How to Bend Sheet Metal: A Step-by-Step Guide

As a fundamental manufacturing process, sheet metal bending can produce high-strength, high-precision parts. However, machining precise angular shapes on metal is not easy. You need to make careful designs, adopt appropriate processes, and have an understanding of material properties. This article will provide you with practical and comprehensive guidance to help you gain a more specific understanding of the entire bending process.

Before You Bend: Define the Required Result

Before starting metal bending, you must first clarify the requirements for production, including material grade, sheet metal thickness, finished angles, inner radii, flange dimensions, bending direction, and so on. If this information is missing, a variety of completely different sheet metal parts will likely be manufactured.

Below, I will give you a bending requirements checklist.

NOTE: The above parameters are only used to illustrate what information a complete requirement should contain. As for the specific information, it still depends on your sheet metal fabrication project.

Choose the Right Tools and Bending Method

Once you have determined your specific parts requirements, you can select the appropriate machining methods and tools based on the project.

How to Bend Sheet Metal in 7 Steps?

Alright, once you have completed all the preparatory work, you can start bending the sheet metal. We divide all processes into 7 steps, so that you can clearly understand what needs to be done in each step

Step 1: Review Drawings and Plan Bending Sequence

First, you need to review the drawings of the bent parts. If the part contains features such as holes or slots, it is also necessary to check whether these features will be affected by the bending process.

In addition, if your part is an L-shaped bracket with only one bend, this step is relatively simple. However, if your parts are U-shaped parts, Z-shaped parts or custom enclosures, then planning the bending sequence is particularly important. This is because it will directly determine whether the part can be completed.

As for complex parts, it’s best to simulate the manufacturing process in CAD software or a bending programming system first.

Step 2 : Calculate the Flat Pattern

During the bending process, the material on the outer side of the bent area is stretched, while the material on the inner side is compressed. Therefore, we also need to calculate the bending allowance. Here is a formula:

$$BA = \left( \frac{\pi}{180} \right) \times A \times (R + K \times T)$$

Where:

• BA: Bend allowance,
• A: Bend angle
• R: inner bend radius
• K: K-factor
• T: Material thickness

It should be noted that the bending angle in the formula is not necessarily equal to the finished inner angle marked on your drawings. Before performing calculations, you must confirm the angle definitions used in the drawings and CAD software.

K factor is a design parameter. It is used to estimate the elongation of sheet metal parts during the bending process.. It describes the position of the neutral layer in the thickness direction of the plate and is mainly used for flat pattern dimension calculations. A better understanding of the role of K-factor will help you more accurately predict dimensional changes after bending.

Typical Starting K-Factors for Air Bending

Step 3 : Cutting, Deburring and Preparing Blanks

Once you have confirmed the unfolded dimensions, you can process the flat blank through laser cutting, stamping, CNC cutting and other processes. After the blanking is completed, do not start bending immediately, but check the dimensions, hole positions, and cutting edges of the blank material.

If there are large burrs or micro-cracks near the bending line, it will affect the quality of the parts. Therefore, before bending, you still need to complete the following preparations:

• Remove burrs and sharp edges
• Check for cuts or cracks near the bend line
• Remove oil, metal shavings, and foreign objects from the die contact surfaces
• Make sure there is enough distance between holes, slots and bend lines
• Check if bend relief is needed between adjacent flanges
• Confirm the relationship between the material grain direction and the bend line

When bending by hand, you also need to mark the bend lines accurately. You can use a steel ruler or a fine-tip marker to mark the position, but we do not recommend cutting deep grooves along the load-bearing bend lines.

CNC bending usually relies on back gauges for positioning. The positioning reference edge of the part must be straight and burr-free.

Step 4 : Set Up Dies, Fixtures or Bending Equipment

When you use vises or simple fixtures, the clamping edge must be sufficiently straight and rigid, and must also be able to cover the entire bending length.

It is important to note that the clamping blocks on both sides should remain parallel, and the edges should not be too sharp, otherwise scratches may be left on the inner side of the sheet material. For longboards, sufficient support is essential. This is to prevent the workpiece from sagging due to its own weight or sliding under force.

If you are using a CNC press brake, then you need to select appropriate upper and lower dies based on the material, plate thickness, bending length, target angle, and inner radius. Additionally, you need to confirm the allowable line load of the dies and the tooling installation status.

