Part made using CNC tube bending whether for exhaust systems, hydraulic lines, or farm gates helps make the world run daily. CNC tube bending allows tubes to be formed accurately and efficiently.
The bending radius has limits. Trying to bend too small of a radius will distort and even tear the tubes. We suggest you work with the stock bend radius of your tube bending vendor or consult them first. Seaborn uses double stack CNC tube benders with programmable bend radi. What this means is our machines can form tubes with two different bend radius in the same part. The tooling for this needs to be manufactured to work together at time of its order. We can use what we call a programmable radius when we bend tubes at greater than 12 times the tube diameter. Programmable bend radius is not as accurate as hard tooling. At Seaborn we have run CNC tube bending projects from quantity 1 to 100,000 annually.
Understanding how the material in a tube behaves while CNC tube forming is important. The tube bender does not make material or move the material around. Quite simply a tube bender stretches the tube on the outside of the bend radius. We have heard it said that the tube compresses on the inside diameter but from what we can observe this is negligible. Much of the tooling used during tube bending is to maintain the tube shape. The effects of stretching the tube to produce a formed tube are far more evident in square and rectangular tube than round.
Mandrel tube bending is what a lot of people look for. Mandrel bending involves inserting a rod with a tooling attached so that inside diameter is supported. At seaborn we do this with segment mandrels as they perform the best. These segments, often called balls, are connected by flexible links. The mandrels sits at the bending point and is pinched by the tube. To separate the tube from the mandrel the mandrel extractor pulls the mandrel back and out from the bending area. The mandrel needs to have some clearance to the tube if you try to use too tight of a mandrel extractor the tube will be torn when it crimps to the mandrel. Mandrels do help produce a cleaner tube with less visible distortion. Mandrels are the final tool required for high quality bending. They are not the fix all they are believed to be. The mandrel when used does slow the production cycle and increases the part loading time.
Tooling Diagram
The bending die is the first piece of tooling that is needed. This is what will determine the center line radius. The profile of the bending die needs to match the profile of the tube to avoid having severe distortion in the tube shape.
Our double stack benders allow us to use two different bend radius on the same part. Each bend radius will have its own bend die and the difference between the radius of tools working together needs to be accounted for by the pressure dies and clamps.
Double Stack Bender Photo
The clamp is often overlooked but is critical when you are cnc tube forming. It needs to hold the tube and stop it from slipping as the bending arm rotates. There is additional need to ensure the tube O.D. is supported. If it does not do both of these functions the tube will kink and deform badly. Leaving room or enough room for the clamp between bends if often overlooked.
The pressure die supports the O.D. of the tube while tube bending. This die also needs to match the profile of the tube. The pressure die and bending die together capture the diameter of the tube will CNC tube forming. These need to be tight fit. There should also ideally be 5 times the tube diameter left after the last bend so it can be supported properly throughout the bend by the pressure die.
Bender Tooling Photo
The role of the wiper die is missed as the majority of CNC tube benders do not have them or the ability to add them. The wiper die is a fixed tool that interlocks with the bending die to support the inner radius of the tube just before the bending point. On thin wall tubes this piece of tooling has more impact on the bend quality than the mandrel.
A CNC tube bender transport carriage determines where the bends occur and how the tube is oriented / rotated between the bends.
Contact Seaborn Manufacturing today to discuss your next CNC tube forming project