What is the difference between [W]aiting] and [U]nscheduled
When assigning the time usages to activities in different categories, it is important to know when to assign them to category [W]aiting and when to [U]nscheduled.
The table compares the consequences of labeling an Activity as type [W]aiting or as type [U]nscheduled.
The following Activities may bring up discussions about the category they belong to.
If the machine is not manufacturing products because there is no demand from customers, the machine is planned to be not producing. The Activity, e.g. described as ‘No orders’, is defined as type [U]nscheduled.
The table below shows what can be the motive for ranking insufficient presence of personnel under [W] or [U].
Both types of ‘no personnel’ can occur, so define each of them using different descriptions e.g. ‘no operator at machine’ [W] or ‘waiting for operator’ [W] and ‘no personnel scheduled’ [U].
Another argument can be that the choice depends on whether the team can or cannot influence the presence of sufficient personnel. If the team itself is responsible for the planning of the personnel and has the authority to hire additional help, ‘no personnel’ should be labeled as [W]aiting. When this responsibility lies outside the team ‘no personnel’ comes under category [U]nscheduled. However, if we identify ourselves with the machine, we can reason as follows: ‘Here we have a customer with a pocket full of money waiting for the product that I make. I am not able to manufacture it due to the absence of personnel. Therefore, I suffer from a loss of effectiveness, and I would appreciate it if the production team or those responsible for personnel solved this problem for me.’ Using this argument, ‘no personnel’ comes under category [W]aiting.
In many countries, it is required by law to schedule a certain amount of time for breaks during a shift. In The Netherlands, it is 30 minutes for a shift of 8 hours, or 45 minutes for a shift of 9 hours.
At first glance, it seems obvious not to schedule a machine for operation (category [U]) for 30 minutes during the presence of the team within a shift of 510 minutes due to the absence of the operator who HAS TO take a break.
Although it needs thorough discussion, basically nothing stops us from allowing the machine to operate for 510 minutes while the operator is ‘on the payroll’ for only 480 minutes.
The first reaction is usually: ‘This is not going to work…’. However, lets again identify ourselves with the machine: ‘Is there really no possibility of allowing me to run?’. If we do not search for such a possibility, we will not find it either. Once again, we will have ‘accepted’ a (substantial!) hidden loss. This can be avoided by ranking breaks under category [W]aiting.
Some options for eliminating this loss are:
- during the break another operator can be deployed;
- the machine continues to operate without supervision;
- one operator temporarily supervises two machines.
Preventive maintenance is necessary to keep up a high OEE in the long term. It is, therefore, a necessary stoppage for a piece of machinery. This stoppage can also be shortened through a shorter revision time and a better handling of the equipment, so that less maintenance will be necessary. Better preventive maintenance should lead to less, and, subsequently, no corrective maintenance (responding to failures). For these reasons, preventative maintenance is part of the category [W]aiting and, consequently, receives attention.
Again, when identifying ourselves with the machine, register, besides production, all the Activities of the machine required to make the machine run in the [P], [W], [L] and [F] categories, so it is included in the OEE.