Adopting an optimized free forging process can avoid material waste caused by the excessive amount of forging required for the small shafts at both ends of the flange shaft in traditional processes while also avoiding some quality hazards brought about by traditional forging methods to a greater extent.
Traditional forging process for flange shafts
The flange shaft is an important large forging used for transmission in large equipment such as blowers and has a wide range of applications in industry. The approximate shape is shown in Figure 1, and the material is generally 45# steel, 42CrMo, etc. The processing process is generally: forging → rough machining → quenching and tempering heat treatment → precision machining → packaging. This article mainly discusses a new process in the forging process.
Figure.1 Flange Shaft
The flange shaft structure is unique, with a large flange in the middle and several small shaft steps distributed on both sides, which are symmetrical, with a smaller diameter and longer length. The cross-sectional difference between the flange and the small shaft is significant. The traditional forging process is as follows:
- First heat: Heat the raw material steel ingot to 1240 ℃ according to the specification requirements, and after being discharged from the furnace, start pressing the clamp → chamfering → cutting the nozzle → upsetting → rounding out.
- Second heat: upsetting → rounding → marking → pulling out the steps at both ends → completing precision forging and straightening → heat treatment after forging.
The process’s most critical and difficult part is pulling out the steps at both ends after the number printing is completed. This process is shown in Figure 2, and the dimension D in the figure is to ensure the following processing requirements. If there is eccentricity during the forging process, it should be promptly offset, and a large margin should be left. Generally, it should be greater than the flange diameter size of the forging by 50mm-80mm. According to the forging process specifications, dimension A in the figure must be greater than or equal to dimension D/3; otherwise, a concave center may occur during the elongation process, resulting in the forging not being completed properly. However, due to the large diameter of the flange, the D dimension is usually large. At least a D/3 dimension must be left to avoid the concave center, often much larger than the calculated split size at both ends. However, due to the need for forging technology to avoid the concave center, this excess material must also be left, which greatly reduces the utilization rate of raw materials and increases unnecessary costs; according to statistics, the utilization rate of finished materials by this forging method is basically between 30%-35%. Moreover, as the cross-sectional difference between the flange and shaft increases, more additional materials must be left at both ends to meet the requirements of D/3. The waste of materials will become more apparent. The utilization rate of some finished steel ingots is even lower than 30%.
Figure.2 Drawing process diagram of steps at both ends
In actual production, due to the thin thickness of the flange and the large cross-sectional difference between the flange and the shaft, forging defects such as flange deformation, shaft eccentricity, and non-concentricity of the two ends of the shaft are prone to occur during the forging process, which brings great inconvenience to subsequent processing. Even scrap accidents often occur due to insufficient forging dimensions that cannot meet the requirements for precision machining. The specific reasons for these problems and preventive measures are briefly listed in Table 1.
Table.1 Reason Analysis and Rectification Measures for Forging Defects
|Problem||Cause analysis||Preventive and corrective measures|
1) When elongating the small shafts at both ends, due to the large cross-sectional difference, there is a downward tensile force on the flange part that has not been compressed during the compression process. However, the flange is too thin and can withstand less force, resulting in flange deformation and even S-shape.
2) During the process of pulling out the shaft, there is eccentricity phenomenon and misalignment occurs. When misalignment occurs, a flange is used as the fulcrum, but the flange is too thin and can withstand less force, resulting in flange deformation.
1) Reduce the amount of pressing, evenly press down on both sides of the shaft to avoid forming one side separately.
2) Increase the thickness and diameter of the intermediate flange appropriately, increase the force that the flange bears, and increase the margin of the flange diameter.
3) Ensure uniform heating before leaving the furnace for forging, to avoid the occurrence of eccentric processes.
4) Using reasonable tools to create better conditions for misalignment and reduce the stress on the flange.
|Eccentricity of shaft body and non concentricity of shaft bodies at both ends||Due to uneven heating temperature, there is a phenomenon of redness, which refers to the presence of both positive and negative surfaces. During the process of pulling out the shaft, the material on the side with high temperature will move faster than on the side with low temperature, resulting in uneven material flow up and down. The problem reflected is the eccentricity of the shaft, which means the center of the shaft deviates from the center of the flange. As the difference in cross-sectional dimensions increases, this issue becomes more prominent. Improper control of the medium pressure reduction during operation by the operator can also cause eccentricity, such as inconsistent reduction of the same section, eccentric forging with inconsistent centers on the upper and lower anvils, and so on||Ensure sufficient time to return to the furnace, ensure uniform heating of the forging, and ensure uniform temperature in all parts to avoid redness, providing better prerequisites for forging. During the operation process, the operator should strictly control the reduction amount according to the process requirements to avoid eccentric forging of the press. If eccentricity is found during the forging process, it should be promptly corrected, and some auxiliary tools should be used to assist in measuring the eccentricity and different center situations of the forging, and targeted eccentricity should be carried out.|
A clear analysis of the reasons for the above issues has been conducted. Although the corresponding preventive and corrective measures were formulated to prevent and correct the causes individually, they are difficult to avoid in the implementation process. Some problems are difficult to avoid, and several problems are interrelated. In addition, different operators have different operating levels, and the forging process relies on visual observation, resulting in different errors. Therefore, it is difficult to solve the problem completely. Even some measures can seriously affect production efficiency and increase the cost of the production process.
