Research on Two Formulas for Calculating the Diameter of Flanging Hole at the Top of Bucket
Text / Wu Jianping
Abstract: In the design of cold die, the calculation formulas of the diameters of two prefabricated holes for flat round hole flanging are discussed, and the actual data are compared to find the closest calculation formula
Keywords: Flanged prefabricated holes; formula; comparison; true
1 Introduction
In the stamping design data, there are usually two formulas for calculating the diameter of the prefabricated hole for flat round hole flanging. The formula is as follows:
(1)
(2)
Of these two formulas, formula 1 is calculated by a simple bending approximation method, that is, as shown in FIG. 1, as long as the diameter D1 is subtracted from the length of the central layer expansion length of the straight walls participating in the bending h and r, it can be obtained. Formula 2 is determined by the relationship between the volume of the blank and the workpiece before and after deformation, that is, the material volume of D1-d before flanging is equal to the sum of the volume of the height h of the straight wall after flanging and the volume of r part.
Figure 1 Round hole flanging
2 Case calculation comparison analysis
Because the principles derived by the two formulas are different, the calculation results are also different. Take Figure 2 as an example.
Figure 2 Example of round hole flanging
D = Φ115.2mm, H = 16.32mm, r = 1.8mm, t = 1.2mm, D1 = Φ120mm, h = 13.32mm.
Substitute the data into formula (1) to get the diameter of the prefabricated hole:
d = Φ85.83mm
Substitute the data into the formula (2) to obtain the diameter of the prefabricated hole:
d = Φ80.6mm
Obviously, which of the two calculation results should be taken?
Figure 2 is the punching and flanging process of our company's new steel drum. At first, the calculation result of formula (2) (that is, the punching diameter is Φ80mm) is used as the prefabricated hole diameter of the mold. The 16.32mm specified by the process is 2.68mm higher, which means that the diameter of the prefabricated hole is 5.36mm smaller (calculated according to simple bending, if the volume is calculated unchanged, it is 7.3mm smaller) should be Φ85.83mm, which is exactly the same as the formula (1) The calculation result of d = Φ85.38mm is close.
Figure 3 is the punching and flanging process of our company's mid-mouth steel drum.
Figure 3 Example of round hole flanging
D = Φ321.2mm, H = 24mm, r = 1.5mm, t = 1.2mm, D1 = Φ325.4mm, h = 21.3mm.
Substituting the data into equation (1) gives:
d = Φ276.2mm
Substituting the data into equation (2) gives:
d = Φ272.5mm
According to the calculation result of formula (2), the diameter of the prefabricated hole of the mold is Φ272mm. After flanging, the height is found to be 26mm, which exceeds the process requirements by 2mm. , Which is close to the calculation result of formula (1) d = Φ276.2. The calculation also proves that when the flanging diameter is unchanged, as the flanging height increases, the error of the calculation results of the two formulas will increase accordingly.
Still taking Figure 3 as an example, when H = 40 and h = 37.3, the data is substituted into formula (1) to obtain the diameter of the prefabricated hole:
d = Φ244.2mm
Substitute formula (2) to get the diameter of the prefabricated hole:
d = Φ231.7mm
The difference between the two calculation methods is 12.5mm. If the calculation result of formula (2) is used, the flanging height will exceed 6.2mm.
3 Analysis
Why does the theoretically more accurate calculation result of formula (2) produce greater errors in practical application than the theoretically more approximate calculation formula (1)? Analyzing the flanging process, you will find that the material has stretched, expanded, and thinned during the flanging process. The height of the flanging is super high, and the thinner the material is, the worse the flanging height. Since formula (2) is determined based on the constant volume relationship and does not consider the effect of material thinning, the thinning of the material will inevitably lead to excessive deviation of the flanging height. Although formula (1) is determined based on the simple bending relationship, the material is not considered The effect of thinning, but from the actual situation (experimental data), it includes the effect of increasing the height of the flanging material and increasing the thinning of the material. In other words, if there is no effect of the thinning of the material, the calculation result according to formula (1) The flanging height will not be satisfied (it will be lower than the process height requirement), but to meet the process height requirement, the material that is still missing is just made up by the thinning of the material.
4 Conclusion
Combining the analysis results of the above two formulas, formula (1) is closer to the real situation than formula (2), and the punching and flanging of our company's solid cask and asphalt barrel lids also prove this point.
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