Bumping workpieces are a relatively common type of steel sheet metal products for locomotives. The structure is changeable and the processing difficulty is greater than that of general workpieces. This article introduces a process method to achieve large arc bending of workpieces. The method of use is described in detail in conjunction with the specific workpiece.
Three bending forms of bumping workpieces
First is the integral forming of the single-process pressing die, which is suitable for workpieces with more complex shapes. It has the advantages of good forming effect, smooth and flat surface of the workpiece, no indentation, and high processing efficiency. However, the cost of the mold is high and the versatility is poor, usually in general It is used when the process method cannot be formed or the surface of the workpiece has high requirements;
The second is the large arc customized mold for the bending machine. This type of mold is generally suitable for the case where the radius of the workpiece is large, but it does not exceed the limit of the bending machine table. The cost is lower than that of the single-process compression mold. The mold has a certain general purpose.
The third is the multi-bend forming method introduced in this article. The 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 Multi-pass Forming Process of bumping workpiece
The basic principle of the multi-pass forming process is to approximately divide the arc segment into polyline segments, as shown in Figure 1, 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 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 bumping technology
Segmentation of arc segment and determination of bending angle
The workpiece is shown in Figure 2. 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 conditions of the above-mentioned large arc multi-pass forming process, It is processed by multi-bend forming method. According to past experience, combined with the existing mold situation in the workshop, the upper mold adopts R120 arc mold.
Analyze the great arc segment of the workpiece in Fig. 2, and divide this 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, two arc segments). The end) has a smooth transition.
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 Figure 3, it can be seen that the workpiece in Figure 2 is formed by 7 times of bending.
When machining sheet metal 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 is used after splitting The CAD software is directly measured, and the specific bending angle is shown in Figure 3.
Bending line position size and unfolded size confirmation
In order to ensure the accuracy of the expanded dimensions 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 segmented part cross-sectional view into Catia, use the software Genetative Sheet metal Design module to generate the workpiece model, and then export the bending line and the unfolded drawing, as shown in Figure 4; the isometric drawing of the workpiece is shown in Figure 5.
Several problems should be paid attention to in the application of multi-pass forming process
Thin sheet workpiece processing
In production, it was found that some workpieces with small sheet thickness (about 2mm) will 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 release of the sheet is insufficient. , 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.
Calculation of the unfolded drawing of the workpiece when adopting the multi-bend forming process
It must be noted that when using the multi-bend forming process to process large arc workpieces, the expanded drawing must be calculated according to the actual workpiece state, that is, the arc segment approximated by the broken line segment, and the expanded drawing of the workpiece calculated by the arc cannot be used directly. Otherwise, the workpiece must be out of tolerance after processing.
Shape detection of workpiece using multi-bend forming process
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.