Analysis and Control of Ultrasonic Flaw Detection Defects in Upsetting and Stamping Forming of Large Aluminum Magnesium Alloy Flange

Aiming at the quality problem of ultrasonic flaw detection in the near bore region during the free forging upsetting and punching forming process of a large-sized 5083 aluminum-magnesium alloy flange, a finite element analysis model of cake billet punching after upsetting was established. The flow law of material in the near bore region of the flange billet during the punching process was obtained by simulation. It was analyzed that the ultrasonic flaw defects in the near bore region of the flange billet were caused by the radial flow and shunt of the near bore region in the process of flattening the reverse side. The analysis concludes that the ultrasonic flaw quality defect in the near bore region of the flange blank is due to the radial flow in the near bore region during the reverse flattening process. Based on the above analysis, it is proposed to adjust the reverse flattening process in the existing forward punching-reverse flattening-peel punching process, i.e., the punches of forward punching are left in the reverse flattening process to restrain the inward flow of material in the near bore region. Further simulations show that the improved punching process can significantly improve the flow state of the material in the near bore region and avoid the unfavorable factors of radial diversion that lead to quality defects in the near bore region. Production practice shows that the adjusted process program makes the large flange upsetting forming process near the hole region defects have been effectively solved.

Flanges are widely used as shaft and pipe connectors in electric power, chemical, aerospace, and machinery. Under the background of equipment lightweight and energy saving and emission reduction, “replacing steel with aluminum” has become one of the current trends in flange development. Compared with the traditional forged steel flange, aluminum alloy flange has many advantages, such as lightweight, high conductivity, and good corrosion resistance, and can be reused. There are various ways to produce flanges, such as machining, casting, forging, etc. The traditional machining method is simple and easy. Still, the material utilization rate is low, and machining cuts off the material fiber flow line, reducing the mechanical properties of the product, especially corrosion resistance and fatigue resistance; the casting method of production of flanges is prone to shrinkage holes shrinkage and other defects, especially in the final solidification of the thick parts of the casting defects are more pronounced, so that the comprehensive mechanical properties of a serious decline, and the airtightness of the lack of. The forging method has gradually replaced the casting method to become a common method of manufacturing high-performance aluminum alloy flanges. The plastic deformation in the forging process can eliminate casting defects to a certain extent, refine the grain, and produce useful streamlined organization, thus improving the comprehensive mechanical properties of aluminum alloy flange products.
Compared with carbon steel forgings, aluminum alloy forgings are more difficult to form, forging processes, defects are also more types and from different sources, such as various types of inclusions, oxide film, and other defects from the raw material defects of the legacy of coarse crystals and cracks and other defects from the forging process of irrational process conditions, overcooking and other defects from the heat treatment process of the irrational control of the temperature and time and so on. For internal defects in forgings, generally, with the help of non-destructive testing, optical microscopy, scanning electron microscopy, energy spectrum analysis, and other test methods to detect the type of defects in forgings and their causes. Among them, ultrasonic flaw detection is the most effective for non-destructive testing of aluminum alloy forgings to ensure the internal quality of forgings and acceptance. Currently, aluminum alloy forgings die forging forming process research more on different shapes and structures of aluminum alloy forgings, the corresponding process parameters and die structure design and analysis. Chen Zengkui and others have studied the precision die forging forming technology of aluminum alloy support joints by replacing the original free forging process with one die and multiple parts, greatly improving production efficiency and product performance.
Wang Xiaosong et al. analyzed the wrinkling phenomenon during liquid-filled bending forming of large diameter-to-thickness ratio asymmetric aluminum alloy bends and gave solution measures. In studying the flange forming process, scholars combined enterprise production conditions to carry out the corresponding forming process design and analysis work. Liang Lixia for a 6A02 aluminum alloy H-shaped flange isothermal closed die forging process analysis and development, and self-heating die structure design to ensure the stability of the aluminum alloy forming process and to achieve the mass production of products. Wang Chao also carried out 6A02 aluminum alloy flange isothermal plastic forming process research through temperature control, reduced die forging forming force, etc., to ensure the flange forming quality and shape dimensional accuracy. Al-Mg aluminum alloy has been an important application due to good overall mechanical properties, corrosion resistance weldability, etc., in the flange forging. Lin Gao-Yu et al. conducted a numerical simulation of the open forging process for 5083 Al-Mg alloy high neck flanges to optimize the billet shape size and die structure. In addition, Liu Xu et al. studied the corrosion behavior and mechanical properties of 5083 aluminum-magnesium alloy stir-frict welded heads. In summary, the current research on aluminum alloy flanges is mainly focused on the analysis of the forming process, and for small-size flange forgings, the design, and development of die forging forming die structure research has also been carried out. The study’s quality defects and control problems have yet to be reported for the large-size flange’s free forging forming.
In this paper, a series of large-size 5083 aluminum-magnesium alloy flange in the free forging forming process of ultrasonic flaws in the near bore region to launch a study, through the bar billet upsetting-punching process modeling and finite element analysis, investigate the punching process of flange ring billet near the inner hole region of the flow of the material and the formation of the quality of the causes of defects, to improve the process to provide a scientific guide.

