Prime number helical gear machining method and gear hobbing tool

Abstract

The application provides a prime number helical gear machining method and a gear hobbing tool. The prime number helical gear machining method comprises the following steps: casting a gear blank of a prime number helical gear; checking the casting quality and screening the gear blank meeting the casting quality requirement; rough turning the end face, the inner hole and the addendum circle of the gear blank, and leaving a 2mm single-sided allowance of the gear blank; heat treating the gear blank, so that the surface hardness of the gear blank is greater than or equal to HB229 and less than or equal to HB302; fine turning the end face, the inner hole and the addendum circle of the gear blank; mounting the gear blank to the gear hobbing tool; rough hobbing the tooth profile of the gear blank, and leaving a 0.3mm-0.4mm single-sided allowance of the generatrix of the tooth profile; and fine hobbing the tooth profile of the gear blank. The prime number helical gear machining method can improve the strength of the manufactured prime number helical gear and reduce the surface roughness of the prime number helical gear by checking and screening the defective gear blank, improving the surface hardness of the gear blank obtained by casting through the heat treatment process, and improving the surface machining precision of the gear blank through step-by-step turning and step-by-step hobbing.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of prime number helical gear machining, and in particular to a prime number helical gear machining method and gear hobbing tool. BACKGROUND

[0002] The intermediate gear and the crankshaft gear are important parts of a marine medium-speed diesel engine. The intermediate gear and the crankshaft gear are both prime number helical gears with a gear number greater than 100, and the gear strength and the gear profile surface roughness are required to be high.

[0003] In the related art, the gear blank of most intermediate gears and crankshaft gears of a medium-speed diesel engine is made of forged alloy steel. The internal organization of the gear obtained by forging is dense, and the strength is high, so that the gear can be used in relatively strict working conditions. However, the forged alloy steel gear blank has the disadvantages of high price and complex machining process, resulting in high machining cost.

[0004] The cast gear has the advantages of simple machining process and low production cost. However, compared with forging, the internal organization performance of the cast gear is deviated, the strength is low, and the surface roughness is high, so that the cast gear is only suitable for general working conditions and is difficult to be applied to a marine diesel engine. SUMMARY

[0005] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a prime number helical gear machining method and gear hobbing tool. The prime number helical gear machining method is used to manufacture a prime number helical gear through a forging process. The prime number helical gear machining method can improve the strength of the prime number helical gear and reduce the surface roughness of the prime number helical gear, thereby helping to manufacture a prime number helical gear suitable for a marine diesel engine.

[0006] According to the prime number helical gear machining method provided by the present application, the following steps are included: casting a gear blank of a prime number helical gear; checking the casting quality and screening the gear blank meeting the casting quality requirement; rough turning the end face, the inner hole and the addendum circle of the gear blank, with a single side allowance of 2mm; heat treating the gear blank, so that the surface hardness of the gear blank is greater than or equal to HB229 and less than or equal to HB302; fine turning the end face, the inner hole and the addendum circle of the gear blank; mounting the gear blank to a gear hobbing tool; rough hobbing the tooth profile of the gear blank, with a single side allowance of 0.3mm to 0.4mm for the generatrix of the tooth profile; and fine hobbing the tooth profile of the gear blank.

[0007] According to the prime number helical gear machining method provided in the application, the following technical effects are achieved: the prime number helical gear machining method can improve the strength of the manufactured prime number helical gear and reduce the surface roughness of the prime number helical gear, and is helpful to manufacture the prime number helical gear suitable for marine diesel engines.

[0008] According to some embodiments of the application, the casting quality requirement is met by that the surface of the tooth blank has no casting defects under 10 times magnifying glass inspection, and the casting defects include cracks, loose, slag inclusion and foreign inclusions.

[0009] According to some embodiments of the application, the casting quality requirement is met by that the spheroidization level of the metallographic structure of the tooth blank is greater than or equal to 1 level and less than or equal to 3 level, and the ferrite proportion in the metallographic structure of the tooth blank is not greater than 25%.

