1
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
LSS e-Learning
Curriculum under License from
Lean Six Sigma Australasia
91558NSW Vocational Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamental Skills and Knowledge
Lean Six Sigma Fundamental Skills &
KnowledgeConstraint & Time Trap
Identification
Key Objectives
Learn the difference between a capacity constraint and a time trap
Understand the tools to identify a capacity constraint
Takt Rate Analysis
Practice a Load Factor Report Analysis
Understand the tools to identify time traps
Workstation Turnover Time
Using a simple WTT Spreadsheet Analysis
2
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Lean Definitions
The following terms are used frequently to quantitatively describe the output of a process and the critical process steps:
Capacity: The maximum amount of product (output) a process can deliver (produce) over a continuous period of time
Takt Rate: The amount of product (output) required by the customers over a continuous period of time
Time Trap: The process step that inserts the most delay time into a process
Constraint: Any process step that is unable to produce at the exit rate required to meet customer demand (internal or external Takt rate)
Workstation Turnover Time (WTT): The time it takes for all products/services to pass through a workstation once in a processing cycle
What Is a Time Trap?
Time traps insert delay time into a process
Time traps can create long lead times, large downstream inventories, large WIP,
Time traps are principally due to long setup times, machine or human downtime, or quality problems
Time traps can change over time (monthly, weekly, even daily) based upon product mixes or special causes (new product introductions, special orders, etc.)
Time traps can be caused by physical problems (such as process flow, personnel availability, part/supply shortages, equipment availability, others)
Time traps can also be caused by non-physical problems (such as procedures, morale, unsafe work environments, lack of training, others)
There is ALWAYS a time trap in a process!
This is a
Time Trap!!
3
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
What Is a Constraint?
Constraints limit the output capacity of the process (sometimes called bottlenecks)
Constraints have less capacity than the prior or subsequent steps/operations
Constraints are time traps that cannot meet customer demand (a constraint is ALWAYS a time
trap, but a time trap may not be a constraint!)
Constraints can change over time (monthly, weekly, even daily) based upon product mixes or special causes (new product introductions, special orders, others)
This is a
Constraint!!
How Are Time Traps Created?
Poor process flow
Machine capacity
People
Lack of parts
Transportation methods (cranes, foot, etc)
Handoffs
Large batch sizes
Operational deficiencies
Setup
Scrap (low yield)
Downtime
Rework
Distance
Safety concerns
Poor scheduling
Product mix
Excessive WIP
Variability of the process
Stress
Turnover
others
4
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
The Importance of Time Traps
The most limiting step of this process
If we do not understand where the time trap exists, we may end up focusing our project on the wrong process activity
Remember that the Time Trap governs the throughput
Activity 1 2 3 4 5 6 7
Tim
eTime Trap
Exit
Rate
Time Trap Identification
With Constraint Identification, we are interested in finding the operations or processes that will facilitate meeting customer demand
With Time Trap Identification, we are interested in finding the operation or process that will facilitate improving process efficiencies and throughput
Time traps impact efficiencies by requiring more inventory, more equipment, more people, more material, and more time in order to meet customer demand
5
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Pareto Principle and Bottlenecks
Applying the Pareto Principle to time traps means that in most environments, 80% of the inefficiency or delay is caused by 20% of the steps in the process
Turning this around then states that making improvements to 80% of the steps in the process has little to no impact on efficiency or speed
Therefore it is critical that our improvement projects are focused on the time traps
The Importance of Constraints
This time trap is also a constraint…
Unless we attack the constraints, we will continue to be unable to meet customer demand.
Activity 1 2 3 4 5 6 7
Tim
e
One Time Trap Constraints
Max. time to meet customer demand
6
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Project Focus Time Traps or Constraints
Time Traps
Focus on time trap identification if the goal of your project is to improve efficiencies (in inventory, lead time, output rates, others)
Constraints
Focus on constraint identification if the goal of your project is to increase capacity
We priority look at constraint identification firstsince it impacts the customer satisfaction
LSS e-Learning
Curriculum under License from
Lean Six Sigma Australasia
91558NSW Vocational Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamental Skills and Knowledge
Constraint Identification
Takt Rate Analysis
7
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Takt Time and Takt Rate
Takt Rate =Customer Demand
(stated in units per time)
“We can make 6 units per minute”
Example: Takt Rate = pieces/second
Number of Units to Produce
Production Time AvailableTakt Rate =
Takt Time = Customer Demand
(stated in time per unit)
“It takes 10 seconds per unit”
Example: Takt Time = seconds/piece
Production Time Available
Number of Units to ProduceTakt Time =
We will use Takt Rate whenreferring to Customer
Demand
We use Takt Time when describing the output of a
given step/task
Note: Takt is German for “metronome” or musical beat
Example ofTakt Rate Analysis
Takt Rate = “Customer Demand”
An excellent workstation visual control tool used to help operators maintain a customer rhythm to throughput is a Takt Board
In this Takt Board example
the hourly Takt rate is pre-planned to take into account shift activities such as breaks, lunch and meetings
The customer daily demand is 450
Did Operation 3 meet Takt Rate?
