Just-In-Time (JIT) Manufacturing


Just-In-time manufacturing, or JIT, is a management philosophy aimed at eliminating manufacturing wastes by producing only the right amount and combination of parts at the right place at the right time. This is based on the fact that wastes result from any activity that adds cost without adding value to the product, such as transferring of inventories from one place to another or even the mere act of storing them.


The goal of JIT, therefore, is to minimize the presence of non-value-adding operations and non-moving inventories in the production line. This will result in shorter throughput times, better on-time delivery performance, higher equipment utilization, lesser space requirement, lower dpmís, lower costs, and greater profits. 


JIT finds its origin in Japan, where it has been in practice since the early 1970ís. It was developed and perfected by Taiichi Ohno of Toyota, who is now referred to as the father of JIT. Taiichi Ohno developed this philosophy as a means of meeting customer demands with minimum delays. Thus, in the olden days, JIT is used not to reduce manufacturing wastage, but primarily to produce goods so that customer orders are met exactly when they need the products.


JIT is also known as lean production or stockless production, since the key behind a successful implementation of JIT is the reduction of inventory levels at the various stations of the production line to the absolute minimum. This necessitates good coordination between stations such that every station produces only the exact volume that the next station needs. On the other hand, a station pulls in only the exact volume that it needs from the preceding station.


The JIT system consists of defining the production flow and setting up the production floor such that the flow of materials as they get manufactured through the line is smooth and unimpeded, thereby reducing material waiting time.  This requires that the capacities of the various work stations that the materials pass through are very evenly matched and balanced, such that bottle necks in the production line are eliminated. This set-up ensures that the materials will undergo manufacturing without queueing or stoppage. 


Another important aspect of JIT is the use of a 'pull' system to move inventories through the production line. Under such a system, the requirements of the next station is what modulates the production of a particular station.  It is therefore necessary under JIT to define a process by which the pulling of lots from one station to the next is facilitated.


JIT is most applicable to operations or production flows that do not change, i.e., those that are simply repeated over and over again. An example of this would be an automobile assembly line, wherein every car undergoes the same production process as the one before it.


JIT has likewise been practiced successfully by some semiconductor companies. Still, there are some semiconductor companies that donít practice JIT for the simple reason that their operations are too complex for JIT application. On the other hand, thatís precisely the challenge of JIT Ė creation of a production set-up that is simple enough to allow JIT.


Guidelines for Successful JIT Implementation


1)  Make the factory loadings uniform, linear, and stable.  Fluctuations in manufacturing loadings will result in bottlenecks.

2)  Reduce, if not eliminate, conversion and set-up times.

3)  Reduce lot sizes.  This will smoothen out the flow of inventories from one station to another, although this may necessitate more frequent deliveries or transfers.

4)  Reduce lead times by moving work stations closer together and streamlining the production floor lay-out, applying cellular manufacturing concepts, using technology to automate processes and improve coordination.

5)  Reduce equipment downtimes through good preventive maintenance.

6)  Cross-train personnel to achieve a very flexible work force.

7)  Require stringent supplier quality assurance since an operation under JIT can not afford to incur errors due to defects.

8)  Use a control system to convey lots between workstations efficiently; the use of a kanban system is an example of this


Kanban Systems


Kanban systems are often associated with JIT implementation. In fact, some people have the misimpression that JIT requires the use of a kanban system.  Having a kanban system is not a strict requirement of JIT implementation, but their use as a tool for practicing JIT has become quite popular owing to its simplicity.


A kanban is a card attached to the carrier or container of a lot used to match what needs to be produced in a work station and what needs to be delivered to the next station. As mentioned, a JIT system is basically a 'pull' system, which means that what needs to be produced in a particular station depends on what the next station needs. Ultimately the production is therefore modulated by end customer orders.  Kanbans, which contain information about the lots and quantities involved, are therefore used to facilitate the execution of this 'pull' system.  With this 'pull' system, no parts that can not be processed in succeeding stations will be produced.


There are two types of kanban assigned to every lot, namely, a production kanban (P-kanban) and a conveyance kanban (C-kanban). The P-kanban  denotes the need to produce more parts while the C-kanban denotes the need to deliver more parts to the next station. No parts can be produced unless authorized by a P-kanban. On the other hand, a C-kanban triggers the 'pulling' or 'withdrawal' of units from the preceding station. C-kanbans are also known as 'move' or 'withdrawal' kanbans.


See Also:   Cell Manufacturing Just-In-Time (JIT)TPMTQMKaizen6-Sigma5S Process




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