[0010] According to some embodiments of the application, the heat treatment step comprises: heating the tooth blank to 920℃ and keeping; rapidly cooling the tooth blank to normal temperature; heating the tooth blank to 560℃ and keeping; naturally cooling the tooth blank to room temperature.

[0011] According to some embodiments of the application, the tooth blank is kept at 920℃ for 3h, and the tooth blank is kept at 560℃ for 4h.

[0012] According to some embodiments of the application, the tooth blank is rapidly cooled by air cooling.

[0013] According to some embodiments of the application, the number of teeth of the prime number helical gear is greater than 100, the tooth blank is coarsely rolled and finely rolled by using a gear hobbing machine, and before the coarse rolling step, the following steps are further included: a prime number spur gear with the same number of teeth as the prime number helical gear is manufactured; a large prime number tooth division gear plate is manufactured to match the prime number spur gear, the large prime number tooth division gear plate includes a avoiding slot for avoiding the gear set of the gear hobbing machine; the original tooth division gear hobbing gear plate in the gear hobbing machine is replaced by the large prime number tooth division gear plate, and the original tooth division gear hobbing gear in the gear hobbing machine is replaced by the prime number spur gear.

[0014] The gear hobbing tooling provided in the application is used to implement the prime number helical gear machining method provided in the application.

[0015] According to some embodiments of the present application, the gear hobbing tool comprises a base, a pressing plate and a mandrel, the base is provided with a mounting hole, the mandrel is inserted into the mounting hole, the mandrel is used for positioning the inner hole of the gear blank, the pressing plate is installed on the base, the base comprises a first end face, the pressing plate comprises a second end face opposite to the first end face, and the second end face axially presses the gear blank against the first end face.

[0016] According to some embodiments of the present application, the gear hobbing tool comprises a backing ring, and the base is installed on the backing ring.

[0017] The gear hobbing tool provided by the present application is used to implement the prime number helical gear machining method provided by the present application, and accordingly has the beneficial effects provided by the prime number helical gear machining method, which will not be repeated here. BRIEF DESCRIPTION OF DRAWINGS

[0018] The above and / or additional aspects and advantages of the present application will become apparent and be readily understood from the following description, taken in conjunction with the following drawings, in which:

[0019] Figure 1 is a flowchart of the prime number helical gear machining method according to an embodiment of the present application;

[0020] Figure 2 is an internal schematic diagram of a gear hobbing machine used in the prime number helical gear machining method according to an embodiment of the present application;

[0021] Figure 3 is an internal schematic diagram of a gear hobbing machine used in the prime number helical gear machining method according to an embodiment of the present application;

[0022] Figure 4 is a structural schematic diagram of a clamp unit according to an embodiment of the present application;

[0023] Figure 5 is a structural schematic diagram of a base according to an embodiment of the present application, wherein preferred tolerances are exemplarily labeled;

[0024] Figure 6 is a structural schematic diagram of a mandrel according to an embodiment of the present application, wherein preferred tolerances are exemplarily labeled;

[0025] Figure 7 is a structural schematic diagram of a backing ring according to an embodiment of the present application, wherein preferred tolerances are exemplarily labeled.

[0026] LIST OF REFERENCE NUMERALS:

[0027] Large prime number split tooth gear plate 110, split tooth gear plate 120, split tooth gear plate 130, bridge gear 140, base 210, first end surface 211, fourth end surface 212, mounting hole 213, mandrel 220, first shaft section 221, second shaft section 222, third end surface 223, pressing plate 230, grommet 240, fifth end surface 241, sixth end surface 242, tooth blank 310. DETAILED DESCRIPTION

[0028] Embodiments of the present application are described below in detail, examples of which are shown in the drawings, wherein the same or similar notations represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary, only for explaining the present application, and cannot be understood as a limitation of the present application.

