The Swiss spindle manufacturer Step-Tec AG has been developing and producing motor spindles for mold making, production and aerospace since 1995. These high-output precision spindles have enabled reliable machining in machining centers of leading machine manufacturers around the world for years.

Today Step-Tec AG develops and builds some 70 different types of spindle in diameters ranging from 90 mm to 320 mm, covering a performance range of 1 to 82 kW, that deliver torques of up to 1200 Nm on its most powerful spindle.

In the current difficult market environment, Step-Tec is focusing on the development of new technologies in spindle construction, with the intention of positioning the tool manufacturer perfectly for the long-awaited upturn in the economy.

Step-Tec is presenting several of these new developments and enhancements which are designed to help satisfy the ever-increasing quality demands in parts machining and also take into account the improved efficiency of the requisite machine infrastructure.

OPTICOOL motor spindle

The proven-and-tested oil-lubricated HVC 140 mold making motor spindle serves as a basis for retrofitting the OPTICOOL motor spindle technologically to reflect the state-of-the-art.

On one hand, the cooling system on the whole spindle has been perfected, which means that the naturally occurring but unwanted temperature rise of the stator is separated from the front spindle bearings by an additional cooling barrier. This has been shown to lead to lower bearing temperatures, which positively influences the service life of key components and reduces the thermal expansion of the spindle nose or the tool even more. This is immediately and positively reflected in the machining quality or the dimensional stability of the parts.
 
At the same time, the multi-speed stator winding used to date has been replaced by a four-pole winding, doing away with the previously used extensive constructive pole switching.
While reengineering the spindle nose, the labyrinth was modified at the same time to ensure that oil drops from the bearing lubrication no longer discharge on the work piece when at a standstill or while rotating. This is a requirement, for instance, when machining graphite electrodes.
The complete sensor system installed to monitor the spindle and the milling process has been retrofitted in line with the latest trends for online data exchange (machine - spindle). The familiar ‘black-box’ has been made ‘Profibus-compatible’ with the SDM2. This makes it possible to monitor the spindle and machining process online, by connecting the spindle to the machine’s CNC controller over a plug-in interface.
It goes without saying that the number of parameters that can be monitored has been increased at the same time, and their information content refined. Besides the actual values familiar to the user, such as bearing and motor temperatures, tool changing signals and speeds operated, all recorded depending on the actual time a new type of 3D acceleration sensor has been developed in-house and integrated into our new mold-making spindles. This sensor enables now vibrations that occur during machining to be recorded in all three directions (x, y and z). More precise conclusions concerning the source of where vibrations originate from can be drawn from the now 3 direction-independent signals, in order to be able to influence the machining process positively in a focused manner.

Besides assigning a direction to the vibrations, each final hour of events is recorded and saved, similar to the cockpit recorder in an aircraft. In the event of a ‘crash’ (> 30 g) or any other malfunction, all of the events leading up to the fault can be reproduced. Important conclusions concerning the cause of the outage can be drawn from this and correctional measures can be introduced to reduce machine standstill times.

RFID in spindle modules
As sophisticated a milling spindle might be, such spindles are considered wear parts which need to be maintained and replaced when their service life has elapsed. However several major clients (machine manufacturers) are now moving toward requesting an integrated identification system from the sub-suppliers of their core modules, with regard to quality assurance and the process reliability of their machines. In contrast to full operating data collection via SDM, which is mainly to be found on high-end motor spindles, Radio Frequency Identification (RFID) technology offers a cost-effective method of data storage.
RFID refers to a process for wireless data transfer via an electromagnetic field. Technologically this identification and tracing system is extremely simple and affordable.

Some time ago Step-Tec decided to integrate these tags (passive transponders) into certain types of spindles. They contain the spindle ID as well as the machine data, and the maintenance technicians can read this into the glass tag before the motor spindle is replaced. The spindle manufacturer can read out and evaluate the machine data (event history) with a scanner. This makes it possible to identify the motor spindle exactly and insures fair granting of warranty based on the monitored incidents. These tiny glass tags are of little importance when it comes to costs, but do lead to considerable savings being made in the logical support for a motor spindle during its complete life-cycle.

Cost-optimized spindle bearing lubrication
Spindle bearings in high-speed spindles are mainly oil-air lubricated and require extensive and costly peripherals accordingly, for which the machine manufacturer usually has to bear the cost. For-life grease lubrication on the other hand places physical restrictions on the speed of the bearing due to the grease service life and its deterioration. Therefore spindles with for-life lubrication were simply not a choice for high speed mold making spindles.
The optimum solution to both well-known lubrication systems takes the form of a grease relubrication system, which counts as the most environmentally-friendly lubrication system over the entire life cycle, and follows the trend toward green machines. In-between times Step-Tec equips various spindle systems with this lubrication system, hence delivering motor spindles optimized toward cost and performance.
In a comparison of the lubrication systems, speeds in a higher region of up to 1.8 n dm (x106) can be reached today with hybrid bearings using Step-Tec continuous grease relubricating system. Further advantages of spindles fitted with relubricating cartridges include a service life up to three times longer than that of ‘for-life lubricated bearings’. Owing to its simple design, this lubrication systems is extremely solid and low maintenance. Grease consumption is no longer an issue because the rolling elements are continually supplied with new grease.

The great operating reliability of this relubrication system and its perfect positioning in the cost/performance comparison explains the increased use of these types of motor spindles in both production and mold making.

Step-Tec “in-line spindle“ with grease relubricating cartridge

For further information:

Step-Tec AG
CH-4542 Luterbach

Come and visit us at the EMO 2009 in Milan.
Hall 7, Stand E20D