Are grinding machine safety guards overdesigned?
VDW tests the minimum wall thickness of safety guards
Guards on grinding machines are particularly important for ensuring operator safety. Grinding wheels seldom burst, but when they do, there is a great risk of serious injury to the machine operator. Recent studies suggest, however, that the enclosures commonly used in gear grinding machines, for example, could be overdesigned at present. Investigations conducted by the VDW, the German Machine Tool Builders’ Association, and the Institute of Machine Tools and Factory Management (IWF) at TU Berlin reveal that it is possible to use safety guards which are up to 70 percent thinner, depending on the width of the grinding wheel. These findings are now leading to changes in ISO standardisation.
Will overdesigned safety guards soon a thing of the past?
The minimum wall thicknesses for safety guards are specified in ISO Standard 16089 Machine tools – Safety – Stationary grinding machines. There is a directly proportionate link between the requirements concerning primary protective covers for gear grinding machines and those for the full enclosures located further away. The reason for this is that no specific safety precautions were initially specified for the safety guards of gear grinding machines, which do not normally have a primary protective cover. This is because the preceding standard, EN 13218 Safety of machine tools – Stationary grinding machines, did not explicitly include gear grinding machines. However, this proportionate scaling has been repeatedly questioned, for example by the Japanese association JMTBA, because it results in overdesigned polycarbonate safety guards and screens.
Major simplifications are possible
The member companies of VDW Working Group 5, which is responsible for machine tool component safety, therefore concluded that new specification tables were required for the full enclosures of stationary grinding machines. A two-year project was thus launched by the IWF (TU Berlin) in 2012 to develop the necessary test equipment.
“The ensuing burst and impact tests showed that the thickness of the enclosure wall can be reduced by up to 70 percent, depending on the width of the grinding wheel,” explains Simon Thom, group leader for machine tool technology at IWF (TU Berlin). “This is very good news for machine tool manufacturers, who are keen to avoid excess weight in their machines. Reducing the thickness of a sheet steel housing by half a millimetre, for example, will save 4 kg/m2 in weight.” This also yields indirect savings because the motors for opening and closing correspondingly lighter steel gates can be less powerful or are rendered entirely superfluous.
Unity among the partners
It is not only the industrial companies and the scientists who agree that guards are overdesigned in such machines. The DGVU (German Statutory Accident Insurance System) based in St. Augustin and the BGHM trade association in Hanover also carried out similar tests on a burst test stand, with comparable results. The burst tests were conducted over eight years. Then, at the end of 2019, the BGHM presented its report covering a total of over 400 burst grinding wheels and more than 800 usable impact events. Based on this, a safe design convention stipulating 3 mm for sheet steel with different grinding wheel widths was drawn up in conjunction with the VDW.
The consolidation of the results in Germany was motivated not least by comparable studies abroad. The Japanese JMTBA association carried out tests which found that some of the previous standard specifications set out in ISO 16089 could be reduced by up to 30 percent.
Finally, in January 2020, a standardisation meeting was held in Tokyo, where the Japanese and German findings were compared. The experts agreed that the Japanese results for adapting the specification tables for the primary protective cover, and the German results for the design of the full enclosure should be incorporated into the ISO standard. A consolidated working paper will soon be prepared by the ISO Secretariat at DIN in Berlin and submitted to the relevant public as a so-called “Committee Draft” for comments. This is scheduled for completion by October 2020.
Further investigations ongoing
Nevertheless, the existing results of the study on full enclosures in Project 20438 “Safely dimensioned machine enclosures” of the IGF (Industrielle Gemein-schaftsforschung) are being corroborated empirically and theoretically.
“We’re also using simulations to highlight the worst case scenario. As our burst tests have shown, this occurs when the outer edge of the fragment hits the guard. We can reproduce this type of impact in models with different materials, grinding wheel widths and safety guard thicknesses. In this way we have succeeded in simplifying the extremely complex burst tests,” reports Simon Thom. “Our plan for this year is to propose even simpler dimensioning procedures.” The reduced minimum wall thicknesses which are now to be specified in the ISO standard could therefore be made even thinner on the basis of the further test results.
