The 4 Secrets You Will Never Know About Thick Plate Forming Process
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The 4 Secrets You Will Never Know About Thick Plate Forming Process

Views: 148     Author: Site Editor     Publish Time: 2021-08-10      Origin: Site

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There are about 23 kinds of pallet bodies commonly used in railway freight cars, which can fix the coupler and prevent deformation and displacement under the action of dynamic load during operation; about 12 kinds of commonly used safety pallets can prevent the coupler or the pallet body from falling off, resulting in the role of traffic incidents. There are a total of 35 kinds of the two, and the corresponding molds are as many as 7 sets. Increasing the order quantity of spare parts will significantly increase the manufacturing cost of tooling and molds. The original pallet body forming process is hot pressing. The heating of the sheet not only increases the production cost but also the product quality is barely marginal. At the same time, the heating of the sheet correspondingly reduces the carbon content of the sheet, resulting in a decrease in the mechanical properties of the sheet. Therefore, it is necessary to re-examine the new process method and mold structure to realize the process transition from hot pressing to cold pressing.


Investigation


The thickness of the pallet body and the safety pallet is 16mm, the material is Q235A, and both are thick plate forming parts. The product picture of the pallet body is shown in the figure. The compression depth is 16mm, 24 mm, 35 mm, 40 mm, 45 mm, 50 mm, 55 mm. After hot pressing, the work pieces are stacked in stacks under the action of thermal stress and gravity, The flatness of the two wings is 1.1~1.4mm, and the flatness of the lower part A is arc-shaped uplift 0.8~1.2m, which cannot meet the technical requirements of the product. The structure of the safety pallet is similar to the shape, structure, and size of the pallet body, and also has the quality problem of poor flatness.

Thick plate forming

Process Analysis


Calculation of Forming Force

According to the stamping die design manual, the cold forming force P=4x0.6x1.3x210x16x16x 38/(16+15)=205t, 4 is the number of bending of the sheet metal, 0.6 is the theoretical constant, 1.3 is the working condition coefficient, and 210 is the plate The width of the material, 16 is the thickness of the sheet, 38 is the tensile strength of the material, and 15 is the forming fillet radius of the work piece, so it is possible to cold press on a 31.5-ton hydraulic press.


Determination of Rebound Angle

The key to the design of the compression mold lies in the determination of the rebound angle and the amount of anti-deformation. The relative bending radius of the formed work piece is the ratio of the forming fillet radius to the thickness of the sheet material, 15/16=0.94, the value is small, so the forming fillet is not considered The spring back only considers the spring back of the bending angle, the value of the reverse deformation of the spring back angle and the thickness of the sheet, the yield strength of the material, the tensile strength of the material, the forming angle, the shape of the work piece, and the pressure tonnage of the equipment, The gap of mold forming is related, and there are many influencing factors. The theoretical calculation formula is an empirical formula, and the rebound angle of the work piece is difficult to accurately control. For this reason, the cold press realistic test is carried out and the numerical simulation analysis is carried out on the JSTAMP software.

Thick plate forming

Schematic diagram of workpiece angle


● According to the mold design manual, the theoretically calculated rebound angle is 1.0°, and the flatness of the two wings is calculated to be 1.31mm, and the flatness of the lower part is 3.32mm, which is relatively large.

Numerical table of cold pressing flatness of pallet body


1 2 3 4 5 6 Average Value
Two wings 1.2 1.4 1.5 1.3 1.3 1.6 1.38
Bottom 1.8 2 1.9 2.2 1.8 2 1.95

● Using the existing hot press mold, there is no rebound angle and anti-deformation. As shown in the figure, the cold press test is carried out under the pressure of 240T of the hydraulic press. After the cold press test, the work piece is reshaped and drilled to ensure that the test material is not wasted. The flatness values are shown in the table. It can be seen that the actual rebound of the two wings is greater than the theoretical calculation, and the actual rebound of the bottom is less than the theoretical calculation.


● Using STAMP software, 3 times of spring back numerical simulation calculation analysis was performed under the 260t state, and the spring back amount was only 0.48 mm, which was less than the theoretically calculated value. The simulation curve of the rebound trend of the work piece is shown in the figure.


To develop a complete experimental program, students must have the following abilities: clarify the purpose of the experiment, state the relationship between the independent variable and the dependent variable, describe the method of observing or measuring the variable, and list the important steps and experimental equipment. The purpose of the experiment has been given and is not included in this scale. In this exploratory experiment, irrelevant variables such as branch selection, treatment, and bud processing will affect the experimental results; the experimental period is longer, which involves the problem of experimental data recording; at the same time, the branch treatment method and concentration selection involved in this experiment These are all things that are not involved in classroom teaching and need to be checked by students themselves. Therefore, three elements are added: the awareness of controlling variables, the design of tables to record experimental data, and the review of data.

Thick plate forming

Compare the numerical difference between hot pressing, cold pressing, and simulation analysis, while taking into account the convenience of mold adjustment, determine the value of rebound angle and anti-deformation, the rebound angle of the two wings is 1.2°, and the bottom anti-deformation The deflection value is 2.5 mm.


Mold Design

Thick plate forming

Thick plate forming

Thick plate forming

Schematic diagram of the mold structure

1.3.8----Upper mold insert, 2.6.7----Lower mold insert, 4----Lower phantom,5----Upper phantom.

Determine the mathematical model of the compression mold according to the rebound angle and the amount of anti-deformation. As shown in the figure, the two wings rotate down 1.2°, the bottom is upturned by 2.5mm, and the size of the arc center 250 is adjusted to the straight line intersection size 261, the arc center The size of 380 is adjusted to the straight line intersection size 370 to ensure that the expanded size of the neutral layer is equal, that is, when the mold is finished, it is expected to rebound to the initial state of the work piece, so that the total length of the folding line remains unchanged, and the mold design is guaranteed The precision. Parametric design is carried out under CREO2.0 three-dimensional design software. When the mathematical model changes, the corresponding characteristics of the compression insert and the mold body and the two-dimensional drawings will change and adjust accordingly. The fillet radius R15 is in the working part of the mold. After the design is completed, mark and modify, as shown in the figure, it is convenient for the rapid and accurate regeneration of the three-dimensional parts of the mold, and the efficiency of the design is improved. The final mold structure is shown in the figure.


The upper and lower inserts of the original mold are all fixed in the stop. When the mold bugles or there are impurities between the insert and the stop of the mold body, it will take too much internal and external time for the mold to replace the inserts. It conforms to the lean concept of quick mold change. The fixing method of the insert is changed to the freeway of canceling the stop of the upper insert. The force has a tendency to shift to the center, but there is no possibility of changing the size of the working chain. The lower insert is still fixed at the top of the mold body. Limiting the force of the insert has the possibility of outward displacement to change the size of the working chain. When the mold is replaced with other products, only the outer 4 inserts are replaced instead of all the press-shaped inserts, which reduces the replacement time of the mold and reduces the cost of mold manufacturing and maintenance.


Verification And Conclusion

● The amount of anti-deformation was adjusted from 2.5 mm to 1.5 mm, and the mold has been mass-produced, realizing the technological transformation of cold pressing.

● Appropriately increase the equipment pressure, and strive to reduce the elastic deformation and rebound angle at the corners to ensure the rigidity and dimensional stability of the work piece.

● Carry out flexible mold design as much as possible to avoid all replacement of mold inserts.

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