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Applications combination technology hard turning and grinding
Versatile application of the combination technology hard turning and grinding
The advantages of hard turning and grinding are obvious. Where, in the past, one had to decide which of the two machining processes to use, combination machines now allow the users to choose the process best suited for the machining of their specific workpieces.
EMAG follows the path of combination machining with consistency. Of interest are machines that allow the use of combination technologies in the manufacture of medium and large batches of top-quality, high-value workpieces. The machining technology is chosen in accordance with customer requirements and workpiece quality specifications. Stable components can be machined using the scroll-free turning method, whilst thin, delicate workpieces are machined using grinding technology.
Application examples of combination machining hard turning and grinding
- Finishing a gearwheel with hard turning and grinding operations on an EMAG VSC 250 DDS
- Combination machining hard turning and grinding of shafts. All precision-machining processes on a single machine: CBN grinding, hard turning and scroll-free turning, providing exceptional flexibility in the precision-machining of shafts.
A typical example of combination machining (hard turning and grinding) is the machining of gearwheels. The shoulders are finish hard turned. Because of the high demands made on their quality, the bore and cone are pre-turned and finish-ground. To achieve this, the machine has been equipped with two grinding spindles, one of which is designed to machine the bore, with the second one machining the external sections of the component. As only a few hundredth of a millimetre have to be ground away, the grinding tools are designed for finishing only. Meanwhile, this process has – to a large extent - replaced single-process grinding machines and can, by rights, be considered state of the art.
Another example of the practical application of this combination technology (hard turning and grinding) is the machining of scroll-free seats. A pressure ring needs to have its outside diameter and its face machined, whereby the O/Ds surface must be scroll-free. In this case it would be appropriate to hard finish-turn the face and to pre-turn and then finish-grind the O/D. The grinding wheel is dressed by plunging it into an axis-parallel positioned profiling roll. The grinding process too is of the plunge-cut type. This process makes absolutely sure that scroll marks are avoided. Yet another interesting example of combination machining is the machining of nuts with internal ball tracks, as used in ball screws. These nuts need to have the internal thread, the face, the O/D and the shoulder machined. The concept used allows for the face, the O/D and the shoulder to be hard turned and the internal thread on the ball track to be ground. A machine like the VSC, equipped with Y- and B-axis, is ideal for the purpose. The high-precision B-axis allows the setting of the lead angle of the thread, whilst the Y-axis serves as infeed axis for the machining of the ball track. The machine is equipped with two grinding spindles, which – for pre-turning and finishing work - can be equipped with a variety of tools. The grinding tool profiles are dressed with a separate dressing attachment equipped with diamond profile dressing rolls. The machine is suitable for the use of both conventional and CBN grinding wheels. A 2.5-D measuring probe serves to ascertain the exact angular position of the workpiece. It can also be used for the post-process control of the hard turned surfaces.
The advantage of this concept over conventional, sequential processes is that all quality-defining surfaces can be machined in a single setup. Re-clamping errors that affect in particular the alignment of face and O/D to the centre line of the ball groove are thus avoided.
