Cermet inserts can't quite replace the coated carbide inserts in heavy roughing operations with interrupted cuts, but in semifinishing and finishing cermet inserts outperform carbide. They permit a higher surface speed while maintaining an acceptable surface finish with good tolerance holding property and increased tool life. Because the cermet surface is slick it presents less friction to the chip flowing over the cutting edge which decreases the possibility of build-up when machining high alloy steels and cold-formed, low-carbon steels. Cermet inserts are available from several suppliers with a wide selection of pressed-in chipbreaker configurations or ground-in chipbreakers.
The cermet inserts work at surface speeds from 100 to 1000 sfpm. On multi-spindle-automatics, positive inserts made of cermets avoid build-up encountered when running carbide inserts with low surface speeds. Also cratering is reduced due to the low heat transfer properties of the cermet material.
The recommended cutting speed for turning unalloyed steel with approximately 200 HB is 250 to 800 sfpm with 0.002" to 0.015" fpr and depth of cut of 0.004" to 0.150". Alloy steels up to hardness of 300 HB will have satisfactory tool life when machined between 200 and 600 sfpm with the depth of cut and feedrate mentioned above.
Face milling with cermet inserts can be achieved with the same cutting speeds as turning with chip loads per insert from 0.002" to 0.12". Milling is performed dry, while turning can be dry or with coolants.
Up to the present, cermets are widely used in Japan with good results in reducing machining costs. They deserve a greater consideration for material removal in the United States.
COPYRIGHT 1989 Gardner Publications, Inc.
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