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294 Part IV: Quality Assurance
Part IV.B.5
supplier. More and more manufacturers and suppliers are using PCI as an important
part of their contract to ensure quality.
A process capability analysis is simply the comparison of the distribution of a
process output with the product tolerances. As noted by Kotz and Lovelace (1998),
results of process capability analysis have proven very valuable in many ways.
Deleryd (1996) has developed a list of the 13 most common ways of using the
results of process capability analysis:
1. As a basis in the improvement process.
2. As an alarm clock.
3. As specifications for investments. By giving specifications for levels
of process capability indices expected to be reached by new machines,
the purchasing process is facilitated.
4. As a certificate for customers. The supplier is able to provide the
results from the process capability studies conducted when the actual
products were produced with the delivery.
5. As a basis for new construction. By knowing the capability of the
production processes, the designer knows how to set reasonable
specifications in order to make the product manufacturable.
6. For control of maintenance efforts. By continuously conducting process
capability studies it is possible to see if some machines are gradually
deteriorating.
7. As specifications for introducing new products.
8. For assessing the reasonableness of customer demands.
9. For motivation of coworkers.
10. For determining priorities in the improvement process.
11. As a base for inspection activities.
12. As a receipt for improvement.
13. For formulating quality improvement programs.
In order to implement a process capability analysis, one needs to consider the
following:
1. The target value specification, which is usually defined by the
customer.
2. The specification limits, which should be defined by the customer, or
by his technical staff, and should be agreed upon by the manufacturer.
Furthermore, the specification limits should be such that they allow
for manufacturing variability without jeopardizing proper function
of the product.
3. An analysis of the process that allows the manufacturer to determine
if his/her product can meet the customer’s specifications.