Assembly Line Balancing

Dr. Dileep S. More Operations Management Group IIM Calcutta

Objectives

• Understand the concept of assembly line balancing • Study a general procedure to balance the line • Study advantages of line balancing

Introduction

• The first movable assembly line was created by Ford to manufacture the Ford Model T • Ford installed a capstan and a thick cable to move the cars between assembly stations

Ford’s assembly line concept

A Line with Multi Operators

A

2 minutes per unit

B

3 minutes per unit

C

5 minutes per unit

D

1 minutes per unit

E

4 minutes per unit

Process Cycle Time = Throughput Rate = Process Capacity = Overall Process Utilization =

A Line with Single Operator

A

2 minutes per unit

B

3 minutes per unit

C

5 minutes per unit

D

1 minutes per unit

E

4 minutes per unit

Process Cycle Time = Throughput Rate = Process Capacity = Overall Process Utilization =

Line Balancing

Workstation-1 Workstation-2 Workstation-3

A

2 minutes per unit

B

3 minutes per unit

C

5 minutes per unit

D

1 minutes per unit

E

4 minutes per unit

Process Cycle Time = Throughput Rate = Process Capacity = Overall Process Utilization =

The objective of Line Balancing problem is to decide on the allocation of the activities to various Work stations, so as to achieve a desired out put rate, to maximize the line efficiency without violating the precedence constraints.

Line Balancing- Nomenclature

• Task: A necessary step to be performed • Workstations: The specific manufacturing or assembly stations defined to perform specific tasks. • Precedence Diagram: The relationships among tasks imposed by the product design and production method 2 A 1 B 1 G 1.4 H C 3.25 D 1.2 E .5 F 1

Line Balancing- Nomenclature

• Actual Cycle time of line (Ca)

2 A 1 B 1 G 1.4 H C 3.25 D 1.2 E .5 F 1

Maximum number of workstations = Cycle time = Minimum number of workstations = Cycle time = If number of workstations are = 3 Cycle time = Range of cycle time = 3.25 …… Total time

Line Balancing- Nomenclature

Desired Cycle Time (Cd) (Takt Time): The maximum time available to any workstation to complete all the tasks assigned to it. • The allowable time to produce one product at the rate a customer demands it. • Takt is Customer or Market dependent; thus, as the demand changes, then the Takt has to be recalculated. • Example: Desired output rate = 20 units/hour. ….so the desired cycle time would be…. If Desired output rate = 30 units/hour. ….so the desired cycle time would be….

Line Balancing- Nomenclature

• Minimum Number of workstation: The total time to make one unit divided by the Takt time (desired cycle time)

Mmin =

t

Cd

i

• It is necessary to round the number up • Mmin is the lower limit of the number of workstations that can be created

Line Balancing- Nomenclature

• Workstation cycle time (pi): The sum of the process times of each one of the tasks assigned to the work station • Workstation ideal time (hi) = Cd - pi • If the ideal time of each workstation is 0, the line is perfectly balanced

Line Balancing- Nomenclature

• Total ideal time of line = M * Cd – Σ pi • The line efficiency: The time needed divided by the time allocated (Takt time)

E=

i = 1

ti

M * Cd

• The balance delay of line: The percentage of wasted time or 100% - the efficiency

Methodology

• • • • • • Step 1: Define the tasks & their times (ti) Step 2: Draw & label a precedence diagram Step 3: Determine Takt time/desired cycle time Step 4: Calculate minimum number of workstations (Mmin) Step 5: Choose a task assignment rule (Heuristic) Step 6: Assign tasks until the assigned time is equal to the Takt time and recognize precedence constraints • Step 7: Determine the total ideal time and the line efficiency

Heuristic Rule - 1

• Rank Position Weight: Choose the task that has the largest positional weight....

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