The wheels are the core components that ensure smooth driving of vehicles, and the stability of the wheel structure will directly affect the safety of vehicle operation. During vehicle operation, the wheel rims will be subjected to radial load impacts due to their contact with the road surface. If the vehicle turns or deviates from a straight line, the body will apply axial stress to the wheel rims. If there are defects in the wheel casting, it will affect the stability of the wheel.
Therefore, when casting wheels, it is necessary to strictly check for casting defects and take effective measures to repair them in a timely manner in order to ensure the safety of vehicle driving.
Zhao Hui and others took train wheels as the research object, analyzed the folding casting defects of wide wheel rims in depth, and used the methods of pre forming molds and forging die modifications to solve the problem of folding casting defects of wide wheel rims. Although this method can effectively control the casting defects of wheel outer rim surface folding, this method did not effectively clean the surface of casting defects when repairing wheel folding casting defects, If not repaired properly, it can lead to porosity in the repaired casting defect location.
Zhang Mingbo and others analyzed the causes of weld cracking in C380CL steel wheels and believed that the mismatch between welding technology and welding materials led to weld cracking. This research has played a good role in enlightening the research in this paper, but this method needs to adjust the process parameters in the wheel manufacturing process to optimize the wheel casting quality when dealing with the wheel weld cracking.
The pressure sealing method is currently a commonly used method for repairing casting defects in pipeline materials. The advantages of this method are mainly reflected in its ability to repair casting defects in dynamic environments. The production cost of high-strength steel wheels is very high. For cast wheels with casting defects, an effective post welding repair method can be adopted to repair the casting defects, which can greatly save casting costs. Therefore, ZHY Casting will apply pressure sealing method to repair welding defects in high-strength steel wheel casting, and will
By using value simulation, analyze the welding repair and sealing effect of high-strength steel wheel casting defects, and provide theoretical basis for practical applications.
1. Welding repair method for casting defects of high-strength steel wheels based on pressure sealing
The high-strength steel wheels studied by ZHY Casting mainly use 40CrMnMo ultra-high strength steel, with a yield strength of 926 MPa. The chemical composition is shown in Table 1.
| C | Mn | Si | Cr | O |
| 0.41 | 1.10 | 0.26 | 1.10 | 0.26 |
1.1 Assessment of wheel weldability
The carbon equivalent of high-strength steel wheel casting materials is calculated using the following formula:
According to the standards formulated by the Welding Society, the weldability of the casting material for the high-strength steel wheels studied in this article is poor. Therefore, a reasonable preheating temperature needs to be set during welding repair of casting defects, and post heat treatment is required after welding repair.
1.2 Design of pressure plugging method
The method of applying pressure to seal the leakage is to first combine the specific situation of casting defects in high-strength steel wheels, so that the casting defect test piece of high-strength steel wheels is locally tightened under the pressure stress of the welding rod. When plugging, only the part where the casting defect is located should be welded. It is necessary to tighten one section after another, and then tighten one section after another. The operation should be repeated, and once all casting defects are plugged, the repair can be stopped. The welding repair of this method belongs to the segmented repair mode, which is particularly suitable for the crack casting defect shown in Figure 1. The schematic diagram of the repair process is shown in Figure 2.
This method can decompose one crack casting defect into multiple small segments and perform cyclic operations in a local repair manner to complete the overall casting defect repair. This repair method can ensure accurate repair of crack casting defects. In the direction of welding, the cooled weld seam is the repaired weld seam, and no welding rod pressure is applied at this position. The welding rod only applies pressure to the crack area to seal the leak.
