Bending machines are common equipment in modern mold processing. They can save labor costs and solve problems more quickly. Many factories purchase bending machines for bending sheet metal. However, when faced with the choice of a bending machine, many people are at a loss and don't know how to choose. When selecting a bending machine, we should consider various factors comprehensively. Below, I will introduce the selection criteria for bending machines. How to choose a bending machine:
If the selection of a bending machine is improper, production costs will increase, and it may not be possible to recover the cost of the machine. Therefore, several factors need to be carefully considered when making a decision.
1. Workpiece:
The first important consideration is the parts you want to produce. The key is to purchase a machine that can complete the machining tasks with the shortest workbench and the smallest tonnage.
Carefully consider the material grade, maximum processing thickness, and length. If most of the work involves low-carbon steel with a thickness of 16 gauge and a maximum length of 10 feet (3.048 meters), then a bending force of more than 50 tons is not necessary. However, if a significant amount of work involves bottoming or forming with bottom dies, a machine with a tonnage of 160 tons should be considered.
Assuming the thickest material is 1/4 inch, bending a 10-foot workpiece requires 200 tons of force, while bottoming or forming with bottom dies requires at least 600 tons. If most of the workpieces are 5 feet or shorter, the tonnage can be reduced by approximately half, significantly reducing the cost of purchase. The length of the workpiece is quite important in determining the specifications of the new machine.
2. Deflection:
Under the same load, the deflection of a 10-foot machine's workbench and slide is four times that of a 5-foot machine. This means that a shorter machine requires fewer shim adjustments to produce qualified parts. Reducing shim adjustments also shortens setup time.
The material grade is also a key factor. Compared to low-carbon steel, stainless steel typically requires an increased load of around 50%, while most grades of soft aluminum require a reduced load of around 50%. You can always obtain a tonnage chart from the bending machine manufacturer, which shows the estimated tonnage required per foot length for different thicknesses and materials.
3. Bending radius:
When using free bending, the bending radius is 0.156 times the die opening distance. During free bending, the die opening distance should be eight 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 bending radius of the part is approximately 0.078 inches. If the bending radius is almost as small as the material thickness, bottoming or forming with bottom dies is required. However, the pressure required for bottoming or forming with bottom dies is about four times greater than that for free bending.
If the bending radius is smaller than the material thickness, a punch with a front-end radius smaller than the material thickness and the help of stamping bending method should be used. This requires 10 times the pressure of free bending.
For free bending, the punch and die should be processed at 85° or less (slightly smaller is better). When using this set of molds, pay attention to the clearance between the punch and die at the bottom of the stroke, and the excessive bending that compensates for the springback and keeps the material at around 90°.
Usually, the springback angle generated by the free bending mold on a new bending machine is ≤2°, and the bending radius is 0.156 times the die opening distance. For bottoming or forming with bottom dies, the die angle is generally 86-90°. At the bottom of the stroke, there should be a gap slightly larger than the material thickness between the punch and die. The forming angle can be improved because the tonnage for bottoming or forming with bottom dies is larger (about 4 times that of free bending), reducing the stress that usually causes springback within the bending radius range.
Stamping bending is similar to bottoming or forming with bottom dies, except that the front end of the punch is processed to the required bending radius, and the clearance between the punch and die at the bottom of the stroke is less than the material thickness. By applying sufficient pressure (approximately 10 times that of free bending) to force the front end of the punch to contact the material, springback is essentially avoided.
To select the lowest tonnage specification, it is best to plan for a bending radius greater than the material thickness and use free bending as much as possible. When the bending radius is larger, it often does not affect the quality of the workpiece and its future use.
4. Bending accuracy:
The requirement for bending accuracy is a factor that needs to be carefully considered and determines whether a CNC bending machine or a manual bending machine is needed. If the bending accuracy requirement is ±1° and must remain consistent, the focus should be on CNC machines.
The repeat accuracy of the CNC bending machine's slide is ±0.0004 inches, and precise angles require such accuracy and good molds. The repeat accuracy of the manual bending machine's slide is ±0.002 inches, and under the conditions of using appropriate molds, it generally produces a deviation of ±2-3°. In addition, CNC bending machines are prepared for rapid tooling, which is an undeniable consideration when bending many small-batch parts.
5. Tooling:
Even with a full rack of molds, do not assume that these molds are suitable for the newly purchased machine. The wear of each mold must be checked by measuring the length from the front end of the punch to the shoulder of the table and the length between the shoulder of the die.
For standard molds, the deviation per foot should be around ±0.001 inches, and the total length deviation should not exceed ±0.005 inches. As for precision-ground molds, the precision per foot should be ±0.0004 inches, and the total precision should not exceed ±0.002 inches. It is best to use precision-ground molds for CNC bending machines and standard molds for manual bending machines.
6. Length of the bent part:
Assuming bending a 10-gauge low-carbon steel sheet measuring 5x10 feet at a 90° angle, the bending machine would need to apply an additional 7.5 tons of pressure to lift the steel sheet, and the operator must be prepared for the 280-pound straight edge to drop. Manufacturing such a part may require several strong workers or even a crane. Bending machine operators often need to bend long edge parts without realizing how strenuous their work can be.
