Why hard turning is up to three times faster than grinding
Hard turning allows a metal rate removal of up to 25 times higher than grinding thanks to the higher rigidity of the tooling. The rigidity is higher by a factor of up to 6 times. The diameter of a boring bar in case of hard turning is determined by the diameter of the hole, the profile depth of the thread and the tolerance for the CBN tool tip. The rigidity of this boring bar and the possible cutting volume are therefore solely dependent on the internal diameter and the length of the ball screw nut.
The diameter of a grinding spindle is heavily dependent on the pitch angle. The greater the pitch angle, the lower the rigidity of the spindle and the lower the possible metal rate removal. This leads to higher cycle times. The trend towards ball screw nuts with a large pitch which makes grinding even less suitable as a machining technique.
| Thread turning | Thread grinding | |
|---|---|---|
| Metal rate removal | 150 -1500 mm³/min | 10-60 mm³/min Depending on grinding geometry and flank geometry |
| Possible tool rigidity | 15 – 100 N/µm | 0.1 – 8 N/µm
Depending on possible maximum shank diameter, corresponding to the disc diameter and thread pitch. |
Highest accuracy class IT 1-2. Even after 20 or 30 years
The Hembrug Mikroturn machines are capable of making ball screw nuts from Ø 10 mm to Ø 500 mm in the highest accuracy class IT 1-2 having hardness 58-70 HRC. The machines have a high repeatability of 0.1 µm thanks to the hydrostatic main spindle and guideways equipped with high resolution, direct measuring systems. The oil temperature is kept at 20 ± 0,1° C with the aid of an external cooler creating a very stable process. The oil bearings throughout ensures that this high degree of accuracy can still be delivered even after 20 of 30 years.
| Thread turning | Thread grinding | |
|---|---|---|
| Achievable accuracies
Pitch errors Roughness Ra Accuracy class |
0.5 – 2 µm 0.2 – 0.5 µm IT 1-2 |
0.5 µm* 0.1 – 0.4 µm* IT 1–5 *According to the bibliographical references. |
Simple programming and fast changing
User-friendly software enables you to simply program the thread profile without the need to write G-codes. The software offers the possibility to change the type of product very quickly. It takes just a few minutes to program a different contour, which can be retrieved again later. In this way, you can easily program a wide range of products in a single machine.
A wide variety of different profiles
Apart from a Gothic thread contour, it is also possible to create METRIC, UNIFIED, WITHWORTH, ACME, ROUND, TRAPEZOIDAL and NPT thread contours and even screw thread calibre contours. Depending on the type of machine, the Mikroturn® machines can make ball nuts with a diameter from 10 mm to 500 mm in diameter.
