Regarding the knowledge of bending stainless steel tubing or pipes, there is a more detailed description in our other article, please click here to read: How bending the stainless steel pipe or tubing
Bending stainless steel
Although it is possible to bend stainless steel into different shapes, the process may require considerable direct pressure for specialized tools. When we talk about bending high-end stainless steel materials, attention turns to increased bending difficulties. The difficulty often depends on the thickness of the tubing.
Thick-walled tubing usually needs increased force to bend. Furthermore, specific sizes and shapes of tubes may require their set of bending equipment. The possibility of spring back occurring also poses a significant challenge to bending stainless steel tubing.
Bending 304 stainless steel tubing
304 stainless steel tubing is a kind of hollow round steel, which is widely used in various architectural decoration fields such as stair handrails, fence railings, courtyard gates, and so on. In the process of bending, it is required to be smooth, accurate in angle, and not burst.
304 Stainless tubing can be very difficult to bend or form, especially at larger diameters, because it is harder, less malleable, and tends to have thinner walls in relation to tubing diameter than other tubing materials. Other materials in which wall thicknesses are thin relative to tube diameter may be similarly difficult to bend and form.
At present, there are two methods for making stainless steel pipes into arcs on the market.
Four most effective cold bending processes of stainless steel pipes
It is pretty tough to deal with stainless steel tubing. However, some techniques can help simplify the process. This section will discuss how to bend stainless steel tubing using the most effective methods.
Mandrel Tube Bending
Mandrel bending of stainless steel pipe is often done on a rotary draw tube bending machine. A mandrel is a tool put inside a tube to ensure its shape remains intact while bending. Mandrels may come with additional ball-shaped steel to ensure they stay inside the curved sections of bends during the bending process. The setup for mandrel tube bending includes:
- A pressure dies – this die holds the tangent (or the straight section) of the tub.
- A clamp die – rotates the steel tubing around the bend die.
- A mandrel – supports the tubing interior around the bend and may come with some articulating balls.
- A wiper dies – contacts the tubing right before the inside radius’s tangent point, wiping against the workpiece to prevent wrinkles on the inside radius.
Mandrel tube bending dominates the stainless steel tubing bending landscape, especially in applications with tight radii
When you think of how to bend stainless steel tubing to a radius, you should choose mandrel bending. This is because the method provides maximum control over ovality and wall thinning. Using a mandrel in the inner diameter (ID) helps to support the flow of materials during bending. Likewise, the pressure die supports the outer diameter (OD). The elements combine to control the tube OD and ID throughout the bending process. Mandrel tube bending helps prevent the most common bending issues, most importantly, spring back. It also prevents wrinkles, flattening, and kinks.
Profile roll bending or angle bending is an effective process for larger workpieces. It generally involves three rolls put in a pyramid-like position with either vertical or horizontal milling orientation, depending on the size of the section. The rolls move such that they can produce large, usually specific radii.
The machine determines which rolls move to which side. The middle roll’s location determines the radius of the tube or pipe. The top roll may move up and down on some machines to give the desired angle. On other machines, two bottom rolls move while the top roll stays stationary. Manufacturers use roll bending for producing spirals. The operator can produce continuous coils by lifting the tube after a revolution. In this case, the workpiece should have a large radius and a one-diameter pitch. However, if it has a larger coil pitch, there will be the need for an additional roll. This roll helps to guide the tube outward during the forming of the coil.
This method is similar to the mandrel tube bending process, just without the mandrel. It increases the tubing part’s precision to achieve complex blends with no deformities. In this method, the machine is supported using clamps. The clamps allow the pulling of the tube towards a shape that has a similar radius as the pipe. With this principle, draw bending helps to get sharp bends on the tube while retaining high-level accuracy and consistency. Manufacturers often use the rotary draw bending method on tubing parts used on structural frameworks and machines. Typical examples are roll cages, bicycle handlebars, railings, etc.