Yesterday: 443 Units 1.61 Units/ labor hr
Today: 445 Units 1.62 Units/ labor hr
Hour Takt Rate Actual +- Diff
7-8 AM 60 53 -7 Down for 5 min
8-9 AM 60 59 -8
9-10 AM 45 48 -5 Skipped prodn meeting
10-11AM 60 61 -4
11-12 PM 30 34 0 Took late lunch
12-1 PM 60 59 -1
1-2 PM 60 58 -3
2-3 PM 45 44 -4
3-4 PM 30 29 -5
Totals 450 445
Step 1: Write in the number of units produced and the units/hour from yesterday
Step 2: Write in the number of units to produce and the units/hour goal for today,
confirm the takt rate for each hour (account for breaks and lunch)
Step 3: Each hour, write in the number of units produced in the previous hour
Step 4: Write in the cumulative difference between the scheduled units
produced and the actual units produced
Step 5: Write in any comments (frame welder down, no glass) as a reason for
meeting or not meeting the takt rate.
Comments
Main Production Board: Operation 3
Number of Units to Produce
Production Time AvailableTakt Rate =
Constraint Identification
The Constraint is the operation or process that produces below the Takt Rate
8
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Process Lead Time
Aided exercise:Constraint vs. Time Trap
Task Time above = The total amount of time needed to accomplish the operation
1. Which operation is time trap?
2. If the takt rate is 75 units per hour, is there a constraint?
3. What if the customer is demanding 85 units per hour?
Operation
1Task Time
=
30 sec/unit
Operation
2Task Time
=
40 sec/unit
Operation
3Task Time
=
45 sec/unit
Operation
4Task Time
=
35 sec/unit
Input Output
Aided exercise cont:Constraint vs. Time Trap
We will aid you with this one but can you workout the math conversion using the Takt Rate & Takt Time formulas?
1. Which operation is time trap?
2. If the Takt Rate is 75 units per hour, is there a constraint?
3. What if the customer is demanding 85 units per hour?
1. One Time Trap
2. Max. Takt Time to meet customer demand is 48 seconds per unit
30 sec
Per
unit
40 sec
Per
unit
45 sec
Per
unit
35 sec
Per
unit
Activity 1 2 3 4
Tim
e (s
ecs)
50 -
45 -
40 -
35 -
30 -
25 -
20 -
30 sec
Per
unit
40 sec
Per
unit
45 sec
Per
unit
35 sec
Per
unit
Activity 1 2 3 4
Tim
e (s
ecs)
50 -
45 -
40 -
35 -
30 -
25 -
20 -
3. Time Trap & Constraint
45 sec
Per
unit
3. Takt time
42 seconds per unit
9
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Constraint Exercise: Load Factor Analysis
Good Rhythms Co.
We are the owners of Good Rhythms Co and need to know the following to maximize production capabilities.
The customer demand appears to be high compared to our production abilities. What do you think?
1. What is the net operating time (hours per week)?
2. What is the factory Takt Rate (units/hour)?
3. What is the time trap in the process? What is its’ capacity (in units per hour)?
4. Is the time trap a constraint (can it produce to the takt rate – Yes/No)?
5. If an additional piece of equipment is purchased to increase capacity at the time trap, what is the new capacity?
Constraint Exercise
The Process
Operation 1 Operation 2
Operation 3
Operation 4 Ship
This production process is a four step operation
10
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Constraint Exercise
Basic Operating Data
The company has a customer demand of 16,000 units per week.
The factory operates:
5 days per week
3 shifts per day
Each shift receives a 20 minute paid lunch
Each shift receives 2 x 10 minute paid breaks
Constraint Exercise
Operating Capacity
Operation Capacity/Mach # Machines
Operation 1 60 units/hr 3
Operation 2 25 units/hr 5
Operation 3 35 units/hr 5
Operation 4 80 units/hr 2
11
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Results Constraint Exercise
Load Factor Analysis
1. What is the net operating time (hours per week)?
__________________________________________
2. What is the factory takt rate (units/hour)?
__________________________________________
3. What is the capacity time trap in the process? What is its’ capacity (in units per hour)?
__________________________________________
4. Is the time trap a constraint (does it take longer than the takt rate – Yes/No)?
__________________________________________
5. If an additional piece of equipment is purchased to increase capacity at the time trap, what is the new capacity?
__________________________________________
Constraint Exercise: Load Factor Analysis Good Rhythms Co.
