Tube bending is any metal forming processes to a desired shape using the tube bending equipment and tooling technology, there are different bend types to use, which mode of tube bending is chosen depending upon applications, as with bent parts, the tolerances and appearance requirements help determine the proper method, tubes can be bent either manually or automatically, or using a combination of both methods.
While the procedures are the same for bending round tubing, rectangular tubing, oval tubing and square tubing, square and rectangular material require special consideration. Using a wide range of materials, tube sizes, and bending methods, our experts work with your team to meet applicable safety guidelines and industry standards. We also use non-destructive examination procedures in our tube bending services to assure the performance.
Tube Bending Methods
The four main modes of tube bending—freeform, compression, rotary draw, and roll bending are most methods to bend tubing.
Compression Bending
Compression bending is the easiest and most common type of tube bending, this bending mode is used when the roundness of the bend is not critical, and when the objective is more about high output to get the lowest price per tube.
In addition to speed, some of the advantages are that no oil is used inside the part and that you don’t use a mandrel inside the tube, which is why the bend is a little out of round. Because you don’t use oil, no cleaning of the part is needed afterward. A lot of times cleaning the part consumes as much time as bending it.
This is not a precision form of bending method, because there can be some deformation of the pipe due to a lack of internal support.
Compression bending is used a lot in the furniture industry, to bend lawn mower handles, and for generator frames.
Rotary Draw Bending
One of the most common modes of bending is rotary draw bending. It is typically used to bend a tube three to four times the centerline radius of the tube diameter.
This type of bending requires a lot more tooling than compression bending. Three pieces of tooling are needed. One, you need a bend die. It forms the tube to the specified bend. Second, you always need a clamp die. It holds the tube while you’re bending it. Third, you need a pressure die. As it’s being bent, the part naturally wants to kick out. This tool applies pressure to the back of the tube and follows along as the tube is being bent to prevent this.
If you’re bending thin-wall tube or a tight radius, you may need three other pieces of tooling. You’ll need a mandrel to go inside of it, which keeps your tube round as it is being bent. The bend radius and tube thickness determine the number of balls in the mandrel.
In addition, a wiper die is needed to bend thin-wall tube. It prevents the tube from rippling. Normally, when you bend a piece of tube, material gathers on the inside radius, which results in a large lump or ripples at the end. The wiper die wipes, or smooths, those ripples or lumps away, pushing the metal farther from the bend.
The sixth piece of tooling you might need is a collet for when you’re making more than one bend on a part. You need the collet to be sized for the tube diameter. It holds the tube as it is bent and then pushes it forward to get it ready for the next bend.
Most rotary bending machines are oriented for right-handed or left-handed bends, but some are outfitted to bend in both directions.
Roll Bending
Roll bending involves the use of a machine with three rollers, called a jig. It can be used to bend both sheet metal and metal bars. It works by putting the bar into the jig and manually lowering and pressing the middle roller against the bar. As the rollers are rotated, the bar moves along and force is applied to the bar as it goes back and forth along the rollers until it reaches the desired shape.
Roll bending can be good for circular fabrications, such as wheel rims.
Freeform Bending
One of the most unique bending machines is a CNC freeform bender. It allows you to make bends of any radius and without straights between the bends.
The tube is pushed through a ceramic ring with tooling designed for the tube size. That is the only tooling needed. As the tube moves through the ceramic ring, the computer controls the motion of the ceramic ring to form the tube. It’s that simple. You can make a multibend part two days after it has been ordered without any tooling charge.
In addition to the minimal tooling requirement, very little marking occurs on the tube because the only thing touching the part is the ceramic ring. You get a mark-free part, and because no oil is used inside the tube, it does not have to be cleaned.
5 Tips of Custom Bends
1. Centerline Radius
As a rule, the tightest achievable centerline radius is one times the pipe or tube diameter. Whenever possible, choose a centerline radius of 1.5 times or greater than the tube diameter. This will save labor costs.
2. Wall Thickness
During tube and pipe bending, the wall on the outside radius can thin up to 33%, depending on the radius and other factors. You can minimize this thinning by using some of the bending tooling, such as a mandrel. This is important to keep in mind if your application involves high pressure or flow. A thicker wall may be necessary to achieve the desired results.
3. Straight Length Between Bends
Typically, a straight section between bends should be two to three times the tube diameter, depending on the radius. (An exception is using freeform bending, which does not require a straight.)
4. Tolerances
The industry standard is still considered to be ±1 degree on bend angles. A more stringent standard is ±0.5 degree. Tighter tolerances, even to ±-0.2 degree, can be accomplished with laser-controlled spring back technology if the application requires it. Lineal tolerances normally are ±0.062 in. or tighter. The industry standard for ovality is 8% to 4%. This can be improved upon if the application calls for it.
5. Drawings
It’s important that part drawings include the pipe or tube specs, material type, centerline radius, and any other details about the scope of the project. If available, STEP files or 3D models can be provided along with your drawing.
Factors That Influence Bending Process
The tube bending process, whether it is hot or cold, alters the properties of the tube, and therefore different factors needs to be taken into consideration as part of the manufacturing decisions to reduce the amount of distortion in bent sections.
Wall Thickness. Bending round, square, or rectangular material involves stretching the outside diameter (OD) of the bend and compressing its ID. Consequently, a heavier wall thickness allows for a tighter bend radius and more material stretchability with less distortion.
Method of Bending. This is a key factor in controlling distortion. A correctly chosen procedure can help to produce consistent tolerances and accurate parts. Generally, smaller material requires rotary draw bending or compression bending, which can incorporate wiper dies and mandrels. Induction and increment bending should be used with larger material bent to a larger radius. Design distortion and material size are important factors for determining the bending method.
In many cases, there is no better factor than experience. Many trained bending artisans know what is required to produce an acceptable product.
Size of Material. Larger material bent to a smaller radius has a greater chance to distort than smaller material bent to a larger radius. Design and planning are necessary to help solve bending problems before they arise.
Tooling. After the parts have been designed, the method of bending has been chosen, and procedures to bend to proper tolerances are established, the machine must be set up with the proper tooling. Based on design conditions, tooling that can be used includes bend die, clamp block, follower block, mandrel, and wiper die. All or some of this tooling may be required.
Internal and External Lubricant. Lubricants decrease the friction between tooling and material to be bent. When friction is reduced, material flows smoothly through the bending equipment, allowing the machinery to perform its designed operation efficiently.