Double-tooth sun gear machining method and inner hole allowance determining method

Abstract

The invention discloses a double-tooth sun gear machining method and an inner hole allowance determining method, and relates to the technical field of gear machining. The machining method of the double-tooth sun gear sequentially comprises the steps of blank forging, semi-finish turning, outer circle tooth A hobbing, inner hole and two end face coating of an anti-seepage agent, carburizing, quenching, shot blasting, finish turning, inner hole tooth B rough gear shaping machining, inner hole tooth B fine gear shaping machining, outer circle tooth A grinding machining, burn inspection, magnetic powder inspection, tooth part precision detection and bench work. The inner hole allowance is determined by adopting test bars with the same material and the same process, and accurate reservation is realized through quantitative calculation by detecting the radial hardness distribution rule of the test bars. The core technology is a combination method of differential seepage prevention, test bar allowance quantification and staged machining, the machinability of inner hole and end face seepage prevention is ensured before carburization, the performance is ensured through normal hardening of outer teeth, hardened layer residues and material waste are avoided through precise allowance, and the bearing performance of the inner teeth is ensured.

Description

Technical Field

[0001] This application belongs to the field of gear machining, and in particular relates to a method for machining a double-tooth sun gear and a method for determining the inner hole allowance. Background Technology

[0002] In fields such as new energy vehicles, construction machinery, and precision transmission equipment, planetary gearboxes have become core transmission components due to their high transmission efficiency and strong load-bearing capacity. To meet the lightweight requirements of planetary gearboxes, the sun gear adopts an internal and external tooth design to shorten the overall length of the gearbox. To ensure operational reliability and service life, the external teeth of the sun gear require a tooth surface hardness of HRC58-HRC62 and a tooth accuracy of GB10095-5 grade, while the internal teeth require a hardness greater than HB320 and a tooth accuracy of GB10095-8 grade. In the current production process, due to the high hardness of the external teeth, a carburizing and quenching heat treatment process is required. After carburizing and quenching, the inner hole will harden simultaneously, resulting in increased hardness and difficulty in machining the inner hole, which conflicts with the subsequent cutting requirements of the internal teeth. Summary of the Invention

[0003] To address some or all of the technical problems existing in the prior art, this application provides a method for machining a double-toothed sun gear and a method for determining the inner hole allowance.

[0004] A method for machining a double-tooth sun gear, the method comprising the following steps in sequence: blank forging, semi-finish turning, hobbing the outer diameter A tooth, coating the inner hole and both end faces with an anti-seepage agent, carburizing, quenching, shot peening, finish turning, rough shaping the inner diameter B tooth, fine shaping the inner diameter B tooth, grinding the outer diameter A tooth, burn inspection, magnetic particle inspection, tooth accuracy testing, and fitter work; in the semi-finish turning process, a set allowance is reserved for the inner hole and both end faces, the allowance being determined by an allowance determination test bar experiment.

[0005] Preferably, the coarse shaping teeth are made using indexable shaping cutters, and the fine shaping teeth are made using integrally coated shaping cutters.

[0006] A method for determining the allowance of the inner bore of a double-toothed sun gear includes the following steps: S1: Prepare a margin determination test bar, wherein the margin determination test bar and the double-tooth sun gear are made of the same material and undergo the same carburizing and quenching heat treatment process, and the surface of the margin determination test bar is coated with an anti-seepage agent before carburizing and quenching. S2: The remaining allowance test bar is cut radially after carburizing and quenching treatment; S3: Using a hardness tester, starting from the outer surface of the test bar cross-section determined by the aforementioned margin, measure the hardness every 1 mm along the radial direction inward, and record the hardness value of each test point and the corresponding distance from the outer surface. S4: Identify the critical test point where the hardness value is close to HB320. Using the critical test point as a reference, continue to measure 3 consecutive test points in the radial direction and calculate the hardness fluctuation value of the 3 test points. S5: Determine the hardness fluctuation value. If the hardness fluctuation value is less than HB5, determine the margin as the distance between the critical detection point and the outer surface of the test bar. If the hardness fluctuation value is greater than or equal to HB5, determine the margin as the distance between the critical detection point and the outer surface of the test bar minus 1mm.

[0007] This application has the following advantages and positive effects: (1) Before carburizing, a carburizing agent is applied to the inner hole and both end faces to isolate the carburizing hardening and ensure the machinability of the inner hole. The outer teeth are then carburized and quenched normally to achieve the high hardness requirement. This precisely solves the core contradiction between the need for hardening of the outer teeth and the need for machinability of the inner hole, so that the performance indicators of the inner and outer teeth accurately match the design requirements.

[0008] (2) The inner hole allowance is precisely reserved based on the test bar test data. This avoids the hardened layer residue in the inner hole caused by insufficient allowance, and also prevents material waste and excessive cutting caused by excessive allowance. At the same time, it can retain qualified substrate to ensure the load-bearing performance of the inner tooth.

[0009] (3) By testing test bars of the same material and process as the sun gear, and combining the radial hardness distribution law, the allowance is quantitatively calculated, which effectively eliminates interference from material batches and heat treatment parameter fluctuations, ensuring that the allowance setting of different batches of products is both accurate and consistent, and greatly improving process stability. Attached Figure Description

[0010] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for further understanding of the embodiments of this application and constitute a part of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a cross-sectional view of the double-toothed sun gear; Figure 2 This is a schematic diagram of the area where the anti-seepage agent is applied to the inner hole of the double-toothed sun gear before carburizing; Figure 3 This is a schematic diagram showing the distribution of test points for determining the hardness of the test bar based on the allowance. Explanation of reference numerals in the attached figures: 1-Double-toothed sun gear, 1.1-Inner hole, 1.2-Outer circle A tooth, 1.3-Inner hole B tooth, 1.4-End face, 2-Anti-seepage agent, 3-Remaining amount determination test bar. Detailed Implementation

[0011] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions of this application will be clearly and completely described below in conjunction with specific embodiments and corresponding drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0012] This embodiment focuses on machining the double-toothed sun gear 1 adapted to the planetary gearbox. The sun gear adopts an integrated structure that combines external and internal teeth to meet the requirements of lightweight and compact design of the gearbox.

[0013] like Figure 1 As shown, the outer circle A tooth 1.2 of the double-tooth sun gear 1 has a tooth surface hardness requirement of HRC58-HRC62 and a tooth accuracy grade of GB10095-5. The inner hole 1.1 of the double-tooth sun gear 1 contains an inner hole B tooth 1.3, which has a tooth surface hardness requirement of greater than HB320 and a tooth accuracy grade of GB10095-8.

[0014] like Figure 2 As shown, end face 1.4 refers to the two ends of the sun gear axis. In the semi-finish turning process, the two end faces 1.4 need to be reserved. This allowance is removed during the subsequent finish turning to eliminate the deformation and hardened layer caused by carburizing and quenching, and to ensure the flatness and dimensional accuracy of end face 1.4, so as to provide a reliable positioning reference for subsequent internal gear shaping, external gear grinding and other processes.

[0015] The following details the specific processing steps: First, the blank is forged and pretreated. Alloy structural steel bars matching the design requirements of the sun gear are selected and forged into sun gear blanks through die forging. After forging, the blank undergoes appropriate heat treatment to eliminate internal stress generated during forging, refine the material grains, and ensure the stability of material properties during subsequent processing.

[0016] Next, semi-finish turning is carried out, and the forged blank is turned on a lathe. When turning the outer diameter, the machining allowance required for subsequent gear hobbing and grinding is reserved. When turning the inner hole 1.1 and the two end faces 1.4, the set allowance is reserved. This allowance needs to be calculated from the test results of the subsequent allowance determination test bar 3.

[0017] Subsequently, the preparation and simultaneous heat treatment of the allowance determination test bar 3 were carried out. Alloy structural steel material from the same batch as the sun gear was selected and machined into a cylindrical test bar. The surface of the test bar was ground and polished to a smooth state. An anti-seepage agent 2, identical to that used for the inner hole 1.1 of the sun gear, was uniformly coated onto the entire surface of the test bar and allowed to air dry naturally after coating. The prepared test bar and the semi-finished sun gear blank were placed together in a carburizing furnace and subjected to the same carburizing and quenching processes to ensure that the heat treatment state of the test bar was completely consistent with that of the sun gear, providing an accurate basis for subsequent allowance calculations.

[0018] After heat treatment, the test bar is tested and the allowance is calculated. The test bar is radially cut using a wire cutting device, and the hardness of the cross-section is measured using a Brinell hardness tester, as shown in the attached figure. Figure 3 As shown, starting from the outer surface of the test bar, test points are selected radially inward at fixed intervals (1 mm). Multiple measurements are taken at each test point, and the average value is used as the final hardness value for that point. The measured hardness data are checked one by one to find the critical test point (HB320) where the hardness value is close to the maximum allowable pre-machining hardness of the internal gear. Using this critical test point as a reference, three consecutive test points are selected radially inward, and the hardness fluctuation value between these three test points is calculated. The hardness fluctuation value is used to determine the trend of material hardness change. If the fluctuation value is small, i.e., less than HB5, it indicates stable hardness change, and the margin is the distance from the critical test point to the outer surface of the test bar. If the fluctuation value is large, i.e., greater than HB5, it indicates unstable hardness change, and the margin is the distance from the critical test point to the outer surface of the test bar minus 1 mm, ensuring that the hardness of the internal gear meets the standard after subsequent machining.

[0019] The purpose of the hardness test is to find the machinable hardness boundary of the inner hole 1.1 of the double-tooth sun gear 1. After carburizing and quenching, a high-hardness hardened layer will form on the surface of the inner hole 1.1, with a hardness far exceeding HB320, making machining difficult. The allowance is the cuttable thickness reserved for subsequent precision turning and gear shaping processes. It needs to be just enough to remove the hardened layer and retain the internal suitable substrate. By using radial hardness testing of the test bar, the position where the hardness drops to HB320 can be accurately found. This position is the boundary between the hardened layer and the machinable substrate. The distance from the outer surface of the test bar to this boundary point is the thickness of the hardened layer that must be removed, i.e., the basic allowance. If the hardness fluctuates greatly in the last 3mm, it indicates that the hardness inside the hardened layer is unstable, and the allowance needs to be appropriately reduced to avoid removing too much substrate and causing insufficient hardness of the inner tooth. If the fluctuation is small, it indicates that the hardened layer boundary is clear, and the basic allowance can be set to ensure that the hardness of the inner tooth meets the requirements after subsequent machining.

[0020] After determining the allowance, the external gear is hobbed. A hobbing machine is used to hob the outer circle of the sun gear to ensure the integrity of the external gear tooth profile after hobbing, while reserving the machining allowance required for subsequent gear grinding to ensure that the external gear can meet the design accuracy requirements after subsequent precision grinding.

[0021] After gear hobbing, the inner hole 1.1 and both end faces 1.4 of the sun gear are coated with an anti-seepage agent 2. The outer teeth and other surfaces not requiring anti-seepage coating are left uncoated. During coating, ensure the anti-seepage agent 2 coating is uniform and of the required thickness. Allow it to air dry naturally after coating to prevent carburizing hardening of the inner hole 1.1 and end faces 1.4 during the carburizing process. Then, place the sun gear in a carburizing furnace and perform the predetermined carburizing and quenching process to achieve the designed high hardness on the outer tooth surface.

[0022] After quenching, the sun gear needs to be shot peened. A shot peening machine is used to spray cast steel shot at high speed onto the surface of the sun gear to remove the oxide scale and decarburized layer on the tooth surface. At the same time, it increases the residual compressive stress on the tooth surface, enhances the fatigue resistance of the external teeth, and provides a good surface condition for subsequent processing.

[0023] After shot peening, precision turning is performed. Using the outer circle after shot peening as the positioning reference, the two end faces of the sun gear are precision turned to the design dimension by 1.4, ensuring the flatness of the end face by 1.4. At the same time, the inner hole by 1.1 is precision turned to the design dimension, completely removing the hardened layer on the surface of the inner hole by 1.1, ensuring that the surface of the inner hole by 1.1 is smooth and the dimensional accuracy meets the requirements of subsequent internal gear machining.

[0024] Internal gear machining is divided into two steps: rough shaping and fine shaping. For rough shaping, an indexable gear shaper is used with appropriate machining parameters to quickly remove excess material from the inner hole (1.1mm), leaving room for fine shaping and improving machining efficiency. After rough shaping, fine shaping is performed to ensure that the internal gear profile accuracy and surface roughness meet design requirements, satisfying assembly and usage needs.

[0025] After the internal gears are machined, the external gears are ground. A gear grinding machine is used for precision grinding to eliminate deformation caused during heat treatment, ensuring the hardness and precision of the external gear surfaces meet design standards and guaranteeing smooth transmission.

[0026] Finally, subsequent inspection and fitter work are carried out. Magnetic particle testing equipment is used to inspect the sun gear for burns and overall flaw detection, checking for defects such as tooth surface burns, internal cracks, and inclusions. The tooth accuracy of the internal and external teeth is checked using a gear measuring center to ensure that all indicators meet the design requirements. In the fitter work stage, burrs and sharp edges on the surface of the parts are removed, and surface oil stains are cleaned, completing the entire machining process of the double-tooth sun gear 1.

[0027] It should be noted that, unless otherwise expressly specified and limited, the term "connection" or its synonyms should be interpreted broadly in this document. For example, "connection" can be a fixed connection or a detachable connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium; it can be the internal communication of two elements or the interaction between two elements. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances. Furthermore, expressions such as "first" and "second" are merely used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. At the same time, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. In addition, the terms "front," "rear," "left," "right," "upper," and "lower" in this document refer to the placement states shown in the accompanying drawings.

[0028] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A method of machining a double toothed sun gear, characterized in that, The processing method comprises in sequence: blank forging, semi-finishing turning, gear hobbing processing of the outer circle A teeth, coating anti-permeation agent on the inner hole and two end faces, carburizing, quenching, shot blasting, finishing turning, rough gear shaping processing of the inner hole B teeth, fine gear shaping processing of the inner hole B teeth, gear grinding processing of the outer circle A teeth, burn inspection, magnetic particle inspection, tooth precision detection and bench work.

2. The method of claim 1, wherein, The rough gear shaping uses an indexable gear shaping cutter, and the fine gear shaping uses an integral coating gear shaping cutter.

3. A method of determining the bore allowance of a double toothed sun gear, characterized in that The method comprises the following steps: S1: a margin determination test bar is prepared, the margin determination test bar is made of the same material as the double-tooth sun gear, and is subjected to the same carburizing and quenching heat treatment process, and the surface of the margin determination test bar is coated with an anti-permeation agent before carburizing and quenching; S2: the margin determination test bar is cut along the radial direction after being subjected to carburizing and quenching; S3: a hardness tester is used to measure the hardness every 1 mm inward along the radial direction from the outer surface of the cross section of the margin determination test bar, and the hardness value and the distance from the outer surface of each detection point are recorded; S4: a critical detection point with a hardness value close to HB320 is identified, 3 continuous detection points are measured inward along the radial direction from the critical detection point as a reference, and the hardness fluctuation value of the 3 detection points is calculated; S5: the hardness fluctuation value is judged, if the hardness fluctuation value is less than HB5, the margin is determined to be the distance of the critical detection point from the outer surface of the test bar, and if the hardness fluctuation value is greater than or equal to HB5, the margin is determined to be the distance of the critical detection point from the outer surface of the test bar minus 1 mm.

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