Dressing technology enables completely new possibilities in grinding with metal bonded CBN and diamond wheels. Article by Fritz Studer AG.
Alfred Mair, Head of Grinding Technology at Fischer AG, faces a challenge. The company, a manufacturer of high-precision spindles, has reached its limits in the grinding of exotic materials such as titanium and hard-to-machine hard materials under the increasing quality demands from the customers. That, plus their need to increase productivity, can’t be solved by conventional grinding machines.
Then came Fritz Studer AG’s S41 CNC universal cylindrical grinding machine. Specifically designed for large workpieces, it has a length between centres of 1000/1600 mm and a centre height of 225/275 mm. It processes workpieces with high precision up to a maximum weight of 250 kg, just as effectively as small and medium-sized workpieces. But the key for Fischer is the fully integrated WireDress dressing system.
“We had high hopes that we could use metal-bonded grinding wheels for a measurable and reproducible highest quality, have a higher productivity, more universal machining options as well as reduced tool costs,” Mair explains his expectations.
STUDER configured the S41 with WireDress based on additional requirements from Fischer. Thus, the machine received a special high-speed external grinding motor spindle, an innovative proprietary product of Fischer, in which the axial growth is particularly small.
In addition, the spindle is tapered at the rear end, avoiding possible collision situations. This is a specific benefit for face/shoulder grinding with the spindle at an angle. The S41 is supplemented with a fully automatic workpiece magazine and handling system, which ensures fully automatic series production of the high-quality precision components in a stand-alone operation.
“I am blown away,” says Mair. “Three to five times faster than with conventional technology, with absolute reproducibility, ground in a tolerance range of less than 1μm! I have never seen anything like that! I am extremely impressed.”
The Secret Behind
But how does this dressing technology work? Michael Klotz, project manager for development at Studer, explains, “It is a well-known fact that metal-bonded grinding wheels are much more durable and dimensionally stable when machining difficult-to-machine materials and ultimately enable higher productivity. The problem with this is that metal bonds can only be dressed to a very limited extent using conventional methods in the grinding machine. In addition to this, there is a high dressing tool wear associated with a low cutting ability. This is neither an operator-friendly, nor a high quality and process consistent dressing method.”
Any grinding machine with 45,000 operating hours on its log will wear. The question is, will you buy a new one, or refurbish the old one? Find out in this article from STUDER.
LMT Kieninger specialises in highly demanding machining tasks and manufactures special tools for die and mould making. One of its equipment is the Studer S40 Grinding Machine, which has been in use for 14 years now.
“The S40 was the Rolls Royce of grinding machines. But the machine still wears over time and after intensive use,” admits Heiko Braun, Group Manager of Cylindrical/Surface Grinding and Assembly at LMT Kieninger.
It was clear to LMT Kieninger that they should send the cylindrical grinding machine to the STUDER factory in Switzerland for an overhaul. STUDER provided them with a loan machine for around three months and took care of everything from—from collection through to customs formalities.
“We were very satisfied with the loan machine. Apart from a few little things, we were able to continue grinding as usual,” sums up Braun.
What’s special about machine overhauls at STUDER is that it is the only company to refurbish the machines’ guideways to the original specifications. After the assemblies have been reinstalled, the machine geometry is equivalent to that of a new machine.
“This point in particular really convinced us. We notice the difference. Since the overhaul, we have been grinding with the precision of a new machine. I can only recommend a machine overhaul. Everything went without a hitch, the investment has paid off and a 1,600 mm machine is worth its weight in gold for us,” says Braun.
Rebuild—New from Old
A rebuild, or a machine overhaul, makes sense—and not just economically. The operator gets his familiar machine back and continues where he stopped before the overhaul. The difference is that his old machine is like new.
In STUDER‘s factory, specialists disassemble the machine into all its individual parts. The guideways are completely refurbished, the assemblies overhauled, the wear parts in the electric cabinet replaced, and the hydraulic and lubricating system as well as all valves replaced. If old spare parts can no longer be obtained, STUDER provides an alternative solution. The casing and components are sand-blasted and then given a fresh coat of paint.
After assembly, the geometry is like that of a new machine. Commissioning is carried out by STUDER Customer Care, including a functional and geometry inspection, which are all CE-compliant.
