What advantages does roll leveling have over other methods?

Compared to other methods, roll leveling is an easy and fast way to obtain flat parts, sheets or strips with high accuracy. Manual leveling, for example, was once reserved for workers with the most extensive and longest experience, but today anyone can learn quickly and easily how to level sheet-metal parts with roll leveling machines.

 

Why is leveling necessary after lasering, plasma-cutting or punching?

Cutting by means of thermal manufacturing processes such as lasering, oxyacetylene cutting and plasma cutting introduces a great deal of heat into the material. This gives rise to a huge temperature gradient within the material, which in turn leads to edge stress and hardening. Parts and sheets cut by such methods are affected accordingly by distortion. As for punching, internal stresses in the material are released in addition to the parts being deformed by the punching operation.

 

Can all materials be leveled?

It is possible to level all metals with a fracture strain of at least five percent and a pronounced 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 can say: What can be bent can also be leveled.

 

Can hardened materials be leveled?

Yes and no. If a material has a fracture strain after hardening, then you can assume that it can be leveled within certain limits. However, high forces combined with small roll diameters are necessary to work such workpieces. If, on the other hand, the material has no fracture strain, then there is a risk of cracking or even fracturing. Only leveling tests can reveal whether leveling is at all possible and, if so, what results are likely.

 

Do the properties of a material change during leveling?

Practice indicates that no changes to mechanical properties such as yield strength or dimensions occur in ferrous metals under normal circumstances. Stainless steels differ in that they have a tendency to harden after being leveled several times. With NF metals this is not necessarily the case. With soft metals such as aluminium and magnesium there is a risk of material abrasion or lowering of the yield strength.

 

What needs to be set on a leveling machine in addition to the entry and exit values?

In principle nothing, because modern leveling machines work with bank adjustment. The leveling rolls are grouped in the upper and lower roll frame, so there is no longer any laborious feeding of individual rolls. The operator only has to set values for the machine's entry and exit. Exceptions are high-capacity leveling machines on which the deflection of the leveling rolls can be adjusted.

 

How do I find the correct setting values?

The most important setting parameter is the sheet thickness of the process material. For example, to level a 30-mm thick steel plate, the entry value must be smaller than 30 mm and the exit value must equal approximately the sheet thickness. This is only a rough guideline however. To help the user, modern machines are equipped with a proposal manager and value database which recommend specific setting values and can also be fed with new values.

 

What basic points should a sheet-metalworking company consider when buying a leveling machine?

The machine's design depends on the materials to be leveled. The key parameters of a leveling machine include the diameter, pitch and number of leveling rolls. Generally speaking: the smaller the pitch and the leveling roll diameter, the better the result. Of critical importance in this connection is that the leveling rolls are sufficiently supported against deflection. To cope with daily production, the leveling machine should also be equipped with a quick-change system for the leveling rolls. This enables easy changing of the leveling rolls and thorough cleaning of the leveling unit. Dirt or material residues in the machine not only impair the leveling results but can also damage the leveling machine.

 

Does the number of leveling rolls have a bearing on the quality of results?

The process material is subjected to mechanical alternating bends on the machine. The intensity of the alternating bends is reduced toward the machine outlet. The higher the number of leveling rolls, the greater the number of alternating bends. General speaking: the more alternating bends, the better the leveling result. At least five rolls are required to make any effect at all. However, with five rolls you can achieve only a rough level of planarity. For thin material you tend to need more leveling rolls 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.

 

After leveling the sheets they are still not flat – What can be done?

There are three main reasons for this: If the sheet-metal part is still bent in the same direction as before the leveling, then the leveling machine was set too low at the entry. The sheet-metal part is under-leveled. This can be corrected by a second pass through the leveling machine with a higher entry setting. If the sheet-metal part is bent in the opposite direction to before the leveling, then the leveling machine was set too high at the entry. The sheet-metal part is over-leveled. As a counter-measure the operator should check in this case whether the exit value corresponds to the sheet-metal thickness of the process material and if necessary lower the entry setting. It is also possible however that the sheet-metal part simply cannot be leveled on the leveling machine in question. In this case the only thing to be done is to check whether the material can be leveled on a different leveling machine or whether the material is at all suitable for leveling.