When the blade is blunt, the plastic deformation zone will be expanded, the crack at the blade edge happens lately, the shearing section is uneven. If the clearance between the blades is big, the blank is easy to bend, it causes the section not perpendicular to the axis; if the clearance between the blade is too small, the blade is easily damaged. If the blank is not supported well, two cracks on the direction of the upper and lower will not be parallel, the blade will tilt.
If the shearing speed is fast, the plastic deformation zone and the processing hardening are concentrated, the upper and lower cracks are in the same direction, smooth section can be obtained. When the shearing speed is slow, the situation is opposite.
In order to improve the shearing efficiency and quality, we often use high-speed shear blanking process and blue brittle* blanking process. The axial and lateral movement of cracks are eliminated by high speed shearing, and the crack growth along the circumferential direction is accelerated. The stress concentration at the tip of the cracks make the plastic zone is smaller, the brittleness of the material is increased, the plasticity is reduced.
Thus the inclination of the broken face is greatly improved. For normal medium strength carbon steel, shear speed should be controlled at 5m/s~7m/s according to the above theory.
The blue brittleness blanking is shearing rod at the blue brittleness temperature range 300℃~450℃. Shearing rod in blue brittleness temperature can get better shearing accuracy than that of the room temperature. The blue brittleness of the steel increases, the plasticity decreases, the section collapses small , the ellipticity keeps small and the heating energy consumption is greatly reduced, good blank quality and section quality can be obtained.
*Blue brittleness is steel mechanical properties change caused by deformation aging. The tensile strength and hardness of the steel are increased near 300 ℃, and the section elongation and shrinkage are decreased. The tenacity of most alloy steels with ferrite pearlite structure decrease with temperature increasing at about 300 ℃. It occurs on the steel surface with a blue oxide film, so it is called blue brittleness. Blue brittleness occurs in low alloy steels with low alloying elements annealing or normalizing.
Our
ZQ42 series Shearing Equipment and
SJ45 series Horizontal Bar Shearing Machine can use blue brittleness blanking with good quality.