One of the most significant fundamental relations in lean manufacturing is the relation between the inventory, the throughput, and the lead time. The inventory and the throughput are usually easy to measure. The lead time, however, is more difficult. You would need to take the time when a part enters the system and then take the time again when a part leaves the system. Luckily, the lead time can easily and accurately be calculated using Little’s Law, one of the most fundamental laws in lean manufacturing (and also many other places).
In my last post, I described how supermarkets work in theory. But while knowing the theory helps, actually creating a working supermarket is much more difficult. Are there situations where supermarkets are not so useful? (Hint: Yes!). And what is needed to have a working supermarket? Let’s find out!
Kanban, FiFo lanes, and supermarkets are the backbone of many pull system. Some people even define lean production through its use of kanban and supermarkets. Yet why are supermarkets so useful? First we will look at what exactly makes an inventory into an supermarket. My next post will then give tips and hints on the practical use of supermarkets on the shop floor.
One of the most significant insights of the Toyota Production System is its concept of pull production. While often misunderstood, the essence of pull production is a clearly defined limit on the work in progress. Push or pull actually has nothing to do with the direction of the information or material flow. But why does this limit on work in progress make so much difference? Why do pull systems vastly outperform push production systems?
A few weeks ago I wrote an article on the Cuban economy, focusing on commerce (See How a Planned Economy Can Screw Up an Entire Country – Analogy between Cuba’s Communist Economy and Push Systems). On the same visit I not only saw supermarkets, but I also had a look at industry. Unfortunately there are no visitors allowed in their government factories. Nevertheless, I was able to catch some glimpses of different industries.
One popular and well-known concept of the Toyota Production System is the elimination of waste, in Japanese also called muda (無駄). It is one of the three evils of manufacturing systems, the others being unevenness (mura, 斑) and overburden (muri, 無理). In this post I would like to go through the details of waste with you. This includes the traditional seven types of waste – of which I am a big fan. For completeness sake I also included a lot more types of waste I have come across in industry. However, you have to decide yourself if these additional wastes are not themselves a waste.
Over Christmas I escaped the cold weather in Germany and relaxed on the warm beaches in Cuba. Of course, being a lean expert, I was also interested in the Cuban economy. As a communist economy (or more precisely, a socialist economy), it is based on centralized planning. In comparison, the capitalist system of the US (and most of the rest of the world) leaves most business decisions to individual entrepreneurs. This is somewhat similar to push and pull in manufacturing. Push systems also rely on centralized planning, while pull systems have their signal from inside the system to match the customer demand. As capitalism outperforms communism, pull usually outperforms push. Hence, in this post I would like to show you the shenanigans that happen in Cuba due to the effects of centralized planning. Warning: Lots of images ahead!
Eliyahu Goldratt developed different methods on how to manage production systems. These methods are nowadays known as the Theory of Constraints, or TOC for short. One key method described is called Drum-Buffer-Rope, or DBM for short. Similar to Kanban or CONWIP, it aims to constrain the work in progress (WIP) in the system. There is much discussion on which method is better than the other, although the result often depends heavily on with which method the respective author earns its living. In this post I will present how Drum-Buffer-Rope works, and discuss its advantages and shortcomings.