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Sheet metal is always bent into different shapes or structures for different applications. However, whether the sheet metal can be bent successfully is influenced by an important parameter that is called bend radius. In this article, we will explain what is bend radius and how to measure it for you.

What Is Bend Radius of Sheet Metal?

In engineering definition, bend radius always means inner bend radius. And inner bend radius of sheet metal means the vertical distance from the random point on the inner arc of the part to the center point of a circle. You can understand it easily based on the picture below:

From this picture, you can see a stainless steel is bent into a specific angle (90 degrees), and there is outer radius and inner radius. The inner bend radius should be set correctly so that the parts can be manufactured successfully. That is to say, in CAD and CAM system, setting the correct bending radius is essential for generating accurate planar unfolding diagrams. It is highly relative to precision of parts.

Why Is Bend Radius Important?

Bend radius shows its importance in design, manufacturing and machining because it has direct impact on the structure, appearance, strength, manufacturability, precision and cost of the parts. The extreme small inner bend radius would lead to cracking on parts. What’s more, bend radius is the key stress concentration point that determines the ultimate strength of the parts. Also, parts are manufactured to achieve perfect assembly. Accurate bend radius can guarantee the complex parts can be assembled tightly.

What Factors Can Affect Bend Radius?

Actually, materials themselves, manufacturing methods and part designs are key factors that can affect bend radius. Engineers should consider the above factors, otherwise, the parts can’t be manufactured.

Selected Materials

The mechanical properties of the materials is the core reason that affects inner bend radius. Different engineering materials have different ductility which determines their capability of preventing cracking.

For example, 304 stainless steel needs relatively large bending radius to prevent cracking due to high word hardening rate. On the contrary, aluminum alloy like 5052-H32 can bear smaller radii because its softer.

In practical case, in order to reduce weight, aluminum alloy is always used to make bracket with compact design by applying smaller bending radius. While carbon steel is usually bent by applying larger bend radius for avoiding cracking and high strength.

Selected Bending Methods

The selection of bending methods can directly affect the real bending radius of parts. The common bending methods are air bending and bottom bending.

Air bending: the inner bend radius is typically 1/8 to 1/6 of the opening width of the die’s V-shaped groove, it means that changing die can change bend radius, but mechanical properties of materials and springback should be considered.

Bottom bending: materials are pressed into die, the inner radius is typically equal to the tip radius of the die punch. The precision is higher but flexibility is lower. Bottom bending is usually used to make precision connector or shield cover to ensure consistent angle and radius.

Design of Sheet Metal Parts

In parts design, especially bending angle is relative to bend radius. When bending angle is smaller than 90 degrees, the materials have relatively smaller deformation, so smaller bend radius can be considered. However, if the material is bent with angle larger than 90 degrees, it undergoes plastic deformation, at this time, extreme bend radius is not suitable. The designer should test whether the selected bend radius cause over-stretched on the outer side according to the bending angle.

What Is Minimum Bend Radius?

The minimum bend radius means the min inner bend radius that materials can be bent safely without cracking or other damage. It is expressed as n x the materials thickness(t), such as 1t, 1.5t, 2t, etc.

Why it is called minimum? Because if the set bend radius < minimum bend radius, the materials would be destroyed with cracking. Therefore, in real bending, the set bend radius ≥ minimum bend radius can ensure the quality of parts.

Why Minimum Bend Radius Matters?

Setting minimum bend radius is to mitigate failure risks caused by stress overload. When a parts is subjected to loads, the bending area becomes a stress concentration zone, and if there is small cracking lead by over small bend radius during bending, the cracking would become lager quickly during subsequent dynamic vibrations or static loads.

For instance, the titanium alloy bracket in aerospace may cause potential risks because fatigue fracture is very easy to occur. Hence, obeying minimum bend radius is very necessary.

Is A Higher or Lower Bend Radius Better?

It depends on the sheet metal parts applications. Larger bend radius allows for more uniform stress distribution, reduces stress concentration, and improves fatigue life of parts. That is why lager bend radius is the optimal selection for structure parts that bear loading.

