Gear steel refers to the general name of the steel used for processing and manufacturing gear.
Commonly used gear steels are
- Low carbon steel such as 20# steel,
- Low carbon alloy steel such as: 20Cr, 20CrMnTi, etc.
- Medium carbon steel: 35# steel, 45# steel, etc.,
- Medium carbon alloy steel: 40Cr, 42CrMo, 35CrMo, etc
The above can be called gear steel. Gear steel after carburizing quenching generally in the Rockwell hardness of 58-62 degrees.
This article mainly shares the CBN tool for hard turning gear steel.
Gear steel properties
Hardenability is one of the important performance indicators of gear steel, which is mainly to ensure the hardness of the core of different sizes of gears, and is conducive to controlling the deformation of gear heat treatment.
42CrMo gear steel has the characteristics of high strength, high hardenability, good toughness, small deformation during quenching, high creep strength and lasting strength at high temperature, etc. Common fields: large gear for locomotive traction, supercharger transmission gear, pressure vessel gear, rear shaft, rod and spring clamp with great load.
20CrMnTiH is a good performance of carburized steel, high hardenability, after carburizing and quenching with a hard and wear-resistant surface and tough core. It has high low temperature impact toughness, medium weldability, good machinability after normalizing, common fields: gear, tooth ring, gear shaft cross and so on.
Carburizing and quenching process
Carburizing and quenching is a common heat treatment process for metal materials, which can make the surface of the carburized workpiece obtain high hardness and improve its wear resistance. The traditional process mainly includes: low temperature tempering, pre-cooling direct quenching, one-time heating quenching, carburizing high temperature tempering, secondary quenching cold treatment, induction heating after carburizing and other processes.
Quenching technology has been widely used in modern machinery manufacturing industry. Important parts of machinery, especially steel parts used in automobiles, aircraft and rockets, are almost all quenched. In order to meet the different technical requirements of various parts, various quenching processes have been developed.
The processing difficulties of carburized and quenched gear steel
(1) The surface hardness of gear steel parts after carburizing and quenching is high and difficult to process, some enterprises use grinding technology, but the grinding process requires skilled workers to operate, and it is easy to appear waste products, and the grinding efficiency is low, affecting the production efficiency;
(2) The use of advanced carburized gear to replace the grinding process, but do not understand the turning tool material, choose traditional carbide tools, especially the use of CNC lathe processing, there will be severe wear on the first, the same affect production efficiency, and the cost has not been effectively reduced;
(3) Some carburized gears have intermittent conditions. If the end face has oil hole group holes, or the inner hole part has a keyway, etc., it is intermittent cutting. This kind of situation requires higher performance of the tool, not only better wear resistance, but also stronger impact toughness.
Tool material for processing carburized quenched gear steel
The turning tool can be replaced by grinding with carbide cutting tools, ceramic cutting tools and PCBN cutting tools, carbide cutting tools because of its low hardness, not suitable for turning carburized gear, can be replaced by grinding hard turning gear steel processing only ceramic cutting tools and PCBN cutting tools.
Ceramic tools and PCBN tools can be hard turning carburized gear, but the ceramic knife has limitations, that is not suitable for intermittent cutting, can only be used for continuous cutting conditions in the finishing process, such as intermittent conditions are easy to break the knife. Therefore, in continuous cutting conditions, users can choose the appropriate tool material according to the actual processing situation.
If the carburized gear encounters intermittent working conditions, or in the case of a slightly larger margin, the PCBN tool is the best choice. Such as China’s Valin super hard, in the field of intermittent cutting carburized gear has a very good tool grade – BN-H21 grade, intermittent cutting carburized gear effect is good.
PCBN tools for hard turning gear steel – continuous turning
The CBN tool for continuous hard turning gear steel is BN-H05 or BN-H10, aiming at the rapid development of the automotive industry and the upgrading of the tool performance technology, in order to further improve the processing efficiency, Valin has also developed and launched the coated CBN blade for continuous hard turning gear steel workpiece.
PCBN tool for hard turning gear steel – intermittent turning
The CBN tool for intermittent hard turning gear steel is BN-H10 or BN-H21, aiming at the rapid development of the automotive industry and the upgrading of the tool performance technology, in order to further improve the processing efficiency, Valin has also developed and launched the coated CBN blade for continuous hard turning gear steel workpiece.
The CBN tool of roughing gear steel is BN-S20, which can fill the whole blade and improve the roughing efficiency from the parameters of cutting depth and cutting speed.
When selecting CBN tool for hard turning gear steel, it is necessary to select the appropriate brand according to continuous and intermittent, coarse and fine turning conditions, so as to achieve the goal of increasing efficiency and reducing cost.
The hardness of carburized gear steel parts is high, for the process parts that cannot be turned, it is necessary to choose the appropriate Valin CBN grinding wheel to grind, and the Valin diamond roller for CBN grinding wheel dressing.