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:

T ej T ej

is a constant

Total Work Content

 Aggregate of work elements

T wc



j n

  1

T ej

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

d



nT c



T wc nT c

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