If you have questions, we have the answers.
Do you have any questions about the benefits of a roller leveler or our roller leveling equipment? We have compiled the answers to our customers’ most frequently asked questions about roller leveling.
Which leveling methods exist?
Hammer and flame
A conventional flattening technique. The part is heated and then hammered into a flat condition. This technique is very time consuming and requires highly skilled workers.
Fabricators also use rolling machines to remove rough flatness defects. Tight flatness requirements cannot be achieved with this procedure as internal stresses remain in sheet metal parts. Handling is very challenging for large and heavy flame-cut parts. Time requirements can easily exceed 25 minutes per part.
The same is true for straightening presses commonly used for laser and flame-cut parts. Time requirements of 20 minutes per part are not unusual.
Roller leveling is essentially a bending process. The out of flat part, sheet or plate is deformed by a series of alternating bends. These alternating bends are created by passing the part, sheet, or plate between upper and lower sets of leveling rollers. The leveling rollers are offset by half of the roller pitch in the direction of the traveling material. As a result, the sheet metal takes a wave-like path through the precision leveler. This wave should be greatest at the entry into the machine and smallest at its exit (comparable to a decaying sinusoidal curve). The elastic-plastic alternating bends and the constant decline of bending intensity thereby produce flat and nearly stress-free parts, sheets and plates.
Servo-hydraulic precision levelers
Servo-hydraulic precision levelers meet high expectations and achieve the tightest tolerances. An example is the ARKU FlatMaster®. The leveling rollers are spaced with minimal roller pitch and have excellent support. The leveling gap control feature maintains a constant leveling gap even with varying widths and cut-outs. In combination with small roller diameters these features provide dead-flat and stress-relieved parts in just one pass.
What advantages does roller leveling have over other methods?
Other methods are time consuming and do not release as much stress. Roller leveling is an easy and fast way to obtain flat parts, sheets or strips with the highest precision. Manual flattening, for example, was once reserved for workers with the most extensive and longest experience, as it requires a lot of skill. Today anyone can learn quickly and easily how to level sheet metal parts with roller levelers.
High time savings with a roller leveling machine
|Calculation time expenditure||Method 1:
Leveling with roller leveler FlatMaster® 120
|Number of parts to be leveled per year||30.000||30.000|
|Expenditure of time per part in minutes||20||2|
|Overall time expenditure per year
|Calculation of the hourly rate||Method 1:
Leveling with roller leveler FlatMaster® 120
|Collaborators per machine and working shift||2||2|
|Hourly rate (full costs) in EUR||65,--||150,--|
|Overall costs for leveling per year in EUR
Savings potential of using a roller leveler: ca. 500.000 EUR per year.
Note: This is a simplified extract of the ARKU calculation tool for economic efficiency of precision levelers for parts. Individual calculations can be conducted on request.
Does the number of leveling rollers affect the quality of the results?
The process material is subjected to mechanical alternating bends in the machine. The intensity of the alternating bends is reduced towards the leveling unit outlet. The higher the number of leveling rollers, the higher the number of alternating bends. General speaking: the more alternating bends, the better the leveling result. At least five rollers are required to trigger any effect at all. However, with five rollers you can achieve only a rough level of flatness. For thin material you tend to need more leveling rollers than for thick material. Experience indicates that at least 11 to 13 rolls are needed on parts leveling machines in order to achieve good tolerances.
Why is leveling necessary after lasering or plasma-cutting or after stamping?
Thermal manufacturing processes such as laser, oxy-fuel or plasma cutting introduce a great deal of heat into the material. The resulting temperature gradient within the material leads to stresses and edge hardening. Parts and sheets cut by such methods are distorted.
As for stamping and perforating internal stresses in the material are released in addition to the parts being deformed by the punching operation.
What should a sheet-metal fabricator consider when buying a leveler?
