Carburizing and quenching distortion control method for gear shaft with large length-diameter ratio
By employing a specific mounting method and a stepped heating process during carburizing and quenching, the problem of deformation control for gear shafts with large length-to-diameter ratios was solved, improving the yield and reducing production costs.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-09
- Publication Date
- 2026-03-10
AI Technical Summary
Large length-to-diameter ratio gear shafts undergo significant deformation during carburizing and quenching, making control difficult and resulting in low finished product qualification rates and high production costs.
Specific mounting methods and heating processes are adopted, including applying anti-seepage coating before carburizing, adjusting the mounting direction after carburizing, and using a stepped heating process to reduce deformation during heat treatment.
This effectively reduced the deformation of the gear shaft, improved the finished product qualification rate, and lowered production costs.
Smart Images
Figure CN121629149A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to deformation control during heat treatment of gear shafts, and more particularly to a method for controlling distortion during carburizing and quenching of gear shafts with a large length-to-diameter ratio. Background Technology
[0002] In the manufacturing of hardened gears, carburizing and quenching is the most mainstream heat treatment process, but the prominent technical problem at present is the control of gear distortion.
[0003] For carburized and quenched gears, especially gear shafts with a large length-to-diameter ratio, the deformation is significant, influenced by numerous factors, and difficult to control, making it one of the technical challenges in gear manufacturing both domestically and internationally. Current research and analysis have yielded a series of results. For example, a collaborative research center has been established at the University of Bremen in Germany, comprised of over 20 experts in materials science, processing technology, mathematics, and process control engineering, forming 12 research groups specifically to study deformation problems in the production process. Their project is named "Distortion Engineering" (SFB570 project). The research direction is to link workpiece distortion with various stages of production, using a systematic approach to analyze and study the cross-correlation between its subsystems. The aim is to establish a procedure for controlling system distortion in the production process, comprehensively solving the problem of workpiece deformation control. Currently, the project is underway, and preliminary research results indicate that the final deformation of workpieces in industrial production is not entirely caused by heat treatment and quenching. The quenching process merely releases potential deformation factors, which have gradually accumulated in various production processes, such as design, material selection, casting, forging, machining, heat treatment, and grinding. Therefore, deformation control should be a comprehensive system control engineering approach throughout the manufacturing process.
[0004] Significant deformation during carburizing and quenching not only increases or eliminates the grinding required for subsequent gear machining, leading to scrap and increased costs, but also affects the gear's manufacturing precision, reduces its load-bearing capacity, and ultimately significantly shortens its service life.
[0005] According to a survey by the Federation of German Industries (VDMA), in 1995 alone, the increased costs in the German power transmission manufacturing sector due to the elimination of deformation amounted to 850 million euros, while the losses due to the decline in the performance of components caused by deformation could reach billions of euros.
[0006] One of the prominent problems in the manufacturing process of carburized gears in my country is deformation, which has long remained unresolved. This is especially true for shaft gears processed by carburizing and quenching, particularly those with a length-to-diameter ratio greater than 10. In single-piece or small-batch production, the deformation problem during carburizing and quenching is particularly troublesome due to the difficulty in standardizing various aspects such as materials, design, forging, machining, and heat treatment. The deformation is large, irregular, and difficult to control, resulting in 3-4 or even more scrapped pieces out of 10, leading to low finished product yield and high production costs for shaft gears with large length-to-diameter ratios. Summary of the Invention
[0007] The purpose of this invention is to provide a method for controlling distortion during carburizing and quenching of gear shafts with a large length-to-diameter ratio, so as to reduce workpiece deformation caused by carburizing and quenching processes and improve the finished product qualification rate of gear shafts with a large length-to-diameter ratio.
[0008] To achieve the above objectives, the present invention can adopt the following technical solutions: The method for controlling distortion during carburizing and quenching of large length-to-diameter ratio gear shafts according to the present invention includes controlling the mounting method of gear shaft parts during carburizing and quenching, as well as the heating method during carburizing and quenching. Mounting methods include: Before carburizing, apply anti-carburizing coating to the carbon layer of the gear shaft, and then carburize the gear shaft after it is mounted around the tooling frame. After carburizing, the convex surfaces of all gear shafts are adjusted so that they face the tooling before being fixed on the tooling frame for quenching. Heating methods include: A stepped heating process is used for both carburizing and quenching.
