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Milling Cutters
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A milling cutter will give an efficient performance only when it is properly used. Correct operating conditions will enable the milling cutter to machine a whole batch of workpieces between grinds.
During operation the cutter is dulled due to wear caused by rubbing of the chip on the face and by the abrasive action of the work on the flank which contacts the cutting surface. During operation the wear on the flank is at all times in advance of the wear on the face until finally the area of wear merges with the crater. From that moment on, the wear sharply increases in intensity as the partly destroyed edge can’t cut normally. So-called catastrophic wear of the tool sets in. To remedy the situation, thick layers of metal have to be ground from the tooth face and flank to restore the correct geometry of the cutting edge.
In view of this, the milling machine operator should never allow the cutter reach the catastrophic wear stage; he should remove the cutter for resharpening immediately after normal wear is detected. The beginning of dulling is indicated by chatter, the appearance of a rough machined surface and excessive heating of the cutter due to increased friction.
Friction always increases the temperature of the cutting tool. This, in turn, impairs the hardness of its cutting edge and intensifies dulling. Therefore, a cutter becomes dull both due to wear and to excessive heating during milling.
The life of a milling cutter is determined by the time of its continuous operation between grinds.
Actually there exist several types of milling cutters. In vertical mills, milling cutters with solid shafts are usually used. Milling cutters with keyed holes are predominantly for use in horizontal mills. End mills are designed for cutting slots, keyways and pockets. Two fluted end mills can be used to plunge into work like a drill. End mills with more than two flutes should not be plunged into the work. Ball end mills can produce a fillet. Formed milling cutters can be used to produce a variety of features including round edges.
EXERCISES
1. Find all the words with – ed endings in the text. State their origin. Translate the sentences into Russian.
2. Find in the text synonyms for the following English words:
Because of, side, in the end, to permit, to put right, considering, to discover, to cause weakening, for that reason, in fact, to employ, to manufacture.
3. Choose the definition that fits each word or phrase as it is used in the text:
| performance | 1. The act of performing a play, dance, or other form of entertainment. 2. The standard to which someone does something such as job or examination. |
| face | 1. The front side of your head. 2. One side of a coin. 3. One flat side of an object. |
| life | 1. The period of time from birth until death. 2. Living things such as plants or animals. 3. The period of time during which something is good enough to be used. |
| work | 1. Physical or mental activity. 2. Employment for earning a living. 3. Things or parts made of certain materials or with certain tools. |
| cutter | 1. A small fast sailing-ship. 2. A tool that cuts. |
4. Look at the picture below and say where each type of milling cutterscan be employed:
5. Put these words in the right order to make up a sentence:
1. Cutter, due to, during, operation, wear, the, dulled, is.
2. Edge, cut, normally, sets in, catastrophic, partly, so-called, wear of the tool, can’t, destroyed, the, when.
3. Temperature, the, friction, of, increases, always, the, cutting tool.
4. Several, cutters, actually, types, there, milling, of, exist.
5. Pockets, designed, slots, end, mills, cutting, and, are, keyways, for.