Abstract
The common principles of axial gear shaving, the structure of gear shaving machines, and the crowned gear mechanism. It elaborates on a simple method for adjusting the taper, angle, and crowned amount of the machine tool based on the precision measurement report of the gear parts. Finally, specific examples are provided to demonstrate how to apply this method.
1. Introduction
Gear shaving is a precision processing method for gears. Common gear shaving machines can achieve both radial and axial gear shaving. For axial gear shaving, it is often necessary to adjust the taper, angle, and crowned gear mechanism of the gear shaving machine according to the precision measurement report of the parts to be processed. The determination of the adjustment amount can be calculated according to the formula given in the machine tool operation manual, but the calculation formula is relatively complex and inconvenient for use in the production site. This article introduces a simple and easy-to-use method for calculating the adjustment amount.
2. Gear Shaving and Crowned Gear Mechanism
2.1 Axial Gear Shaving Processing Principle
The principle of axial gear shaving processing. During the shaving process, the disc shaving cutter engages doubly with the gear to be shaved, and relative sliding occurs on the tooth surface due to the different speeds at the engagement points when freely rolling (i.e., the shaving cutter drives the gear to rotate), thereby realizing cutting processing. The shaving process is essentially a comprehensive process of extrusion and relative sliding.
Additionally, to shave crowned gears, the workbench of the gear shaving machine should also oscillate within its vertical plane.
2.2 Common Motion Axes of Gear Shaving Machines
Common motion axes of gear shaving machines include the Z-axis, X-axis, A-axis, and B-axis.
- Z-axis: Vertical direction, with the positive direction being upward. Its function is the axial feed motion of the tool rest slide.
- X-axis: Horizontal direction from left to right, with the positive direction being rightward. Its function is the axial feed motion of the workbench.
- A-axis: Tool rest rotary motion, used to adjust the axial intersection angle between the shaving cutter and the workpiece.
- B-axis (spindle): Rotary motion of the shaving cutter.
2.3 Crowned Gear Mechanism
The role of the crowned gear mechanism is to process a crowned amount along the tooth direction of the part. The common crowned gear mechanism of gear shaving machines adopts a four-bar linkage mechanism, with its moving slider as the driving part moving horizontally along the X-axis. The angle α between the crowned amount adjustment guide rail and the horizontal direction is used to adjust the size of the crowned amount. When α = 0°, a non-crowned gear is processed.
When the moving slider moves to the right. The dashed line indicates the state when the moving slider is at X = 0. When the moving slider 1 moves to the right, the workbench not only moves to the right but also rotates clockwise by an angle β. After rotation, at X = 0, a center distance deviation ΔZ is produced. When the center distance changes, the tooth thickness at the location of the workpiece becomes smaller, with the maximum tooth thickness at the center of the workpiece and decreasing towards the end face, thereby generating a crowned shape along the tooth direction.
When the moving slider moves to the left. Similarly, the dashed line indicates the state when the moving slider is at X = 0. When the moving slider 1 moves to the left, the workbench not only moves to the left but also rotates clockwise by an angle β. After rotation, at X = 0, a center distance deviation ΔZ is produced, resulting in a crowned shape along the tooth direction.
3. Adjustment of Gear Shaving Machines
3.1 Adjustment Operations
The adjustment of gear shaving machines mainly includes taper adjustment, angle adjustment, and crowned amount adjustment. The structure of the taper and crowned amount adjustment parts of common gear shaving machines.
- Taper Adjustment: Loosen the locking screw 1 first, then turn the square head 7, and read the value from the scale 2.
- Crowned Amount Adjustment: Loosen the locking screw 3 first, then turn the square head 5 to adjust the crowned amount.
- Angle Adjustment: On common gear shaving machines, simply tap the “A-axis” button on the operation panel to achieve adjustment (for older machines, loosen the locking screw and turn the square head to adjust).
3.2 Adjustment Calculations
The gear shaving machines in our company are mainly products of Chongqing Machine Tool Company and Nanjing No. 2 Machine Tool Company. For machines from the same manufacturer, the adjustment calculation formulas for different models within the same series are basically the same. This section specifically explains the representative YK4232 and Y4232CNC gear shaving machines.
- Taper Adjustment Calculation: For Chongqing Machine Tool YK4232 and Nanjing No. 2 Machine Tool Y4232CNC gear shaving machines, the taper adjustment calculation formula is H = (545ΔS) / (B sin α).Where:
- H is the adjustment amount of the taper mechanism (mm), which needs to be adjusted through the dial indicator.
- ΔS is the conical amount of the workpiece gear (mm).
- α is the pressure angle of the workpiece gear (°).
- B is the tooth width of the workpiece (mm).
- fHb左 and fHb右 are the helix tilt deviations of the left and right tooth surfaces in the precision measurement report (mm), respectively.
- Both fHb左 and fHb右 should be substituted as positive and negative values to determine the adjustment direction of the dial indicator based on the positive and negative values of H.
- Crowned Amount Adjustment Calculation: For Chongqing Machine Tool YK4232 and Nanjing No. 2 Machine Tool Y4232CNC gear shaving machines, the crowned amount adjustment calculation formula is tan γ = (2150ΔS) / (B² tan α).Where:
- γ is the rotational angle of the crowned gear mechanism (°).
- ΔS is the required crowned amount of the workpiece (mm).
- α is the pressure angle of the workpiece (°).
- B is the tooth width of the workpiece (mm).
- Angle Adjustment Calculation: For Chongqing Machine Tool YK4232 and Nanjing No. 2 Machine Tool Y4232CNC gear shaving machines, the angle adjustment calculation formula is A = tan⁻¹(F / B).Where:
- A is the rotation angle of the tool rest (°).
- F is the tooth direction error on the tooth width of the workpiece (mm).
- B is the tooth width of the workpiece (mm).
- P is the dial indicator swing amount (μm).
- Both fHb左 and fHb右 should be substituted as positive and negative values to determine the swing direction of the dial indicator based on the positive and negative values of P.
3.3 Calculation Example
A part is processed using a Chongqing Machine Tool YK4232 gear shaving machine. The precision measurement report shows the average values of fHb左 and fHb右 as -6.9μm and 13.2μm, respectively. Let’s calculate the adjustment amounts for taper and angle using the simplified formulas.
Taper Adjustment Calculation:
The simplified formula for taper adjustment is given by:
H = [(fHb左 + fHb右) / 2] × 80
Where fHb左 and fHb右 must be substituted as positive and negative values. Substituting the given values, we get:
H = [(-6.9μm + 13.2μm) / 2] × 80
H = [6.3μm / 2] × 80
H = 3.15μm × 80
H = 252μm
The positive value of H indicates the direction of adjustment on the dial indicator.
Angle Adjustment Calculation:
The simplified formula for angle adjustment is given by:
P = [(fHb左 – fHb右) / 2] × 10
Again, fHb左 and fHb右 must be substituted as positive and negative values. Substituting the given values, we get:
P = [(-6.9μm – 13.2μm) / 2] × 10
P = [-20.1μm / 2] × 10
P = -10.05μm × 10
P = -100.5μm
However, since we are dealing with practical adjustments, we can approximate this to:
P ≈ -100μm
The negative value of P indicates the direction of dial indicator swing.
In conclusion, for the Chongqing Machine Tool YK4232 gear shaving machine, the taper adjustment amount is 252μm, and the angle adjustment amount is -100μm. These calculations can guide the operator in making the necessary adjustments to achieve the desired gear accuracy.