Simulation and Analysis for Layout of Aerospace Sheet Metal Process with Lean Concept Chikong Huang 1, Hsien-Ming Chang 2 and Chia-Hui Lin 3

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1 Materials Science Forum Vols (2006) pp online at (2006) Trans Tech Publications, Switzerland Online available since 2006/Jan/15 Simulation and Analysis for Layout of Aerospace Sheet Metal Process with Lean Concept Chikong Huang 1, Hsien-Ming Chang 2 and Chia-Hui Lin 3 1,2,3 Institute of Industrial Engineering and Management, National Yunlin University of Science & Technology 123, Section 3, University oad, Touliu, Yunlin, Taiwan 640,.O.C 1 huangck@yuntech.edu.tw, 2 g @yuntech.edu.tw, 3 g @yuntech.edu.tw Keywords: Lean Production, Job Shop, Cellular Manufacturing, Sheet Metal Process, Simulation. Abstract. Aerospace industry is a value-added and technology integrated industry. Sheet metal parts are important portion of aerostructures. The sheet metal production line combines five different routing types together. This study tries to make a comparison between job shop layout and cellular layout with lean concept. According to precedence diagram of sheet metal fabrication process, the model and measurement indicators can be constructed. The simulation software SIMPOCESS is then used to simulate the real-world cases under dynamic conditions. After the verification and validation process, we analyze the results that collected by simulation and provide the suggestions for the layout of aerospace sheet metal process. 1. Introduction Aerospace industry is a value-added and technology integrated industry. In addition, it is a technique-intensive, capital-intensive, and labor-intensive industry. It also integrates the mechanical, electronic, material, chemical and information technology. Sheet metal parts are important portion of aero-structures. There are thousands of different sheet metal parts in one aircraft. The attribute of sheet metal production line combines different processes of parts together (Sule 1994). According to the contour and function requirement, the aircraft sheet metal part includes five major processes are stretch forming, hydro forming, brake bending, roll forming and drop hammering.because of low quantity requirement of each part number, it is hard to achieve the economic quantity of automatic production. Therefore, introducing group technology and fabricating the parts by part family are suitable ways in aerospace industry. Many factors can influence the configuration of a manufacturing facility, and ultimately the efficiency of its operation. These may include product variety, operation times, production demands, process costs, number of moves, and so forth. (ichard E. Billo, 1998) This study tries to use software to simulate the process flow and figure out characteristics of both job shop and cellular layout for sheet metal shop to satisfy the requirement of customer and lean concept. 2. Literature eview 2.1 Lean Production In the early 1990s, the aerospace company that is the focus of this study initiated a lean approach to production using Kawasaki Production System (L. Bamber et al. 2000). Boeing introduced lean manufacturing in It succeeded to construct a moving assembly line in 1999 at Long Beach Plant by building B717 aircraft (Business Week 2001). Boeing 747 final assembly line introduced moving line technology in The results presented highly optimized production flows and processes, reducing cost and flow time from the traditionally 24 days to the targeted possible 18 days (oberto F. Lu 2002). Lockheed Martin applied lean techniques to the F-16, F-22 and C-130J in The simulation technology applied in aerospace, which can be used to cover a product s lifecycle, from conceptual design, through predefining detailed manufacturing processes to the final product assembly without any physical application required. Industrial demand is now increasing due to the significant benefits of simulation become more widely known e.g. cost saving, more efficient processes, shorter lead times etc. (Craig A. Murphy et al. 2001). Daniel W. Halpin and Marc All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of the publisher: Trans Tech Publications Ltd, Switzerland, (ID: /04/08,12:34:40)

2 908 Progress on Advanced Manufacture for Micro/Nano Technology 2005 Kueckmann explore the relationship between simulation and the emerging topics of Lean Thinking and lean construction (Daniel W. Halpin et al. 2002). In this paper, we use the lean concept to create the indicators as evaluation criteria; use simulation software as a tool to simulate the real-world sheet metal processes of Job shop and cellular layout under dynamic conditions. 3. Modeling 3.1 Problem Analysis In this section, we will briefly describe the background and problem of production and precedence diagram of sheet metal process Problem Description Due to the investment of aerospace industry is high and the pay back period is long, the type of aircraft production belongs to make-to-order system. Quality, cost and delivery on schedule are the basic principle of production line management. The management levels of aircraft factory not only think about the balance of supply and demand, but also pay attention to adjust the organization/layout to absorb the fluctuation from market and reduce cycle time. Many evidences from literature review show cellular layout have good performance in assembly line, but the flow process of part fabrication is more complex than assembly line. There are five forming process constructed by 14-task centers in sheet metal production line. Process flows of sheet metal parts are complex in aerospace industry. Bottleneck of capacity will cause interaction effects between task centers in both the upstream and downstream. To figure out the results of job shop layout and cellular layout applied in fabrication line, this study assumes both the manpower and machines are limited, and it tries to develop the suitable layout to meet both lean principle and requirements of customers Precedence Diagram Consider the construction of task center: Some are depend on forming machines, e.g. stretch forming, hydro forming, rolling, brake bending etc. Some are depending on manpower, e.g. straightening, bench work etc. Consider the characteristics of task center: Some are common resource of difference processes, e.g. heat treatment, bench work etc. Some task centers just serve for one process, e.g. Stretch forming, rolling, joggling. The precedence diagram is shown as Figure 1. i=1 SB S NC i=2 SH S F i=3 i=4 SJ Q i=5 S SS Figure 1. Precedence Diagram of Sheet Metal Parts

3 Materials Science Forum Vols Measurement Indicators Base on the lean concept of waste reduction, cost reduction and continuous improvement, evaluation and measurement indicators are total throughput, cycle time and difference of percent utilization Define Parameters i : Process identification number. i =1~5 (1: Brake bending parts, 2: Hydro forming parts, 3: Joggling parts, 4: olling parts, 5: Stretch forming parts) ij : Identification number in the jth task center of process i. k : Layout identification number. k =1~2 (1: Job Shop Layout, 2: Cellular Layout) p i : Part proportion of process i. i=1~5 N : Total throughput of each process in unit period of time. n i : Total throughput of process i in unit period of time. T ij,setup : Setup time of form block in in the jth task center of process i. T ij,run : un time of sheet metal parts in the jth task center of process i. T ij,queue : Queue time of sheet metal parts in the jth task center of process i Objective Function The throughput of sheet metal factory shall higher than the requirements of assembly line to satisfy delivery schedule of each project. Therefore, control the cycle time to survive in the competitive market. educe the difference of percent utilization of machine/manpower to construct a balancing production environment. Total throughput, cycle time cost and difference of percent utilization of part are the evaluation factors in this study. Objective functions define as equation (1), (2), and (3): (1) Maximize Throughput (N): Maximize the total throughput of each process. Shown as equation (1): Max. N = ni = N pi (1) i i (2) Minimize Cycle Time (T i,cycle ): Minimize the total cycle time of each process. Shown as equation (2): Min. T. = ( T + T + T ) (2) i, cycle j ij, queue ij, setup ij, run (3) Minimize Difference of Percent Utilization ( U k ): Minimize the difference of percent utilization of resources in the same system/layout, shown as equation (3): Min. U = U U (3) k k, max k, min 3.3. Create Simulation Model The job shop layout put the same function resource in same task center. The cellular layout put the resources in the same cell when the machine/manpower needed in the same routing of sheet metal parts. 4. Simulations and Analysis 4.1 Simulation Procedure Step 1. Determine demand of sheet metal parts. Step 2. Base on relationship of each process to create the precedence diagram. Step 3. Determine the resources of sheet metal shop, including manpower and machines. Step 4. Generate block diagram of simulation software-simprocess. Step 5. Construct the relationship of each block (task center). Step 6. Collect and input the capacity parameters of each block (task center). Step 7. Use the Simprocess to simulate the sheet metal production line. Step 8. If he simulation model can satisfy the requirements of customer, run the simulation model 30 times and go to step 9.Otherwise, go back to step 3 and rearrange the resources. Step 9. Collect total throughput(n), cycle time(t i,cycle ) and difference of percent utilization( U k ) of sheet metal parts that gather from simulation report.

4 910 Progress on Advanced Manufacture for Micro/Nano Technology 2005 Step10.Analysis and evaluate the information collected from simulation results and provide suggestions. 4.2 Determine Simulation Parameters Estimate Total Throughput Project A, B, C and D belong to 4 different components, which required by 4 different tier one aircraft manufacturing companies. Consider the aircraft delivery quantity, schedule of each project, and 5% extra requirement. The total requirement quantity is EA/month at least esource Allocation The job shop layout and cellular have the same resources. The manpower in job shop layout is single-function operators, but in cellular layout are multi-skill operators. 4.3 Data Analysis Apply the total throughput, cycle time and the difference of percent utilization of resources as the evaluation indicators. Analysis the data that collected from Simprocess simulations after repeating 30 times, for the job shop and cellular layout Total Throughput Calculate the total throughput of each process after simulation, the result shown as Table 1. CaseⅠ - Transport right away versus every 2 hours: Transport right away: The total throughput of job shop layout (36,317 EA) is larger than cellular layout (36,253 EA). The total throughput of cellular layout is 98.74% of job shop layout. Transport every 2 hours: The total throughput of job shop layout (34,360 EA) is smaller than cellular layout (35,118 EA). The total throughput of cellular layout is % of job shop layout. CaseⅡ - Job Shop versus Cellular Layout : In job shop layout, the total throughput of transport every two hours is 94.61% of transport right away. In cellular layout, the total throughput of transport every two hours is 96.86% of transport right away. Table1. Total throughput of each process Transport right away Transport every 2 hours outing Job Shop Cell Job Shop Cell S 1,867 1,868 1,804 1,846 SH 17,798 17,787 16,800 17,136 SS 1,356 1,356 1,312 1,340 SB 13,430 13,377 12,640 12,953 SJ 1,866 1,865 1,804 1,843 Total 36,317 36,253 34,360 35, Cycle Time Collect the cycle time in each approach, the result shown as Table 2: CaseⅠ - Transport right away versus every 2 hours: Transport right away: The cycle time of job shop layout is shorter than cellular layout in 4 processes (hydro forming, stretch forming, bending and joggling) of sheet metal parts. The cycle time of job shop layout is 54%-91% of cellular layout except rolling process (105%). Transport every 2 hours:

5 Materials Science Forum Vols The cycle time of job shop layout is longer than cellular layout in each process of sheet metal parts. The cycle time of job shop layout is times of cellular layout. CaseⅡ - Job Shop versus Cellular Layout : In job shop layout, the cycle time of transport every two hours is times of transport right away. In cellular layout, the cycle time of transport every two hours is times of transport right away. Table 2. Cycle time of different approach (Unit: Hour) outing Transport right away Transport every 2 hours Job Shop Cell Job Shop Cell S SH SS SB SJ Difference of Percent Utilization Collect the Percent Utilization in each approach, the result shown as Table 3 and 4: Table3. Percent Utilization in job shop layout esource Name Percent Utilization (U) Transport right away Transport every 2 Hrs Joggler 89.47% 89.47% NC outer 82.80% 82.80% Bench Work 66.27% 64.41% Hydro Forming Machine 64.95% 63.23% Power Brake 77.68% 75.86% Stretch Forming Machine 90.93% 90.93% Hand outer 84.51% 83.51% Straightening 88.41% 85.42% oller 86.12% 86.12% U 25.98% 27.70% Table4. Percent Utilization in cellular layout esource Name Percent Utilization Transport right away Transport every 2 Hrs Joggler 89.47% 89.47% NC outer 82.80% 82.80% Straighten.outer&Bench-S 80.31% 80.31% Straighten.outer&Bench-SJ 80.30% 80.30% Hydro Forming Machine 64.95% 63.61% Power Brake 77.68% 76.52% Straighten.outer&Bench-SS 58.52% 58.52% Straighten&Bench-SB 83.72% 83.99% Straighten&Bench-SH 89.57% 87.87% Stretch Forming Machine 90.93% 90.93% oller 86.12% 86.12% U 32.42% 32.42%

6 912 Progress on Advanced Manufacture for Micro/Nano Technology 2005 CaseⅠ - Transport right away versus every 2 hours: Transport right away: The difference of percent utilization of the task centers in job shop layout (25.98%) is smaller than cellular layout (34.42%) in each process of sheet metal parts. Transport every 2 hours: The difference of percent utilization of the task centers in job shop layout (27.70%) is smaller than cellular layout (34.42%)in each process of sheet metal parts. CaseⅡ - Job Shop versus Cellular Layout : In job shop layout, the difference of percent utilization is 25.98% if transport right away. If transport every 2 hours, it will increase to 27.70%. The percent utilization of upper stream is the same, but the down stream is reduced which caused by late coming of WIP when transport every two hours. In cellular layout, the difference of percent utilization is 32.42% if transport right away. If transport every 2 hours, it is the same. The percent utilization of upper stream is the same, the variation of down stream is from -1.70% to 0.27% when transport every two hours. 5. Conclusion From the model construction and validation process, this study provides the following suggestions: 1. In job shop layout of sheet metal shop, line balance is a key factor of performance. Bottlenecks occur when load and capacity is not balance and impact the performance. 2. In cellular layout of sheet metal shop, manager must focus on resource allocation on each process/cell to make sure the throughput can reach the demand. From the evaluation and analysis process, this study provides the following conclusions: 1. In the real-world situation (transport parts every two hours), the total throughput/cycle time of cellular layout is better than job shop layout. But in the ideal condition (transport right away), the total throughput/cycle time of cellular layout is worse than job shop layout. 2. Transportation frequency influences the total throughput/cycle time. Due to more interfaces and transportation point in job shop layout, the influence of transportation frequency of job shop layout is higher than cellular layout. Therefore, increase the transportation frequency can improve the performance of total throughput/cycle time. 3. The difference of percent utilization of the task centers in job shop layout is smaller than cellular layout of sheet metal parts. The influence of transportation frequency to job shop layout is higher than cellular layout. 4. In job shop layout, the difference of percent utilization is 25.98% if transport right away. If transport every 2 hours, it will increase to 27.70%. The percent utilization of upper stream (NC outer, joggling, stretch forming etc.) is the same, but the down stream (Bench work, straightening etc.) is reduced which is caused by late coming of WIP (work in process) when transport every two hours. 5. In cellular layout, the difference of percent utilization is 32.42% if transport right away; and if transport every 2 hours is the same. The percent utilization of upper stream (NC outer, joggling, stretch forming etc.) is the same, the variation of down stream (Bench work, straightening etc.) is from -1.70% to 0.27% when transport every two hours. eference [1] Business Week, 2001, Boeing Goes Lean, 06/04/2001 Issue 3735, p94b, 3p; (AN ) [2] Craig A. Murphy &Terrence D. Perera, 2001, The Definition and Potential ole of Simulation within an Aerospace Company, Proceedings of the 2001 Winter Simulation Conference, B. A. Peters, [3] Daniel W. Halpin and Marc Kueckmann, 2002, Lean Construction and Simulation, Proceedings of the 2002 Winter Simulation Conference, E. Yücesan, C.-H. Chen, J. L. Snowdon, and J. M. Charnes, eds.pp

7 Materials Science Forum Vols [4] L. Bamber and B.G.Dale, 2000, Lean production: a study of application in a traditional manufacturing environment, Production Planning & Control, Vol. 11, No.3, pp [5] oberto F. Lu, 2002, Manufacturing Process Modeling of Boeing 747 Moving Line Concepts, Proceedings of the 2002 Winter Simulation Conference, E. Yücesan, C-H. Chen, J. L. Snowdon, and J. M. Charnes, eds, pp