Four Principles of Lean

1. Pull

It is a system in which customers create a demand for goods, and then the products or goods are manufactured in response to the customers' demand or need. This system aids in the reduction of wastes such as cost, inventory, waiting, and overproduction. The quantity produced in this system is just enough to meet the needs of the customer. Because products can be built better in a pull system, pull system businesses increase customer satisfaction. Kanban can be used to provide signals in pull systems, resulting in a more organized, efficient, and profitable business.

For example, suppose you own a bakery that makes cakes. The idea is that you know what your customers need on a daily basis by taking orders. If orders are taken one day in advance, say for 30 cakes, only 30 cakes should be produced the next day based on customer demand, reducing overproduction, inventory, and waste of the cakes, and fresh cakes would be sold every day, increasing customer satisfaction.

2. One-piece flow

This concept in lean is completely contradictory to batch production. In a one-piece flow, each product is sent to its respective process one at a time, resulting in less WIP (Work in Progress) than in batch production. This system aids in increasing speed and completing the process more quickly. The product's cost is reduced as well because the processing time is reduced, and waste is reduced. This system also aids in the detection of errors at any stage. One-piece flow can be used in large-scale production because the process is consistent, with no downtime and proper production planning.

Assume you're making a chocolate cake with four steps: baking the base, slicing, applying the cream, and finishing. Then the slicing, cream application, and finishing should be done one at a time, rather than gathering 3-4 bases and slicing them and forwarding them to the next process, which will increase the WIP and also decrease the efficiency, which will ultimately increase the faults.

3. Takt

Takt is a shortened form of the German word Taktzeit, which means "measure." Among the lean principles, it is said to be a heart. It provides a consistent, continuous rhythm that acts as a heartbeat for the manufacturing process. The takt time is represented by,

For example, if an industry works 9 hours per day (540 minutes per day), it has 1 hour of lunch break (60 minutes) and 15 minutes for daily meetings, the total available production time in a day is 465 minutes, which is required to calculate the takt time.

4. Zero defects

The goal of zero defects is to identify errors and defects as closely as possible during the process and correct them before the product moves on to the next process. As the Zero Defects approach views prevention as the fundamental principle of quality, this helps to reduce defects, increase efficiency, and maintain quality standards.

For example, while preparing cakes step by step, quality standards are defined; if any of the cakes discovered that the cream was not perfectly spread, the process will stop and the worker will be asked to correct the defect.