Balancing of a Assembly Line

Line Balancing

Aim – It only applies to assembly lines. It aims at minimizing the idle time along the line by dividing work equally among members. Tasks are grouped in such a way that they have equal time requirement.

When is line Balancing is Done

· When the line is initially set-up

· When the changes are made in process / desired output rate

Difficulty associated with LB – Not feasible to combine certain activities

Necessity of line balancing – In absence of line balancing, it might create morale problem for workers at slower station who work continuously

(Draw Precedence Diagram)

Cycle Time = Longest time at the any of the work element OR (Operating Time / Desired Output Rate)

CT = 1 min

(In Question, it may be given as 480 units per 8-hour day, Hence CT = 8*60 min per day / 480 units per day = 1 minute per cycle)

Theoretical Minimum number of workstations, Nmin = Sum of time at all WS / CT = (0.1+1.0+0.7+0.5+0.2) / 1.0 = 2.5 = 3 Workstations

Rules in Assigning task

1. Choose new WS if

a. All preceding tasks are completed

b. Task Time is less than or equal to Time Remaining

2. Always first assign the task with greatest task time to a workstation, in case there is a choice between work elements. In case task time is same, choose the element having greatest number of followers.

3. For every new WS, always start with cycle time

WS	Time Remaining	Eligible	Assign Task	Revised Time remaining	WS Idle Time
1	1.0	A,C	C(0.7)	0.3 (1.0-0.7)
	0.3	A	A(0.1)	0.2	0.2
2	1.0	B	B(1.0)	0	0
3	1.0	D	D(0.5)	0.5
	0.5	E	E(0.2)	0.3	0.3

Total Idle time = 0.2 + 0.3 = 0.5 minutes

Balance Delay in % (% of idle time on assembly line) = Total idle time * 100/ (Actual No of WS * Cycle Time)

=0.5*100/(3*1) = 16.7%

Line efficiency = 100% - Balance delay% = 83.3%

Other considerations in line-balancing

1. Technical considerations –

a. Skill requirement of different tasks - If the skill requirements of tasks are quite different, it may not be feasible to place the tasks in the same workstation

b. Incompatible tasks - If the tasks themselves are incompatible (example – Use of fire and flammable liquids), it may not be feasible even to place them in stations that are near to each other

2. Variable tasks by human –

a. Reasons for variation are Fatigue, boredom and failure to concentrate on the task at hand.

b. Absenteeism can also affect the balance

Other approaches to achieve smooth flow of production

1. Make parallel workstations – They increase the workflow and provide flexibility

2. Cross-train workers / Dynamic line balancing – It helps workers perform more than 1 task. In case they are idle, they can assist other workers who are temporarily over-burdened

3. Mixed model line - Design a line to handle more than 1 product on the same line. The different products are similar in many ways and hence, the process applied on them is also same