[0009] Specifically, during carburizing, a four-stage heating process is used to gradually raise the temperature to the required carburizing temperature; during quenching, a three-stage heating process is used to gradually raise the temperature to the required quenching temperature.
[0010] The advantage of this invention lies in its comprehensive control over the deformation of gear shaft parts with large length-to-diameter ratios during heat treatment, as well as the deformation patterns during heating or cooling. This control is achieved through the assembly of gear shaft parts and the temperature rise during carburizing and quenching, which greatly reduces the deformation of the gear shaft, improves the yield of the gear shaft, and lowers the production cost of gear shafts with large length-to-diameter ratios. Attached Figure Description
[0011] Figure 1 This invention relates to a gear shaft part that has undergone carburizing and quenching treatment.
[0012] Figure 2 yes Figure 1 Analysis of the deformation of gear shafts during carburizing.
[0013] Figure 3 yes Figure 1 Analysis of deformation of gear shafts during quenching.
[0014] Figure 4 yes Figure 1 Installation diagram of the gear shaft on the tooling fixture before carburizing.
[0015] Figure 5 yes Figure 1 Installation diagram of the gear shaft on the tooling fixture before quenching.
[0016] Figure 6 yes Figure 1 Carburizing process diagram of gear shaft.
[0017] Figure 7 yes Figure 1 Quenching process diagram of gear shaft. Detailed Implementation
[0018] The method of the present invention will be described in detail below through specific examples to facilitate understanding by those skilled in the art.
[0019] Figure 1 The part shown is a gear shaft with left and right helical teeth at both ends. The total length is 2195mm, the maximum diameter is 212mm, and the length-to-diameter ratio is greater than 10. After carburizing and quenching using conventional methods, the maximum radial runout of the gear shaft reached 8mm, resulting in a batch of scrapped parts during the grinding process.
[0020] Analysis revealed that the root cause of gear shaft deformation lies in stress. When the stress exceeds the elastic limit of the material, it causes gear deformation. There are three main types of stress that cause deformation during carburizing and quenching in the heat treatment process: thermal stress, structural stress, and mechanical stress caused by workpiece weight and other factors.
[0021] The deformation caused by thermal stress follows these rules: during heating, the face that heats up quickly has a smaller tip circle diameter, while the face that heats up slowly has a larger tip circle diameter; during cooling, the face that cools up quickly has a larger tip circle diameter, while the face that cools up slowly has a smaller tip circle diameter; the greater the temperature difference, the greater the stress, and the greater the final deformation.
[0022] During heating or cooling, if the temperature change exceeds the phase transformation point, a structural transformation will occur within the material. The asynchronous nature of this transformation in different parts of the gear will generate structural stress. During quenching, the temperature change during cooling is much faster than during heating, resulting in significantly greater structural stress during cooling than during heating. The effect of structural stress is the opposite of thermal stress. During quenching and cooling, the surfaces that undergo martensitic transformation first and cool faster have a smaller final tooth tip circle diameter; conversely, the surfaces that cool more slowly have a larger diameter. The greater the temperature difference, the greater the structural stress, and ultimately, the greater the deformation.
[0023] This shaft gear is a large-sized shaft gear. During the carburizing and quenching process, heat treatment plays a major role. Theoretically speaking, its deformation law is as follows: During carburizing, heating plays a dominant role, with the outside heated first and the inside later. The temperature difference between the inside and outside during the heating process leads to dimensional deformation after carburizing. The deformation results and stress are as follows: Figure 2 As shown: Gear shaft A on the tooling fixture is subjected to tensile and compressive stresses, causing it to bend and deform inward.
