 5.7 5.9 4.4 3.9 5.8 4.8 4.5 4.8 5.5 4.7 8.1 4.6 83.91 61 156 207 257 300 386 434 473 521 626 672 711 761 811 855 15 1475.00 1 Release slider 5 1445.00 1 6 4 1485.00 1 5 3 1310.00 1 4 2 1455.00 1 3 1 97.00 12.84 13.24 87.33 6.23 7.13 99.00 5.18 5.37 96.33 8.84 9.18 98.33 5.50 5.59 16 Nr. Workstation 3 Ref. quant. Zy mz 2 3 4 5 6 7 8 9 10 11 12 13 14 15 80 125 80 105 120 60 125 125 60 100 100 90 80 120 100 15 10.0 6.7 10.9 7.9 4.5 13.5 5.8 6.7 16.9 8.4 8.4 9.5 10.7 6.4 8.3 134.57 71 163 218 265 305 400 440 480 538 634 680 721 772 817 863 15 Fold board 7 8 1470 1 Release board Unforeseen task (Readjust folded board, get motors from store) End of unforeseen task 2016-11-20 ∑L/n ∑ ti / n 1 L ti F L ti F 32.0 46.2 78.20 103 585 2 L ti t= L 100 ti 98.00 8.79 8.97 39.10 39.10 17 Appendix 2: REFA sheet Z2-Workstation 4 Nr. Workstation 4 Ref. quant. Put housing in assembly box 1 Release housing Add all buttons Release last button Add support grid Release support grid Add board and fix it Release board Add battery holder 6 7 End of interrupted activity 2016-11-20 5 6 7 8 9 10 11 12 13 14 15 L ti F 95 85 100 100 100 105 110 90 120 105 120 85 75 105 100 15 3.7 4.3 3.4 3 3.1 2.9 2.4 3.9 2 2.9 2.1 4.3 5.6 2.9 3.3 49.80 3.7 110.3 149 193 233 287.1 327 362 403 448 482 528 625 663 699 15 L ti F 85 100 90 95 90 90 105 100 100 100 100 100 100 105 80 15 32.1 22.7 28.2 24.3 29.8 27.3 19.2 21.1 21.3 21.5 22.0 22.1 22.1 19.6 37.7 371.00 35.8 133 177 217 263 314 346 384 424 469 504 550 647 683 736 15 L ti F 85 95 75 80 95 100 95 80 85 115 100 105 110 90 105 15 4.3 3.5 5.7 4.9 3.7 3.2 3.8 4.8 4.3 2.1 3.1 2.8 2.6 4.1 2.9 55.80 40.1 137 182 222 267 318 350 388 428 471 507 553 650 687 739 15 L ti F 95 90 115 105 100 105 100 90 95 100 95 95 70 110 80 15 3.9 4.2 2.2 2.9 3.5 2.8 3.4 4.2 3.7 3.6 3.7 3.8 6.3 2.7 5.4 56.30 44 141 185 225 270 320 354 393 432 475 511 557 656 690 745 15 L ti F 75 90 105 100 100 110 100 100 115 100 115 115 110 100 100 15 6.4 4.4 3.0 3.6 3.5 2.3 3.3 3.3 2.0 3.4 2.0 2.1 2.4 3.5 3.4 48.50 50.4 145 188 228 274 323 357 396 434 478 513 559 658 693 748 15 1535 1 Release battery holder Waiting (Wait for housing transferred from workstation 7) End of waiting Interruption due to personal reason (Personal break) 4 1445 1 5 3 1415 1 4 2 1440 1 3 ∑L/n ∑ ti / n 1 1495 1 2 Zy mz L ti L ti F 40.0 40.00 90.4 15.6 10.5 4.8 10.8 10.8 106.0 284.2 400.6 445 524 52.50 L 100 ti 99.67 3.31 3.32 96.00 23.74 24.73 94.33 3.51 3.72 96.33 3.62 3.75 102.33 3.31 3.23 L ti F t= 40.00 40.00 52.50 52.50 18 Nr. 8 Workstation 4 Unforeseen task (Readjust added battery holder) End of unforeseen task 2016-11-20 Ref. quant. Zy mz L ti F 1 2 3 4 2.1 190 5 6 7 1.7 2.1 1.6 230 325 359 8 9 10 11 12 13 14 1.8 60.5 2 2.2 480 619 660 695 15 ∑L/n ∑ ti / n 74.00 L ti t= L 100 ti 74.00 74.00 19
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