Shear (sheet metal)

A panel scissors or shears is a motorized or manually operated machine tool for cutting metal sheets, plastic sheets or cardboard boxes. When cutting the sheet is just sheared between a fixed and a movable knife in one operation.

The special feature of the guillotine shear is that they are long, straight sections allows. , The cut length is generally from two meters up to 15 meters, however, are feasible. The cuttable material thicknesses depending on the design of the machine between fractions of a millimeter and 200 mm.

Before cutting the material lies on a straight Pad - the machine table - and is tensioned by the hold-down on the table in the cutting position. The lower blade is mounted flush with the table while the upper blade at gate-guided scissors just shuts down or is out at swing beam shears on a circular path.

It is important that there is a clearance between the lower and upper knives. The smaller the gap, the better the cut surface, but it also increase the necessary machining forces and thus the burden of cutting tools.

In order to obtain a right-angled to the material surface sectional area, the upper blade must shave to 3 ° through the panel, because the line of action of the shear force also is not perpendicular with an angle of 2 °. In swing beam shears this is easy to ensure by the position of the rotational axis. Plate which is pressed on the front panel remains, plan very well, while the rear is down falling section, especially if it is narrow compared to the average length, bent and twisted. To be used in this section, it must be mostly directed. Also, it is favorable to reduce the drop height with a sloping board.

The location of the cut on the sheet may be indicated by the shadow of a taut wire. Kerf and cutting angle can be adjusted and thickness of good machines depending on the material properties (aluminum, steel).

When lever guillotine shears the upper blade is bolted to a long flexible lever. The cutting is done by rapid downward pivoting of the lever by hand - only by inertia (moment of inertia ), the required high instantaneous power can be applied. The balancing of the lever is in its upper position ( open scissors - risk of accident) takes a counterweight, which also increases the flywheel. On motor with flywheel scissors is sometimes the reacceleration immediately to hear after the cut.

To protect against slipping while cutting the material is clamped by a clamp. The hold can be by hand or machine (pneumatic, hydraulic) driven. Shears have a (sometimes motorized) adjustable stop, to which the sheet is pushed before the hold-down.

Motorized Shears often have a flywheel ( flywheel ) to keep the engine power -to-install low. For safety, they have a two-hand operation.