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Sheet Metal Shear

Metal Shears

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sheet metal shear

  Trouble-free for 25 years.
"I've formed millions of pounds on this 70 ton PRESS BRAKE in the past 25 years. Its dependable, accurate and we've only changed a motor bearing.

I highly recommended it to any fabricator that wants a trouble-free press brake."

Alex Szabo, Cutting Edge Fabrication, Langley, BC

Sheet Metal Shear

One of the most complex aspects of metalworking involves the shearing process, which is highly technical, as it involves factors such as clear structure, slippage planes, brittle fracture and anisotropy. If you work with a sheet metal shear it's important to understand that both tensile stress and compressive stress are factors.

When you do a cut, a shear goes through horizontal stress, vertical stress, and torsional stress. When the knife contacts the metal you are shearing, the top surface is put under tension. At the same time, with the support of the lower knife the bottom surface is put under compression.

The elastic tolerance of the metal is exceeded at a certain point, it is stressed in shear until its maximum strength is exceeded, and then the piece breaks away completely from the parent metal. The sheared edge will be clean and close to the perpendicular if the knives are sharp and the clearance between the top and bottom knife edges are correct. So to ensure accurate shearing the crosshead and bed have to be rigid enough to resist deflection.

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During shearing there are three internal stresses working: twist, camber and bow. Twist pertains to the tendency of the off cut to spiral and curl up. This is a result of excessive rake in the knife, but it can be mitigated if the knives are sharp and the clearance and rake are set properly.

Camber is when a sheared strip has an arc while laying flat. It is not caused by rake, but rather by internal stresses, inferior material, or improper clearance. Like with twist, it occurs most severely on off cuts that are narrow. Bow is when a piece of sheared material humps in the center, which is usually caused by deficiencies in the material.

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Shears are meant to deliver precise vertical blows, just like press brakes, which is why their basic design is the same. For example, the housing is strongly constructed so as to provide the utmost structural support for the machine. Also, the bolster plate is secured to the press bed, so it can position and support the die assembly.

The bed acts as a stationary mounting surface for the lower die or blade. The ram carries the upper blade and is placed on the front of the housing, so it can maneuver vertically. Its basic design is meant for rigidity.

The drive works to give vertical motion to the slide and can either be mechanical or hydraulic. Gibs provide a sliding surface for the ram, and finally, the drive gives vertical motion to the slide – it may also be mechanical or hydraulic.

A metal sheet shear is a tool that is extremely useful in the metalworking industry, for various purposes. Like press brakes, there are many different models available for purchase.

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