How To Choose Sheet Metal Bending Machine
Expected buyers are advised to consider carefully what to buy from the end use of the machine, known possible deflection variables of the machine, and the bending radius of the parts before buying.
You have realized that the company should consider buying a bender, so it is your responsibility to specify its specifications and recommend a new bending machine. This responsibility is not small, once the choice is not appropriate, your production costs will rise, bending machine can not anticipate cost recovery. Therefore, there are several factors that need to be check before ordering.
Bending Workpiece
The first important thing to consider is the parts you want to produce. The main point is to buy a machine that can complete the processing tasks with the shortest worktable and the smallest tonnage.
Carefully consider the material grade and the maximum processing thickness and length. If most of the sheet beding is low carbon steel with a thickness of 16 gauge and a maximum length of 10 feet, the air bending force need not be greater than 50 tons. However, if you are engaged in a large number of bottom die forming, maybe you should consider a 150-ton bending machine.
Well, assume that the thickest material is 1/4 inch, that it takes 165 tons to bend 10 feet freely, and that it takes at least 600 tons to bend with a bottom concave die. If most of the workpieces are 5 feet or less, the tonnage is almost half, thus greatly reducing the purchase cost. Part length is very important to determine the specifications of the new metal bending machine.
Deflection
You should also consider the possible deflection of this machine. Under the same load, the deflection of the worktable and slider of the 10-foot machine is four times that of the 5-foot machine.
Material grade is also a key factor. Compared with low carbon steel, the load required by stainless steel usually increases by about 50%, while soft aluminium of most brands decreases by about 50%. You can always get the tonnage table of the machine from the bender manufacturer, which shows the tonnage estimates required for each foot length under different thickness and materials.
Bending radius of parts
Next, we must focus on the bending radius of the part.
When air bending is used, the bending radius is 0.156 times of the opening distance of the die. In the free bending process, the opening distance of the die should be 8 times the thickness of the metal material. For example, when forming 16 gauge low carbon steel with a 1/2 inch opening distance, the bending radius of the part is about 0.078 inches. If the bending radius is almost as small as the material thickness, the bottom die must be formed. However, the pressure required for forming a bottom die is about four times greater than that required for free bending.
If the bending radius is less than the thickness of the material, the punch with the front corner radius less than the thickness of the material should be used, and the method of imprint bending should be resorted to. In this way, 10 times the free bending pressure is required.
As far as air bending is concerned, punches and dies are machined at or below 85 degrees (smaller is better). When using these dies, attention should be paid to the gap between the punch and the die at the bottom of the stroke, and to the excessive bending of the material which is enough to compensate for the springback.
Usually, the springback angle of the air bending die on the new bending machine is less than 2 degrees, and the bending radius is equal to 0.156 times of the opening distance of the die.
For the bending of the bottom die, the angle of the die is generally 86 - 90 degrees. At the bottom of the process, there should be a slightly larger gap between the punch and the concave die than the thickness of the material. The forming angle is improved because the bending tonnage of the bottom die is larger (about four times that of the free bending), which reduces the stress that usually causes springback within the bending radius.
Accuracy
The requirement of bending accuracy is a factor that needs careful consideration. It is precisely this factor that determines whether you need to consider a CNC bender or a manual bender. If the bending accuracy is required to be [1], and cannot be changed, you must focus on the CNC machine.
CNC bending machine slider repetition accuracy is (+0.0004 inches), forming accurate angle must use such accuracy and good die. The repetition accuracy of the slider of the hand-controlled bending machine is (+0.002 inches), and the deviation of (+2~3 degrees) will generally occur under the condition of proper die. In addition, CNC benders are ready for rapid die loading. When you need to bend many small batches of parts, this is an undoubted reason to consider.
Press brake bending tools
Even if you have a full shelf of moulds, don't think these moulds are suitable for newly bought machines. The wear of each die must be checked by measuring the length between the front end of the punch and the shoulder of the die.
For conventional dies, the deviation per foot should be about (+0.001 inches) and the total length deviation should not be more than (+0.005 inches). As for precision grinding dies, the accuracy per foot should be (+0.0004 inches) and the total accuracy should not be greater than (+0.002 inches). It is better to use precision grinding die for CNC bending machine and conventional die for manual bending machine.
Indeed, we often make the mistake of buying only a new bender and not the right die to match it.
Edge Length of Bending Parts
One factor that people often neglect is the length of the bending edge of the material in front of the bender.
Assuming that a 10-gauge low-carbon steel plate of 5 *10 feet is bent at 90 degrees, the bender must apply an additional 7.5 tons of pressure to lift the plate, and the operator must be prepared for a straight drop of 280 pounds. Making this part may require several strong workers or even a crane. Bender operators often need to bend long-sided parts, but they do not realize how hard their work is.
Now there is a kind of supporting device suitable for the workshop engaged in this kind of work. This device can be improved according to the needs of old and new machines. With this device, only one person is needed to form long-edged parts. It;e called cnc controlled sheet follower or cnc controler bending aids.