[0029] In the description of the present application, it is understood that the orientation description, such as "center", "lengthwise", "transverse", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, only for the purpose of facilitating the description of the present application and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0030] In the description of the present application, the meaning of several is one or more, the meaning of multiple is more than two, greater than, less than, more than, etc. are understood as not including the number, above, below, etc. are understood as including the number. If it is described that the first, second is only used for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or implicitly indicating the sequence of indicated technical features.

[0031] In the description of the present application, unless otherwise explicitly limited, the words such as setting, mounting, connecting, etc. should be broadly understood, and the person skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0032] The cost of the casting process is low, and the casting process is often used in the related art to replace the forging process to manufacture parts to reduce production cost.

[0033] However, the quality of the blank obtained by casting is generally poor, and the performance of the part obtained by machining cannot meet the requirements of strict working conditions (for example, the gear of the gear box of the marine diesel engine). One problem in the application of the casting process to manufacture gears is that the surface roughness of the cast part is large, which affects the meshing and transmission of the gear. Another problem is that the strength of the cast part is not enough, and the service life of the gear used in diesel engines with heavy load is low, and tooth breakage is prone to occur.

[0034] In order to improve the quality of the product and make the gear based on the manufacturing process meet the requirements, the prime number helical gear machining method provided by the application refers to Figure 1 The prime number helical gear machining method comprises the following steps:

[0035] Casting a tooth blank 310 of a prime number helical gear;

[0036] Checking the casting quality and screening the tooth blank 310 meeting the casting quality requirements;

[0037] Coarsely turning the end face, inner hole and addendum circle of the tooth blank 310, and leaving a 2mm margin on one side of the tooth blank 310;

[0038] Heat treating the tooth blank 310, so that the surface hardness of the tooth blank 310 is greater than or equal to HB229 and less than or equal to HB302;

[0039] Finely turning the end face, inner hole and addendum circle of the tooth blank 310;

[0040] Installing the tooth blank 310 to the gear hobbing tool;

[0041] Coarsely hobbing the tooth profile of the tooth blank 310, and leaving a 0.3mm-0.4mm margin on one side of the generatrix of the tooth profile 310;

[0042] Finely hobbing the tooth profile of the tooth blank 310.

[0043] According to the prime number helical gear machining method provided by the application, the tooth blank 310 with defects is removed by checking and screening, the surface hardness of the tooth blank 310 obtained by casting is improved by heat treatment process, and the surface machining accuracy of the tooth blank 310 is improved by step-by-step turning and step-by-step hobbing. The prime number helical gear machining method can improve the strength of the manufactured prime number helical gear and reduce the surface roughness of the prime number helical gear, which is helpful for manufacturing the prime number helical gear suitable for marine diesel engines.

[0044] On this basis, it is also necessary to further clarify the screening standard. On the one hand, it is necessary to avoid too strict standards leading to too low casting yield and too high production cost. On the other hand, it is necessary to avoid too loose standards leading to the performance of the prime number helical gear product being unable to meet the requirements.

[0045] Specifically, first, visible defects on the blank 310 can be checked. Exemplarily, first, the casting quality requirement can include that the surface of the blank 310 is free of casting defects including cracks, porosity, slag inclusion, and foreign inclusions under 10 times magnification. The naked eye inspection can conveniently and quickly screen the blank 310, and remove the blank 310 with obvious quality defects.

[0046] Next, the microstructure of the blank 310 can be further checked to more finely evaluate the casting quality. Exemplarily, after the naked eye inspection, the casting quality requirement can further include that the blank 310 has a spheroidization level greater than or equal to level 1 and less than or equal to level 3, and the ferrite content in the metallographic structure of the blank is not greater than 25%.

[0047] The basis for the level division and the calculation method of the ferrite content can refer to the existing standards in the industry, for example, refer to the relevant contents of GB / T9441 “Metallographic Examination of Ductile Iron”, which will not be repeated here.

