Spiral bevel gears play a crucial role in gear transmission, and their performance directly affects the efficiency and service life of the gear transmission. To obtain spiral bevel gears with excellent mechanical properties and long service lives, many scholars at home and abroad have conducted in-depth studies on the forming, heat treatment, and surface treatment of spiral bevel gears. This article focuses on the research and analysis of the compound forming characteristics of a certain type of spiral bevel gear, aiming to provide valuable references for the practical engineering application of the compound forming of spiral bevel gears.
1. Introduction
The traditional forming process of spiral bevel gears includes steps such as pouring steel ingots, blooming, blanking, upsetting, punching, ring rolling, and machining. However, this process has several drawbacks, such as wasting raw materials and energy, and resulting in poor product quality. Moreover, the internal structure of the formed parts is uneven, and the comprehensive mechanical properties are relatively poor. In response to these shortcomings, and in combination with the favorable policies of energy conservation, emission reduction, and environmental protection advocated by the country, as well as the strong promotion of “Made in China 2025”, the compound forming technology of casting and forging has been developed.
2. Compound Forming Process of Spiral Bevel Gears
The compound forming process of casting and forging, also known as the casting blank forging process, refines the blank by forging the cast blank formed by casting in a precise mold into a complex and high-quality forging part. The specific process for the compound forming of spiral bevel gears is as follows: molten iron is poured to form the casting blank of the spiral bevel gear, followed by rough forging and then finish forging. This process significantly reduces the process flow and repeated heating, and the obtained formed parts have fine and uniform microstructure, with excellent comprehensive mechanical properties.
For the compound formed spiral bevel gear parts studied in this article, the main dimensions are shown in Figure 1. The material used for the casting and forging parts is 20CrMoH low alloy steel, with a casting volume of approximately 430,808 mm³. The casting temperature is selected as 1520°C, and the pouring time is 518 s. The mold material for forging is die steel H13, and the forging deformation amounts are set as 10%, 20%, 30%, and 40%, respectively. The calculation of the deformation amount is the ratio of the difference between the maximum cross-sectional area after deformation and the cross-sectional area before deformation to the area of the blank before deformation. The forging speeds are set as 10, 20, 30, and 40 mm/s, respectively, and the forging temperatures are 850, 950, 1050, and 1150°C, respectively. The ambient temperature is 25°C, the die preheating temperature is 200°C, and the friction coefficient is 0.65.
3. Microstructure of Spiral Bevel Gear Casting and Forging Composite Moldings
3.1 Microstructure of Spiral Bevel Gear Castings
According to the main dimensions of the spiral bevel gear casting and forging composite moldings in Figure 1, sand casting is adopted, with a casting temperature of 1520°C and a pouring time of 518 s. The obtained microstructure of the spiral bevel gear casting is shown in Figure 2. It can be seen that the microstructure of the spiral bevel gear casting mainly consists of gray-black pearlite and white ferrite, without a recrystallized structure.
3.2 Influence of Forging Process Parameters on the Microstructure of the Moldings
3.2.1 Influence of Forging Deformation Amount
An experiment was conducted to study the influence of the forging deformation amount on the internal microstructure of the spiral bevel gear casting and forging composite moldings. The casting temperature was set as 1520°C, the pouring time was 518 s, the forging deformation amounts were 10%, 20%, 30%, and 40% respectively, the forging speed was 20 mm/s, the forging temperature was 1050°C, the ambient temperature was 25°C, the die preheating temperature was 200°C, and the friction coefficient was 0.65. The microstructures of the spiral bevel gear casting and forging composite moldings under different forging deformation amounts are shown in Figure 3.
It can be observed from Figure 3 that during the compound forming process of the spiral bevel gear, with the increase of the forging deformation amount, the grains of the spiral bevel gear casting and forging composite moldings gradually become finer, and the new recrystallized nuclei all appear at the grain boundaries or high dislocation density areas. When the forging deformation amount reaches a certain value, the grain boundaries gradually start to form and new recrystallized nuclei appear, and then dynamic recrystallization occurs again. After dynamic recrystallization occurs, with the increase of the deformation amount, the grains are significantly refined and homogenized, indicating that by choosing an appropriate forging deformation amount, a casting and forging molding with fine and uniform microstructure can be obtained. The grains in Figure 3 (d) are fine, and the structure is relatively uniform.