The machine's design depends on the materials to be leveled. The key parameters of a leveling machine include the diameter, the roller pitch and the number of leveling rollers. Basically: the closer the roller pitch and the smaller the leveling roller diameter, the better the result. Essential is a sufficient support of the leveling rollers against deflection. To cope with daily production, the leveler should also be equipped with a quick-change system for the leveling rollers. This enables easy changing of the leveling rollers and thorough cleaning of the leveling unit. Dirt or material residues in the machine can degrade the leveling results and cause more wear on parts in the leveling unit.
Can all materials be leveled?
It is possible to level all metals with an ultimate elongation of at least five percent and a distinct yield strength. If these values are unknown, a material's suitability for leveling can be determined by leveling tests. As a rule of thumb we say: “if you can bend it, you can level it”.
Can hardened materials be leveled?
Yes and no. If the material has an elongation at fracture after hardening, you can assume it can be leveled to a certain degree. However, high forces combined with small roll diameters are necessary to work such material. If the material has no elongation at fracture, there is a risk of initiating cracks or even fractures. Only leveling tests can indicate whether leveling is possible and what the results will be.
Does roller leveling change the material properties?
No changes to mechanical properties such as tensile strength or dimensions occur in ferrous metals under normal circumstances. Stainless steels differ, tend to harden after being leveled several times. This -is not necessarily valid for non-ferrous metals. Particularly soft metals such as aluminum and magnesium have a risk of material abrasion or lowering the yield point.
Sheet metals and sheet metal parts.
Why level sheet metals and sheet metal parts?
Various causes create internal stresses and shape issues in sheet metal:
- Residual stresses from the rolling mill
- Mechanical and thermal cutting
Such defects and shape issues are problematic for subsequent processes.
What happens when unleveled sheet metal parts are processed?
Bending parts that are out of flat results in dimensionally inaccurate parts causing rework and scrap.
Welding preparation for out of flat parts is generally cumbersome and time consuming. Welding warped parts with the use of welding robots reduces process reliability and increases set-up and welding times, which leads to increased costs and additional problems with heat influences. Heat from welding releases stresses in parts causing additional problems with process reliability, re-work and scrap.
Why level out residual stress and flatness defects in coils?
The most common flatness defects are coil set and cross bow. Coil defects mostly arise during the milling process or the following cutting operation.
Plastic deformation in the re-coiling process causes coil set. Crossbow is created by an uneven cooling of the rolling stock across the strip width (residual stress) or slitting.
In summary, coil defects are usually caused by the rolling process in the mill or by subsequent cutting or slitting processes.
What happens when unleveled coils are processed?
Stamping and punching
Coil defects and internal stresses complicate subsequent forming processes. This typically results in lower quality products and can even potentially result in a damaged die. Furthermore, coil defects can cause machine down time and reduce machine availability.
Cutting and blanking
Cutting processes release internal stresses, which results in visible deformations of the material. These coil defects hinder accurate cutting and blanking. Because these blanks are usually subsequently processed, the flatness is a crucial quality criterion.
Roll Forming is a continuous bending operation of a metal strip. Consecutively aligned roller stands form the material into the desired shape. Residual stresses and coil defects hinder a specific and accurate forming of the metal strip. The high process velocity of such roll forming lines in combination with coil defects significantly impacts the process reliability.
Setting up a roller leveler
What needs to be set on a leveler in addition to the entry and exit values?
In principle nothing, because modern leveling machines work with bank adjustment. The leveling rollers are summarized in the upper and lower roller mill and no longer need to be adjusted individually. The operator only has to modify values for the inlet and the outlet of the machine. Exceptions are high capacity levelers, where even the deflection of the leveling rollers can be adjusted.
How do I find the correct setting values?
The most important setting parameter is the material thickness . For example, to level a one inch thick steel plate, the entry is closed deeper than one inch and the exit value is set approximately equal to the plate thickness of one inch. This is only a rough guideline. Advanced levelers are equipped with a setting database helping the operator by recommending specific settings and new settings can be added to the database as well.