Assembly Line Balancing

Introduction to Industrial Engineering

The Line Balancing Problem

The problem is to arrange the individual processing and assembly tasks at the workstations so that the total time required at each workstation is approximately the same.

Nearly impossible to reach perfect balance

Things to consider

Sequence of tasks is restricted, there is a required order

Called precedence constraints There is a production rate needed, i.e.

how many products needed per time period

Design the line to meet demand and within constraints

Terminology and Definitions

Minimum Work Element Total Work Content Workstation Process time Cycle Time Precedence Constraints Balance Delay

Minimum Work Element

Dividing the job into tasks of a rational and smallest size

Example: Drill a hole, can’t be divided

Symbol – Time for element j: is a constant

ejT

ejT

Total Work Content

Aggregate of work elements

n

jejwc TT

1

Workstation Process time

The amount of time for an individual workstation, after individual tasks have been combined into stations

Sum of task times = sum of workstation times

Cycle time

Time between parts coming off the line Ideally, the production rate, but may

need to be adjusted for efficiency and down time

Established by the bottleneck station, that is station with largest time

Precedence Constraints

Generally given, determined by the required order of operations

Draw in a network style for understanding

Cannot violate these, an element must be complete before the next one is started

Balance Delay

Measure of line inefficiency due to imbalances in station times

c

wcc

nT

TnTd

Method – Largest Candidate Rule

List elements in descending order of T Assign elements to first station, from top

to bottom of list, minding constraints, and not causing sum to exceed cycle time

Continue assigning elements to stations where each station < cycle time, largest assigned first, until all assigned

EXAMPLE