3.2.2 Influence of Forging Temperature
An experiment was carried out to study the influence of the forging temperature on the internal microstructure of the spiral bevel gear casting and forging composite moldings. The casting temperature was set as 1520°C, the pouring time was 518 s, the forging deformation amount was 40%, the forging speed was 20 mm/s, and the forging temperatures were 850, 950, 1050, and 1150°C respectively. The microstructures of the spiral bevel gear casting and forging composite moldings under different forging temperatures are shown in Figure 4.
From Figure 4 and Figure 3 (d), it can be known that in the compound forming experiment of the spiral bevel gear, with the increase of the forging temperature, the internal grains of the spiral bevel gear casting and forging composite moldings change from coarse to fine and then become slightly coarser, and the new recrystallized nuclei all appear at the grain boundaries or high dislocation density areas. The grains are relatively fine and the structure is relatively uniform at 1050°C.
3.2.3 Influence of Forging Speed
An experiment was performed to study the influence of the forging speed on the internal microstructure of the spiral bevel gear casting and forging composite moldings. The casting temperature was set as 1520°C, the pouring time was 518 s, the forging deformation amount was 40%, the forging speeds were 10, 20, 30, and 40 mm/s respectively, the forging temperature was 1050°C, the ambient temperature was 25°C, the die preheating temperature was 200°C, and the friction coefficient was 0.65. The microstructures of the spiral bevel gear casting and forging composite moldings under different forging speeds are shown in Figure 5.
It can be seen from Figure 5 and Figure 3 (d) that in the compound forming process of the spiral bevel gear, with the decrease of the forging speed, the internal grains of the spiral bevel gear casting and forging composite moldings change from coarse to fine and then become slightly larger, and the new recrystallized nuclei all appear at the grain boundaries or high dislocation density areas. When the forging speed reduces to a certain value, the grain boundaries gradually start to form and new recrystallized nuclei appear, and then dynamic recrystallization occurs again. After dynamic recrystallization occurs, with the decrease of the forging speed, the grains are significantly refined and homogenized, indicating that by choosing an appropriate forging speed, a casting and forging molding with fine and uniform microstructure can be obtained.
4. Summary and Conclusion
To sum up, the internal pearlite and ferrite of the spiral bevel gear casting appear as fine and uniform recrystallized structures in the compound formed casting and forging moldings through forging. During the compound forming process of the spiral bevel gear, the forging process parameters have a significant influence on its internal microstructure. In order to obtain a compound formed spiral bevel gear with a refined and uniform internal microstructure, the following compound forming parameters should be selected: the casting temperature is 1520°C, the pouring time is 518 s, the forging deformation amount is 40%, the forging speed is 20 mm/s, the forging temperature is 1050°C, the ambient temperature is 25°C, the die preheating temperature is 200°C, and the friction coefficient is 0.65.
The following is a summary of the research results in a table format:
| Research Content | Findings |
|---|---|
| Microstructure of Spiral Bevel Gear Castings | Mainly composed of gray-black pearlite and white ferrite, without a recrystallized structure. |
| Influence of Forging Deformation Amount on the Microstructure of the Moldings | With the increase of the forging deformation amount, the grains of the moldings gradually become finer, and new recrystallized nuclei appear at the grain boundaries or high dislocation density areas. Choosing an appropriate forging deformation amount can obtain a molding with fine and uniform microstructure. |
| Influence of Forging Temperature on the Microstructure of the Moldings | With the increase of the forging temperature, the grains change from coarse to fine and then become slightly coarser, and new recrystallized nuclei all appear at the grain boundaries or high dislocation density areas. The grains are relatively fine and the structure is relatively uniform at 1050°C. |
| Influence of Forging Speed on the Microstructure of the Moldings | With the decrease of the forging speed, the grains change from coarse to fine and then become slightly larger, and new recrystallized nuclei all appear at the grain boundaries or high dislocation density areas. Choosing an appropriate forging speed can obtain a molding with fine and uniform microstructure. |
| Optimal Compound Forming Parameters of Spiral Bevel Gear | Casting temperature of 1520°C, pouring time of 518 s, forging deformation amount of 40%, forging speed of 20 mm/s, forging temperature of 1050°C, ambient temperature of 25°C, die preheating temperature of 200°C, and friction coefficient of 0.65. |
In addition, to further enhance the understanding of the compound forming technology of spiral bevel gears, the following are some related research summaries:
5. Related Research on Spiral Bevel Gear Forming
5.1 Research on Warm Forging Near-Net Forming for Spiral Bevel Gear
A study investigated the warm-forging technology of spiral bevel gears within the temperature range of 873 K to 1073 K. Based on the rigid-plastic finite element method, numerical simulations were conducted using DEFORM V11.0 software to explore the influence of different process parameters on the gear-forming quality and forming force during the warm forging process. Through nine groups of numerical simulation experiments, the influence laws of various forging speeds, die preheating temperatures, friction factors, and workpiece heating temperatures on the effective stress and strain of spiral bevel gears were systematically analyzed. The best combination of process parameters with the minimum forging force was obtained through the orthogonal experiment, providing a theoretical basis for the optimization design of the precision forging process of spiral bevel gears and offering a new idea for studying the precision-forging-forming process of other complex parts.
