China Yawei Sheet Metal Shearing And Bending Machines

China Yawei Sheet Metal Shearing and Bending Machines

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China sheet metal press brake manufactures suppliers

China sheet metal bending machines manufactures uppliers

Shearing and Bending Machines Anhui Yawei Made in China
The two most basic and oldest metal working operations are shearing and
bending. Shearing is defined as the mechanical cutting of large sheets of
metal into smaller pieces of predetermined sizes. A shearing operation that
completes an entire perimeter is known as blanking, with the resulting
workpiece being called a blank.
Bending is defined as the creation of three dimensional shapes out of two
dimensional stock. There is virtually an unlimited variety of shapes that can
be produced in both sheetmetal and plate thickness’ by bending.
Shearing Machines
Most shearing operations are accomplished by the action of two blades, one
fixed and one moving vertically, meeting progressively from one side of the
material to the other much like ordinary hand shears. The angular alignment
of the blades is called the rake. Also to be considered is the blade or knife
clearance to each other. Both rake and clearance are a function of the type
and thickness of the material to be cut.
The “slip-plane” is the final cracking from both the top and bottom of the
work after the descending upper blade partially cuts through the work. This
upper blade is usually inclined in relation to the bottom blade, 1/2 to 2-1/2
degrees. This concentrates cutting pressure exactly at the juncture of the
blades and assures a cut exactly parallel to the blades. The slight offset
also helps clean material from between the blades.
Shearing is also done on a “shearing die” mounted in a stamping press,
however most shearing is accomplished with a machine designed especially for
the operation and is called a “shear.”
The typical shear consists of:
• a fixed bed to which one blade is attached
• a vertically moving crosshead which mounts on the upper blade
• a series of hold-down pins or feet which hold the material in place while
the cutting occurs
• a gaging system, either front, back, or squaring arm, to produce specific
workpiece sizes
Metal Shears may be operated manually, mechanically, hydraulically, or
pneumatically. They can also be classified by their design. “Gap” and
“gapless” shears are defined by their side frames and the maximum size sheet
they can handle. “Right angle” shears have two blades set at a 90 degree
angle to each other and will cut simultaneously in two directions. “CNC”
shears are programmable to cut various sizes by automatically feeding
material into the blades. “Ironworkers” are designed to cut angle and bar
stock and to perform punching operations.
The sharpness of the knives or blades critically determine the edge quality
of the cut and the accurate size of the workpiece. Dull or improperly gapped
or positioned blades will create in the cut piece, either:
• a camber or deviation from a straight edge on the drop side of the shear
• a bow which is the tendency of the sheared part to arch in the center
• a twist which is the angular distortion of the part from end to end
Another common shearing operation is known as “slitting.” This operation
begins with a master coil of a given width. Material from the master coil is
fed through a series of rotary knives set to produce a group of more narrow
stock widths for subsequent processing.
Sheet metal Bending brakes
Bending produces shapes in metal by the exertion of force beyond the
material’s yield point but below it’s maximum tensile strength. During
bending, the metal is stretched over it’s external radius and compressed
through it’s internal radius. The mid-point between these points is called
the neutral axis and is the location from which mathematical calculations
Bending can be performed in stamping dies designed for forming, but the
greater majority of bends are made in “press brakes.” Like many other
machines used in metal fabrication press brakes may be mechanical or
hydraulic in operation. In a typical bending operation, a piece of stock is
placed between a set of upper and lower dies. Then a moving ram lowers the
upper die, forcing the work into the fixed lower die. In some press brake
designs, a lower die raises up against a fixed upper die.
Principle terms used in bending include:
• bend allowance refers to mathematical factors which determine the final
part size
• bend angle is the final angle from 180o to which the part is bent
• bend radius refers to the distance from the tangents that extend from the
remaining flat surfaces of the part
• springback is the tendency of the bent flange to return back to its
original shape. Such springback can amount from 2 to 4 degrees depending
upon the material
Press brake operations are divided into two categories; air bending and
bottom bending.
In the air bending mode, the male die does not force the
workpiece completely into the female bottom die. Less pressure or force is
required than in bottom bending. However, there are trade offs in respect to
springback and bent flange accuracy. In bottom bending, the work is
completely pressed into the female die and the internal radius is accurately
formed by the male die. Thus consistently accurate flange sizes are possible.
However, bottom bending does have limitations in respect to maximum work
thickness, usually no greater than 1/8 inch.
Dies used in press brake work are of four major types:
• acute angle dies, used mostly for air bending
• gooseneck dies, used for bending return flanges
• offset dies which produce two bends with a single press stroke
• rotary dies which, as they move upon the work, form the bend by forcing it
over a die anvil
Gaging, which means positioning the work between the closing dies is
accomplished by pins or stops located usually behind the dies. These devices
are often computer controlled, allowing quick, repeatable set-ups for maximum
press brake productivity.
Another bending operation is called “folding.” A folding machine uses a
bending leaf located in front of upper and lower clamping jaws. Bends can be
made between zero and 180 degrees, making the folding machine sometimes more
versatile than the press brake.


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