Vocabulary

sequence послідовність, ряд

domain область

Text 2

9. Read, entitle the text and speak about the developments in tools.

James Watt made significant improvements on the steam en­gine invented by Thomas Newcomen. This was accomplished by John Wilkinson on a boring machine he built in 1775 — the first machine tool. Machine tools that followed in the 19th century were the screw-cutting lathe, metal planer, and milling machine. Eli Whitney, the American who invented the cotton gin about 1793, was also a pioneer in the use of precision tools to mass-produce inter­changeable parts.

The chief innovations are numerical control, or NC (control by means of tape containing nu­merical information), and computer control. Al­though the control methods are changing, the basic machine-tool operations remain the same; they include turning, milling, drilling, boring, grinding, planing, shaping, shearing, and pressing. The cutting part of a machine tool is called the cutting tool. The actual cut­ting is done by a sharp point or a sharp edge. A tool with one cutting point is called a single-point tool.

Text 3

1. Read the text and express your attitude to its content.

Metal Processing Operations

Hole Making. The principal methods of making and enlarging holes are drilling, reaming, and boring.

Drilling. The most common drilling machine is the upright sensitive

drill press. The table is ad­justable in height and tilt angle, and a powered

spindle (holding the drill bit) can be fed down into the workpiece by a hand-operated lever. The manual feed gives the operator a feel for the

cutting action of the drill — hence the term "sensitive." Power feeds are added to the larger drill presses.

Gang drills essentially are upright drill presses placed side by

side, with a common table. Parts can be easily drilled, reamed, counterbored, and so forth by being transferred from one spindle to the next without lost time for tool changing. When the workpieces become too large to be moved conveniently around on the drill-press ta­ble, a radial drill is used. The radial drill has a horizontal arm that extends out from the main column. The independently driven drilling head mounted on the arm can be swung in an arc, raised or lowered, or tilted.

When holes are needed in groups, a multi­ple-spindle drilling head is used. In most cases the positions of the drills can be adjusted within the overall cluster arrangement almost at random. A turret-type drill press is one of the most effective types for offering a variety of cutting tools. Tool selection, speeds, and feeds can be numerically controlled.

Boring. Boring is the process of enlarging and truing an existing hole. Often, when a hole is drilled, it is not exactly centered on the desired location. For this reason the hole is drilled undersize by %₂ to %e inch (0.08-0.16 cm); the hole can be bored to the desired diameter and centered. Boring often is done on a lathe with the work mounted in a chuck and the boring bar mounted in the tool-post holder on the compound. Jig boring machines, which resemble vertical mills, are used for precision hole loca­tion and boring.

Reaming. Reamers are used to produce ac­curate hole size and good finish. Holes are often drilled 0.015 to 0.03 inch (0.038-0.076 cm) undersize to allow for reaming.

Turning. Turning is the process of machining round stock on a lathe. The commonest use of the lathe is for machining workpieces to various

diameters. Other operations include drilling, boring, threading, knurling, and tapering.

The lathe's quick-change gear box provides an easy way of changing feeds. Feed is the amount that the tool (mounted on the carriage) advances per revolution of the workpiece. The feed de­termines the finish obtained.

Other operations of metal treatment are: grinding, planing nd broaching.

Electron-beam welding is increasingly fa­vored where the cost of the equipment can be justified by the production volume. Ultrasonic welding and machining has found wide acceptance in nondestructive testing, weld­ing, and machining.