“Over 20 people work on machine overhauls at STUDER. This shows the value of rebuild and retrofit at the company. The customers are always enthusiastic about the transformation and are delighted to put an as-new machine into operation at an excellent price-performance ratio,” says Marcos Cotarelo, Divisional Head and Customer Care Consultant at STUDER.
Expanding the Component Range
If the customer wishes to expand his component range at the same time as the overhaul, he can do it with a retrofit. During the machine overhaul, the machine can be modified or retrofitted to the customer’s requirements. This opens up new production possibilities on the same machine. Ingold Tools AG has taken advantage of this STUDER service.
Ingold Tools has been producing high-precision and complex parts for spindle, compressor, hydraulic, and general machine manufacturing since 1946. Its machinery include a variety of CNC and conventional machines, including robotics and automation solutions for turning, milling/drilling, honing, lapping, barrel finishing, sand-blasting, laser marking, as well as surface and cylindrical grinding.
The cylindrical grinding shop already has several conventional and CNC STUDER machines. A further machine is currently being overhauled in the STUDER production halls—an 18-year old S21 with two external spindles and continuous fine adjustment of the turret wheelhead (B-axis fine), which the two managing directors Christoph Jenzer and Edgar Stich recently took on as a second-hand machine.
The S21 will not only be updated in line with the latest developments, but will also be retrofitted to suit the needs of Ingold Tools. In particular, the cylindrical grinding machine will have an additional internal grinding spindle for internal cylindrical grinding and the relevant fixture for swiveling the tailstock into the park position. The S21 will also have a new spindle cooling system with its own circuit, as well as a hydraulically swiveling dressing unit. For all grinding machines to have the same mounting, the universal tool headstock will also be upgraded from MK4 to MK5.
“This deal is perfect for us. Thanks to the retrofit, we get the second-hand machine with 50 percent new hardware,” says Jenzer.
The S21 is the second factory-rebuilt STUDER machine at Ingold Tools. In 2016, the company took on a second-hand S31 machine, which STUDER overhauled.
“We grind to a bearing tolerance and diameter of 1 mm. STUDER guarantees this accuracy after the overhaul. Either way, an overhauled STUDER will run just as long as a new machine,” says Stich.
Jenzer and Stich see a further advantage of the machine overhaul in the operation—their employees don’t need to get used to a new machine with a new control system.
Ingold Tools has relied on STUDER since its establishment. The first external cylindrical grinding machine was a Type 01 from 1955. This was still in use when Jenzer joined the company 13 years ago.
“We like working with STUDER. The service personnel are quick to respond, and our customer care consultant supports us wherever he can. It’s not without reason that we have so many STUDER machines,” he says.
A new machine? Jenzer and Stich both agree that they wouldn’t rule it out, as a new machine always offers advantages that an old one doesn’t have, such as faster travel in all axes, simpler set-up of the machine, and easy programming with less technical knowledge. But the employees are looking forward to the overhauled S21, which will soon be on its way to Inkwil in Bern.
Increasing global demand for Arrow Precision’s crankshafts recently prompted a search for a premium quality, highly-productive grinding machine that had the capabilities to grind crankshaft main bearing journals and pins to the company’s challenging dimensional and surface finish standards. Here’s what drove the company to select Studer.
StuderWIN software helps the operator achieve complex grinding tasks.
Established in 1974 by David Arnold, and currently under the direction of David’s son Ian, Arrow Precision continues to abide by the founder’s guiding principles of quality, innovation and service. The Hinckley, Leicestershire-based business’ highly skilled workforce have access to a wide range of premium quality machine tools enabling the company’s high-quality connecting rods and crankshafts to deliver ultimate levels of performance.
Having gained a global reputation for the components it produces, Arrow Precision now supplies three main automotive sectors. The company manufactures OE connecting rods and crankshafts for use in performance production road cars for prestigious customers throughout the world. In addition, a custom service is provided offering unique forgings, custom designs and the one-off manufacture of complete sets of rods for classic and vintage cars. Last but not least, the motorsport industry’s insistence on dealing with vendors with high-levels of technical expertise, flexible manufacturing process, and fast delivery times, means that Arrow Precision is now a major supplier to this most challenging of automotive sectors.
Increasing global demand for Arrow Precision’s crankshafts recently prompted a search for a premium quality, highly-productive grinding machine that had the capabilities to grind crankshaft main bearing journals and pins to the company’s challenging dimensional and surface finish standards. Having assessed several machines from leading manufacturers against a demanding list of criteria, a practical demonstration of a Studer S41 CNC universal grinding machine convinced Arnold that the advanced Studer offering was the ideal answer to the company’s requirements.
