When designers set a bend radius too tight, the metal can crack or twist. This causes parts to fail and production to stop. A clear guide to bend radius can cut these risks. It shows you how to pick the right radius for each metal and thickness and tool setup.
Sheet metal bend radius guidelines provide rules for the smallest radius you can safely bend sheet metal without causing damage. The guidelines vary by material type and thickness, helping you prevent cracking and distortion. Knowing these guidelines ensures precise, strong, and reliable metal parts.
Next, we will look at detailed tables and real examples. You will get clear steps to avoid defects and cut rework. Stick with us to learn practical and valuable tips.
What Is Bend Radius in 板金加工？
曲げ半径とは、曲げの中心から金属の内面までの距離のこと。曲げがどの程度きついか、あるいは広いかを示す。半径が小さいほど、曲げは鋭くなる。半径が大きいと滑らかな曲がりになります。この値は、外側の端ではなく、曲げの内側を基準にしています。
In sheet metal, the bend radius is usually equal to the metal’s thickness. But this can change depending on the material and the application.
To avoid cracks and deformation during bending, it’s important to follow the minimum bend radius. This is the smallest inside radius you can apply to a material without causing damage. Materials, thickness, and bend angles all affect this limit. Harder or thicker metals need larger radii to stay intact.
How to Calculate the Minimum Bending Radius?
Using the correct bend radius helps prevent cracks, stress marks, and part failure. A quick way to figure this out is by following a few rules of thumb based on material type and thickness.
Understanding the Formula
The minimum bend radius depends on how thick the metal is and what kind of metal you’re bending. A simple rule is:
Minimum Bend Radius = Thickness (T) × Material Factor
Each material has a different factor. Soft metals need smaller bend radii. Harder metals need larger ones. This gives you a fast and easy way to avoid bending problems.
Key Variables to Consider
Three things change the bend radius you should use:
- Thickness (T): Thicker sheets need more room to bend.
- 材料の種類： Softer materials like aluminum can bend tighter. Harder ones, like stainless steel, need more space.
- Bend angle: Sharper angles usually need a bigger radius to stay crack-free.
The thicker and harder the sheet, the bigger the bend radius must be.
Use of Minimum Bend Radius Charts
To save time, many engineers and press brake operators use bend radius charts. These charts show recommended radii based on material and thickness.
Here’s a simplified reference table:
| 素材 | T = 1–6 mm | T = 6–12 mm | T = 12–25 mm |
|---|---|---|---|
| アルミニウム | 1 × T | 1.5 × T | 2–3 × T |
| スチール | 0.8 × T | 1.2 × T | 1.5–2.5 × T |
| ステンレス・スチール | 2 × T | 2.5 × T | 3–4 × T |
These values help you bend metal safely. Just find your material and thickness, then multiply to get the right inside radius.
Minimum Bend Radius Calculator
Tooling and Equipment Impacts
Tooling plays a direct role in the final bend radius. Your choice of dies and punch affects how the metal forms and how accurate the bend will be.
How does V-Die Opening Influence the Bend Radius？
The size of the V-die opening controls how the material bends. A larger V-die opening creates a larger inside radius. A smaller opening gives a tighter bend.
As a general rule:
V-die opening = 8 × Material Thickness (for air bending)
If the V is too small, the material might crack. If it’s too large, the bend may lose definition and cause springback.
The Role of Punch Tip Radius in the Final Bend
The punch tip radius helps shape the inside of the bend. A small punch tip gives a sharper bend. A larger punch tip creates a smoother curve.
For clean results:
- Match the punch radius to the desired inside bend radius.
- For softer materials, smaller punch tips work better.
- For harder materials, use a larger tip to avoid cracking.
Air Bending vs. Bottoming vs. Coining: Effects on Radius
Different forming methods affect bend radius outcomes.
- Air Bending: The punch doesn’t press all the way into the die. The radius depends on the V-die size, not the punch. Offers flexibility but less precision.
