The machine’s wheel spindle installed in Bonfiglioli is the 20,000 rpm high-speed version, while the work spindle has a maximum rotation speed of 1,500 rpm. The combination of the two motors, alongside the processing with a worm wheel, allows for a good number of starts. The replacement of the worm wheel is simple and quick because the fitting is based on an HSK 63 connection. This connection ensures the repeatability and quality of the fastening, also because the grinding process has recently become more forceful on the workpiece, with significant power and torque values involved. The HSK connection also contributes to the overall stiffness and the better surface quality, with obvious advantages in the final application of the gear (less noise, power absorption, heat generation, etc.).

The structure of the G 250 HS is now consolidated and confirmed by numerous applications in the automotive field – among the most demanding sectors in absolute terms – thanks to the excellent dimensional and thermal stability.

The cast iron base is well dimensioned and benefits from thermostat control within a very narrow temperature range by using the recirculation of the cutting oil, which is circulated inside the structure in special channels near the critical points.

The machine can be in stand-alone setup, with a dedicated oil tank, or it can work with a centralised system. Samputensili sets some basic parameters (such as pressure, filtering level and temperature), but can intervene if the centralised oil has different characteristics. In some plants, for example, it was necessary to increase the oil pressure in the machine through a booster pump, while in other installations with centralised oil a self-cleaning filter was added to achieve the ideal filtration specifications.

In any case, the required parameters are not excessive thanks to the study carried out by Samputensili, in collaboration with the University of Bologna, on the shape of the nozzles. It is, in fact, a very important detail in the optimisation of the cutting process: the nozzle shape, together with the aforementioned pressure and flow rate values, allows to reduce costs and consumption without compromising the machine’s quality and productivity.

The synchronisation between the wheel spindle and the work carrier table is essential to obtain workpieces whose final shape is as specified by the design allowance. For this reason, the motorisation uses an integrated direct drive with direct Heidenhain encoders, all synchronised by the numerical control. The other axes are driven by ball screws and brushless motors and are measured by Heidenhain optical scales.

Another very important aspect in the size change-over is the automatic synchronisation of the wheel with the roller and of the wheel with the first workpiece, based on an integrated acoustic contact sensor that detects the contact. The first workpiece of the batch requires a different synchronisation to the rest because an absolute reference must be taken between the wheel, roller and workpiece. After that, only a relative reference is needed via an induction sensor (simpler and faster). On this specific machine, which handles relatively small modules, a special timing device has been developed that is suitable for working with small modules.

The maintenance of the machine is favoured by an intelligent layout of the various users, as well as by the simplicity of its construction: all the utilities (pneumatic, hydraulic, electric cabinet) are easily accessible. The sensors on the machine further help to monitor the parameters: the standard G 250 HS provides signals useful for quickly understanding the cause of a possible problem, while with additional sensors, it is possible to monitor each parameter and to signal in advance the exceeding of the different thresholds to perform predictive maintenance – after setting an optimal, a warning and an alarm value.