Numerical Control Machine | Types of Control System In Numerical Control


Three types of control are used for the operation of machines.

1. The first and simplest type of control is to station one or more workers at a machine to observe the production and activate the controls as needed.

2. The second type of control is to assist the human being by arranging the machine to control itself, partially or fully. This type of control uses pre-set stops, jigs, templates, cams, and other hardware attached to the machine. Some of these machines are semiautomatic, and others are fully automatic in their operation.

3. The third type of control operates a machine with the use of information stored on punched cards, punched tape, magnetic tape, or other nonhuman means for holding and programming information. This type of control is known as "numerical control," because numbers are involved. Only a minimum of human controlling assistance is needed. For some jobs, it will be advantageous to use numerical control rather than the hardware type of control. Numerical control may make a machine either semiautomatic or fully automatic.

01- Types of Control System In Numerical Control - why cnc machines

Numerical Control:

Machines can be controlled with the use of information stored on tapes, or on other devices, which can store and make available information when needed. Suitable equipment is needed for interpreting the information on the tape and sending the signals to the machine at the proper time. Suitable devices must be installed on the machine to receive these signals and cause the machine to follow their commands. These devices actuate the controls on the machine. Numerical control is flexible in that tapes are easily changed for different jobs. When all of the units needed to provide the signals and to control a machine through a complete cycle of operation are combined, the combination is called a "system." Thus, numerical control is called as system.

01- numerical control machines - types of control system in numerical control

The information needed for controlling the operation of a machine comes from the drawing of the desired part. Since numerical control locates all points on a drawing by their X and Y coordinates, it is preferable to have drawings dimensioned using this kind of coordinate system. This will eliminate the need for computing coordinates from conventional drawing dimensions. The axes for the coordinate dimensioning system should be located so that the coordinates of all points will be positive. Drawings should specify a curve by giving either its algebraic equation or a list of the coordinates of points through which the curve passes. A trained person with sufficient knowledge and skill must study a workpiece drawing and decide upon a manufacturing method or a sequence of steps for the complete machining cycle. He then must write the instructions for a complete machining cycle in the desired sequence. These instructions must then be translated to information, which can be stored on a tape, or other device. Information may be placed on a paper tape by means of punched holes.

Numerical control of machine tools can result in several important advantages. These advantages include faster production, because all ma­chine functions can be programmed to operate at their most efficient rate and simultaneously where possible. Non-cutting periods can be re­duced to a minimum, and thus machines can be utilized to their fullest extent. Since the time required to produce a workpiece remains con­stant, it can be accurately predicted for determining costs. Machines can be set up easier and faster. Higher quality workpieces can be produced, including obtaining closer dimensional tolerances. Less scrap is possible, because human mistakes can be almost entirely eliminated. Monotonous machine operating jobs are eliminated, and numerical con­trol changes the skill required for machine tool operation. The special tooling required for a workpiece can be reduced, with resulting reductions in tool maintenance and tool storage costs. Engineering changes of parts can be made with less cost, since there is less special tooling to change. Making a new tape is relatively inexpensive. Lead time, or the time required to make the special tooling so that production of a part can be started, can be considerably shorter. When the production of the desired quantity of work-pieces has been completed, the tape used for numerical control can be easily stored for use again at some future time. An important limitation of numerical control is the relatively high cost of the machine tool and the additional equipment which is needed. Numerical control, if available, may result in a lower overall workpiece cost, especially when quantities to be produced are low and intermediate.

Manufacturing Methods Of Composite Materials | Composite Processing Methods

Reinforced Composite materials moulding methods

The use of fibre materials to reinforce plastics is widespread. Injection moulded parts such as water tanks, helmets, trays, ducts etc., In such application the reinforcing material is normally in the form of short rovings (Definition: rovings are long and narrow fibre), mixed with and injected with the carrier material. A considerable industry has also built up using woven materials as well as rovings, mainly with epoxy and polyester resins (bending agents), to provide large reinforced plastic parts, or to provide strength to vacuum formed parts.

Techniques for making such large parts involve the use of liquid resin systems in combination with fibrous reinforcement. A male or female single surface mould is used, giving good surface finish on one side only. The moulds are inexpensive, such materials as wood or plaster of paris or reinforced plastics being often used. The technique is to apply a gel-coat to the surface to ensure good surface finish, then to follow this up with layers of reinforcement and further resin, ensuring that the resin thoroughly impregnates the material.

01- hand lay up process for composites - composite fabrication process

Hand lay-up is the simplest and oldest process for moulding of reinforced plastics. It is a popular method for large and complex items manufacturing. It is a low volume production method. Resin and mat are placed on the mould by hand, with brushes and squeegees used to distribute the resin and eliminate air bubbles. Since parts are normally large, and the process is relatively slow, slow room temperature curing resins are normally used, with external heat, usually radiant, applied to speed up the curing as appropriate and when required.

The process is unpleasant, and many of the materials used give rise to allergic reactions. There is some concern for the health of the workers involved.

01- spray lay up process - composite processing methods

The spray-up process is essentially similar. Continuous glass fibre roving is fed through a fibre chopper and spray gun. Roving and fibre are sprayed together onto the mould surface building up the part wall thickness as desired. Since chopped roving is being used, as against woven mat or preform, the strength of the finished article is not equal to that of a good hand-laid product.

To achieve denser, higher quality products, hand or sprayed parts may, during the curing process, be subject to compacting forces by bag-moulding, i.e. by placing a flexible sheet over the lay-up and using vacuum or pressure to apply uniform force over the surface of the moulding. This may take place in an autoclave, providing heat as well as pressure.

Another technique used is filament winding. In this a continuous roving or tape is passed through a bath of resin then wound on a mandrel. When cured the resultant product is very strong, due to the high reinforcement content and its excellent disposition. The process is, of course, limited to axis-symmetric products.

Other than these methods still lot of methods are followed in reinforced fibre industries. Some of the methods currently in use are:

1. Matched die moulding

2. Compression moulding

3. Low pressure low temperature compression moulding

4. Transfer compression moulding

5. Resin transfer moulding

6. Reaction injection moulding

7. Injection moulding

8. