Assembly planning

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Assembly planning

  1. 1. ASSEMBLY LINE BALANCING
  2. 2. Hierarchy of Facility Planning Location: is the placement of a facility with respect to customers, suppliers, and other facilities with which it interfaces. Structure: consists of the building and services (e.g., gas, water, power, heat, light, air, sewage). Layout: the configuration of departments, work centers, and equipment with particular emphasis on movement of work through the system . Handling System: consists of the mechanism by which all interactions required by the layout are satisfied (e.g., materials, personnel, information, and equipment handling systems). Facility Planning Structural Design Facility Location Facility Design Layout Design Handling System Design
  3. 3. Designing Product Layouts • Product Layout – GOAL: arrange workers or machines in the SEQUENCE that operations need to be performed. Sequence = Product Line or Assembly Line – Short lines: few operations – Long lines: large operations – BENEFITS: ability to divide required work into a series of elemental tasks
  4. 4. Line Balancing – The process of deciding how to assign tasks to workstations. • GOAL: obtain task groupings that represent approximately equal time requirements – Minimizes idle time – Results in a high utilization of labor and equipment
  5. 5. • Idle time = task times are not equal among workstations – Fast stations: experience periodic waits from slower workstations • Unbalanced lines are undesirable – Inefficient utilization of labor and equipment – Create morale problems Unbalanced Line
  6. 6. Balanced Line • Smooth flow of work • Maximum utilization of labor and equipment
  7. 7. How To Determine The Workstations • Line balancing – involves assigning tasks to workstations ASSUMPTION: – one workstation will be handled by one worker
  8. 8. Cycle Time • The maximum time allowed at each workstation to perform assigned tasks before the work moves on • Establishes the output rate of a line • Example: – Cycle time = 2 mins – Rate = one unit for every 2 mins
  9. 9. Example 1 Suppose that the work required to fabricate a certain product can be divided up into five elemental tasks, with the task times and precedence relationships as shown in the following diagram: Minimum cycle time = longest task time = 1.0 min Maximum cycle time = sum of the task time = 0.1 + 0.7 + 1.0 + 0.2 = 2.5 mins Maximum time: if all tasks were performed at a single station 0.1 min 0.7 min 1.0 min 0.2 min
  10. 10. Output Rate = Operating cycle time per day Cycle time Assume that the line will operate for 8 hours per day (480 mins)
  11. 11. If cycle time = 1.0 min: Output Rate = 480 mins per day = 480 units per day 1.0 min per unit If cycle time = 2.5 mins: Output Rate = 480 mins per day = 192 units per day 2.5 min per unit Therefore, The output must fall in the range of 192 units per day to 480 units per day
  12. 12. Minimum Workstations Needed Theoretical M in. Number of Workstations, N N = Sum of task times (T) Cycle time (C) t t
  13. 13. • This is sometimes referred to as the balance delay. It can be computed as follows: Percentage of idle time Where: N actual = actual number of stations. Percentage of idle time of the line = Idle time per cycle___________________________ N actual X Cycle Time X 100
  14. 14. It can be computed as follows: Efficiency = 100% - percent idle time Efficiency of the line
  15. 15. Example 2 Task Predecessor Task Time (in mins) A - 0.2 B A 0.2 C - 0.8 D C 0.6 E B 0.3 F D, E 1.0 G F 0.4 H G 0.3 ∑t = 3.8
  16. 16. Q U E S T I O N 1. Draw A Precedence Diagram
  17. 17. A C B D E F HG 0.2 min 0.2 min 0.8 min 0.6 min 0.3 min 1.0 min 0.4 min 0.3 min
  18. 18. Q U E S T I O N 2. Assuming an 8-hr workday, compute the cycle time needed to obtain an output of 400 units per day.
  19. 19. S O L U T I O N Operating Time Cycle Time = __________________________ Desired Output Rate 480 minutes per day = ___________________________________ 400 units per day = 1.2 minutes per cycle
  20. 20. Q U E S T I O N 3. Determine the minimum number of workstations required.
  21. 21. S O L U T I O N ∑ t N min = _____________ Cycle Time 3.8 minutes per unit = ________________________________________ 1.2 minutes per cycle per station = 3.17 stations
  22. 22. Q U E S T I O N 4. Assign tasks to workstations using this rule: assign tasks according to greatest number of following tasks. In case of a tie, use the tiebreaker of assigning the task with the longest processing time first.
  23. 23. Station Time Remaining Eligible Will Fit Assign (task time) Revised Time Remaining idle 1 1.2 A,C A,C A (0.2) 1.0 1.0 C, B C, B C (0.8) 0.2 0.2 B, D B B (0.2) 0.0 0 E, D none - 0.0 2 1.2 E, D E, D D (0.6) 0.6 0.6 E E E (0.3) 0.3 0.3 F none - 0.3 3 1.2 F F F (1.0) 0.2 0.2 G none - 0.2 4 1.2 G G G (0.4) 0.8 0.8 H H H(0.3) 0.5 0.5 - - 0.5 1.0 min S O L U T I O N
  24. 24. S O L U T I O N A C B D E F HG STATION 1 STATION 2 STATION 3 STATION 4 Time = 1.2 min Time = 0.9 min Time = 1.0 min Time = 0.7 min
  25. 25. Q U E S T I O N 5. Compute the resulting percent idle time and efficiency of the system.
  26. 26. S O L U T I O N 1.0 min. Percent idle time = _______________ x 100 4 x 1.2 min. = 20.83% Efficiency = 100% - 20.83% = 79.17%
  27. 27. • Skill requirements • Human factors – Fatigue, boredom, failure to concentrate, absenteeism, etc. • Space limitations Other Factors
  28. 28. A job has four tasks; task times are 1 minute, 1 minute, 2 minute, and 1 minute. The cycle time would be 2 minutes and the output rate would be 30 units per hour. Parallel workstations
  29. 29. Parallel workstations Bottleneck 1 min. 1 min.2min.1 min. 30/hr 30/hr30/hr 30/hr
  30. 30. Parallel workstations 1 min. 1 min.1 min. 2 min. 2 min. 60/hr 30/hr 30/hr 30/hr 30/hr 60/hr
  31. 31. • Cross train workers • When bottlenecks occur, the worker with temporarily increased idle time can assist other workers who are temporarily overburdened. • It is used most often in lean production systems. Dynamic line balancing
  32. 32. • To design a line to handle more than one product on the same line. • Products have to be fairly similar, so that the task involve are pretty much the same for all products. • Offers great flexibility in varying the amount of output of the product. Mixed model line

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