What is Numerical control? Applications, Advantages, Limitation

NC machine

What is NC machine?

Numerical control is defined as the form of programmable automation in which numbers letters and symbols control the operation. This instruction is designed to do a particular job. NC machines has capability to change the program for each job ie when job changes the program instruction is also changed. It is easier to change the program instruction than to modify the production equipment. This flexibility reduces the overall production cost.

Advantages and Limitation of NC

Advantages of NC
  • Greater manufacturing flexibility – NC can easily adapt to the engineering design changes and a shift in the production schedule.
  • Reduced manufacturing lead time – the job can easily and quickly set up with NC.
  • Reduced non-productive time – In case of complex machining NC seems helpful to reduce the non-productive time. Because of quick/ automatic tool changing, quick setting up, and reduced workpiece handling time.
  • Reduced fixturing – the fixture required in NC operation are simpler and less costly because NC tape does positioning instead of jig and fixture.
  • Reduced inventory - this is the result of fewer setup reduced lead time.
  • Quality control improved – No risk of human mistakes. It produces the part with high accuracy. It also reduce the man-hour for inspection.
  • Greater operator safety.
  • Reduce the scrap – the high accuracy of NC machine helps to reduce scrap material.
  • Reduced floor space requirement – since the one NC can do variety of operation it replaces several conventional machines.

Disadvantages and Limitation of conventional NC
  • High investment cost and Maintenance cost – most complex and sophisticated technology cost more than the conventional machine.
  • Require skilled operator – finding and training of NC personnel should be considered.
  • Tearing and wearing of punch tape and less reliable punch tape component.
  • Part programming mistake in punched tape.
  • No optimal feed and speed – conventional NC machine does not provide an option to change the cutting speed and feed during the operation.
Five hole and eight hole perforated paper tape as used in telegraph and computer applications
Five hole and eight hole perforated paper tape as used in telegraph and computer applications

Applications of numerical control technology

Numerical control technology has application in a wide variety of production operation such as metal cutting, automatic drafting, spot welding, press working, assembly, inspection, etc. However, NC finds its principle application in metal machining operations. It is built to do virtually entire metal removing process. (Example for metal working Turning, sawing, Grinding, Milling, Drilling, boring).

The production jobs where the numerical control machines are most appropriate are listed below.
  • The NC technology is suitable to sequence/series of machining process.
  • Job geometry is complex, expensive. Mistakes in the process lead to high loss.
  • It is expected engineering design changes in future.
  • High metal removal is required.
  • The workpart required 100% inspection.
  • There must be close tolerance on workpart.
  • When many operations need to be done when processing. It is frequently processed in batches of small lot sizes.

What Are The Temperature Limitations For Refrigeration Cycle (Reversed Carnot)?

coefficient of performance of refrigerator

Even though the reversed Carnot cycle is impossible, here it is used to show the temperature limitation of the Refrigeration cycle.
Coefficient of performance of refrigeration system that working on reversed Carnot cycle is
(COP)R =T1/(T2-T1 )
T1 = Lower temperature (temperature to be maintained in the refrigerator)
T2 = Higher temperature (temperature of cooling water/air available for heat rejection)

Why Is Carnot Cycle Not Possible In Heat Pump And Refrigerator?

reversed Carnot cycle pv and Ts diagram

Read: COP of air refrigerator working on reversed carnot cycle with PV and Ts diagram

In working of refrigerator, the term Carnot cycle represents the reversed Carnot cycle. As we know that, between the fixed temperature limits, a heat engine operating on Carnot cycle give highest possible efficiency. Similarly, a refrigerator working on reversed Carnot cycle give the highest possible coefficient of performance. Even though no heat engine and refrigerator used Carnot cycle. This is because that the isentropic process of Carnot cycle requires a high speed of air while the isothermal process of Carnot cycle requires extremely slower speed. This large variation in speed of air is simply not possible.

COP Of Air Refrigerator Working On Reversed Carnot Cycle with PV and Ts Diagram

reversed carnot cycle pv diagram ts diagram

Introduction to the Air Refrigerator working on reversed Carnot cycle

In these type of refrigerator, a reversed Carnot cycle is considered. For a heat engine, the highest possible efficiency is achieved by the Carnot cycle. Similarly in refrigeration cycle highest possible coefficient of performance is obtained when the system is working on reversed Carnot cycle. However, it is not possible to make an engine operating on the Carnot cycle, or it is not possible to make a refrigerating system working on reversed Carnot cycle. This hypothetical heat cycle is used as a standard of comparison.

- Air Refrigerator working on Bell-Coleman cycle with PV and TS diagram (reversed Brayton or Joule Cycle)
- Mechanism and working of a vapour compression refrigeration system - with PV And TS diagram

What Is Refrigeration Load? Cooling Load, Heating Load

chair pillow radiation curtain window

Cooling load

Cooling load is defined as the average rate at which the heat is removing from the cold space by refrigeration equipment. Similar to the unit of refrigeration it is also expressed in Ton of refrigeration (TR).  The building design, internal equipment, occupants, and outdoor weather conditions may affect the cooling load. Following are the common sources of heat that contribute to the cooling load of refrigeration equipment.

What is Unit of refrigeration or Rating for Refrigeration - Derivation

refrigeration shop

Unit of refrigeration

Rating for Refrigeration indicates the rate of removal heat. The unit of refrigeration is expressed in terms of ton of refrigeration (TR). One ton of refrigeration is defined as the amount of refrigeration effect (heat transfer rate) produced during uniform melting of one ton (100kg) of ice at 0°C to the water at the 0°C in 24 hours.