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Where Did You Use Mistake Proofing Last?

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One of the most powerful techniques which is common in Lean and Six Sigma is Mistake Proofing (Poka - Yoke). We must try and apply the appropriate mistake proofing mechanism wherever relevant. To refresh our thoughts, the three approaches are Warning, Shut down and Auto-correction.

Do reply to this message about the latest mistake proofing implementation that you carried out so that others can learn from it.

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Good day sir,

This is Pradeep from GB group 7 Feb batch.

During my tenure in Singapore, I am an incharge of cleanroom process . The process is to stack 200 sheets (3 micron sheet on one base). It was found that there is some stack shift of 50 microns for every 8 stacks. The critical X's were temperature of the base, parallism (spec < 10 microns ) between base and sheet carrying head and the Sheet thickness.

The last two were corrected and found ok. But still the occurance of  one out of 35 could be seen. The set point was 50 deg C. When base temperature reduced to 40 deg, the stack shift was observed ( same machine) at the same rate of occurance during production. Hence the mistake proofing was done. 

It also been observed that the bonding strength between sheet was low upto 40 Deg C and kept on increased to 70 Deg C then stabilized. So recommonded and implement 70 Deg for all material and machines ensuring no quality problem.

The reduction in defective reflected for a cost down of S $10 K per month.

Hope I could answer for mistake proofing.

With regards



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  • 3 weeks later...

Dear VK,

I remember one implementation which was of "warning" Poka-Yoke.

In the assembly of machines we have similar looking parts means the Geometry is same the only diffrence is the mech. strength of the material ( one is Heat treated casting & the other is normal), so there were problems of wrong part assembly if both the parts are moving at the same time in the shop floor.

I have introduced a simple Poka-Yoke by changing the color of the job card (Yellow) for the Heat treated parts in the shop floor.

Two years down the line not a single case of wrong part assembly due to this reason is reported after the implementation.

Hope the group shall find it intersting as it is a very simple poka-yoke(no investment) with 100% success.


Rajeev Kamboj


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  • 3 weeks later...

Dear Shri Khatri,

This is my favorite topic and basically, as a Civil & Structural Engineer, I try to mistake-proof all my operations as in Civil Engineering almost everything has to be "done right the first time". We can't construct any floor of a multistory building twice.

As its success involves cooperation of many, especially after the emergence of mistake-proofing idea, I have found the soft-skills part of it rather more challenging than the creativity part of it.

The last time I attended Mistake-proofing was " for a bottled water'.

The problem is " how to mistake-proof a fresh bottled water from spilling over when someone opens it up ?".

I came up with several ideas when brainstormed with my team.

However, for the interest of the group and to invite many creative thoughts, I refrain from giving the near-proof solution now. I hope you will agree with me.



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Dear SJ,

Yes. I appreciate these ideas and I have seen these kind of bottles.

However, don't we have to see the cost-benefit of the mistake-proof ideas/solutions.?

It is better to implement only those ideas which are cost-effective.

There are some more ideas which could have done it with lesser cost.


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  • 1 month later...

Dear SJ,

The idea we got was "to fill the bottle with less water".

Perhaps, fill less by an amount equal to the spilled water.

For example , if the content is 150ml and the spill water is 20ml ( due to poor bottle quality- shell thickness being too thin), then the actual content to be filled is 130 ml and price it & sell it for 130 ml only.

The superiority of this mistake-proof idea lies in the fact that:

1. It does not require redesign of the bottle (increase the height or girth)

2. It does not require increasing the shell thickness (thicker bottle)

3. Existing bottles can be re-used, if necessary.

4. Less price

5. Collateral saving by avoiding water spilling over important office documents. (which mostly happens inadvertently)

6. Simplest in implementation.

7. Less water consumption instead of wasting that much water.


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  • 5 months later...

Hi VK,

I have a case where we work on crawling data from websites along with their domain URL.  While we do so there are many cases where there is link re-directing to a different domain.

As a warning Poka-Yoke, I suggested that we check the domain URL while updating the same to the database, if there is a difference in the domain URL then it would be moved for manual updation of correct domain .


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Dear Senthil,

How is the check done on domain URL? if its done manually then there still remains the possibility of errors but if its done by the system and the system warns/ stops the user from further actioning then probably its a warning mistake proofing.

I have recently intoduced mistake proofing in a system where the operators were capturing the information from one system and typing it in some other system as this 2nd system doesn't allow pasting of copied data and thus there were occurances of making typo errors. As a part of mistake proofing now the 2nd system is made to talk to the 1st system so that the data can be pulled out from 1 and be auto filled in 2nd and remain deactivated, there by not only reducing the no. of typo errors zero but also the overall TAT of processing a query.


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  • 3 weeks later...

Hello  Guys,

I dont have real time experience for the  implementation of Poka-Yoke ( Mistake proofing) but for an idea i can give some examples where we can see in our daily life like Fire  Extinguish Sprinklers, Car door indicator, Brake light indicator and many more.

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Dear Rajeeb

Your Idea is good. Can U say that your idea is full proof mistake proofing.

Reason- 1. There is still a possibility that a non heatreated parts can mix up with Heatreated parts even though yelow job card has been put on boxes/ pallet when you moved those parts to machining area for machining.

