Threaded hole machining method for carburizing steel electric drive axle main reduction gear

Abstract

The invention discloses a carburizing steel electric drive axle main reduction gear threaded hole machining method which comprises the steps that threaded hole machining is adjusted to heat treatment post-machining, carbon stripping treatment is carried out on the position of a threaded hole after heat treatment, and then drilling and tapping are carried out; the process route comprises the steps of material preparation, carburizing and quenching, finish turning and carbon stripping, and drilling and tapping. According to the method, due to the fact that the hardness of carburizing steel can be reduced along with increase of the depth, the surface hardness of the carburizing steel is reduced till the threaded hole can be machined through a conventional tool by reserving a finish turning carbon stripping layer and removing a carburizing layer through finish turning after carburizing and quenching, and due to the fact that the threaded hole is adjusted to be machined after carburizing and quenching, deformation caused by carburizing and quenching is avoided; and it is guaranteed that the threaded hole machining position degree is 100% qualified. Compared with an original process route, two procedures are reduced, the machining quality of the carburizing steel electric drive axle main reduction gear threaded hole is improved, and the machining efficiency of the electric drive axle main reduction gear is greatly improved. The method is stable, reliable and convenient to operate, and the machining quality of products can be guaranteed.

Description

Technical Field

[0001] The invention relates to a method for machining a threaded hole of a carburized steel electric drive axle main reduction gear, belonging to the technical field of mechanical machining. Background Art

[0002] There are many process methods for machining threaded holes of carburized steel electric drive axle main reduction gears in mechanical processing. At present, the main processing method is still to process the threaded holes before carburizing and quenching, to protect the threads from seepage during carburizing and quenching, and to rethread after heat treatment. The process route is: drilling and tapping → thread anti-seepage protection → carburizing and quenching → rethreading → fine turning. The threaded holes of the electric drive axle main reduction gear are assembled with the differential housing, and the position of the threaded holes is required to be high. Due to the structure of the electric drive axle main reduction gear, the deformation is large after carburizing and quenching. The position of the threaded holes cannot be corrected by rethreading alone, and the surface hardness of the parts reaches 58-62HRC. It is impossible to correct the position of the threaded holes by other process methods, resulting in excessive position of the threaded holes after carburizing and quenching, and it cannot be assembled with the differential housing. At the same time, this process method requires protection and rethreading of the threads, which is inefficient.

[0003] The invention discloses a process method for processing a threaded hole of a carburized steel electric drive axle main reduction gear. The process method effectively solves the problem of excessive carburizing and quenching of the threaded hole of the electric drive axle main reduction gear. Summary of the invention

[0004] The purpose of the present invention is to provide a method for processing threaded holes of carburized steel electric drive axle main reduction gears, so as to solve the problem that the threaded holes are deformed during the carburizing and quenching process, resulting in the inability to assemble and low processing efficiency.

[0005] The technical solution of the present invention is a method for processing threaded holes of carburized steel electric drive axle main reduction gears. The method is to adjust the threaded hole processing to processing after heat treatment, perform carburizing treatment on the threaded hole position after heat treatment, and then perform drilling and tapping; the process route is: material preparation → carburizing and quenching → fine turning and carburizing → drilling and tapping.

[0006] In the aforementioned method for processing threaded holes of carburized steel electric drive axle main reduction gears, the carburized steel electric drive axle main reduction gears are made of 20MnCr5HH carburized steel, with a surface hardness of 58-62HRC, a core hardness of 35-45HRC, and a carburized layer depth of 1.0-1.3mm after carburizing and quenching.

[0007] In the aforementioned method for processing threaded holes in a carburized steel electric drive axle main reduction gear, the material preparation is as follows: before heat treatment, the decarburization allowance of the gear blank is determined based on the carburized layer depth of the processed parts, the Rockwell-C hardness distribution band in the terminal hardenability test in the raw material execution standard, and the surface depth hardness after carburizing and quenching.

[0008] In the aforementioned method for processing threaded holes of carburized steel electric drive axle main reduction gears, the fine turning and stripping of carbon is as follows: using a vertical lathe to turn off the stripping allowance, and fine turning the reference outer circle and the positioning end face; (1) The three-jaw chuck clamps the outer circle against the flat end face, turns the reference outer circle and the positioning end face, and completes the processing by clamping the end face and the outer circle at one time, ensuring that the verticality of the end face and the outer circle is ≤0.015mm; (2) After the turning fixture drives the main reduction gear to turn over, the three-jaw chuck clamps the machined outer circle to level the machined end face, and the other end face is turned to remove the carbon stripping residue to ensure that the end face and the reference outer circle runout is ≤0.03mm, and the parallelism with the end face is ≤0.03mm.