Peitzmeier reaps the benefit of innovation
When Ulrich Peitzmeier sowed the seeds of his start-up business five years ago, he had little expectation of such a quick harvest from the risk and hard work that he put into the project. Peitzmeier Maschinenbau GmbH produces long-belt grinding machines for use in surface processing of stainless steel, steel and aluminium components across a wide range of industry sectors. In the UK, these machines are represented by deburring and surface finishing expert Ellesco.
“When I started the business it was just me. I was fortunate to have a 50m2 garage that I used as an assembly area for the initial machines. That lasted for two years before I had to upscale for the first time in 2017. A further move saw floorspace increase to 300m2, but our plan is to double this in 2020 to be better able to manage the influx of orders that saw us working to full capacity in 2019,” says Ulrich Peitzmeier. Employee numbers have also grown, with Ulrich now working alongside six colleagues who between them generated 1.4 million Euro of turnover in 2019, a figure that will grow considerably this year.
For such a young business, export sales are a major element in its success, with almost 70 percent of its sales coming from markets outside of Germany, with the UK, Netherlands, Poland, Russia, Qatar, India and China all presenting good market growth for the business. This growth is due in part to Ulrich Peitzmeier’s previous experience in machine tool sales, but also down to the traditional methods still employed by many for surface and edge preparation.
“We find that between 80 to 90 percent of the people we speak to still remove edges when processing metal with an angle grinder by hand,” he says. “This opens up so many opportunities to highlight the benefits of our machines and their automation of the grinding and deburring process, eliminating time from the operation and also reducing risk to operators.”
Deburring and polishing by hand is tiring work and brings with it its own health and safety issues. The result is that very few people want to do it, so automation had to be the way forward. By removing the bulk of human intervention in the process quality and consistency is also improved dramatically. This will increase further as more robotic systems become available, which is part of the Peitzmeier strategy. “In the world of high-quality consumer items, stainless steel cooker hoods for example, manufacturers attach great importance to this high level of consistency. We are seeing similar moves in the automotive sector also,” says Ulrich Peitzmeier. “This is something that gives us great optimism for the future and will allow us to maintain a full order book.”
One of the key advantages of Peitzmeier is its agility and ability to tailor machines to suit a customer’s specific needs. The design of the Peitzmeier Omni-Grind machines is modular, a system that was developed from day one of the company’s existence.
“Modularity is our unique selling point,” says Ulrich Peitzmeier. “Because we had the advantage of starting with a blank piece of paper, from the beginning we opted for the modular system. Many of our competitors, on the other hand, had a history of manufacturing machines for the woodworking industry and simply adapted their systems to the metalworking sector, creating compromises. Confirmation that our approach was correct came at the 2016 EuroBLECH trade fair, where the design was awarded an innovation prize.
For such a relatively small company, Peitzmeier provides a full service to customers from development and design, through to production and after-sales service. It keeps tight control on its supply base, with most components locally sourced. For example, the control system is manufactured in Verl, Peitzmeier’s hometown, while spindle drives come from Bielefeld, and the motors from Lippischen, both less than an hour’s drive away.
Focusing on quality rather than volume, Peitzmeier has just three machines in its portfolio, all of which can be adapted to suit. These are the Omni-Grind Twin, the Omni-Grind Portal and the Omni-Grind Dura, covering small to midsize, large and heavy parts and large heavy metal plate respectively. Each machine can be equipped with individual modules to match individual applications. Automation can also be tailored to suit a customer’s requirements, with programmable five-face grinding possible. The rigid machine construction makes it possible to process parts measuring from 2 m to 12 m in width, depending on machine type.
Where craftsmanship and high-tech go hand in hand
For over a century, Okuma, represented in the United Kingdom by NCMT, has been developing grinding machines for the highest quality demands. Though a lot has changed since the beginning, some aspects remain the same. Okuma CNC grinders still achieve their high precision, productivity and longevity due to a symbiosis of craftsmanship and state-of-the-art technologies.
Okuma is the only single-source CNC provider in the industry to develop and produce all hardware components, the controls and the software for the machine tools in-house. The development and production from one single source leads to a perfect combination of hardware, software and electronics. Due to their outstanding precision and high productivity, the grinding machines can be found in several industries. They are used for a wide range of materials including soft, high-strength and temperature-resistant materials as well as sintered alloys, Inconel or chrome-plated workpieces.
