How Sheet Metal Bending Machine Works

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Introduction

Sheet metal bending machines are the backbone of modern metalworking industries, enabling the transformation of flat metal sheets into complex shapes and structures. From automotive parts to household appliances, the versatility of these machines is unmatched. But how exactly do they work their magic? Let's delve into the inner workings of sheet metal bending machines and uncover the mechanics behind their precision and efficiency.

Sheet metal bending is the manufacturing process by which most enclosures, electrical boxes, brackets and components are formed through the use of a machine known as a CNC press brake.  (Panel Bending machines can also be used, although their operation is outside the scope of this feature.)

Sheet metal is bent when it is forced between two tools by the press brake: an upper tool (known as a punch) and a bottom tool (known as a die).  The press brake controls the movement of either the punch or the die and provides the press force using hydraulic rams or electrical servo motors.  The bend angle is predominantly determined by the depth of penetration of the punch within the die.

Press brake 

Capabilities

The maximum force provided by the press brake determines the maximum bend length for a combination of thickness of sheet metal, bend radius and bend angle. The force required to bend sheet metal increases with bend length, external bend angle and sheet metal thickness, and it decreases with increasing bend radius.  Hydram&#;s press brakes have varying capabilities and maximum bend length of 4 metres and a maximum force of 250 tonnes are available. The table below illustrates some typical examples for 90 degree bends:

Sheet Metal Part Design And Complexity

Components vary in complexity, from parts with a single bend, through to parts with multiple bends with multiple flange lengths. Modern pressbrakes are equipped with adjustable backstops, driven by servo motors, against which the components are offered by hand or robotic manipulator. The closer the backstop to the tooling, the shorter the resulting flange is and vice versa.

On complex parts, the backstops adjust after each bend to the corresponding distance required for the next bend. The movement of the backstops and the press brake tooling is synchronised by a CNC controller.  CNC programs can be generated online on the machine user interface or by an offline programming (or CADCAM) software package.

Press Brake Tooling

A variety of press brake tools is available to suit different sheet metal bending tasks. The characteristics of the upper and lower tools are varied according to the requirements of the sheet metal component.  A number of bending examples are illustrated below:

Thicker metal is generally processed with a larger bending radius, and this can be achieved by increasing the top tool radius and the distance across the die opening &#; or V-width.

&#;Tools For Sheet Metal Bending Thick Metals

Components that require a sharp bend angle require &#;over bending&#; tooling.  Both the top and bottom tools in this case have a more acute angle.

&#;Tools For Sheet Metal Over Bending Acute Angles

Components that have more than one bend often require special top tooling to provide clearance for existing flanges.  Without this clearance the component would collide with the tool before the subsequent bend operation was complete.  This type of tooling is often referred to as gooseneck.

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&#;Tools For Sheet Metal Bending Tight Clearance

To provide clearance in extreme cases, the top tool can be suspended from the press brake beam using modified clamps. These extended clamps provide far greater clearance for large flanges, so long as the metal bending machine has sufficient stroke length to accommodate the overall tool height.

Folded Sheet Metal Blank Development

When designing sheet metal components with folds or bends it is necessary to create a flat pattern or blank development of the part.  This blank is then laser cut or CNC punched before arriving at the press brake for folding.  In creating the blank, it is important that the design takes into account the bend radius formed by the press brake tooling.  The bend radius has the effect of decreasing the developed blank size. The larger the radius, the smaller the blank, as shown in the example below:

The bend radius varies with the material thickness and the tooling used for bending the material.  It is therefore essential that the designer is aware what tooling will be used to bend the material and have a good appreciation what affect this has on the bend radius.  Likewise, to ensure accuracy of the bent component, the metal bending machine operator needs to know what radius the part has been designed with so that the correct tooling choice is made.

Bending Process

1. Setup: The operator selects the appropriate tooling and enters bending parameters into the CNC control system.

2. Material Preparation: The metal sheet is loaded onto the machine and aligned with the back gauge.

3. Bending: The hydraulic cylinders apply force to the punch, pressing it into the die and bending the metal sheet to the desired angle.

4. Springback Compensation: Some materials exhibit springback, meaning they return to their original shape after bending. Advanced CNC systems can compensate for springback to achieve precise bend angles.

5. Unloading: Once the bending process is complete, the finished part is removed from the machine for further processing or assembly.

&#; Video

Most manufacturing companies need to do sheet metal bending at some stage of their production process. Sheet metal bending refers to bending or cutting sheet metal into specific shapes or joining it to other metal sheets to create metal parts.

In this article, our machinery maintenance and repair experts present the most common techniques for bending sheet metal in an industrial setting. We&#;ll cover their advantages and disadvantages, and the tools required for each technique.

What equipment is needed to bend sheet metal?

Sheet metal bending requires the use of specialized tools if you want precise and high-quality end results. Shears, manual bending machines and hydraulic bending machines are the basic tools for bending sheet metal.

Shears

Shears cut sheet metal into pieces. They can be manual or electric and are often used to cut specific geometric shapes in a sheet of metal before bending it.

Manual folding machines

A manual bending (or folding) machine is the standard tool for bending sheet metal. It is often used for simple bends and is available in different sizes depending on the thickness of the sheet. It is also relatively easy to operate and transport, making it a popular choice for small machining companies or workshops.

Hydraulic folding or bending machines

A hydraulic bending machine is a more advanced sheet metal bending tool. This machine contains a hydraulic system that can bend thicker and larger sheets. It is also equipped with a digital control system that allows different types of bends to be programmed and performed automatically. It is ideal for large manufacturing companies that need to produce large quantities of sheet metal parts.

What are the different techniques for bending sheet metal?  

Multiple tools mean multiple metal bending techniques. To choose the method that best suits your business, it is necessary to understand the differences between the possible approaches.

Manual folding

If you do not have a bending machine, you might be able to bend metal sheets by hand. First, you need to calculate the bending tolerance of the sheet according to the type of metal you are using. Next, indicate the bend lines with a marker and cut your sheet to the appropriate dimensions. Place the plate firmly within a vise grip using a wooden block as a guide for the form or angle you will be bending the sheet into.

Next, use a wooden hammer to gently pound the sheet against the wooden block until the metal has changed shape. This method is only recommended for sheets up to 2 mm thick, as thicker sheets may break.

Although manual bending is a simple and quick method, it does not guarantee the level of quality and accuracy that a bending machine can offer. For thicker sheets or more complex bends, it is recommended to use a bending machine to avoid breaking the sheet.

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