After the mold installation is completed, you still need to check whether the upper and lower molds are aligned, whether the mold surface is clean, and whether the mold is properly locked.

Step 5 : Position and Support The Workpiece

This step is crucial. Because whether the workpiece can be accurately positioned directly determines the bending line position and flange dimensions.

When placing workpieces, you need to confirm that both left and right positioning points are in contact, and check whether the workpiece is suspended due to burrs, warping, or foreign objects on the surface.

Step 6 : Trial Bending and Compensate For Springback

Trial bending is a critical step to ensure that angles and flange dimensions are stable, especially when processing new materials, new plate thicknesses, or new mold combinations.

After completing the trial bending, it is still necessary to measure the actual angle of the processed workpiece, because the material will rebound to a certain extent after processing.

If the angle is too large or too small, you need to pay attention to correcting the slide stroke, target angle or corresponding compensation parameters. If the flange size is incorrect, you need to check the back gauge position and the developed dimensions.

Additionally, you should not specify a uniform over-bending angle for all materials. Each material and thickness has its specific bending radius. If you’re still not very clear, you can use our bending calculator below to perform calculations:

Step 7 : Bend and Inspect Parts

After the bending test results are qualified, you can use the confirmed parameters for sheet metal fabrication.

If using manual tools, you should pay attention to applying force evenly and slowly along the entire bending line. If using a CNC press brake, you should also ensure that the workpiece maintains stable contact with the backgauge and complete each bending operation in the specified sequence.

At the same time, you must conduct strict inspections of the sheet metal parts to ensure that all specifications meet the established requirements.

How to Bend Sheet Metal Without a Brake?

If you don’t have a press brake, you can still use bench pliers, angle steel, wooden clamps, C-shaped clamps or manual edge bending pliers for simple bending.

Method 1: Bench Vise and Angle Iron

You can clamp the sheet metal between two straight angle irons, aligning the bend line with the edges of the angle irons. Then, you can apply even pressure to the sheet metal using a long wooden board or a soft-faced hammer.

Many people use this method to make small brackets, cover plates, and simple right-angle bent parts. The advantage of this method is that the tools are readily available.

Method 2: Wooden Blocks and Clamps

For thin sheets that are wider than ordinary vises, you can clamp the sheet metal between the edge of the workbench and a flat wooden board or angle iron, and then gradually fold up the overhanging part.

It should be noted that this method is only suitable for longer but structurally simple bending parts.

Method 3: Hand Seamer

Hand seamer are suitable for making small flanges, thin-sheet edges, HVAC seams, and similar applications. During operation, you can form the material in sections along the bend line.

Limits of Hand Bending

Manual bending is only suitable for small-sized and structurally simple parts, but it cannot provide the same precision and repeatability as bending machines. We do not recommend manual bending in the following situations:

• Material is too thick
• Bend lines are too long
• Tight tolerances
• Multiple bends
• Material is prone to cracking
• Finished products require assembly consistency
• Mass-produced parts

How to Bend Different Sheet Metal Materials

As we mentioned above, different materials cannot use exactly the same bending coefficient. Therefore, before you start bending, you should confirm the material grade, hardness, actual plate thickness, grain direction, and so on.

Low Carbon Steel

Low carbon steel has good ductility, making it a common bending material for industrial components. However, although the forming effect of low carbon steel is quite good, you still need to pay attention to removing burrs from the bending area.

At the same time, you should check for scale on the surface of hot-rolled sheets, as it can affect the positioning of the rear stop and leave contaminants on the die.

Stainless Steel

Stainless steel requires greater mechanical pressure for bending and also has significant springback issues. In addition, austenitic stainless steel undergoes work hardening during forming. If this material is repeatedly bent, it will increase the risk of cracking and dimensional loss of control.

Therefore, when you need to manufacture stainless steel bending parts, you need to pay attention to using inner radii that comply with the specific grade of stainless steel. At the same time, you also need to compensate for springback according to the actual trial bending situation.

Aluminum Alloy

Aluminum alloy can be said to be a relatively common sheet metal material, but each of its grades has different bending capabilities. When you need to use this material for bending, you need to specify grades such as 5052-H32, 6061-T6.

And when conditions permit, you can adjust the layout to ensure that the bend lines avoid unfavorable grain directions as much as possible. For materials prone to cracking, you should increase the inside radius.

