Process-oriented tolerancing using the extended stream of variation model

Current works on process-oriented tolerancing for multi-station manufacturing processes (MMPs) have been mainly focused on allocating fixture tolerances to ensure part quality specifications at a minimum manufacturing cost. Some works have also included fixture maintenance policies into the tolerance allocation problem since they are related to both manufacturing cost and final part qual- ity. However, there is a lack of incorporation of other factors that lead to increase of manufacturing cost and degrade of product quality, such as cutting-tool wear and machine-tool thermal state. The allocation of the admissible values of these process variables may be critical due to their impact on cutting-tool replacement and quality loss costs. In this paper, the process-oriented tolerancing is ex- panded based on the recently developed, extended stream of variation (SoV) model, which explicitly represents the influence of machining process variables in the variation propagation along MMPs. In addition, the probability distribution functions (pdf) for some machining process variables are ana- lyzed, and a procedure to derive part quality constraints according to GD&T specifications is also shown. With this modeling capability extension, a complete process-oriented tolerancing can be con- ducted, reaching a real minimum manufacturing cost. In order to demonstrate the advantage of the proposed methodology over a conventional method, a case study is analyzed in detail

Derivation and application of the stream of variation model to the manufacture of ceramic floor tiles

One of the main problems in the manufacture of floor tiles is the dimensional variability of the ceramic product, which leads to the product having to be classified into different dimensional qualities with an increase in cost. In this paper we propose a novel way of modelling the dimensional variability of ceramic floor tiles by the adaptation of the Stream of Variation model. The proposed methodology and its potential applicability contributes to the integration of process knowledge in the ceramic tile industry and allow tile manufacturers have a new methodology for process improvement, variation reduction and dimensional control

Merkmalentstehungs- und -wechselwirkungsanalyse (MEWA) für das prozessorientierte Toleranzmanagement in der Montage

Die Lösung von Toleranzproblemen stellt eine große Herausforderung bei der Verwirklichung funktionaler und wirtschaftlicher Produkte sowie Prozesse dar. Das Toleranzmanagement (TM) nimmt sich dieser Herausforderung an und beschäftigt sich mit den Auswirkungen von Abweichungen und der Vergabe von Toleranzen. Produkte, Prozesse und Betriebsmittel sollen robust geplant und implementiert werden, sodass sowohl die Entstehung als auch die Auswirkungen von Abweichungen begrenzt werden. Insbesondere bei der Merkmalentstehung in unterschiedlichen Materialflüssen, bspw. auf zwei unterschiedlichen Montagelinien, stoßen bestehende Methoden des TM an ihre Grenzen. Ziel der vorliegenden Dissertation ist deswegen die Entwicklung einer Methode zur Dokumentation, Analyse und Gestaltung der Merkmalentstehung im Materialfluss sowie der damit verbundenen Prozess- und Betriebsmitteltoleranzen. Das Zielbild für den Einsatz einer modularisierten Merkmalentstehungs- und -wechselwirkungsanalyse (MEWA) in der Montage sieht skizzenhaft wie folgt aus: - Aufstellung und Dokumentation der Merkmalentstehungsbäume (MEB) welche grundsätzliche Merkmalszusammenhänge und die Materialflüsse beschreiben. - Statistische Analyse der MEB: Hypothesentests und Regressionsanalysen. - Kausale Analyse der MEB: Analyse der MEB, der Materialflüsse und der statistischen Ergebnisse durch die AnwenderInnen. - MEB und Materialflüsse gestalten: Bereinigung des Materialflusses, Austausch der Module oder Reduzierung der Module im MEB.Solving different tolerance problems is often a huge challenge for achieving functional and economic products and processes. Tolerance management meets those challenges and deals with variation impact and tolerance allocation. Products, processes and production equipment have to be planned and implemented in a robust way to limit the occurrence as well as the impact of variation. However, existing tolerance management methods encounter their limits, particularly regarding the handling of characteristic formation in different material flows in the assembly, e.g. in two different assembly lines. Therefore, the aim of the research is the development of a method for the documentation, analysis and design of characteristic formation in the material flow as well as the linked process and production equipment tolerances. The vision for the application of the modularized “characteristic formation and interaction analysis CFIA” in the assembly is as follows: - Deployment and documentation of the characteristic formation trees (CFT) which describe basic characteristic relationships and material flows. - Statistical analysis of the CFT: hypothesis tests and regression analyses. - Causal analysis of the CFT: analysis of the CFT, material flows and statistical results by users. - Design of the CFT and the material flow: revision of the material flow, ex-change of modules, or reduction of modules