What are two / four shear blade designs?
The lower blade is generally at 90°, but the upper blade is usually at 87°. This slight angle allows lower cutting force than if the upper blade has a square edge.
90° blades are called “four-edge” blades and can be turned to use all of its 4 edges. Angled blades are called “two-edge” blades and can be turned to use only 2 edges. The edges that have angles more than 90 cannot be used for shearing.
What is the clearance distance for Shear Knives?
Clearance distance is the perpendicular size between the shearing blades. Exact cutting clearance depends on plate thickness and material strength. If the cutting clearance chosen is too small, shears have to apply far more force to cut through material. If the upper and lower cutters are too far apart, less force is needed for shearing metal plate, but when the upper cutter is lowered material deformation occurs at the edges. Therefore, cutting clearance is a key factor for edge quality.
A good rule of thumb is that clearance distance should be 10% of the thickness of cutting material. For example, if cutting mostly 16 gage the clearance distance should be around .005 to .006 inches. It is important that the clearance is the same all the way across. Otherwise, you will have to shim up the loose spot.
Common steel grades for manufacturing metal cutting Guillotine Shear Blades
We use Alloy tool steel to manufacture shear blades that are subject to impact loads and require high wear resistance. Shear blades made out of Alloy Tool Steel offer improved hardness, toughness, and wear resistance.
Most shear blade manufacturers produce a variety of blades under different classifications. At MASTERCUT we use D2 (HCHC) which can be suitable for up to 1/4” steel on mechanical shears and up to 3/8″ steel on hydraulic shears. Although this blade will maintain sharpness longer than other types, it is also brittle and subject to fracturing or chipping when shearing harder metals or heavier gauges. This is due to the blades made of HCHC steel lack shock absorbing qualities.
For shears that are rated at 1/2” or heavier capacities we offer High Carbon Shock Resisting blades. A shock-resisting blade will not maintain edge sharpness as long as the D2 (HCHC), but it does provide the necessary shock resisting characteristics to withstand the loads of heavier plates. Also, this blade offers the necessary hardness to minimize the problem of chipping when shearing metals such as stainless steels or T1 plate.
Shear blades made out of Sintered Alloy have high strength and can give multiple time life compare with other types of blades. These blades are expensive, but pay off when used in a high-volume production. They are mainly used for thinner materials.
Tungsten Carbide is another steel grade that is mainly used for shear blades cutting very thin materials with precise clean edge. These blades are better to use with a minimum clearance distance (the blades almost touching each other).
How to get rid of defects and factors that influence cut accuracy..
There is a great article (we could not make it better!) please read it if you are using shearing technology.