[0009] In the aforementioned method for processing threaded holes of carburized steel electric drive axle main reduction gears, the drilling and tapping is processed by a three-axis machining center, which specifically includes the following steps: (1) Position the outer circle and end face of the precision machined part, and clamp the reference outer circle of the three-jaw chuck against the machined end face; (2) Use a general carbide drill to drill the thread bottom hole, ensuring the position accuracy is ≤0.15mm; (3) Use general carbide chamfering to chamfer the hole; (4) Use a general-purpose carbide tap to tap the threads.

[0010] Beneficial effects of the present invention: Compared with the prior art, the method of the present invention utilizes that the hardness of carburized steel decreases with increasing depth, and by reserving a carburized layer for fine turning, and removing the carburized layer after carburizing and quenching, the surface hardness is reduced to a level that allows threaded holes to be processed with conventional tools. Since the threaded holes are adjusted to carburizing and quenching before processing, the present invention avoids deformation caused by carburizing and quenching, and ensures that the threaded hole processing position is 100% qualified. Compared with the original process route, two processes are reduced, which not only improves the processing quality of the threaded holes of the carburized steel electric drive axle main reduction gear, but also greatly improves the processing efficiency of the electric drive axle main reduction gear. This method is stable and reliable, easy to operate, and can ensure the processing quality of the product. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 This is the surface depth hardness test report of 20MnCr5HH material; Figure 2 Execute the Rockwell-C hardness distribution band in the end hardenability test of standard DIN EN 10084-2008 for 20MnCr5HH material; Figure 3 is a schematic diagram of a tooth blank; Figure 4 It is a schematic diagram of carburizing and quenching; Figure 5 It is a schematic diagram of the lathe benchmark after heat treatment; Figure 6Schematic diagram of carbon stripping for fine turning; Figure 7 Schematic diagram of drilling and tapping. DETAILED DESCRIPTION

[0012] The present invention is further described below in conjunction with the accompanying drawings and embodiments, but they are not intended to limit the present invention.

[0013] Embodiment of the present invention: The material of the electric drive axle main reduction gear is 20MnCr5, the surface hardness after carburizing and quenching is 58-62HRC, the core hardness is 35-45HRC, and the carburized layer depth is 0.8-1.1mm. It is required to process 16-M16*1.5-7H threaded holes, the bottom hole depth is 45mm, the effective thread length is 35mm, the hole chamfer is C1, and the position accuracy is Φ0.3mm.

[0014] 1. Gear blank preparation: During gear blank processing, according to the surface depth hardness test report of 20MnCr5HH material after carburizing and quenching ( Figure 1 ) and Rockwell-C hardness distribution band in the end hardenability test of 20MnCr5HH ( Figure 2 ) It is known that when 1.5mm of the surface of the main reduction gear is removed after carburizing and quenching, the surface hardness has been reduced to below 49HRC. The hardness of conventional drills and taps is generally 60-65HRC, which is completely processable. Therefore, a 1.5mm stripping layer margin is reserved for the gear blank ( Figure 3 ).

[0015] 2. Carburizing and quenching: Carburize and quench the main reduction gear blank directly; use a combined furnace or a multi-purpose furnace ( Figure 4 ).

[0016] 3. Fine turning and carbon stripping: Use a vertical lathe to turn off the carbon stripping allowance, and fine turn the clamping outer circle and positioning end face: 1) Turning reference: Three-jaw chuck clamps the outer circle against the flat end face, and the tool can be a T-shaped turning tool made of CBN coating material. The radius of the turning tool tip arc is R0.4, the spindle speed is 100r / min, the feed rate is 0.25mm, and the tool speed is 40mm / min. Turn the end face and the outer circle, and complete the processing by clamping the end face and the outer circle at one time, ensuring that the verticality of the end face and the outer circle is ≤0.015mm ( Figure 5 ).

[0017] 2) Carbon stripping: After the turning fixture drives the main reduction gear to turn over, the three-jaw chuck clamps the turned outer circle and the turned end face, and the other end face is turned to remove the carbon stripping allowance. The tool can still use the same T-shaped turning tool with CBN coating material. The turning tool tip arc radius is selected as R0.4, the spindle speed is 100r / min, the feed rate is 0.25mm, and the tool speed is 40mm / min. Ensure that the outer circle roundness is ≤0.02mm, the end face and the outer circle runout is ≤0.03mm, and the parallelism with the end face is ≤0.03mm ( Figure 6 ).

