Monday, November 30, 2009

Intelligent GMN UHS Spindles from Jena Tec UK

In addition to our own manufactured range of high quality B&T customised spindles for milling, turning, boring and grinding, Jena Tec represents a high quality German brand GMN Nuernberg in the UK market for high speed and high frequency machining spindles.

In this issue, we've provided some detail information about GMN's capability in ultra high speed grinding spindles. Conventionally supplied by air bearng spindles which have some limitations and disadvantages in terms of cost and running efficiency, GMN's UHS series provides a robust oil lubricated grinding spindle for exceptionally high speeds up to 250,000RPM coupled with an exacting stability and geometric tolerance. A minimised oil/air dosing system means just the right amount of lubrication gets to the spindle and reduces maintenance and running costs throughout the life of the spindle.

Jena Tec's automation division can offer the UHS series from GMN including integration or retrofit to existing machines. If you would like to discuss how we can offer you the advantage of higher speed and better process performance from your grinding machine, then give our UK office a call on +44 (0)1623 726010 or by email to

Intelligent Spindles from GMN**

Processing small internal diameters with optimum cutting speeds requires high rotational speeds. New GMN spindle ball bearings with very high speed characteristics permit 250,000 revolutions per minute, for instance, with comparatively high spindle rigidity and load capacity. Optimized lubrication of high speed spindles offers great potential for increasing performance. Furthermore on-demand minimal lubrication lowers oil consumption and increases service life. In future integrated data loggers will monitor the condition of the spindle, store the operating parameters and guarantee high availability. GMN has a long track record of supplying a wide range of high frequency spindles of up to 180,000 rpm. However, around two-thirds of the spindles supplied for internal grinding operate with maximum speeds in the 30,000 to 90,000 RPM range.

250,000 RPM for small bores
To operate efficiently, a machine tool spindle must have the appropriate load capacity, rigidity and dynamic run out. In order to guarantee these characterisitcs even for extremely high speeds, the GMN development department was faced extraordinary challenges. Breaking points are reached due to the high centrifugal forces, a compact design has to ensure subcritical operation with sufficient distance to the first critical speed, high precision hybrid ceramic bearings have to be designed specifically for the demands of high speed spindles. These challenges were met wth the the help of current advances in motor technology and the use of further developed GMN spindle ball bearings. It is now possible to efficiently grind small internal geometries with up to 250,000RPM. The GMN grinding spindles used for this purpose have a comparatively large and rigid mounting and a powerful sychronous motor. Consequently, they are not only suitable for special applications at maximum speeds but can also be used flexibly and efficiently in a relatively large rotational speed range.

Integrated lubrication module
These days, ball bearings with permanent grease lubrication or oil/air lubrication are predominantly used in machine tool spindles. Yet both methods have their disadvantages which can be overcome by an innovative micro-dosing system combined with appropriate lubrication strategies. Compared with today's oil/air lubrication method, a significant reduction of the lubricant quantity necessary can be achieved and the systematic performance limits of grease lubrication. I.E. Limited usable life of grease at high temperatures and speed, are to be exceeded. Minimizing lubricant quantities makes ecological and economic sense. It facilitates the inegration of an oil reservoir in to the spindles and ideally requires no more external components. The problems associated with waste oil disposal are also defused. Operating costs of machine tools can exceed acquisition costs several times over if calculated over a normal life cycle. These costs are therefore a decisive factor for many users when making an investment decision. An integrated lubricant cartridge means that high maintenance external components can be dispensed with. The lubricant reservoir only needs to be replaced at relatively long intervals. An almost instant dosage of lubricant ensures that the adjustment of the lubricant quantity matches demand based on the exact measurements of the bearing. This increases reliability and efficiency of the bearing and reduces the quantity of the lubricant needed.

Third generation spindles for machine tools
Spindles are also becoming more and more intelligent. Miniaturised electronics which are integrated in the spindle stores the sensor signals, processes them and reports any exceeding of critical values to the overall machine control system. Important operating data can be accessed during the entire running time of the spindle and can also be analyszed with regard to optimising the process, machine and spindle. In addition, the aim is to go for bearing condition monitoring and consequently early damage detection,based on these intelligent systems is possible. Evaluating temperature sensors, position sensors and vibration sensors will increase precision and productivity of the production process. Additional sensors, on the other hand, harbor the risk of reducing the availability of the spindle system further, therefore, as few additional sensors as possible should be employed and for the time being, a more intelligent analysis of available signals should be aimed for.

** Reproduced from an article by Dr. Bernd Moeller, Head of Engineering Spindle Technology Division at GMN Paul Mueller Industrie GmbH & Co. KG in Nuernberg, Germany.

For service and support on design, selection, repair and replacement of spindles from GMN in the UK from Jena Tec go to or call our UK office on +44 (0)1623 726010