1.3 Design of Pressure Sealing Welding Rod
Considering that the high-strength steel wheel casting material studied in the article belongs to metallic materials, it is easily affected by heat during the pressure sealing process, resulting in softening of the area and affecting the repair effect. Therefore, based on practical standards, the J107Cr welding rod with a slightly lower tensile strength than high-strength steel wheel casting material is used as the welding repair material in the article. Its chemical composition is shown in Table 2.
| C | Mn | Si | Cr | Mo | V | S | P |
| 0.08 | 2.03 | 0.47 | 1.71 | 0.59 | 0.097 | 0.011 | 0.021 |
1.4 Design of operating methods
1.4 1. Clean the test piece before applying pressure to seal the leak
ZHY Casting used an IPG nanosecond high pulse laser to clean the surface of high-strength steel wheel casting specimens. The basic information is shown in Table 3. The cleaning process parameters are shown in Table 4.
| Output wavelength/nm | Average power/W | Pulse width/nm | Maximum scanning speed/(mm · s ^ -1) | Maximum pulse frequency/kHz |
| 1 064 | 200 | 60 | 10 000 | 50 |
| Power/W | Scanning frequency/kHz | Scanning speed/(mm · s ^ -1) | Cleaning speed/(m · min ^ -1) | Cleaning frequency/time |
| 135 | 46 | 6 000 | 3 | 1 |
After cleaning the surface of high-strength steel wheel casting specimens, JSM IT300 scanning electron microscope was used to analyze the morphological changes of the specimen surface before and after cleaning, and the changes in surface composition were detected.
1.4 2 Preheating methods
The schematic diagram of preheating method is shown in Figure 3. The contour of the high-strength steel wheel casting defects specimen is circular, so a circular preheating tube is used in the article. After placing the specimen horizontally, combined with the size of the preheating flame, the distance between the preheating tube and the specimen is controlled. Generally, 40mm is the optimal distance between the two.
1.4 3. Temperature control method for post heat treatment
After welding repair, it is necessary to immediately use the BYH23-LCD-42 track heater to perform post heat treatment on the pressure sealed specimen. The temperature of the post heat treatment is set to 450 ℃, the insulation time is set to 3 hours, and then slowly drop to room temperature. The temperature control of post heat treatment is shown in Figure 4. When the temperature is consistent with room temperature, surface grinding operations need to be carried out on the repair location to reduce surface roughness.
1.4 4. Setting of pressure plugging process parameters
The setting of pressure plugging process parameters directly affects the effectiveness of welding repair. Therefore, the process plan in Table 5 is set in the article, and the surface morphology changes of the specimen are analyzed using JSM-IT300 scanning electron microscope. Based on the GB 2650-1989 and GB 2652-1989 standards, the mechanical properties of the repaired specimens were analyzed using a microcomputer tensile testing machine (model: HY-939A). The welding machine used is the Shanghai Electric Welding Machine Double IG BT Module Industrial Argon Arc Welding Machine ZX7-315S/T. The heat input and inter pass temperature parameters of the welding machine are shown in Table 5.
| Parameter type | Option 1 | Option 2 | Option 3 | Option 4 |
| Welding current/A | 245 | 245 | 245 | 245 |
| Arc voltage/V | 27 | 27 | 27 | 27 |
| Welding speed/(mm · min ^ -1) | 385 | 385 | 385 | 385 |
| Preheating temperature/℃ | 105 | 105 | 105 | 105 |
| Inter channel temperature/℃ | 105 | 155 | 205 | 155 |
| Heat input/(kJ · min ^ -1) | 1. 00 | 1 05 | 1 05 | 1 05 |
Based on the above operation process, complete the welding repair of casting defects in high-strength steel wheels based on pressure sealing, using SPSS 21 Analyze the welding repair effect using statistical software.
2. Experimental analysis
2.1 Cleaning effect
Table 6 shows the changes in chemical element content on the surface of high-strength steel wheel casting specimens before and after laser cleaning.
| C | Mn | Si | Cr | O |
| 0.41 | 1.10 | 0.26 | 1.10 | 0.01 |
When there is a high content of O in the chemical elements on the surface of the specimen, it can lead to the presence of oxidation pollutants on the surface, which can affect the welding effect. After laser cleaning, the O content on the surface of the specimen decreases, indicating that the oxide layer on the surface of the specimen is effectively cleaned, and the residual amount of oxide is very small, which is more conducive to welding repair.
Figure 5 shows a comparison of microscopic images of the surface of the specimen before and after laser cleaning.
