Ball Screw Whirling
Ball Screw Whirling – Replaces Thread Grinding Ball Screw Whirling
World class ballscrew manufacturers discover huge advantages in whirling.
Producing both aerospace flight control actuators and commercial ballscrew assemblies for linear motion control, companies like Thomson Industries and Umbra Cuccinetti have eliminated several processing operation steps by whirling the ball threads in hardened materials without previously roughing. Whirling using CBN cutting inserts with either a full round or gothic arch profile has allowed them to produce finish quality screws in a single pass.
Leistritz, a machine tool builder in Nuernberg, Germany with offices in Allendale N.J. has developed a unique process solution by combining precision follower rests, an economic re-sharpenable tool system & high speed whirling head with a rigid and accurate CNC controlled machine tool. With bed lengths up to 8m long ball screws can be whirled to finish tolerances in a single pass in full material. By clamping the finished outer diameter in carbide “V” jaws, the follower rests on either side of the cut guarantee near zero concentricity of the thread.
Whirling is a dry cutting process and coolant is not used, thus saving the expense of maintaining a coolant system and disposing of toxic grinding swarf. The tangential cutting action of the whirling process combined with optimum speeds & feeds permit machining of steels as hard as 65hrC with minimal heat transferred to the workpiece. After whirling the material is only slightly warm to the touch with an increase of approx. 20-25°F above ambient. Since whirling is done cutting from the tailstock towards the chuck, any slight lead variation due to this temperature increase is “behind” the cut not effecting the cool/stable bar yet to be whirled. Lead accuracies of ±0.0005″/foot are easily attained when cutting stable materials. Leistritz machines are laser calibrated at the factory and installation site to insure positioning accuracy.
Ball forms of 0.062″ ball to 0.500″ have been efficiently whirled in this manor with a huge time savings when compared to grinding. Leistritz whirling machines can offer a 8 to 10 times savings factor over thread grinding without any fear of surface cracking. Since whirling uses ideal cutting geometry the material never reaches a critical temperature and stress does not enter the work. Screws that are whirled have excellent surface finishes down to Ra 8 microinches and are not visibly different to ground screws.