The first important thing about lean is the definition of a process that is is a set of linked activities. 


Example: In waterfall project management for IT, the process can be: Analyze, Develop, Test and Deploy.
Example: In Scrum, we have this iterative process: Sprint Planning, Daily Scrum (each day), Sprint Review, Sprint Retrospective.

The lead time is the time that passes from the start and the end of the process. In Lean, we want to shorten the lead time avoiding waste in production.

Before discussing waste, look at the two kinds of production, Push and Pull.

  • Push production is when I make many goods, and then I try to find a customer. Frequently is based on a batch system where you take one step at a time for each good in the process;
  • Pull production is when I make a few goods based on the customer’s request. The process starts from the customer’s request and follows all the steps before beginning another cycle, so you need to release a good before beginning with the production of another one.

Look at this example in the IT field:

Example: An example of PULL production is the famous Kanban Board. On these boards, we have some steps (the board's columns) that each element needs to follow to be done. For instance, we can have the column: To-do, In Development, Ready for testing, and Done. It is a pull method because people get the work from each column when they are free to work. They move the elements to the next column when the job is done. In addition, we control the max number of elements for each column for limiting the Work In Progress (WIP). In this way, we avoid the up-front production (the waste) by saying that you can't have more than three elements in the "In progress" column. So if you have three elements in progress, you can't put another one in the "In progress column", forcing people to end the development of other items before starting another one. Obviuslly we say three just for giving an example. The wast stay that you analyze and put in the to-do colum the item just in time for work on it.
Example: An example of PUSH production is when you assign a task directly to a person, staying on his work queue. In this way, it became difficult to know when the work would be finished. In addition, you don't have accurate control over the number of jobs in progress. If you have a change of requirements, you may waste a lot of work made upfront from the people.

You can look that in Kanban, you shorten the lead time by limiting the work in progress, and in this way, you remove waste.
But what’s the definition of waste in Lean? In easy words, non-value-added activities are a waste, and you need to remove them and keep only the value-added ones.

In Lean value-added activities are the activities that:

  • The activity needs to transform the form or function of service of the product;
  • The customer is willing to pay for the transformation;
  • Done the first time correctly.

The non-valued-added activities are all the other, so it’s unnecessary.

Another example of lean is the lean thinking used in Scrum:

Example: In Scrum, we adopt lean thinking by removing waste. A way to remove waste in the scrum process is by adopting a short sprint, and at each of these sprints, we look at the output (the increment and the process for making it) for getting early feedback. In this way, we avoid working for more months and then find that the output of the process doesn't fit the stakeholder's expectative. So in each sprint, we do the transformation (the increment) that add value (so the customer is willing to pay for it), and we avoid unnecessary work with the early feedback (so we try to do it the first time correctly). 

For the exam you need to remember that:

  • Lean is about pull production;
  • Pull production is when I make a few goods based on the customer’s request;
  • Push production is when I make many goods and try to find a customer;
  • Lean remove waste by maintaining only the value-added activities;
  • Value-added activities are those need to make a transformation that the customer will pay. In addition, this transformation is done the first time correctly.

References:

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