Method for precisely evaluating the grinding amount of the tooth surface of a disc gear after heat treatment

Abstract

This invention discloses a method for accurately evaluating the grinding amount of disc gear teeth after heat treatment. Through a comprehensive study of the main deformation indicators of the gear after heat treatment, especially those highly correlated with the grinding amount along the common normal, including diameter change and helix angle change, the intrinsic relationship between various deformation indicators and the grinding amount of the gear teeth is revealed. This leads to a calculation formula for the grinding amount of the gear teeth after heat treatment, providing a scientific basis for gear design, gear manufacturing, heat treatment process development, post-heat deformation quality assessment, and subsequent processing plan formulation. Although many factors affect the final grinding amount of the gear due to heat treatment deformation, the influence of other factors is relatively small; and diameter measurement is relatively easy at the heat treatment site. This application calculates Δ by measuring the diameter change of the gear before and after heat treatment. Wd The method of adding / subtracting correction amount to the pre-reserved grinding allowance for gear hobbing to evaluate the actual grinding amount is simple, accurate, and more operable.

Description

Technical Field

[0001] This invention relates to gear machining, and more particularly to a method for accurately evaluating the amount of grinding on the tooth surface of a disc gear after heat treatment such as carburizing and quenching. Background Technology

[0002] In gear manufacturing, the teeth are first machined, then heat-treated (commonly carburizing and quenching depending on the material), and finally finished. After heat treatment (carburizing and quenching), the machined gears undergo deformation. For disc gears (gears with a diameter-to-thickness ratio ≥2, including spur gears, spiral gears, and bevel gears), the deformation mainly includes expansion and contraction of the addendum circle diameter, changes in tooth direction, changes in tooth profile, and circumferential warping of the rim end face. Their characterizing parameters mainly include changes in addendum circle diameter, helix angle, pressure angle, taper, ellipticity, and circumferential runout of the rim. For disc gears that require grinding after heat treatment, these deformations are ultimately reflected in the amount of tooth surface grinding. Tooth surface grinding is a comprehensive reflection of relevant deformation indicators and is the most fundamental indicator. The quality of deformation control during heat treatment will ultimately be reflected in the actual amount of tooth surface grinding. In other words, the main purpose of deformation control is to ensure that the actual amount of tooth surface grinding is uniform and appropriate.

[0003] In actual production, due to the different deformation locations of the disc gear workpiece after heat treatment, the grinding amount of each gear tooth and different parts of each tooth varies in the final process—grinding. Some positions require more grinding, some require less, and some positions even have no grinding amount, resulting in the scrapping of the gear. Furthermore, the effective hardened layer depth and surface hardness remaining after grinding in positions with a large grinding amount may be lower than the drawing requirements, resulting in a higher scrap rate and increasing the processing cost of the gear.

[0004] If the grinding amount of the gear teeth can be accurately assessed after heat treatment, and remedial measures can be taken in time for gears that do not meet the requirements (such as reverse deformation treatment, straightening, press quenching correction, etc.), and scrap gears without grinding amount can be picked out in time and no further processing can be carried out, then the gear processing cost can be greatly reduced and the scrap rate can be reduced. Summary of the Invention

[0005] The purpose of this invention is to provide a method for accurately evaluating the grinding amount of disc gear tooth surfaces based on the deformation index of gears after heat treatment. By using the method of this invention to predict the maximum and minimum grinding amount of the gear tooth surface after heat treatment and the actual effective hardened layer depth of the tooth surface after grinding, the effective hardened layer depth of the drawings, the grinding allowance of the tooth surface during hobbing, and the target effective hardened layer depth during carburizing and quenching can be determined more reasonably during design, process preparation, and post-heat treatment quality inspection, thus providing guidance for subsequent production.

[0006] To achieve the above objectives, the present invention can adopt the following technical solutions: The method for accurately evaluating the grinding amount of disc gear teeth after heat treatment, as described in this invention, first sets the addendum circle diameter of the gear before carburizing to d, the tooth width to B, and the normal module to m. n The pressure angle is α, and the helix angle is β. The change in wear on one side of the gear due to the expansion and contraction of the tooth tip circle after heat treatment is calculated according to formula (1): (1) In the formula: Δ d This represents the expansion value of the tooth tip circle diameter; Maximum grinding amount Δ of gear tooth surface wmax and minimum grinding amount Δ wmin Then we can calculate according to equations (2) and (3) respectively: (2) (3) In the formula: W 预留 Allow for grinding allowance on one side of the common normal during gear hobbing; k is a coefficient related to the pressure angle. Generally speaking, the commonly used pressure angles for gears are 20° and 25°. When the pressure angle α = 20°, k is taken as 0.17; when the pressure angle α = 25°, k is taken as 0.21.