1. Flange upsetting process

Figure 1 for a large specification 5083 aluminum-magnesium alloy flange, its diameter and thickness are relatively large, the inner hole relative to the outer diameter is small, wall thickness is large. The shape of the flange specifications is generally used as shown in Figure 2, free forging upsetting punching process flow for manufacturing (Figure 2 arrow for the upper mold downward loading direction). The punching process site is shown in Figure 3.

Figure.1 A large specification 5083 aluminum-magnesium alloy flange

Figure.2 Flange upsetting process flow
(a) upsetting; (b) forward punching; (c) reverse flattening; (d) punching wad.

Figure.3 Flange on-site production punching process
(a) Positive punching; (b) reverse flattening; (c) punching the skin; (d) flange forging.
As can be seen from Fig. 2 and Fig. 3, the forward punching process is smooth; with the punch pressed in, the material in the outer region of the punch upward driven biscuit billet outer disk rises out of the anvil, biscuit billet forward punching, the top shape of its shape for the straw hat shape, the bottom shape for the saucer shape, as shown in Fig. 2b and Fig. 3a. To facilitate the completion of the final punching process, the blank needs to be flipped and flattened, as shown in Figure 2c and Figure 3b. After flattening the billet on the reverse side, a punch is used to punch off the even skin of the forward punching to obtain the flange forging, as shown in Fig. 2d and Figs. 3c and 3d.
When the upsetting formed flange forgings were processed into flange products by removing the remnants, it was detected by ultrasonic flaw detection. It was found that there were dense defects in the near bore region of about 30-50mm, i.e., the ring area pointed by the arrow in Fig. 3d, and the ultrasonic morphology was as shown in Fig. 4, in which the horizontal coordinates were the depth of the flawed flange products in the thickness direction. The vertical coordinates were the height of the waveforms, i.e., the degree of the flaws detected, and it could be seen that in the near bore It can be seen that in the region near the inner hole, the flange has a greater degree of flaws at different depths. Among them, the defect degree is relatively large when the depth is about 25mm (small and medium box area in Fig. 4). The analysis considers that the dense defects in this area are micro-cracks or loose organization. The quantitative calibration results of the defective grass echo (large box area in Fig. 4) show that the maximum size reaches Φ0.75mm.

Figure 4 Ultrasonic flaw detection results of flange defects

2. Finite element analysis of the flange punching process

Given the ultrasonic flaws in the near bore area of 5083 aluminum-magnesium alloy flange products, we set up a model based on the punching process parameters of cake blank after upsetting in the actual production. We carried out finite element simulation analysis to investigate the causes of ultrasonic flaws in the near bore area of the flange products.

2.1 Simulation parameters and model establishment

Given the simple axisymmetric structure of the aluminum-magnesium alloy flange cake billet, Deform-2D software is used for simulation. The billet is considered a plastic body, the punch and the lower anvil are regarded as rigid bodies, the friction between the billet and the mold is selected as shear friction, and the friction factor is taken as 0.4. The thermal conductivity between the billet and the mold is 11N.(s.mm.°C)^-1. The downward speed of the punch is 20mm.s^-1. The model and simulation parameters are shown in Table 1. In the simulation of positive punching, the punch stops when the thickness of the skin is 25mm, which is the same as the thickness of the skin at the end of the actual positive punching.
Table.1 Simulation parameters of the punching process

2.2 Analysis of simulation results

Figure 5 shows the temperature distribution of the biscuit at different steps during the punching process, where the box represents the maximum value of the field volume. The triangle represents the minimum value of the field volume, and the following is the same. Because the bottom of the punching area of the biscuit billet, the punch, and the lower flattening anvil have been kept in contact with each other during the punching process, the heat loss is greater. The temperature drop is more obvious, and the overall temperature of the skinned area decreases to about 340°C, as shown in Fig. 5a. At the end of the reverse side flattening, the temperature of the blank near the inner hole region continues to decrease, as shown in Fig.5b, the temperature drop region expands, especially on the surface of the reverse side, the temperature drop is more.

Fig.5 Temperature distribution of biscuit blanks at different working steps in the punching process
(a) End of forward punching; (b) End of reverse flattening.

