Mathias Knollmann

• The aim of PPC is to ensure the achievement of the logistic targets while maintaining productivity and quality targets. If order due dates are missed, a common intuitive reaction of production planners is to adjust planned lead times. How often and to what extent updates are reasonable has previously been unclear because, while trying to improve the logistic target achievement, planned lead time adjustments may actually cause an opposite effect, which is known as the Lead Time Syndrome of Manufacturing Control (LTS). Although the LTS was described as early as 1977, the cause-and-effect relationships in the LTS still have not been sufficiently investigated. Thus, this thesis has the overall target of investigating the influence of the LTS of manufacturing control on logistic target achievement by firstly validating the LTS line of argumentation by Mather & Plossl (1977) and secondly developing a roadmap to mitigate the LTS in practice. For the validation initially a mathematical model of LTS interactions by means of the Funnel Model and statistics is presented, which also enables determining the main triggers of the LTS. The insights are then validated and extended in a control theoretic model of the LTS and transferred into strategies to avoid or dampen the LTS. Finally, the derived propositions are evaluated and confirmed in a case study of a job-oriented manufacturing process. To develop a roadmap in the second step, the questions of when, how often, and on which value should planned lead times be adjusted are addressed. The results are finally transferred into a methodology to avoid the LTS in practice. In summary, this thesis validates the LTS line of argumentation and shows the relevance of the problem in today’s manufacturing systems. The roadmap finally transfers the results from theory into practice to support planners in the process of decision-making and prevent accidentally wrong adjustments that might lead to a decrease in performance.