can be that even though there are unoccupied machines, there is no or only a little material, and when an operator starts to work, the material drops to zero and idle time and waiting is again created. On the other hand, large work-in-process causes waste, for example, in packaging and controlling area. When the parts start to be moved on a large volume at the end of the shift on the conveyor, the packaging and controlling staff is overloaded and this can decrease quality of their work. The work-in-process is optimal when it fulfills several conditions:
1. The operator (or machine) in the bottleneck is sufficiently replenished with the material, and thus, never waits or stops working during the shift.
2. All other operators (or machines) with similar process time as the operator (or machine) in the bottleneck process are sufficiently replenished.
3. All other operators (or machines) have sufficient stock of material that ensures that it is possible to start working without any delay.
Table 3 shows the accumulation of work-in-process during the morning shift. The shift starts at 6.00 and finishes at 14.00 which represents 450 minutes of available process time during this shift. At the start of the shift with operators 1 to 4 we had 2.42 minutes and 1.86 minutes of work-in-process respectively. At the end of the shift, the work-in-process had increased with every operator. In the last column % of individual loss at each operator is calculated and from that average team loss is calculated. For example with operator 1, % of individual loss is (8.77 ÷ 450) × 100 = 1.95%. Totally, at the start of the shift we had only 4.28 minutes of work-in-process, but at the end of the shift the number had increased to 29.79.