Chipping is a process of removing metal from a workpiece by means of a cutting instrument such as a chisel and a hammer. This process is used when a large piece of metal has to be removed from a workpiece; this process is very labour-consuming' and is applied only in cases when the workpiece cannot be machined. Chipping is used in cases when it is necessary to cut off a piece of metal from sheet metal. Chipping of large parts is always done on an anvil but very of ten it is done in a bench vice. The workpiece to be tooled is fixed during the cutting process in the bench vice.
There are different tools used in metal-working shops for chipping stocks such as chisels. A chisel is a tool made of very hard steel, having a cutting edge at one end of the blade. This cutting edge is wedge-shaped. Under the effect of an external force applied to the wedge it cuts into the metal. The work of the wedge depends mainly on its cutting angle. The cutting edge of the chisel should be sharpened to an acute angle so as to provide for the best cutting ability, depending on the stock to be chipped. The harder the metal, the larger should be the cutting angle of the chisel and vice versa. An angle of about 70 is suitable for most work. Fig. 2 shows a scheme of the process of cutting into metal, and the angles of the wedge.
a – bar with an obtuse angle; b – bar with an acute angle
Fig. 3 . Process of Chipping by Means of a Chisel:
1 - front cutting face; 2 - front rake; 3 - cutting angle; 4 - back cutting face;
5 -clearance angle; 6 - lip angle
Fig. 3 shows the process of chipping by means of a chisel, as well as cutting angles. The plane АО called the "front cutting face" or the "top face" is given a
backward and sidewise slope for sliding the chips off the tool in a convenient direction while the plane OB is called the "back cutting face". Being formed between the front and back cutting faces of the chisel the angle AOB is known as the lip angle. The angle BOC is the clearance angle which is formed by the back cutting face of the chisel and the surface of the work to be treated. The slope in the direction of the chisel length in which the chip moves is called the "front rake" or "true rake". The angle AOC formed by the lip angle and clearance angle is known as the "cutting angle". There are different types of chisels such as flat chisels, cape chisels, etc.
Hammers are striking tools used in chipping, bending and other operations. Hammers are made of a solid piece of forged tool carbon steel, their weight depending on the stock to be removed.
1. labour-consuming – трудоёмкий
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