[0048] The blank 310 can reach the required surface hardness through different heat treatment processes. Exemplarily, the heat treatment step includes: heating the blank 310 to 920°C and keeping; rapidly cooling the blank 310 to room temperature; heating the blank 310 to 560°C and keeping; and naturally cooling the blank 310 to room temperature.

[0049] Specifically, in order to ensure the heat treatment effect, the blank 310 can be designed to keep at 920°C for 3h, and the blank 310 can be designed to keep at 560°C for 4h. The heating can be carried out in a special heat treatment furnace, for example, an air furnace.

[0050] In addition, in the present application, air cooling is preferably used to rapidly cool the blank 310, for example, an industrial fan can be used to blow and dissipate heat to achieve rapid cooling. It can be understood that using water cooling will make the cooling speed of the blank 310 too fast, and the blank 310 is prone to generate excessive stress or even crack when cooling. Compared with ordinary water, using oil or coolant as the medium for water cooling can reduce the cooling speed to some extent, but the cost is relatively high and the reduction amplitude is sometimes difficult to achieve the expected effect. At the same time, oil and coolant can also change the metallographic structure of the blank 310.

[0051] The present application uses a gear hobbing machine to rough hob and fine hob the blank 310. The rough hob uses a rough hobbing cutter, and the fine hob uses a fine hobbing cutter. When the gear hobbing machine processes a prime number helical gear, there is a generating motion between the hobbing cutter and the blank 310. In the gear transmission chain for generating the generating motion in the gear hobbing machine, one gear (that is, the split tooth and toothed hanging wheel 120 in the gear hobbing machine) must have a number of teeth that is an integer multiple (including the case where the number of teeth is equal) of the number of teeth of the prime number helical gear to be processed.

[0052] Some ship prime number helical gears have a tooth number Z greater than 100 (referred to as large prime number helical gears), and generally, the hobbing machine manufacturer will only provide a corresponding tooth dividing gear for the prime number helical gears with Z less than or equal to 100, so there is no suitable tooth dividing gear as a tooth dividing and engaging gear 120 to generate a generating motion.

[0053] In the related art, the differential compensation method is often used to process the prime number helical gears with Z greater than 100, that is, the required tooth dividing and engaging gear 120 is selected according to the imaginary tooth number (Z+△Z) instead of the actual tooth number Z. The disadvantage of the differential compensation method for processing the large prime number helical gears is that after the hobbing cutter starts to hob the gear from the starting point to the ending point, the hobbing cutter cannot quickly return to the original position without cutting, and the hobbing cutter must be reversed and moved backward to the original position, which theoretically causes the processing time of the large prime number helical gears to be about twice as long as that of the non-prime number helical gears; the compensation tooth dividing error△Z generated by the differential compensation method will be superimposed in the differential motion during the movement process, causing misplacement and tooth disorder, and affecting the gear processing precision. Other technical details of the differential compensation method can be referred to the prior art, which will not be described here.

[0054] In order to overcome the disadvantages caused by the differential compensation method, in the present application, before the rough hobbing step, a prime number spur gear with the same tooth number as the prime number helical gear is made, and the prime number spur gear is used to replace the original tooth dividing and engaging gear 120 in the hobbing machine. That is, the present application self-makes a prime number spur gear matched with the large prime number helical gear to be processed, and uses the prime number spur gear as the tooth dividing and engaging gear 120, so that the hobbing machine can directly process the required large prime number helical gear without using the differential compensation method for fitting. When the hobbing cutter starts to hob the gear from the starting point to the ending point, the hobbing cutter can quickly return to the original position without reversing and retreating, and no compensation tooth dividing error△Z is generated.

[0055] It should be noted that since the structure inside the hobbing machine is not adapted to the prime number spur gear with a tooth number greater than 100, after the prime number spur gear is installed as the tooth dividing and engaging gear 120, the gear set inside the hobbing machine will interfere with the tooth dividing and engaging gear plate 130 on which the tooth dividing and engaging gear 120 is installed, causing the hobbing machine to be unable to operate.