Galvanized Sheet

When it comes to galvanized sheet metal, you must not only consider whether the base material can be bent, but also assess whether the coating can withstand the tensile and compressive stresses in the bent areas.

Before machining, you should keep the die clean. Meanwhile, you should select an appropriate bending method based on the specific appearance requirements.

Common Sheet Metal Bending Problems and Fixes

Regarding the various problems you may encounter during sheet metal bending, I have also specially prepared a troubleshooting table for you here, so that you can quickly solve the problems you encounter through it.

How to Prepare CAD Files and Drawings

Clear and complete CAD files can help customers and manufacturers reduce quotation communication issues. For bending parts, manufacturers not only need to know the flat pattern profile, but also need to confirm the finished shape, material, plate thickness, bending direction, angle and critical tolerances.

Typically, customers need to submit 3D models in formed state, 2D unfolded files, and PDF engineering drawings. The specific supported formats should be based on the processing factory’s requirements.

3D Final Models

The 3D model should show the final state of the part after bending.

Common file formats include:

• STEP or STP
• IGES (use only if supported by the machining shop)
• Native files from SolidWorks, Inventor, etc.

2D Unfolded File

DXF or DWG files are typically used for laser cutting and stamping. Two-dimensional files should be output at a 1:1 scale, with clear distinction between cutting lines and bending lines.

Engineering Drawings

CAD models are used to represent geometric shapes, while engineering drawings are used to define manufacturing and acceptance requirements.PDF drawings must include at least the following:

• Material grade or alloy designation
• Temper, hardness, or heat treatment condition
• Nominal plate thickness
• Surface treatment
• Finished bend angle
• Inner bend radius
• Critical flange dimensions
• Angular and linear tolerances
• Hole position and assembly datum
• Appearance surface or no indentation zone
• Grain direction requirements
• Quantity

Conclusion

That’s all the content about how to bend sheet metal. We believe that after reading this, you will be able to understand the entire process of sheet metal processing.

Of course, as an established manufacturer, DSR can also provide you with excellent metal bending services. Whether it’s prototype processing or mass manufacturing, we can complete parts manufacturing tasks for you very well. If you have any needs, please contact us immediately!

FAQ

Q1: How to curve sheet metal by hand at home? 

A: First, you need to find a sturdy cylinder with a radius close to that of the target arc. You can secure it firmly to a stable workbench using a C-clamp. Then, you also need to lay the metal sheet flat on the cylinder. You hold one end with one hand or a clamp, and apply downward pressure evenly along the curvature of the cylinder with the other hand.

For thicker plates or those that are difficult to bend directly, you will also need to use a rubber mallet or plastic soft-faced hammer. 

Q2: How to make a 90 degree bend in sheet metal?

 A: First, you need to mark a clear bend line on the sheet metal. Next, use two angle irons with sharp, straight edges to clamp the sheet metal in place, ensuring the bend line is precisely aligned with the edge of the lower angle iron. Next, place a flat, long strip of hardwood or another angle iron flush against the surface of the suspended sheet metal. Next, you can find a flat, long hardwood strip or another angle steel rod to press tightly against the surface of the suspended board. You hold both ends with both hands and apply even force downward, or use a rubber mallet to tap evenly along the bend line.

Q3: What is the easiest way to bend sheet metal?

 A: Bending method using a table-mounted vise in conjunction with angle iron clamps.

Q4: Should you heat metal to bend it?

A: It depends on the type and thickness of the metal. For the vast majority of common thin sheet metal parts, the industry standard practice is to use a cold bending process.

Q5: What tool bends sheet metal?

 A: Press brake, pan and box brake, slip roller and hand seamer.

Q6: How thick of sheet metal can you bend by hand?

A: For mild steel, the thickness is approximately 1.5 millimeters. For aluminum sheet, the thickness is approximately 3 millimeters.

Q7: What are the three types of bending?

A: Air bending, bottoming and coining.

Q8: What are the limitations of metal bending?

A: Minimum bending radius limitations, springback effects, hole position and edge deformation and material grain direction.

Q9: Is it better to bend forward or backward?

A: Not at all. This is primarily determined by the rolling grain of the material and the orientation of the burrs along the edges.

Q10: How to bend sheet metal in solidworks?

 A: You can use the sheet metal toolbar to ensure the accuracy of the physical deformation and the flat pattern.