The importance of leveling parts in metal fabrication


The left part still shows a springback which prevents it from being completely flat. The right part was leveled after passing through a parts grader.

The sheet and plate delivered to a metal fabrication company looks quite flat. But appearances can be deceptive, and this is especially true with metal. What may appear flat at first glance is likely to lose its flatness during manufacture.

This makes sense when you consider what happens to the raw material before it is delivered to the store. Sheets and sheets come from rolling mills. In metal service centers, these coils are unwound, straightened and finally cut to length. Although the leaves appear flat, they still have stress inside. (The stress is evident in the grain of the material.)

When these materials are cut using a thermal energy source, such as a laser or plasma cutting machine, the stress is released and the results are evident. The parts become uneven. This goes for thin and thick metal parts.

This also applies to ferrous and non-ferrous parts. The use of assist gas when cutting indeed plays a big role in this process. For example, when oxygen is used to cut carbon steel, the oxygen reacts with the metal in an exothermic reaction. This introduces a large amount of heat into the cutting area, which allows the cutting process to take place quickly. (The by-product of this chemical reaction is an oxidized edge, which must be cleaned to allow the paint to adhere.) However, the extra heat also releases more stress in the metal. Cutting with nitrogen, an inert gas, reduces the heat input compared to oxygen, but even with the milder process, the stresses are still released.

This can become particularly inconvenient for the fabrication shop with the new laser cutting technology as some parts can tip over on the slats after being laser cut and become an obstacle for the cutting head, especially when cutting speeds reach 30 m / min. or more and an acceleration of more than 2 m / s² has become the norm. A very expensive piece of manufacturing technology runs the risk of being destroyed by an uneven part on the cutting bed.

Any cutting process is capable of releasing the stress introduced first during winding. This stress is probably most evident in the springback of metal after cutting or punching. (Punching works the material to the point that additional stress is released in the material. This can be seen on newly punched parts, for example.)

Combat material constraints

What should metal manufacturers do to combat the stresses introduced during winding and released after parts are cut or punched? This is where a coin leveling machine can help. It can provide flat parts for applications where it is absolutely necessary that downstream manufacturing processes receive leveled parts to ensure higher productivity and less scrap during bending and welding.

A workpiece leveling machine ensures flatness through a series of rollers that apply pressure to the sheet or plate. The rollers work the material as it passes through the machine. The intensity of the pressure applied to the material reduces and eventually eliminates the stresses that are introduced at the metal service center.

How are these rolls organized? It depends on the material, material thickness and desired specifications. The variables of a workpiece leveling machine include:

  • The number of rollers.
  • How the rollers are spaced in the machine.
  • How the rolls are arranged and supported.
  • Rigidity of the roller frames and the whole machine.
  • Roller support (supported length, arrangement of rollers).
  • A gap control system and its ability to keep the gap stable.
  • Efficiency of electric power consumption.
  • Easy to clean leveling and support rollers and machine maintenance.

The leveling process can provide a high degree of precision, but it really depends on the application, thickness and type of material. For example, a leveler can provide flatness of 0.5mm / m to 1mm / m for parts intended for cranes and mining equipment and this would be considered very good. This flatness, however, would not work for a manufacturer of saw blades, which require 0.1mm / m or better. Fortunately, the same part leveling machine that supplies parts acceptable to the heavy equipment maker can produce even more high tolerance parts for the saw blade maker.

This is how the leveling process works.

By lengthening the metal, the rollers of the machine de-stress and flatten the parts.

As for the size of the parts to be leveled, it all depends on the diameter of the roller. Each roll diameter in combination with the roll spacing and the design of the roll frame, media roll and machine frame has its specific operating window. In general, small roll diameters are used for thin materials and larger rollers are used for thicker materials. Leveling machines can generally flatten parts from 0.2mm to almost 70mm.

The leveling of parts can also be very nuanced. For example, manufacturing companies in the aerospace industry often work with aluminum. A thick part for these workshops is 5mm which could be considered thin for a manufacturer working on mining equipment. This aluminum stock is often heat treated to help the material achieve greater strength. After heat treatment, the aluminum is soft and maintained at temperatures of -18 degrees C (0 degrees F). If parts are instantly leveled after cutting, the part leveler faces two main challenges. First, the material is soft, so the rollers should be soft to avoid deforming it. Second, cold parts interacting with a higher ambient temperature can introduce condensation to the surfaces of the parts, so the components of the leveling machine should be made of stainless steel or coated steel to prevent corrosion.

Handling difficult materials

Workpiece leveling machines produce a simple result, but they are complex machines. For this reason, they can handle materials that are difficult to form.

Examples include perforated and heat treated materials. Both often exhibit medium or edge waves. Special measures and techniques are required to flatten parts or sheets.

For (some) perforated sheets and heat treated materials, advanced roller control is used to increase leveling pressure in some areas and to reduce pressure in others. With this controlled leveling process, the material elongates in the longitudinal direction if necessary. Medium and edge waves can be reduced or even suppressed.

Another difficult material to handle is the high tensile strength material. In this case, a high capacity machine is needed. Very large roller diameters are combined with corresponding roller spacing to reduce this material stress and provide good flatness.

What about the operator’s experience?

Any advanced manufacturing technology will require a committed operator. This is where an experienced, but above all curious, operator can make a real difference. If it is willing to spend time tweaking and testing parts to achieve good leveling results, the fabrication shop can benefit from efficient level part processing and better results in the leveling business. downstream manufacturing.

In theory, leveling is a straightforward and easy process. In addition to the speed of the roller, an operator only has to adjust two other parameters: the leveling deviation at the entry and exit and the angle of introduction of the part into the machine. By finding the right combination, the operator can optimize leveling results.

Of course, calculation tools built into the equipment controls can help. When entering thickness, yield strength and material type, the control offers leveling parameters. Usually these settings can provide good results, but if the operator is looking for better results, they now have a baseline to start tweaking.

Reap the benefits

Leveling parts can help metal fabricators increase their throughput and productivity. Reports from metal fabrication companies that incorporate a part leveling machine into their operations indicate that after part leveling, they are about 25% more productive in their bending operations. Leveled parts bend more precisely, which means less rework and more consistency. In the welding department, this results in parts that fit into simple jigs and have constant gaps. The welders are happy. The result is less scrap and increased productivity.

The interior plan of a workpiece leveling machine is shown.

This interior shot of a parts grader shows the rollers and the electromechanical leveling system that flattens the parts.

This is especially true with robotic welding. Tighter, more consistent spaces allow less filler yarn to be used, smoother stitch lines, and a faster automated process.

Part leveling machines can also create new opportunities for a business. For example, if a company wishes to serve architectural clients, the fabrications of ceilings and facades must be absolutely flat. It is a necessity for every part because a non-conforming part can stop an installation.

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