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double-sided face milling on camshafts using pcbn inserts

Milling of cams on camshafts poses a number of significant challenges. First, the cams are usually hardened to be able to withstand wear, heat and pressure. They also have stringent demands on the quality of surface finish which could sometimes be as high as 0.6 microns. The positional and dimensional accuracy must also be very high. That is why, in times past, after the initial hardening and grinding, the machining was a laborious manual process which required a high level of skill and experience. This process could take as long as two days to complete.

However, with the use of solid polycrystalline cbn inserts which are hardened and produced specially for milling of hardened camshaft material, it is now possible to complete the milling of the camshaft within a few hours. In addition, the use of specially designed cutters that have inserts arranged all around them make it easy to perform face milling and chamfering on the cams at the same time.

Basic Face Milling of Cams
A circular cutter with spaces for hundreds of solid square-shaped inserts is commonly used for multiple-face milling of cams. This type of cutter usually has a tapered spline cutter mounting system that makes it easy to mount and remove. During cutting, more than one cam may be machined simultaneously. Camshafts with two cams in each set may be machined with two cutters while those with three cams per set can machined with three cutters.

Basically, the cutting speed for this kind of milling ranges from 120 m/min to 250 m/min depending on the material and the type of cbn inserts used. The feed rate may be set to a value between 0.1 mm/tooth and 0.5 mm/tooth with the depth of cut set to 3 mm or less. Examples of polycrystalline cbn inserts used for this type of milling include: the SNGA, SNGW, CNGA, and CNGW 0903 series. These inserts have a zero degree clearance angle which is ideal for milling of hardened materials like grey cast iron and ductile iron. They also have solid edges which enhance the rigidity of the insert and the quality of the finished cam surface.

High Speed Milling of Camshafts
Although hardened materials like the S55C medium carbon steel usually require slow machining, it is possible to use polycrystalline cubic boron nitride (pcbn) inserts to mill the camshaft at a relatively rapid rate. For instance, a RNMN 090300 insert combined with an R220.70-0063-09-6 milling cutter can machine a camshaft rod, with a hardness of 60 HRc, at a cutting speed of 500 m/min and a feeding speed of 3300 mm/min. Thus, within one to two hours, the milling of the cam could be completed by an experienced machinist. Without the need to change or re-index the inserts, the milling operation can proceed continuously with very minimal human effort or interruption. This allows new cams to be produced efficiently. In addition, reconditioning and reproduction of existing cams can also be accomplished in very short time.

Conclusion
The quality and speed of milling that can be achieved with polycrystalline cbn inserts depends on the type of material, CNC machine, milling cutter, and the shape and grade of insert used. Machinists may combine the use of specially designed cutters with the toughest grade of insert to achieve high production efficiency.

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