Leveling sheet metal: how to eliminate internal stress in the workpiece after laser cutting

07/9/2019 | Leveling |

Businesses, industries and commerce primarily focus on three things: quality, delivery time and efficiency. Only companies in control of their processes will successfully prevail against the competition over the long term. The same applies to the metalworking industry. Raw materials in ideal condition for further processing are a key factor here. However, sheets are often out-of-flat and have internal stresses. These defects impair the efficiency of downstream processing. That is why leveling the parts after processing, for example laser cutting, is essential. Read this article and find out all about leveling sheet metal along with the factors you need to consider.

Out-of-flat sheets with internal stresses impair efficiency

Stress-relieved sheets are essential for all downstream production processes in sheet metal fabrication. However, internal stresses are an almost inescapable byproduct of the processing. Laser cutting in particular is notorious for creating and releasing these stresses. The cutting laser generates a vast amount of heat where it hits the material. This, in turn, creates a massive temperature gradient resulting in internal stresses. In addition, this cutting process also hardens the edges. The consequence: deformed parts. These are problematic when it comes to efficient downstream processing. The only solution: you have to level the sheets.

Leveling sheets which are about to be laser cut is important in order to minimize scrap and the amount of effort involved in rework. The objective is to significantly reduce both internal stresses and flatness defects. Roller leveling is a proven approach in this regard. But remember: not all roller levelers are made equal. Specific characteristics and features of the machines ensure consistent leveling quality. These include the block design of the leveling unit, the correct roller configuration, the amount and quality of the support rollers, and the number and diameter of the leveling rollers. Small leveling rollers, a small roller pitch, a large number of leveling rollers, and very good support are essential to fulfill the demanding flatness requirements.

Leveling sheet metal with the roller leveler – How it works

In the field of forming technology, roller leveling generally refers to a bending process using rotating tools. In other words, roller leveling is a bending process that utilizes rollers. It is an excellent means of rapidly and easily flattening sheet metal. This approach reduces the stresses and flatness defects by means of elastic-plastic alternating bending. When using a roller leveler, the panels run through a series of alternating bends. The machine’s leveling rollers are arranged with an offset from the infeed to the outlet. As a result, a roller can always sit in between two opposite rollers, subjecting the material to large and then progressively smaller alternating bends. This bending process resembles a diminishing sine wave.

The alternating bending movements when using a roller leveler achieve flat parts which are nearly free of internal stresses. This is critical for efficient and problem-free downstream processing. It is important that the bending of the part at the machine infeed is larger than the largest existing bend. This is the only way to ensure that the alternating bending has optimum sufficient effect on the material being leveled. The leveling process eliminates the internal stresses and flatness defects, creating a leveled part. At the same time, the roller leveler has no effect on flat sections of the part. These remain unchanged.

Roller leveling for greater efficiency

Roller leveling is the cost-effective approach for material thicknesses between 0.1 mm and 50 mm (0.004” – 2”). Panels with reduced internal stresses can generally be leveled in one run in a matter seconds. Multiple runs may also be necessary depending on the geometry. Yet even if a part has to be run through the leveler twice, roller leveling is still a rapid and, thus, cost-effective process. For example:

Imagine that you had to level 30,000 parts per year. Manual leveling carried out by an employee with a press brake would require 10 minutes per part. In contrast, a roller leveler completes the task in less than one minute. At a cost of $65 per hour for the manual leveling and $150 per hour for machine leveling, this would deliver a cost reduction of $250,000 per year. A quarter of a million simply by leveling your parts with the proper machine. It is obvious that roller leveling represents a simple, rapid and, above all, economical approach to sheet metal leveling in comparison to other methods.

Leveling sheet metal and achieving the highest quality

In addition to the cost aspect, the quality of manual sheet metal leveling can also be a disadvantage. People are not machines. Their working processes cannot be 100% standardized and therefore no two parts will have the same flatness results. Leveling manually, which relies on human capabilities, cannot guarantee consistent quality. Additionally, the specialists who can accomplish this task are also rare. In comparison, a roller leveler ensures reliable results. The leveler should also ideally be equipped with overload protection to guarantee a long service life. Hydraulic systems have proven their value in this regard. These hydraulics enable a safe work environment while dealing with extreme forces. They also enable essentially wear-free leveling gap control. These systems hold the machine in position during the leveling process, regardless of the forces generated. This ensures the best-possible results.

All of the characteristics of high-quality levelers combine to ensure rapid and good quality leveling results with reliable processes. Modern roller levelers automatically calculate the right settings so that the operator only needs to make minor corrections. Machines are now also capable of checking the flatness, which enables automated leveling for numerous applications.

Eliminate internal stresses to create high-quality parts

In summary, leveling parts with a roller leveler is one of the fastest, easiest and cost-efficient methods of leveling. It ensures high-quality sheet metal parts. This is a key factor for sheet metal processing.