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Vacuum Heat Treatment Process of Machine Tool Spindle
1 Principles of material selection for machine tool spindles
Spindle is one of the key parts of machine tool spindle components, which mainly plays the role of supporting transmission parts and transmitting torque. The reasonable selection of main shaft materials should follow the following principles:
1) The selection of materials should meet the performance requirements, which is the primary principle for the selection of materials for spindle parts. Since the main motion of the machine tool is provided by it, the motion accuracy of the spindle during operation will have a direct impact on the processing quality of the workpiece, so it must be ensured that the spindle has a good quality when working. High motion accuracy. The rotation accuracy of the spindle is not only affected by static factors such as the original machining accuracy and assembly accuracy of the spindle, but also by dynamic factors such as force deformation, motion pair wear, impact load, thermal deformation, and vibration during operation. . Therefore, the main shaft parts should not only ensure high original geometric accuracy, but also must ensure their mechanical properties such as stiffness, strength, wear resistance, impact resistance, thermal stability and vibration resistance, and these properties are closely related to the main shaft material. .
2) The selection of materials should meet the requirements of processing technology. Materials with good mechanical properties may not have good processing technology. Due to the requirements of high geometric accuracy, spindle parts often use multiple grinding processes. Although some non-ferrous metal alloy materials have The mechanical properties meet the requirements of use, but the grinding process is very poor, and it is almost impossible to use grinding methods to ensure the surface geometric quality requirements. These materials are naturally not suitable for use as spindle parts.
3) The selection of materials should meet the economic requirements. If the materials that meet the requirements of use have high costs of resource elements such as process costs, supply difficulties, and environmental damage, then the selection of such materials is obviously not in line with the requirements of market economy, environment and social development. Therefore, the selection of materials must meet the requirements of economic and social development.
4) The selection of materials should meet the habitual requirements of materials. In engineering practice, the materials that meet the requirements of usability, craftsmanship and economy are often not the only ones, which requires consideration of the habit of materials.
2 Material selection and vacuum heat treatment of the main shaft
The performance requirements of machine tool spindles with different work requirements are different, and the processing technology is also different, so the materials selected and the corresponding vacuum heat treatment process will also be different.
2.1 Material selection and vacuum heat treatment process of common machine tool spindle
Ordinary machine tools are often used for workpiece processing with general accuracy requirements. The spindle of the machine tool is usually supported by rolling bearings, and the journal that directly affects the rotation accuracy of the spindle has no direct motion wear. Therefore, according to the force characteristics of the spindle under alternating load when it is working, generally Select materials with better comprehensive mechanical properties.
2.1.1 Typical materials and vacuum heat treatment process
The most commonly used material for the spindle of ordinary machine tools is 45# structural steel or 40Cr medium carbon alloy steel. The vacuum heat treatment process generally adopts the overall surface vacuum quenching or overall quenching and tempering. Conventional vacuum heat treatment process for low temperature tempering. According to needs, the hardness can generally be controlled in 3 states such as 42~47HRC, 45~50HRC or 48~53HRC.
In engineering practice, sometimes in order to obtain better wear resistance, the surface hardness should be increased, usually 50#, 55#, 50Cr, 65Mn and other structural steels with high carbon content are selected. The hardness of the low temperature tempering after vacuum quenching Up to 52~57HRC.
2.2 Material selection and vacuum heat treatment process of precision machine tool spindle
The precision of the workpiece processed on the precision machine tool is very high, so the precision of the spindle of the precision machine tool is higher. In order to improve the efficiency of the machine tool and reduce the cost of use, the working accuracy of the spindle is required to have lasting retention. Therefore, in the process of In the design of spindle support, dynamic pressure, static pressure or dynamic and static pressure sliding bearings with high centering accuracy are often used.
2.2.1 Typical materials and vacuum heat treatment process
1) 38CrMoA1A vacuum heat treatment process: vacuum annealing → quenching and tempering → high temperature stress relief → vacuum nitriding. Vacuum annealing: fully annealed to eliminate forging stress, before cutting;
Quenching and tempering: 930°C*3h oil or water cooling, 650°C*5~6h high temperature tempering, HB265~295, metallographic inspection, the ferrite content at 10 mm from the surface is less than 5%, before the outer circle finishing;
High temperature stress relief: 630℃*5h furnace cooling, 350℃ air cooling, to eliminate the residual stress caused by cutting, after rough grinding the outer circle; vacuum nitriding: 500℃ ~ 520℃*5 h + 550℃ ~ 560 ℃*25 h two-stage nitriding, the depth of the nitrided layer is not less than 0.45 mm, the hardness is more than 950HV, the embrittlement is not more than 2 grades, and it is carried out before the cylindrical fine grinding.
2) 9Mn2V. Vacuum heat treatment process: spheroidizing annealing → quenching and tempering → intermediate frequency quenching → artificial aging.
Spheroidizing annealing: 760℃*4h or 690℃*6h, spheroidization grade 1.5~5, network grade 1~3, before cutting; quenching and tempering: 800℃*3h oil cooling, 630℃~650℃ High temperature tempering, HB250±30, before the outer circle finishing;
Intermediate frequency quenching: 2500 cycles of continuous heating and cooling, straightening when there is obvious deformation, water cooling at 850 °C, undercooling less than 5 mm, hardened layer 3~5 mm, low temperature tempering at 180 °C * 8 h, after outer circle finishing ;
Artificial aging: 160 ℃ * 12~24 h, before cylindrical fine grinding.
Selection of vacuum heat treatment equipment: RVA series vacuum annealing furnace produced by SIMUWU is a high-quality product for vacuum heat treatment process. Good temperature control accuracy and temperature control uniformity ensure the effective progress of the vacuum heat treatment process. SIMUWU specializes in the manufacture of vacuum furnaces, has more than ten years of relevant experience, and has a good reputation in the field of vacuum furnace manufacturing. The product line includes vacuum air quenching furnace, vacuum oil quenching furnace, vacuum brazing furnace, etc., which are widely sold in developed and developing countries.
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