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Home >> Technical FAQs >> turning of camshafts with polycrystalline cbn inserts

 

turning of camshafts with polycrystalline cbn inserts

The camshaft controls the movement of the poppet valves in the engine. It has pairs of oblong-shaped lobes called cams. These cams protrude out of the shaft and they point in different directions. As the camshaft rotates, the cams press against the valves and open them. Camshafts are made of different types of materials such as grey cast iron, medium carbon steel and ductile iron. Camshafts made of medium carbon steel are strong and hard but machining them takes a longer time than other softer materials. Hence, they are usually used for low volume production.

Camshafts made of medium carbon steel usually contain chromium and other additives which make them hard to turn or mill. Camshafts are also difficult to machine because of the strict quality demands on the surface finish and dimensional accuracy. That is why polycrystalline cubic boron nitride cbn inserts are used with specially designed cutters to reduce the time required to complete the detailed machining process. Here are some details about the turning of the outer diameter of the round journal portion.

Turning of Journal Outer Diameter
The journal of the camshaft is the section in between each set of cams. The cutting data and tool inserts selected for turning these sections depends on the type of material to be machined. Hardened materials like FCD 600, the spheroidal graphite iron casting, also known as ductile iron, will require low cutting speed and a solid tool insert that can provide the desired hardness. Camshafts with materials such as FC 250 grey cast iron may be machined at a higher speed with tipped cutting inserts.

Journal Turning of FCD 600 Material
The ductile iron casting offers high tensile strength and its hardness ranges from 170 to 270 HB. Due to the hardness of this material, use the VNMG 160408 insert with a standard chip breaker. To turn the journal section of the camshaft, set the cutting speed to 158 m/min, the feed rate to 0.25 mm/rev, and the cutting depth to 1.0 mm. No coolant is required for this operation.

Journal Turning of S55C Material
This medium carbon steel material offers very high size accuracy and straightness, and it minimizes wear in high speed automotive applications. It has a hardness rating of 229 – 285 HB. When turning the journal section of camshafts made of S55C steel, use the DNMG 150408 polycrystalline cbn insert with a chip breaker that can stop the chips from wrapping and prolong the tool life. Set the cutting speed to 200 m/min, the feed rate to 0.2 mm/rev, and the cutting depth to 0.5 mm.

Journal Turning of FC 250 Material
FC 250 is a grey cast iron material that is softer than S55C and FCD 600, hence it can be machined at a higher speed without a chip breaker. Use the DNMA 150412 polycrystalline CBN insert which offers a tool life that is at least 1.5 times longer than ceramic grade CVD inserts. For this operation, set the cutting speed to 300 m/min, the feed rate could 0.15 mm/rev with a cutting depth of 0.5 to 1 mm.

Conclusion
Due to the shape of the camshaft, it is important to work at relatively low speeds to minimize vibration during turning. Pay close attention to the kind of material used to make the shaft when selecting cutting conditions and cbn inserts.

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