Another efficient method of bending stainless steel tubing is compression bending. This method bends the material around a stationary bend die using a compression die. The system involves the initial clamping of the tube behind the rear tangent point. After this, the compression die helps to “compress” the workpiece against the bend die. Compression tube bending works best for symmetrical workpieces. These are tubes with identical bends on either side. The bending of these tubes occurs in one setup on machines with two bending heads. So, you might want to choose this method when the roundness of a bend is not the most critical consideration. Compression bending is ideal for speed and economy when aiming to get higher output at lower costs. However, we do not recommend this method for tubes with a centerline radius (CLR) less than two times the bend diameter. That is, you will need at least a 2-inches centerline for a 1-inch tube bend to get the desired bend quality.
Stainless Steel Tubing Bend Radius Chart
The bend radius of a tube is the radius measured to the tube’s centerline. Bend radius tooling often differs, depending on the tube bender. However, the most common ones are usually in line with specific rules of thumb.
- Standard Draw Bend Radius is 2 x D: This means that a tube with an OD of 20mm will require a bend radius of 40mm. Tighter bend radii like ½ x D are possible. However, it is often costlier to get anything below 2 x D.
- Minimum Roll Bending Radius is 7 x D: Material properties and wall thickness affect the minimum roll bending radius. Therefore, sticking with the 7 x D guideline is technically safe. It is also advisable to allow a wide tolerance in bend radii.
4 tips of bending stainless steel tubing process
When processing stainless steel pipes, stainless steel tube manufacturers should carefully consider the material and type of stainless steel pipes:
- If the unit size of the stainless steel tube is thicker, the bending force required will be greater, and as the thickness of the stainless steel tube increases, the bending force in the selection of the bending equipment should also be greater.
- Under the unit size of stainless steel tube processing and bending, the greater the tensile strength, the smaller the elongation rate, so the greater the required bending force, the greater the bending angle.
- If the thickness of the stainless steel tube corresponds to the bending radius in the design drawing, the unfolded size of a bent workpiece should be the addition of the right-angled sides minus the thickness of two stainless steel tubes, so that the design accuracy requirements can be fully met.
- If the yield strength of the stainless steel pipe is larger, the elastic recovery will be larger. If the angle of 90 degrees of the bending part can be obtained, the angle of the pressing knife should be designed smaller.
Further Reading: Angle Roll: 5 Tips for Choose the Best Angle Roller
Five important notes of curved stainless steel tubing
Notes 1#: Bend Radius
When we talk about bend radius it refers to the radius measured at the center line of the tube. The bend radius is a fundamental parameter for the bend feasibility analysis of a box: it is essential because it is the value that defines the coefficient which will indicate the degree of difficulty of cold bending. Bending metal tubes is a process that is done using special tube bending machines with particular tools.
Notes 2#: Yield Strength
Another essential consideration for stainless steel tubing bending is yield strength. It is one of the characteristics of steel materials that may give the likelihood of spring back formation. Materials with higher yield strength will have a greater elastic-to-plastic strain ratio. Such materials will also show more spring back than those with lower yield strength.
Therefore, it is vital to determine the yield strength of your steel material before bending. Every bend gives a reasonable amount of strain. Therefore, the yield strength should be considered with respect to the specific amount of strain expected.
Notes 3#: Material Thickness
Material thickness variations are a great challenge when it comes to bending stainless steel tubes. It particularly plays a significant impact when fabricators try to achieve specific bending tolerances. The gauge of various stainless steel is often talked about with respect to averages. However, the actual material thickness falls within a specific range in reality.
Therefore, a slight variation in thickness can significantly affect the bend angle by some degrees. This often affects results, especially when you need tight tolerances. It is essential to know that some materials may need more bending power than others during custom tube fabrications. Thicker stainless steel grades will require greater force than thinner ones.
The strain involved in bending thicker materials around given radii is higher than that of thinner materials around the same radii. The thicker the walls, the higher the pressure the tube can withstand. Likewise, tubes with thinner walls are more susceptible to collapse during bending.
