How to Select CNC Press Brake Dies and Key Considerations During Operation

In actual production, CNC press brake dies encounter a wide range of issues, and operator errors can significantly reduce their service life. Let’s now explore how to select the right CNC press brake die and the key points to keep in mind during its use.

First, select the CNC press brake die; it must meet the process requirements during production.

1. Select heat-treatment processes appropriately. Heat treatment for CNC press-brake dies includes annealing after steel forging, high-temperature or low-temperature tempering after rough machining, quenching and tempering after finish machining, and stress-relief low-temperature tempering after electrical discharge machining and wire EDM. Improper heat treatment is a major cause of premature failure in CNC press-brake dies; only when cold and hot working processes are well coordinated can optimal die life be ensured.

2. Rational mold surface strengthening technologies. The primary objectives of surface strengthening for CNC press brake dies are to enhance wear resistance, corrosion resistance, and lubrication performance.

3. Eliminate stresses generated during electrical discharge machining. Prior to wire-cutting, the superposition of two stress fields can easily reach the material’s strength limit, leading to microcracks and significantly reducing the service life of stamping dies. Moreover, the workpiece undergoes a state of tensile stress due to quenching, and the thermal stress induced during wire-cutting is also tensile; thus, these measures help extend the die’s service life.

4. Excellent lubrication at operating temperatures. Typically, below 250°C, wear is predominantly oxidative; relative friction between die halves or between the die and the workpiece leads to the formation of an oxide film that repeatedly forms and spalls, resulting in minimal wear. Die operating temperatures can be categorized as low, ambient, or cyclic; temperature has a significant impact on the wear resistance of steel. Wear generally decreases with increasing temperature, but excessively high temperatures markedly reduce die hardness. Between 250°C and 300°C, the wear mechanism transitions to adhesive wear, reaching a peak in wear rate. Above 300°C, oxidative wear becomes dominant, adhesive phenomena worsen, and extensive sintering and molten wear occur.

Secondly, the following points should be noted when using CNC press brake dies in practice:

1. Why can a 88-degree bending die produce a 90-degree bend? This is because metal sheet stock has a certain degree of springback: for ordinary cold-rolled sheet, an 88-degree die angle is sufficient; for stainless steel, an 86-degree angle will do. For materials with particularly high springback, the angle may even be as low as 83 degrees. Aluminum, on the other hand, has low hardness and limited springback, so the die angle must be 90 degrees. Does this make it clear now? In addition, the die angle is primarily determined by the material’s springback characteristics, while the bending pressure also influences the final bend angle.

2. What is the typical quenching hardness for press brake dies? The heat treatment for press brake dies is typically HRC 47–52. However, the appropriate quenching hardness for a press brake die also depends on the material and design of the die; excessively high hardness can easily lead to die fracture. Therefore, higher hardness does not necessarily translate into greater durability, and very high hardness can be difficult to work with. Generally, a reasonable hardness range is HRC 47–52.

3. When bending corners or creating press folds, set the bend angle to 30 degrees; first perform the corner bend, then press the fold edge. For R-shaped bends, select the corresponding R upper die and R lower die.

4. When bending long workpieces, avoid using combined dies to minimize tool‑edge indentation; moreover, because the external corner radius r of the V‑shaped groove in a single‑slot lower die is relatively large, bending indentations are less likely to occur, making single‑slot dies the preferred choice.

5. For products with exceptionally high bending hardness or excessive plate thickness, do not use dies to bend reinforcing bars or other cylindrical products; the use of upper dies No. 103 and No. 116 is strictly prohibited, as they can easily damage the dies.

After use, promptly return the press brake die to its designated template and arrange it according to the labeling. Thoroughly clean any dust from the die to ensure more accurate operation next time.