[0007] Δ dmax Δ dmin Let represent the maximum and minimum changes in diameter before and after heat treatment, respectively; positive values ​​are taken for increases and negative values ​​for decreases. C β This is the correction value for the effect of helix angle variation on grinding capacity; C represents the correction value for the impact of other comprehensive factors on grinding volume.

[0008] C β C is an empirical value, determined based on product characteristics and production conditions. Since the effect of the helix angle on wear is inconsistent along the tooth width direction, the influence of helix angle variation must be considered when calculating the maximum wear, and a correction value C must be added. β The effect of helix angle variation is not considered when calculating the minimum wear amount.

[0009] It should be noted that the evaluation method of this invention is more accurate when the circumferential runout of the wheel flange is ≤1.5mm. However, when the runout is greater than 1.5mm, the calculation error is relatively large, so caution should be exercised when using the evaluation method of this invention.

[0010] If the measured circumferential runout of the wheel rim is 0.5 mm, C β Taking 0.15 and C = 0.1 is more appropriate; if the end jump is small, C βThe value of C can be appropriately decreased, and vice versa. Similarly, the value will vary slightly depending on the workpiece and production conditions, and needs to be gradually optimized through practical experience.

[0011] It should be noted that the calculation method of this invention is suitable not only for disc gears but also for external gear rings. For internal gear rings, since the wear amount increases as the diameter decreases, the opposite is true for external gear rings. Therefore, the maximum wear amount should be calculated based on the minimum diameter, and the minimum wear amount should be calculated based on the maximum diameter.

[0012] The advantages of this invention are: The inventors of this application conducted a comprehensive study on the main deformation indicators of heat-treated gears, especially those with a high correlation to the grinding amount of the common normal. They revealed the intrinsic relationship between various deformation indicators and the grinding amount of the gear tooth surface, and thus obtained a calculation formula for the grinding amount of the gear tooth surface after heat treatment. This provides a scientific basis for gear design, gear manufacturing and heat treatment process planning, post-heat deformation quality assessment and subsequent processing scheme formulation.

[0013] Although many factors influence the final wear amount of gears due to heat treatment deformation, the changes in diameter and helix angle have a significant impact, while other factors have a smaller impact. Furthermore, diameter measurement is relatively easy at the heat treatment site, while other parameters are difficult or even impossible to measure. This application calculates Δ by measuring the diameter change of the gear before and after heat treatment. Wd The method of adding / subtracting correction amount to the pre-reserved grinding allowance for gear hobbing to evaluate the actual grinding amount is simple, accurate, and more operable. Attached Figure Description

[0014] Figure 1 This is a schematic diagram showing the relationship between the change in pitch circle diameter and the change in grinding amount.

[0015] Figure 2 This is a schematic diagram showing the relationship between the change in helix angle and the change in grinding volume.

[0016] Figure 3 This is a simplified diagram of the external gear ring. Detailed Implementation

[0017] The method of the present invention will be described in more detail below with specific examples to facilitate understanding by those skilled in the art.

[0018] Let the addendum circle diameter of the gear before carburizing be d, the tooth width be B, and the normal module be m. n The pressure angle is α, and the helix angle is β; the specific parameters of the experimental gear are shown in Table 1: Table 1 The material is 18CrNiMo7-6, and the heat treatment process is: carburizing - high temperature tempering - quenching - low temperature tempering.

