Process Analysis A process is a set of tasks to be performed in a

defined sequence Process analysis describes how a process is

doing and can be improved Process flow diagrams describe pictorially the

process and the flow of product and information in the process

Process performance is measured based on capacity, efficiency and effectiveness

A Sequential Process: Four-Station Assembly Line

20 min/unit 8 min/unit 15 min/unit

Task A Task B Task C

10 min/unit

Task D

Process Times for Tasks and Systems

The process time of a task is the time it takes to perform the task

The bottleneck time is the time of the longest process time in the system

The throughput time is the time it takes for a product to go through production or for a customer to receive service from start to end (assuming no waiting)

Cycle Times and Bottleneck Pacing The system cycle time is the average time

between completion of successive units of product or departures of successive customers

The system cycle time is the process time of the bottleneck The bottleneck limits the output of the

process! Other tasks in process are blocked tasks

that create surplus inventory or starved tasks that experience idle time as they wait to start their tasks

Determining Capacity Capacity is the number of units of product

that a process can produce in a specified time period (e.g. units per hour)

For service processes, capacity is the number of customers who can be served in a specified time period

The capacity of a process is the inverse of the cycle time. To calculate capacity per hour:

1 hour/cycle time in hours = 60 min/cycle time in minutes

Bottleneck Management

1. Release work orders to the system at the pace set by the bottleneck

2. Lost time at the bottleneck represents lost time for the whole system

3. Increasing the capacity of a non-bottleneck task is a mirage

4. Increasing the capacity of a bottleneck increases the capacity of the whole system

5. Capacity at a station can be increased by lowering the process time.

Capacity Analysis

Two identical sandwich lines Each line has two workers and a toaster to perform the three

operations All completed sandwiches are wrapped

Wrap

37.5 sec/sandwich

Order

30 sec/sandwich

Bread Fill Toast

15 sec/sandwich 20 sec/sandwich 40 sec/sandwich

Bread Fill Toast

15 sec/sandwich 20 sec/sandwich 40 sec/sandwich

Theory of Constraints

Five-step process for recognizing and managing limitationsStep 1: Identify the constraintStep 2: Develop a plan for overcoming the constraintsStep 3: Focus resources on accomplishing Step 2Step 4: Reduce the effects of constraints by offloading

work or expanding capabilityStep 5: Once overcome, go back to Step 1 and find new

constraints

© 2011 Pearson Education, Inc. publishing as Prentice Hall

Capacity Analysis

Wrap

37.5 sec

Order

30 sec

Bread Fill Toast

15 sec 20 sec 40 sec

Bread Fill Toast

15 sec 20 sec 40 sec

Toast station has longest processing time – 40 seconds The two parallel lines each deliver a sandwich every 40

seconds so every 20 seconds a sandwich will come off one of the lines (40 seconds/2 lines)

At 37.5 seconds, wrapping and delivery has the longest processing time and is the bottleneck

Capacity per hour is 3,600 seconds/37.5 seconds/sandwich = 96 sandwiches per hour

Throughput time is 30 + 15 + 20 + 40 + 37.5 = 142.5 seconds = time customer must wait for sandwich assuming no waiting at any of the stations

Measures of Process Performance

Capacity affects revenue potential Efficiency measures how well processes

make use of inputs (e.g. labor, material, equipment) and affects costs and profits

Effectiveness measures how well the process delivers the customer promise Quality Speed (throughput time) Flexibility & responsiveness Safety