PIPE AND TUBE BENDING PROCESSES
Key Considerations in Pipe And Tube Bending Processes
Pipe and tube forming is widely used across many industries. These include aerospace, automotive, and home appliances. This process allows pipes to be shaped or bent for use in various applications. However, certain common issues are often encountered during pipe and tube bending. These include pipe and tube deformation, ovalization, and surface cracking.
Such issues typically stem from factors like inadequate die lubrication or incorrect material selection. They can also result from improper wall thickness or low bending ratios. Therefore, it is essential to consider certain critical factors during pipe and tube bending processes. Proper material selection and the use of appropriate dies are crucial. Accurate bending ratios must also be determined to minimize these challenges.
Fundamental Principles, Mechanical Effects, and Challenges
Pipe and tube bending involves altering the direction of materials. This is done either hot or cold to achive the desired orientation. During this process, various deformations occur at the bending points. The inner portions of the bend compress, whereas the outer portions stretch and thin out. Meanwhile, the middle sections generally remain relatively unchanged.
The stresses and forces generated during bending cause molecular dislocations on the pipe’s inner surface. Tensile stresses also develop on the outer surface. This process gives rise to mechanical effects such as tension, elongation, compression, and contraction.
Factors Affecting Pipe and Tube Bending
Material Selection
Material selection in pipe and tube bending should align with the application area. It must also meet customer requirements and suit the material’s intended function. Various materials, such as steel, stainless steel, aluminum, and copper, can be used. For instance, copper and copper-plated steel (bundy) tubes are commonly utilized in the shock loops and discharge mufflers of compressor motors manufactured in our facility. At this stage, it is crucial to consider if the material is welded or seamless. Factors like annealing status and hardness must also be carefully evaluated.
During material selection, diameter and wall thickness are crucial factors. Orders for non-standard pipes are typically not accepted for quantities below 3,000 meters. For such special orders, dependency on a specific supplier can pose challenges. Evaluating standard pipe and tube dimensions during the design phase offers economic advantages. This approach simplifies procurement and positively impacts production timelines.
Forming Methods
To minimize the problems encountered during bending processes, the forming method must be carefully chosen. Using the correct method and equipment will enhance the efficiency and quality of bending operations.
- Bending by Hand And Apparatus
Thin-walled tubes made from soft materials like aluminum, copper, or brass can be bent manually. This process can be done either cold or hot when high precision is not required. Molds are prepared in accordance with the desired shape of the parts to be bent. The bending process is carried out by securing the mold to a vice. Depending on the requirements, the bent sections of the tube walls can be annealed. This can be done at specific points during the process or bent without annealing.
- Manual Machine Bending
The forming process begins with positioning stops at the starting point of the bend. After each bend, the tube is fixed to the next stop. The bending angles are adjusted using switches. By measuring the parts produced from these settings, any deviations can be addressed by readjusting the switches and stops. This ensures that the bending process achieves the desired angles and radius accurately.
- Bending on CNC Machines
CNC machines perform tube bending operations automatically and in series, providing high precision and repeatability.
- Bending Pipes with Dies
In die-based pipe and tube bending, performance may differ from roller bending. The same level of efficiency might not always be achieved. However, it is necessary for certain operations. The bending must be done with the radius specified by the die. A different radius cannot be selected.
- Bending Pipes with Advanced Technological Machines (Laser Bending)
Advanced technological bending machines have the capability to perform bends with multiple radii, rolling systems, and laser cutting operations. These machines operate with a robotic mechanism. It automatically places the pipe and tube into the machine and handles the process.
Wall Thickness of Pipe and Tube
The wall thickness of pipes is critical for their durability. It also directly impacts the pipe’s strength. Wall thickness determines the pipe’s capacity to withstand internal pressure. It also reduces the risk of deformation during the bending process. Thick-walled pipes can withstand higher pressures and show less deformation. Pipes with thin walls are lighter. They are suitable for use in low-pressure systems. However, these pipes require more precise handling during bending. Otherwise, there is a risk of breaking the pipes.
Bending Radius
The bending radius refers to the radius at which the pipe and tube is bent. A smaller bending radius means a sharper bend. Difficulties may arise depending on the material properties of the pipe or tube. The bending method also plays a significant role. Determining the correct radius during the bending process is crucial. It helps maintain the structural integrity of the pipe.
A smaller bending radius makes pipe bending more difficult. Practically, we take the bending radius as 1.5 times the pipe diameter (1.5D). For example, if the pipe diameter is 12 mm, we would bend it at a minimum radius of 12 x 1.5 = 18 mm. This ratio varies based on the precision of the machines. It also depends on the pipe wall thickness and material type. Nowadays, pipes can even be bent with a 1D radius.
