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Is safe really safe? It’s safe to say: yes!

The VDW’s Technology Conference at the METAV 2014 themed around safety technology for metal-cutting machine tools

Frankfurt am Main, in March 2014. – The safety of technical products is an issue on everyone’s lips. Are residual risks really unavoidable? And what residual risks are in fact still acceptable? Besides the ethical and moral aspects involved, experts are also discussing specific technical questions that have to be answered by engineers. Machine tools, in particular, pose stringent requirements for safety features and reliability. Under the aegis of the METAV 2014, experts will in Düsseldorf on 11 March be reporting on the current status of developments. After all, German machine tools are already very safe, and we want things to stay that way.

“German machine tools rank second to none, and that’s not only in terms of safety”, is how Professor Dominic Deutges of the Lower Rhine University of Applied Science summarises the status quo. “But this was already the case before the EU Machinery Directive and the associated standards were issued.”

Since 1995 at the latest, when this directive was introduced, statutory stipulations for defining the requirements for safety and health protection in Europe have been harmonised. They require that the use of a machine shall not entail any avoidable hazards for the operator. His/her physical safety has to be assured by the product’s design.

“Risk assessment is one of the crucial elements in evaluating conformity when it comes to CE-labelling of machines”, says Thomas Kraus, an expert at the VDMA in Frankfurt am Main. “Technical safety measures that act independently of the machine operator’s behaviour take priority over safety instructions. Current developments favour the use of non-contact safety features instead of separating protective features.”

Minimising residual risks – but how?

Residual risks are unfortunately unavoidable here; the task is to minimise them. The hazard potential of machine tools – rooted in the action of powerful forces when machining large moved masses, or high workpiece weights – has always been reduced by major fit-for-purpose technical efforts. Accident figures have been falling for years – evidence enough that these measures are working. Now, however, this has to be evidenced theoretically as well, with the aid of statistical calculations for the safety-relevant control chains, since this is what ISO 13849-1 demands.

“In order to implement new concepts, since the introduction of ISO 13849-1 the elements of functional safety have played a crucial role. Mechanical functional modules in the safety chain, in particular, constitute a challenge in regard to determining the probability of failure. The incorporation of operational dependability takes on major importance”, is how Kraus explains the conceptual conflict between empirically based design and the mathematical evidence meanwhile required.

Work has long since been ongoing in expert bodies for drawing up specific standards dealing with the safety of individual machine groupings, with VDW companies closely involved. This is necessary in order to meet what are sometimes extremely disparate requirements, e.g. between metal-cutting and forming machines.

“For the machinery manufacturer, the challenge here is to evidence that the safety functions operating in a machine achieve the performance level stipulated in the safety standard concerned.” Ralf Kesselkaul from the Wood and Metal Employers’ Liability Insurance Association in Mainz is familiar with the discussions from long years of experience. “Safety standards are not least a helping hand for design engineers in their practical work. They are intended to assist them in systematically analysing the risks involved, assessing hazards, and eliminating residual risks as far as possible.”

It’s precisely this risk assessment factor, however, that is continually contentious.

“In purely electrical control chains, calculating the performance level is pretty simple, and safety can be affordably increased by means of redundancies”, explains
Heinrich Mödden from the German Machine Tool Builders’ Association (VDW). “But it’s not possible to transfer this approach to the entire machine tool. The clamping of workpieces, for instance, has been validated by extensive field operation, and is very safe, but by reason of theoretical considerations has repeatedly been called into question.
This is why we are examining how the operational dependability of our design principles can be evidenced.”

