SAWING PROCESS: Definition, Snagging, Types & Friction Sawing

What is the meaning of sawing?

Sawing operations
Fig. 1 Various Sawing operations

In sawing process, the cutting tool is a blade (saw) having a series of small teeth, each tooth removing a small amount of material with each stroke or movement of the saw.
With this process various shapes can be produced on metallic and non metallic materials.
Sawing is an efficient bulk-removal process and can produce near-net shapes from raw materials.
As the width of cut (kerf) is small hence wastage associated with this process is also less.

Explain saw blade configuration?

Saw teeth

Spacing of tooth is in the range from 0.08 to 1.25 teeth per mm.
A wide variety of sizes, tooth forms, tooth spacing, and blade thicknesses and widths are available.
Saw blades generally are made from high-carbon and high-speed steels (M2 and M7).
On harder materials are carbides or HSS tipped steel blades are used for sawing.

What is snagging?

In order to prevent snagging (catching of the saw tooth on the workpiece) atleast two or three teeths should be in constant contact with the workpiece.
This is why thin materials, especially sheet metals, can be difficult to saw.
The thinner the stock, the finer the saw teeth should be, and the greater the number of teeth per unit length of the saw.

Check out these articles for complete information related to the processes.
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What are the different types of saws?

Hacksaws have straight blades and reciprocating motions.
They are used to cut off bars, rods, and structural shapes.
They may be manual or power operated. Because cutting takes place during only one of the two reciprocating strokes, hacksaws are not as efficient as band saws.
Power hacksaws:
Power hacksaws blades are usually 1.2 to 2.5 mm thick and up to 610 mm long.
For high strength alloys to carbon steel the rate of strokes ranges from 30 per minute to 180 per minute.
The hacksaw frame in power hacksaws is weighted by various mechanisms, applying as much as 1.3 kN of force to the workpiece to improve the cutting rate.
Hand hacksaw:
Hand hacksaw blades are thinner and shorter than power hacksaw blades, which are used for sawing sheet metal and thin tubing and contain 1.2 teeth per mm .
Circular saws:
For high production sawing, circular saws (also called cold saws in cutting metal) are used and this process is called cutting off.
Cutting off operations also can be carried out with thin, abrasive disk.
For cutting large cross sections cold sawing is mostly used in the industry. Cold saws are available with a variety of tooth profiles and sizes and can be fed at any angle into the workpiece.
In modern machines, cutting off with circular saws produces relatively smooth surfaces with good thickness control and dimensional accuracy due to the stiffness of the machines and of the saws.
Band saws:
Band saws achieve continuous cutting action because of continuous, long and flexible blades.
Vertical band saws are used for straight as well as contour cutting of flat sheets and other parts supported on a horizontal table.
Also available are computer-controlled band saws with the capability of guiding the contour path automatically.
Power band saws are available as well; they have higher productivity than power hacksaws because of their continuous cutting action.
Cutting speeds for sawing high-strength alloys are up to about 60 m/min and 120 m/min for carbon steels with HSS (High Speed Steel).

What is friction sawing?

Friction sawing is a process in which a mild-steel blade or disk rubs against the workpiece at speeds of up to 7,600 m/min. A narrow zone in the workpiece is soften as the frictional energy is converted to heat.
The action of the blade, which can have teeth or notches for higher cutting efficiency, pulls and ejects the softened metal from the cutting zone.
The heat generated in the workpiece produces a heat-affected zone on the cut surfaces.
Thus, the workpiece properties along the cut edges can be affected adversely by this process.
The cooling of blade is not dependent on any fluid because only a small portion of the blade is engaged with the workpiece at any time.
This friction sawing process is suitable for hard, ferrous metals and reinforced plastics but not for nonferrous metals, because of their tendency to stick to the blade.
Friction sawing disk as large as 1.8 m in diameter are used to cut off large steel sections.
Friction sawing also is commonly used to remove flash from castings.

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