Bending Angle
When the bending angle of the pipe and tube is very small, they may appear unbent. This is due to the material’s flexibility and springback. This situation arises from the material’s springback characteristic. As the bending angle increases, the importance of the back support roller and the opposite back support roller becomes more significant. Due to the springback characteristic, the pipe may need to be bent 1 to 2 degrees more. This compensates for the expected springback to achieve the desired angle.
Jaw Allowance Outsıde The Bendıng Area
The straight sections of the pipe and tube are important for jaw allowance. They ensure proper placement and support during the shaping process. A small jaw allowance increases the risk of clamping marks on the pipe and tube. For the bending process, space must be left fot the clamping jaws. This allows them to hold and rotate the pipe outside the bending point.
Pipe and Tube Length
The length calculation of pipes that undergo bending can be done theoretically. Today, thanks to drawing programs, calculating these lengths has become possible and much easier. Especially for multi-bend parts, these drawing programs are very practical for determining lengths. This approach allows for quick determination of the preliminary cost. It also helps estimate how much of the pipe and tube will be cut.
However, even if the lengths of the pipes to be bent are calculated using programs, deviations can occur in these values. These deviations can stem from various factors such as material properties, tolerance of the pipe and tube diameter, precision of the roller group, machine settings, burrs, lubrication deficiencies, human errors, formation of the pipe and tube, gaps and tightness, and the condition of the equipment surfaces.
Materıals Used For Bendıng Dıes
Suitable materials should be selected for the dies of the pipes to be bent. High-strength products, special alloys, and manufacturing steels can be used. When using these materials, it is important to pay attention to parts that will undergo heat treatment. Due to heat treatment, some parts may deform. Therefore, normalization should be done before the heat treatment process.
Additionally, grinding allowance or plunge erosion allowance can be left to reduce deformations. Parts that only require surface hardening can also be preferred. Care should be taken to prevent the parts from becoming brittle during the hardening process. Therefore, the knowledge and experience of the heat treatment specialists should be considered.
Die Surface
The surface and precision of the die for the pipes to be bent directly affect its functionality and optical use. Additionally, the surface of the roller group varies depending on the part to be bent. The roller group should be processed and heat-treated after normalization, if possible. Surface roughness is sometimes necessary in pipe and tube bending. Without it, the pipe may slip, causing dimensional deviations. It is important to maintain a balance between surface roughness and applied pressure.
Dıe Precısıon
Precise processing of the roller and jaw groups ensures minimal deformation during pipe bending. This helps maintain the desired shape. This allows for bending with the desired dimensions and accuracy. Misalignment, jaw tightness, or looseness can affect bending dimensions. It can also cause the roller group to wear out more quickly. This condition also increases the formation of marks on the pipe and tube.
Bending Force and Machine Capacity
The bendability of the pipe and tube depends on the machine’s capacity. Furthermore, the strength of the machine’s mechanical parts should be suitable for this capacity. The size and shape of the parts we wish to bend must also be compatible with the machine.
The Effect of Mandrel
When bending is done without a mandrel, deformation and necking can occur in the pipes. Additionally, factors such as bending force, angle, radius, and wall thickness can lead to collapsing and ovaling. Using a mandrel during bending helps maintain the structural integrity of the pipe and tube, resulting in higher quality and more precise bends.
The Importance of Rear Support in Pipe and Tube Bending
When precise bending is required, having rear support is essential. Making these parts longer provides a cost advantage. They can be reworked if wear occurs, extending their usability. In each operation, we can observe a reduction of approximately 15-20 mm in length.
Production Tolerances of Pipes and Tubes
We can follow current pipe and tube production standards from TSE and DIN standards. Let’s assume the pipe and tube diameter tolerance is 0.1 mm. In precision bending, these tolerances must be considered in the machine equipment. Pipe and tube diameters may vary depending on the manufacturers’ production methods. For example, one company might produce Ø42×2 pipes, while another company produces Ø42.4×2 pipes. This difference can cause issues in the roller group of the bending machine. As a result, the roller group may need to be re-adjusted.
Elasticity-Springback in Bending
Even if the operator bends the pipe and tube at a specific angle, the desired angle may not be reached. This is due to factors like material properties and springback. This is normal. The pipe and tube can exhibit elasticity and springback. As the pipe and tube wall thickness and bending angle increase, springback also tends to increase. This happens proportionally to the material’s properties. In such cases, an average of a 2-degree adjustment is made in the bending apparatus or machine to achieve the desired angle. For example, for a pipe and tube that is intended to be bent at 88 degrees, we can set the machine to 90 degrees and then make the bend to correct the situation.