[0019] 1. The effect of tooth tip circle expansion and contraction on grinding amount If the tooth tip circle diameter expands by Δ after heat treatment d (Take a positive value when expanding and a negative value when shrinking), so the expansion amount of the pitch circle diameter can be considered approximately Δ. d The original Δ below the pitch circle d / 2 portion moves outward to the pitch circle, that is, Δ below the pitch circle before expansion. d The tooth thickness at / 2 is the tooth thickness at the pitch circle after expansion, equivalent to an increase in the pitch circle tooth thickness, and vice versa. If we approximate the gear teeth as trapezoids, such as Figure 1 As shown, based on the geometric relationship of gear parameters, the change in unilateral wear Δ caused by the expansion and contraction of the tooth tip circle is... Wd It can be approximated by formula (1): (1) Measured diameter expansion Δ of the gear after heating d The value is 1.4 mm. Calculated according to formula (1), Δ Wd It is 0.24 mm.

[0020] 2. The effect of helix angle variation on grinding capacity Assuming the change in helix angle after heat treatment is Δ β ,according to Figure 2 The change in unilateral wear amount Δ caused by the change in helix angle can be calculated. Wβ : It is worth noting that increasing or decreasing the diameter or pressure angle will cause the common normal to increase or decrease, and correspondingly, the wear amount will also increase or decrease. However, the effect of the helix angle on the wear amount differs from that of the diameter. The effect of the helix angle on the wear amount is inconsistent along the tooth width direction. Figure 2 It can be seen that the grinding amount at one end is unaffected, while the grinding amount at the other end is significantly affected by Δ. Wβ Furthermore, regardless of whether the helix angle increases or decreases, the grinding amount increases. The larger the absolute value of the change in the helix angle, the more grinding amount needs to be reserved. Therefore, the change in the helix angle in the formula is taken as the absolute value.

[0021] Based on the practical experience of those skilled in the art, the helix angle of the test gear generally increases by about 3′ after heat treatment. According to the above formula, the wear amount of this type of gear increases by about 0.16 mm due to the change in helix angle.

[0022] 3. The influence of other deformations on grinding amount After heat treatment, the pressure angle of the test gear generally increases by about 5′, and the resulting change in the wear amount along the common normal is about 0.02 mm, which is negligible compared with the wear amount caused by changes in diameter or helix angle.

[0023] The effects of taper and ellipticity on wear amount are mainly reflected in their influence on diameter variation. Taper deformation and elliptic deformation will result in different diameters at different locations, thus leading to different wear amounts at different locations. Taper means that the diameters of the two end faces of the gear are different, while ellipticity means that the diameters of different parts of the circumference are different. Therefore, the wear amount variation calculated according to formula (1) actually reflects the effects of taper deformation and elliptic deformation.

[0024] The impact of gear warping on wear is complex. Gear warping is mainly manifested in the circumferential runout of the gear rim. Practice has shown that when the circumferential runout of the gear rim is small, the error in calculating wear using the above formula is smaller, and vice versa. This may be because circumferential warping alters the geometric relationship between the common normal length and other characterizing parameters.

[0025] 4. Calculation of the maximum and minimum grinding amounts of the gear tooth surface after heating Based on the above analysis, although many factors affect the grinding amount, the changes in diameter and helix angle have a greater impact, while other factors have a smaller impact. Furthermore, in the heat treatment process, diameter measurement is relatively easy, while other parameters are difficult or even impossible to measure. Therefore, for convenience, Δ is calculated using formula (1). Wd The actual wear is evaluated by adding the pre-reserved wear allowance for gear hobbing and then adding / subtracting the correction amount, as detailed in formulas (2) and (3): (2) (3) In the formula: Δ wmax Δ wmin These are the maximum and minimum grinding amounts, respectively. W 预留 Allow for grinding allowance on one side of the common normal during gear hobbing; k is a coefficient related to the pressure angle. Generally, the commonly used pressure angles for gears are 20° and 25°. When the pressure angle α = 20°, k is taken as 0.17; when the pressure angle α = 25°, k is taken as 0.21. Δ dmax Δ represents the maximum change in diameter before and after heat treatment. dmin This represents the minimum change in diameter before and after heat treatment; positive values ​​are used for increases and negative values ​​are used for decreases. C β This is the correction value for the effect of helix angle variation on grinding capacity; C is the correction value for the influence of other comprehensive factors on grinding amount. Since other deformation forms and processing and other factors also have an impact on grinding amount to varying degrees, C is a comprehensive reflection of these influencing factors.

