Hard Turning Perfects Finished Parts for Small-Batch Production

Shops that process high-volume automotive jobs often use hard turning for finish work, but the cost of cubic boron nitride (CBN) inserts makes this strategy look out of reach for smaller projects. New advances in the efficiency of CBN insert technology make the tooling more efficient and cost effective for small-batch jobs, enabling shops to skip the use of grinding equipment altogether and gain the advantages of single-machine processing.

Finish work typically means moving workpieces to grinding machines for secondary processing, but multi-process machines add economies of scale, as one piece of equipment handles numerous processes in a single clamping. Not only does that approach save time, but it also eliminates the errors that can creep in when operators must unclamp and reclamp workpieces back and forth from one machine to another.

If you're focused on upfront costs alone, this strategy looks more expensive than the alternative. After all, CBN inserts for hard turning can cost 10 to 20 times the price of conventional tooling, and that disparity isn't likely to disappear, given the material costs involved. But a machine with a fast spindle and CBN inserts that feature today's advanced geometries can leverage tool life, cost per edge and overall productivity to produce up to 300 times more per-part cost effectiveness than conventional tooling.

Conventional wisdom suggests that adding more equipment also adds more capabilities. That's true – but it's only more efficient if that additional equipment performs functions that a shop's existing machines can't handle. To keep up with high-mix, low-volume production, shops need versatility and production flexibility. Lathes offer both, especially compared to grinding machines – and when hard turning enables a lathe to rough and finish a workpiece, even a less-advanced model can handle the work, provided that it offers the rigidity and vibration damping necessary for good tool life with CBN tooling. CBN tends to be more brittle than carbide or steel, so proper stability and toolholding are a must for successful hard turning.

Wiper geometries can make a big difference in machining at the higher speeds and feeds necessary for hard turning. Because of those machining parameters, heat develops at the insert edge and softens the surface in the cutting zone, essentially plasticizing the workpiece surface. Coolant extends tool life in these continuous cutting applications, so long as it doesn't make contact with the hot tool tip, where it can cause thermal shock and damaging microfractures.

Seco Tools offers numerous innovations in CBN tooling to master new and challenging materials, including workpieces with transitions between varying degrees of hardness. The Secomax™ Flowing Radii Chipbreaker, for example, uses a new smooth radius chip breaker to handle those types of hardness variations. We laser machine this chip breaker to give it a continuous radius along the cutting edge, which promotes consistent chip formation and evacuation as the tool moves from hard to soft surface areas.

Along with specialized chip breakers, we also maximize the number of cutting edges with solid-style instead of brazed-tip inserts. Solid inserts can feature as many as 20 cutting edges, compared with only between two and eight on brazed-tip inserts. Several grades also feature bimodal distribution of grain sizes to deflect cracks and extend tool life.

CBN tooling brings high-end solutions to manufacturers who previously skipped hard turning on smaller jobs because of the initial costs involved. Shops that spend the additional amount up front can realize substantial long-term savings – especially through process optimizations. Seco Tools continues to build inserts that handle new materials, approaches and challenges.