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Sheet metal bending is another processing form of sheet metal bending and forming. The sheet metal is mainly bent in a straight line through the sheet metal press brake, which is suitable for processing narrow and long linear parts. The bending operation of the bending machine is completed by the upper and lower bending dies fixed on the sliding block and the table.
Bending equipment and tools
According to the different bending methods, the sheet metal bending machine has two forms: bending and pressing. Traditionally, they are called bending machines and press brakes. At present, the most widely used bending machine is the hydraulic sheet metal bending machine. Figure 1-1 shows the structure of the W67Y-160 sheet metal bending machine, where WC means bending machine, 67 is sheet metal bending press, Y is hydraulic transmission code, and 160 means the nominal pressure of the press is 160kN. The sheet metal bending machine is composed of a frame, a sliding block, a workbench, and an oil cylinder. It uses high-pressure oil as power when working, and uses the cylinder and piston to move the sliding block and the mold to complete the bending work of the sheet. With the development of computer control technology, the traditional sheet metal bending machine has gradually undergone numerical control transformation. The stroke adjustment of the slider and the adjustment of the back gauge positioning are mostly electric quick adjustment and manual fine adjustment, and most are equipped with digital display devices. , And can be equipped with a numerical control system to realize automatic control of the back gauge and slide stroke. The gauge accuracy of this kind of numerical control mechanism is generally up to ±0.1mm, and it can continuously process workpieces with multiple different bending angles. Fast bending has greatly improved production efficiency. At the same time, CNC hydraulic sheet metal bending machines have also appeared.
No matter what equipment is used for sheet bending, the processing is mainly realized by the bending die installed on the bending machine. The bending die installed on the bending machine can be divided into general and special molds. Figure 1-2 is general bending. The shape of the end face of the mold.
The upper mold is generally V-shaped. There are two types: straight arm type and curved arm type. The angle of the upper mold with smaller rounded corners is made 15°, and the fillet radius of the upper mold is made into a set of several fixed sizes. In order to change according to the needs of the workpiece.
The lower mold is generally made of several fixed notches suitable for the bending parts of the machine tool on 4 faces. Generally, V-shaped and rectangular, both obtuse and acute-angled parts can be bent. The length of the lower mold is generally the same as the work. The tabletops are equal or slightly longer. The height of the upper and lower dies of the bending die needs to be determined according to the closing height of the machine tool. When the general bending die is used, the bending angle of the bending parts is usually less than 18°.
Special bending dies must be used for bending parts with large production volume or special shapes of parts. Special bending dies can be used in conjunction with general bending dies, or parts can be bent separately. Figures 1-3 are special bending dies used on bending machines.
Using the special mold shown in Figure 1-3 (a) can realize the formation of multiple bending parts at one time, and the production efficiency is very high; and the mold shown in Figure 1-3 (b) is the special bending mold used in the last process, because the parts The opening is very small, and the universal bending die can only complete the bending of the first few processes.
Operation steps and methods of press brake
Before operating the press brake, you should make preparations for the operation. The main contents are as follows: first, remove the obstacles on the work surface and the machine tool, and lubricate the machine; second, check whether all parts of the machine work normally, and find problems in time For repairs, especially check whether the pedal is flexible. If there is a car connection phenomenon, it is never allowed to use it.
Generally speaking, the bending machine can be operated according to the following methods and steps.
- Lower the slider of the bending machine to the lowest position and adjust the lowest point of the slider so that the closed height of the slider to the working table is 20-50mm larger than the total height of the upper and lower bending dies.
- Raise the slider, install the upper and lower molds. The general steps are: first put the lower mold on the workbench, then lower the slider, and then install the upper mold. When installing the upper mold, keep the two ends parallel, move from one end of the slide block to the fixed mold groove and move in. Push to the middle position of the slider to balance the force of the machine tool and fix it firmly with screws.
In order to prevent the upper mold from falling down and hurting the lower mold or hurting your hands during installation, you can put a few wooden blocks on the lower mold, preferably a few wooden sticks of the same diameter, which can not only prevent the above accidents, but also use wooden sticks to support When the upper mold is pushed inward, it is both labor-saving and safe due to the parallelism.
