The ISO definition states that quality control is the operational techniques and activities that are used to fulfil requirements for quality. This definition could imply that any activity whether serving the improvement, control, management or assurance of quality could be a quality control activity. What the definition fails to tell us is that controls regulate performance. They prevent change and when applied to quality regulate quality performance and prevent undesirable changes in the quality standards. Quality control is a process for maintaining standards and not for creating them. Standards are maintained through a process of selection, measurement and correction of work, so that only those products or services which emerge from the process meet the standards. In simple terms quality control prevents undesirable changes being present in the quality of the product or service being supplied. The simplest form of quality control is illustrated in the Figure below. Quality control can be applied to particular products, to processes which produce the products or to the output of the whole organization by measuring the overall quality performance of the organization.
Quality control is often regarded as a post event activity. i.e. a means of detecting whether quality has been achieved and taking action to correct any deficiencies. However, one can control results by installing sensors before, during or after the results are created. It all depends on where you install the sensor, what you measure and the consequences of failure. Some failures cannot be allowed to occur and so must be prevented from happening through rigorous planning and design. Other failures are not so critical but must be corrected immediately using automatic controls or
fool proofing. Where the consequences are less severe or where other types of sensor are not practical or possible, human inspection and test can be used as a means of detecting failure. Where failure cannot be measured without observing trends over longer periods, one can use information controls. They do not stop immediate operations but may well be used to stop further operations when limits are exceeded.
If you have no controls then quality products are produced by chance and not design. The more controls you install the more certain you are of producing products of consistent quality but there is balance to be achieved. Beware of the law of diminishing
returns.
It is often deemed that quality
assurance serves prevention and quality control detection, but a control
installed to detect failure before it occurs serves prevention such as reducing
the tolerance band to well within the specification limits. So quality control
can prevent failure. Assurance is the result of an examination whereas control
produces the result. Quality Assurance does not change the product, Quality
Control does.
Quality Control is also a term used as
a name of a department. In most cases Quality Control Departments perform
inspection and test activities and the name derives from the authority that such
departments have been given. They sort good products from bad products and
authorize the release of the good products. It is also common to find that
Quality Control Departments perform supplier control activities which are called
Supplier Quality Assurance or Vendor Control. In this respect they are
authorized to release products from suppliers into the organization either from
the supplier's premises or on receipt in the organization.
Since to control anything requires the
ability to effect change, the title Quality Control Department is in fact a
misuse of the term since such departments do not in fact control quality. They
do act as a regulator if given the authority to stop release of product, but
this is control of supply and not of quality. Authority to change product
usually remains in the hands of the producing departments. It is interesting to
note that similar activities within a Design Department are not called quality
control but Design Assurance or some similar term. Quality Control has for
decades been a term applied primarily in the manufacturing areas of an
organization and hence it is difficult to change peoples perceptions after so
many years of the terms incorrect use.
In recent times the inspection and
test activities have been transferred into the production departments of
organizations, sometimes retaining the labels and sometimes reverting to the
inspection and test labels.
Control of quality, or anything else
for that matter, can be accomplished by the following steps:
-
Determine what parameter is to be
controlled.
-
Establish its criticality and whether
you need to control before, during or after results are produced.
-
Establish a specification for the
parameter to be controlled which provides limits of acceptability and units of
measure.
-
Produce plans for control which
specify the means by which the characteristics will be achieved and variation
detected and removed.
-
Organize resources to implement the
plans for quality control.
-
Install a sensor at an appropriate
point in the process to sense variance from specification.
-
Collect and transmit data to a place
for analysis.
-
Verify the results and diagnose the
cause of variance.
-
Propose remedies and decide on the
action needed to restore the status quo.
-
Take the agreed action and check that
the variance has been corrected.
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