1. Chipping metal and chipping tools

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.

Fig. 2.

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

Exercises

I. Use the following words and phrases in sentences of your own:

to chip, chisel, stock, mechanical tools, blade, wedge, edge, cutting angle, acute angle, plane, lip angle, clearance angle, cape chisel, front rake, to strike, to forge, solid

II. Retell the text giving answers to the following questions:

1. What is chipping? 2. What instruments are used in chipping? 3. What is a chisel? What types of chisels do you know? 4. What does the work of a chisel depend on? 5. What does the angle of the cutting edge of a chisel depend on? 6. Why is the top face of a chisel given a certain slope? 7. What is the front rake? 8. What plane is called the "front cutting face"? 9. What plane is called the "back cutting face'9 10. What is the clearance angle, the lip angle and the cutting angle?

III. Fill in the blanks with prepositions by, from, in, of, on:

1. Chisels are used ... removing stocky … works. 2. Chisels are usually made ... a high grade steel. 3. The cutting edge …. a chisel is ... the form ... a wedge. 4. The correct cutting angle ... a chisel depends ... the strength ... a stock to be chipped. 5. Stocks are chipped … means … a chisel and a hammer.

IV. Supply antonyms for the following words:

hard, large, suitable, convenient, backward, long

V. Make up adverbs from the following words and translate them into Russian:

different, hard, main, external, large, convenient

VI. Change the following sentences using the Infinitive Construction and translate them into Russian:

Example: The chisels which are to be used for chipping metals are made of high grade steel. The chisels to be used for chipping metals are made of high grade steel.

1. Different types of chisels are made of a good grade chisel steel which has to be forged, annealed, and then hardened and tempered. 2. Chisels which must be applied for chipping metal stocks are made of hard steel. 3. Working a metal to a desired shape by forging produces the best combination of physical characteristics for parts which will be highly stressed. 4. An auxiliary equipment which will be used together with the forging hammer must withstand the vibration or impact of the forging blows. 5. The weight of hammers depends on the stock which will be removed. 6. The work required to separate the chip from the stock will depend upon the material which is to be machined and the separation area.

VII. Translate the following sentences, observing different meanings of the words and word combinations given in italics:

1. There are different means of chipping stocks. 2. Chipping is performed by means of such instruments as a chisel and a hammer. 3. It means that you have to remove some more metal from the workpiece. 4. By no means should this chisel be used for this workpiece. 5. A chisel must by all means be applied for removing some metal from the work piece.

VIII. Make up questions to which the italicized words are the answers:

1. The workpiece to be tooled is fixed during the chipping process in the bench vice. 2. A chisel is a tool made of very hard steels. A chisel has a cutting edge at one end of the blade. 4. The cutting edge of a chisel is wedge-shaped. 5. The angle between the two edges of the tool in the plane of the true rake is called the "lip angle".

IX.Using the following words and word combinations describe the drawing shown in Fig. 2:

a chisel, to be a tool of very hard steel, to have a cutting edge, to be wedge-shaped, to be under the effect of an external force, to cut into metal, the work of the wedge, to depend on the cutting angle, to be sharpened to an acute angle, to provide the best cutting conditions