From Figure 5, it can be seen that before laser cleaning, there are oxide crystals on the casting defects surface of the high-strength steel wheel casting specimen; After laser cleaning, the oxide crystals on the surface of high-strength steel wheel casting specimens with defects were effectively removed, and the steel matrix material of the specimens did not undergo structural phase transformation, indicating that laser cleaning not only effectively removes pollutants at the casting defect location, but also does not damage the matrix structure. The cleaning effect is effective.
2.2 Analysis of plugging process
We studied the effect of heat input and inter pass temperature changes on the welding repair effect during the pressure sealing process of high-strength steel wheel casting defects welding repair using the method described in the article, in order to determine the appropriate repair process. Taking the repair process plan in Table 5 as an example, analyze the mechanical performance changes of the repaired specimens. The specific results are shown in Table 7.
| Indicators | Option 1 | Option 2 | Option 3 | Option 4 |
| Heat input/(kJ · mm ^ -1) | 1. 00 | 1. 05 | 1. 05 | 1. 45 |
| Inter channel temperature/℃ | 105 | 155 | 205 | 155 |
| Tensile strength/MPa | 1 045 | 1 025 | 980 | 1 025 |
| Yield strength/MPa | 926 | 926 | 926 | 926 |
| Elongation after fracture (%) | 19 | 18 | 18 | 18 |
| Weld center | 38 | 33 | 24 | 22 |
| Heat affected zone | 39 | 37 | 68 | 55 |
According to Table 7, as the heat input increases and the interpass temperature increases, the impact absorption energy at the center of the weld seam with welding and casting defects decreases significantly; The tensile strength and yield strength of the weld metal decrease, and the change in elongation after fracture is not significant. It can be inferred that in order to improve the impact toughness of welding and casting defect locations and ensure the effectiveness of welding repair, it is necessary to set the heat input and interpass temperature reasonably. Taking into account the data in Table 7, it is necessary to set the heat input to 1 during the pressure plugging process when repairing casting defects in high-strength steel wheels in the article 00 kJ/mm, with an interpass temperature of 105 ℃.
Figure 6 shows the change in critical fracture stress at the repair location of high-strength steel wheel casting defects after welding pressure sealing repair at different preheating temperatures.
As shown in Figure 6, as the preheating temperature increases, the fracture stress at the welding repair location of casting defects in high-strength steel wheels increases; When the preheating temperature is 120 ℃, the fracture stress at the welding repair location of casting defects is consistent with the yield strength of the steel. This indicates that the preheating temperature of 120 ℃ is the most reasonable, which can avoid the occurrence of welding cold cracks in the repair process of pressure plugging of the specimen.
2.3 Analysis of Microscopic Results
Figure 7 is a comparison of the microstructural changes on the surface of high-strength steel wheels after welding repair of casting defects.
By comparing Figure 7, it can be seen that after pressure sealing was applied to the casting defect location of high-strength steel wheels, the casting defect location cracks were effectively repaired, and there were no cracks or pores.
2. Conclusion
After pressure sealing and repair, the wheel was inspected under a microscope and no issues such as pores or cracks were found, meeting the repair standards. This indicates that it is feasible to use J107Cr welding rod to repair the casting defects of cracks on high-strength steel wheels. After welding repair, no obvious abnormalities were found on the surface structure of the wheel, proving that the method proposed in the article can effectively enhance the stability of the wheel.
The pressure sealing method should pay attention to the following points in actual welding repair work:
(1) When repairing casting defects in high-strength steel wheels through welding, although the pressure sealing method is feasible under the conditions set in the article, there are certain safety hazards in actual operation. Operators must wear protective clothing and use protective tools;
(2) The pressure sealing method needs to be carried out by experienced and highly skilled personnel, and cannot be operated by beginners to avoid causing casting defects to become larger and larger, which is not only time-consuming and laborious, but also increases the repair cost;
(3) Before using the pressure sealing method, it is necessary to analyze the safety and weldability of the wheel casting material to avoid wasting effort.