Proceedings of the
35th European Safety and Reliability Conference (ESREL2025) and
the 33rd Society for Risk Analysis Europe Conference (SRA-E 2025)
15 – 19 June 2025, Stavanger, Norway

Derivation of an Updated Aging Curve for Polycarbonate Vision Panels Used as Safeguards in Machine Tools

Eckart Uhlmann1,2, Mitchel Polte1,2, Nils Bergström1,a, Dietmar Auhl3, Justus Schönebeck 3, Magdalena Goslinska3, Oliver Löschke3 and Eduardo Filipetto3

1Institute for Machine Tools and Factory Management IWF, Technische Universität Berlin, Germany.

2Fraunhofer Institute for Production Systems and Design Technology IPK, Berlin, Germany

3Department of Polymer Materials and Technology, Technische Universität Berlin, Germany

ABSTRACT

Safety regulations for machine tools require an adequate protection of operators from potential hazards, such as ejected workpiece or tool fragments. To meet these requirements, machine tool manufacturers implement different safety measures. A key component of these measures are polycarbonate (PC) vision panels, which provide essential protection while allowing the operator to observe the machining process. Newly manufactured PC is characterized by its high ductility allowing it to absorb impacts with substantial kinetic energy from ejected parts in the event of an accident. However, exposure to cooling lubricant (CL)-water mixtures cause the onset of degradation processes, which result in the accelerated aging of the material. The degradation progressively reduces the protective performance of PC vision panels, limiting their long-term effectiveness as a safeguard. This behavior is accounted for in the design of PC vision panels by using an aging curve defined in international standards. Nevertheless, the aging curve has become outdated due to the implementation of the REACH regulation, which has caused a significant change in the composition of CL. This paper proposes a new aging curve for REACH-compliant, mineral oil-based, amine-containing, and boron-free CL. The updated aging curve is derived from accelerated aging experiments conducted under elevated temperatures and CL concentrations. It is demonstrated how the results of accelerated aging procedures can be translated to industrial operating conditions in machine tools. The PC specimens were analyzed by means of Charpy and safeguard impact tests according to ISO 23125. For the first time, the proposed aging curve facilitates the assessment of PC vision panel aging under REACH-compliant CL. Furthermore, the established procedure provides a framework for deriving additional aging curves for other CL formulations.

Keywords: Safety, Machine tools, Polycarbonate, Aging, Cooling lubricants, S-N curve.


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