- Detail

Long porous thick plate punching die

I. preface

the beam shown in Figure 1 is an important part of a heavy equipment, which is made of A3 steel and has a large number. The technological analysis shows that: (1) the shape of the beam is simple, the yield strength of the material is low, and the stamping process performance is good; (2) The geometric characteristics of this part are slender, many holes, and material thickness. On ordinary presses, only single hole or multi hole (≤ 3 holes) stamping dies can be used for stamping, so the production efficiency and dimensional accuracy are not easy to guarantee, and the process economy is very poor; (3) The working platform of non stamping equipment such as plate shears and folding machines is of sufficient size (especially in the length direction) and large force. Exploring and studying the use of them to complete the stamping work of long porous thick plate parts is of great significance to tap the potential of equipment and improve the process quality

Figure 1 crossbeam

according to the actual situation of our factory, q is now adopted × Model 2500 plate shears are used as process test equipment

II. Die structure and working principle

1 The die structure

long porous thick plate punching die is shown in Figure 2. Before the installation and commissioning of the mold, the lower indenter and accessories of the plate shear need to be removed, and the installation screw holes should be machined on the upper tool rest and the working platform

Figure 2 punching die for long porous thick plate

1 Upper mold base 2 Base plate 3 Punch 4 Guide side plate (discharge plate)

5 Workpiece 6 Female die 7 Fixing plate 8 Guide sleeve 9 Guide post 10 Lower mold base

2 Working principle

the working principle of the long porous thick plate punching die is [1, 2]: when the die is in the upper limit to be worked position, the blank strip (b =.5) can be placed on the die 6 from one side of the machine tool, and rely on the guide side plate 4 and the positioning pin (not shown in Figure 2, installed on the die 6). When the die is working, the upper die moves down with the upper knife rest of the plate shear, the punch 3 can complete the punching of each hole of the workpiece, and the waste materials fall from the concave die hole. Finally, the upper die reaches the bottom dead center and moves upward with the upper tool rest, and the punch 3 exits the female die 6. At the same time, the rigid unloading assembly (i.e. the guide side plate 4) forces the workpiece stuck on the punch 3 to demould. At this point, the stamping of the beam is completed

III. parameter calculation

1 The maximum allowable punching force of the machine tool

so far, the professional books published in China, hedge 5, and the calculation of the cutting force of the structure composed of the experimental platform all use p = L.T τ， Some increase the safety factor by 30% and evolve into Pmax = 1.3lt τ。 Experiments have proved that the maximum blanking force occurs at about 1/3 of the thickness of the sheet metal extruded by the punch when the flat bladed ordinary all steel blanking die is used for blanking. The material stress at the cutting edge of punch and die exceeds the material yield limit σ S ends the plastic deformation, and the stress value reaches the shear strength of the material τ Cracks are produced at the cutting edges of male and female dies and are cut and separated. Therefore, the position where the maximum Pmax is generated is at 1/3 of the punch extrusion thickness, using P = Lt τ The formula calculation is not accurate enough. It is recommended to use timmerbeil formula to calculate thick material（ δ ≥ 4mm) maximum blanking force during blanking [1]:

in the formula, P machine max - Maximum blanking force of machine tool, n

L - length of blanking line, mm

T - thickness of stamping part, mm

t '- initial stage of blanking, punch extrusion depth into sheet metal, mm

τ—— According to timmerbeil's introduction, (1-t'/t) is a coefficient related to the yield strength ratio of the punching material 1-t'/t, and the value of 1-t'/t=0.66 can be obtained from the nomograph given by timmerbeil, and the relationship between them is roughly 1:1 linear (Fig. 3)

Figure 3 1-t'/t coefficient nomograph

known Q × The 2500 plate shears can shear plates with a maximum thickness of 13mm, a maximum width of 2500mm, a tensile strength limit of ≤ 500MPa, a yield strength limit of ≤ 260mpa, and a shear strength limit of ≤ 240mpa. Accordingly, l = 2500mm, t = 13mm τ＝ 240mpa, 1-t'/t=0.66 (take the lower limit), substituting into formula (1) can calculate: P machine max = 4056kn

2. The maximum blanking force required for the workpiece is shown in Figure 1. The beam made of A3 steel has σ b＝470MPa、 σ s＝240MPa。 Therefore, l = π × twenty × 38＝2386.4mm、t＝10mm、 τ＝ 380MPa, 1-t'/t=0.66 is substituted into formula (1), and the maximum blanking force of the workpiece can be obtained: P max = 5985.091kn

IV. design of main parts

1 When punch

thick plates are pressed, the working parts of the punch, i.e. punch and die, have to bear greater compressive stress, especially at the sharp corners, lugs, broken line intersections, etc. of the punch with non-circular section, the contact stress is much greater than the average compressive stress, significantly reducing the service life and the melting range of 220 ~ 240 ℃. Therefore, high alloy tool steel must be used to make working parts. The punching punch material can be Cr12MoV steel, with heat treatment hardness of 58 ~ 62Hrc. In order to meet the p-max

(1) the convex die structure with oblique edge or wavy edge can make the rigid surface impact and linear punching of the conventional flat edge into the shearing of the oblique edge and circular edge with point contact, which has a good noise reduction effect. Generally, the height of the inclined blade and the height of the wave arc top are () t, and the maximum should be ≤ 3T. The measured noise reduction of this kind of die is 2 ~ 13dB, and the blanking force is reduced by 40 ~ 80%. However, because the punching diameter of the beam is small and the height is too large, it is not only difficult to make, but also the punch is easy to break due to uneven stress, which will also cause the material to slip under pressure, causing the workpiece to warp. If it is required to take the total elongation and distortion under the * force, which will affect the quality of the workpiece, it is rarely used

(2) the stepped punch structure (Fig. 4) has the dual effect of reducing blanking force and noise. In the design, the punch is divided into two groups and arranged according to the transverse symmetrical spacing of the die, which can realize p-max ′ = p-max/2 ＜ p-machine max. Finally, we decided to adopt this step punch structure

Figure 4 step punch structure

2 Die

due to the large transverse size of the die, the die should be designed as an assembly, that is, it is composed of a die sleeve and a die seat. This can not only save valuable materials, but also simplify the processing technology, easily ensure the dimensional accuracy and use requirements, and facilitate installation and maintenance. The female die seat can be made of 45 steel, and the heat treatment hardness is 28 ~ 32hrc; Cr12MoV steel with heat treatment hardness of 58 ~ 62Hrc is still recommended for female die sleeve

v. conclusion

(1) the process test proves that the design of the punching die for long porous thick plates is successful, has the use value and promotion significance, and widens the application range of non stamping equipment

(2) with the step punch structure, P max ′

(3) because the maximum closing height of the plate shear is small, the geometric size of the die should be minimized on the premise of convenient use and sufficient strength

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