Push vs Pull Principle
The pull principle is one of the main blocks in lean manufacturing > pull manufacturing. The customer demand determines which good will be produced and in which quantity. Max/Min inventory levels are agreed with suppliers and customers. This gives you the opportunity to limit overproduction.
In a pull process a workstation or process step is only being triggered when the downstream processes are free to take the output. This means that only when the customer initiates a need the value adding is started. By this a customer can be seen as internal as well as external one. This is lovely as you make sure that only what you will sell will be produced.
Pull is always to prefer against push. As it allows you to manage the WIP and inventories in between workstations which has a straight impact on your lead time. To successfully install a Pull System you have three choices, it is either the well known continuous flow installed, sequential pull or the replenishment pull.
All three types of connection will help you to achieve different levels of Pull in your environment.
No matter what it always comes down to three factors in your system:
Having max one piece of inventory between two process steps
Having a fix production sequence
and having a max number of parts waiting
Thinking about the three types of a Pull System, the continuous flow system has the highest level of Pull, as all three factors are highly involved. Only One Piece at the time and in between two process steps which means a fixed sequence as well as max one part waiting for the next process step.
If you have several workstation linked in one main manufacturing process working on one final product you have a work cell or simply a production line, depending on the shape you can call it e.g. U-cell.
With the sequential pull system you will have the second best choice of a pull manufacturing. It will have a fixed quantity, the sequence of production is defined but with a max number of WIP allowed between process steps. Basically you will allow buffers in your manufacturing. This can typically be seen in FiFo lines (First in First out).
Last but not least we have a look on the Replenishment Pull. This is in other words your supermarket in the production and your third and last option of implementing pull. The supermarket has a maximum number of components, parts or products waiting to be worked or processed on. But it is not known which one will be next. This type of inventory is usually steered or controlled using the Kanban systematic.
To put it in a nutshell - the following table should be fine to give you an overview:
