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Research on the application of die CAD with CAXA

Abstract: by deriving some formulas of stamping theory and theoretical mechanics, and using some functions of electronic drawing board, approximate solution in die design can be realized. This method has certain generalization and practicability. Key words: stamping die; CAXA； Electronic drawing board; Plate center of gravity classification No. in Chinese drawing: tp391.72; Tg385.2 document identification code: B0 introduction in the process of using the electronic drawing board drawing software, the CAD function of CAXA is excavated by combining theory with practice by drawing on some functions of the popular CAD software in the market. This will greatly improve the efficiency and accuracy of mold design. Two application examples are given below. According to the stamping theory, the length of the strain neutral layer is constant, and the strain neutral layer must pass through the center of the section. In practical work, the general sheet metal sections we contact are parallel. In fact, the length of the neutral layer becomes the length of the center line between two parallel planes under pressure. We can use this method to calculate the blank length of bending parts with various bending forms. Let's take a blank with a bending angle of 90 ° as an example to illustrate this problem. The calculation formula for the developed length of the blank is as follows: l=l1+l2+ π/2 (r+x0t) =l1+l2+1.57 (l+x0t) (1), where: L - the developed length of the bending part, [l] is mm; R - inner bending radius of bending part, [R] is mm; L1, L2 -- length of straight edge of bending part, [L1, L2] is mm; T - is the original thickness of the bending part, [t] is mm; X0 - neutral layer inward displacement coefficient, see Table 1. Table 1 (No. steel) r/t

0.1

0 Further strengthen the research and development of new products and the opening up of emerging utilization markets 25

0.5

1.0

2.0

3.0

4.0

> 4

0.32

0.35

0.38

0.42

0.445

0.47

0.475

0.5

according to the above formula, the blank developed length of the sheet metal shown in Figure 1 is: l=8+8+1.57 (2+2 × 0.42)=20.4588 mm。 In the specific operation of the electronic drawing board, figure 1 shall be drawn first. During the drawing process, attention shall be paid to the use of the "equidistant line" command to conveniently make the neutral layer of the sheet (i.e. the center line in the figure). Then use the "perimeter" command in the "query" menu to query the centerline. The result screen displays the length and total length of the "straight line" and "circular arc" segments of the blank, indicating that l=20.712 mm, which has only 0.25 mm error with the result calculated by the formula. The reason for the error is that the neutral layer inward shift is not considered. However, such a small error is completely allowed in the stamping calculation (free tolerance), and the result obtained by computer query cannot be smaller than the theoretical result, and will not produce the result of small material. This result can be applied to practice. 2 determine the resultant action point of the die pressure center during blanking or the resultant action point of the punching pressure of each process of the multi process die, which is called the die pressure center. During the design, the pressure center of the die shall be consistent with the center of the slider of the press. If it is inconsistent, eccentric load will be generated during stamping, resulting in sharp wear of the die, the slider and guide rail of the press, and reducing the service life of the die and the press. Therefore, in the blanking die, multi punch, punching die and multi station continuous die, the die pressure center must be determined. Determine the pressure center of sheet metal (Fig. 2) by theoretical method. The peripheral dimensions are S1, S2, S3, S4, S5 and S6. The coordinate positions of point O of the pressure center are x0 and Y0, and the blanking forces acting on the periphery are F1, F2, F3, F4, F5 and F6 (parallel force system). According to the principle that "the sum of the moments of each component force to an axis is equal to the moment of the resultant force to the coaxial", the following two formulas can be obtained. Where x1, X2, X3, x4, X5, X6 and Y1, Y2, Y3, Y4, Y5 and y6 are the X and Y axis coordinates of each blanking force respectively. Because the blanking force F is proportional to the peripheral dimension, that is, fn=snt τ (t is the sheet thickness, τ It refers to the shear strength of the sheet metal), so the above formula can also be expressed by the peripheral dimensions as follows: observe the above formulas. In the pressure of the mold, since the electronic universal testing machine system is a closed-loop system, to identify which part of the system shows a fault, first disconnect the circuit in the system to make the system an open-loop system If the signal time of the sensor is normal, the response signal of the displacement sensor must be disconnected to make the system open-loop At this time, the resolution is announced from the task station that a signal controls the movement of the actuator, and then the response value of the sensor is measured. After repeated several times, when the measured response data of the sensor is a linear transition line, it is determined that the essence of the normal center of the sensor is the synthesis of the centroid of the sheet contour. According to the principle that the centroid of a homogeneous object coincides with the center of gravity in theoretical mechanics. The "face center of gravity" of sheet metal can be directly obtained by using the "center of gravity" command in the "query" menu of the electronic drawing board. To find out the "line center of gravity", after making the contour line of the sheet metal in the electronic drawing board (closed), use the "equidistant line" command to equidistant 0.01 inward to get a new closed contour line (the surface of 0.01 is equivalent to a line). When "querying" the "center of gravity", use the "surface center of gravity" of the outer contour line minus the "surface center of gravity" of the inner contour line to get the line center of gravity of the sheet metal (i.e. the mold center), and then design the mold based on this. For example, there is a sheet with the following dimensions: s1=15, s2=5, s3=5, s4=15, s5=20, s6=20. Substitute into the above formula to get: xo=30.35714, yo=27.14285. By using the electronic drawing board, the results can be directly obtained by "querying" according to the above method (x0=30.357, y0=27.143). 3. Summarizing the above two examples has universality and generalization for mold design, and can reduce artificial calculation errors. In the aspect of software use, it is explained that as long as we are familiar with the functions, the drawing software such as CAXA can really have CAD functions. References [1] edited by Lu Yan Stamping technology Harbin: Harbin Institute of Technology Press 1980. [2] edited by haotongsheng Theoretical mechanics Beijing China University of mining and Technology Press 1982.Two Examples of Applying CAXA to CAD of moulds DiesSONG Qi-hai，LIU Wu-han， LU Tao(Designing Institute of Yun Ma Aircraft Manufacture Factory,Anshun,Guizhou,China,561019)Abstarct:This article proves that the calculation in CAD of moulds dies can be achieved by combining certain functions of CAXA (an electronic drawing plate) with deduction of certain equations in stamping theory and theoretical mechanics,which is of application and popularization value. Key words:sta

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