The model discussed in this article is installed in Bonfiglioli, an Italian multinational company that, in its business units (Power Transmission Solutions, Mechatronic Drives & Solutions, and Mobile & Wind Solutions) offers know-how and experience for the development of its customers within increasingly competitive markets.

The choice of the G 250 HS is part of this quest: quality of the workpieces made, reliability and productivity are some of the constraints that Bonfiglioli has imposed in its choice of the machine. The first eye-catching detail of the G 250 HS is the workpiece loading system: it is in fact equipped with a rotary table with a double work spindle. This allows the workpiece to be loaded and unloaded while the machine is running: while a gear is being machined within the working range of the machine, the other is positioned in a protected area designed to ensure safe access (automatic or manual). Handling the machined component and positioning a new blank is therefore possible by keeping the wheel rotating and the oil flow active: the rotation time of the table is less than 2 seconds, thus reducing downtime.

This work strategy also has a significant impact on the production stability and reliability of the plant.

Other solutions interrupt the flow of liquid and stop the tool (or require a movable panel to protect the external environment from possible projections of liquids or shavings), generating additional heat resulting from the stop and restart of the spindle and requiring more energy than simply maintaining the rotation speed and generating continuous mechanical stress on the components. Therefore, the different approach caused by the table’s two positions has significant overall benefits that go well beyond the machine’s productivity.

On the table there is a pair of work carrier devices composed of a centre and tailstock that grip and hold the component to be ground into position using a centring cone. Depending on the shape of the workpiece, an active clamping spindle with a gripper can be mounted or, for simple gears, a hydraulic expansion system can be used. This is a sound idea for managing loading and unloading in both automatic and manual modes: the user can thus flexibly decide the best approach based on the number of batch items, the process set up or to stay productive even in the case of a temporary stop condition of the automation.

In terms of flexibility, each workpiece holding device can be quickly replaced thanks to a quick-change-over system that allows the switching time between one batch and the next to be limited to a few minutes.

The G 250 HS can grind complex gears with small diameter worm wheels thanks to the particular shape of the wheel head.

There are two sizes of ceramic wheels that can be used in particular: 160 mm dressable up to 115 mm, and 120 mm dressable up to 70 mm. On the same machine, optimisation work was also carried out for the form wheels: Bonfiglioli has reported a diameter limit of 30 mm linked to its available tools.