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.

[Interview]
Interview with Peter Steger, Grob-Werke GmbH & Co. KG, Mindelheim, Germany

In this interview with Peter Steger, a design engineer at the Grob company in Mindelheim and a member of this VDW working group, it clearly emerges how meticulously critical interactions between man and machine have to be tackled in order to master the increased risk involved. In this context, the above-mentioned Type C standards give the design engineers argumentative backing with operating modes defined in general terms (such as “Service Mode”) that are also regularly addressed in the working group itself. In addition, some firms are adopting their own individualised approaches, in order to avoid the universally deplored manipulation with manufacturer-specific operating modes; this means certain maintenance activities at the machine are carried out only by the compa-ny’s own service personnel.

Peter Steger from Grob-Werke GmbH & Co. KG in Mindelheim explains how manufac-turers are supporting users of their machines in their thrust for more occupational safety.

Peter Steger, Grob is acknowledged as a model company when it comes to occu-pational safety: how do you handle this issue internally with your own machine operators?
Peter Steger: For working safely with machine tools, it’s vital that the employees con-cerned are adequately briefed about the dangers involved in working with machine tools and about the protective measures for averting them. Apart from the operator training courses themselves, our operators accordingly receive regular briefings on the subject of health and safety.

Besides general instructions on safety-compliant behaviour, the insights gained from the relevant risk assessment of the workplace involved and the equipment used there are incorporated. In this case, for example, the hazard-related factors when working with machine tools and the protective measures that have to be complied with. The protection concept for our operators is rounded off by additional information on site (such as an operating manual for safety-compliant working with the machine tool.

And what about the instructors for the operators?
Peter Steger: We additionally send our forepersons to external seminars held by the Employers’ Liability Insurance Association, to raise their awareness of their managerial duties and remits – not least in regard to occupational safety. I am delighted to note that above all our new young forepersons are being trained by outside lecturers, and are thus learning even more about the important role played by the duty of care for employees The experience they gain in these outside seminars helps the forepersons, since they can utilise the tips in actual practice to optimum effect.

So it’s also a tip that customers should take on board?
Peter Steger: Definitely. What’s important for our people counts just as much for our customers.

And how does Grob train its customers?
Peter Steger: When we sell extensive production lines, we offer our customers training courses specifically tailored to the requirements of the customer concerned. For multi-purpose machines, we have a range of complementary training modules: these include for example, process-compliant programming, helical interpolation and geometrical calibration. We also, of course, always talk about how to handle the machines safely, and provide examples from actual practice.

Could you cite a typical example for us?
Peter Steger: When our customers are already working with one of our machining cen-tres, we show them ways and options for increasing their productivity. Thanks to our training courses, they become even more familiarised with our machines, and learn how to operate them safely. New customers, too, benefit from our training courses, which contribute towards proactive safety and demonstrate efficient working practices. Various measures are presented for reducing the stress on machines and tools, shortening the make-ready times and ensuring full capacity utilisation at the machine. This in its turn contributes towards upgrading quality levels. Working with machine tools, after all, stands and falls with the quality of the control system.

How can it contribute towards occupational safety?
Peter Steger: As far as I’m concerned, this primarily includes malfunction and error messages on the consoles of the machines’ control systems, which tell the operators the reasons for a machine standstill, for example.

How else do you support users in terms of occupational safety?
Peter Steger: We make sure that no hazards can be created by the machine when separating safety guards are opened, and that it can be operated without manipulating any protective features.

This applies primarily to make-ready mode: what regulations have to be complied with in this situation so typical for production operations?
Peter Steger: The important ones are Operating 2 and 3 as EN 12417, plus in the future MSO 2 and 3 in accordance with FDIS ISO 16090 “Safety of Milling Machines”. MSO stands for “Mode of Safe Operation” and FDIS for “Final Draft International Standard”. In these safe operating modes, the staff can safely operate a machine in very many func-tions even when the door is open, using a portable device. They can try out movements in the machine, for instance, without manipulating the production line in any way.

How do you proceed in your own production operations?
Peter Steger: For our own highly qualified personnel, we have internally defined the “Grob operating mode”, which goes beyond the functions of the normative operating modes MSO 2 and 3 that I’ve already mentioned. These operating modes restrict opera-tions by imposing limits, regarding the speed, for example. For everyday work in test runs, however, these limits are not very helpful. With the “Grob operating mode”, you can overcome these limits without manipulating the machine.

So you’re offering safety without any loss in speed, meaning without any impair-ment of productivity: wouldn’t this function be of interest to customers as well?
Peter Steger: For them, there are already the normative operating modes MSO 2 and 3 that I’ve already mentioned. We do, of course, get asked, of course, to enable the “Grob operating mode” for customers’ maintenance staff as well. But given the ongoing stand-ards situation, this is not permissible without appropriate measures and processes to be put in place by the customer concerned.

What do you think about the use of electronic safety switches of Type 4 as defined in ISO 14119 “Safety of interlocking devices”, which protect the machine against manipulation using radio technology, for example – keyword RFID?
Peter Steger: Without a doubt, there is an interesting new trend towards highly encoded safety switches designed to preclude the possibility of manipulation. This signifies the end of the line for the “Golden Tongue”, a multi-purpose key for manipulating protective features. You see, it enabled staff operators to make the control system erroneously believe that the guard door is closed and locked.

What topics can visitors to the Grob stand at the EMO Hannover 2017 learn more about in terms of occupational safety?
Peter Steger: Visitors to our stand at the EMO Hannover 2017 will learn more about occupational safety, ergonomics and the relevant courses available. Our customer train-ing team will be there on the spot and presenting courses designed to provide our cus-tomers with valuable tips on how to handle our machines.”

hordon kim / hordon@icnweb.co.kr