CNC Machining: An Overview

CNC is a process by which machining parts are manufactured with the help of computers that control the machine tools. Thanks to CNC (Computerized Numerical Control) technology, the manufacturing process of almost all the machining parts has now being automated since it allows to use a set of instructions to control the machining through a program with the minimum human intervention.

CNC technology can be applied to a wide range of operations such as processing, assembly, inspection, as well as work on metal sheets, and more. Other than this, numerical control is used more frequently in different machining processes of metals or aluminium such as turning, drilling, or milling. As a consequence of the configuration, machining operations allow manufacturing at an accelerated rate, resulting in bulk manufacturing that is also much cheaper and much more accurate.

A new approach to optimize machining operations is adaptive control. While the material is being machined, the system detects the conditions of operations such as the force, the temperature of the tip of the tool, rapidity of wear of the tool and surface finish. Then it converts this data into control of advance and speed that allows the machine to cut in optimal conditions and obtain maximum productivity. It is expected that adaptive controls, combined with numerical controls and computers, will produce greater efficiency in metalworking operations.

Advantages & Disadvantages of CNC Machining

Here are some advantages of CNC Machining:

  • Better accuracy and better product quality.
  • Greater uniformity in the products produced.
  • An operator can operate several machines at the same time.
  • Easy processing of complicated appearance products.
  • Flexibility to change design and models in a short time.
  • Easy quality control.
  • Reduction in inventory, transfer and manufacturing costs in the models and clamps
  • It is possible to satisfy urgent orders.
  • Experienced operators are not required.
  • Operator fatigue is reduced.
  • Greater security in the work.
  • Increase in working time in machinery cutting.
  • Easy control according to the production program, which facilitates the competition in the market.
  • Easy administration of production and inventory, which allows the determination of objectives or policies of the company.
  • It allows simulating the cutting process in order to verify that it is correct.

However, not all are advantages and among the disadvantages, some can be cited as the following:

  • The high cost of machinery.
  • Lack of options or alternatives in case of failures.
  • It is necessary to program the selection of cutting tools and the sequence of operation for efficient operation correctly.
  • Maintenance costs increase since the control system is complicated and the need arises to train service and operation personnel.
  • It is necessary to maintain a large volume of production to achieve greater efficiency of installed capacity.

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The most common type of machines used with CNC

#1 Lathes

Lathes are considered the oldest machine in the world. The basic lathe has the following main parts: bed, head, tailstock and sliding trolley. The types of lathe exist for diverse CNC applications can be listed as follows: fast, horizontal, vertical and automatic mechanical lathes. Each category influences a wide variety of lathes and attachments, which also depends on the volume of production required.

It is customary to specify the size of the mechanical lathe with the maximum admissible diameter and the distance between centers. This is due to the fact that when the tailstock is flushed with the end of the bed, the maximum diameter on the guides must be greater than the nominal diameter.

Modern lathes are built with the capacity of speeds, rigidity and mechanical consistency to take full advantage of new and stronger tool materials. The optimum speeds for turning depend on factors such as the material of the CNC, its condition, depth of cut, and the type of cutting tool. Cutting speeds must always be increased in the following order:

high-speed steels, cast alloys, brazed carbide, adjustable carbide.

Remember, as the depth of cut increases; speed must be reduced.

#2 Drilling/Grinding machines

The vertical drills are usually designated by a dimension that indicates in approximate the diameter of the largest circle that can be drilled in its centre, under the machine. The modern heavy-duty drills of the vertical type, completely retransmission with gears for the speed of advance and are built with a column of the box type, unlike the old ones that had a cylindrical column. The size of the radial drill is designated by the length of the arm, which represents the radius of a piece that can be drilled in the center. Helical drills are the common tools for drilling and are manufactured in many sizes and lengths.

#3 Machining centres

New advances in the machines and tools are the machining centers. This is a machine that can have about 100 tools or more with an automatic changer of their own. It is designed to perform various operations on different surfaces of the workpiece. The machining centers can produce complex parts with great accuracy and speed.

#4 Milling machines

Cutters with multiple teeth known as milling cutters are used in milling machines. The milling is usually done through a cut or peripheral. The standard mouthpieces and tool holders of the milling machines allow the exchange of tool holders and milling cutters for face milling, regardless of the construction or the size of the machine.

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The classification of the milling machines is based on its design, operation and purpose.

The milling machines of the column and gusset type have the table and the trestle supported on the vertically adjustable gusset that is wedged to the face of the column. The table is then advanced in a long way on the trestle and this gets placed crosswise on the board to give three advance movements.

The machines of the fixed bench are of simple and rigid construction; its main use is the work of a high volume of production. These milling machines are usually equipped with attachments to hold the workpiece easily and can be built as single or multiple spindles.

In general, it is considered that the two kinds of milling that represent all the forms of its processes are: the peripheral and the front fixed.

Each one has its advantages and the choice depends on numerous factors, such as the type and condition of the equipment, the duration of the tools, surface finish and machining parameters.

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