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Six Sigma Targets In Manufacturing


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Sometimes people tell us that getting to 3.4 defects per million (DPMO) is very difficult in manufacturing. Most manufacturing processes have a process capability target of around 1.33 or at best 1.67. This corresponds to a target of 4 to 5 Sigma Level.

First of all, just because we have a Six Sigma project, it does not mean that every project needs to end up at 3.4 DPMO. Where 3.4 DPMO corresponds to a Six Sigma process. A project that can improve performance from 2.3 Sigma Level to 3.2 Sigma Level is still a Six Sigma project.

The biggest challenge in manufacturing is to identify the critical tolerances that are really important from a functional point of view for the product. Usually, on a drawing, there may be several tolerances and not all of them may be important. Setting the right tolerances on them (not too loose and not too tight) becomes very important. I find that these values are sometimes derived not based on any analysis but based on what was done historically. The specs get copied from version to version and it becomes very hard to trace the reasons why the specs were put there in the first place. Setting too tight of specs without reason may be one reason why getting to Six Sigma is tough in manufacturing.

What are your thoughts? Do you have a different point of view on this topic?

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  • 1 month later...

SJ,

Rightly said.

Firstly SixSigma approach should not be a project. It should be a way of life. The approach has to be induced in the system through DFSS. DFSS not only helps to improve Quality, also avoids overdoing quality. SS has to start from the concept stage. Right design with proper quality standards need to be decided to make the Sigma level more accurate.

(Eg) Keeping a tolerance of 10microns instead of 50microns or vice versa will definetly have an impact on the Sigma level or other wise the sigmalevel calculation by itself is wrong. This sigma level will not depict the product performance.

Initially for setting the right Q-standards, VOB, VOC & VOP need to be detailed.  Tools like QFD / DFMEA will descibe these requirements in a better way & ensure proper standards are in place.

All the AQ's - "Attractive qualities" & MBQ's - "Must be Qualities" are to be listed & circulated to the manfacturing. A person producing a component must know its effect on the final product. This requires a good Knowledge management technique followed in the company.

The hidden factories need to be identified & tagged. All the special causes need to be addressed on top priority. Came to kow that Toyota management will approve Lean / SS projects only if there is no hidden factory & the process is out of special causes.

A good process control must be in place. This is a primary requirement for collecting data. Also some of the other SS requirements such as MSA study to be done periodically to ensure proper measurements.

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Dear SJ,

I had not seen this topic earlier. But very interesting aspect is brought out by you regarding specs and tolerances.I have observed this quite often in many drawings which come to us from the customers.Some times when we ask a specific clarification to the customer as to why it is so much etc on some dimensioning they are not able to clarify. As you rightly mentioned, the original designer will not be there and also the original thinking,approach and reasoning for the tolerances will not be known,therefore one has to go by history and caryy over the data version to version??

One more interesting thing happens in a ODM model, where design and manufacturing is outsourced. After Approval of the part by the customer, the outsourcing supplier does not give the exact/correct version of the drawing to the customer, with proper design dimension and tolerances..Till that time everything is fine..BUT

.. when the next time when the customer goes in for a modification/up gradation of the design, using the drawings got from the earlier ODM, the customer is in trouble and the new outsourcing partner too???

Any comments??

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  • 2 weeks later...

Dr.P.L.Narasimhan

I agree with the author that all process cannot be controlled with in 3.4 defects. The significant factors are identification of critical proceseses and controlling the process variation within close limit by process capababilty study and controlling random factors.

The design specifications also should be wider than the procees control limits.

Since the tolerance act in cumulative way, wherever possible control the critical tolerances from datum.

As the author indicated tolerance should not be given as a routine procedure as it increases the cost of manufacturing.

 

narasimhan

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Guest V.B.MANIAN Manian

 

Hi all,

       Per the topic herein, broached upon by SJ sir & further opined & affirmed to by others, including some prospective solutions by the respondents, which has been informative, we get to understand that unreasonably tight setting of spec limits is many times a road block on the Six Sigma path in manufacturing. However, if I am not digressing from the topic, we probably have not discussed the reasons behind this mindset, arresting or rather changing which for the better ( before implementing the solution(s) ) would give a new direction in the six sigma journey, which (six sigma) is still at a very nascent stage or even alien in many of the developing countries.

 In my opinion from a manufacturing / production perspective, a few reasons for the above can be :-

1) Resistance to change or not willing to come out of the conventional/historical comfort zone (tight spec limits) which has been prevalent for long irrespective of scope for improvement, once production/manufacturing process has been well established. We can even term it as a ‘Complacency'.

2) It's a normal production (worker in production) mentality of showing one upmanship over something innovative & improvisive in the current operation status, due to a know all attitude, work ego arising from vast experience, etc.

3) A wrong belief that whatever has been going on for long is right until production/ manufacturing suffers in the market (due to rigid spec limits), other things being normal.

4) Inability (due to poor knowledge, awareness, etc) to view & incorporate dynamism as a business need for continued sustenance & growth.

5) Reluctance to bring to notice, observed discrepancies/flaws in the manufacturing process for correction & improvement as long as it is within acceptable limits, for whatever reasons (eg, don't care attitude), which can be attributed to the tight spec limits.

6) Even if the need (for flexibility in spec limits) is identified, further identifying the critical ones (spec limits) still remains a challenge for various reasons, eg poor analysis as pointed by SJ sir.

