4. Consider the mathematical notion and tell what you know on

the topic.

Continuity

A continuous function may be described roughly as one whose graph contains no sudden jumps, so that if may be drawn without lifting the pencil from the paper. Thus a function is continuous at x = c if, when x is just greater than or just less than c, its values are nearly equal to ƒ(c).

Definition: If lim ƒ(x) and lim ƒ(x) both exist and

x→c + 0 x→c ─ 0

equal ƒ(c), ƒ(x) is continuous at x = c. Otherwise ƒ(x) is discontinuous at x = c.

5. Write and retell an abstract оf some interesting publication according to the plan.

1) The title, 2) The name of the author, 3) The name of the journal, its

number, year, place of edition, volume, number of pages, figures, tables, 4) A range of problems covered / considered, 5) Characteristics and evaluation of the publication (facts layed out, problems raised, grounding, conclusions, prospects).

METAL PROCESSING EQUIPMENT

UNIT 14

Text 1

1. Read, translate and retell the text.

Machine Tool

Machine tool is any of a wide variety of tools, usually large, rugged, and power driven, for cut­ting, shaping, or forming metal. Precision of operation makes is possible to produce hundreds of identical parts, all so much alike that they may be freely interchanged or substituted in assembly or repair, without hand-fitting.

Machine- tools are known to serve four main purposes: 1) they hold the work or part to be cut; 2) they hold the cutting tool (or tools); 3) they impart to the cutting tool or work the motion required for cutting or forming the part; 4) they regulate the cutting speed and the movement between the tool and work.

The most common machine-tools are lathes, which perform cutting operations mostly, milling machines, drilling machines and grinders.

Lathes. In addition to the engine lathe, there are quite a number of higher-production lathes, in­cluding tracer lathes, Swiss-type automatic screw machines, turret lathes, and single- and multispindle automatic lathes. Tracer lathes are similar to the engine lathe, but the tool path may be guided by a template-tem­plate type, tracing the operation is automatic, but the operator has to position the tracing-tool unit for each cut and return it to the starting position for the next cut. Swiss-type automatic screw machines are designed to produce small-diame­ter parts, such as shafts for clocks or watches. The cutting tools are arranged in a radial pat­tern around the

workpiece. A unique feature is that the stock can be fed longitudinally while

it is being cut to generate curved surfaces. Accu­racies on small production parts may be held to 0.0005 inch (0.0013 mm).

A turret lathe is made with two turrets, one at the tailstock end of the machine and the other mounted on the cross-slide. Each of the tools on either of the turrets can be indexed (rotated) and locked into position and then brought up to the stock for the desired cut. On a manual-type tur­ret lathe, the operator does the indexing, but the tools are fed into the workpiece by power.

"Single-spindle automatics" are turning ma­chines whose movements are directed by gears and cams. Automatics can be used for bar or in­dividual pieces held in a chuck, which are then referred to as "chuckers." These machines are fast but are economical only for large production runs. One person can operate two or more ma­chines of this type simultaneously. Multispindle automatic lathes are built some­what similar to the single-spindle automatics but are equipped with four, six, eight, or more spin­dles. Either the bar stock or individual pieces may be held in the chucks. After the necessary cuts are made at each station, all the chucks ro­tate, or index around. This continues until all workpieces have been machined. A newer concept in turning is the numerically controlled lathe with a built-in computer.

Transfer Machines. The highest degree of auto­mation in metalworking production is made pos­sible by the transfer machine. A transfer ma­chine is essentially a combination of individual machine tools arranged in the required sequence, connected by material-handling or transfer de­vices and integrated by interlocking controls. On these specially built machines, hundreds of op­erations are performed and inspected automati­cally. On large parts such as automotive engine blocks, part-turnover and orienting devices often are used between groups of work stations to present new surfaces to the horizontal, vertical, or angular machining units.

Vocabulary

shape форма

cut різати

rugged міцний, жорсткий, шерохуватий

precise точний

serve a purpose мати призначення

milling machine фрезерний верстат

drill свердлити

grind шліфувати

hand-fitting ручна підгонка

turret головка верстата

longtitudinal feeding повздовжня подачa

transverse feeding поперечна подача

curved не прямий

tailstock задня опірна центруюча бабка

lock стискати

trace слід

tracing-tool unit креслячий пристрій

workpiece заготовка

lathe токарний верстат

template матриця

spindle вал, стрижень, вісь

turn точити, обточувати

chuck зажимний патрон, оправка