Thus, it is advisable to set the bending power right to prevent inconsistencies and material deformation. You must choose the proper process and set the machine appropriately.
Notes 4#: Welded Tubing vs. Seamless Tubing
Both seamless and welded tubing can be bent. However, seamless tubing often bends better if the desired radius is tight. On the other hand, the thinner walls of welded tubing make them useful for larger-diameter applications. The seam of welded pipes may interfere with the consistency of bends. This is due to the stress concentration point that forms on the tube.
Stress concentration gives welded tubing 20% less working pressure than seamless tubing. We cannot also overlook the possibility of improper weld forming, leading to the tube not being perfectly round. This prevents proper bending of welded tubing.
Notes 5#: Cleaning after bending
- While stainless steel is resistant to corrosion, it is not immune to it. Bending the tubing can create small cracks or crevices on the surface of the metal, which can be breeding grounds for corrosion. To prevent corrosion, it is important to properly clean and finish the tubing after bending.
- Lubricants used in bending can be fairly heavy. Great care must be taken when lightly chlorinated mineral oil is used. Since stainless steels are not very resistant to chloride ions, additional cleaning may be required in these cases.
- Any ferrous contamination on the surface could cause surface staining. This can occur very soon after installation when the component is exposed to humidity in the air.
- Particular care must be taken during each manufacturing step and the cleanness of the surface must be ensured before and after every work phase.
Read More: How To Bend Stainless Steel Sheet Metal Parts?
Applications of bending stainless steel pipes
Stainless steels come in a variety of grades with unique benefits, Section bending machine can bend stainless steel tubes, pipes, beams, bars, angles, channels, and other specialized shapes for:
- Food & pharmaceutical processing
- Medical & hospital industries
- Vessels & storage tanks
- Marine industry
- Subsea & offshore equipment
- Construction materials & architectural accents
- Railings & roofing supports
- Commercial lighting
- Boilers & HVAC
- Aerospace products
- Safety & security industries
Advantages of stainless steel pipe for bending
The mechanical properties and features of stainless steel vary by grade.
BIT series profile bending machine can adaptably bend steel to a large or tight radius. Because of its strength and work hardening rate, stainless steel bending requires more robust, high-powered equipment and tooling than carbon steel bending.
While stainless steel may cost more than other material (such as aluminum profiles) options on the front end, its strength and durability lend proven value over the course of its lifecycle. Further benefits of stainless steel for bending include:
- Corrosion & rust immunity
- Extreme temperature resistance
- Impact resistance
- Attractive, modern appearance
- Hygienic for food & medical use
- Range of diameters & wall sizes
- Flexible fabrication & machinability
- Recyclability & sustainability
- Value over the lifecycle
- Versatility (pliable or strong, depending upon the grade)
Further reading： Stainless Steel Pipe Sizes
- How hard is it to bend stainless steel tubes? Steel tube bending can be very difficult due to the hardness of the material. However, choosing the right fabricator with proper knowledge of processes and tooling can help make the process more seamless.
- Is mandrel tube bending better than roll bending? The method you choose depends on your bending requirements. Mandrel bending is preferred for bending operations with tighter radii to prevent flattening, wrinkles, and kinks. On the other hand, roll bending is ideal for thinner tubes with a large bend radius.
- What are the applications of stainless steel tubing? Many industries use stainless steel tubes for various applications. They are used in home appliances, automotive and aerospace parts, electronic devices, plumbing systems, medical devices, and many more.
- What is cold bending? Generally, a cold bending machine is used for multiple rolling forming. weakness is: Steel pipe diameter is limited If the bending radius is too small, the diameter of the steel pipe is prone to deformation
- What is hot bending? Fill the stainless steel tube with sand, fill it up, and bend it with high-temperature heat treatment. This method is the most ideal; The disadvantage is: that the hot bending process cost is too high, the cost is large, and it is not suitable for mass production