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Инженерная механика |Machinery Technologies

Final Certification |Итоговая Аттестация

Lesson 1

Read the text: Designer’s Guide to Metalcutting Machinery

Grasping the mysteries of metalcutting machinery eases once you understand the terminology that tends to mislead. For example, industry often refers to the entire machine itself as the “machine tool.” This can be confusing because all metalcutting machines use cutting “tools” made from hard carbide, hard steel, or diamonds. In addition, machinists sometimes refer to jigs and fixtures as “tooling.”

Some shops and machine builders make a distinction between machine tools for mass production and those for support activities such as cutting prototypes, repair parts, dies and molds, or jigs and fixtures. They often call this kind of equipment tool-room machinery.

Mass-production operations such as casting and forging are limited as far as dimensional precision and surface smoothness. Thus, the fit and finish needed for highly engineered products usually requires some sort of stock removal by machine tools.

Exceptionally rugged to endure the stress of high-volume runs, production machinery also emphasizes fast output. Parts for this kind of machining often come preshaped to their approximate final dimensions by such operations as casting or forging. A forging, for example, might just need one surface milled and a few holes drilled and tapped.

Other parts don’t come preshaped. Instead, the machine tool cuts gross amounts of metal from plate, bar stock, or weldments. These parts often have intricate geometries needing extreme precision, such as those for aerospace. In other cases, stock such as rod or bar closely approximates the final shape. Machine tools can make small circular or tubular parts in high volumes using relatively light cuts.

Industries such as automotive, consumer products, and farm equipment have large, special-purpose machines built to work in assembly-line fashion. The machines drill, ream, tap, and mill parts as they pass from station to station. Called transfer lines, the machines are often what is meant when automotive companies are said to be purchasing “tooling” for a new model.

Chipmaking

Metal cutting can be thought of as the art and science of “chipmaking.” Knowledgeable machinists run jobs to produce the optimal chip, usually helical or comma shaped. Controlling chip size, shape, and color help machinists keep jobs running correctly. These chip parameters depend on the material being cut, the machine tool’s feed rate and depth-of-cut, and the rake angle (the angle between the chip face and a normal to the workpiece surface) of the tool bit, among other variables.

The cutting tool actually deforms some of the workpiece material plastically and then pushes the chip off. Removing unwanted material from the workpiece in this fashion eventually shapes the part.

In all conventional metalcutting (not, for example, electrical-discharge machining), either the workpiece rotates; the cutting tool rotates; or the machine tool or workpiece “translates” (moves in a flat plane). The workpiece rotates in turning and boring; the cutting tool rotates in drilling and milling; and either the cutting tool or the workpiece translates in shaping, planing, and broaching.

 

1. Match the left part with the right:

1. Parts for this kind of machining	a) often have intricate geometries.
2. These parts often have	b) the material being cut.
3. This can be confusing because	c) often come preshaped to their approximate final dimensions.
4. These chip parameters depend on	d) all metalcutting machines use cutting “tools”.

 

2. Complete the sentences with the suggested words: actually, plastically, off, shapes

The cutting tool ____ deforms some of the workpiece material ____ and then pushes the chip ____. Removing unwanted material from the workpiece in this fashion eventually ____ the part.