Shearing metal sheet
In metal sheet/plate shearing, unlike bending, instead of bending, the material is cut along its whole length. Our sheet metal guillotine can cut metal sheets and plates up to a length of 8,000 mm. The machine develops a maximum pressing force of 600 tonnes. Shears each have two cutters, and the bottom cutter is permanently connected to the table. The moveable upper cutter is guided along a vertical link. The cutters are arranged so that a cutting clearance is created between the blades. Guillotines each have two cutters, and the bottom cutter is permanently connected to the table. The moveable upper cutter is guided along a vertical link.
The correct cutting clearance
An important quality characteristic for metal sheet shearing.
The width of this gap should always be selected as small as possible. If the upper and lower cutters are too far apart, less force is needed for shearing metal sheet/plate, but when the upper cutter is lowered material deformation occurs at the edges. These then have to be straightened and deburred in a further step. If the cutting clearance chosen is too small, shears have to apply far more force to cut through materials.
This results in a greater load on the machine and cutters. In order not to overload our machines and nonetheless achieve very good cutting quality, the optimum cutting clearance has to be chosen depending on the material and sheet or plate thickness.
With our CNC-controlled machines, only the material and sheet thickness have to be chosen. The upper cutter is positioned at an optimum distance from the bottom cutter. Before shearing the material is placed on the machine table and moved into the correct position. CNC-controlled stops (gauges) help to quickly align the sheets on the shearing table. With older shears a wire illuminated from above is used; it throws a shadow on the metal sheet panel, when the workpiece is inserted.
The metal sheet or plate is clamped with a hold-down and is therefore secured against possible slipping. If very long and narrow sheet metal strips are required, the shear forces that act on the metal can cause deformations. Only the material behind the upper cutter is affected by this effect, as the part in front of the cutter is fixed by the hold-down. As there is no hold-down attached behind the cutter, twisting or torsion can occur, with which the cut sheet metal strips are highly deformed. A small cutting clearance is decisive to cut narrow sheet metal parts without twisting.
What problems can occur during cutting?
If very long and narrow sheet metal strips are required, the shear forces that act on the metal can cause deformations. Only the material behind the upper cutter is affected by this effect, as the part in front of the cutter is fixed by the hold-down.
As there is no hold-down attached behind the cutter, twisting or torsion can occur, with which the cut sheet metal strips are highly deformed. A small cutting clearance is decisive to cut narrow sheet metal parts without twisting.
In which cases is laser cutting better than shears?
The choice of which method to use depends on several factors:
- What material length do you need for your workpieces?
We can cut metal sheets and plates up to a length of 16,000 mm with a Laser. Shorter sheet metal blanks up to 8,000 mm can also be cut using a sheet metal guillotine.
- What quality must the cut edge have?
The fact is that with sheet metal shearing only a third of the material is actually cut. The rest is torn off by the upper cutter through mechanical stress. This causes sharp burrs on the cut edges, which may have to be removed. In several jobs this can be ignored. If quality is not so very important, shearing is the fastest and most inexpensive alternative. Metal blanks cut by laser, especially with sheet metals, produces perfect material edges, which do not have to be reworked. In the case of thicker materials (metal plates), this advantage is unfortunately lost, as then the edges have to be reworked.
- Speeds of the different methods
The speed of the laser cut reduces steadily with increasing material thickness. Especially with metal plate, it can make sense to cut the plates to size with our plate shears or guillotines. In the case of sheets, lasering is far better than shears, as blanks can be cut faster, with unbeatable precision and cleanly.
- Comparison of the energy expended during cutting
Laser cutting uses up a lot of energy. Operating 4,000 and 6,000 watt cutting heads requires a considerable amount of energy. Adding nitrogen as an oxidation inhibiting shielding gas is an economic cost, which is not necessary at all with metal sheet or plate shearing. The energy requirement is also less for shearing, as the mechanical force is increased by flywheels and the cutting takes place mechanically.
- Combination with other production steps
Subsequent machining steps should also not be ignored. It is often necessary to make holes and cutouts in cut metal sheets or plates. In this case, after shearing, the workpieces must be taken to the Milling machine for further machining. Valuable time is lost as a result. This transport is not necessary with laser cutting, because the laser not only cuts the blank but also makes any cutouts and holes in the same work operation.
Which method should be used?
Shearing or laser cutting? In some cases, this is not an easy decision to make. The method chosen depends on the type and thickness of material. Our CAD employees choose the optimum machining method for your order, so that you receive your blanks as quickly as possible and in top quality.
What types of sheet metal shears are there?
A differentiation can be made between two different types of shears.
Variable rake plate shears
In the case of variable rake plate shears (also called variable rake guillotine) the cutting process takes place by guiding upper cutter straight through the material. It is important that the upper cutter does not cut through the metal sheet panel absolutely vertically. The line of action of the shear force is not at right angles, but deviates by around two degrees. If the upper cutter us adjusted to this deviation by cutting through the material with this angle too, this balances out this deviation and results in a right-angled material edge.
Swing beam shears
In the case of swing beam shears the upper cutter is not guided by a link straight through the material, from the top down. The swing beam cut involves a circular movement. The cutter touches the material at right-angles with an extremely small cutting clearance. Due to the circular cutting movement, during cutting the upper cutter distances itself from the bottom cutter, so that the difference in shearing force is balanced out automatically and a straight cut results. This cutting method is particularly suitable for thick metal plates.