With distances between centres of 1,000/1,600 mm, centre heights of 225mm/275mm and the capability of machining workpieces with a maximum weight of 250kg, the Studer S41 CNC universal cylindrical grinding machine was designed to accommodate medium to large workpieces. While majority of daily grinding tasks can be efficiently performed on the machine, the S41 can also be configured for single-purpose use.
Studer’s S41 boasts a wide range of advanced technical features, such as the StuderGuide guideway system, high-precision axis drives with linear motors, and extremely fast direct drive of the B-axis, ensuring great flexibility, high precision and short auxiliary times. Given the diverse nature of the S41’s users, potential customers are able to choose from a large number of wheelhead variants. With up to four grinding wheels, the S41 fulfils virtually every requirement for complete machining.
The S41 is based on a robust Granitan S103 mineral casting machine bed. Developed and produced in the company’s own plant using the most modern industrial techniques, The advantageous material structure, has proven its value over many years. The excellent dampening characteristics of the S41’s machine base ensure outstanding surface quality of all ground workpieces. The use of Granitan S103 extends the service life of the grinding wheels, leading to reduced downtimes. In addition, temporary temperature fluctuations are compensated by the favourable thermal behaviour of this remarkable material.
The Studer S41’s versatile universal workhead enables both live spindle grinding and grinding between centres. The machine can also be fitted with a specially designed chuck workhead for chuck applications. The workhead is mounted on low-maintenance roller-bearings that have an excellent roundness accuracy of below 0.0004mm (optional, 0.0002mm). Fine adjustment allows for cylindricity corrections in the 1µm range during live spindle operations. As with the machine’s tailstock, its workhead is also equipped with an air cushion lift-off to simplify movement during setup and resetting.
The machine’s direct-drive workhead is primarily used for live spindle grinding of heavy workpieces and for high-precision C-axis applications. When form grinding, the range of parts is expanded by the design configuration of the S41’s direct drive. This design also allows the installation of a high-precision measuring system directly on the spindle.
To an ever-increasing extent, the claim of ‘complete machining’ includes the ability to efficiently perform accurate form and thread grinding operations. These processes are made possible by the position of the S41’s speed-controlled C-axis. The standard C-axis with measuring system on the drive motor is suitable for thread grinding. A direct measuring system is mounted on the workhead spindle (C-axis) to ensure the highest form accuracy. Acceleration and grinding forces are absorbed without difficulty through the high dynamic rigidity of the axis drives.
The machine’s generously dimensioned tailstock barrel, designed for the deployment of Morse 4 taper centres, glides in the tailstock housing. Its centre pressure can be adjusted with the delicate precision required for grinding high-precision workpieces. If required, the tailstock can be equipped with a hydraulically actuated barrel retraction for workpiece changeover. Fine adjustment enables cylindricity corrections in the range below 1 µm when grinding between centres. An air cushion lift-off facilitates simple movement during setup and resetting. A cooling lubricant is passed through the tailstock and totally covers the barrel and diamond holder, to guarantee optimum thermal stability.
Arrow’s S41 is equipped with an Arobotech automatic 3-Point Steady Rest.
The recently installed S41 is now fully operational on two-shifts and delivering on all of the claims made by Studer. Also, in some areas the machine is exceeding Arrow Precision’s expectations. For example, as the flexible machine can perform both external and internal precision grinding tasks, in addition to the external grinding of crankshafts journal and pins, the S41 is used to grind internal features such as flywheel location bores. Crankshaft bores that previously took 30 minutes to grind on a manual machine now take less than three minutes to complete. As well as producing outstanding levels of surface finish on crank journals and pins, the Studer S41 is now achieving sub-micron levels of diameter grinding accuracy.
“As demand for our crankshafts has grown to such an extent that a strain had been placed on our existing grinding resources, we decided to source a new, high-precision CNC universal cylindrical grinding machine,” Arnold explained. “As achieving the specified diameter and surface finish characteristics of crankshaft journals and pins constitutes, the most critical crankshaft machining process, the highest standards of precision grinding is of paramount importance, therefore our new grinding machine needed to be of the highest possible technical standard.”
Since the company manufactures crankshafts in series production and in short runs, in addition to producing runoffs, it re required a machine with great flexibility and quick change over times.
