Machinery's Handbook, 31st Edition
Shearing 1407 where F = shearing force (lb); τ = shear strength of the material (lb/in 2 ); and A = cutting area (in 2 ). The cutting area is calculated as (13a) where b = length of the cutting material (in.), and T = thickness of material (in.). A bT = This calculated shearing force needs to be increased by 20 to 40 percent, depending on whether the following conditions exist: an enlarged clearance between the blades, variations in the thickness of the material, the obtuseness of the cutting edge angles, and other unpredictable factors. The real force of the shearing machine is (14) Shearing with Straight Inclined Blades: Shears with straight inclined blades are used for cutting material of relatively small thickness compared with the width of cutting. Using inclined blades reduces the shearing force and increases the range of movement necessary to disjoin the material. The penetration of the upper blade into the material is gradual and as a result, the shearing force is lower. The shearing force can be calculated as (15) tan F n k UTS T 2 λ φ = where n = 0.75 to 0.85 (for most materials); k = 0.7 to 0.8 (ratio UTS / τ ); λ = the relative amount of penetration of the upper blade into material (Table 3); and, f = angle of inclina- tion of the upper blade. 3. Table 3. Relative Amount of Penetration of the Blade into the Material . F F 13 M =
Thickness of material T , inch (mm)
< 0.04 in. (< 1.0 mm)
0.04–0.08 in. (1.0–2.0 mm)
0.08–0.16 in. (2–4 mm)
> 0.16 in. (> 4 mm)
Material
Plain carbon steel Medium steel
0.75 to 0.70 0.70 to 0.65 0.65 to 0.55 0.50 to 0.40 0.65 to 0.60 0.60 to 0.55 0.55 to 0.48 0.45 to 0.35
Hard steel 0.50 to 0.47 0.47 to 0.45 0.44 to 0.38 0.35 to 0.25 Aluminum and copper (annealed) 0.80 to 0.75 0.75 to 0.70 0.70 to 0.60 0.60 to 0.50 The real force of the shearing machine is (16) Shearing with Rotary Cutters: The rotary shearing operation is much like shearing with straight inclined blades because the straight blade may be thought of as a rotary cutter with an endless radius. It is possible to make straight line cuts as well as to produce circular blanks and irregular shapes by this method. Fig. 4 illustrates the conventional arrangement of the cutters in a rotary shearing machine for the production of a perpendic ular edge. Only the upper cutter is rotated by the power drive system. The upper cutter pinches the material and causes it to rotate between the two cutters. . F F 13 M =
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