Hard nuts to crack when it comes to machine tool safety
Standards on the safety of machine tools are currently being revised by the VDW (German Machine Tool Builder Association). The VDW’s working group for “Safety engineering in metal-cutting machining” is especially tasked with the Type C Product Safety Standards coming first in terms of importance, e.g. ISO 16089 for grinding machines, ISO 16090 for milling machines and ISO 23125 for lathes. They all refer to the Type-B Standard ISO 13849-1, in which what are called safety functions are given probability-referenced ratings as models for control chains.
This theoretical approach intermeshes with operationally validated practice already established in the field. Despite a demonstrably high level of safety in German machine tools, however, further clarification is still needed, since the importance of safety functions is not yet perceived from a harmonised viewpoint in the above-mentioned standards, because there are technology-specific differences in interpretation. The recently expanded company participation in the VDW’s working group has increased the need for clarification still further, since besides metal-cutting processes, presses and lasering machines were also included last year. The latter have no normative stipulations at all for safety functions.
Insurers take a stance on operating modes
Another controversial issue is a machine’s “operating modes”, e.g. when the machining process has to be set up and meticulously observed in operation. Trouble-shooting and maintenance can be particularly problematic in this context, if safety features are deac-tivated for the purpose: in the case of the “Golden Tongue” (as a manipulatively feigned signal erroneously communicating that “Guard doors are closed and locked”), the acci-dent risk, according to surveys conducted by the DGUV (German Statutory Accident Insurance Agency) is approximately 10 to 20 times higher than in undisturbed production operations. Now, in January 2017, following nationwide consultation, the DGUV an-nounced a position paper that so far is manifestly aimed only at machinery manufactur-ers. It is entitled: “Instructions for manufacturers on risk assessment of machines and machinery systems with reference to the aspect of measures to counteract manipulation of safety features.”
Because the manipulation of safety features, however, is closely connected with opera-tional framework conditions, involvement of the VDW is essential, so that the DGUV’s paper takes a holistic approach. The intention is to present a harmonised standard on the VDW’s “Safety Day” at the EMO Hannover on 19 September 2017.