Revision No.”D” Date: 12/2/16 HTNA

Page 1 of 3 Section ll.9.6

HTNA SUPPLIER QUALITY MANUAL

SECTION II.9.6 – MISTAKE PROOFING

(POKA-YOKE)

PURPOSE: To define the suppliers’ ability to identify steps within the process that have the potential to produce

nonconforming material and to put devices in place to prevent and monitor for recurrence.

SCOPE: This applies to all suppliers of purchased production intent parts to HTNA.

EXPLANATION:

1. Mistake Proofing (Poka-Yoke)

Poka-Yoke refers to the highly reliable devices or innovations that either detect abnormal situations before they

occur at a production process or, once they do occur, will stop the machine or equipment and thus prevent the

production of defective products.

A. The idea behind mistake proofing is to relieve some of the burden of the operators so that there is no need

to double check previously inspected items. Poka-Yoke’s can be implemented during the DFMEA,

PFMEA, first run capability, and mass production stages as a continuous improvement (Kaizen) idea,

however the sooner the Poka-Yoke can be identified in the development process the better. Remember the

most effective systems are those that are simple, dependable, and affordable.

B. There are three main methods of Poka-Yoke’s that can be used to control the process depending on the use,

location, and/or cost. It is important to identify which method works best with the process and the systems

that are already in place. The three different methods are as follows:

Prevention

Detection

Containment

C. The Poka-Yoke methods of prevention, detection, and containment can be further broken down into six

separate methods to control them. Listed below are the six methods of preventing defective material from

being passed from one process step to the next.

Different size/staggered guide pins

Error detection and alarms

Limit switches

Counters

Sequence

Check list

2. Plan-Do-Check-Action:

In order to properly implement a Poka-Yoke device one first must understand Deming’s circle of Plan-Do-

Check-Action (PDCA). Deming’s PDCA circle is important to understand since it dictates the method by

which to properly resolve any issue until completely closed.

Like most tools it is important to identify and document the problem and follow the proper steps to ensure total

resolution. As each step in the process is completed so should each section of the pie be shaded in to show

current status of the problem. For convenience, a listing of all issues should be summarized into an Open Issue

Sheet (See SQM Section II.2.8, Open Issue Sheet). The following is a brief example of the method for

performing a PDCA.

Revision No.”D” Date: 12/2/16 HTNA

Page 2 of 3 Section ll.9.6

HTNA SUPPLIER QUALITY MANUAL

Deming’s Circle

D

P A

C

SECTION II.9.6 – MISTAKE PROOFING (POKA-YOKE)

Plan - Identify Top 3 defects in scrap cost Capability Studies

Determine Top 3 failure modes Evaluate data

Do - Kaizen - continuous improvement Should enhance productivity and/or

Brainstorm quality

Fishbone Diagram Train Employees

Check - Evaluate the data on the implemented changes

Action - Confirm improvement Develop Standardized Work

Prepare countermeasure as required Update Poka-Yoke list

Repeat PDCA as required

3. 5 Why’s

The 5 Why’s is an additional tool to be used to identify root cause. The basic philosophy behind the 5 Why’s is

to ask “Why” continuously until the root cause is actually determined. Each time “Why” is asked a series of

additional questions must be asked. If none of the following questions results in the root cause of the problem

one must ask the addition question of “Why”.

Will addressing the direct cause prevent recurrence?

If not, can I see the next level of cause?

If not, what do I suspect as the next level of cause?

How can I check and confirm the next level of cause?

Will addressing this level of cause prevent recurrence?

The team should confirm root cause by asking the following questions. In order to prevent recurrence the

answers to the following questions should all be ”yes”, otherwise root cause has not been correctly

identified.

Have I found the root cause of the problem?

Can I prevent recurrence by addressing this cause?

Is this cause linked to the problem by a chain of cause/effect relationships that are based on fact?

Does the chain pass the “therefore” test?

If I ask “Why?” again, will there be no other identifiable problem?

Once the root cause has been identified it is important to answer the questions below. The idea is to determine

who, what, where, when, why, and how to develop a method that prevents this problem from recurring.

Why did we have the problem?

Why did the problem get to the customer?

Why did our “system” allow it to occur?

TASK METHOD

Revision No.”D” Date: 12/2/16 HTNA

Page 3 of 3 Section ll.9.6

HTNA SUPPLIER QUALITY MANUAL SECTION II.9.6 – MISTAKE PROOFING (POKA-YOKE)

SUPPLIER RESPONSIBILITIES:

1. Develop a system that allows employees to openly make suggestions to change that which may directly impact

the method in which they perform their job. The system must be able to meet the following Poka-Yoke

requirements:

Must prevent defects from getting by

The design must be based on actual processing conditions

The devices should be economical

The devices must be simple with long life and low maintenance

2. Develop control mechanism that either prevents a mistake from being made or makes the mistake obvious at a

glance. One of the following Poka-Yoke Regulatory Functions must be in place:

Control Method: Halts operation until abnormality is corrected

Warning Method: Alerts worker in the event of an abnormality

3. Develop a documented process to audit all the Poka-Yoke devices throughout the process. Identify known

“bad” components and run them through the process to ensure that current Poka-Yoke systems are in place and

are effective. Incorporate Poka-Yoke devices into a preventative maintenance schedule to evaluate wear or

damage.

4. The Poka-Yoke device should provide at-the-source quality inspection with immediate feedback.

5. Must be able to eliminate the mass production of defective product and end-of-line quality inspection.