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A complete guide for mastering tube bending.
We at Herber produce and deliver tube bending machines of premium quality. To ensure that you get the maximum performance and potential out of your machine, it is important that the actual tube bending process is carried out perfectly. Even though we are always here to support you when needed, it is, of course, beneficial if you can independently handle common issues that may occur during the bending process. That is the purpose of this guide.
Although this guide is customized to fit Herber machines, it can in many cases be applicable to other types of tube bending equipment as well.
Please note that this guide is general and should not be considered a complete solution to every possible issue in tube bending. If you are using a Herber machine and have any questions or uncertainties, please contact our Service & Support team for the correct guidance.
The tube bending process begins with positioning a straight tube into the bending machine. The tube is inserted until it reaches the tube stop, which ensures consistent length and alignment for each bend. Once positioned, the tube is firmly clamped between the clamp die and the bend die to prevent any sliding or movement during bending. This is one of the most crucial parts of getting a good bending result without variation.
The bending operation starts as the machine clamps the tube and draws the tube around the bending die and its contour to achieve the desired bend radius and angle. During this stage, the pressure die applies force on the outer side of the tube, guiding the material smoothly and maintaining pressure to ensure that the bends are being formed constantly. Incase a pressure die assist are used, the stretch of the material can also be guided to maintaining even wall thickness throughout the bend.
Inside the tube, a mandrel may be used to support the internal structure, prevent collapse or wrinkling, while a wiper die positioned near the tangent point helps minimize surface imperfections on the inner bend. Together, these components ensure a clean, accurate bend with minimal deformation.
Once the set bend angle is reached, the machine stops, and the dies release the tube. The collet may then reposition or rotate the tube if additional bends are required. After all bends are completed, the finished tube is removed and inspected.
Your machine is equipped with several tools, each with a specific function in the tube bending process. If any of these tools are incorrectly adjusted, it can affect the bending result and the quality of the tube. Understanding how tube bending works therefore starts with knowing the tools and their individual roles.
1. Bend Die
The bend die determines the bend radius and serves as the main form around which the tube is shaped. To achieve a simple setup and optimal results without requiring special mandrels or wiper dies, the following general guidelines apply to the relationship between the bend radius and the tube diameter:
2. Clamp Die
The clamp die holds the tube firmly against the bend die during bending. In many modern designs, the clamp die is integrated with the bend die. Some manufacturers use interchangeable clamping sections to accommodate different tube lengths and shapes.
General guidelines:
3. Pressure die
The pressure die supports the tube from the outer side during bending and ensures smooth material flow. Several designs exist:
4. Mandrel
The mandrel supports the inside of the tube during bending and helps maintain roundness, especially in thin-walled tubes.
Different designs are used depending on the application:
In general, the mandrel diameter should be about 0.5 mm smaller than the tube’s inner diameter for tubes up to 60 mm, and about 1 mm smaller for larger dimensions.
5. Wiper Die
The wiper die prevents wrinkles on the inside of the bend. Commonly used when the bend radius is smaller than 1.5 × D. It’s working length is often around 2 × D.
6. Collet
The collet holds the tube during feeding, rotation, and positioning between bends. It’s gripping accuracy is essential for repeatability and bending precision.
General recommendations:
7. Tube Stop
The tube stop ensures that the tube is inserted to the correct length before clamping, providing consistent positioning. The design of the tube stop depends on the collet system. If the collet moves past the mandrel, the rear part of the stop should be beveled to prevent the mandrel from catching and bending the mandrel rod.
Before starting the tube bending process, it’s important to make sure the machine and all tools are correctly installed and aligned. The following steps describe a general setup procedure that applies to most Herber tube bending systems.
Please note that these are general guidelines. Always follow specific instructions for your machine model and tool type.
1. Safety and preparation
2. Mounting the Bend Die and Clamp Die
Tip: The clamp die length should be around 2 × D to ensure proper grip and prevent slippage.)
3. Setting up the Pressure Die
4. Mounting and Adjusting the Mandrel
Start with the mandrel slightly retracted and move it forward gradually during test bends to find the optimal position.
5. Installing the Wiper Die
Wiper dies are typically used when the bend radius is smaller than 1.5 × D.
6. Collet and Tube Stop Setup
Different collet designs are available (standard, nut-type, or integrated), and this requires slightly different mounting methods.
7. Final Adjustments
Even with the correct setup, various issues can occur during tube bending.
Below are some of the most common problems, their likely causes, and general recommendations for how to correct them.
Please note that these are general guidelines. Actual adjustments may vary depending on tube material, tooling type, and machine configuration.
Tube bending is a craft that demands precision, knowledge, and the right tools. At Herber, this is what we do every day. We combine technical expertise with real-world experience to help you achieve the perfect bend. Whether you use a Herber machine or another brand, our team is always ready to support you.