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Advanced Manufacturing: Medical Machining Shifts Into High Gear—With a Laser Assist
July 19, 2018
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Maximizing Tool Life, Part Quality
To machine medical parts and features as small as the hexalobes in bone screws while preserving tool life, Tsugami/Rem Sales LLC (Windsor, CT) has equipped several machines in its portfolio with custom speed-quadrupling units.
Standard spindles on Swiss-style machines typically spin live tools at 6000 to 8000 rpm, said Derek Briggs, Swiss product manager for Tsugami/Rem Sales. “When you are performing fine surfacing and five-axis contouring, engraving or etching, you need extremely high rpms because the tools are very small; you typically have an 0.125″ [3.175 mm] or smaller ball end mill that you are doing fine contouring with, and you’re cutting on center during these types of operations. You need very high spindle speeds to keep the surface footage at an acceptable level for tool life and meet surface finish requirements.”
Tsugami’s solution is an attachment using gear reduction that multiplies spindle speed by up to four times without taxing the spindle motor to reach an optimal speed, such as 20,000 rpm. Tsugami/Rem Sales can even integrate the high-speed spindles made by NSK America and run them up to 80,000 rpm.
Most Swiss-style lathes use a gear train that runs three or four spindles simultaneously when the motor is turned on, Briggs said. With just one modular spindle with reduced gearing going faster than the rest, “you’re not taxing the other spindles. It’s nice to get higher spindle speeds for that fine surfacing and small five-axis work that the medical market is looking for more and more today.”
While a standard thread whirling attachment will certainly do the job, if a machine is dedicated solely to producing bone screws all day, manufacturers should consider requesting ceramic bearings instead of more standard steel roller bearings. With ceramic bearings, operators can tighten the preload more than on steel, stiffening the system and maintaining maximum spindle speeds. Ceramic bearings dampen very fine harmonics and vibration when cutting bone screws and can also take the heat of higher rpms, dispersing heat much better.