Chapter 6
Chapter 6
Chapter 6
Process Design
Chapter 6
Learning Outcomes
➢ Throughput rate (or flow rate) is the rate at which items emerge
from the process, that is the number of items passing through the
process per unit of time.
➢ Cycle time, or takt time, is the reciprocal of throughput rate; it is
the time between items emerging from the process. The term
‘takt’ time is the same, but is normally applied to ‘paced’
processes like moving-belt assembly lines. It is the ‘beat’ or
tempo of working required to meet demand.
➢ Throughput time is the average elapsed time taken for inputs to
move through the process and become outputs.
➢ The number of items in the process (also called the ‘work-in-
progress’, or in-process inventory) as an average over a period
of time.
➢ The utilization of process resources is the proportion of available
time that the resources within the process are performing useful
work.
What should be the
objectives of process
design?
➢ Operations principle: standardizing processes can
give some significant advantages, but not every
process can be standardized
➢ Standardization means ‘doing things in
the same way’ or, more formally, ‘adopting
a common sequence of activities, methods
and use of equipment’.
➢ But why not allow many different ways of doing the same
thing? That would give a degree of autonomy and
freedom to individuals and teams to exercise their
discretion. The problem is that allowing numerous ways of
doing things causes confusion, misunderstandings and,
eventually, inefficiency.
What should be the
objectives of process
design?
➢ Operations principle: the design of any process should
include consideration of ethical and environmental issues
➢ With the issues of environmental protection becoming more
important, process designers have to take account of ‘green’
(sustainability) issues.
➢ To help make more rational decisions in the design activity, some
industries are experimenting with life cycle analysis. This technique
analyses all the production inputs, the life cycle use of the product
and its final disposal, in terms of total energy used and all emitted
wastes.
How do volume and
variety affect process
design?
The overall nature of any process is strongly influenced by the
volume and variety of what it has to process.
The concept of process types summarizes how volume and
variety affect overall process design.
In manufacturing, these process types are (in order of
increasing volume and decreasing variety) project, jobbing,
batch, mass and continuous processes.
In service operations, although there is less consensus on the
terminology, the terms often used (again in order of increasing
volume and decreasing variety) are professional services,
service shops and mass services.
Process type
➢ Batch processes
➢ may look like jobbing processes, but do not have the same degree of variety. As the name implies,
each time batch processes produce more than one item at a time. So each part of the process has
periods when it is repeating itself, at least while the ‘batch’ is being processed.
Process type
➢ Continuous processes
➢ have even higher volume and usually lower variety than mass processes. They also
usually operate for longer periods of time. Sometimes they are literally continuous in
that their products are inseparable, being produced in an endless flow. They often have
relatively inflexible, capital-intensive technologies with highly predictable flow.
➢ Professional services
➢ are high-contact processes where customers spend a considerable time in the service
process. These services can provide high levels of customization (the process being highly
adaptable in order to meet individual customer needs). Professional services tend to be
people based rather than equipment based, and usually staff are given considerable
discretion in servicing customers.
➢ Service shops
➢ have levels of volume and variety (and customer contact, customization and staff discretion)
between the extremes of professional and mass services
➢ Mass services
➢ have many customer transactions, involving limited contact time and little customization. Staff are likely to have
a relatively defined division of labor and have to follow set procedures.
How are processes
designed in detail?
Processes are designed initially by breaking them down into their individual
activities.
Often common symbols are used to represent types of activity.
Process Mapping -The sequence of activities in a process is then indicated by
the sequence of symbols representing activities.
Alternative process designs can be compared using process maps and
improved processes considered in terms of their operations performance
objectives.
Process performance in terms of throughput time, work-in-progress and cycle
time is related by a formula known as Little’s law: throughput time equals work-
in-progress multiplied by cycle time .
Variability has a significant effect on the performance of processes, particularly
the relationship between waiting time and utilization
Process mapping
Process visibility
It is sometimes useful to map such processes in a way that
makes the degree of visibility of each part of the process
obvious.
This allows those parts of the process with high visibility to be
designed so that they enhance the customer’s perception of
the process.
Throughput time, cycle time and work-in-progress
the first stage is to understand the nature of, and relationship
between, throughput time, cycle time and work-in-progress.
As a reminder; throughput time is the elapsed time between
an item entering the process and leaving it; cycle time is the
average time between items being processed; and work-in-
progress is the number of items within the process at any
point in time.
Little’s law (John Little)