Performed by forcing an upper blade and lower blade past each other with a desired offset. Typically, one blade is stationary. The workpiece is placed between an upper vertical blade and a lower stationary blade.
The upper blade forces the workpiece against the lower blade, shearing the metal. A shear normally consists of a shear table, shear blades (upper and lower), workpiece holding devices, and gaging devices. The gage insures consistent lengths. The hold-down devices hold the workpiece in position, in addition to preventing workpiece edge buckling during the cutting process.
The first step in fabricating a sheet metal component is cutting the piece to size. Shearing machines and shearing machinery perform this function. Some shearing machines use a scissor-like, angular shear action to cut metal into sheets or strips. Larger machines use a straight shear action with the blade fixed at an angle as opposed to the angular movement.
The angular configuration of the blades is called the rake. Both rake and clearance are a function of the type and thickness of the material to be cut. The typical shear consists of a fixed bed to which one blade is mounted, a vertically advancing crosshead and a series of hold-down pins or feet that hold the material in place while the cutting occurs. A gauging system with stops is used to produce specific workpiece finish sizes.
There are three different types of systems used. Those for sheet/plate material, those for angles, and those for bar stock. Squaring and bow-tie shears are for sheet and plate material. Angle and bar shears are for angle and bar stock materials. In general, most shearing systems have both a stationary and moveable blade the shears the workpiece. Shearing operations are done with the action of two blades, one fixed in the shear bed and the other moving vertically with little or no clearance.
The shear angle of the upper blade is the most important factor of shearing and is denoted as the amount of rise in inches per feet. The shear angle should be kept as low as possible to reduce the amount of distortion in narrow workpieces. While the upper blade is mounted at an angle or slope with respect to the horizontal lower blade, only basic straight-line cutting or flat sheet stock can be performed with a shear.
Several types of shearing machines can be used to meet your specific needs. Air/pneumatic shears, which use pneumatic cylinder to power the crosshead and upper blade. Manual shears, which are driven or powered by hand or with manual force that is magnified with screw, lever or another mechanism. Servo driven shears, they are driven by a direct connection to a servo motor.
Mechanical shears, have a moving blade driven by a rotary motor through a screw, toggle, lever or other mechanism. Hydromechanical shears, are driven by a hydraulic cylinder or hydraulic motor. Hydraulic shears, which are driven or powered by a hydraulic cylinder. Hydraulic presses can generate extremely high forces to cut metals or other materials.