Material Flow

The movement of physical items throughout the value stream.
In mass production, products move in large batches to centralized processes. They are propelled at the direction of an overall planning system (see illustration below). In Lean production, process steps for different product families are bundled together in a fixed process sequence whenever possible. This allows small quantities of product to flow directly from step to step as soon as a pull signal is received from the next process downstream and from the end customer.