The Whirling process capitalizes on the
latest advancements in cutting tool materials to quickly produce threads
and screws to tolerances previously requiring grinding. Difficult
threading operations, such very long shafts or very wide profiles
can be easily machined by whirling. The superior surface finishes
and closer tolerances of screws machined by whirling are ideal for
today's demanding clients. CNC control gives the possibility to machine
threads of variable or unusual pitches, tapered or variable root diameters,
single or multiple starts. Ball Screws, Acme Screws, Worm Shafts,
Feedscrews for Injection Molding are all excellent examples of workpieces
ideally suited to whirling. The machine shown is capable of machining
screws up to 4.252 diameter by 80" long. Long screws are supported
by high precision follower rests on each side of the cut and traverse
with the tool slide over the entire length of the screw. This machine
has been designed from the first thought for whirling and has the
inherent rigidity for cutting deep, wide profiles in tough materials
and the necessary accuracy for cutting precision, close tolerance
screws. The main spindle is actually a ultra precision rotary "C"
axis having high torque and a resolution of 0.001 degrees.
Hard Whirling
Perhaps the most exciting metalcutting breakthrough is the recent
introduction of hard whirling. LEISTRITZ has developed a process for
precision machining hardened steels. Using a CBN insert, steels as
hard as 65 HRc can be machined. CBN or Cubic Boron Nitride is the
hardest material known to man, next to diamond. CBN has uniformly
high hardness and abrasion resistance in all directions. The superior
edge retention and hardness of CBN permits more effective cutting
with less tool wear, which helps maintain part geometry for greater
precision. Combine this tool material with the gentle, tangential
cutting action of whirling, and you get a revolutionary process for
cutting precision threads in hard materials. Like all whirling operations,
hard whirling is done dry, without coolant. The chips, glowing orange
hot, carry away nearly all of the heat of the cutting, leaving the
workpiece cool. This minimizes any thermal geometry variations. The
surface finish and profile accuracy is amazingly precise. Producing
Ball Screws with hard whirling can eliminate a number of previously
mandatory steps in the processing. For example, a typical ball screw
would be rough machined in the soft state, case hardened, straightened,
and finish thread ground. Very often long screws, that do not necessarily
require thread grinding are ground, only to remove distortions and
lead variations created by heat treating. A hard whirled ball screw,
for example, can be machined to finished dimensions and tolerances
without further machining. On screws that demand thread grinding,
the hard whirling process can still save on machining time and minimize
work-in-progress. Finish thread grinding is one of the most time consuming
operations on long screws. By machining the thread profile to nearly
ground accuracy, hard whirling reduces the amount of material to be
ground and thus reduces the grinding time. This process allows us
to stock as a raw material case hardened bars, thus completely eliminating
the need for heat treatment in the process. This can greatly reduce
the total process and improve lead times to our customers.
In summary, the advantages of whirling are dramatic for many applications
being done by conventional means today. Whirling is a viable process
for machining screws or worms, and should be considered by anyone
machining these parts.
