Line balancing: Concept and Method

The line balancing refers to the arrangement of production line efficiently, so that there is a smooth flow of production without any delay between workstations. The objective of the line balancing function is to divide the tasks efficiently among workstations to minimize the idle time of men and machines.

Terms related to Line Balancing

Productivity: The ratio of output over input. The input may be man, machine, material, and money.

Lead Time: Summation of production times which starts when the request is made by the customer and ends at delivery of the product.

Task Precedence: The order by which tasks are completed which is represented by graph etc.  

Bottleneck: Delay in the production process that reduces the production rate. The balancing of the line overcome the bottleneck.

Idle time: A duration when the system is not in operation but is available.

Takt times: The time that shows the speed of manufacturing to meet customer orders. Takt time is a pre-requisite procedure for line balancing tasks and is a process of production swiftness that aligns production with client demand.  

Cycle Time:  The cycle time refers to how often the production line can generate the product with current resources and staffing which indicates how the line is currently set up to run. The cycle time can be found by dividing the required units to production time available per day.

Objectives of Line balancing

• Allocation of the same amount of work among all
•  Avoid overloading and under loading
• To develop smooth task precedence
• To complete the customer order on time
• To avoid bottlenecks and idle times.

Steps in Line Balancing Technique

1. Determine Cycle time:  Cycle time demonstrates  the maximum time allowed to a workstation: The cycle time can be expressed by this formula: Cycle Time = available time/ Required output

2. Divide tasks into workstations: The tasks should be arranged into workstations; with the condition that the total time of tasks in a workstation should not exceed the Cycle time.

3. Determine idle time, Total Operation time and total cycle time.

Idle time can be determined by the formula: workstation working time – cycle time.

Total operation time is the sum of total operation time of workstations.

Total cycle time = total idle time + total operation time

4. Determine Balance Efficiency: The balance efficiency can be determined by total operation time/ total cycle time.

Example:

A Precedence diagram of tasks is given below. The line operates for 7 hours per day and an output of 550 units per day is required as per customer order; determine the balance efficiency?

Step 1: Determine Cycle Time:

Cycle Time = Available Time / Required Output

Available time:  7 hours = (7*60 minutes) = 420 minutes

420/550 (units per day) = 0.76 minutes

Cycle time = 0.76 minutes

2. Divide tasks into workstations with the condition that the total time of tasks in a workstation should not exceed the Cycle Time.

Step3: Determine Idle time, Total Operaiton Time and Total Cycle Time

Idle time: workstation working time – cycle time

Idle time of workstation 1: 0.65- 0.76= 0.11

Idle time of workstation 2: 0.7- 0.76 =0.06

Idle time of workstation 3: 0.65-0.76= 0.11

Idle time of workstation 4: 0.7-0.76=0.06

Total idle time: 0.11+0.06+0.11+0.36 = 0.34

Total operation time: actual operation time of ws1 + ws2+ws3+ws4

 0.65+0.7+ 0.65+ 0.7 = 2.7

Total cycle time = Total operation time + idle time

= 2.7+ 0.34 = 3.17

Step 4: to find out balance efficiency:

Balance efficiency = total operation time/ total cycle time

                                                        2.7 /   3.17 * 100 = 85

So total balance efficiency is 85%

The Conclusion: The measured balance efficiency is 85%, so the manager has to further improve balance efficiency by up to  15% by removing 15% of idle time.