Hard Turning quenched parts CBN inserts realized turning instead of grinding
With the development of modern technology, more and more high hardness quenched parts appear in the processing site. At first, many people choose grinding as the last process to make sure the dimension and precision of the quenched parts. But as cutting tools industry continuous research and practice, it finally researched cutting tools which can use turning instead of grinding-Carbide alloy inserts, Ceramic Cutting Tools and Cubic Boron Nitride inserts.
The following will introduce turning instead of grinding process and what machining occasion can use turning instead of grinding process.
Part 1 The meaning of turning instead of grinding process and machining technology
Turning instead of grinding process is using turning process as finishing process or the last process instead of grinding process to make sure the dimension and precision required by the drawings.
When the quenched parts appear, grinding is the main process, grinding process can make sure the dimension of the quenched parts, especially for precision requirement.For example, shaft hardened parts process:Turning–Heat-treatment-Grinding. But with the hardened parts mass production and the appearance of more large and complex hardened parts, the processing efficiency is very low for grinding.Large scale quenched parts has large deformation and allowance after heat-treatment.Grinding process just can small allowance grinding, and we can’t find corresponding grinder when machining complex quenched parts. We finally researched cutting tools which can realize turning instead of grinding through cutting tools industry continuous research and practices. They are carbide alloy inserts, ceramic cutting tools and cubic boron nitride inserts.
Above three kinds cutting tools, carbide alloy inserts is the first one to be researched,and it is the main cutting tools for machine manufacturers. Second is ceramic cutting tools and cubic boron nitride inserts. Quenched parts which is through heat-treatment has high hardness and well wear-resistance. And it need consider cutting tools hardness,wear-resistance and impact roughness when choose inserts materials.
Compared above three kinds cutting tools,
According to hardness,cbn inserts＞ceramic cutting tools＞carbide alloy inserts，According to toughness：cbn inserts＞carbide alloy inserts＞ceramic cutting tools.
We can see that it has most advantages when CBN inserts machining quenched parts.
Part 2 Processing Status of choosing turning instead of grinding process
In current times, we have realized turning instead of grinding process, but turning process can’t absolute instead grinding process to turning quenched parts. For example, when it required high precision, we can choose grinding process to machining quenched parts, so what processing status can choose turning instead of grinding? We will analysis as follows:
(1) When machining complex surface on the CNC machine, turning instead of grinding process can reduce 1/3～2/3 labors, and it also can assure high position accuracy.
(2) The inner hole which shape is complex. For example, if using grinding process, the shape of the grinding wheel will be required complex, sometimes it can’t use grinding, so it will be better with turning process.
(3)When Several surface of one parts (Cylindrical, bore, face, stage sets, trench) all need grinding, we can use turning process, only need one process finish it which can subtract grinding tooling.
(4) It can be easily deformed when the quenched parts after heat-treatment and the small allowance will easily lead to waste, so it need large allowance, After heat-treatment, we can use superhard cutting tools cut large allowance and use grinding to reduce the waste rate which caused by large deformation. we can choose CBN inserts with good toughness large allowance hard turning work piece.
(5) When machining Surface high-frequency parts with large processing load variation, we can choose superhard cutting tools ,the work piece surface Organization and physical and mechanical properties of the work piece surface will be better than use grinding process, and it also can extend the work piece lifetime.
Part 3 The cutting tools materials of turning quenched parts instead of grinding
We have introduced three kinds cutting tools materials which can use turning instead of grinding: carbide alloy cutting tools, ceramic cutting tools and cubic boron nitride inserts, and already analysis from hardness and toughness. CBN inserts is the most suitable cutting tools for machining quenched parts. Because high hardness of quenched parts through heat-treatment, quenched parts belongs to difficult to machine aterials, and we can divide suitable machining range depend on different hardness.
Carbide Alloy Cutting Tools: It only suit for machining quenched which hardness below HRC45 because of its low hardness. And the processing effect is well when low speed machining parts.
Ceramic Cutting Tools: As we all know, Large Brittleness is the disadvantage of the ceramic cutting tools, and it only suit for machining small allowance quenched parts which hardness is between HRC45 and HRC55, and it need avoid interrupt turning.
Cubic Boron Nitride Inserts: It has high hardness and wear-resistance and well impact resistance, so it suit for machining quenched parts which hardness above HRC45. Especially Halnn superhard researched non-metal adhesive BN-S20 grade CBN inserts, not only can large allowance turning quenched parts, but also can interrupt turning,solved the problems which traditional CBN inserts can’t rough machining and interrupt turning.
Halnn is one of Chinese national tool brand enterprise which include CBN inserts design, producing, technology and service. And Halnn cutting tools can high efficiency machining high hardness materials in different machining industry. And it is widely used for high hardness materials, high hardness work piece after heat-treatment, and other difficult to machining materials parts field. Since established, Halnn already built long terms cooperation with many machinist manufacturers and cutting tools have covered 90% market in high-speed and high-hardness turning field in China.
The following will introduce the cutting parameters of Halnn superhard non-metal adhesive BN-S20 grade CBN inserts
Part 4 The cutting parameter of Halnn superhard non-metal adhesive BN-S20 grade CBN inserts
Linear speed: Higher the work piece hardness, lower the cutting speed . When hard turning quenched parts with BN-S20 grade CBN inserts, the cutting speed which the inserts can bear are 80~200 m/min, and the common range are 90~150 m/min; when with large allowance or heavy interrupt turning,the linear speed need keep 50~100 m/min.
Cutting Depth: When turning hardened parts instead of grinding, the cutting depth usually is 0.1~0.3. When large allowance machining workpiece, BN-S20 grade CBN inserts can bear about 7mm cutting depth and one step finished.
Feeding Rate: The feeding rate usually can be chosen between 0.05 and 0.25m/r, the data details depend on the roughness and the producing rate. When the roughness required Ra=0.3~0.4µm,use CBN Inserts instead of finish grinding .Turning will be economic than grinding because of high processing efficiency.
Part 5 Conclusion
With the development of turning instead of grinding process, it has helped manufacturers solve many difficult machining problems, and with the constant development of modern technology, it will appear more and more high hardness difficult to machine materials. For cutting tools industry, we only continue Innovation, research new high hardness, high quality and high efficiency cutting tools materials to satisfy the customer requirement.
