Principles of Bending with a Press Brake
Key Parameters in Sheet Metal Bending with a Press Brake
As previously mentioned, sheet metal bending with a press brake is one of the essential processes in various production industries. To achieve optimal bend quality and desirable results, the following key parameters must be considered:
A: Raw Material (Sheet)
The material type, thickness, quality, hardness, and dimensions of the sheet are determining factors in achieving the desired bend quality. Softer sheet materials (such as aluminum) are easier to bend with less force, while harder, more rigid materials (such as stainless steel) require greater force. For instance, bending an ST37 steel sheet of a certain thickness may require 100 tons of force, whereas a stainless steel sheet of the same dimensions and thickness would need 160 tons.
Additionally, purchasing sheets from unreliable sources may result in materials with properties that differ from what was ordered, which can affect the quality of the final bend.
Thickness and dimensions also impact bend quality. Thinner, smaller sheets generally bend more easily and with better quality, while thicker and larger sheets require greater precision and bending force. It has also been observed that sheets with higher thicknesses that have been previously cut with a plasma cutter may not reach the desired bending accuracy due to changes in material properties around the cut area (the bend angle may not be consistent along the sheet length).
Press brakes by Bozorg Dayani Machinery Manufacturing provide maximum bending accuracy and quality for various sheet alloys.
B: Bend Angle
The bend angle is a crucial parameter in the press brake bending process and has several effects on the quality and precision of bending. The impacts of bend angle are as follows:
- Stress and Strain: The bend angle affects stress and strain distribution in the sheet. Sharper bends (smaller angles) generally create higher stress in the bend area and may lead to cracking or sheet fracture. Therefore, for hard materials, sharp bends (angles less than 60 degrees) require high levels of skill and precision.
- Elasticity of Metals: When a sheet is bent, it typically regains some of its original shape, attributed to its elastic properties. Generally, reversible changes are called elastic changes, while non-reversible changes are called plastic changes. Numerous articles on this concept and metal stress-strain curves are available for further reference. The bend angle has a direct effect on the degree of spring-back. Larger angles generally result in less spring-back, while smaller angles experience greater spring-back. Calculating the spring-back is challenging and can only be determined with experience and skill. Thus, an experienced bending operator can estimate the spring-back or determine the desired bend angle through trial and error on initial samples.
- Accuracy and Formability: The bend angle affects the final shape accuracy of the bent piece. If the angle is not correctly set, the final product may deviate from the desired specifications. For example, in frame manufacturing, if the wrong angle is chosen, the final frame dimensions may not match your intended design. It is advisable to inspect the first sample with the desired specifications and, if accurate, proceed with production.
- Cold Zone: The cold zone in bending refers to the area of the sheet where permanent deformation (i.e., bending) occurs (specifically where the sheet is compressed between the punch and die). This zone is affected by mechanical stresses from bending and is usually near the bending location. The sharper the bend angle, the more noticeable the cold zone effect, which, as previously mentioned, may cause cracking or warping in the sheet. Any unwanted deformation in the bending area, such as warping, cracking, or deformation, is referred to as the cold zone effect.
- Structural Strength and Safety: Precise adjustment of the bend angle can enhance the structural integrity of the part. Incorrect angles may compromise the part’s ability to withstand loads in its final application.
- Design and Aesthetics: In cases where the appearance of the final product is important, the bend angle and the way it is achieved can significantly impact the aesthetic appeal of the piece. Well-executed bends add a refined look to the final product.
In conclusion, selecting the appropriate bend angle for press brake bending should be based on the specific needs of the project and the type of sheet material used, to prevent potential issues and achieve high production quality.
Key Parameters in Sheet Metal Bending with a Press Brake
As discussed earlier, sheet metal bending with a press brake is a critical process in various production industries. To achieve the best bend quality and desirable results, the following key parameters should be considered:
C: V-Die Opening, Bend Length, and Bend Radius
The V-die opening size is crucial in the press brake bending process, and not every V-die size is suitable for bending every sheet. Generally, the V-die opening should be no less than four times and no more than twelve times the sheet thickness; otherwise, the resulting bend quality will be unsatisfactory. For more on this, refer to the article “Selecting the Right V Opening for Bending with a Press Brake.”
Bend length also affects stress distribution in the bend area. Longer bends can reduce stress in the bending area, decreasing the likelihood of cracking. Additionally, as bend length increases, bending accuracy usually improves due to more uniform pressure distribution along the bend. Bend length also influences the final appearance and surface quality of the part; longer bends typically yield better results.
The bend radius (bend edge) affects the degree of sheet deformation. Larger bend radii usually result in gentler deformation, applying less stress to the material, thus reducing the risk of cracking. Different materials have unique mechanical properties, and the bend radius should be selected accordingly. For high-strength materials, a larger bend radius should be used to prevent fractures. In some applications, the bend radius can also impact the final strength and functionality of the part. Smaller radii may be more susceptible to damage under specific loading conditions. Overall, choosing the correct bend length and radius in the press brake bending process not only significantly impacts the final product quality but also improves the part’s performance and durability. Engineers and designers must carefully consider these parameters during design to avoid potential issues in production and end use.
D: Bend Depth
Bend depth is the vertical distance between the bend axis and the point where the sheet was positioned horizontally before bending. This depth determines the bend angle and the amount of deformation in the material. Bend depth is a crucial parameter in the press brake bending process and influences the shape and quality of the final piece.
Bend depth causes the sheet to deform and dictates its final angle. Shallow depth can lead to wider angles, while deeper bends can create sharper angles. Additionally, bend depth affects the stability of the final part; deeper bends generally have better structural characteristics and are more resistant to external stress. Parts with an appropriate bend depth also typically have better fatigue properties, as stress distribution within them is better controlled.
Bend depth should be chosen based on the length and thickness of the sheet. Thicker sheets generally require greater bend depth to achieve the best results. The choice of bend depth should also consider the type of material and its mechanical properties. Some materials respond better to deeper bends, while others may require shallower bends.
Bend depth is a critical parameter in the design and production of bent parts using a press brake. Choosing the correct bend depth not only affects the accuracy and quality of the final part but also influences its performance, strength, and durability. Engineers should accurately calculate and set the bend depth, considering material characteristics and design requirements.
E: Working Speed
Bending speed can impact the final quality and precision of the bend. An incorrect speed can cause defects. High speed may not allow the metal to form properly, increasing the likelihood of cracking or surface deformation. Low speed, however, raises production costs. Bozorg Dayani Machinery’s press brakes consider all of the above factors, and our specialists provide the necessary guidance on speed.
F: Tool Type and Quality
The tools used (punch, die, die holders, etc.) should be high-quality and suitable for the type of bend. Bozorg Dayani Machinery Manufacturing is proud to use premium materials and high-quality steel in its production.
G: Machine Settings
Precision in setting up the press brake, including bending force, punch stroke length, different angles, V-die selection, and more, is essential for successful bending. It’s important to note that many of these setup considerations are addressed in both models of Bozorg Dayani press brakes (PLC and CNC). By entering initial values, you can avoid complex adjustments, as the device handles this process automatically.
Conclusion: Press brake bending involves specific principles and rules, as covered in this article. However, given the material properties (metals), achieving an accurate and desirable bend angle requires both knowledge of these principles and practical experience. A seasoned bending operator with years of experience on a press brake will acquire the skills and expertise to help you achieve the highest bending quality. Adhering to the guidelines outlined in this article is also essential. Bozorg Dayani Machinery Manufacturing is proud to offer quality products along with scientific, technical, and engineering support throughout all stages of production.