[0018] 4. Drilling and tapping: Processed by three-axis machining center ( Figure 7 ).

[0019] 1) Use the precision-turned outer circle and end face for positioning, and clamp the machined outer circle with a three-jaw chuck to level the machined end face.

[0020] 2) Use Φ14.5 general carbide drill to drill the thread bottom hole, the tool speed is 1500r / min, the feed rate is 65mm / min, the position accuracy is guaranteed to be ≤0.1mm, and the hole depth is 45mm.

[0021] 3) Use a general carbide chamfering cutter to chamfer the hole C1.

[0022] 4) Finally, use a general carbide tap to tap the thread, with a tool speed of 600r / min, a feed rate of 30mm / min, and an effective thread hole depth of 35mm. The processing is completed.

[0023] The method of the present invention reserves a decarburizing layer before heat treatment, then directly performs carburizing and quenching, performs fine turning and decarburizing after heat treatment, and finally performs drilling and tapping. After carburizing and quenching, the excess of the carburized layer is removed during fine turning and decarburizing, so conventional tools can be used for drilling and tapping, eliminating the traditional threaded hole protection process method and eliminating the influence of heat treatment on the position deformation of the threaded hole. See the specific process flow for details. Figure 3-Figure 7 The process is stable and reliable, and the operation is simple and convenient. It does not affect the product characteristics, but can improve the processing quality and efficiency.

[0024] This specification describes examples of embodiments of the present invention, and it is not intended that these embodiments illustrate and describe all possible forms of the present invention. It should be understood that the embodiments in the specification can be implemented in a variety of alternative forms. The drawings need not be drawn to scale; some features can be enlarged or reduced to show the details of specific components. The specific structural and functional details disclosed should not be interpreted as limiting, but are merely representative bases for teaching those skilled in the art to implement the present invention in various forms. It should be understood by those skilled in the art that the multiple features illustrated and described with reference to any of the figures can be combined with the features illustrated in one or more other figures to form embodiments that are not explicitly illustrated or described. The illustrated combined features provide representative embodiments for typical applications. However, various combinations and variations of features consistent with the teachings of the present invention can be used for specific applications or implementations as needed.

[0025] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for machining threaded holes of carburized steel electric drive axle main reduction gears, characterized in that: The method is to adjust the threaded hole processing to processing after heat treatment, decarburize the threaded hole position after heat treatment, and then drill and tap; the process route is: material preparation → carburizing and quenching → fine turning and decarburizing → drilling and tapping.

2. A method for machining threaded holes of carburized steel electric drive axle main reduction gears according to claim 1, characterized in that: The carburized steel electric drive axle main reduction gear adopts 20MnCr5HH carburized steel, and the surface hardness after carburizing and quenching is 58-62HRC, the core hardness is 35-45HRC, and the carburized layer depth is 1.0-1.3mm.

3. The method for machining threaded holes of carburized steel electric drive axle main reduction gears according to claim 1, characterized in that: The material preparation is as follows: before heat treatment, the carbon stripping allowance of the gear blank is determined according to the carburized layer depth of the processed parts and the Rockwell-C hardness distribution band in the terminal hardenability test in the raw material execution standard and the surface depth hardness after carburizing and quenching.

4. The method for machining threaded holes of carburized steel electric drive axle main reduction gears according to claim 1, characterized in that: The precision turning and carbon stripping includes: using a vertical lathe to turn off the carbon stripping allowance, and precision turning the reference outer circle and the positioning end face; (1) The three-jaw chuck clamps the outer circle against the flat end face, turns the reference outer circle and the positioning end face, and completes the processing by clamping the end face and the outer circle at one time, ensuring that the verticality of the end face and the outer circle is ≤0.015mm; (2) After the turning fixture drives the main reduction gear to turn over, the three-jaw chuck clamps the machined outer circle to level the machined end face, and the other end face is turned to remove the carbon stripping residue to ensure that the end face and the reference outer circle runout is ≤0.03mm, and the parallelism with the end face is ≤0.03mm.

5. A method for machining threaded holes of carburized steel electric drive axle main reduction gears according to claim 4, characterized in that: The drilling and tapping is processed by a three-axis machining center, specifically comprising the following steps: (1) Position the outer circle and end face of the precision machined part, and clamp the reference outer circle of the three-jaw chuck against the machined end face; (2) Use a general carbide drill to drill the thread bottom hole, ensuring the position accuracy is ≤0.15mm; (3) Use general carbide chamfering to chamfer the hole; (4) Use a general-purpose carbide tap to tap the threads.

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