How can statistical process control help quality planning and control?

sunandaC

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In theory if you know the specification – the characteristics to be measured and the standards to be achieved, delivering products or services to that specification should be easy. Unfortunately this is not the case. The transforming and the transformed resources are never perfect.

Transforming resources

Transformed resources

The chef may be suffering from a cold or be untrained in one aspect of preparation or cooking.
The waiting staff may be recently recruited and uncertain about their job, or they all might have been to a party the night before.

The cleaners may not have turned up or have done a thorough job as needed to make the restaurant look clean and smart.

Material from suppliers may be of varying quality such as interruptions to the electricity supply or bruised and rotten vegetables.

A customer may be particularly demanding or even unpleasant making it difficult for the restaurant and its staff to satisfy them.



By checking variables and attributes managers can ensure that the service or products are being deliver to the specification. One important technique in doing this is statistical process control (SPC).

Using SPC we can:

Calculate the likelihood of a process being in or out of control

Set control limits based on those likelihoods

Provide control charts to monitor a quality characteristic

Make decisions about whether a process is in control or not and therefore whether action is needed to find and rectify a problem.

How can acceptance sampling help quality planning and control?

If you are an employer and you want to recruit 20 graduates it is likely that you will interview each one of them. If the batch size is large or the items of lesser value, we need a simpler, quicker and cheaper means of testing a sample to decide if the whole batch is OK or not = this is acceptance sampling.

If you were the quality controller overseeing the manufacture of light bulbs it would be too time consuming to check each of the thousands made each day, and. if the check involved seeing how long they lasted it would destroy the entire output. If you were the quality controller for the marking of an A level examination, it would be impossible to check that every one of the thousands of examiners had correctly marked every one of hundreds of thousands scripts.

Using acceptance sampling we can:
decide the best size of sample to use judge the acceptable number of defects in a batch which results in the batch being rejected for a specified level of risk decide whether as batch should be accepted or rejected and make decisions about the action needed to find and rectify the problem.
 
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