Turning technology and tool selection for superhard material HRC45\HRC58~68
With the continuous development of the manufacturing industry, the world's machine tool manufacturers have been seeking new technologies to reduce the production costs of machined parts and finished products. This makes ultra-hard turning a new processing technology that is currently of concern to various manufacturers. It is expected that in the near future, ultra-hard turning technology will develop more mature and be widely used.
I. Superhard turning technology
Ultra-hard turning is defined as the machining process for turning workpieces with high hardness materials above HRC45. Generally, the hardness of the workpiece material can reach the range of HRC 58-68, and the material of the cutting tool is basically CBN (cubic boron nitride).
Ultra-hard turning technology offers a new option for machining that does not require ultra-high precision grinding. Of course, some of the high precision requirements of the workpiece, the workpiece easily deformable and the special requirements of the workpiece, the grinding process is more suitable choice. Although ultra-hard turning is not a complete replacement for ultra-high precision grinding, it has been able to replace a considerable part of precision grinding, which has reduced the expensive production costs in the grinding manufacturing process. At present, the surface roughness of workpieces with superhard cutting is generally Ra0.2～Ra0.4, the roundness can reach 0.0005mm, and the dimensional accuracy can be controlled within 0.003mm. After turning, it was found that the ultra-hard turning process is 4 to 6 times more efficient than the general grinding process.
Turning a hard part of the HRC62 without the use of turning fluid cooling will generate a lot of heat. In general ultra-hard turning, the temperature in the turning point area can be as high as 926 °C.
In fact, local high temperature heating can help the completion of the turning process. The high heat of the turning point of the tool pre-anneals and softens the turning layer of the workpiece, making the workpiece easier to turn.
During this turning process, most of the heat is generated by the peeling of the chips. In order to obtain a beautiful surface finish quality, the turning depth should be reduced as much as possible during the last turning, generally within 0.25 mm.
Current ultra-hard turning has been widely used in the manufacture of automotive parts. Shanghai Automotive Gear Factory has been very successful in applying this technology to mass production. They use the turning instead of grinding after the carburizing and quenching of the gears to carry out the final precision machining of the finished product. Part design tolerances and surface finish requirements can be achieved. The surface roughness of the workpiece to be machined can reach Ra0.2～Ra0.4, the roundness can reach 0.0005 mm, and the tolerance band of 0.003 mm can reach 1.67.
Turning a hard part of the HRC62 without the use of turning fluid cooling will generate a lot of heat. In general ultra-hard turning, the temperature in the turning point area can be as high as 926 °C.
In fact, local high temperature heating can help the completion of the turning process. The high heat of the turning point of the tool pre-anneals and softens the turning layer of the workpiece, making the workpiece easier to turn.
During this turning process, most of the heat is generated by the peeling of the chips. In order to obtain a beautiful surface finish quality, the turning depth should be reduced as much as possible during the last turning, generally within 0.25 mm.
Current ultra-hard turning has been widely used in the manufacture of automotive parts. Shanghai Automotive Gear Factory has been very successful in applying this technology to mass production. They use the turning instead of grinding after the carburizing and quenching of the gears to carry out the final precision machining of the finished product. Part design tolerances and surface finish requirements can be achieved. The surface roughness of the workpiece to be machined can reach Ra0.2～Ra0.4, the roundness can reach 0.0005 mm, and the tolerance band of 0.003 mm can reach 1.67.
Das gegenwärtige Ultrahartdrehen ist bei der Herstellung von Kraftfahrzeugteilen weit verbreitet. Die Shanghai Automotive Gear Factory hat diese Technologie sehr erfolgreich in der Massenproduktion eingesetzt. Sie verwenden das Drehen anstelle des Schleifens nach dem Aufkohlen und Abschrecken der Zahnräder, um die endgültige Präzisionsbearbeitung des fertigen Produkts durchzuführen. Teiledesigntoleranzen und Oberflächenanforderungen können erreicht werden. Die Oberflächenrauheit des zu bearbeitenden Werkstücks kann Ra0,2 ～ Ra0,4 erreichen, die Rundheit kann 0,0005 mm erreichen und das Toleranzband von 0,003 mm kann 1,67 erreichen.
