Precision machining technology for modern hard materials

Hofer presented the latest developments in gear grinding machines at the European Machine Tool Show in Hannover.
Gear grinding technology is currently very popular. With the Precision Machining technology of hard materials, the latest machine tools can be made more efficient, safe and flexible. In addition, other technologies such as "topological grinding" and "high speed grinding" can also improve this performance.

A trend has emerged in recent years as more and more gears are grinding to meet ever-increasing precision requirements. This trend is also reflected in the number of Hoffler sales: in the past five years, the number of gear grinding machines delivered by the company has increased by a factor of two.
Gear manufacturers need to constantly meet new requirements, lower processing costs, shorter machining times and greater flexibility. However, it is difficult to make more progress in the direction of this trend if it relies solely on current production methods.
Current machine technology is more efficient and safe Modern grinding machines directly control the grinding process by inputting power and recording all important parameters. By comparing the data, the grinding wheel can be recorded. When necessary, the grinding process adjustment program can be recorded in relation to the wear condition. The feed motion is related to the tracing data.
The grinding process is measured and analyzed by measuring buttons or automated grinding programs to optimize the tonality of each defect. Tests conducted by the Technical University of Munich (TU Muenchen) have shown that different forms of grinding wear have a significant effect on pitting losses.
In order to obtain the most regular tooth surface damage, it is necessary to continue to fix the gear to the gear grinding machine soil after the end of the gear forming process.

For many years, the Hofer gear grinding machine has always offered the possibility of grinding the test piece or the thrust ring before or after the gear is formed, with a certain clamping force applied. Cylindrical grinding is only possible after the gear grinding machine has finished grinding the test piece.
Benefits of the “Complete Machining Process” It is now possible to avoid re-clamping or machining on the same machine on the same machine. Modern vertical technology allows for higher turning speeds, making it possible to grind cylindrical parts on gear grinding machines.
The complete machine tool solves the problem between time and precision loss by avoiding repeated clamping during the machining process and simplifying the internal logistics of the enterprise. It can complete the clamping and machining of the workpiece at one time. As a result, non-productive shafting time and costs are reduced.
Hofer integrates drilling, surface grinding and cylindrical grinding in the finishing technology of gear grinding machines. In fact, a variety of machine tools are required to complete the above processing tasks. At the 2007 EMO European Machine Tool Show in Hannover, Hofer exhibited the newly developed "Rapid 1250 MFM (Multi-Funktions-Maschine)" machine tool, which enables drilling while drilling and The top of the tooth is rounded.
The complete machining process in the gear shaping can improve the concentricity between the gear and the center hole. The complete machining process also optimizes the distribution of the hardening deformation occurring on the gear and the center hole, so that the grinding damage can be obtained as stable as possible. And ultra-high stress surface carburization depth.
Next, Hoffler also presented the newly developed grinding head for the gear profile grinding machine "Rapid 650" to "Rapid 6000" series at EMO. This series of grinding heads is capable of gear grinding on five interconnected shafts and drives these grinding heads with a torque motor. Important features of these grinding heads include dual adjustment systems, direct drive electric spindles, 3D measuring systems and feed rates of up to 12000 mm/min. These features can be used to gain unique advantages, such as the option to combine "topological grinding" and "high speed grinding" as described above.
Topological grinding In order to achieve technological advances, it is necessary to find solutions such as free-forming with topological gear profile grinding to minimize tooth surface deviation. Hofer has developed a method to obtain optimized axis features by means of the topology gear profile shape that needs to be achieved. This is also the purpose of optimizing the contour of the grinding wheel.
Depending on the algorithm, topological corrections or topological changes to the gear shaping can be carried out – depending on the permissible deviations – for one or both faces.
The example shows a result of optimizing the gear forming process based on a topological algorithm. The method of topological correction - or "depending on the final tooth profile" - can alleviate the surface pressure experienced by the helical gear at the point of entry and the point of engagement. This technology can be used to reduce the size of the gearbox.
High-speed grinding technology In order to significantly shorten the machining time of gear forming, Hoffler has developed High-speed Grinding (HsG) for contour grinding at very high feed rates. For example, in the same Q'w (processing energy rate. The unit is mm3/mm/s, which refers to the cutting volume (cubic centimeters) that can be completed per unit area (square millimeter) in unit time (seconds). Under the high-speed grinding technology, the machining time can be shortened by increasing the feed rate, so that the depth of the material cut into the grinding wheel is relatively reduced, so that the material can be cooled and cleaned better. In the case of the same grinding wheel life. It is also possible to provide better cooling of the workpiece by supplying more cooling oil to the contact surface. However, the biggest impact of high-speed grinding technology is that the residual heat generated by the grinding process can be made larger from the workpiece. Exported within the city's range. This reduces the risk of burns, and grinding burns often leads to more serious damage.
A graphical simulation of the results of a study published by Gleason-Fart in 2O05, ie the relationship between the risk of burn burn and the feed rate in the range of 12000 mm/min, and Hoff The gear grinding machine produced by Le company is able to achieve this feed speed. Of course, this is just a purely graphical expression. It only shows the theoretical relationship. However, from this figure it is also possible to achieve the result that if the risk of grinding burns is to be as low as possible at the highest possible feed rate, it should be: higher processing at higher feed rates. The rate can be ground.

