4-6 7001a 2-16 a 7 constraints time traps uoc7001a_91558nsw clr.pdf

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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

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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!!

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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

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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

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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

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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

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Constraint Identification

Takt Rate Analysis

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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

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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

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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

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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




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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

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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

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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:

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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.

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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

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