The Mikroturn 200 L replaces grinding process in the production of ultra-precision threaded spindles

The Mikroturn® 200 L is the first Mikroturn to be used for the hard turning of ultra-precision threaded spindles in tolerance class C0. In addition to producing threaded spindles, the machine can also be used for the hard turning of ball screw nuts. The Mikroturn® replaces the traditional grinding process to deliver considerable time and cost savings. This is possible because hard turning can eliminate a large number of processing steps compared to grinding.


Steps in the traditional grinding process                            Steps in the new hard turning process
Centreless grinding of blank spindle                                                 Shorten blank material
Apply centres                                                                                          Apply centres
Harden over the complete length                                                       Harden. Only where necessary
Centreless grinding                                                                               Hard turning rough + finish operation
Wind threaded profile
Apply centres
Finish grinding
Align if necessary

The advantages of the hard turning process are numerous. The comparison above makes it clear that hard turning does away with a number of processing steps for a shorter overall processing time. The hard turning process also makes use of standard (CBN) inserts. These are lighter and less expensive than profiled grinding stones and easy to adjust. In a production environment where small quantities of many different kinds of spindles are made on a daily basis, the time savings are considerable. Hard turning also makes it possible to program free profile shapes, such as asymmetrical profiles. The processing process itself is also a third faster than comparable grinding processes, amongst other things because more material can be machined per cycle with hard turning than grinding.

The Mikroturn® 200L is able to approach or even improve on the grinding quality thanks to the excellent positioning accuracy of 1 micron and roundness accuracy of 0.1 micron. The machine has a base of natural granite and an integrated system of vibration dampers. Both the main spindle and the guideways are fully hydrostatic, which guarantees precision over the entire lifecycle due to the absence of metal-on-metal contact. The Mikroturn® 200 L is able to produce spindles with a total lead error of less than 4 microns over a length of 400 mm and a contact angle variation of less than 3 degrees. The diameter deviation is less than 2 microns and the achievable surface accuracies lie between (Ra) 0.1 and 0.4.

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