For each inspection, irrespective of whether carried out in the receiving section, in production or for machine capability tests, characteristics must be defined with whose help the quality requirements can be monitored.
8.2 Planned quality 173 Equipment, activities and inspections must be established for each
charac-teristic with the aid of specifications.
These characteristics are defined and summarized in the inspection and testing planning. Since process characteristics and product characteristics can be used simultaneously, the MES system has at its disposal all of the quality-related data it needs for analyses, certificates and control loops.
With the MES, inspection and test plans can be prepared which are valid for articles, article groups, operations, customers, suppliers, standards and/or processes, depending on requirements.
Even as early as the design process, it becomes clear which characteris-tics of the product are relevant to quality. When an FMEA is used, a corre-sponding weighting can be obtained from the risk priority numbers. The integration of the FMEA into the MES allows defined characteristics to be taken over directly here. Alternatively, characteristics can also be trans-ferred by reading in data from CAD drawings. This avoids duplicated data input, liable as this is to error.
Assignment of the inspection equipment to be used (or inspection equipment groups) makes it possible to control which measuring equip-ment can be used for quality data acquisition. Here the inspector is assisted by the measuring instruments and measuring equipment being connected directly. This saves time, prevents incorrect inputs and increases accep-tance at the data acquisition stations.
The use of the MES system means that all product-specific data (work plans, etc.) are already available in in-production inspection planning.
These data can be accessed, for example, to create the characteristics cor-responding to each operation which has a relevance to quality. By making a comparison between the work plans and the inspection plans the MES is able at an early stage to reveal deficiencies in the inspection and testing planning. A direct linking together of quality assurance and production planning makes available all information about the machines involved, the tools and molds used, and the individuals logged onto machines without
Fig. 8.2. Dynamization history
174 8 Quality assurance with MES
anything having needed to be done separately regarding data input or inter-facing. With monolithic standard systems these data may under certain circumstances have to be maintained twice.
The production of variants makes special demands on inspection and testing planning. Here the same type of products are being manufactured and only differ in details. If every product has to be looked after with sepa-rate inspection plans this would call for an enormous amount of planning.
The remedy for this problem are so-called specification lists. The contents of an inspection plan can thus be limited to a list of the characteristics to be inspected without specifications actually being given. In a separate list solely the specific features of all product variants to be produced are de-fined. Alternatively, configuration features can be used. Here the inspec-tion planning for each characteristic determines how the specificainspec-tions are obtained from the design dimensions. The tolerance and plausibility limits of the characteristic are relatively predetermined. The order itself will thus include the target values to be used and from these the remaining specifi-cations are calculated. From these functionalities it can be seen how an MES system supports the inspection planner. Using these planning vari-ants reduces maintenance effort to a minimum. At the same time potential faults due to data redundancy are avoided.
When these methods are used for dynamization the inspection frequency can be markedly reduced since empirical values are available. These func-tions are used primarily in receiving controls. Dynamization requires plan-ning beforehand as to what rules it should follow. Apart from the use of the usual standards (ISO 2859, ISO 3951, and so on) the MES system pro-vides the inspection planner with the means for creating his own rules.
Alternatively, a dynamicized inspection can also be used in production following the occurrence of a non-conformance, for example, to increase the inspection interval temporarily in order to see how effective a correc-tive measure is.
To enable him to meet the requirements for gapless documentation of all quality-related data along the full value chain, the user of an MES system has the possibility of using a production control plan. These control plans con-tain all planning data for the entire production process. A control plan brings together the data from several inspection plans. The user can either maintain his data within the control plan or within the specific inspection plans.
Any change made to the planning requirements must be clearly docu-mented. For this reason the MES provides all relevant data (control plan, inspection plans, specification list entries, and so on) with version numbers and the reasons for changes. Release and activation of a version status ensures that only authorized persons can pass modifications on into the production process. Furthermore, changes can be planned at a preliminary
8.2 Planned quality 175 stage and specifically activated at a fixed point in time. The version
man-agement applet allows automatic documentation of when, why and by whom changes were made. The MES keeps these data available for re-search purposes such as, for example, into the history of particular parts.
If the MES includes an initial sample inspection, the user receives sup-port in imsup-porting the corresponding characteristics into production inspec-tion plans. All relevant settings are imported and can be edited if so de-sired. Even this reduces the planning effort and prevents those errors which can occur when quality characteristics are copied manually.
8.2.4 Inspection equipment: reducing measurement