Uniform Plant Loading - Just In Time

To use the JIT concept, it is essential that production flows as smoothly as possible. To maintain uniform flow, Japanese companies have shown that by having a uniform master schedule, imbalances in loading at lower level work stations are minimised. The analogy is drawn that a ripple in the pattern of production in the master production schedule can become a wave of demand at lower levels.

Worse still, as the MPS oscillates, the demand for capacity at lower levels sends shock waves through the system. The Japanese method of solving this problem, is to freeze the master schedule over a pre determined horizon, usually at least six weeks. In addition, instead of producing in batches, Japanese companies attempt to create as much uniformity as possible. Consider the master schedule entry below. 

Product           Week 1            Week 2            Week 3

A                       50                     50                   50

B                     100                     100               100

C                     150                      150              150

Instead of completing 50 of batch A before going on to produce 100 of batch B, and the 150 of batch C, the JIT approach, based on uniform loading would be to produce a uniform daily schedule needed, i.e. 

A, BB, CCC, A, BB, CCC, A, BB ... ... ... ... ... ... 

This would produce a uniform, repetitive schedule at the lowest level work centre. The purpose of the Kanban cards is, therefore, to: 

• link fabrication and sub-assembly to final assembly using frozen MPS - repetitive schedules
• balance all other production (maintain synchronisation)
• Make local adjustments to maintain flow - Jidoka.