Crooking (Straightness—Fig. 4)

This defect, related to strip width and thickness, as well as to material strength and the previous cold-rolling direction (residual stresses), results in a workpeice curved along its plane (the surface stays flat).

To reduce crooking, fabricators should reduce the shearing angle and perform precuts along the rolling direction.

Crooking also results from using a guillotine shear, with the blade ram only supported at its ends rather than over its entire length. During shearing, the blade becomes crooked due to the cutting force and will tend to open in the center.

To eliminate the root cause of this problem, select a shear with adjustable blade pads that will oppose this deflection and keep the blade perfectly linear.

Bowing (Fig. 5)

Here, the workpiece no longer is flat—its edges raise from the plane and the material bows. This defect results from improper cutting angle and excessive workpiece-material strength.

To reduce this effect, fabricators should reduce the shearing angle and use a back support to hold the workpiece.

Poor Edge Quality

During shearing, material initially deforms plastically in a very small region (H in Fig. 6), causing a residual deformation. Afterward, the upper blade penetrates the material and forms a clean zone (I), exhibiting neat and regular cutting.

Close to the end of the shearing action, material gives in and cracks, producing a rough and irregular surface known as the fracture zone (J), which extends into the edge burr (K). The fractured zone often is not perpendicular to the plate but occurs at a variable angle (L).

To improve edge quality, focus on adjusting the blade clearance and on controlling blade wear. MF

Article submitted by Gasparini; www.gasparininorthamerica.com.

Industry-Related Terms: Burr, Center, Draw, Edge, Lines, Plastic Deformation, Plate, Ram, Shearing, Strips, Stroke, Surface, Thickness, Twist
View Glossary of Metalforming Terms

 

See also: Gasparini North America

Technologies: Coil and Sheet Handling

Comments

Must be logged in to post a comment.
There are no comments posted.

Subscribe to the Newsletter

Start receiving newsletters.