Suitability of the Pipe and Tube for Bending
During the bending process, the designer must check the pipe’s diameter, wall thickness, and length. They must also consider bending radii and the possibility of collisions with the machine. The quality control team should compare the analysis reports of previously received pipes with those of newly received pipes, using a sample pipe and tube for comparison. Especially in welded pipes, personnel must ensure the weld is facing outward during bending. The responsible person must also check the integrity of the weld. In addition to the material, the formability of the pipe and tube must also be checked. Pipe and tube bending control can be performed through simulation before starting the bending process. In machines where simulation is not possible, wire bending can be used to check positions. This helps prevent collisions with the floor or machine.
Different Bending Radii in the Same Part
Bending with a single radius is practical, but parts with different radii increase costs. With multi-layered, rolling system, or mold-based pipe and tube -forming machines, it is possible to bend parts with different radii. This eliminates the need to change rollers or remove the pipe and tube.
Surface Deformation in the Pipe and Tube
The main causes of surface deformations in pipe and tube bending processes include the adjustment, precision, pipe wall thickness, pipe hardness, mandrel gap, bending radius, bending angle, and mandrel group clearance. Additionally, the operator’s experience and the use of standard materials are of critical importance.
Roundness of the Pipe and Tube
If the pipe and tube is not perfectly round, it may be due to crushing, collision, or roller adjustments during pipe and tube production. Some pipes may show indentations when held and rotated with gloves. This can cause issues when the pipe and tube enters the mandrel. When the rollers and clamping jaws close, there is a higher chance of these marks increasing. These factors must be considered when handling and transporting the material.
Pipe and Tube Surface
Shiny pipes are at risk of scratching during bending and other processes. The areas being bent and the outer side of the bent areas may become dull due to stress. Additionally, there is a risk of slippage from the mandrel during the bending process. Therefore, these factors should be considered when selecting the pipe and tube.
Transportation Process
It is important to prevent damage and protect pipes during production and delivery. Pipes that are transported and stacked may become crushed due to reasons such as rope hanger imbalance, careless handling with a forklift, improper placement in the vehicle, and collisions. Pipes should be transported carefully and slowly during shipping to avoid damage. Bended pipes should be handled in a way that prevents them from damaging each other.
Pipe and Tube Cutting
During pipe and tube cutting, burrs or form defects at the pipe and tube ends may occur. In such cases, the cutting process should be carried out with consideration of the pipe’s material and wall thickness. The angles and sharpness of the saw blades should be checked, and cutting oil suitable for the operation should be used.
Effect of the Welding Direction
The pipe should be placed in the mandrel with the seam direction inward. When the welding seam direction is outward, the formation of pores in the pipe may increase. There is also a risk of the pipe and tube bursting at the welded area due to stress.
Lubricants Used in the Bending Process
The oils used in bending are different from regular machine and hydraulic oils. These oils reduce the wear on the mandrel and assist in the bending process.
Operator’s Influence
The operator plays a crucial role in reducing problems and risks during the forming process. In pipe and tube bending, having an experienced operator makes it easier to produce pipes without errors and more efficiently.
Conclusion and Recommendations
Pipe and tube bending operations require consideration of various factors, such as material selection, equipment precision, and operator experience. The most common issues encountered during these processes include deformation, surface scratches, ovalization, and errors in the welded areas. To minimize these problems, it is essential to first choose the correct material, carefully evaluate its properties such as hardness, seam condition, and wall thickness.
During bending, the proper adjustment of the mandrel and roller groups will reduce both surface deformations and bending errors. In particular, controlling the rear supports and machine capacities is crucial in precision bending. Correctly determining mechanical parameters such as jaw clearance, bending radius, and angle will help maintain the structural integrity of the pipe and tube.
Operator experience is a direct factor influencing pipe bending quality. Having trained and experienced operators prevents defective production and increases production efficiency. Additionally, the correct use of bending oils reduces mandrel wear and enhances the pipe’s bending performance.
Finally, it is important to ensure that pipes are protected from crushing and deformation during transportation and storage. Considering all of these factors will improve quality in pipe and tube bending processes, reduce production costs, and optimize process efficiency. This way, more reliable and durable parts are produced for industrial applications.
Epta’s Approach
At Epta, we provide innovative solutions for pipe and tube bending and forming. Our expert R&D team designs and manufactures custom automatic machines tailored to our clients’ needs. With a commitment to continuous improvement, we integrate the latest technology into our production processes, delivering high-quality, efficient solutions. Our dedication to quality and customer satisfaction solidifies our position as a trusted industry partner.
For detailed information and collaboration opportunities, contact us today!