5.2 Research on the Tooth Shape of the Preform for Cold Precision Forging of Spiral Bevel Gear
Two tooth shape schemes, namely uniform diffusion tooth shape and non-uniform diffusion tooth shape, were proposed. By using the DEFORM-3D software, the cold precision forging process of gear blanks with different sizes was studied when these two tooth shape schemes were adopted, and the optimized tooth shape of the cold precision forging preform was determined.
5.3 Research on the Tooth Shape and Taper of the Preform for the Forging Step of Closed Hot Die Forging
The forming process of gear blanks with different tooth sizes and tapers similar to the trapezoidal tooth shape scheme in the hot die forging process was analyzed using the DEFORM-3D software. By comparing the metal flow direction and equivalent stress-strain distribution in the forming process of each scheme, the influence rules of tooth shape and gear taper on the hot die forging of gears were studied, and the optimized tooth shape and taper of the preform were determined.
5.4 Research on the Casting Process and Pouring Scheme of Spiral Bevel Gear
Comprehensively analyzing the structural characteristics, material composition, quality requirements, and technical requirements of the hot die forging step of the spiral bevel gear, the casting process and casting drawing were determined. Two casting schemes were designed, and their sizes were calculated respectively. The AnyCasting software was applied to analyze and compare the filling solidification process and defect prediction of the two pouring schemes to determine the best pouring scheme. The influence of different process parameters (pouring temperature and pouring speed) on the forming quality of the casting was studied, and the best process parameters were determined.
6. Significance and Application of the Research
The research on the compound forming characteristics of spiral bevel gears has important significance. Firstly, it provides a theoretical basis and practical guidance for the actual production of spiral bevel gears, helping to improve the quality and performance of the gears. Secondly, it promotes the development and application of new forming technologies, such as the compound forming technology of casting and forging, which has the advantages of saving materials, reducing energy consumption, and improving product quality.
In practical applications, the optimized compound forming parameters obtained in this study can be used in the production of spiral bevel gears to ensure that the gears have excellent mechanical properties, long service lives, and stable performance. For example, in the automotive industry, high-quality spiral bevel gears can improve the transmission efficiency and reliability of the vehicle, reducing noise and vibration. In addition, in the field of machinery manufacturing, the application of this technology can also improve the performance and quality of various mechanical equipment.
7. Future Research Directions
Although this study has achieved certain results, there are still some aspects that can be further explored and studied in the future. For example, more in-depth research can be conducted on the influence of material properties and microstructures on the compound forming process. Exploring new materials or optimizing the composition of existing materials may further improve the performance of the formed parts.
In addition, the combination of other advanced manufacturing technologies with the compound forming technology of casting and forging can also be investigated. For instance, integrating intelligent monitoring and control systems to achieve real-time monitoring and adjustment of the forming process, thereby improving the stability and repeatability of the process.
Furthermore, studying the fatigue and damage mechanisms of the compound formed spiral bevel gears under different working conditions can provide a basis for the design and life prediction of the gears, ensuring their reliability and safety in actual use.
In conclusion, the research on the compound forming characteristics of spiral bevel gears is a complex and challenging task. With the continuous progress of technology and the development of related research, it is believed that more advanced and practical results will be achieved in this field, providing more powerful support for the manufacturing and application of high-quality spiral bevel gears.
