What are the working principles of press brake tooling?
There are many types of press brake tooling, so what is the working principle of the JUQUAN CNC press brake? Let's explore it together.
Press brake tooling consists of a frame, a worktable, and a clamping plate. The worktable is placed on the frame and consists of a base and a pressure plate. The base is connected to the clamping plate through hinges. The base is composed of a seat shell, a coil, and a cover plate. The coil is placed in the recess of the seat shell, and the top of the recess is covered with a cover plate. When the coil is energized by the wire, it generates a magnetic force on the pressure plate, thereby clamping the sheet metal between the pressure plate and the base. The electromagnetic clamping allows the pressure plate to be shaped for various workpiece requirements and can process workpieces with side walls. The operation is also very simple.
When purchasing a press brake, the potential buyer should carefully consider the final purpose of the machine, known variables that may occur in the machine, and the bending radius of the parts before making the payment.
Workpiece
The first important consideration is the parts you want to produce. The key point is to buy a machine with the shortest worktable and the smallest tonnage that can complete the machining tasks. Carefully consider the material grade, maximum processing thickness, and length. If the majority of the work involves 16-gauge low carbon steel with a maximum length of 10 feet, then a tonnage of no more than 50 tons is required for free bending. However, if a significant amount of bottoming dies forming is involved, a 150-ton machine should be considered.
Deflection
Under the same load, the deflection of a 10-foot machine's worktable and ram is four times that of a 5-foot machine. This means that shorter machines require fewer shim adjustments to produce qualified parts, reducing setup time.
Material grade is also a key factor. Compared to low carbon steel, stainless steel typically requires about 50% more load, while most grades of soft aluminum require about 50% less. You can always obtain a tonnage chart from the press brake manufacturer, which shows the estimated tonnage required per foot length for different thicknesses and materials.
Bending Radius of Parts
For 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 die opening distance, the bending radius of the part is approximately 0.078 inches. If the bending radius is close to or smaller than the material thickness, bottoming dies forming is required. However, bottoming dies forming requires approximately four times the pressure compared to free bending.
If the bending radius is smaller than the material thickness, a punch with a front-end radius smaller than the material thickness is used, and the embossing bending method is employed. This requires 10 times the pressure compared to free bending. For free bending, the punch and die are processed at 85° or less (slightly smaller is better). When using this set of tooling, pay attention to the gap between the punch and die at the bottom of the stroke and ensure enough overbending to compensate for springback and keep the material at approximately 90°.
Generally, the springback angle produced by free bending tooling on a new press brake is ≤2°, and the bending radius is 0.156 times the die opening distance. For bottoming dies bending, the die angle is generally between 86 to 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 is improved because bottoming dies bending requires higher tonnage (about four times that of free bending), reducing the stress that typically causes springback within the range of the bend radius.
Press brake bending is similar to bottoming die bending, except that the front end 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 material thickness. By applying sufficient pressure (approximately 10 times that of air bending), the front end of the punch is forced to contact the material, essentially eliminating springback. To select the lowest tonnage specification, it is best to plan for a bend radius greater than the material thickness and to use air bending whenever possible. Larger bend radii often do not affect the quality of the part or its future use.
Precision
Bending accuracy requirements are a critical factor to consider, as they determine whether you need a CNC press brake or a manual press brake. If the bending accuracy requirement is 1° and must remain constant, you should focus on a CNC machine.
The repeat accuracy of the slide on a CNC press brake is 0.0004 inches, requiring such precision and good tooling for forming accurate angles. In contrast, the repeat accuracy of the slide on a manual press brake is 0.002 inches, and under suitable tooling conditions, it generally results in a deviation of 2-3°. Additionally, CNC press brakes are prepared for quick tool changes, making them an undeniable choice when you need to bend many small batch parts.
Tooling
Even if you have a rack full of press brake tooling, do not assume that these tools are suitable for a newly purchased machine. Each tool must be inspected for wear by measuring the length from the front end of the punch to the shoulder and the distance between the die shoulders.
For standard tooling, the deviation per foot should be around 0.001 inch, with a total length deviation not exceeding 0.005 inches. As for precision-ground tooling, the precision per foot should be 0.0004 inches, with a total precision not exceeding 0.002 inches. It is best to use precision-ground tooling for CNC press brakes and standard tooling for manual press brakes.