“Furthermore, as we are often tasked with manufacturing crankshafts with really short lead times by our autosport customers, we needed a fast, extremely efficient machine,” said Arnold. “In addition to the S41 proving its outstanding flexibility, speed and technical capabilities, it helped our purchasing decision that we were aware of Studer’s excellent reputation for the quality of the company’s machines and for if its levels of customer service. The assistance provided by Mark Maurice of UK Studer agent Micronz was invaluable in helping us to specify the machine, arranging a demonstration at Studer’s HQ in Switzerland, ensuring a trouble-free installation and organising our operators’ training.
“As our operators received excellent on-machine training, and as Studer’s controls and software is so intuitive, our staff soon mastered the S41. Although, it helps that on the rare occasion that we have a problem, Studer personnel are just a phone-call away and able to provide and instant solution.
“Not only has the exceptional speed and efficiency of our new Studer CNC universal cylindrical grinding machine removed the possibility of production bottlenecks from our grinding department, the extra capacity it has created and the additional capabilities it provides has opened-up addition commercial opportunities for us.
STUDER is awarding the “Fritz Studer Award” for the sixth time. Participation in this competition provides young researchers with a platform for their creative solutions. The goal of the award is to advance and strengthen innovative developments in the machine industry.
For this competition STUDER is looking for work and research results with the following content:
Innovative machine concepts or components for precision machine tools
Alternative materials in machine construction
Simulation models for dynamic and thermal behavior of machine tools
Control and sensor concepts for machine tools
Digital Solutions to support the grinding process
New or advanced manufacturing technologies, especially in precision machining, such as grinding, hard turning etc.
Requirement: Substantiated results and feasibility
The research prize is aimed at graduates from European universities and technical colleges. Anyone who has focused on scientific topics or applied research areas in their student research project, college work or dissertation is invited to participate. The applicant should also be able to produce substantiated results or partial results from their research work. What is crucial for the assessment? Firstly, the feasibility of the findings in the machine industry. Secondly, the approach must be new. Scientific content, form and accuracy of the statements will also be assessed.
A prestigious jury will assess the submitted entries and choose the winner or winners. The jury includes:
Dr.-Ing. Konrad Wegener, Director of the Institute of Machine Tools and Production at ETH Zurich
-Ing. Hans-Werner Hoffmeister, Head of Production Technology Department at the Institute for Machine Tools and Production Technology at TU Braunschweig
-Ing. Frank Fiebelkorn, Head of Research and Technology at Fritz Studer AG.
The winners will receive a reward of CHF 10,000, the Fritz Studer Award and a certificate. The award ceremony will take place in mid-February 2021.
Studer’s S31 grinding machine performs complex and varied grinding tasks precisely and reliably, and can be used to produce small to medium-sized workpieces with a distance between centres of 400, 650, 1,000 and 1,600mm and a centre height of 175mm in individual, small batch and high-volume production. With a high-resolution B-axis of 0.00005 deg, the swivelling wheelhead enables efficient external, internal and surface grinding in a single clamping.
With its machine bed made from solid Granitan S103, the universal cylindrical grinding machine features high dimensional stability due to its favourable thermal behaviour, with the mineral casting equalising short-term variations in temperature. Studer’s S31’s redesigned machine base geometry and innovative base temperature control ensure quick and stable production. The fixing of the dressing device on the double T-slot of the longitudinal slide drastically reduces the complexity of setup and changeover. Further, the S31 features StuderGuide guideways with their damping component in the direction of movement.
Based on the Studer T-slide concept, the S31 has an extended X-axis stroke of 370mm—enabling a large number of wheelhead variants, which can be precisely tailored to customers’ requirements. Its turret wheelhead can be equipped with several grinding wheels, and with the Studer Quick-Set software for grinding wheel alignment, changeover times are reduced by up to 90 percent.
Studer’s S31 enables grinding of different diameters and cones with just one grinding wheel and without time-consuming intermediate dressing—all made possible by the direct drive on the B-axis with a positioning scatter of <1in.
Over 1,500 international visitors—including customers, experts and industry representatives—experienced new metalworking technologies and current trends in the manufacturing industry at the Grinding Symposium 2019, a three-day trade event held by the United Grinding Group in Thun, Switzerland.
Packed with technology presentations and lectures, the Grinding Symposium also featured FutureLAB—which highlighted the future technologies in the metalworking and manufacturing industries.
