As shown in Figure 1, the part on the left has an elastic shape and is not completely flat, while the part on the right has been flattened by a part leveling machine.
Flat, stress-free parts can increase bending and welding production efficiency, ensuring customer satisfaction.
Regarding material stress
Although the metal sheets delivered to the sheet metal factory appear flat enough, appearances can be deceiving, especially for metal materials. Materials or parts that appear flat may become flat during the machining process due to machining stresses.
Therefore, understanding what happens to raw materials before they are sent to the sheet metal plant is essential. Sheet metal originates from rolled coils.
In metal processing service centers, these coils are unwound, straightened and finally cut to a specific length. Although the sheet appears flat, internal stresses are still present (mainly in the metal's microstructure).
When performing thermal cutting (such as laser or plasma cutting) on these materials, tension is released, making the parts uneven. This is true for both thin metal parts and thick metal parts.
This applies to ferrous and non-ferrous metal parts. During the cutting process, the use of shielding gases plays a significant role.
For example, when oxygen is used to cut carbon steel, an exothermic reaction occurs between the oxygen and the metal. This introduces a substantial amount of heat into the cutting area, allowing for faster cutting (a byproduct of this chemical reaction is an oxidized edge, which needs cleaning before painting).
However, the additional heat also releases more tension from the metal. Compared to oxygen, cutting with an inert gas like nitrogen can reduce heat input, but even with gentler processes, stress is still released.
As the stress is released, the parts become irregular. This presents challenges for production shops using newer laser cutting technologies.
During laser cutting, some parts may tilt or bounce on the grid, potentially colliding and damaging the cutting head, especially when cutting speeds reach 30 m/min or more and accelerations exceed 2 m/s 2 which has become an industry standard.
A very expensive component of laser cutting equipment can be damaged by parts that ricochet due to stress.
Any cutting process can release the tensions generated during material winding. This stress is evident in the phenomenon of springback of the metal after cutting or punching (punching can introduce new stresses due to work hardening, visible in punched parts).
Combating material stress
How does a sheet metal manufacturing plant handle stresses introduced during coiling and released after cutting or stamping? Part leveling machines can be extremely useful.
Part leveling machines can provide sheet metal factories and their downstream manufacturing processes with the flat parts they need, ensuring greater production efficiency and reducing waste in bending and welding operations.
Part leveling machines (as seen in Figure 2) achieve flatness by applying repetitive bending forces to the sheet or metal part through a set of leveling rollers.
As the metal material passes through the leveler, the rollers exert pressure on it. The tension applied to the metal reduces and eventually eliminates its internal stresses.
How are these leveling rollers arranged? It depends on the type of metallic material, its thickness and the desired level of flatness.
Part leveling machine variables include the number of leveling rollers; the central distance between the rollers; roll layout and support method; rigidity of the roller structure and the entire machine; roller support (length and arrangement of support rollers); gap control system and its ability to maintain a consistent gap; and energy consumption.
It is also essential to consider how easy the leveling and support rollers are to clean and maintain the machine.
As the leveling rollers gradually apply pressure and flatten the parts, the roller frame, driven by a motor, can be removed from the machine tool. Depending on the size of the part to be leveled, the leveling pressure is determined by the diameter of the leveling rollers. The diameter of each roller, combined with its position, machine frame design, supporting rollers and the machine frame itself, has its corresponding operating display window.
In general, smaller roller diameters are used for thinner materials, while larger diameters are used for thicker materials.
Leveling machines can typically handle parts with a thickness of 0.2 mm to almost 70 mm.
The flatness accuracy provided by leveling is based on the application of the metallic material and varies according to its thickness and type.
For example, for metal parts used in the manufacture of cranes and mining equipment, a flatness of 0.5 mm to 1 mm provided by a leveling machine is considered excellent. However, for saw blade manufacturers requiring flatness of 0.1 mm/m or greater, such flatness would be inadequate.
Fortunately, a high-precision parts leveling machine can provide flat parts for heavy equipment manufacturers and produce parts with tighter tolerances for saw blade manufacturers.
For example, aerospace manufacturing companies typically use aluminum materials. 5mm is considered a relatively thick part for these companies, but for mining equipment manufacturers this thickness is too thin.
This aluminum material is often heat treated to achieve greater strength. After heat treatment, aluminum becomes soft and is stored at -18°C.
If these parts are leveled immediately after punching, the leveling machine will face two main challenges.
First, because the material is soft, leveling rollers must handle it carefully to avoid deformation.
Secondly, when frozen parts come into contact with a higher ambient temperature, condensation forms on the surface of the part. Therefore, the leveler components must be made of stainless steel or coated steel to prevent corrosion.
Straightening difficult materials
The result of a part leveler is simple: flat parts. However, they are complex machines, capable of managing material deformations that are difficult to correct, such as those of perforated and heat-treated materials.
These materials generally exhibit mid-wave deformations or edge-wave deformations. Correcting such pieces or sheets requires specialized measurements and techniques.
For some perforated and heat-treated materials, advanced leveling roll bend control can specifically increase leveling pressure in certain areas of a part or sheet while reducing it in others.
Through this controlled leveling method, the material is lengthened longitudinally as needed, which can reduce or even eliminate midwave and edge deformations.
High tensile strength materials are another challenging type to handle.
Processing of such materials requires a high-powered machine, using very large diameter leveling rollers combined with matching roller spacing, to reduce material stress and provide good flatness, while eliminating mid-wave and edge warping. .
Operator leveling experience
Any advanced manufacturing equipment requires a skilled operator with extensive experience. Most importantly, a curious, knowledge-seeking trader can really make a difference in results.
If they are willing to spend time adjusting and testing parts for optimal leveling, the factory can achieve efficient leveling of higher quality parts and products in downstream manufacturing processes.
Theoretically, leveling is a simple task. In addition to the speed of the leveling rolls, the operator only needs to adjust two other parameters: the leveling clearance at the entrance and exit and the angle at which the part enters the machine. By finding the right combination, operators can optimize grading results.
Of course, computational tools integrated into the equipment control system can help. After entering the thickness, yield strength and material type, the control system generates suggested leveling parameters.
Normally, these parameters already guarantee good leveling results. If operators are looking for even better results, these leveling settings can serve as a starting point for adjustments.
Benefits of leveling
Part leveling can help sheet metal factories increase production and productivity.
Reports from sheet metal manufacturing plants indicate that integrating part leveling machines into their production process increases bending operation production rates by about 25% after part leveling.
Flat parts bend more precisely, which means less rework and greater consistency in product quality.
In the welding department, this translates into a significant simplification of jigs and accessories, greater assembly precision and the appreciation of welders. There is a significant reduction in defects, leading to greater productivity.
This is especially true for robotic welding. Firmer, more consistent welds mean using less filler, smoother welding production lines and faster automation processes.
Part leveling machines can also open up new business opportunities for a company.
For example, if a company wants to serve customers in the construction industry, the roof and facades it provides must be perfectly flat. Each plate must maintain this consistency, as any non-conforming plate can interrupt installation projects.
