Choosing the wrong bending machine can lead to skyrocketing production costs and prevent the machine from ever recouping its investment. Therefore, several factors must be carefully considered when making the decision.

Part

A crucial consideration is the parts you need to produce; the key is to purchase a machine that can complete the processing tasks, with a shorter worktable and lower tonnage.

Carefully consider the material grade and the larger processing thickness and length. If most of the work involves 16 gauge low carbon steel with lengths up to 10 feet (3.048 meters), the free bending force need not exceed 50 tons. However, for extensive bottom-die forming, a machine tool with a 160-ton capacity may be worth considering.

Assuming thicker materials at 1/4 inch, a 10-foot free bend requires 200 tons, while bottom-die bending (corrective bending) necessitates at least 600 tons. If most parts are 5 feet or shorter, the tonnage is roughly halved, significantly reducing acquisition costs. The part length is quite important in determining the specifications of the new machine.

Scratch Change

Under the same load, the deflection of the 10-foot machine table and slider is four times that of the 5-foot machine. This means that the shorter machine requires less shimming adjustment to produce qualified parts. Reducing shimming adjustment also shortens preparation time.

Material grade is also a critical factor. Compared to低碳 steel, stainless steel typically requires a load increase of about 50%, while most soft aluminum grades reduce the load by approximately 50%. You can always obtain a tonnage chart from the bending machine manufacturer, which shows the estimated tonnage required per foot of length for different thicknesses and materials.

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When free bending, the bending radius is 0.156 times the die opening distance. During the free bending process, the die opening distance should be 8 times the thickness of the metal material. For example, when forming 16-gauge low-carbon steel with a 1/2-inch (0.0127 meters) die opening distance, the part's bending radius is approximately 0.078 inches. If the bending radius is almost as small as the material thickness,

Bottom-die forming must be conducted. However, the pressure required for bottom-die forming is about four times greater than that for free bending.

If the bending radius is less than the material thickness, a punch with a rounded corner radius less than the material thickness must be used, and the help of embossing bending method is required. This means a pressure 10 times greater than free bending is needed.

For free bending, the punches and dies should be machined at 85° or less (slightly less is preferable). When using this set of molds, pay attention to the clearance between the punch and die at the bottom of the stroke, as well as the overbend sufficient to compensate for springback and maintain an approximately 90° bend.

Typically, the springback angle on a new bending machine for free-form bending dies is ≤2°, with the bending radius equal to 0.156 times the distance from the die opening.

For bottom-dished mold bending, the mold angle is typically 86 ~ 90°. At the bottom of the stroke, there should be a gap slightly larger than the material thickness between the male and female molds. The forming angle is improved due to the higher tonnage of bottom-dished mold bending (about 4 times that of free bending), which reduces the stress within the bending radius range that usually causes springback.

The embossed bending is similar to bottom die bending, with the only difference being that the front end of the male mold is machined to the required bending radius, and the clearance between the male and female molds at the stroke bottom is less than the material thickness. Sufficient pressure (about 10 times that of free bending) is applied to force the front end of the male mold to contact the material, thereby basically avoiding springback.

In order to select a lower tonnage specification, plan for bending radii greater than the material thickness, and employ the free bending method as much as possible. Larger bending radii generally do not affect the quality of the finished product or its future use.

Curvature

The requirement for bending accuracy is a factor that must be carefully considered. It is this factor that determines whether a CNC bending machine or a manual bending machine is needed. If the bending accuracy requirement is ±1° and cannot be compromised, a CNC machine must be the focus.