Thanks to the fact that the gear grinding machines from Hofer can work at very high feed speeds, they offer a significant increase in productivity. However, higher feed rates also place demands on the dynamic performance of gear grinding machines because the feed motion is directly related to other axial movements. Therefore, without the help of modern direct drive technology, high-speed grinding technology will not be discussed.
Higher precision with torque motors The mechanical properties of gear grinding machines have a significant impact on productivity: conventional gear grinding machines cannot achieve processing parameters determined by modern drive technology and materials. With the introduction of torque motor technology in the late 1990s, it has been difficult to encounter previous gear machining processes on modern gear grinding machines.
The accuracy of the horizontal spindle largely determines the accuracy of the gear grinding machine. Compared with the traditional turbine-worm drive technology, the torque motor and the optical encoder work together to bring greater advantages: for example, the torque motor is not worn and the accuracy is ensured throughout the life of the gear grinding machine. Since the machine frequency of the horizontal spindle can be neglected, people can also obtain up to 3.6 billion step increments on the machine to control the deviation of the helical gear rotation direction. For current production requirements, higher stiffness and higher speed are also one of the advantages.
It must be pointed out that the use of a torque motor on a gear grinding machine requires additional control. In the 1990s, Hofer developed a special optimization algorithm for the "BWO" (Backward Wave Oscillator) control system for the automatic optimization of horizontal spindles. After several years of cooperation between Hofer and Siemens, the algorithm can also be used in the Siemens 840D control system. At present, Hofer's daily work in the background is mainly to optimize the system to ensure that the machine can be used without interference.

There is no end to the precision requirements. It is important to emphasize that the material of the bed for high-precision grinding machines requires polyester synthetic materials. The quality of the mineral cast structure affects the vibration characteristics of the bed and thus fundamentally affects the optimization of the position adjustment of the system: the attenuation characteristics of the mineral cast structure can be increased by a factor of 25 compared to gray cast iron. Therefore, the thermal characteristics of the mineral cast structure are very slow, so that a design structure which cannot be obtained by gray cast iron can be obtained. For example, a gantry for an internal/external tooth grinding machine.
With the continuous improvement of the quality of gear processing, we can now add additional terms to the German quality standard DIN 1. Marine gearboxes are ground to the German quality standard DIN 1, and most users are able to accept such quality. However, it should be pointed out that although the marine gearbox can be said to have achieved better grinding quality according to the German quality standard DIN 1, there are already some users who cannot continue to accept such quality levels. It is necessary to limit the deviation by means of topology. It is necessary to analyze the segmentation process by means of FFT (Fast Fourier Transform, fast Fourier transform, fast algorithm of discrete Fourier transform), and then determine the corresponding order extremum. In extreme cases, it is also necessary to limit the waviness caused by the machine's kinematics.
During the optimization of the load and pressure, the deviations that occur during the gear forming process are relatively difficult to detect. Therefore, the correction plane for removing interference requires higher accuracy because the gearbox produces an excitement in a wider range of errors in the grinding path of the gear interference zone - these phenomena are mainly located in the micrometer or in certain parts.
In 2004, Hofer developed a grinding machine that not only optimizes the grinding process with topology according to the German quality standard DIN 1, but also achieves pre-defined ripples. Degree requirements. The background to this idea is the requirement due to gear interference or to compensate for the phenomenon of ripple formation from the opposite direction. Grinding and analysis of ripple amplitudes below 0.1 μm can now be performed, allowing for differential handling of loads and disturbances in modern gear forming processes.