- Start the adjustment mechanism of the slider to make the upper mold enter the slot of the lower mold, and move the lower mold so that the center line of the apex of the upper mold is aligned with the center line of the slot of the lower mold to fix the lower mold.
At present, on some bending machines, taking into account the convenience of installation and debugging of the upper and lower molds, the lower mold is also designed as a lower mold pad and a lower mold split, which are connected in the form of a U-shaped notch, although the subsequent mold replacement is more Convenient, but the first installation and debugging should still be carried out according to the above steps.
- Raise the slider and adjust the stopper mechanism installed on the back of the worktable according to the bending size, so that the upper die mouth and the bending line of the sheet material coincide. If the equipment has digital display or numerical control function, it can be adjusted by electric power, and its positioning size It can be directly displayed or programmed and controlled. If the equipment does not have an electric adjustment function, the positioning size of the blank can be manually adjusted when it is working. The structure of the stopper mechanism is shown in Figure 1-4.
Among them: the bracket 5 is fixed in the T-shaped groove on the side of the workbench with a fastening handle 6 and can be adjusted up and down. The slider 2 can move back and forth along the bracket 5 to adapt to the required position. If the adjustment amount is small, the baffle plate 1 can also be adjusted back and forth by the fine adjustment nut 4 and fastened with the handle 3.
When working, the measured size A value is generally marked. The A value needs to be tested and then adjusted appropriately. The bending size can only be determined after the first inspection, self-inspection, and special inspection are passed.
In the formula, A——the distance from the side of the lower die to the baffle, mm;
B——The width of the lower die slot, mm;
C——The distance from the side of the lower die to the edge of the slot of the lower die, mm;
L——The distance from the bending line to the edge of the blank, mm.
It is required to adjust the bending angle. The bending angle only needs to adjust the depth of the upper mold entering the lower mold, and it is easy to meet the requirements. Generally, after several bending trials with waste materials, the bending work can be determined.
For parts that need to be bent multiple times, the order of bending is generally: from outside to inside. That is, first bend the corners of the two ends, and then bend the corners of the middle part, and the previous bend must consider the reliable positioning of the second bend, and the latter bend does not affect the formed part of the previous bend, as shown in Figure 1-5.
Processing methods of common bending parts
The universal bending machine is used with some special dies for bending, which is not only quick to put into production, but also very economical. Therefore, it is widely used in production. Figure 1-6 shows the common bending part and its bending die.
- When bending a blank with a bent edge, the distance from the center of the lower die slot to its edge should not be greater than the length of the straight side of the bending part. The dimension d in Figure 1-7 (a) must be smaller than the dimension c, otherwise When the blank cannot be placed, and the semi-finished product has been bent into a hook shape and then bent, the lower mold with avoiding grooves should be used, as shown in Figure 1-7(b).
- The choice of the upper mold should also be determined according to the requirements of the shape and size of the part. The fillet radius of the working end of the upper mold should be slightly smaller than the bending radius of the part. Generally, the straight arm type is used. When the straight arm type upper mold is blocked, it should be replaced with a curved arm type upper mold.
- When the general bending angle is more complicated for processing, according to the number of corner molds, the bending radius, and the shape of the order, the shape needs to be adjusted and changed many times and the upper and lower molds. The mold during bending manufacturing is very important, and its characteristic mold structure And the number of parts produced by bending, sometimes cannot be produced. The general principle is: when bending, the deformation should be bent from the outside to the inside, that is, bend the outer corner first, then bend back. The possible positioning of the back and inner bends must be considered before the second bend, and the subsequent bend cannot affect the shape of the previous bend.
- When using a general bending die to bend apart on a press brake, the width B of the lower die slot (see Figure 1-2) should not be less than twice the sum of the bending fillet radius R of the part and the material thickness: Plus a gap of 2mm, that is, B>2(t+R)+2. In this way, when bending, the blank will not be blocked or produce indentation and scratches. At the same time, in order to reduce the bending force, a wider notch should be used for hard materials, and a smaller notch should be used for softer materials. The notch will bend the straight side into an arc.