5) Quality Defects

The loss arising from non-conforming products is most obvious when the product has to be scrapped. Less obvious are the losses arising from non-conforming products which are corrected through rework, or accepted on concession following a review.

There are two main categories of defects:

1. Sporadic defects which result from a sudden, adverse change in the status quo. Usually these attract attention and prompt action is taken by operators and supervisors / managers to restore the status quo.
   
   
2. Chronic defects which result from adverse conditions that have become accepted as normal over time. Solving chronic problems requires management involvement to discover breakthrough solutions which change the status quo. This will likely require the collection and analysis of complex data to determine solutions. For example, design of experiments may be applied to discover the optimum equipment settings which are robust to noise (variation).

6) Start-up

Start-up losses are yield losses that occur during the early stages of production from machine start-up to stabilisation. The volume of these losses varies with:

• the stability of the processing conditions
• maintenance levels of equipment, jigs, operators' skills, etc.