This mixup can happen also at Heatreament shop where non heattreatedparts & heattreated parts are store.

whether colour changing of jobcard can solve your problems completely

whether any body having any idea apart from this

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  • 1 month later...

Hi All,

I was working in TVS - NPD Quality... We had a brainstorming on Improving Customer safety while driving...

Example 1

We formed a team & came out with an idea for Side Stand wich is the most dangerous Accident creator...

Normally, we used to see persons driving bikes/Scooterettes with side stand open... To avoid such error, we introduced a beep alarm... (ie) when you start the vehicle with side stand open... the beeper will blow... and alert the rider...

Example 2

During Vehicle assembly stage, there are lot of chances that the wiring for various components (Headlight, Horn, Indicator light etc) are wrongly assembled... To avoid this, we decided to use color codings for wires... Blue for Head Light, Green for Indicator etc... This solved the wrong assembly


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Dear Rajeev,

First I would like to understand the manufucturing process of casting.Are the casting done seperately for Heat treated and Non Heat treated parts ?

or from a batch of say 100 casted parts you selected say 40 for heat treatment.

if former is the case then you add a mark in pattern itself before going for casting for heat treated parts.Thus it wil be clearly visible to the user that this part belongs to Heat treated catagory.


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Dear Amit,

As I mentioned in the begining itself that the castings are exactly same in geometry menans they are produced from the same patterns & the Heat treatment process is done later on.

Introducing the Yellow job card for the HT castings is to give it a clear visibilty in the shop floor for the operatives to be more careful as I mentioned it is a "warning type" of POKA YOKE.

Also we must appreciate in manufacturing that the visual controls are the best on shop floor.

Hope I have cleared some of your doubts.


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Hi Rajeev,

Color coding is a good way to identify. You can also try the other method. Normally, the heat treatment will have an effect on the dimensions. The dimension for heattreated (Normalisi / annealing—> Nitriding) casting will vary upto 35microns. If the casted part has any control dimension parameters like, drilled hole etc, it can be utilised. Design your pallet in such a way that only the non heat treated part will enter the locator in the pallet.. This will further improve the Poka-Yoke rating…

One more example,

Normally in any press-shop there is a high frequency of accident (ie) persons loosing fingers while loading the component urgently & pushing the start switch simultaneously.

To avoid such accidents, currently the press machines are designed with dual start switches. The ram will operate only if both the switches are operated (which means both hands are occupied on switches eliminating the chance of hand related accidents)


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Hello Shalini,

As you said inspection, checklist may also come under the category of mistake proofing. I will give an example for this in many automobile companies which dont follow latest technologies like shutdown alarams have the manual inspection of machines regularly to find out any defects in machines. As soon as you find out any oil dripping out from machine you will sort it out where this can be done thru inspection so you r avoiding mistake in this case.

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Alright let me twist this discussion with an eg ...manual inspection/ check with certain device:

If a sales agent is suposed to collect a set of documents from a customer, his manual cross verification through a checklist with a square boxes (for doc collection) will immediately tell him whether he has collected all the relevant docs or not. Therefore, this check list will warns him of collecting either an inomplete or incorrect set of docs.

Similarly, a stencil used for checking manually whether an application form is correctly filled or not aids in warning probable mistake/s and thus acting as mistake proofing (warning) device.

Views please.

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  • 2 months later...

hi all

mistake proofing is the method of avoding mistake to happen

in my previous assignment, i have some problem with temperature maintenance of chip manufacturing. i experieced some characteristic abnormality in fucntioning of multilayer ceramic chip capacitor that i needed to prove and submit my report

i was handed a machine completely for a week and at each temperature i produced batch of chips and proceeded until to the end of the process. (the problem i observed is the malfucntion of thermostats.) The experimented batch of chips with abnormal temperature having 5% of the abnormality as same as in mass production.

i recommonded to change design of thermostats and heating unit. after change i analysed the product. The abnormality reduced  from 1% to 0.05 %.

with regards


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  • 8 months later...

The most recent area I used mistake proofing was in building product configurators. The product configurators were built to convert the bill of materials (BOMs) definition process for various product families for a client, from a manual process to an automated process.

In addition to generating BOMs based on product knowledge and engineers' tacit knowledge by converting such knowledge into logical rules, the configurator was able to warn users when they chose incompatible features, which then formed the basis for a second round of improvements.

The project was part of an Engineering Lean initiative at an MNC's product development division. The cycle time reduction because of this lean initiative was immense and brought many tangible benefits.

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  • 2 weeks later...

One good example that I implemented sometime back in manufacturing was using Kanban system. For a switch assembly required for one of the car, Exact number of components for each switch required were put in a box. The operator would thus have to ensure that all the parts are being assembled for the switch. This was done as there were complaints of missing parts during inspection. I thought that it was a good example of mistake proofing.



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From above discussion what I understand, check list is consider to be mistake proofing or not that depends on situtation how we use.

1) If process is contineous and we check on some instances (oil leakage on visit) then check list is not a mistake proofing.

2) If process is not contineous (just instances like collecting documents) and we check on instances when it happen then chek list is mistake proofing.

views pls

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