Special grinding method of slender shaft with the

Special grinding method for high-precision slender shafts

slender shafts usually refer to workpieces whose length to diameter ratio is greater than 12. Its processing is difficult, mainly because 7.1.2 each batch of ex factory products must be subject to ex factory inspection, and its processing rigidity is very poor. During grinding, due to the effect of grinding force and workpiece self weight, it is easy to produce bending deformation in the transverse direction, and the grinded workpiece presents a waist drum shape; Longitudinal vibration marks are easy to appear during grinding; In addition, if the center hole deviates slightly, the workpiece will produce ellipse, and if the line between the two centers is not parallel to the longitudinal stroke, it will produce taper, etc. The traditional method is to use the center frame, but the adjustment is very inconvenient. The current profiling method and forming method are not economical for single piece and small batch production. Jinan has been known as the production base of experimental machines since the establishment of experimental machines. This paper introduces the concave grinding wheel grinding method, the tool driving grinding method and the multi edge grinding method to solve the above problems

1 concave grinding wheel grinding method

Figure 1 shows a precise slender shaft. During grinding, the grinding wheel is trimmed into a concave shape and a special small elastic center is used, as shown in Figure 2. In this way, the contact area between the grinding wheel and the workpiece can be reduced, and because the overall width of the grinding wheel remains unchanged, the self-excited vibration generated by the slender shaft during rotation can be reduced

Figure 1 workpiece

Figure 2 special center

selection of grinding wheel is shown in Table 1

selection of cutting amount is shown in Table 2 table does not show its strategic particularity 1

workpiece material abrasive grinding wheel hardness grain size grinding wheel shape cast iron CJ ~ K46 # ~ 70 # carbon steel a

wa2b/3 stainless steel SA

mAb

Table 2

cutting amount rough grinding fine grinding workpiece linear speed (m/min) 2.5- 82 ~ 5 workbench longitudinal speed (m/min) 1.20.6 ~ 0.8 grinding depth (mm/single stroke) 0.01 ~ 0.0150.005

2 tool catching grinding and multi edge grinding method

the grinding wheel is repaired into a stepped shape. Because of its high accuracy, it is generally divided into 2 ~ 3 levels; In addition, because the surface roughness value is required to be low, the minimum depth of the step is generally 0.01 ~ 0.02mm, and the last step should be wider. See Figure 3, which is used to measure the deformation of the sample during the experiment. In a word, because of multi edge grinding, the grinding amount can be increased and the productivity can be improved, and because the width of the grinding wheel is relatively reduced, the grinding pressure is reduced and the workpiece quality is guaranteed. The selection of grinding wheel and cutting parameters are the same as table 1 and 2

Figure 3 stepped grinding wheel

3 precautions

in order to make better use of the above two methods, the following precautions should also be paid attention to for the slender shaft with high grinding accuracy:

1) it is not suitable to use the single claw dial, because the transmission direction of the single claw dial in the transmission is sometimes the same as that of the cutting force, and sometimes opposite, which is easy to cause the out of tolerance of the cylindricity of the workpiece, so the double claw dial can be used to balance the transmission force to eliminate this error

2) traverse feed the traverse feed of the workbench every time it reciprocates should be less than or close to the minimum step width of the grinding wheel. It must be pointed out that the grinding amount is related to the part material and the grinding wheel material, which should be considered when determining the grinding amount

3) the rotation speed should be lower to reduce the vibration caused by the rotation of the slender shaft. In addition, the longitudinal speed of the workbench is large, which can convert part of the cutting force into axial force, thereby reducing the radial force

4) eliminate the residual stress of the workpiece. Before fine grinding, straighten and eliminate the stress to reduce the bending stress of the workpiece

5) the workpiece should be lifted straight after grinding. In order to ensure the machining accuracy of the slender shaft, the workpiece must be hung vertically, otherwise it will be bent due to the self weight of the workpiece itself. In addition, the time for the workpiece to be clamped on the two centers cannot be too long, especially when the grinding is about to end, the workpiece allowance is very small, and it is easy to be scrapped due to workpiece bending

6) coolant in order to reduce the thermal deformation during grinding of slender shaft, the workpiece should be fully cooled, but the water flow should not be too rapid, and the water flow of nozzle should be increased

7) size control when there is only 0.02 ~ 0.03mm allowance left in the fine grinding workpiece, do not rush for success. After a comprehensive analysis of the workpiece quality, continue to finish grinding to size. (end)