Smaller bend radius allows compact design of parts, improving space utilization.

For example, in the internals metal frames of consumer electronics, a compact L-shaped or U-shaped structure is often achieved by using a smaller bending radius to provide space for the battery.

What Is the Standard Bend Radius of Sheet Metal?

In manufacturing, some standard bending radius are used widely for reducing costs and standardized production. Usually, the bend radius is highly relative to thickness of materials. For instance, 1mm thickness plate use 1mm bend radius.

Standard Bend Radius of Common Metal

Different metals have different standard bend radius due to their properties and structure. Here we will introduce standard bend radius of some common engineering materials.

Stainless Steel Sheet Metal

Stainless steel, especially 304, has good ductility but undergoes rapid work hardening. The recommended inner bending radius of 304 is usually larger. As for 304 sheet metal plate, the standard inner bend radius is 1.5t-2t. Larger bend radius can avoid cracking during bending and reduce stress concentration.

Aluminum Sheet Metal

The bend radius of aluminum alloys varies by grades. Soft pure aluminum has great ductility, its standard bend radius can be small up to 0.8t or even 1t. However, high-strength 7075 aluminum is highly brittle, the standard bend radius may be 2.5t-3t or even larger.

Titanium Sheet Metal

Titanium sheet metal is more difficult to bend compared with aluminum and stainless steel sheet metal. The yield strength to elastic modulus ratio of titanium is high, which means the springback is large. The recommended bend radius of commonly-used TC4 titanium alloy is about 2.5t to 3t. Titanium parts is lightweight and heat-resistant, the bend radius should be larger because the strength of parts would change under high temperature.

Copper Sheet Metal

Pure copper like C110 has great ductility and is very easy to bend. Its standard bend radius can be very small, ever smaller than 0.5t. Different from pure copper, brass like C260 is harder and its standard bend radius is about 1t. The smaller bend radius make copper be an ideal material for making bus bar, achieving compact design.

Does Plastic Have A Bending Radius?

Yes, as a kind of engineering material, plastic has bend radius when they are bent. When bending plastic, you should also consider how to set reasonable bend radius to avoid cracking.

How to Measure Bend Radius

There are various methods for measuring minimum bend radius. It depends on where you want an approximate value or high precision. Now let us explore these methods.

Use Radius Gauge

This method is simple and quick, just use a radius gauge set, and match the gauge blade to the inside curve of the bend.

Use Calipers

This is common manual calculation method. It can’t support direct measurement. The inside bend radius need to be measured based on the following formula:

R_i​=R_o​−t

This formula means:

• Ro: the outside radius
• T: the thickness of sheet metal
• Ri: the inside radius

Use the Chord and Height Method

This method is more accurate. If you can measure the arc, you can calculate the inner bend radius based on this formula:

R=C²/8H​+H/2

This formula means:

• C: chord length
• H: arc height

Use CMM

CMM means coordinate measuring machine. This measurement method is usually used to calculate the bend radius of precision parts like medical components.

الخاتمة

Bend radius is a key parameter during bending sheet metals. Understanding its meaning and learning how to measure bend radius is very vital for bending parts with high precision and high quality. Only define reasonable bend radius, the sheet metal parts can be make successfully.

Tuofa bending service can provide professional recommendations for your sheet metal bending project. If you have any question about material selection or bending techniques, welcome to contact us!

الأسئلة الشائعة

Do I need to mark the bending radius on my drawing?

Yes. If the bend radius isn’t marked, the manufacturers may apply their standard bend radius to machine. Marking defined bend radius can influence the final functions and appearance of sheet metal parts.

Is the minimum bending radius a fixed material property?

Not always. It is influenced by many reasons such as the grades of materials, the thickness of materials, the bending angles, heat treatments, etc.

Why is the actual radius of the sheet metal part lager than the designed?

It is always caused by springback. All metal will have a certain degree of elastic recovery after bending. The common solution is to apply die compensation design or adopt the bottoming process to force the material into greater plastic deformation, thereby reducing springback.