Shearing (manufacturing)

Shearing, also known as die cutting, is a process which cuts stock without the formation of chips or the use of burning or melting. Strictly speaking, if the cutting blades are straight the process is called shearing; if the cutting blades are curved then they are shearing-type operations. The most commonly sheared materials are in the form of sheet metal or plates, however rods can also be sheared. Shearing-type operations include: blanking, piercing, roll slitting, and trimming. It is used for metal, fabric, paper and plastics.

Principle

A punch (or moving blade) is used to push a workpiece against the die (or fixed blade), which is fixed. Usually the clearance between the two is 5 to 40% of the thickness of the material, but dependent on the material. Clearance is defined as the separation between the blades, measured at the point where the cutting action takes place and perpendicular to the direction of blade movement. It affects the finish of the cut (burr) and the machine's power consumption. This causes the material to experience highly localized shear stresses between the punch and die. The material will then fail when the punch has moved 15 to 60% the thickness of the material, because the shear stresses are greater than the shear strength of the material and the remainder of the material is torn.

Two distinct sections can be seen on a sheared workpiece, the first part being plastic deformation and the second being fractured. Because of normal inhomogeneities in materials and inconsistencies in clearance between the punch and die, the shearing action does not occur in a uniform manner. The fracture will begin at the weakest point and progress to the next weakest point until the entire workpiece has been sheared; this is what causes the rough edge. The rough edge can be reduced if the workpiece is clamped from the top with a die cushion. Above a certain pressure the fracture zone can be completely eliminated. However, the sheared edge of the workpiece will usually experience workhardening and cracking. If the workpiece has too much clearance, then it may experience roll-over or heavy burring.

Shearing Operations

This section describes various operations that are based on shearing process. In punching, the sheared slug is generally discarded in blanking, the slug is part itself and the rest is generally scrap later to be recycled. The following processes are commonly sharing operations :

1.Die Cutting

Die-cutting refers to the operation, where the parts produced have a wide variety of uses (a)Perforating is punching several holes in a sheet;(b)Parting sharing the sheat into two or more pieces; (c)notching is removing pieces of various shapes from the edge of a sheet (d) slitting, and lancing involves leaving a tab on the sheet without removing any material.

2.Fine blanking

Very smooth and square edges can be produced by fine blanking. A basic die design in which a have V-shaped stringer (impingement) locks the sheet tightly in place and prevents the type of distortion of the material. Fine blanking involves clearance on an order of 1% of the sheet thickness, as compared with as much as 8% in ordinary shearing operations. The thickness of the sheet typically ranges from 0.5 to 13mm with a dimensional tolerance of ⍊0.5mm. Fine blanking is usually carried out on triple-action hydraulic presses, triple meaning that the movement of the punch, pressure pad and die are controlled separately.

3.Slitting

Slitting is a shearing operation, typically carried

out with a pair of circular blades, similar to those on a can opener. The blades follow either a straight line or a circular or curved path. Straight slitting is commonly used in cutting wide sheets, as delivered

by rolling mills, into narrower strips for further processing into individual parts. Slitting operations may cause various planar distortions of the slit part or strip. Also, a slit edge typically has a burr which can be rolled over the sheet's edge using a set of rolls. There are two basic types of slitting equipment:(a) the driven type, in which the blades are powered; and (b) the pull through type , in which the strip is pulled through idling

4.Sheet rulers

Sheets of soft metals, thermoplastics, paper, leather and

r, and

rubber can be blanked into various shapes

rubber can be blanked into various shapes using steel-rule dies. Such a diet consists of a hardened steel blade that is first bent to the shape to be sheared (similar to a cookie cutter) and then supported on a flat base. The die is pressed against the sheet and cuts to the shape of the steel rule.

5.Nibbling

lades.

4. Steel rules

lastics, paper, leather, and

Sheets of soft metals, thermoplastics, paper, leather, and

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rule dies. Such

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pull-through type, in whh idling blades.

5.Nibbling

In this operation, a machine called a nibbler moves a straight punch rapidly up and down into a matching die cavity. The sheet is fed through the punch die gap, making several lapping holes; this operation is similar to making a large elongated several other ver holes by successively punching several closely-spaced holes with a paper punch. Intricate slots and notches can thus be produced using standard punches; the sheet can be cut along any path by manual or automatic control. The nibbling process is economical for small production runs.

In this operation, a machine called a nibbler moves a straight punch rapidly up and down into a matching die cavity. The sheet is fed through the punch die gap, making several lapping holes; this operation is similar to making a large elongated several other ver holes by successively punching several closely-spaced holes with a paper punch. Intricate slots and notches can thus be produced using standard punches; the sheet can be cut along any path by manual or automatic control. The nibbling process is economical for smallr, and

rubber can be blanked ich

a diet consists of a hrst bent to the shape

to be s

In this operation, a machine called a nibbler moves a straight punch rapidly up and down into a matching die cavity. The sheet is fed through the punch die gap, making several lapping holes; this operation is similar to making a large elongated several other ver holes by successively punching several closely-spaced holes with a paper punch. Intricate slots and notches can thus be produced using standard punches; the sheet can be cut along any path by manual or automatic control. The nibbling process is economical for small

Tool materials

• Low alloy steel is used in low production of materials that range up to 0.64 cm (1⁄4 in) thick
• High-carbon, high chromium steel is used in high production of materials that also range up to 0.64 cm (1⁄4 in) in thickness
• Shock-resistant steel is used in materials that are equal to 0.64 cm (1⁄4 in) thick or more

Tolerances and surface finish

When shearing a sheet, the typical tolerance is +0.1 inch or −0.1 inch, but it is feasible to get the tolerance to within +0.005 inch or −0.005 inch. While shearing a bar and angle, the typical tolerance is +0.06 inch or −0.06 inch, but it is possible to get the tolerance to +0.03 inch or −0.03 inches. Surface finishes typically occur within the 250 to 1000 microinches range, but can range from 125 to 2000 microinches. A secondary operation is required if one wants better surfaces than this.

See also

• Alligator shear
• Shear (sheet metal)
• Stamping (metalworking)

References

General sources

• Degarmo, E. Paul; Black, J. T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, ISBN 0-471-65653-4.
• Todd, Robert H.; Allen, Dell K.; Alting, Leo (1994), Manufacturing Processes Reference Guide, Industrial Press Inc., ISBN 0-8311-3049-0.
• Wick, Charles; Veilleux, Raymond F. (1984), Tool and Manufacturing Engineers Handbook: Forming (4th ed.), SME, ISBN 978-0-87263-135-9.

External links

• Shearing Capacity Guide