Machining of crankshaft connecting rod hole of the

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Machining of connecting rod hole of diesel engine crankshaft

the small end of connecting rod of diesel engine crankshaft is embedded in the connecting rod with tin bronze or copper based powder metallurgy sliding bearing sleeve, and then the workpiece surface is obtained through rough boring and fine boring machining. The connecting rod small end hole of Bengbu diesel engine factory is shown in Figure 1, and the disk test is required). The dimensional accuracy of the parts is 35h7, and the surface roughness is within Ra0.8 M. previously, this requirement can be met when using tin bronze bearing sleeve. However, after changing a certain copper based powder metallurgy material, the surface roughness accuracy of the parts can not meet the requirements, and there are vibration marks on the surface, and the chips are in the form of collapse. The extrusion method has been tried, which not only adds a process, but also the processed surface roughness is not ideal

figure 1

the factory's original tool: the material is YG6 (or yt30), the main and auxiliary deflection angles are 45 °, and the front angle in the cutting depth profile γ P=3 °, small back angle 5 °~ 7 °, large back angle 8 °~ 10 °, tip width 0.15 ~ 0.2mm, rake face roughness value Ra0.8 m, rake face roughness value Ra0.4 M. The surface quality of the machined parts is as above, and the tool wear is fast, so the dimensional accuracy of the parts cannot be maintained for a long time. Zero Zhong Huaining said, "1. Strengthen the standard training and promote the roughness of the surface of the penetration parts, which is composed of theoretical roughness and roughness caused by abnormal reasons. Theoretical roughness refers to the surface roughness caused by tool geometry and cutting motion; roughness caused by abnormal reasons refers to the surface roughness caused by chip accretion, scale, vibration, friction, uneven cutting edge, chip scratch and other factors in the processing process (Figure 2)

figure 2

for theoretical roughness, it is known through calculation that when the arc radius of the tool tip is r ε= When 0, the arithmetic mean deviation of contour RA is

when R ε When ≠ 0, the arithmetic mean deviation Ra of the contour is

for the roughness caused by abnormal reasons, we believe that the machining of this workpiece is mainly caused by vibration, friction, uneven cutting edge and other factors

cutting vibration has two types: forced vibration and self-excited vibration: forced vibration is caused by external periodic forces, such as the instability of machine tool movement, including the radial runout of the spindle, the centrifugal force caused by installation error, uneven workpiece material, intermittent chip and chip chipping, etc. Self excited vibration is caused by the change of force in the cutting process, such as the change of friction between chips and tools. In this processing, we believe that the vibration is mainly caused by chip breaking, the change of friction between chip and tool, the force generated by tool wear, and the cutting depth resistance FY

after the above analysis, we adopt the following methods to improve the cutting condition of the tool:

1) according to the theoretical analysis, increase the arc radius r of the tool tip ε It can reduce the theoretical roughness value and increase the arc radius of the tool tip to R ε= 0.3mm。

2) for vibration, reduce the cutting edge arc radius R β、 Increase front corner γ P improve the sharpness of the tool, change the chip type, reduce the cutting depth resistance FY, and reduce the vibration (Fig. 3). The main deflection angle and auxiliary deflection angle are not moved for the time being

figure the production of plastic processing enterprises above the scope of our country has reached 61.886 million tons 3

3) wear resistant tool materials are selected to improve the wear resistance and dimensional stability of tools. The selected tool material is pcd002

4) improve the grinding quality of the front and rear blade surfaces. The surface roughness value of the rear blade surface is ≤ 0.1 M, and the front blade surface is a grinding mirror. Make the cutting edge more flat, reduce the change of friction between chips and tools, and the force generated by tool wear

5) reduce the back angle appropriately, so that the CD part of the back cutter surface (Fig. 3) can be ironed with the workpiece surface to obtain a smaller roughness value on the workpiece surface

the improved tool: the material is pcd002, the main and auxiliary deflection angles are 45 °, and the front angle in the cutting depth profile γ P=8 °, small back angle 6 °, large back angle 12 °, tool tip arc radius γε= 0.3mm, the front knife surface is a grinding mirror, and the roughness value of the rear knife surface is within ra0.1 M

after use, the chip has changed from broken to about 3mm long strip and knot, the surface vibration pattern disappears, and the machined part surface roughness value is 0.68 ~ 0.73 m, which meets the requirements of the drawing, and the tool can maintain the dimensional accuracy of the part for a long time, and the tool life reaches tens of thousands of pieces

further clamp the standard tensile specimen on the hydraulic universal testing machine. Improvement measures: there are spiral knife marks on the machined surface. After analysis, it is found that the theoretical roughness, the main deflection angle can be changed to 90 °, and the secondary deflection angle can be changed to 2 ° ~ 3 °, so as to further eliminate the vibration and the residual area height caused by the theoretical roughness. (end)

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