III. Where can numerical control systems be used? Read the text to learn more about NC systems.

In 1775 John Wilkinson, an English ironmaker, invented the first modern machine tool. It was a boring machine that enabled the workers to drill precise holes in metal. Many refinements have been incor­porated in machine tools since that time.

By the middle of the 20th century some machine tools had been linked together in series for use in mass production. And in the 1950s the first machines with numerical control were introduced.

Numerical control, commonly called NC, is a system of automat­ing machine tools. Let's have a look at some examples of NC systems application.

The system known as computer numerical control (CNC) has a number of machine tools, each of which is directed by its own com­puter. So when you want to adapt a CNC machine tool to a different job you just change the control programme, or software of the com­puter. They are very easy in operation, their programming is simple and you can always test it. Moreover, they are cheaper to maintain and are generally more accurate in comparison with standard machine tools. CNC systems are used with a wide range of machine tools such as milling machines and lathes. Many are equipped with graphic displays that show the shapes of the workpiece and can even produce three-dimensional views of the components.

When several CNC machine tools receive instructions from a large central computer that stores and processes operational procedures, we can speak about a direct numerical control (DNC). This single computer controls more than 100 machine tools.

A further development in the automation of machine tools is the "machining centre". This machine has automatic tool changers and performs a lot of machining operations on a workpiece with the help of more than 100 different cutting tools. One machining centre can do the work of eight or more standard machines. They are particu­larly useful when you need to produce large and complex components with the high degree of accuracy.

In general, all machine tools that are equipped with NC systems have a lot of advantages. One of the most important advantages is the absence of necessity to design, build and store the numerous fixtures.

IV. Answer the following questions.

1. What is the main advantage of CNC machines?

2. What is the difference between CNC and DNC machines?

3. How many tools may a DNC machine contain?

4. What is the main principle of work of machining centres?

5. If you were a director of a steel factory would you like to install there machine tools with NC systems?

 

V. Say if the following sentences are true or false. Correct the false sen­tences.

1. John Wilkinson invented the first modern NC machine tool.

2. Nowadays NC systems are hardly ever used in industry.

3. CNC machine tools are more accurate in comparison with standard machine tools.

4. One machining centre may perform the work of 100 standard machines.

5. If a worker wants to produce a complex component with high degree of accuracy he should use one of the NC machine tools.

 

VI. Read the following summary of the previous text and fill in the miss­ing information with the words given .

Automation of machine tools began in the 20th century. In the 1950s the first machines with … were … .

Numerical… is a system of automating machine … .

Computer … control machine tool is directed by a … . CNC machines are easy in … and they are … to maintain.

In … system a single computer may … more than 100 machine tools.

Machining centres may … a lot of machining … on a … at a time. One machining centre may do the work of eight… machines.

… NC systems have … advantages.

computer	in general	introduced	tools	perform
a lot of	numerical control	operation	numerical	operations
control	direct numerical control	standard	cheaper	workpiece

 

VII. Annotate the text.

18.