# On the relationship between drawbead and pressing surface

(3) single reinforcement resistance analysis.
As shown in Figure 1, the resistance of semicircular ribs consists of two parts: bending resistance and friction resistance. The bending resistance at points ①, ③ and ⑤, the reverse bending resistance at points ②, ④ and ⑥, plus the friction force at three R angles, is the total resistance of the sheet through the single reinforcement. The sheet metal is bent at point ①, then straightened and recovered at point ②, reversely bent at point ③, straightened at point ④, bent again at point ⑤, straightened again at point ⑥, and then entered the initial state of the second rib (double bars) for the next cycle. If it is a single rib, the sheet will then enter the management surface. Therefore, the resistance of the reinforcement is the sum of bending and anti bending forces plus the friction force at each fillet.
(4) resistance analysis of double reinforcement.
Figure 1 single reinforcement structure
Figure 2 double reinforcement structure
As shown in Fig. 2, when the distance between double ribs is 25 mm, the maximum resistance coefficient of double round reinforcement can reach 0.6, and the resistance coefficient of reinforcement in AutoForm ranges from 0.1 to 0.9; 0.1 refers to the small resistance with certain resistance, and the resistance coefficient of single round reinforcement ranges from 0.1 to 0.3; 0.4 to 0.6 refers to the drawing die with large feeding amount but large feeding resistance to reach the specified thinning rate; 0.7-0.9 In order to lock the reinforcement, it is often used in the situation where the material is hardly moved. The resistance coefficient of 0.4-0.6 is square bar (rectangular bar) or double round bar combination. In this range, the drawing die has more material movement, and generally the feed rate is 30mm Above all, this kind of drawing die has strict control on the feeding speed, which requires not only sufficient feeding resistance, but also enough material to flow in. Double round ribs can better meet this demand, and it is more appropriate to use double round bars to adjust the feeding resistance.
It can be seen from Fig. 2 that the sheet metal enters the initial state of the second rib after passing through the friction force, bending force and reverse bending force of the first rib. Therefore, the feeding resistance of the double round bars is approximately the superposition of the resistance of the two single ribs. In the debugging process of drawing die, the resistance of double ribs is closely related to the height and R angle of bars. The relationship between the height of bars and the resistance is exponential function. That is, when the height of bars increases, the resistance of bars increases, and when the height of bars decreases, the resistance also decreases, and the change rate is more sensitive and obvious than other factors.
With the increase of the feeding resistance shared by drawbead, the resistance shared by the pressing surface decreases, that is, the dependence on the opposite side is reduced, and it is easier for fitters to debug a stable drawing die.
Conclusion
When debugging the drawing die, it is necessary to recognize the relationship between the drawbead and the elements of the pressing surface, allocate more feeding resistance to the drawbead, and weaken the effect of the blank pressing surface. The drawbead provides a relatively stable approximate constant resistance, while the management surface can obtain a variable feed resistance by adjusting the air cushion pressure. The superposition of the two results in a stable and locally fluctuating resistance of the main body, so as to adapt to the fluctuation of mechanical properties of sheet metal, drawing oil, cleaning oil, temperature, friction coefficient, etc.