Bone Screws


Replace Your Screw Machine Whirling with Leistritz Whirling

Bone Screws

For those looking for a faster, more-economical method of producing Bone Screws, whirling as a separate operation -is just what you’re looking for.

By Ralph Wehmann

The Leistritz concept is to turn bone screws blanks in existing swiss-type turning centers without the thread. This would allow an even shorter cycle time and greater throughput per machine. Then, with a whirling only machine, whirl the thread. Leistritz whirling machines have the necessary following supports to permit whirling of screws with any profile in virtually unlimited lengths in the shortest possible time. Whirling by Leistritz can outperform whirling in a turning center by a factor of 2 or possible 3:1! Most Bone Screws even in their longest designs and in either 316L stainless steel or Titanium are whirled in under 60 seconds!

The Leistritz LWN-65MED machine has a very unique automatic parts loader and hopper system. The pre-turned blanks with either finished or unfinished heads are dumped into the vibratory hopper which aligns the screw blanks to be oriented tip first and funneled to the staging area. Once “on deck” for the loading process, each screw is measured for length with a light beam and the proper CNC program is selected to run the appropriate screw length. This is a valuable tool since nearly all bone screws are produced in families of the same diameter. Typical Bone Screws of the same family vary only in length from 10 to a maximum of 100mm in 5mm increments. With the Leistritz LWN-65MED machine all screws within the same family can be produced simultaneously without any set-up.

This processing also allows cell integration of a number of turning centers to each whirling machine. Typically 4 or possibly 5 turning centers produce the blanks (of various lengths) for a single LWN-65MED whirling machine.

Leistritz-a machine tool builder based in N├╝rnberg, Germany, with a branch office in Allendale, New Jersey-has developed a complete line of multi-axis CNC whirling machines. These machines have been designed specifically for whirling and have the inherent rigidity for cutting deep, wide profiles in tough materials and the necessary accuracy for cutting precision, close-tolerance screws. These machines are ideally suited for production environments where there is minimal time to do routine maintenance.

Medical screw manufacturers throughout the country and in Europe are fast discovering this better way to process their production. When production volumes increase to the point where more than one turning center is required, this separation of operations saves even more by maximizing the utilization of all machines in a cell. The low tooling costs combined with short cycle times and mostly no set-up time really proves beneficial to their bottom line.