2 Семестр
Unit 3
Machine tools
Text 3.1
Read and translate the text.
A machine tool uses a power source to modify the shape of metal components of machines. It is a sort of machine used as a tool in the making of other machines. Machine tools were powered in the Middle Ages by humans and animals, and later by the energy captured by waterwheels. After the Industrial Revolution, most machine tools were powered by steam engine and nowadays by electricity. Machine tools can be operated manually, or under automatic control. In the 1960s, computers gave more flexibility to the process. Such machines became known as computerized numerical control (CNC) machines, They could precisely repeat sequences, and could produce much more complex pieces than even the most skilled tool operators.
Let's examine the main features of some of the most commonly used machine tools.
Turning machine
The engine lathe is the most important of all the machine tools. It is used to produce external or internal cylindrical surfaces. The piece is held by the machine and is rotated while a cutting tool removes excess metal from the external diameter. Internal turning consists of enlargen and finishing a hole.
Drilling machine
It is used to produce circular holes in metal with a twist drill. It also uses a variety of other cutting tools to perform the basic hole-machining operations.
Shaper
This is a metal-cutting machine used to produce or modify flat surfaces. The cutting tool moves cutting on the forward stroke, with the piece feeding automatically towards the tool during each return stroke. Shapers can be horizontal or vertical.
Milling machine
This cuts flat metal surfaces. The piece is fed against a rotating cutting tool. Cutters of many shapes and sizes are available for a wide variety of milling operations. Milling machines may be manually operated, mechanicaly automated, or digitally automated via computer numerical control (CNC).
Grinding machine
This removes excessive material from parts that are brought into contact with a rotating abrasive wheel. Grinding is the most accurate of all the basic machining processes, but also the most time consuming.
Press
This is a machine tool that changes the shape of a, workpiece. Historically, metal was shaped by hand using a hammer. Machine presses can be dangerous.
Bi-manual controls (controls which require both hands to be on the buttons to operate) are a very good way to prevent accidents,
Band saw
It is a power tool which uses a blade consisting of a continuous band of metal with teeth along one edge. The band usually rides on two wheels rotating in the same plane. Band saws are used for woodworking, metalworking, or for cutting a variety of other materials, and are particularly useful for cutting irregular or curved shapes. A constant flow of liquid is poured over the blade to keep it cool and preventing it from overheating.
Read the texts about metalworking processes and complete the table.
Machine tool |
Final result |
Description |
turning machine |
external and internal flat surface |
It removes excess metal from the external diameter. It enlarges and inishes a hole.
|
|
specific shape |
It cuts flat metal surfaces. |
|
holes |
It uses a twist drill to make holes. |
|
flat surface |
It cuts the piece. |
|
specific shape |
It changes the shape of a workpiece. |
|
cut pieces |
It cuts various parts using a continuous band of metal with teeth. |
|
finishing |
It removes excessive material from parts. |
Read the texts again and decide if the following sentences are true (T) or false (F).
1 Turning machines remove excess metal from the external diameter and enlarge and finish a hole.
2 Shapers can only be vertical.
3 Drilling machines use a twist drill to make circular holes.
4 Milling machines can only be manually operated.
5 Grinding machines remove excessive material from parts.
6 Band saws use a band of metal with teeth to cut various parts.
7 Presses are not dangerous if operated by both hands
Text 3.2
Read and translate the text.
Computer Numerical control (CNC) refers to the automation of machine tools in manufacturing processes. The machines are controlled by computer software which carries out a series of operations automatically. The first NC machines were built in the 1940s and 1950s. They are " used to cut and shape products, such as automobile parts that need precise specifications. Parts must be carefully planned and prepared by CNC programmers. First they view the three-dimensional computer aided designed part. Then they calculate where to cut, the speed and shape and select the tools and materials. The CNC programmers translate the planned machine operations into a set of instructions. These instructions are translated into a computer aided manufacturing (CAM) program containing a set of commands for the machine. The commands are a series of numbers which explains where to cut and the position of material. The computer checks all the operations made by the machine tools.
Put the sentences in the correct order.
а The planned machine operations are translated into a set of instructions,
b These instructions are translated into a CAM program,
с The program contains a set of commands for the machine,
d It is calculated where to cut and tools and materials are selected,
e The computer checks all the operations made by the machine tools,
f Programmers view the part in its three-dimensional computer aided design.
Unit 4
What is electricity?
Text 4.1
Read and translate the text.
All substances, solids, liquids or gases, are composed of one or more of the chemical elements. Each element is composed of identical atoms.
Each atom is composed of a small central nucleus consisting of protons and neutrons around which orbit shells of electrons. These electrons are very much smaller than protons and neutrons.
The electrons in the outermost shell are called valence electrons and the electrical properties of the substance depend on the number of these electrons.
Neutrons have no electric charge, but protons have a positive charge while electrons have a negative charge. In some substances, usually metals, the valence electrons are free to move from one atom to another and this is what constitutes an electric current.
Read the text again and complete the sentences with the missing information.
Elements make up …..
Identical atoms ….
Atoms consist of …., ….. and ….. .
Inside there are …. And …., while outside …. .
Shells….
Valence electrons
Neutrons do not have
Electricity is generated when
Text 4.2
Read and translate the text.
Electricity consists of a flow of free electrons along a conductor. To produce this current flow, a generator is placed at the end of the conductor in order to move the charge.
Conductors
Electricity needs a material which allows a current to pass through easily, which offers little resistance to the flow and is full of free electrons. This material is called a conductor and can be in the form of a bar, tube or sheet. The most commonly used conductors are wires, available in many sizes and thicknesses. They are coated with insulating materials such as plastic.
Semiconductors
Semiconductors such as silicon and germanium are used in transistors and their conductivity is halfway in between a conductor and an insulator. Small quantities of other substances, called impurities, are introduced in the material to reduce the conductivity.