Figure.6 Flow velocity field of the material at the end of reverse flattening
(a) Vector diagram; (b) Cloud diagram.
Fig. 6 shows the cloud diagram of the flow velocity field distribution of the metal material at the late stage of reverse flattening. From Fig. 6a, it can be seen that the radial flow of the material in the near bore region at the late stage of reverse flattening has a diverging surface, i.e., the material at the inner side of the diverging surface flows radially inward, and the material at the outer side of the diverging surface flows radially outward. The divergent surface of the material in the radial shunt flow process, if the material’s thickness direction is insufficient to replenish, will be pulled in this region for the loose pores. At the end of the reverse flattening, this material radial flow in the opposite direction of the phenomenon is even more serious, as shown in Figure 6b. The reason for this phenomenon is reverse flattening, positive punching near the inner hole region of the material to the inward contraction flow, resulting in the existence of near the inner hole region of the radial flow of the shunt surface, that is, the shunt surface of the material to the inward flow of the shunt surface of the material to the outward flow of the material. This will produce tensile deformation in the area of the shunt surface, the material shrinkage of the protruding part of the material by the extrusion of the upper and lower molds pulled along the radial inward flow, and the outer region of the material to the outside flow. Tensile deformation at a relatively low temperature easy to leads to microscopic cracks or the original cast state organization of the loose pores in the elongation. From the simulation of the location of the flow diversion surface and the forging ultrasonic flaw location consistency can be judged, upset punching flange forging near the inner hole region ultrasonic flaw quality defects are punching process on the opposite side of the pressure level near the inner hole region of the material to the inward flow caused by.

3. Flange punching process improvement

The material analysis of the punching process proves that the shrinkage and deformation of the bore in the punching process is the main factor causing the quality defects in the near bore region of the flange blank. For this reason, it is proposed to retain the forward punching punch in the reverse flattening process to improve the punching process and reduce the taper of the forward punching punch so that it is retained in the inner hole of the cake blank in the reverse flattening process to constrain the material inward flow, to regulate the flow of the material in the region of the near inner hole, and to circumvent the material strain defects occurring in the flow shunt surface due to diversion of the flow. Figure 7 shows the equivalent strain distribution in the near bore region at the end of the reverse flattening before and after the improvement, and the laws are relatively similar. Figure 8 compares the material flow velocity field at the end of reverse flattening in the improved punching process scheme with that before improvement. As shown in Fig. 8a, after the punch is left in the cake blank for reverse flattening, the divergence surface of the material near the center hole is shifted to the left compared with the original process. The velocity field of the material in the near-hole region is close to 0 due to the constraints of the punches inside the hole. The maximum value of the inward flow velocity field is 0.25 mm.s^-1 (at the triangles in Fig. 8a). Figure 8b shows the velocity field of the near bore region before improvement with reverse flattening; it is obvious that there is a radial shunt surface in the near bore region and the maximum value of the inward flow velocity is 5.37mm.s^-1, which is significantly higher than the maximum value of the inward flow velocity of the punch constrained flattening of 0.25mm.s^-1.

Fig.7 Cloud plot of equivalent strain distribution at the end of reverse flattening for different punching processes
(a) Before improvement; (b) After improvement.

Fig.8 Metal material flow velocity field at the end of reverse flattening with different punching processes
(a) After improvement; (b) Before improvement.
Using the reverse flattening process proposed in this paper, the original forward punching punches remain in the borehole improvement measures, the field process implementation, and improve the punching process of the flange forgings for the same ultrasonic testing, ultrasonic shape obtained from the test is shown in Figure 9, compared with Figure 4 can be seen, did not detect obvious defects in waveforms, indicating that the original near the borehole region of the molding defects have been well controlled, the molding quality is intact.

Figure.9 Improved flange ultrasonic flaw detection results

4. Conclusion

• (1) According to a large specification 5083 aluminum-magnesium alloy flange upsetting forming process, the establishment of the flange punching process finite element model, forward punching – reverse flattening process simulation analysis, found that in the reverse flattening process, the material flow to the inner hole region so that the radial flow of the near inner hole region appears in the shunt surface is the near inner hole region of the internal ultrasonic flaw quality defects.
• (2) For the causes of flaw detection defects in the near bore region of the flange, it is proposed that in the reverse flattening process, the punch will be retained in the cake blank during the forward punching process. The internal flow of the material in the near bore region is restrained by the punch to avoid the emergence of the radial flow shunt surface in the near bore region in the reverse flattening and thus eliminate the defects of the flange forging during the original process of molding.
• (3) Simulation results show that the improved program better inhibits the internal flow of the metal material in the near bore region in the reverse flattening of the flange. Production practice shows that the improved program better solves the problem of ultrasonic flaws in the original free forging and forming process of a certain type of large-size 5083 aluminum-magnesium alloy flanges.

Author: Wang Yudi