How to choose a bending machine

Before the prospective buyer pays, it is best to carefully consider what to buy from the end use of the machine, the possible deflection of the known machine, and the bending radius of the part.
You have long realized that the company should consider adding a bending machine, so it is your responsibility to specify its specifications and recommend a new machine. This responsibility is no exception. Once you choose it improperly, your production costs will increase and the bending machine cannot expect to recover costs. Therefore, there are several factors that must be weighed when making decisions.
Workpieces The first important thing worth considering is the part you are going to produce. The point is to buy a machine with the shortest working table and the smallest tonnage that can complete the machining task.
Carefully consider material grades and maximum processing thickness and length. If most of the work is a low carbon steel with a gauge of 16 gauge and a maximum length of 10 feet, the free bending force does not have to be greater than 50 tons. However, if you are engaged in a large number of bottomed die casting, you may want to consider a 150-ton machine tool.
Well, assuming the thickest material is 1/4 inch, a free bending of 10 feet requires 165 tons, while a bottomed die bending (correction bending) requires at least 600 tons. If most of the parts are 5 feet or less, the tonnage is almost halved, which greatly reduces the cost of acquisition. The length of the part is very important for determining the specifications of the new machine.
Flexibility You also need to consider the possible deflection of this machine. At the same load, the 10-foot machine table and the slider exhibit four times the deflection of the 5-foot machine. This means that shorter machines require fewer spacer adjustments to produce qualified parts. Reducing shim adjustments also reduces setup time.
Material grades are also a key factor. Compared with low-carbon steel, the required load of stainless steel usually increases by about 50%, while most brands of soft aluminum reduce about 50%. At any time, you can get the machine's tonnage table from the manufacturer of the bending machine, which shows the estimated tonnage per foot length at different thicknesses and different materials.
The bend radius of the part Next, you must look at the bend radius of the part.
With free bending, the bending radius is 0.156 times the die opening distance. In the free bending process, the die opening distance should be 8 times the thickness of the metal material. For example, when a 16 gauge low carbon steel is formed using a 1/2 inch opening distance, the bending radius of the part is about 0.078 inches. If the bending radius is as small as the material thickness, a bottomed die must be formed. However, the pressure required for forming bottomed dies is approximately 4 times greater than free bending.
If the bending radius is smaller than the material thickness, a punch with a rounded tip radius smaller than the material thickness must be used and the indented bending method should be resorted to. In this way, 10 times the pressure of free bending is required.
For free bending, the punch and die are machined at 85° or less (smaller is better). When using this set of molds, pay attention to the clearance between the punch and the die at the bottom of the stroke, and the excessive bending sufficient to compensate the rebound and keep the material around 90°.
In general, the free bending die produces a springback angle of ≤ 2° on the new bending machine and a bending radius equal to 0.156 times the die opening distance.
For bottomed die bending, the die angle is typically 86 to 90°. At the bottom of the stroke, there should be a clearance slightly larger than the thickness of the material between the male and female molds. The forming angle is improved because of the larger tonnage of the bottomed die bending (approximately 4 times the free bending), reducing the stresses that normally cause springback in the bending radius.
Embossing is the same as bending a bottomed die, except that the front of the punch is machined to the required bend radius, and the gap between the punch and die at the bottom of the stroke is less than the thickness of the material. Due to the application of sufficient pressure (approximately 10 times that of free bending) to force the front end of the punch into contact with the material, springback is substantially avoided.
In order to select the lowest tonnage specification, it is best to plan for a bending radius that is greater than the material thickness, and use free bending as much as possible. Large bending radii often do not affect the quality of the parts and their future use.
Accuracy The bending accuracy requirement is a factor that needs careful consideration. It is this factor that determines whether you need to consider a CNC bending machine or a manual bending machine. If the bending accuracy requires ±1° and cannot be changed, you must look at the CNC machine.
The accuracy of the CNC bending machine slider is ±0.0004 inches. Accurate angles must be formed with this precision and a good mold. Manually controlled bending machine sliders have a repeatability of ±0.002 in., and typically have ±2 to 3° deviations when used with a suitable mold. In addition, CNC bending machines are ready for rapid die-loading. When you need to bend many low-volume parts, this is an unquestionable reason to consider.
Mold Even if you have full racks of molds, don't assume these molds are suitable for newly purchased machines. Each tool must be inspected for wear by measuring the length between the front of the punch to the shoulder and the length of the die shoulder.
For conventional molds, the deviation per inch should be around ±0.001 inch and the total length deviation should not be greater than ±0.005 inch. As for the precision grinding mold, the accuracy per inch should be ± 0.0004 inches, and the total accuracy must not exceed ± 0.002 inches. It is best to use a precision grinding mold for a CNC bending machine, and a conventional mold for a manual bending machine.
Indeed, we often make the mistake of buying only new bending machines without buying the right ones.
The length of the side of the bend One factor that is often overlooked by people is the length of the material in front of the bender.
Assuming that a 10-gauge, low-carbon steel sheet is bent 90° along a 5×10 ft., the pressurizer will probably have to apply an additional 7.5 tons of pressure to lift the steel plate. The operator must prepare for the 280 pound straight edge drop. . Manufacture of this part may require several strong workers or even a crane. Bender operators often need to bend long-side parts, but do not realize how hard their work is.
There is now a kind of charging device suitable for the workshop that is engaged in this kind of work, this kind of device can be improved according to the needs of new and old machines. With this device, the formation of long-side parts requires only one person to operate.

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