Tube bend-ratio and mandrel calculator
Enter diameter, wall thickness and radius to check bend ratios, flattening risk and mandrel need. Machines below are optional references.
No technical details required. Leave a phone number and our team will help select the machine and configuration.
Ask NKAM to call me Zalo → Call NKAM →Will this tube flatten or wrinkle when bent?
The answer lies in two ratios: bend radius divided by tube diameter (R/D), and diameter divided by wall thickness (D/t). The smaller the R/D and the larger the D/t, the more the tube tends to flatten on the outside and wrinkle on the inside. Enter the four values below to see the bend ratios and whether your part needs a mandrel.
Tube cut lengthExpand to enter values and calculate ▾479.07 mm
Tube-wall thinning estimateExpand to enter values and calculate ▾t′ ≈ 1.5 mm · 25%Wall thinning exceeds 20%; confirm whether a mandrel or larger bend radius is needed.
Wall thinning exceeds 20%; confirm whether a mandrel or larger bend radius is needed.
Estimate only; confirm with an actual trial.Talk to NKAM now →Tube weightExpand to enter values and calculate ▾10.654 kg
When is a mandrel mandatory?
A mandrel supports the tube wall from inside during bending. Without one, thin-wall tube at a tight radius will flatten.
Practical rules:
- Large R/D, thick wall → usually bends without a mandrel
- Small R/D or thin wall → a mandrel is needed, and possibly a wiper die as well
- Stainless is harder than carbon steel at the same size: more springback, more prone to wrinkling
- Square and rectangular tube deforms more readily than round tube at the same ratios
A mandrel is not an optional accessory. If your part needs one, it is the condition for the part existing at all — not an upgrade.
NC or CNC?
NC bends one angle at one radius with good repeatability. Enough for simple parts, lower cost, simpler to operate.
CNC controls feeding, tube rotation and bending together. Needed when a part has multiple bends across multiple planes, or when you change programs frequently.
Designations such as 2A1S / 3A1S / 4A2S describe the controlled axes and the number of die stacks. More stacks means several radii on the same part without stopping to change tooling.
How far can this result be trusted?
The tool filters by the nominal capability of the machine. It does not yet account for specific tooling — the same machine bends the part with the right dies and cannot without them.
Send the part drawing. For tube bending a drawing is worth more than any description, and we will tell you exactly which machine, how many axes and which tooling set — including when the answer is that your part requires a mandrel.
NKAM stocked machines to consider after calculating
| Model | Series | Capacity / power |
|---|---|---|
| DW38NC | NC | 38 |
| DW50NC | NC | 50 |
| DW75NC | NC | 75 |
| DW38CNC-2A1S | Đa trục | 38 |
| DW38CNC-3A1S | Đa trục | 18 |
| DW38CNC-4A2S | Đa trục | 34 |
| DW50CNC4A2S | Đa trục | 50 |
| CNC38-6A-2S | Đa trục | 38 |