Verification and repair method of gear hobbing cutter with root removal and grinding

Abstract

This invention discloses a method for verifying and repairing a hobbing cutter with root-cutting and grinding capability, comprising the following steps: A test cut is performed on a gear blank using a hobbing cutter with root-cutting capability, ensuring that the common normal value of the test cut gear blank is equal to the common normal value of the gear to be machined; after the test cut, the common normal of the test cut gear blank is directly ground until the designed common normal value of the gear is reached; the effective involute length, total tooth height, and tooth profile accuracy of the gear blank are tested. If all three indicators are fully qualified, the hobbing cutter with root-cutting capability is deemed suitable for gear hobbing. This invention is simple to operate and has significant effects, eliminating the need for carburizing and quenching processes, saving time and reducing costs, and ensuring that the effective involute length is maintained during gear grinding without grinding the tooth root.

Description

Technical Field

[0001] This invention relates to a method for verifying and repairing a root-cutting and grinding hobbing cutter. Background Technology

[0002] The stress distribution at the tooth root of carburized and quenched high-precision hardened gears has a significant impact on the gear's lifespan and tensile strength. After carburizing and quenching, the gear root surface exhibits compressive stress, capable of withstanding large loads without cracking. However, after grinding, the root surface becomes tensile, easily exceeding the tensile limit and forming micro-cracks, ultimately leading to tooth breakage. Therefore, carburized hardened gears involve pre-cutting the tooth root, ensuring the effective involute tooth surface connects precisely with the tooth root during grinding, while the tooth root itself is not ground. The hobbing cutter used for pre-cutting and leaving the tooth root for grinding is generally for gears with the same parameters. When the number of teeth or the effective length of the involute changes, the inflection point of the tooth root circle 1 and the involute 2, i.e., the product inflection point 3, will change. Figure 1 As shown, this can easily cause the gears to fail. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a simple and low-cost method for verifying and repairing a root-cutting and grinding gear hobbing cutter.

[0004] The technical solution of this invention to solve the above-mentioned technical problems is: a method for verifying and repairing a root-cutting and grinding hobbing cutter, comprising the following steps:

[0005] Step 1: Use a hobbing cutter with residual grinding to perform a trial cut on the gear blank, so that the common normal value of the trial cut gear blank is equal to the residual grinding common normal value of the gear to be machined;

[0006] Step 2: After the trial cut, grind the common normal of the trial cut gear blank directly to the design common normal value of the gear;

[0007] Step 3: Test the effective involute length, total tooth height, and tooth profile accuracy of the gear blank. If all three indicators are qualified, the hobbing cutter is deemed suitable for gear hobbing.

[0008] In the above verification and repair method for the root-cutting and grinding hobbing cutter, if the three indicators fail in step three, the grinding hobbing cutter shall be repaired according to the following three situations:

[0009] First scenario: Effective involute length exceeds tolerance;

[0010] The second scenario: the entire tooth height exceeds the tolerance;

[0011] The third scenario: Both the effective involute length and the total tooth height exceed the tolerance.

[0012] In the above verification and repair method for the root-cutting and grinding hobbing cutter, in step three, for the first case, if the effective involute length exceeds the tolerance, the position of the tool inflection point is changed.

[0013] The effective involute length is out of tolerance when the actual involute length is less than the theoretical involute length. In this case, the inflection point where the root convex of the hobbing cutter connects with the involute of the tool is the tool inflection point. When the tool inflection point moves towards the tooth tip, the inflection point of the involute of the product and the root circle, i.e., the product inflection point, moves towards the tooth root position. After the transfer, the actual involute length of the product increases. When the actual involute length is greater than or equal to the theoretical involute length, the hobbing cutter meets the tooth profile requirements for the gear parameters of the product, and the hobbing cutter is qualified for grinding.

[0014] In the above verification and repair method for the root-cutting and grinding hobbing cutter, in step three, for the second case, if the total tooth height exceeds the tolerance, the tooth profile of the grinding hobbing cutter needs to be reground. The problem that causes the total tooth height to exceed the tolerance is that when the chordal tooth thickness of the grinding hobbing cutter meets the design size, the actual chordal tooth height is greater than the theoretical chordal tooth height. At this time, according to: measured total tooth height of the product - theoretical total tooth height = δ, where δ is the excess value, the tooth tip of the grinding hobbing cutter can be reground, and the amount of grinding is δ.

[0015] In the above-mentioned verification and repair method for the root-cutting hobbing cutter, in step three, for the third case, if the effective involute length and the total tooth height both exceed the tolerance, it is necessary to simultaneously re-grind the tooth profile of the hobbing cutter and change the tool inflection point; the tool inflection point moves towards the tooth tip of the hobbing cutter, while the tooth tip width of the hobbing cutter becomes narrower and the tooth tip of the hobbing cutter is shortened to modify the shape, thereby increasing the effective involute length and shortening the total tooth height.

[0016] In the above verification and repair method for the root-cutting and grinding hobbing cutter, in step three, considering the deformation after carburizing and quenching in actual gear production, the inflection point of the product is shifted downwards towards the tooth root by 0.1~0.3mm.

[0017] The beneficial effects of this invention are as follows: This invention is simple to operate and has obvious effects. It can eliminate the carburizing and quenching process, save time, and reduce costs. It is a method of modifying the grinding hob by reverse deducing from the product's geometric tooth shape, which can ensure that the tooth root is not ground while ensuring the effective involute length during tooth grinding. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the product inflection point.

[0019] Figure 2 This is a flowchart of the present invention.

[0020] Figure 3 This is a schematic diagram of the allowable grinding amount.

[0021] Figure 4 This is a diagram illustrating the three indicators.

[0022] Figure 5 This is a schematic diagram illustrating the repair process for the first scenario.

[0023] Figure 6 This is a schematic diagram illustrating the repair process for the second scenario.

[0024] Figure 7 This is a schematic diagram illustrating the repair process for the third scenario.

[0025] In the diagram, 1 represents the root circle, 2 represents the product involute, 3 represents the product inflection point, 4 represents the root clearance protrusion, 5 represents the tool involute, 6 represents the tool inflection point, A represents the grinding allowance, B represents the tooth profile accuracy, C represents the effective involute length, D represents the total tooth height, E represents the total tooth height after regrinding, F represents the total tooth height before regrinding, G represents the tool involute length before regrinding, H represents the tool involute length after regrinding, I represents the tooth tip clearance length before regrinding, and J represents the tooth tip clearance length after regrinding. Detailed Implementation

[0026] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0027] like Figure 2 As shown, a method for verifying and repairing a root-cutting and grinding hobbing cutter includes the following steps:

[0028] Step 1: Use a hobbing cutter with residual grinding to perform a trial cut on the gear blank, ensuring that the common normal value of the trial cut gear blank is equal to the residual grinding common normal value of the gear to be machined. Figure 3 As shown.

[0029] Step 2: After the trial cut, grind the common normal of the trial cut gear blank directly to the design common normal value of the gear.

[0030] Step 3: Test the three indicators of the gear blank: effective involute length (C), total tooth height (D), and tooth profile accuracy (B). Figure 4 As shown; if all three indicators are fully qualified, the grinding hob is deemed suitable for gear hobbing. If the three indicators are not qualified, the grinding hob should be repaired according to the following three situations:

[0031] First scenario: Effective involute length exceeds tolerance;

[0032] The second scenario: the entire tooth height exceeds the tolerance;

[0033] The third scenario: Both the effective involute length and the total tooth height exceed the tolerance.

[0034] like Figure 5 As shown, for the first case, if the effective involute length exceeds the tolerance, the position of the tool inflection point is changed.

[0035] The effective involute length is out of tolerance when the actual involute length is less than the theoretical involute length. In this case, the inflection point where the root-cutting protrusion 4 of the hobbing cutter connects with the involute 5 of the cutter is called the cutter inflection point 6. When the cutter inflection point 6 moves towards the tooth tip, the inflection point between the involute 2 of the product and the root circle 1, i.e., the product inflection point 3, moves towards the tooth root position. After the move, the actual involute length of the product increases. When the actual involute length is greater than or equal to the theoretical involute length, the hobbing cutter meets the tooth profile requirements for the gear parameters of the product, and the hobbing cutter is qualified for grinding.

[0036] like Figure 6 As shown, for the second case, if the total tooth height exceeds the tolerance, the tooth profile of the hobbing cutter needs to be reground. The problem that causes the total tooth height to exceed the tolerance is that when the chordal tooth thickness of the hobbing cutter meets the design size, the actual chordal tooth height is greater than the theoretical chordal tooth height. In this case, according to the formula: Actual product total tooth height - Theoretical total tooth height = δ, where δ is the excess value, the tooth tip of the hobbing cutter needs to be reground, and the amount of material removed is δ.

[0037] like Figure 7 As shown, for the third case, if both the effective involute length and the total tooth height exceed the tolerance, it is necessary to simultaneously re-grind the tooth profile of the hobbing cutter and change the tool inflection point 6. The tool inflection point 6 moves towards the tooth tip of the hobbing cutter, while the tooth tip width of the hobbing cutter becomes narrower and the tooth tip of the hobbing cutter is shortened to modify the shape, thereby increasing the effective involute length and reducing the total tooth height.

[0038] The changes in the tooth profile of the grinding hob mainly affect the gear tooth profile in the three aspects mentioned above. The tooth profile is indirectly altered by regrinding the grinding hob's tooth profile, and then verified using a hobbing-grinding test piece. This invention is simple to operate and has significant effects, eliminating the need for carburizing and quenching processes, saving time and reducing costs. It involves modifying the grinding hob by working backwards from the product's geometric tooth profile. It should be noted that the modification should fully consider the deformation after carburizing and quenching in actual gear production, and the product inflection point should be shifted downwards towards the tooth root by 0.1~0.3mm.

Claims

1. A method for verifying and repairing a root-cutting and grinding hobbing cutter, characterized in that, The following steps are involved: Step 1: Use a hobbing cutter with residual grinding to perform a trial cut on the gear blank, so that the common normal value of the trial cut gear blank is equal to the residual grinding common normal value of the gear to be machined; Step 2: After the trial cut, grind the common normal of the trial cut gear blank directly to the design common normal value of the gear; Step 3: Test the effective involute length, total tooth height, and tooth profile accuracy of the gear blank. If all three indicators are qualified, the hobbing cutter is deemed suitable for gear hobbing. In step three, if the three indicators fail to meet the requirements, the hobbing cutter will be repaired according to the following three situations: First scenario: Effective involute length exceeds tolerance; The second scenario: the entire tooth height exceeds the tolerance; The third scenario: Both the effective involute length and the total tooth height exceed the tolerance. In the first case, if the effective involute length exceeds the tolerance, the position of the tool inflection point should be changed. The effective involute length is out of tolerance when the actual involute length is less than the theoretical involute length. In this case, the inflection point where the root convex part of the hobbing cutter connects with the involute of the tool is the tool inflection point. When the tool inflection point moves towards the tooth tip, the inflection point of the involute of the product and the root circle, i.e., the product inflection point, moves towards the tooth root position. After the transfer, the actual involute length of the product increases. When the actual involute length is greater than or equal to the theoretical involute length, the hobbing cutter meets the tooth profile requirements for the gear parameters of the product, and the hobbing cutter is qualified for grinding. For the second situation, if the total tooth height exceeds the tolerance, the tooth profile of the hobbing cutter needs to be reground. The problem that causes the total tooth height to exceed the tolerance is that when the chordal tooth thickness of the hobbing cutter meets the design size, the actual chordal tooth height is greater than the theoretical chordal tooth height. In this case, according to the formula: Actual total tooth height of the product - Theoretical total tooth height = δ, where δ is the excess value, the tooth tip of the hobbing cutter needs to be reground, and the amount of material removed is δ. In the third case, if both the effective involute length and the total tooth height exceed the tolerance, it is necessary to simultaneously re-grind the tooth profile of the hobbing cutter and change the tool inflection point. The tool inflection point is moved towards the tooth tip of the hobbing cutter, while the tooth tip width of the hobbing cutter is narrowed and the tooth tip of the hobbing cutter is shortened to modify the shape, thereby increasing the effective involute length and shortening the total tooth height.

2. The verification and repair method for the root-cutting and grinding hobbing cutter according to claim 1, characterized in that, In step three, considering the deformation of the gear after carburizing and quenching in actual production, the inflection point of the product is shifted downwards towards the tooth root by 0.1~0.3mm.

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