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Shearing (metalworking)
Encyclopedia
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 in metalworking and also with paper and plastics.
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.
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Stock
The capital stock of a business entity represents the original capital paid into or invested in the business by its founders. It serves as a security for the creditors of a business since it cannot be withdrawn to the detriment of the creditors...
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
Sheet metal
Sheet metal is simply metal formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes. Countless everyday objects are constructed of the material...
or plates, however rods can also be sheared. Shearing-type operations include: blanking
Blanking (metalworking)
Blanking and piercing are shearing processes in which a punch and die are used to modify webs. The tooling and processes are the same between the two, only the terminology is different: in blanking the punched out piece is used and called a blank; in piercing the punched out piece is...
, piercing, roll slitting
Roll slitting
Roll slitting, also known as log slitting, is a shearing operation that cuts a large roll of material into narrower rolls. The log slitting terminology refers back to the olden days of saw mills when they would cut logs into smaller sections. They would also use these saw mills to cut iron rods...
, and trimming. It is used in metalworking and also with paper and plastics.
Principle
A punch (or moving blade) is used to push the workpiece against the die (or fixed blade), which is fixed. Usually the clearance between the two is 5 to 10% 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 strengthShear strength
Shear strength in engineering is a term used to describe the strength of a material or component against the type of yield or structural failure where the material or component fails in shear. A shear load is a force that tends to produce a sliding failure on a material along a plane that is...
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.
Straight shearing
The processes of straight shearing is done on sheet metal, coils, and plates. It uses a guillotine shearShear (sheet metal)
-Bench shear:A bench shear, also known as a lever shear, is a bench mounted shear with a compound mechanism to increase the mechanical advantage. It is usually used for cutting rough shapes out of medium sized pieces of sheet metal, but cannot do delicate work. For the small shear, it mostly...
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Tool materials
- Low alloy steelLow alloy steelAlloy steel is steel that is alloyed with a variety of elements in total amounts between 1.0% and 50% by weight to improve its mechanical properties. Alloy steels are broken down into two groups: low-alloy steels and high-alloy steels...
is used in low production of materials that range up to 1/4 in. thick - High-carbon, high chromium steel is used in high production of materials that also range up to 1/4 in. in thickness
- Shock-resistant steel is used in materials that are equal to 1/4 in. thick or more
Tolerances and surface finish
When shearing a sheet, the typical tolerance is +0.1 or -0.1, but it is feasible to get the tolerance to within +0.005 or -0.005. While shearing a bar and angle, the typical tolerance is +0.06 or -0.06, but it is possible to get the tolerance to +0.03 or -0.03. 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 shearAlligator shearAn alligator shear, historically known as a lever shear, is a metal-cutting shear with a hinged jaw, powered by a flywheel or hydraulic cylinder. Alligator shears are generally set up as stand-alone shears, however there are types for excavators. The jaw size can range from long...
- Category:Machine tool builders
- Shear (sheet metal)Shear (sheet metal)-Bench shear:A bench shear, also known as a lever shear, is a bench mounted shear with a compound mechanism to increase the mechanical advantage. It is usually used for cutting rough shapes out of medium sized pieces of sheet metal, but cannot do delicate work. For the small shear, it mostly...
- Stamping (metalworking)Stamping (metalworking)Stamping includes a variety of sheet-metal forming manufacturing processes, such as punching using a machine press or stamping press, blanking, embossing, bending, flanging, and coining. This could be a single stage operation where every stroke of the press produce the desired form on the sheet...