To improve cycle time planning in the automotive Body-In-White manufacturing, a better understanding of the adaptive controller's decision as well as the causes for a prolongation of resistance spot welding times is necessary. Thus, we propose an analysis using Random Forest to create a design recovery to increase the understanding of proprietary systems. The analysis suggests that a first decision for a prolongation happens during the transition of phase III to phase IV of the welding process. The first prolongation results in a moderate prolongation and a first mode, besides the reference time, in the distribution of welding times. This is consistent with the frequently proposed controllers in the literature. In later stages of the welding process, a second prolongation decision is sometimes made. If this second decision window is present at welding spots, the distribution of welding times often yields a second mode of highly prolonged times. Furthermore, the analysis suggests that the decision is based on the raw resistance curve values and not a first or second derivative of the curve. Future work is necessary to add further domain-knowledge to the analysis and construct useful decision functions based on the observed resistance curves.

Although anomaly detection is an important task in engineering, in the practical application it is often unclear what an anomaly is and how it affects the planning and oper-ation of complex manufacturing systems. The authors propose a definition of “scientific” anomalies by an approach based on philosophy of science. The idea is to separate measurement noise and prediction errors. Based on this definition, a framework is established and applied to dynamical systems, resulting in two distinct deviation terms separating “scientific” anomalies from measurement noise. These distinct deviation terms can be used in future research to set up a metric and evaluation of the prediction model quality. The framework is demonstrated through an example by conducting an analysis to describe anomalous behavior of cold welding in holding pins.