Complete the Load Factor Analysis Exercise
Show the numbers for each of the five questions
Illustrate the Load Factor Analysis with a Takt Rate bar graph
12
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
LSS e-Learning
Curriculum under License from
Lean Six Sigma Australasia
91558NSW Vocational Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamental Skills and Knowledge
Time Trap Identification
Workstation Turnover Time (WTT)
Time Trap and Workstation Turnover Time
Capacity constraints can be found using Takt rate analysis, but how does one identify a Time Trap in complex inefficient operations?
To determine the time traps in a process one must consider the different operating parameters of both the workstations in the process and the products
flowing through the process
For example
how do setup times, processing times, and batch sizes affect individual workstations?
We can use some fundamental analysis that relate these parameters in a term called Workstation Turnover Time (which is comparable to inventory turns), to calculate the time trap
13
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Definition ofWorkstation Turnover Time (WTT)
WTT is the Workstation Turnover Time
the amount of time to setup and run all parts/products/services at a given workstation once in a processing cycle
Formula
WTTk = [(Setup Time i ) + (Process Time i x Batch Size i )]
Where k = 1 to a number of workstations in the process
Where = The sum or addition of each block (parenthesis)
Where i = 1 to n part numbers routed across that workstation
We will develop this equation later in the program (to help us analytically size batches), but it is important to understand in this application
To determine which workstation is the critical time trap, simply calculate WTT for each workstation in the process
the station with the longest WTT is the critical time trap
Process Constraint Identification:
Understanding WTT
Workstation Z processes three parts: A, B, C
If the parts are run sequentially (one after another), then:
WTT for workstation Z is defined as:
Batch A
Setup A Process A Setup B Process B
Batch B
Setup C Process C
Batch C
Setup A Process A
Batch A
Setup B Process B
Batch B
Setup C Process C
Batch C
WTTZ WTTZ
Workstation Z processes three parts: A, B, C
The parts are not run sequentially (not one after another), then:
WTT for workstation Z is defined as:
Batch A
Setup A Process A Setup B Process B
Batch B
Setup A Process A
Batch A
Setup C Process C
Batch C
Setup A Process A
Batch A
Setup B Process B
Batch B
WTTZ
WTT for workstation Z is the same in both scenarios
Scenario 1:
Scenario 2:
14
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Aided exercise:Workstation Turnover Time Example
WTT = [(SetupA)+(Process TimeA x Batch SizeA)+(SetupB)+(Process TimeB x Batch SizeB)]
[(4 hrs)+(.01 hrs/unit x 1000 units) + (4 hrs) + (.01 hrs/unit x 1000 units)
WTT = [(4 hrs) + (10 hrs) + (4 hrs) + (10 hrs)]
WTT = 28 hrs
Use the data given below to solve for WTT= [(Setup Timei )+(Process Timei
x Batch Sizei)]
Description Value Unit
Setup A 4 hrs
Setup B 4 hrs
Process Time A 0.01 hrs/unit
Process Time B 0.01 hrs/unit
Batch Size A 1000 units
Batch Size B 1000 units
Demand A 35.71 units/hr
Demand B 35.71 units/hr
Available hours 40 hrs/week
WTT = ?? hrs
Product A
Workstation Z
Product B
Aided exercise cont:WTT Example Explanation
Given the workstation data of setup time, process time, and batch size, the WTT in this example is 28 hrs.
This 28 hour WTT is a reflection of the workstation’s inflexibility. Because of the setup time and required batch size, this workstation is injecting delay time into the process.
Calculating WTT for each workstation in the process allows us to find the workstation that is injecting the most delay time. This workstation is the critical Time Trap.
As mentioned, later we will learn how to analytically right batch sizes given workstation data such as setup time, scrap, rework, downtime, etc. As batch sizes are changed due these parameters, WTT will change. So ultimately WTT is impacted by all of these parameters as well.
15
Time Traps and Constraints
91558NSW Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamentals
Key Learning
How to identify capacity constraints in a process
How to identify time traps in a process
Understand the tools used to determine constraints and Time Traps
Takt Rate and Takt Time formulas
Load Factor Analysis
WTT Analysis
LSS e-Learning
Curriculum under License from
Lean Six Sigma Australasia
91558NSW Vocational Graduate Certificate in Lean Six Sigma
Unit 7001A Apply Lean Six Sigma Fundamental Skills and Knowledge
LSS e-Learning
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