Six Sigma Process | Lean Six Sigma, Six Sigma Certification

What do you understand by Theory of Constraints (ToC)?

The Theory of Constraints (TOC) is a management approach to managing the weakest link in a process. A process can have one or more weak links, called constraints, that can be anything that prevents the process from performing to its maximum potential. TOC contends that a few constraints control the performance of a process, and therefore provide a mixture of related processes and interrelated concepts to increase the throughput.

What do you mean by throughput and Drum-Buffer-Rope in TOC?

Throughput – Throughput is the rate at which a process generates money through sales, not through production.

Drum-Buffer-Rope – Drum-buffer-rope is a TOC production planning technique that maximizes the flow of materials in a plant for which there is an immediate customer demand.

What the 5 steps followed in theory of constraints approach?

Theory of constraints has five steps. They are;

  1. Identify the constraint : The constraint must be identified before an attempt is made to improve the throughput.
  2. Exploit the constraint : If a constraint is responsible for reducing the output, then it should be pushed to yield the maximum output.
  3. Subordinate to the constraint : The rest of the process should provide maximum support to the constraint to maximize its throughput.
  4. Elevate the constraint : Improve performance by adding more capacity by way of additional resources.
  5. Do not let inertia set in : If the weak link has been strengthened, go back to step one and implement TOC on the new weakest link.


Whatever is the nature of your business, innovation is critical today. In order to survive competition and be the customers’ choice, you need to come up with really new products and services. All it means is that your ability to manage the change is a direct measure of your success. In other words, timely launch of new products/services in desired quality and price are going to determine your success, apart from cultural change aspect. So whether you want it or not, good project management skills are essential in today’s business to survive and win. Without digressing on other pre-requisites of good project management, let’s focus on one of most important but rarely focused area.
There are several project management techniques and tools available such CPM, PERT and Critical Chain. Immaterial of the base on which these models are structured, out of my experience, everything finally boils to predicting time duration for a task and the delivering as predicted. In small organizations(less than 10 employees), it is more of coordination, multi-tasking and communication that will determine if a task can be completed as predicted. But with organizations involving a few tens of employees, it is all about how resources and efforts are synchronized. There may be lack of knowledge of what is to be done next, on who owns which piece, how & when to escalate lack of clarity on authority and decision making. Additionally unlike bigger organizations, smaller companies will have to manage with inexperienced and understaffed scenarios.
So to make life easy for everyone, if processes associated with project management such as supply chain management processes, finance processes, clearly defined inter-department service levels and authorities, etc., are established well, that will help the organization deliver projects in time. Isn’t this what ‘Process Management’ is all about! Mathematically also it makes sense to focus on process management. For instance, consider the PERT model in which the PERT Time (Task duration) is a function of Optimistic Time (OT), Most Likely Time (MLT) and Pessimistic Time (PT). When OT and PT are wide apart, it means that it is not possible to predict the task duration accurately. In other words, the process on which the task is dependent has high variation. Such a process leads to higher PERT Time. When all the tasks of the project have widely spread OTs and PTs, the overall project duration itself will be high and unpredictable.
In order to have closely defined OTs and PTs, we should have confidence that our processes will consistently deliver on-time. In other words, our process should be statistically under control and stable. Again, it’s Process Management!

Six Sigma has been a successful management approach, and a philosophy for many leading global enterprises. Let’s understand Six Sigma Process – in other words – Six Sigma Deployment Approach.
While the deployment of Six Sigma depends on several factors; the following approach explains Six Sigma process in its simplest form.
Six Sigma as a management discipline puts customer’s interest ahead of others. The process of gathering customer requirements is called as Voice of Customer (VOC). A good deployment program starts with VOC. Customer requirements directly translate into business performance standards. In Six Sigma and many quality management approaches, these performance standards are called as Customer Specification Limits.
Operational metrics and performance measures like KPIs are created based on customer requirements. Such operational measures or KPIs are called as Critical To Quality (CTQ) metrics in Six Sigma.
Output of existing processes is measured against customer requirements. This becomes a benchmark of performance. In Six Sigma, this step is called as Assessment of Current Process Capability.
In case an end-to-end process is not capable of consistently meeting customer requirements, and produces high volume of defects; it is taken up for improvement.
Process improvement approach used in Six Sigma is called as DMAIC. It is the acronym of Define, Measure, Analyze, Improve and Control: a 5 step improvement approach.
In this manner, Six Sigma aims to link Customers, Business Processes, CTQs and process improvement all together.
The real power of a Six Sigma Process is in consistently and iteratively following the above activities.
Thus, an organization following a Six Sigma Process:

  1. Systematically and regularly gathers VOC
  2. Measures its process capability
  3. Identifies improvement opportunities
  4. Uses DMAIC to improve its processes


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