When it comes to setting the push-bend parameters in the production of titanium elbows, this is a process that needs to be precisely controlled, especially in cold push-bending forming, the setting of parameters directly affects the quality of the finished product, such as the uniformity of the wall thickness of the titanium elbow, ovality, surface finish and mold life.
1. Pushing And Bending Speed
Range: Push bends are usually slower, about 5 - 20 mm/s.
Material sensitivity: Titanium alloys are sensitive to deformation rates. Excessive velocity can lead to excessive local temperature rise, increasing the risk of cracking, especially in alloys with high β content, or leading to lubrication failure.
Wall thickness control: A slower speed allows the material to flow more evenly, reducing the risk of over-thinning on the outside and wrinkling on the inside.
Surface Quality: Slow speed helps to achieve a better surface finish and reduces scratches.
Recommendation: Start at a moderately slow speed, e.g. 10 mm/s, and fine-tune according to the actual forming effect, such as observing the wall thickness, the surface, and whether there are signs of cracking. Complex or thin-walled elbows should be used at lower speeds.
2. Propulsion
Range: Mainly depends on pipe diameter, wall thickness, bending radius, titanium alloy grade, lubrication conditions.
Overcoming resistance: It is necessary to overcome the plastic deformation resistance of the material, the friction resistance of the mold, and the friction resistance of the mandrel rod.
Avoid instability: Excessive force can easily cause the tube blank to occur axial instability before entering the bending mold cavity.
Force curve: In actual production, the propulsion force is often graded or curved. In the initial stage, the force is slightly larger to overcome the static friction and initiation deformation, and the force remains relatively stable after entering the stable bending section, and the force may increase slightly towards the end.
Theoretical calculations: Estimation using plastic mechanics formulas.
Finite Element Simulation (FEA): The most efficient way to predict the forming process, wall thickness distribution, required thrust, and potential defects.
Test and commissioning: Prototype in small batches on actual equipment, monitor the thrust with a pressure sensor, and find the minimum thrust range that can be stably formed and defect-free.
3. Mandrel Position And Type
Position : The front end of the mandrel should extend out of the bending die-cutting point at a certain distance. This is one of the most critical parameters.
Too far forward: increased friction may lead to excessive thinning or even cracking of the pipe wall, and increased thrust.
Too far back: insufficient support for the inner side, which is easy to cause wrinkles or cross-section distortion.
XP: The lead is typically 10% - 30% of the pipe diameter. It needs to be fine-tuned according to the actual effect. It is recommended to start with the median value (e.g., 20%) and observe the inner wall quality adjustment.
Selection: Select the appropriate type and number of ball segments according to the bending radius (R/D), wall thickness (t/D). Small R/D or thin-walled tubing requires a stronger mandrel design.
4. Lubrication
Importance: Greatly influences push-flex force, surface quality, wall thickness uniformity, and mandrel exit difficulty.
Lubricant Selection:
Special titanium alloy cold forming lubricant. Common types are high-performance polymer-based pastes and lubricants containing molybdenum disulfide/graphite. Avoid lubricants containing chlorine or heavy metals, which may cause stress corrosion of titanium.
Coating requirements: Apply evenly and sufficiently to the inner and outer walls of the tube blank, and the lubrication of the inner wall is particularly important.
5. Tube Blank State
Material grade: Clarify whether it is pure titanium or titanium alloy Gr5 Ti6Al4V, Gr9 Ti3Al2.5V. The alloy has higher strength, more push-bending force required, and slightly worse formability.
Heat Treated Condition: Annealed is the preferred choice for cold push bending. Hard forming is difficult and easy to crack.
Dimensional accuracy: The tolerance of the outer diameter and wall thickness of the tube blank needs to be strictly controlled, otherwise the mold filling and forming stability will be affected.
End Treatment: The end of the tube should be flat and burr-free for smooth access to the mold and mandrel assembly.
It is understood that compared with other bending processes, the pushing and bending process of titanium elbow has its own rules, and the bending radius, friction coefficient and pushing speed in the pushing and bending process have an impact on the quality of the end product, so many scholars have studied it through computer simulation, experiments and other means. In the early stage of mold design and cold bending production of elbows of other materials, the company has accumulated a large number of process parameters and experience.
In the theoretical study, it is found that when the friction coefficient is 0.02 and the push-bending speed is in the range of 2mm/s to 7mm/s, the wall thickness change rate of the tube blank is relatively stable, about 7.5% to 8%. And when the push-bending speed is 4mm/s, the wall thickness changes less. When the pushing and bending speed is too large, the deformation is mainly in the front end of the titanium elbow, and it is easy to produce that the front end has buckled, and the rear area has not yet been deformed. As a result, the tube blank can not be uniformly and fully shaped. But on the other hand, the pushing and bending speed should not be too small, too small pushing speed will make the material shaping flow quite sufficient, causing the outer arc part to be too thin, in addition, the low speed will also greatly reduce the production efficiency.
Through the actual production test, it is found that the pushing speed of 3.5mm/s to 5mm/s is used in the case of lubricant application, the outer arc thinning rate of the pipe fitting is small, and the quality of the pushed elbow is better. Therefore, in the case of mastering the influence of pushing speed on the quality of the terminal elbow and the empirical parameters, it is necessary to correct and adjust according to the actual situation to achieve better elbow quality. For more information, please contact catherine@hiriger.com.
