The Importance of Roller Leveling in Sheet Metal Manufacturing
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Smooth and stress-free components can enhance the production efficiency of bending and welding processes, ensuring customer satisfaction.
The science of leveling metal strip has two main goals. The first is to make the metal’s surface flat and ripple-free. The second is to neutralize hidden internal stresses that cause twist and bow in parts during secondary operations, such as stamping.
Regarding Material Stress
Metal sheets delivered to sheet metal factories may appear sufficiently flat. However, appearances can be deceiving, especially with metal materials. Even seemingly flat materials or components may become distorted during processing due to processing stress.
Therefore, understanding what happens to raw materials before they are delivered to sheet metal factories is meaningful and necessary. Sheet metal raw materials come from rolled coils. In metal processing service centers, these coils are uncoiled, straightened, and finally cut into certain lengths. Although the sheets may appear flat, they still retain stress. (Stress is notably present in the material’s microstructure.)
When using thermal cutting methods (such as laser or plasma cutting) on these materials, stress is released, causing components to become uneven. This situation applies to both thin and thick metal components.
This scenario also applies to both black and non-ferrous metal components. The use of auxiliary gases plays a significant role in cutting such components. For instance, when oxygen is used to cut carbon steel, it undergoes an exothermic reaction with the metal. This introduces a significant amount of heat into the cutting area, speeding up the cutting process. (The byproduct of this chemical reaction is oxide buildup at the edges, which needs to be cleaned for painting.) However, the additional heat also releases more stress from the metal. Even with the use of a gentler process, such as cutting with inert gas like nitrogen, stress is still released.
Stress release causes components to become uneven, posing particular challenges for production workshops employing new laser cutting technologies. During laser cutting, some components may tilt or lift on the cutting grate, leading to collisions and damage to the cutting head, especially when cutting speeds exceed 30 m/min and accelerations exceed 2 m/s², which have become industry standards. A very expensive component on a laser cutting machine may be damaged by components rebounding due to stress on the cutting bed.
Any cutting process can release stress accumulated during the coiling of the material. This stress can be visibly seen in the form of springback after cutting or punching metal. (Punching induces material work hardening and generates new stress, which can be observed on punched components.)
Dealing with Material Stress
How do sheet metal factories deal with the stress metal materials accumulate during coiling and the stress released from cutting or stamping components? Roller leveling machines can provide assistance. These machines can deliver flat components necessary for sheet metal factories and downstream manufacturing processes, ensuring higher production efficiency and reducing waste during bending and welding processes.
Roller leveling machines achieve flatness by applying repeated bending forces to metal sheets or components using a set of leveling rolls. As the metal material passes through the leveling machine, pressure is applied by the leveling rolls. The intensity of stress applied to the metal material decreases, eventually eliminating its internal stress.
How are these leveling rolls arranged? It depends on the type of metal material, material thickness, and the level of flatness required. Variables of a roller leveling machine include:
- Number of leveling rolls
- Distance between leveling roll centers
- Layout and support method of leveling rolls
- Stiffness of leveling roll frames and the entire machine
- Support of leveling rolls (length and layout of support rolls)
- Leveling gap control system and its ability to maintain gap stability
- Power consumption
- Ease of cleaning leveling rolls and support rolls, as well as maintaining the machine
- As the leveling rolls gradually reduce pressure while stretching the metal, they flatten the components.
The leveling rolls driven by motors can be moved out of the machine tool according to the size of the components to be leveled. The leveling pressure depends on the diameter of the leveling rolls, corresponding to the position of the leveling rolls, machine roll frame, support rolls, and frame design, each having its operating display window. Generally, smaller leveling roll diameters are used for thinner materials, while larger diameters are used for thicker materials. Leveling machines can typically level components ranging from 0.2 millimeters to nearly 70 millimeters in thickness.
The flatness provided by leveling actually differs depending on the application of the metal material, as well as its thickness and type. For instance, for metal components used in manufacturing cranes and mining equipment, if a leveling machine can provide a flatness of 0.5 mm/m to 1 mm/m, it is considered very good. However, for saw blade manufacturers requiring a flatness of 0.1 mm/m or higher, this level of flatness may not be suitable. Fortunately, a high-precision roller leveling machine can provide flat components for heavy equipment manufacturers and produce components with higher tolerances for saw blade manufacturers.
Component leveling can also be highly meticulous. For example, manufacturing companies in the aerospace industry typically use aluminum materials. A thickness of 5mm is considered relatively thick for these companies, but for manufacturers of mining equipment, this thickness is too thin. These aluminum materials usually undergo heat treatment to gain greater strength. After heat treatment, the aluminum material becomes softer and is stored at a temperature of -18 degrees Celsius. If such components are leveled immediately after blanking, the leveling machine must face two main challenges. Firstly, the material is soft, so the leveling rolls must exert gentle pressure to avoid material deformation. Secondly, when the frozen components come into contact with higher ambient temperatures, condensation forms on the component surface, so the components of the leveling machine should be made of stainless steel or coated steel to prevent rust.
Difficult-to-handle Materials for Leveling
The results produced by roller leveling machines are simple—flat components. However, these machines are actually complex devices capable of handling material deformations that are difficult to correct.
For example, punched and heat-treated materials often exhibit intermediate wave deformations or edge wave deformations. Correcting such components or sheets requires special measures and techniques.
For (partially) punched plates and heat-treated materials, advanced leveling roll bending control functions can selectively increase leveling pressure in certain areas of the component or sheet while reducing pressure in other areas. Through this controlled leveling method, the material is elongated in the required longitudinal direction, thereby reducing or even eliminating intermediate wave deformations and edge wave deformations.
Materials with high tensile strength are another type of difficult-to-handle material. Handling such materials requires a high-power machine, combined with leveling rolls of very large diameter and corresponding roll spacing, to reduce material stress and provide good flatness.
Operator’s Leveling Experience
Any advanced manufacturing equipment requires a dedicated operator. An experienced operator, more importantly, one who is eager to learn, can bring about truly different results. If they are willing to spend time adjusting and testing components to achieve good leveling results, the factory can achieve efficient component leveling and higher quality products in downstream manufacturing processes.
In theory, leveling is a simple operation. Besides the speed of the leveling rolls, the operator only needs to adjust two other parameters: the leveling gaps at the inlet and outlet and the angle at which components are fed into the machine. By finding the right combination, the operator can optimize leveling results.
Of course, built-in calculation tools in equipment control systems also provide assistance. After inputting thickness, yield strength, and material type, the control system outputs suggested leveling parameters. Typically, these parameters already ensure good leveling results. If the operator seeks better leveling results, this set of leveling parameters can serve as the basic parameters for adjustment.
Benefits of Leveling
Component leveling can help sheet metal factories increase output and productivity. Data reported by sheet metal factories indicate that incorporating roller leveling machines into their production processes increases the productivity of bending processes by approximately 25% after leveling components. Flat components are bent more accurately, meaning fewer reworks and greater product quality consistency. In the welding department, this means significantly simplified fixture tools and improved assembly accuracy, which welding operators will appreciate. Nonconforming products are drastically reduced, enhancing production efficiency.
This is particularly true for robotic welding. Closer and more consistent welds mean less filler wire used, smoother welding lines, and faster automation processes.
Roller leveling machines can also create new business opportunities for a company. For instance, if a company wants to serve clients in the construction industry, the ceilings and facades it offers must be absolutely flat, with every piece of sheet metal being equally flat, as any piece not meeting specifications could cause construction projects to halt.