Modern high-performance gearboxes generally require gear geometries specifically designed to meet the needs of special construction machinery applications. The gears are specially designed to improve the strength of the tooth root and reduce the meshing noise. The strength of the teeth is enhanced by changing the pressure angle or increasing the gear profile, and the meshing noise of the gears is reduced by increasing the contact ratio between the gears. In general, increasing the height of the teeth or the helix angle of the gear can achieve a greater contact ratio; Change the engagement angle or adjust the gear profile geometry to improve the root strength; Or increase the contact area and meshing between gears to reduce meshing noise.
Typically, the hobbing process is designed to conform to the shape geometry of the gear (for hard machining or direct application) and to optimize manufacturing costs. In order to obtain customized gears, it is necessary to customize standardized tool profiles, and these tools often wear out with the use process, which will inevitably affect the machining accuracy of the gears.
The effect of cutting load on tool profile wear is simulated by the gear, and the resulting wear phenomenon is shown to be correlated with tool life. Gear machining** software provides digital information such as cut length, chip thickness, clearance, as well as the angle of each individual point and the position generated by the engaged cutting edge. In addition, the maximum relative tool tip chip removal describes the deformation load in the rake tip area. The theory of one-dimensional load parameters does not fully explain the wear behavior of the tested gearbox. A characteristic feature of the hobbing process is the deviation from the chip thickness along the cutting edge, which can be up to 5 300 mm for a single slice, and the increase in the size of the cutting unit in the finite element simulation does not reduce the calculation time. A FEM simulation of the hobbing process is shown in Figure 1.
From the standard reference tool profile with a tip, the tip radius is ap0=02mn, mn is the normal modulus of the tool. Use a value of ap0,1=02mn for different tip radii ap0,2=03mn and ap0, 3=0The wear effects of 4mn were analyzed.
In cutting tests, increasing the tip radius will affect tool life. Depending on the tool life, the cutting speed of the horizontal feed also increases with the radius. Shift the tip radius from 02mn to 0The value of 4mn,VC increases by 7% to 30% depending on the framework conditions. When engaged, tip wear is more concentrated in the contours of the small tip radius in the rake tip area. The increase in tip radius is compared to tip wear in Figure 2.
The effect of tip radius on gear wear is related to slice deformation. In the gear hobbing process, the chip material flows through the rake face from the tip and side directions, and when the tip radius is small, the chip material flows between the two tooth faces, where the slice material is compressed and deformed; With a larger tip radius, the amount of deflection on the rake face is reduced, and the ratio of slice volume produced by this tip area is reduced, meaning that a tool with a larger tip radius will reduce the overall deformation load.
In the gear hobbing fast cutting simulation, this change in gear profile results in different wear effects when ap0,1=158 and ap0,2=208 are taken according to the boundary condition profile angles. In the finite element machining process, the change in the temperature of the front end of the tool when the chip is evacuated at a certain cutting arc is shown in Figure 3 (through the rake face direction**) The temperature increases, and the critical crescent of the tool with a larger profile angle wears faster and the cutting speed decreases by 5%.
Often, a larger profile angle results in an increase in the clearance angle of the gear flanks. Simulations show that the effective clearance angle increases from the starting tip radius to the maximum tip radius over the entire flank range. The actual simulated flank clearance angle is from 225° to 30°, when the flank angle increases, the larger cutting relief angle reduces the frictional load between the flank face of the tool and the workpiece material, so that the side wear of the tool slows down, see Figure 4.
In addition to the law of change in the clearance angle, when the profile angle is increased, the cutting length decreases, resulting in an increase in tool life. The estimated profile angle is increased from 158 to 258, and accordingly, the tool increases by 6% and 18% of the feed cutting speed.
The helix angle is a parameter determined by the geometric size of the workpiece, which has a great influence on the wear of the tool. Subject except for the helix angle of 25In addition to the standard gears of 8°, spur gears with a helix angle of 0° are also referenced.
In both cases, spur gears lead to reduced tool life, and correspondingly, crescent wear leads to wear of flank pad width, as shown in Figure 5.
Crescent wear appears earlier in the anterior wing area of the teeth. In addition, flank wear develops more quickly, and cutting the gear for the first time causes more wear.
Particular attention is paid to the extreme flank wear, which is mainly due to the reduction of helix angles in cut length (+32%) and chip thickness (+5%). After this, the slice volume also increases, and the total load in the tip area of the tool increases accordingly as the chip volume increases, reflecting the difference in the load on the rake face, as shown in Fig. 6 and Fig. 7.
When cutting the positive shaft horizontally, the speed is set to a low level (DVC10=8% 32%), and the cutting volume of gears and helical gears is relatively stable.
Through the process simulation, the following conclusions were drawn:
Changing the angle of the tool profile or gear helix during hobbing can cause a change in tool life.
Different wear mechanisms and changes in wear behavior during gear machining are modeled, and finite element simulation analysis enables tool profiles to be evaluated without the need for a second process simulation when machining new gears.
According to the evaluated design criteria for gear machining tools, the application of optimized gear hobbing tools and the selection of corresponding cutting parameters can reduce machining costs.