Thread: Turning Towards Hard Part Machining

Challenge: To meet the tolerance and surface finish demands of high quality components.

Solution: Make the switch from grinding to hard part machining, employing the latest insert geometries and CBN tooling grades.

A Simpler Production Process
Hard part machining has much to offer for machining components whose hardness typically lies within the 55–65 HRC range. Thanks to insert grades based on cubic boron nitride (CBN) and aluminium oxide ceramics, hard part machining has gained considerable ground over grinding. The process can offer the benefits of improved productivity, lower production costs and cost per part, increased flexibility and a simpler production process. In addition, the ability to run without coolant makes hard part machining the environmentally friendly method compared with more traditional grinding.

Sandvik Coromant continues to build on its expertise in the development of CBN and ceramic insert technology to support the growth of hard part machining, especially turning.

The CBN insert program now ranges from grades for tough, interrupted conditions, such as the CB7525, CB7025 and the soon-to-be-launched CB7035 grade, and, for continuous, stable conditions, grade CB7015. In addition, the company has a very competitive mixed ceramic grade, CC6050, which is a low-cost alternative for applications with moderate hardness and surface finish requirements.

Insert geometries also impact machining results and surface finish. The Wiper and Xcel geometries have been developed to meet most machining requirements and cutting strategies. The WH Wipers are the workhorses of hard part machining, offering increased productivity in combination with excellent surface and dimensional quality when compared with standard insert designs. If the component allows for it and has enough clearance towards the shoulder, the Xcel geometry option can provide outstanding productivity. Another alternative for profiling is the CoroTurn TR inserts, which ensure excellent stability. CoroTurn TR CBN inserts featuring a unique insert pocket for increased stability are soon to be introduced.

Safe-Lok Provides Machining Security
Security in any machining process is vital, not least in hard part machining. The Safe-Lok system for fixing the CBN tip to the carbide blank provides a combined brazed and mechanical interlock ensuring strength and reliability with a large cutting depth.

The fixing method supports improved resistance to mechanical and heat loads. This is then reflected in process security and reduced risk of overloading or losing the CBN tip. Thread turning, grooving and milling of hardened components is also possible, thanks to CBN inserts included in the Sandvik Coromant product program.

Reduced Costs Lead to Other Industries
In general, hard part machining has been developed to run without coolant, as the CBN and ceramics insert can tolerate high cutting temperatures, thus saving on coolant costs. Where the thermal stability of the workpiece needs to be ensured, the use of high-pressure coolant (up to 70 bar) together with an appropriate CBN insert may be used for improved chip control.

Hard part machining has already made considerable inroads in the automotive industry, where it is used in the manufacture of drivetrain components such as gears, crown wheel, pinions and shafts, but it has a potential application across many other industries – for example, in the production of bearings and transmission parts.

Originally published in Metalworking World 1.2011, a business magazine published by Sandvik Coromant.

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