Moving necessary materials through a production process within a facility. 

In a Lean production system, material handling is much more than the delivery of materials. A Lean material handling system can act as the primary means of relaying production instructions. Also, a well-designed system can improve the efficiency of production workers by eliminating wasteful activities such as fetching materials, struggling with items and reaching for materials. 

Fixed times, variable amounts 

In this type of handling system, a material handler travels a standard route through a plant at precisely defined intervals, say every twenty minutes. The amount of material that passes through it each day may vary, but the time interval is fixed. During his predetermined, standard route, the material handler picks up kanban cards showing which materials are to be delivered. He then delivers these materials to production locations. This system is often used in conjunction with a leveling box. The collection intervals in the columns of the box correspond to the time required to complete the standard material handling route. This type of system is often used in assembly operations where a large number of components must be delivered to many different points. It is also called mizusumashi or waterspider conveyance . 

Fixed quantities at variable times 

This type of handling system uses signals from downstream locations to deliver exactly the materials needed at the right time and in the right quantities. The material handler receives a signal to retrieve material from a prior process when a trigger moment or a predetermined inventory level is reached. Because the material handler picks up a standard quantity of material from the upstream process (such as one tray, one pallet or one load board), the quantity of material is fixed but the timing of the transfer depends on the need. This type of system is often used in factories with storage areas for materials produced in batches because of long changeover times. When the cell or machine has used all the material in the storage area, the material handler receives the signal to replenish the consumed quantity from upstream processes. 

This type of system is often called a call system or a call-parts system . 

It is less common but possible to use waterspin transport in conjunction with fixed quantities at variable times. In this construction, the material handler moves crisscross from one production process to another, picking up fixed numbers of materials from different processes on a route that changes with time. 

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