- Bottoming: The punch nearly touches the die bottom. The bend radius is closer to the punch tip. More consistent than air bending.
- Coining: The punch fully presses the metal into the die. The radius is equal to the punch tip. Gives the most accurate, smallest bend radius.
Bend Radius in Design Practice
Good design starts with practical bend rules. Using the right bend radius makes parts easier to produce, stronger, and more consistent.
Common Mistakes in Designing with Incorrect Bend Radius
Design errors often come from using bend radii that are too small or not suited for the material. This leads to problems like:
- ひび割れ from over-tight bends
- Deformed edges or wrinkles
- Misaligned holes or features near the bend
- Increased スプリングバック that changes the final shape
Another common mistake is not accounting for bend relief or space for the material to stretch. This can cause tearing or bulging.
Tips for Designing Functional and Manufacturable Sheet Metal Parts
To avoid issues, follow these best practices:
- Set the bend radius to at least 1 × material thickness (or follow the material-specific chart).
- Keep holes, slots, and cutouts away from the bend line (at least 2 × thickness).
- Use consistent bend directions to reduce re-orientation during forming.
- Add bend reliefs at corners when bending flanges to prevent tearing.
- Consider grain direction in metals like aluminum or stainless steel. Bending across the grain reduces cracking.
Simple changes in design can make parts easier and cheaper to produce.
Industry Standards and Tolerances for Bend Radii
Standards help ensure quality and compatibility. Most shops follow values from:
- DIN 6935 または ISO 2768 for general tolerances
- ANSI Y14.5 for GD&T on drawings
- Material supplier data sheets for minimum radius guidelines
The typical tolerance for bend radii is around ±0.25 mm for precision parts. Larger parts or thicker materials may have looser tolerances. Always confirm with the fabricator before finalizing the drawing.
Common Bend Radius Mistakes and How to Fix Them
Small bending errors can lead to big problems in the final parts. Many issues happened because the bend radius wasn’t handled correctly. Here’s how to avoid the most common ones.
Ignoring Springback Compensation
Springback happens when the metal tries to return to its original shape after bending. If you don’t plan for it, the angle and radius can be off.
Fix: Adjust the bend angle in the design to account for the spring back. Use material data, or test bends to find the right compensation. Harder metals like stainless steel need more adjustment than softer ones like aluminum.
Overestimating Material Ductility
Some designs push materials too far, assuming they will bend without issues. However, not all metals can handle tight bends.
Fix: Check the bend radius chart before setting the bend. If the design calls for a tight corner, switch to a more ductile material or increase the radius. Never force a tight bend on hard or thick material.
Failure to Consider Tolerance Stack-Up in Multi-Bend Parts
When a part has many bends, small errors add up. This is called トレランス・スタックアップ. If not planned, the final part may not fit or align.
Fix: Add extra tolerance for each bend in multi-bend parts. Work closely with the fabricator to define clear tolerances. Avoid placing holes too close to bends where the metal can shift.
Mismatched Tool Selection
Using the wrong punch or die size leads to poor bend quality. It can cause large radii, tool marks, or even cracking.
Fix: Match the punch tip radius and die opening to the material and desired bend radius. Make sure tooling suits both the metal type and thickness. Double-check the setup before bending high-volume parts.
結論
Sheet metal bend radius guidelines help ensure accurate, strong, and clean bends. The right bend radius depends on the material, thickness, tooling, and bend method. Using proper values prevents cracking, distortion, and rework. Designers and engineers should always check bend radius charts, apply good design practices, and choose matching tools to get the best results.
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ケビン・リー
レーザー切断、曲げ加工、溶接、表面処理技術を専門とし、板金加工において10年以上の実務経験があります。シェンゲンのテクニカルディレクターとして、複雑な製造上の課題を解決し、各プロジェクトにおける革新と品質の向上に尽力しています。