If the selection of a bending machine is improper, production costs will increase, and it may not be possible to recover the cost of the machine. Therefore, several factors need to be carefully considered when making a decision.
1. Workpiece:
The first important consideration is the parts you want to produce. The key is to purchase a machine that can complete the machining tasks with the shortest workbench and the smallest tonnage.
Carefully consider the material grade, maximum processing thickness, and length. If most of the work involves low-carbon steel with a thickness of 16 gauge and a maximum length of 10 feet (3.048 meters), then a bending force of more than 50 tons is not necessary. However, if a significant amount of work involves bottoming or forming with bottom dies, a machine with a tonnage of 160 tons should be considered.
Assuming the thickest material is 1/4 inch, bending a 10-foot workpiece requires 200 tons of force, while bottoming or forming with bottom dies requires at least 600 tons. If most of the workpieces are 5 feet or shorter, the tonnage can be reduced by approximately half, significantly reducing the cost of purchase. The length of the workpiece is quite important in determining the specifications of the new machine.
2. Deflection:
Under the same load, the deflection of a 10-foot machine's workbench and slide is four times that of a 5-foot machine. This means that a shorter machine requires fewer shim adjustments to produce qualified parts. Reducing shim adjustments also shortens setup time.
The material grade is also a key factor. Compared to low-carbon steel, stainless steel typically requires an increased load of around 50%, while most grades of soft aluminum require a reduced load of around 50%. You can always obtain a tonnage chart from the bending machine manufacturer, which shows the estimated tonnage required per foot length for different thicknesses and materials.
3. Bending radius:
When using free bending, the bending radius is 0.156 times the die opening distance. During free bending, the die opening distance should be eight 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 bending radius of the part is approximately 0.078 inches. If the bending radius is almost as small as the material thickness, bottoming or forming with bottom dies is required. However, the pressure required for bottoming or forming with bottom dies is about four times greater than that for free bending.
If the bending radius is smaller than the material thickness, a punch with a front-end radius smaller than the material thickness and the help of stamping bending method should be used. This requires 10 times the pressure of free bending.
For free bending, the punch and die should be processed at 85° or less (slightly smaller is better). When using this set of molds, pay attention to the clearance between the punch and die at the bottom of the stroke, and the excessive bending that compensates for the springback and keeps the material at around 90°.
Usually, the springback angle generated by the free bending mold on a new bending machine is ≤2°, and the bending radius is 0.156 times the die opening distance. For bottoming or forming with bottom dies, the die angle is generally 86-90°. At the bottom of the stroke, there should be a gap slightly larger than the material thickness between the punch and die. The forming angle can be improved because the tonnage for bottoming or forming with bottom dies is larger (about 4 times that of free bending), reducing the stress that usually causes springback within the bending radius range.
Stamping bending is similar to bottoming or forming with bottom dies, except that the front end of the punch is processed to the required bending radius, and the clearance between the punch and die at the bottom of the stroke is less than the material thickness. By applying sufficient pressure (approximately 10 times that of free bending) to force the front end of the punch to contact the material, springback is essentially avoided.
To select the lowest tonnage specification, it is best to plan for a bending radius greater than the material thickness and use free bending as much as possible. When the bending radius is larger, it often does not affect the quality of the workpiece and its future use.
4. Bending accuracy:
The requirement for bending accuracy is a factor that needs to be carefully considered and determines whether a CNC bending machine or a manual bending machine is needed. If the bending accuracy requirement is ±1° and must remain consistent, the focus should be on CNC machines.
The repeat accuracy of the CNC bending machine's slide is ±0.0004 inches, and precise angles require such accuracy and good molds. The repeat accuracy of the manual bending machine's slide is ±0.002 inches, and under the conditions of using appropriate molds, it generally produces a deviation of ±2-3°. In addition, CNC bending machines are prepared for rapid tooling, which is an undeniable consideration when bending many small-batch parts.
5. Tooling:
Even with a full rack of molds, do not assume that these molds are suitable for the newly purchased machine. The wear of each mold must be checked by measuring the length from the front end of the punch to the shoulder of the table and the length between the shoulder of the die.
For standard molds, the deviation per foot should be around ±0.001 inches, and the total length deviation should not exceed ±0.005 inches. As for precision-ground molds, the precision per foot should be ±0.0004 inches, and the total precision should not exceed ±0.002 inches. It is best to use precision-ground molds for CNC bending machines and standard molds for manual bending machines.
6. Length of the bent part:
Assuming bending a 10-gauge low-carbon steel sheet measuring 5x10 feet at a 90° angle, the bending machine would need to apply an additional 7.5 tons of pressure to lift the steel sheet, and the operator must be prepared for the 280-pound straight edge to drop. Manufacturing such a part may require several strong workers or even a crane. Bending machine operators often need to bend long edge parts without realizing how strenuous their work can be.
