Turning vs. grinding – the hard facts
Turning hardened steel rather than grinding it offers many advantages.
As a single-point contact method, HPT can easily accomplish complex contours without need for the costly form wheels that multi-point contact grinding requires. Similarly, HPT permits machining of multiple operations with just one set-up.
The result is excellent positional accuracy, reduced part handling and less risk of part damage. The environment also benefits from HPT as the technique eliminates grind waste and does not require coolant.
All in all, HPT reduces machine tool costs and gives better production control, quicker throughput and higher quality. Add these plus points together and the cost-savings brought about by switching to HPT are considerable.
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 | Turning | Grinding |
| Method | Single point contact | Multi point contact |
| Profile | Periodic, one | Irregular, many |
| Residual stress | Compressive (mainly) | Compressive (mainly) |
| Surface profile | | |
| HPT produces a better hardened steel surface than grinding. |
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Cost estimates for hard part turning compared to grinding
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| Investment in machine |
| Tools and consumables |
| Floor space |
| Manpower and fixed costs |
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Grinding | Hard-part turning |
HPT generates significant savings in manpower and fixed costs compared with grinding. |
Stability - the key to success
Stability in many different forms is a key success factor in HPT. Not only machine stability, but also rigidity and thermal stability are vital components in producing an accurate, high-quality finished part. High machine rigidity and stability will minimize the impact of variable cutting force on the surface profile produced.
This results in a better process capability. Guiding accuracy and positioning accuracy of the carriage are also important criteria to consider when choosing machines for HPT.
Not surprisingly, the better the stability of your overall machine concept, the closer the tolerances you will be able to keep. Machine thermostability also requires some thought. | | Heat generated at any place in the machine affects the tolerance of the work-piece, so it must be controlled accurately. Removing heat by cooling the spindle or transporting it away in heat-containing chips will pay dividends in better tolerances.
In this respect, vertical lathes (pick-up machines) with no resting place for chips to accumulate are good examples of ‘thermostable machining systems’. Take into account all these stability parameters – machine, tooling and temperature – and choose the correct Sandvik Coromant wiper technology, and you can achieve surface qualities fully on par with grinding. |
| Surface roughness, Rz | |
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| Basic system noise |
| Insert radius |
| 0.4 mm |
| 0.8 mm |
| 1.2 mm |
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| Control stability and experience outstanding surface quality values. |
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| Feed, fn mm/r |
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