Special operating modes reduce the incentive for manipulation

Professor Deutges from the machine tool manufacturer A. Monforts Werkzeugmaschinen GmbH in Mönchengladbach, Germany, was determined to evidence the operational dependability, and so he examined the design options available for upgrading the control chains for tool clamping in terms of functional safety. This the options for upgrading dependability are also illuminated against the background of realistic special operating modes, which are currently being discussed in all the VDW’s bodies. The aim here is to counter the increased risk presented when guard doors are opened by ensuring higher reliability levels for the control systems involved. Because special operating modes necessitate additional engineering, particularly for the control equipment involved, they cannot be achieved without investing in safety technology. With reference to existing stipulations in the ISO 23125 standard, a cost/benefit analysis should also be drawn up for upgrade measures. To quote Professor Deutges: “As you will know, the manipulation report of the IFA Institute for Occupational Safety back then discovered that machines are being manipulated or bypassed because the operators cannot execute certain interventions required by the production technology involved. Special operating modes can help to reduce the incentive for manipulation. Monforts currently offers its customers this option together with an expertise drawn up by the Employers’ Liability Insurance Associations.”

At the VDW’s Technology Conference under the aegis of the METAV 2014 in Düsseldorf, Deutges will be presenting this and other approaches, some of them relatively new. The event is designed to intensify the exchange of news and views between the relevant experts on the development and utilisation of modern-day machine tools, since many machinery manufacturers are currently still working on their own individual solutions. “So it would be a sensible goal”, says Deutges, “to already anchor empirically validated approaches in the C-standards, in order to simplify the procedures involved.”

At Siemens, Patrick Gehlen’s remit is to calculate safety functions and operational dependability. “Safe control chains are the result of reliable products and long years of experience in field operation. The feedback from our customers enables us to continually design-enhance our own products. It’s always interesting to see what solutions customers come up with in order to solve their own very specific problems.”

For calculating the performance level, application-referenced reliability ratios for the safety-relevant components are required, and field data or specifications contributed by component and system vendors can be used to provide the evidence needed. “With the introduction of the new Machinery Directive 2006/42/EC and of ISO 13849-1, our customers’ safety-awareness

levels have risen”, explains Thilo Steigerwald from Bosch Rexroth. “Following a few uncertainties when ISO 13849-1 first came out, I now see definite progress. Bosch Rexroth, for example, provides verified and documented MTTFd values for hydraulic components. We have for years now been supporting machinery manufacturers and end-users in bearing their responsibilities for protecting both the machines and the humans who operate them with standard-compliant cost-efficiency. This is accomplished by means of safe products, competent consultancy and communication of the specific knowledge involved.”

International safety standards have long since ceased to be a ubiquitous given

Despite all the progress that German machinery manufacturers, in particular, have achieved in recent years in terms of making their machines safer, a look at the global market provides plenty of food for thought.

To quote Dominic Deutges: “During trips to China and Taiwan, I have visited numerous manufacturers, and noticed a significant, large difference. This starts with safety enclosures that are far too thin and not locked, and continues with the functional safety of the control system. In some cases, the safety functions that are specified in the international standards had manifestly not been understood at all by the designers.”

In the long term, this may signify a competitive disadvantage for German machine tool manufacturers. “It’s in the interest of all European machinery manufacturers that the internationally valid rules involved are actually complied with. And a constant stream of new regulatory initiatives must never be allowed to put the competitiveness of European manufacturers at risk”, is how Alexander Broos from the VDW sums up the essentials of the situation. Moreover, he adds, even the safest of machines probably cannot rule out the possibility of deliberate manipulation.

This means that all manufacturers have to reconcile the disparate imperatives for maximised flexibility, as demanded by the markets in Germany and Europe, high-speed processes, complexity and ultra-simple operator control, all of this in the context of a holistic safety concept that subsumes both the manufacturer’s and the user’s responsibilities. Broos, who as Department Head Research and Technology at the VDW is thoroughly familiar with the latest trends, has mixed feelings about the future:
“Our strength lies in building highly flexible, highly productive machines. It’s been accepted for years that they’re safe. But it’s important that, given the sheer diversity of applications involved, a “one-size-fits-all” approach is avoided. A machine that is accepted as safe in Germany will also remain safe in the rest of the world. Whether this comparatively expensive technology has a market there, though, that’s a different question entirely.”

Responsible for the content of this press release: Verein Deutscher Werkzeugmaschinenfabriken e.V.

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60325 Frankfurt am Main
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+49 69 756081-33
+49 69 756081-11

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