德国汽车工业质量标准VDA Kapitel 4-07_en

VDA Volume 4: Economical Process Design and Process Control 1 We would like to thank all the companies and their staff who have contri- buted to this workgroup: BMW AG, Steyr Robert Bosch GmbH, Stuttgart Continental AG, Hannover DaimlerChrysler, Stuttgart GFQ Akademie, Bad Kreuznach Ford-Werke AG, Cologne Dr. Ing. h. c. F. Porsche AG, Stuttgart Siemens VDO AG, Babenhausen Volkswagen AG, Wolfsburg Our thanks also go out to all our readers who have submitted improvement suggestions. Oberursel, September 2004 VERBAND DER AUTOMOBILINDUSTRIE E.V. (VDA) VDA Volume 4: Economical Process Design and Process Control 2 Contents Page 1 Economical Process Design und Process Safety 4 1.1 Introduction 4 2 Processes 5 2.1 Process Variables 5 2.2 Definitions 6 2.2.1 Process 6 2.2.2 Capable Process 7 2.2.3 Stable Process 7 3 Process Design 7 3.1 Consideration of new Knowledge in Quality Planning 7 3.2 Communication Basis 9 3.3 Tolerance Specifications and Process Dispersion 10 3.4 Converting Product Requirements into Process Characteristics 11 3.5 Inspection Planning 12 4 Process Qualification 13 4.1 Measurement Equipment Capability and Measurement Uncertainty 13 4.2 Machine Capability 13 4.3 Preliminary Process Capability 15 4.4 Process Capability 15 5 Process Analysis 16 5.1 Distribution Time Models (corresponding to DIN 55319 and DIN ISO 21747) 16 5.2 Process Improvement 20 VDA Volume 4: Economical Process Design and Process Control 3 6 Process Control 21 6.1 Quality Control Chart (QCC) 21 6.1.1 Quality Control Chart for Controlling the Process Location 22 6.1.2 Quality Control Charts for Controlling the Process Dispersion 25 6.2 Recording a QCC 26 6.3 Evaluating a QCC 26 6.4 Use of QCC Before the Series Start 27 6.5 Response Characteristic of a QCC 27 7 Process Assessment 27 7.1 Quantile Method 28 7.2 Effective Parameters (Minimum Process Capability/Process Performance) 29 7.3 Process Capability und Tolerances 30 8 Appendix 32 8.1 Formulas for Calculating Control Limits 32 8.2 Formula Symbols 33 8.3 Examples 35 8.3.1 Quality Control Chart for Moving Averages 35 8.3.2 Operation Characteristic for a Shewhart Chart With Extended Limits 38 8.3.3 Example for Process Analysis and Evaluation of the Long-Term (Process) Capability 40 8.4 Operative Range for Statistical Parameters, Procedures and Aids 46 8.5 Bibliography 48 VDA Volume 4: Economical Process Design and Process Control 4 1 Economical Process Design und Process Safety 1.1 Introduction The application of statistical methods is an essential aspect in an overall quality management system. For example, this can also be seen in relevant sections in national and international rules and regulations for QM - such as ISO/TS 16949:2002 for example - which have the monitoring and measuring of production processes as their subject. The significance of Statistical Process Control (SPC) is one issue that is always emphasized. This document describes several procedures for process qualification, process control and process evaluation that correspond with current, state- of-the art technology. Only processes with measurable (quantitative), continuous characteristics are considered. The quality characteristics that are to be assessed here are seen as inherent characteristics of a product, process or system. As a rule, quality characteristics are also inspection characteristics. Due to rising cost pressures, it is becoming increasingly important to plan processes according to economic considerations. Of particular significance to process planning are small tolerances, a design necessity which often arises due to the product's function. Furthermore, however, it can also be necessary to consider aspects such as Reliability/safety Verifiability Exchangeability Service life Appearance when defining tolerances. To achieve a product's optimal economic viability, the requirements placed on the product and the manufacturing costs must be reconciled. For production planning and execution, the emphasis is naturally on feasibility and verifiability of the product components' characteristics. As a rule, the smaller the tolerance, the more costly the associated processing and inspection processes. VDA Volume 4: Economical Process Design and Process Control 5 Processes should be effective and efficient. This means that the processes produce products that fulfill the stipulated requirements while achieving the greatest possible economic viability, meaning the least possible consumption of resources. These guidelines do not make any claims to completeness. The procedures described here are based on knowledge gained in an empirical investi- gation of the automotive industry (QZ, year 44, pages 761 to 765), in which previous procedures were critically analyzed in conjunction with the evaluation of manufacturing processes. In particular, these guidelines take into account current developments in national and international standardization (see Section 8.4). 2 Processes 2.1 Process Var