Six Sigma is a statistical control device and a form of root cause analysis that seeks to reduce failures in a process to just 3.4 failures per million measurable opportunities, through a structured problem solving system.
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What is a DMAIC process?
Six Sigma is characterised by the acronym DMAIC – usually pronounced “duh-may-ik” - which describes the five distinct segments of the process. These are:
Articulate the problem and use standard Quality tools to prove that it is actually the problem.
Isolate the specific problem and then put it into perspective in relation to the rest of the business. If, once analysed, it’s not the problem you thought it was, it may not be worth spending time and resource on - but you won’t know until you can gauge the issue.
Establish baselines in the process by measuring how well it is doing against expectations.
This means collecting and reviewing the available data, which may mean sales against forecasts, production line failures against throughput, or customer complaints.
Identify and understand the reasons for failure or poor performance.
Once you have solid data, you can investigate this highly important step in a structured way, using tried and tested root cause analysis tools. One of the easiest and best is the 5-Why’s which simply asks the examining team to ask ‘why’ five times. The intention is to drill down to the root cause but many stop too soon. Consider a car not starting in the morning:
- The car won’t start. WHY?
- The battery is dead. WHY?
- The alternator didn’t supply energy to the battery. WHY?
- The alternator belt is broken. WHY?
- The belt was used beyond its recommended replace timescale. WHY?
- Forgot to check when to replace the alternator belt – human error.
We have now deduced that the car won’t start because preventive maintenance wasn’t carried out when needed, and it has resulted in catastrophic failure. 5-Why’s is only one tool available and others such as Fishbone, Failure Modes Affects Analysis (FMEA) , or Voice of the Customer Analysis – or even a combination of them – may be required to get a full picture.
Finding the problem may take the greatest amount of time in this process, but it must be done thoroughly or you can be at risk of not having found the root cause and the problem recurring. Be sure that you actually find the root cause of the problem before trying to fix it.
However, be rational - with the above example of the alternator belt, we could go on to ask why the belt wasn’t replaced in time, and what could be put in place to ensure that it doesn’t happen again, but that could be seen as a step too far.
Test and then implement a solution to the original problem.
With the problem identified a robust solution can be put in place. Because the root cause has been found you can be assured that the problem – in that particular form will not happen again.
There may be more than one answer so all possible solutions need to be reviewed and the benefits of each tabulated, with the option that benefits the company the best being the one that is adopted. The improve phase may also lead to other, knock-on, improvements in related areas of the business, adding to the overall benefit of the change.
Monitor the change to assess the impact on the original problem.
The control phase is important as it signifies the sign-off of the problem and disbandment of the project team. While the issue should now be completely resolved, a suitable quality professional will monitor the original problem to ensure that it really is the case.
The DMAIC process is based on W. Edwards Deming’s Plan-Do-Check-Act cycle, used for the control and continuous improvement of business processes, products and services.
The Plan-Do-Check-Act cycle has the following four steps:
- PLAN – Establish the goals of the improvement and establish a method for achieving those goals
- DO – Put the improvement into action
- CHECK – Study the results and compare them against the expected outcomes
- ACT – Take corrective action where necessary to close the gap between actual and expected results
KPIV & KPOV
At this point, we introduce two more Quality terms; KPIV and KPOV.
The term KPIV is an acronym standing for Key Process Input Variable and relates to the parameters preceding a process under review and how they may affect it.
The key inputs may be physical, such as manufactured product, or notional items that affect the customer like price, durability or features. They are the elements that affect the product service or process at that particular point in it business journey and which may have some impact on it. These are the factors which may need to be examined in detail in order to determine the appropriate ones – key means just that; the elements that directly impact the problem.
Similarly KPOV stands for Key Process Output Variables and relates to the outputs from the process or system. It is these outputs that eventually become the inputs to the next process or system along the line. As with any process-led operation, the next person along the line is a direct customer and care must be taken that issues apparently cured in a Six Sigma exercise are not simply passed on up the line to become a customer’s problem.
The process capabilities of each KPOV need to be measured before any changes are made so that a direct comparison can be made afterwards to gain a realistic picture of how the altered process is performing.
KPIV and KPOV identification can be helped by running a SIPOC exercise. An acronym signifying Supplier, Input Process, Output Customer, SIPOC can be used to map out the KPIV’s and KPOV’s of a particular process and identify which ones are the most important and likely to affect both ends of it. A simple SIPOC diagram, mapping the feeding of the family cat, is shown below:
|Pet Shop||Go Shopping||Open Cupboard||Cat eats||Cat|
|Cat owner||Buy cat food||Take out cat food||Cat fertilises garden||Household|
|Get food home||Fill bowl||Cat catches rodents||Garden|
|Store in cupboard||Put cat food back|
|Place bowl on the floor|
The SIPOC becomes a simple means of identifying the KPIV’s and KPOV’s in any given process and shows how they may linked throughout the whole process segment. The KPIV and KPOV elements become apparent at each part of the SIPOC investigation as every section has its own inputs that must logically be followed by outputs that continue feeding on up through.We should note that unless other tools are used to rank the identified key inputs, they will all be given the same priority, and that may mean analysis of the wrong elements, e.g. those that may only have a small effect on the problem under investigation. It is worth taking extra time to not only identify the key inputs but to also rank them in order of importance so as to focus on the really important issues.
Pros of DMAIC
- DMAIC is a well-defined, well understood process that has been shown to deliver results
- It emphasises attaining attainable goals rather than a series of “would likes” that may not be achievable
- Ensures that senior management buy into the process and sign off the final solution
- Collects data to give problems real-world meaning
- Benefits both internal and external customers
- Will show definable results
- Encourages teamwork and integration
Cons of DMAIC
- Requires specialist knowledge to carry out well
- Solutions driven by data analysis may turn out to be expensive or difficult to implement
- Six Sigma, with its measure of 3.4 defects per million instances, doesn’t rank failures and doesn’t take into account what is important to the customer
- Introducing Six Sigma into a company can carry significant cost in terms of training, and may takes several months to fully implement
DMAIC is a powerful tool when used properly and within defined scope, and offers the potential to completely remove a problem. DMAIC is a root-cause analysis and removal system that should only be used if it is believed that the root cause of a problem can be found.
There is little worth in applying DMAIC to a problem such as world hunger since there is no one root cause and the solution isn’t simple as changing a supplier. Nor will DMAIC help with an international banking crisis, but it will help produce robust processes that might prevent a banking crisis in the future.
Obviously, for DMAIC to work effectively, there also has to be a source of collectable data that can be mined to produce a picture of the current situation. Like any quality process, DMAIC must have real information that can be used to demonstrate what the problem is, which can be compared with data taken after the root cause analysis and improvement steps have been put in place, to show a definite change has taken place.
The intention is that the change in data – production throughput, sales figures, employee satisfaction, etc. – will be positive and therefore demonstrate that the whole process has yielded benefits to the company or organisation.
Six Sigma operations using the DMAIC model are best achieved by small, well-trained teams. The skills of Six Sigma practitioners are generally stated using a karate-type belting system:
Each one of these represents a step forward in the problem solving hierarchy, with the master Back-Belt level being a capable person who would normally run a Six-Sigma team and report out to management, with lower belt members carrying out the work.
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