This article solves the above problems through another new free-forging process. The main idea is to reduce the size of D in Figure 2, thereby reducing the size of D/3 so that it is equal to or slightly larger than the actual material separation needs at both ends, reducing waste caused by excess material separation. The middle flange part meets the process size requirements by increasing the size of B and then using the flange upsetting plate to increase the size of D. The specific process is as follows:
- First heat: Heat the raw material steel ingot to 1240 ℃ according to the specification requirements, and after being discharged from the furnace, start pressing the clamp → chamfering → cutting the nozzle → upsetting → round drawing → marking → shaft drawing, as shown in Figure 3.
- Second heat: As shown in Figure 4, erect the blank and use the upsetting flange plate to upset the flange to the process size → elongate the steps at both ends to the process size → Finish precision forging and straightening → heat treatment after forging.
Figure.3 Optimized forging process diagram
Figure.4 Flange Upsetting
Figure.5 Simulation Process of Flange Forming
The optimized forging process reduces the cross-sectional difference between the flange and the small shaft before the flange forms, greatly reducing the difficulty of forging. Eccentricity and nonconcentricity issues are more easily corrected during the forging process. After the eccentricity and nonconcentricity issues before flange forming are solved, deformation problems during subsequent flange forming processes can be well corrected through tooling. Moreover, due to tooling limitations and eccentricity, non-concentricity only occurs again during the flange-forming process, effectively avoiding these defects. Figure 5 shows the flange-forming process simulated by DEFORM software and the required pressure during the forming process. It can be seen that the forming effect is ideal, but from the perspective of forming pressure, the requirements for equipment pressure are relatively high. Moreover, as the flange diameter increases, the forming pressure will increase, and matching equipment is needed to achieve the flange forming process.
Figure.6 Simulation process of flange upsetting.
Figure 6 shows that the total length of the flange during the upsetting process becomes longer, indicating that all the materials that increase the flange diameter come from the circumferential flange. Some of the materials from the circumferential flange are distributed to the intermediate shaft body, resulting in the total length of the shaft body becoming longer (theoretically, the upsetting diameter should be around 1630mm, while the simulated value shown in Figure 6 (c) is only around 1570mm, indicating that not all the materials from the circumferential flange are used for the increase of the flange outer diameter, Some parts extend inward to form the longitudinal length of the shaft, so when formulating the process, the size of the intermediate flange before upsetting cannot be calculated completely according to the principle of volume invariance. That is, the volume of the flange circumference before upsetting the flange should be equal to the volume of the flange circumference after upsetting the flange. A certain margin must be left to ensure sufficient flange area material meets the process size requirements. When formulating the forging process, when reducing the diameter D, as long as the length of both ends can meet the requirements of D/3, even if it is slightly less than D/3 (because the shaft of the upsetting flange will also be longer in the future), excessive reduction of the diameter D should be avoided as much as possible, because the more reduction, the larger the flange thickness dimension B, which is equivalent to a high middle height when upsetting the flange, not only will it increase the pressure required for upsetting, Due to excessive deformation during upsetting, dimensional defects such as double strand, folding, and even tearing may occur. This should be fully considered when formulating the process. The diameter D dimension should be minimized as much as possible to reduce the difficulty of the flange-forming process and the occurrence of quality problems.
The new process fundamentally solves the problem of raw material waste and greatly improves material utilization. Through statistics, the material utilization rate of the finished product has increased to around 50%. And the use of tooling aids has solved quality problems such as flange deformation, eccentricity, and non-concentricity. At the same time, the added tooling aids are very simple and versatile and can be used to produce various specifications of flange shafts. The actual operation is also relatively simple.
- (1) The new process has solved the problem of low raw material utilization, increasing the material utilization rate of finished products from 30% -35% to 45% -50%. And as the difference in cross-sectional dimensions between the flanges and shafts increases, the material utilization rate will increase.
- (2) The new process greatly avoids quality problems such as flange deformation, eccentricity, and non-concentricity in traditional processes, reduces the difficulty of forging operations, and has strong practicality.
- (3) The flange forming process requires the production of corresponding tooling and accessories, and the forming requires a large amount of pressure, which requires sufficient pressure equipment to cooperate with forging.
Author: Chen Wenquan