[0024] During the quenching process, cooling plays a dominant role, with faster external cooling and slower internal cooling. The temperature difference during the cooling process leads to dimensional deformation after quenching. The deformation results and stress are as follows: Figure 3 As shown: Gear shaft A on the tooling fixture is subjected to compressive and tensile stresses, causing it to bend and deform outwards.
[0025] This invention proposes a method for controlling distortion during carburizing and quenching of gear shafts with a large length-to-diameter ratio, based on the above deformation characteristics: First, before carburizing, apply an anti-carburizing coating to the carbon layer (toothless part) of the gear shaft. Then, after assembling the gear shaft around the tooling fixture, perform carburizing treatment. The assembled gear shaft looks like... Figure 4 ; After carburizing, reverse deformation quenching is adopted according to the actual deformation of the gear shaft. That is, all the convex surfaces of the gear shaft are adjusted to face the tooling before being fixed on the tooling frame for quenching treatment.
[0026] This invention coats the toothless portion of the gear shaft with an anti-carburizing coating before carburizing, and only carburizes the gears at both ends. This reduces the need for machining the carbon layer between carburizing and quenching processes (the traditional process involves carburizing the entire gear shaft, then removing the carburized layer from the toothless portion by machining before quenching), saving processing time and costs. After carburizing, each gear shaft is rotated and adjusted so that its convex surface faces the tooling. This effectively offsets the deformation that occurs during carburizing during quenching, greatly reducing distortion during carburizing and quenching of the gear shaft.
[0027] To ensure uniform temperature of the gear shaft during heating, this invention employs a stepped heating process for the gear shaft during carburizing and quenching. The specific heating process is as follows: During carburizing: First, slowly raise the temperature to 470℃ over 1.5 hours, hold for 2 hours, then continue raising the temperature to 650℃ over 1.5 hours, hold for another 2.5 hours, then continue raising the temperature to 800℃ over 1.5 hours, hold for another 2.5 hours, and finally raise the temperature to 920℃ and maintain it (venting for 1 hour, strong carburizing for 18 hours, maintaining a carbon potential of 1.16%C, diffusion one for 8 hours, carbon potential of 1%C, diffusion two for 10 hours, maintaining a carbon potential of 0.8%C); then lower the temperature to 820℃ and hold for 2 hours, then air cool to room temperature; finally, raise the temperature to 650℃ and hold for another 3.5 hours, then air cool to room temperature to complete the carburizing process. The specific process is as follows: Figure 6 .
[0028] During quenching, the temperature is first raised to 400℃ and held for 1.5 hours. Then, the temperature is raised to 650℃ and held for another 1.5 hours. Finally, the temperature is raised to the carburizing temperature of 845℃ and held for 2.5 hours before oil cooling. After oil cooling to 220℃, the temperature is held for 15 hours, and then air-cooled to room temperature to complete the quenching process. The specific process is as follows: Figure 7 .
[0029] according to Figure 1 The deformation data at seven locations on the gear shafts after carburizing and quenching in one batch (10 shafts) are shown in the table below: The test data above shows that the maximum runout of the 10 gear shafts after carburizing and quenching treatment according to the method of the present invention is only 2.8mm, and the subsequent tooth surfaces can be completely machined, which greatly improves the yield of gear shafts and reduces processing costs.
Claims
1. A method of controlling carburizing quenching distortion of a large length-diameter ratio gear shaft, characterized by: The method comprises a mounting mode of gear shaft parts during carburizing and quenching and a temperature rising mode during carburizing and quenching, wherein The mounting mode comprises: Before carburizing, a carbon layer part of the gear shaft is coated with a permeation-proof coating, and then the gear shaft is mounted around a tooling frame to perform carburizing treatment; After carburizing, all convex surfaces of the gear shafts are faced towards the tooling to be fixed on the tooling frame to perform quenching treatment; The temperature rising mode comprises: Both the carburizing and the quenching adopt a stepwise temperature rising process.
2. The method according to claim 1, wherein during carburizing, a four-section temperature rising process is adopted to gradually raise the temperature to a required carburizing temperature; and during quenching, a three-section temperature rising process is adopted to gradually raise the temperature to a required quenching temperature.