What You Need to Know About Different Bump Bending

Bump Bending is a relatively common type of steel sheet metal product for locomotives. The structure is changeable and the processing difficulty is greater than that of ordinary ones. This article introduces a process method to realize the arc bending of the workpiece, and combines Detailed descriptions of the specific workpiece and the method of use.

In the production practice of the material preparation workshop, there are generally three forming methods for bump bending: one is a single-process molding die for integral forming, which is suitable for bump bending with more complex shapes and has good forming effects, smooth and flat surface of the workpiece, and no indentation. High processing efficiency and other advantages, but its mold cost are high and its versatility is poor, and it is usually used when the general process method cannot be formed or the surface of the workpiece has high requirements.

The second is the bump bending customized mold for the bending machine. This type of mold is generally suitable for the large arc radius of the workpiece, but it does not exceed the limit of the bending machine table. The cost is lower than the single-process compression mold, and the mold has a certain general purpose.

The third is the multi-bend forming method introduced in this article. Its basic principle is to convert the arc into a broken line segment, which can be formed by using existing molds and equipment. Generally, non-exposed parts can be used, with a wide range of applications and low cost. No need to customize the mold, the forming quality is better.

Analysis of Bump Bending Multi- Forming Process

The basic principle of the multi-pass forming process is to approximately divide the arc segment into polyline segments, as shown in the figure. So as to achieve the purpose of processing large arc workpieces with small arc molds. Compared with arc segments, the forming effect of polyline segments is positively related to the number of polyline segments.

With this processing method, it is difficult to avoid prismatic structures on the surface of the workpiece. However, for non-exposed workpieces, the production cycle and cost are considered comprehensively. The process method can be adopted.

Application Examples of Bump Bending

• Segmentation of arc segment and determination of bending angle

The workpiece is shown in the figure. The inner radius of the bending arc of this workpiece is R350, the bending angle is 120°, and the plate thickness is 5mm. Because the working environment of the workpiece meets the use conditions of the above-mentioned large-arc multi-pass forming process, the Multi-bend forming method is used for processing. According to past experience, combined with the existing mold situation in the workshop, the upper mold adopts the R120 arc mold.

Analyze the large arc segment of the workpiece in the figure, and divide the R350 arc segment into 6 polyline segments. At this time, it should be noted that it is generally to ensure that the workpiece arc segment is tangent to the straight line segment (that is, the two ends of the arc segment Part) The transition is smooth. At the point where the arc segment and the straight segment are tangent, the division angle should be set to half of the other segments. According to the figure, it can be seen that the workpiece is formed by 7 times of bending, and the sheet metal is processed on the electro-hydraulic servo bending machine.

When parts, three basic parameters are required, namely the thickness of the sheet, the bending angle, and the size of the bending line position. The first and last split angles are calculated as 6°, and the others are 12°. The bending angle after splitting is directly measured by CAD software. It is concluded that the specific bending angle is shown in the figure.

Bending Line Position Size And Unfolded Size Confirmation

In order to ensure the accuracy of the expanded size of the bending line, there are generally two methods, namely the neutral layer expansion calculation method, and the software-assisted expansion method.

In order to obtain the bending data concisely, quickly, and accurately, the software-assisted expansion method is used for calculation. Directly import the divided part cross-section into Catia, use the software Generative Sheet metal design module to generate the workpiece model, and then export the bending line and the unfolded drawing, as shown in the figure.

Multi-Pass Forming Process Problem

• Thin sheet workpiece processing

In production, it was found that some workpieces with a small sheet thickness (about 2mm) would be severely deformed during processing, resulting in a serious decline in processing accuracy and failing to meet the design requirements. The reason is analyzed because the internal stress of the sheet is not fully released.

Observe that during laser cutting, the batch of sheets has warped due to internal stress. From another point of view, this also provides a preliminary judgment on whether the multi-bend process can be directly used to process thin-plate large-arc workpieces, that is, to observe its deformation during laser cutting. If the deformation is serious, measures must be taken to release its internal stress, otherwise, it will be difficult to obtain a qualified workpiece.

The choice of the security probability threshold also affects the error rate of security prediction. As can be seen from Figure, as the threshold increases, the false alarm rate increases, and the false alarm rate decreases. On the contrary, as the threshold decreases, the false alarm rate decreases. The false alarm rate rises.

When the threshold is between 0.8 and 0.9, the system prediction error rate reaches the lowest. Therefore, a reasonable selection of the security probability threshold can reduce the system prediction error rate. Generally speaking, the system’s false alarm is more harmful than false alarms. Properly increasing the threshold can reduce the false-negative rate. In this case, setting the security probability threshold to 0.9 is more reasonable.

If the production cycle permits, natural aging can be an economical and effective method, but after a long time of aging treatment, the separated workpieces will inevitably produce rust on the surface. The rust remover must be wiped or shot blasted, which increases manpower and Equipment cost, so it is the best choice to directly use steel plates that have undergone sufficient natural failure.

If the production cycle is not allowed, annealing treatment can also be used to eliminate internal stress after the plate is separated, but the hardness of the material decreases after annealing, and the annealing treatment must be comprehensively considered in accordance with the design requirements of the workpiece.

• Calculation of the unfolded drawing of the workpiece

It must be noted that when using the multi-bend forming process to process large arc parts, the expanded view must be calculated according to the actual workpiece state, that is, the arc segment approximated by the broken line segment. The expanded view of the part calculated by the arc cannot be used directly. Otherwise, the part must be out of tolerance after processing.

• Shape inspection of workpiece

It is worth noting that for workpieces processed by the multi-bend forming process, when the general comparison template is used to detect the size of the arc, the comparison template must be designed as an external clamping type, that is, the outside of the workpiece arc is used as the detection surface. If the comparison template is designed with the inner side as the detection surface, and the comparison template interferes with the broken line segment, the template card will inevitably occur, and the detection cannot be realized.

Bending Method of Arc Sheet Metal Parts

In sheet metal processing, we often encounter the bending of some arc parts, and the size of this type of arc part R varies with the structure of the part, and it is usually similar to the bending method of this type of part. They are all formed by bending with a forming die, that is, according to the size of the arc R of the part to be bent, a suitable arc die is selected for bending and forming.

This method of using a forming die to bend the arc R is simple and fast. However, in the actual bending process, due to the rebound of metal deformation, the accuracy of the arc R of the formed part is not high. At the same time, a set of forming arc molds generally can only process arc parts that are larger than their own arc size, and only when the two dimensions are closer, the better the part forming effect.

The poor versatility, narrow processing range, and high cost of forming molds often limit the designer’s choice of the size of the curved arc R of the part in the part design process, and sometimes even have to change the structure and abandon the selection of arc parts. In order to find a better general bending method similar to arc, we used the method of “replace bending with straight”, which broke through the limitation of bending die and solved the bending problem of this kind of workpiece.

Through the improvement of the bending method of arc sheet metal parts, the method of using straight instead of bending and reserved positioning connection parts, turning the curve into straight, solved the bending processing problem of arc sheet metal parts, and ensured the design and processing The continuity of the connection improves the processing quality of the parts.

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