Instead of using two machines – one for higher speed and the other for high torque, the entire processing spectrum is now representable with only one machine. This has become possible thanks to innovative transmissions and results in a sustainable production.
We all agree: The utilization of machine tools must be very high. To get a grip on the classic dilemma of high speeds with reduced torque and vice versa, machine tool manufacturers have been improving the application bandwidth and the utilization potential of their machines with a larger spread of gear ratios between torque and speed. In addition, the cycle times are shortened by the use of highly dynamic synchronous motors coupled with better vibration levels and lower temperatures.
In order to optimize machine utilization and to solve the conflict of the requirement for high speed on the one hand and high torque on the other, the two-speed manual transmissions 2K DUOPLAN HS and 2K DUOPLAN-HWG were developed for AC and DC main spindle drives by the Special Driveline Technology business unit of ZF Friedrichshafen AG. They are used in high-speed machine tool drives for high-speed cutting (HSC) and in RAM installations.
The transmissions provide high torques and are characterized by a high level of operating smoothness combined with low temperatures and vibration levels (< 1mm/s) at high speeds. The planetary drive is only activated when needed. Thus the rotating masses (2K150 HV 63 kgcm²) in direct drive are reduced to a minimum. As a result of the different installation positions, the transmissions can be used, for example, for lathes (horizontal B5) or machining centers (vertical V1).In addition, the transmissions are used in various equipment in which an increase of the torques or a reduction of the speeds is necessary. The transmissions have a coaxial output for direct installation on the spindle. An integrated, torsionally flexible clamp coupling transmits the torque to the spindle. Coolants, emulsions, oils, or air are routed through a hollow shaft.
Other features of the two-speed manual transmissions include the reduced space requirements due to the planetary design as well as the direct installation on all AC, DC, and standard motors with a flange-mounted configuration. Furthermore, the self-sufficient transmissions are characterized by two electromagnetic transmission controls for the input and output side with non-wearing end position monitors. No sealing is necessary on the motor side. Low circumferential backlash, high efficiency, and easy assembly are additional characteristics.
A brief consideration of conventional applications should illustrate the decision to develop a new transmission standard in machine tool applications. Machine tool transmissions with space-saving planetary drives for increased torque are, due to their centric construction, also generally suitable for high speeds. However, the previously used constructions of two-speed transmissions restrict high speeds, since in direct drive i=1:1 (gear step 2; engine speed = transmission output speed), the entire planetary drive with sun gear, planet gears and carriers, and ring gear are powered, although in fact this is only required for the conversion (shift position 1). This is a clear difference to the transmissions presented here. Due to the high rotational mass, vibration levels are adversely affected. Moreover, the acceleration times are lengthened up to the maximum engine speed. For the transmission of high torques in conversion, large diameters are required at the output, which on the one hand increases the rotational masses and requires large seal diameters. This has a detrimental effect on the transmission temperature, since the friction power increases disproportionately to diameter and speed. A distinguishing feature is the primary and secondary circuit to control the force distribution depending on the shift position.
In machine tools, vibration levels are instrumental for the surfaces and temperatures for the accuracy of the parts to be machined, and are thus decisive for the quality. The use of belts at high speeds is technically and economically hardly feasible; even legally prescribed noise emission levels are not able to be observed. Only a direct installation of the transmission on the spindle (INLINE) is possible, whereby coolants, emulsions, oils, or air are routed through a hollow shaft through the transmission (HST).
Through the use of 2K-DUOPLAN-HS and 2K-DUOPLAN-HWG, it is now possible to make the range of applications for machine tools more flexible: Instead of using two machines, one for higher speed and the other for high torque, the entire processing spectrum is now representable with only one machine. This results in further advantages for sustainable production: By the use of transmissions in the machine tool, the resource-conserving use of smaller motors is possible while fewer rotating masses shorten cycle times. By combining different work processes in just one machine, less space is required as well. The risk of setup and clamping errors is significantly reduced, while the versatility, utilization, and efficiency of the machine tool is increased. Another advantage is the reduced temperature development in the transmission, which in turn reduces the installed cooling power of the machine. Since no belts are used in the machine, the noise emission is also reduced. Last but not least, the training effort for machine operators can be concentrated on just one machine, and the field experience is also limited to one machine.