Craftsmanship for highest quality
In addition to the modern technologies that Okuma is constantly developing and optimising, the machine tool manufacturer also relies on skilled craftsmanship that has become rare. In the CNC grinders, for example, hand-scraped sliding surfaces are used on the guideways and mounted components. The manufacturing process of hand scraping is very time-consuming and requires a high degree of skill and experience. Nevertheless, it is worth not neglecting this demanding manufacturing method, as the resulting sliding surfaces have a degree of durability, precision and quality that could not be achieved with other methods. With the exceptionally long service life and availability of the machines, Okuma ensures that the total cost of ownership (TCO) remains as low as possible.
In-house developed control facilitates operations
All Okuma CNC grinders are equipped with the in-house control OSP-P300GA, which was developed specifically for grinding applications. The control has an intuitive user interface, and very little user input is required. In addition, the control is easy to customise and can be modified and individualised with apps allowing for ergonomic and productive workflows. An example for this is an app for determining the optimal dressing parameters, which can be used to perform dressing simply, quickly and with highest precision.
All-in-one processing from a single source
In addition to stand-alone standard machines, Okuma offers complex production cells. This not only means an automation of the grinding processes. Rather, it covers the entire machining of a workpiece including turning and milling operations on Okuma machines. Users benefit from the consistently high manufacturing quality of Okuma solutions and only need to be familiar with one type of control. As a result, the Okuma solutions can be used for a wide range of applications, and only one operator is needed to control and monitor the entire manufacturing cell. Especially in times of a shortage of skilled workers, this proves to be a considerable advantage.
Okuma Europe GmbH is the Germany-based sales and service affiliate of Okuma Corporation, a world leader in CNC machine tools, founded in 1898 in Nagoya, Japan. The company is the industry’s only single-source provider, with the CNC machine, drive, motors, encoders, spindle and CNC control all manufactured by Okuma. Okuma’s innovative and reliable technology, paired with comprehensive, localised service protection, allows users to run continuously with confidence, maximising profitability. Along with its industry-leading distribution network, Okuma facilitates quality, productivity and efficiency, empowering the customer and enabling competitive advantage in today’s demanding manufacturing environment. For more information, contact:
High calibre, high precision
Jones & Shipman Hardinge to handle Super Precision sales and support in UK & Ireland
Sales and technical support for the acclaimed Hardinge Super Precision (SP) range of turning and turn/grinding machines are now being handled in the UK and Ireland by Jones & Shipman Hardinge.
Based at its UK headquarters at Clifton Dunsmore near Rugby, Jones & Shipman Hardinge represents the interests of sister companies in the Hardinge group, i.e. Kellenberger, Hauser, Voumard, Tschudin and Usach, and now the SP products which were previously sold and supported from Germany. The company also represents the interests of Okamoto grinding solutions in the UK.
As Jones & Shipman Hardinge UK managing director Mike Duignan explains, while filling a niche roll, SP machines are widely recognised as production machines of the highest calibre:
“Machines in the SP and SP Quest range can offer combined turning and grinding systems specifically designed to optimise the high precision machining of complex parts. As well as their turning capability, the machines can be equipped with grinding spindles, giving them the capability of maintaining a continuous machining accuracy of 3 microns over extended periods of operation”, he explains.
Super Precision machines offer a very compact footprint and, with turnkey packages or optional automation, can operate as a stand-alone single machine or within a multi-cell environment.
“These machines are a perfect complement to our well-established capability across the spectrum of grinding,” adds Mike Duignan. “They allow us to offer an optimal solution for customers’ high precision, complex parts production, be it grinding, super precision hard turning or a combination of both.”
Hardinge, Inc. is the trusted global provider of high precision, computer-controlled machine tool solutions for critical, hard-to-machine metal parts and advanced workholding accessories. With over 125 years of experience, Hardinge offers the largest variety of metal-cutting turning machines, grinding machines, machining centres, collets, chucks, index fixtures, repair parts, standard and specialty workholding devices, and other machine tool accessories. Hardinge’s solutions can be found in a broad base of industries including aerospace, agricultural, automotive, construction, consumer products, defence, energy, medical, technology, and transportation. Headquartered in Berwyn, PA, the company designs, manufactures, and distributes machine tools in over 65 countries across North America, Europe, and Asia.
For UK enquiries, contact: