Sandvik Coromant introduces new thread whirling inserts and holders for sliding head lathes

The growing use of bone screws, spinal screws, implants and other medical components means machine shops in the medical supply chain are constantly seeking ways to boost throughput times. With this in mind, the new thread whirling inserts and holders from Sandvik Coromant are designed to thread long, slender components from rough stock, at high speeds, without the need for a dedicated thread whirling machine.

Fast and accurate:
Thread whirling is preferred to conventional single-point threading techniques due to its speed – the smooth, tangential cutting action minimizes cutting forces to give high metal removal rates. This, in combination with the rigidity of a sliding head machine, results in precisely completed threads in a single pass. The upshot is improved productivity and manufacturing economics when mass-producing threaded medical components on sliding head machines such as Citizen, Star, Tsugami and Tornos models.

The new inserts from Sandvik Coromant can be quickly and easily mounted in the ring holders. Once complete, the user only has to insert the ring over the spindle screw, turn the ring anti-clockwise to the bottom position, and tighten the ring screw. To begin cutting, tilt the spindle unit in relation to the desired helix angle of the screw, and program the ring off-centre (in relation to the thread diameter). For optimum tool life, the whirling ring and component should rotate in the same direction (climb milling).

With their stronger cutting edges, inserts in the whirling ring apply even cutting pressure to create precision threads without bending the parts, which are typically long and slender. Furthermore, chip control is superior to single-point threading, enabling more continuous and productive machining. Deeper thread forms such as Acme threads are also achieved more easily.

Medical screw standards:
Standard inserts for HA and HB threads fit all CoroMill 325 whirling rings and follow thread standard ISO 5835-1991 for medical screws. Inserts for other thread forms can be ordered from Sandvik Coromant’s non-standard range. All Sandvik Coromant thread whirling inserts are available in GC1105 – the first-choice grade for medical machining. GC1105 offers sharper edges and a burr-free component surface when machining stainless steels and titanium.

In a titanium (Ti-6Al-4V) bone screw machining trial on a Tsugami sliding head lathe, the CoroMill 325 ring and inserts led to a 500 per cent increase in the number of components produced in comparison with a competitor product – completing 1,100 HA4 threads (3.5 mm diameter x 1 mm pitch x 25 mm long) before requiring new inserts, against just 215 using the competitor.