II. Continuous processing stability
An important sign of turning hard materials is to ensure the stability of continuous processing. This is related to the overall dynamic rigidity of the machine tool, the turning tool, and the heat treatment state of the workpiece.
The main part of the bed is filled with a polymer (artificial marble) to increase its damping coefficient (generally 8 times that of a cast iron bed). At the same time, the combination of linear rolling guides will have a huge impact on the turning process of super-hard materials, and greatly reduce the vibration caused by turning, and increase the time for rapid return to static rigidity. The test results show that the improvement of the machine tool effectively suppresses the chipping of the tool caused by the vibration of the machine tool and prolongs the service life of the tool. The accuracy of the workpiece to be machined is greatly improved, the dispersion of the tolerance zone is reduced, and the surface quality of the workpiece is improved.
Another important factor in machine tools is the performance and accuracy of the integration of the various moving axes. Including machine tool accuracy, geometric accuracy, electronic control functions, error compensation, and general adjustment and thermal deformation effects. This is because the final machining result of the workpiece is completely determined by the performance and accuracy of the machine.
Usually used in the roughing of the car, the turning depth is greater than 0.25mm; The CBN knife is used in the finishing of the car, and the turning depth is less than 0.25mm.
In order to achieve the desired effect of turning of superhard materials, it is also necessary to control the heat treatment state of the workpiece. Generally, the quenching hardness change requirement is less than 2 points between HRC. If the workpiece is a carburized part, the consistency of the depth of the carburized layer is also controlled. Generally, the depth should be controlled within 0.8 to 1.2 mm.
III. Advantages of turning hard materials
Compared to the grinding process, turning of superhard materials has the following advantages:
1. Both “soft turning” and ultra-hard turning can be performed on one lathe. One machine tool is equivalent to two machine tools, which saves space in the factory and reduces the capital investment in purchasing machine tools.
Usually used in the roughing of the car, the turning depth is greater than 0.25mm; The CBN knife is used in the finishing of the car, and the turning depth is less than 0.25mm.
In order to achieve the desired effect of turning of superhard materials, it is also necessary to control the heat treatment state of the workpiece. Generally, the quenching hardness change requirement is less than 2 points between HRC. If the workpiece is a carburized part, the consistency of the depth of the carburized layer is also controlled. Generally, the depth should be controlled within 0.8 to 1.2 mm.
III. Advantages of turning hard materials
Compared to the grinding process, turning of superhard materials has the following advantages:
1. Both “soft turning” and ultra-hard turning can be performed on one lathe. One machine tool is equivalent to two machine tools, which saves space in the factory and reduces the capital investment in purchasing machine tools.
3. In the super-hard turning process, the workpiece with complex shape can be processed by the single-point turning feature of the turning tool. The grinding machine can only grind complex workpieces with a shaped grinding wheel;
4, One program setting can complete multiple turning operations, saving time for workpiece handling and re-installation, and reducing workpiece damage;
5, super-hard turning can easily reach the surface roughness of Ra0.2 ~ Ra0.4;
6, super-hard turning lathe can adapt to different specifications of the workpiece, especially the mold industry. Satisfy the processing of different batches and complex workpieces;
7. The chips for super-hard turning are easier to handle than the grinding chips and meet the environmental protection requirements;
8. Tool inventory costs are low.
Turning superhard is a practical technology to provide good economic and better quality of work, especially in the economic benefits of high dynamic stiffness of the machine becomes more apparent. The ultra-hard turning process is not much different from the general turning process. Most manufacturers can introduce this new technology and apply it to actual production.
Looking forward to the future, with the continuous improvement of turning technology and machine tool performance, the new technology of ultra-hard turning will gradually become perfect and more widely used.