There could be more (or may be even solutions to the above) that others may think fit to comment upon & take the discussion further, if it so warrants.

 Thanks & rgds

  

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Shri Manian has brought to fore , an extremely important aspect of any Improvement project , in an manufacturing set-up, i.e. CHANGE MANAGEMENT. Any six sigma project is a doubtful contender on the scale of sustainability of the improvements, without proper Change management !!

 As pointed by him, Complacency, Resistance to Change, Traditional Mindsets, " Whats-wrong-with-what-was-happening-till-now" kind of mentality, will always try to de-rail the gains, unless a proper change management is carried out considering the potential failure modes.

 At the same time , a Good Change management execution, will convert a seemingly minor improvement in a process, into a mani-fold benefit grosser of a project.

Regarding DPMO levels, my experience tells, that Percentage shift from the baseline, for a sustained period, is far more encouraging to the shop floor process owner than the numbers. The Proof of a good pooding is in its taste, afterall!!

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  • 2 months later...

Hai all

Impact of the tolerance setting definitely effects on product cost Also getting six sigma levels with tight tolerance too difficult - no doubt. But,

Designer can identify must be qualities and AQ and circulate to manufacturing.

No problem for critical parameters, he can fix tight tolerances as per requirement .

For non critical parameters how can fix the tolerance ?

Tight tolerance is a subjective. Tolerance tight or widen depends on selected process and process capability not depends on product.

Designer calculates parameters & tolerances based on product functional requirement. Not on process capabilities. So,

By default, Some times designers give narrow tolerance.

If the designer is the responsible for the process cost, Quality cost and product cost, they will estimate tolerances rightly and release the product.

Right design with right process selection definitely gives good sigma level output.

Thanks & Rds

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  • 3 months later...
  • 3 weeks later...

Hi ALL;

what is the best practice for measuring sigma level for process inside manufacturing plant, taking in consideration that the plant is producing various products through subsquent manufacturing processes.

For example if we have 3 consequitve processes A,B, &C  and 3 Different Products X,Y, & Z

If any one have real or scientific way for that plz advice

Thanks & Regrads

 

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Hi

During the design of the product, FOS (Factor of Safety) needs to be considered, in normal designer fix a FOS of 1.5 to 3 based on the thump rule. This is not applicable to all dimension and needs to be analyzed carefully. Usaullay, it is the practice that the critical dimension are mating part or any torque / pressure created on the part. When the product is designed for a particular application, engineers are more cautious and tolerance will be tight. Over a period of time, this will be over engineering and value engineering needs to be applied. this is a cycle of over engineering and value engineering. thanks

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I think, manufacturing depends upon the saving of cost of production. It leads to the role of importance of research and development in each product design. That is improvement of manufacturing design without decreasing of the Quality of the product.

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  • 2 weeks later...

Hi All,

I would like to comments something, perhaps it helps.

Six sigma is not viewing only as metric (how many sigma level or sigma capability our process is). But it is used as methodology, DMAIC (which proven improvement methodology beside deming cycle PDCA). Then, if there is an improvement project which use DMAIC methodology eventhough has not arrived in 3,4 DPMO yet, it is still 6 sigma project.

Thanks

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Dear sir,

         I am working as Assistant Manager in Manufacturing of iron castings in the foundry.

In our company we have following the 5 -S  system training program.The objective of this system are the followings: i) Sort out the wanted/unwanted ii) Disposal of unwanted/un used iii) Re-organising based on usuage iv) Recover money thro' hidden valuables.This system is used for the following: 1) To improve overall employee morale 2)Better retrievability and visual control 3) Inventory optimization 4) Minimize process wastage 5) To improve productivity 6) Ensure safe working environment. So,ourselves to implement and sustain 5 S Techniques to create a green&clean environment for all of us and project a possitive image to our customers and strive to achieve custromer delight.And it is started to eliminate Delay of delivery,Defective Product,Dissatisfied customer,Declined Profit,Demoralized employees.

 

 

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Yes Pven San,

It is good to start with 5S. 5S is the starting point for everything in TQM, gradually you can train people on other aspects of TQM. Please form a group for 5S implementation. Create checklists, do a n audit, create a competition, give awards, let all this be done by theemselves as groups. rotate the responsisbility to different people as leadres, it works. If you have aby questions pleas ask. I can guide you thru, How many people are there in your place?

5s is not only for shop floor reeember!!...Sripathy

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  • 2 weeks later...

Hello Everyone,

This topic is very interesting.

A project is known to be six sigma project if it makes business sense and return the revenue on investment at least 1:10.

It is very true successful six sigma project leads to shift of sigma level, no matter whether u achieve 3.4DPMO or not but your sigma level must be improved whether it is from 2 to 3.

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In Iron making i.e at Blast Furnace, it works with two Sigma and intrestingly, non of top management chalanged this and never asked raise sigma rating. Actually Sigma rating is the tollarance  So, sigma rating which is a parameter judge your defect rate  varies from Sector to Sector. For example, in auto sector equipment need to operate at higher sigma to avoid rejection which is otherwise is very costly while on the other hand in a Granite crusher unit you can operate equipment at lower sigma and not loosing much. Raising sigma level even for a single point call for investment. So, decide cooly, do you really need to elevate your Sigma level.

On the other hand, 5-S concept is just like "KAR SEVA". No investment but high return. High return in term of increase in Equipment availability, boost in moral of working people and increase in space availability for further productive job. BUT you need to keep asking your staff/ Operator to clean, clean and clean...

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