[0026] To be conservative, a correction value should be added when assessing the maximum wear, and a correction value should be subtracted when assessing the minimum wear. After gear heat treatment, the diameter expands and contracts differently at various locations, requiring measurement of the diameter at several points. The maximum wear is then calculated based on the diameter at the maximum point, and the minimum wear is calculated based on the diameter at the minimum point. As mentioned above, the effect of the helix angle on wear is inconsistent along the tooth width direction, ranging from 0 for small values ​​to Δ for large values. Wβ Therefore, when calculating the maximum grinding capacity, the effect of the helix angle change must be considered, and a correction value C should be added. β When calculating the minimum grinding amount, the effect of the helix angle change is not considered.

[0027] C β C is an empirical value, determined based on product characteristics and production conditions. For the test gears and gears with approximate parameters shown in Table 1, the circumferential runout of the rim generally does not exceed 0.35 mm. When the tooth width is 180, the module is 12, the helix angle is 15°, and the circumferential runout of the rim is 0.5 mm, C... β Taking 0.15 (this data is similar to the approximately 0.16 mm increase in wear due to helix angle change calculated in the section on the effect of helix angle change on wear, proving that the calculated data and empirical data are consistent), C is more suitable at 0.1. Using this as a boundary, when the tooth width, module, helix angle, and end runout are relatively small, C... β The value of C can be appropriately decreased, and vice versa.

[0028] It should be noted that the evaluation method of this invention is more accurate when the circumferential runout of the wheel flange is ≤1.5mm. However, when the runout is greater than 1.5mm, the calculation error is relatively large, so caution should be exercised when using the evaluation method of this invention.

[0029] It should be noted that the calculation method of this invention is suitable not only for disc gears but also for external gear rings. For internal gear rings, since the wear amount increases as the diameter decreases, the opposite is true for external gear rings. Therefore, the maximum wear amount should be calculated based on the minimum diameter, and the minimum wear amount should be calculated based on the maximum diameter.

[0030] Figure 3 The external gear ring shown is one of the applicant's main products. Its parameters are as follows: d=960, B=158, α=20°, β=4°, m n =9mm, the single-sided grinding allowance of the common normal during gear hobbing is 0.37 mm, the material is 18CrNiMo7-6, and the heat treatment process is carburizing-high temperature tempering-quenching-low temperature tempering.

[0031] This product has a relatively small helix angle and tooth width; when calculating C... β Take 0.10, which is slightly smaller than the test product in Table 1. Other values ​​are the same as above. The calculation results are shown in Table 2.

[0032] Table 2 As can be seen from the data in Table 2, the maximum calculation error is 0.12 mm and the minimum is 0.01 mm. It is evident that the calculation accuracy using formulas (2) and (3) of this invention is fully sufficient to meet engineering requirements.

Claims

1. A method for accurately evaluating the grinding amount of the tooth surface of a disc gear after heat treatment, characterized in that: Let the addendum circle diameter of the gear before carburizing be d, the tooth width be B, and the normal module be m. n The pressure angle is α, and the helix angle is β. The change in wear on one side of the gear due to the expansion and contraction of the tooth tip circle after heat treatment is calculated according to formula (1): （1） In the formula: Δ d This represents the expansion value of the tooth tip circle diameter; After heat treatment, the change in helix angle is Δ β The change in unilateral wear amount Δ caused by the change in helix angle Wβ for: ； The maximum grinding amount Δ on the gear tooth surface wmax and minimum grinding amount Δ wmin Calculate according to equations (2) and (3) respectively: （2） （3） In the formula: W 预留 Allow for grinding allowance on one side of the common normal during gear hobbing; k is a coefficient related to the pressure angle. ; Δ dmax Δ represents the maximum change in diameter before and after heat treatment. dmin This represents the minimum change in diameter before and after heat treatment. C β This is the correction value for the effect of helix angle variation on grinding capacity; C represents the correction value for the influence of other comprehensive factors on the grinding amount.

2. The method for accurately evaluating the grinding amount of the disc gear tooth surface after heat treatment according to claim 1, characterized in that: When the pressure angle α = 20°, k = 0.17; when the pressure angle α = 25°, k = 0.

21.

3. The method for accurately evaluating the grinding amount of the disc gear tooth surface after heat treatment according to claim 1, characterized in that: When the end runout is ≤1.5mm, C β =0.15±0.05, C=0.1±0.05.

Images