Abstract: This paper mainly analyzes the implementation process and effect of the spinning process of the symmetrical disk hub by analyzing the spinning deformation performance of 6061 aluminum alloy.
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1. Introduction <br> <br> alloy wheels with light weight, low cost, the advantages of high strength and aluminum has strong thermal conductivity, can significantly extend the life of automobile, motorcycle tires, truck tires, in particular high load Life expectancy. (According to the test data of the European wheel manufacturer "ALCOA", the aluminum alloy wheel allows the tire to extend the service life by up to 20%).
2. Proposal of the topic
In recent years, with the continuous improvement of the production process of wheel manufacturers in the international market, the European and American wheel industry has gradually replaced the traditional wheel production process with strong-spinning aluminum alloy wheels. The domestic wheel industry is also developing towards the advanced aluminum alloy wheel production process. . Below is a typical wheel hub that a manufacturer needs to order (Figure 1). The wheel material is 6061 aluminum alloy (equivalent to the domestic grade LD30).
3. Wheel spinning processing equipment
PT30501CNC two-wheel horizontal powerful spinning machine, the diameter range of the workpiece is φ100~φ1000mm, the longitudinal stroke of the rotary wheel is 1900mm, and the maximum rotation pressure is 30 tons. These machine parameters indicate that the spinning machine meets the requirements of the strong spinning process of the hub.
4. Aluminum alloy wheel spinning process plan
4.1 Spinning material 6061 alloy aluminum spinning performance analysis 6061 aluminum alloy belongs to Cu-Mg-Si-Mn aluminum alloy, its chemical composition is as follows:
Cu-0.15%~0.4%, Mg-0.45%~0.9%, Si-0.4%~0.8%, Mn-0.15%; the mechanical properties of the material under solution and aging are:
σb≥320Mpa, δ5≥12%, ψb≥25%, HB≥120.
Therefore, the value of the rotatability index of 6061 alloy aluminum in solution-aging state - single pass limit reduction rate:
Φmax=ψb/(0.17+ψb)×100%=0.25/(0.17+0.25)×100%=60%.
The value of this index indicates that its spinability is worse than that of high-strength steel. In the spinning process, it should be properly heated if necessary, and the workpiece heating temperature is 310 ° C ~ 350 ° C. In addition, in order to improve the spinnability of the aluminum alloy, some mineral elements - lanthanum and cerium (0.02%) can be appropriately added.
4.2 The choice of the spinning process of the hub is like this kind of symmetrical disc-shaped hub. The spinning process can generally adopt the two methods of taking the plate splitting or the casting (forging) blank for strong spinning. The split-type spinning process is to pass the disc-shaped slab through the layering process with the splitting wheel, so that the blank is split into two equal parts in the middle, and then the forming wheel can be gradually formed by the forming wheel; It is a strong rotary forming process for casting aluminum blanks or forged blanks. The spinning pressure reaches the requirements of the hub profile size. The weight of the hub produced by the strong spinning process can be reduced by about 25% compared with the weight of the forged wheel. This is because the strong rotation The process can be rotated to reduce the thickness of the section, and the thickness of the hub can be appropriately reduced under the premise of meeting the requirements of the wheel strength index.
Since the vertical and horizontal ball screw of our factory's PT30501CNC machine tool has an angle of 75°, when the rotary wheel programming track moves only along the radial direction of the workpiece, the rotary wheel has a partial displacement in the axial direction during the actual movement of the machine tool, so that during the spinning process The end face of the outer edge of the splitting wheel is subjected to a certain axial pressure, and its reaction force directly acts on the ball screw drive part of the machine tool, which affects the service life and accuracy of the machine tool. Therefore, this structural form is not conducive to the splitting of the wheel hub. Based on the above analysis, we chose a strong spinning process to form this symmetrical dish-shaped aluminum hub.
4.3 Wheel hub strong spinning process precision forging blank first pass strong rotation second pass strong spin forming to CNC workshop machine addition wheel finished products.
5. Process plan implementation process
5.1 Tooling design Spinning mandrel material selection, profile surface roughness Ra0.4~Ra0.8um; forming wheel preform angle °, fillet radius mm, material selection, heat treatment hardness.
5.2 Spinning blank design Solid modeling software (Solidworks, MastCAM, etc.) is used to draw the solid shape of the hub spinning parts and to find the metal volume. The die forging blank is calculated according to the volume invariance design.
5.3 Strong spin process implementation effect The first pass spin process parameters: S=0r/min, feed ratio F=0mm/r, second pass strong spin process parameters: S=0r/min, F=0mm/r .
At the beginning of the process test, two times of strong spin forming were carried out with the R15 forming wheel, and piled up and cracked defects were generated during the test. Subsequently, the Rmm wheel was changed to the R forming wheel, and the transition fillet radius on the spinning mandrel was increased, and the peeling and cracking defects were eliminated. We believe that this accumulation and peeling defects are mainly due to the small radius of the fillet of the spinning wheel and the absence of the pre-formed angle. When the spin forming is performed, the metal stress area is small, some metals cannot participate in the deformation, and the workpiece profile is complicated. The material flow is not smooth when deformed; the Rmm arc crack at the bottom of the blank is mainly due to the fact that the radius of the fillet Rmm of the spinning blank and the mold tire is too small, resulting in a serious stress concentration during the deformation process, and the material deformation rate is the largest at this point. , reaching about 65%, has exceeded the spinning limit reduction rate of 6061 aluminum alloy (LD30) by 60%, resulting in serious work hardening phenomenon.
The above test analysis shows that there is a certain design problem in the initial spinning blank and the spinning mold tire. The spinning blank should reduce the metal thickness of the spinning forming part under the premise of satisfying the metal volume requirement of the workpiece (that is, increase the height of the blank and reduce the outer diameter of the blank under the premise of ensuring the volume of the metal). This reduces the spinning reduction rate and reduces the problem of spinning work hardening; the radius of the transition fillet on the surface of the spinning die is generally small, and the processed profile finish does not reach the design requirement of Ra 0.8 mm. According to the results of the previous spinning process test and the quality analysis, we have made appropriate adjustments to the spinning process of the subsequent test pieces, changing the three passes into two passes, and the forming wheels are all Rmm. The accumulation and peeling defects were basically solved, but the inner and outer profiles of the large end of the workpiece were torn. We believe that this phenomenon occurs because the material of the part is in the form of incompletely veneering during the two-pass spinning process. The reason why the metal can extend forward is because the rotating wheel carries the blank surface metal forward. When moving, the tensile stress is generated inside the material instead of the compressive stress state. For the problem of workpiece tearing, we changed the pre-forming angle of the rotating wheel from ° to °, and the outer diameter of the spinning blank was changed from φ427mm to φ421mm, thereby reducing the thickness of the material in the spinning deformation zone and reducing the thinning rate of the pass. The trajectory of the spinning wheel was also corrected to make the material flow more smooth and the problem of workpiece rupture was solved.
The solution spinning treatment of the hub spinning parts ensures the stable shape and size of the aluminum alloy wheel hub products, and at the same time improves the mechanical properties of the hub.
6 Conclusion
It is feasible to use the strong spinning process to rotate the 6061 aluminum alloy wheel on the PT30501CNC two-wheel horizontal powerful spinning machine. However, it is necessary to design and manufacture a reasonable spinning mandrel and a rotating wheel, and select a reasonable spinning process. The parameters can be used to solve the defects such as accumulation, peeling and cracking that occur during the spinning of the hub.
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