“Our aim in presenting these future technologies is to create a dialogue with our customers and to discover more about their individual expectations and requirements,” explained Christoph Plüss, chief technology officer at United Grinding Group.
Through the 16 lectures at the symposium, attendees were able to discuss opportunities and challenges in the cooperation of human and machine, the potential of artificial intelligence (AI) and machine learning in the manufacturing industry, and practical production topics.
The 13 technology presentations provided opportunities for attendees to experience the latest machines and solutions—from the Mägerle MFP 30, an innovation in machining aircraft engine blades, to the European premiere of the Studer S31 for machining very long workpieces; and from the extensive services offered by the United Grinding Group’s Customer Care department through to the production of ultra-hard tools using laser on an EWAG LASER LINE ULTRA.
The United Grinding Group is one of the world’s leading manufacturers of precision machines for grinding, eroding, laser cutting, measuring and combination machining. Its corporate brands include Mägerle, Blohm, Jung, Studer, Schaudt, Mikrosa, Walter and EWAG.
The S31 performs complex and varied grinding tasks precisely and reliably. It can be used to produce small to medium-sized workpieces with a distance between centers of 400, 650, 1000 and 1600 mm and a center height of 175 mm in individual, small batch and high-volume production. With a high-resolution B-axis of 0.00005° the swiveling wheelhead enables efficient external, internal and surface grinding in a single clamping.
The foundation of the universal cylindrical grinding machine is the machine bed made from solid Granitan S103. This provides high dimensional stability thanks to its favorable thermal behavior, while the mineral casting largely equalises short-term variations in temperature. STUDER has redesigned the machine base geometry and added an innovative base temperature control. This ensures quick and stable production. The fixing of the dressing device on the double T-slot of the longitudinal slide drastically reduces the complexity of setup and changeover. A further highlight: The S31 features StuderGuide guideways with their damping component in the direction of movement.
Very Wide Range Of Wheelhead Variants
The S31 is based on the STUDER T-slide concept. It now has an extended X-axis stroke of 370 mm. This enables a large number of wheelhead variants, which can be precisely tailored to the customer’s requirements. Customers can choose between the turret wheelhead with continuously variable B-axis or B-axis with 1° Hirth coupling. The turret wheelhead can be equipped with several grinding wheels. Thanks to the software for grinding wheel alignment, STUDER Quick-Set, changeover times are reduced by up to 90 percent. The new S31 enables grinding of different diameters and cones with just one grinding wheel and without time-consuming intermediate dressing. This is made possible by the direct drive on the B-axis with a positioning scatter of <1“.
StuderWIN enables reliable programming and efficient operation. StuderTechnology also automatically calculates the optimal grinding parameters in a matter of seconds, based on just a little information. This means good quality and a stable process at the first attempt. The optional integrated modules such as StuderForm, StuderThread or StuderContourBasic, extend the functionality of the machine.
The S31 is equipped with a Fanuc 0i-TF and is optionally available with the Fanuc 31i-B for High Speed Machining (HSM). The PCU manual control unit enables setup of the machine close to the grinding process. Non-productive times can be reduced to a minimum with the electronic contact detection function. In addition, the standardised loader interface enables automation of the S31.
Studer launched the favorit, a CNC universal cylindrical grinding machine with a 1,600 mm centre distance for long workpieces, and the capacity for single part and series production fitted with automation. Visible grinding process is possible with full enclosure.
It can be adapted to other grinding tasks through measuring control, balancing system, contact detection and longitudinal positioning options. Precision, performance, and safety are ensured with a solid Granitan machine bed.
The wheelhead can be automatically positioned in 3-degree increments, to accommodate a belt-driven, external or internal grinding spindle.
Practice-oriented grinding software with “pictogramming” enables less experienced users to programme grinding and dressing cycles efficiently. An optional StuderGrind software also enables programming of special applications—like grinding wheel profiling, for complex workpiece shapes.
Studer has developed the S131 and S151 grinding machines, following the success they had with the S141. The S131 is smaller than the S141—with a swing diameter over the table of Ø250 mm and a maximum grinding length of 175 mm for internal and 125 mm for external grinding. It is available for workpieces with a maximum length of 300 mm.
The S151 is larger than the S141—it has a swing diameter over the table of Ø550 mm and a maximum grinding length of 400 mm for internal and 150 mm for external grinding. It is available for workpieces with a maximum length of 700 mm.