[0056] Therefore, the prime number helical gear processing method further includes making a large prime number tooth dividing gear plate 110 matched with the prime number spur gear, the large prime number tooth dividing gear plate 110 includes a avoiding slot for avoiding the gear set of the hobbing machine; and replacing the original tooth dividing gear plate in the hobbing machine with the large prime number tooth dividing gear plate 110.

[0057] Figure 2 and Figure 3 Exemplarily shows a part of the gear set inside the hobbing machine, referring to Figure 2 and Figure 3 , Figure 2For the case of installing the prime number spur gear without replacing the original split tooth gear plate 130, the split tooth gear plate 130 will interfere with the gear set. Specifically, in addition to the split tooth gear plate 120, the bridge gear 140 is also installed on the split tooth gear plate 130, the split tooth gear plate 120 is engaged with the bridge gear 140, and the bridge gear 140 is engaged with the differential gear in the gear box through the gear set. Due to the increase in the number of teeth, the diameter of the split tooth gear plate 120 increases accordingly, resulting in the need to correspondingly reduce the bridge gear 140, so that the gear engaged with the bridge gear 140 will interfere with the split tooth gear plate 130.

[0058] Figure 3 For the case of installing the large prime number split tooth gear plate 110, it can be seen that by adding the avoidance groove, interference can be avoided, so that the gear hobbing machine can operate normally.

[0059] In addition, in order to ensure the reliability and service life of the large prime number split tooth gear plate 110, while compensating for the weakening effect of the avoidance groove on the strength of the large prime number split tooth gear plate 110, the material of the large prime number split tooth gear plate 110 can be designed as 40Cr (the material of the original split tooth gear plate of the gear hobbing machine is mostly HT250), and quenching and tempering heat treatment is performed to make the hardness of the large prime number split tooth gear plate 110 reach HB292~HB320.

[0060] The application also provides a gear hobbing tool for implementing the prime number helical gear machining method provided by the application.

[0061] The gear hobbing tool includes a base 210, a pressing plate 230 and a mandrel 220, the base 210 is provided with a mounting hole 213, the mandrel 220 is inserted into the mounting hole 213, and the mandrel 220 is used to position the inner hole of the gear blank 310. The pressing plate 230 is installed on the base 210, and the base 210 includes a first end face 211. The pressing plate 230 includes a second end face opposite to the first end face 211, and the second end face axially presses the gear blank 310 against the first end face 211.

[0062] Exemplarily, referring to Figure 4 and Figure 5 , the base 210 includes a containing chamber, the mounting hole 213 is located at the center of the containing chamber and coaxial with the containing chamber, the containing chamber has an upward opening, the first end face surrounds the opening, and the pressing plate 230 is installed at the opening position by means of a stud bolt, so as to press the gear blank 310.

[0063] Continuing to refer to Figure 4 , the gear hobbing tool can further include a grommet 240, and the base 210 is installed on the grommet 240.

[0064] In order to ensure the assembly effect and improve the machining quality, it is also necessary to further limit the assembly tolerance.

[0065] Exemplarily, referring to Figure 6 The mandrel 220 has a first shaft section 221 matched with the mounting hole 213 and a second shaft section 222 matched with the inner hole of the tooth blank 310, and the mandrel 220 includes a third end surface 223 perpendicular to the axial direction, the third end surface 223 is in contact with the base 210 to position the mandrel 220, the coaxial error of the first shaft section 221 and the second shaft section 222 (based on the second shaft section 222) should be less than or equal to 0.015 mm, and the perpendicularity error of the third end surface 223 (based on the axis of the second shaft section 222) should be less than or equal to 0.020 mm.

[0066] Referring to Figure 5 The base includes a fourth end surface 212, the fourth end surface 212 is in contact with the spacer ring 240, and the perpendicularity error of the fourth end surface 212 (based on the axis of the mounting hole 213) should be less than or equal to 0.020 mm.

[0067] Referring to Figure 7 The spacer ring 240 includes a fifth end surface 241 and a sixth end surface 242, the fifth end surface 241 is used to contact the fourth end surface 212, and the sixth end surface 242 is opposite to the fifth end surface 241, and the parallelism error of the fifth end surface 241 and the sixth end surface 242 (based on the fifth end surface 241) should be less than or equal to 0.020 mm.

[0068] In the description of the present specification, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example", or "some examples" and the like means that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present application. In the present specification, the exemplary description of the above terms does not necessarily mean the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0069] In some alternative embodiments, the functions / operations mentioned in the block diagram can not occur in the order mentioned in the operation diagram. For example, depending on the functions / operations involved, two blocks shown in succession can actually be executed substantially simultaneously or the blocks can sometimes be executed in reverse order. In addition, the embodiments presented and described in the flowcharts of the present application are provided by way of example, with the purpose of providing a more comprehensive understanding of the technology. The disclosed method is not limited to the operations and logical flows presented herein. Alternative embodiments are contemplated in which the order of various operations is changed and in which sub-operations described as part of larger operations are independently executed.

[0070] While the embodiments of the application have been shown and described, it is to be understood that the embodiments can be varied, modified, substituted and changed by those skilled in the art without departing from the principles and spirit of the application, the scope of which is defined by the claims and their equivalents.

Claims

1. A method of machining a prime number helical gear, characterized by, The prime number helical gear machining method comprises the following steps: casting a tooth blank of the prime number helical gear; checking the casting quality and screening the tooth blank meeting the casting quality requirement; roughly turning the end face, inner hole and addendum circle of the tooth blank, and leaving a 2mm single side allowance; heat treating the tooth blank so that the surface hardness of the tooth blank is greater than or equal to HB229 and less than or equal to HB302; finely turning the end face, inner hole and addendum circle of the tooth blank; mounting the tooth blank to a gear hobbing tool; roughly hobbing the tooth profile of the tooth blank, and leaving a 0.3mm-0.4mm single side allowance of the generatrix of the tooth profile; finely hobbing the tooth profile of the tooth blank; the heat treatment step comprises: heating the tooth blank to 920℃ and keeping; quickly cooling the tooth blank to room temperature; heating the tooth blank to 560℃ and keeping; naturally cooling the tooth blank to room temperature; the number of teeth of the prime number helical gear is greater than 100, and the tooth blank is roughly and finely hobbed by using a gear hobbing machine, and before the rough hobbing step, the method further comprises: manufacturing a prime number spur gear with the same number of teeth as the prime number helical gear; manufacturing a large prime number tooth division gear plate matched with the prime number spur gear, the large prime number tooth division gear plate comprising an avoiding groove for avoiding the gear set of the gear hobbing machine; replacing the original tooth division and tooth engagement gear plate in the gear hobbing machine with the large prime number tooth division gear plate and replacing the original tooth division and tooth engagement gear plate in the gear hobbing machine with the prime number spur gear.

2. The prime number helical gear machining method according to claim 1, characterized by, The casting quality requirement is met, including that under the inspection of a 10 times magnifying glass, the surface of the tooth blank is free of casting defects including cracks, loose, slag inclusion and foreign inclusions.

3. The prime number helical gear machining method according to claim 2, characterized by, The casting quality requirement is met, including that the spheroidization level of the metallographic structure of the tooth blank is greater than or equal to 1 level and less than or equal to 3 level, and the proportion of ferrite in the metallographic structure of the tooth blank is not greater than 25%.

4. The prime number helical gear machining method according to claim 1, characterized by, The tooth blank is kept at 920℃ for 3h, and the tooth blank is kept at 560℃ for 4h.

5. The prime number helical gear machining method according to claim 1, characterized by, The tooth blank is quickly cooled by using air cooling.

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