What Does JIT Do

 

JIT attacks waste.  Waste is anything not adding value to the product.  The following are examples of waste:

 

·        Product waiting to be processed

·        Re-working defective product

·        Moving product from work station to work station

·        Finished goods inventory sitting, waiting to be purchased

·        Overproduction

·        Inefficient processing

·        Unnecessary motions

·        Product defects

 

Thus, by eliminating waste, the benefits of JIT can start being realized.

 

“Push” vs. “Pull”

In a push system, material is pushed into the downstream work stations regardless of whether resources are available.  In a pull system, material is pulled to a work station just as it is needed.  In order to achieve the pull system, the Japanese implemented the Kanaban (Japanese for card or signal).  In between work stations, kanbans are positioned.  Each kanban can hold a pre-determined quantity of work in process units.  Work can only commence if your respective down stream kanban is empty.  If the kanban is full, then you can not start work.  Thus, the pull system is implemented because you will not start work until the down stream station pulls product out of the kanban which triggers (signals) you to start work.  As can be seen, you will not be able to push material to the subsequent down stream station.

 

 

JIT Production Layout

 

The JIT objective of a production layout is to minimize movement of people and material.  Additionally, the layout should be conducive to increased communication by operators.  JIT requires the following:

 

·        Work cells for product families

·        Moveable or changeable machines

·        Short distances in between stations

·        Little space for inventory

·        Delivery directly to work areas

 

As an example, please refer to the figure below:

 

The process layout depicts a process where like processes are grouped together.  In the JIT Work Cell layout, pieces of each process are grouped together.  This contributes to having a cell staffed with multi-disciplinary workers that can work on any process within that cell which is opposed to the process layout.  Some of the JIT layout tactics are:

·        Work cells should be built for families of products

·        Distances should be minimized

·        Equipment should be movable and flexible

·        Employees should be cross trained to work at any station within the work cell

·        The cell should be U-shaped to maximize visibility and communication

·        Since the space is minimized, inventory can not be allowed to accumulate

 

 

Line Stop

 

In a JIT system, quality is first priority, productivity is second.  Each worker has the authority to stop the line to correct quality problems.  In order to achieve this, the management team must be COMPLETELY bought in to the JIT philosophy.  In other words, JIT will not happen over night; and, the first time an employee stops the line (it will happen many, many times), management must be supportive to address the quality problem now for the productivity gains later.

 

 

Reducing Inventory

 

Minimizing inventory is an underlying principle of JIT.  However, in order to implement JIT, inventory can not be automatically reduced as depicted below:

 

As can be seen, inventory hides many of the production problems within a system.  If this problems are not uncovered and resolved, eliminating the inventory will do nothing more than shut down an operation or more severely, put an operation out of business.  So, JIT encourages eliminating inventory by addressing the underlying problems that inventory hides so that the inventories can be reduced.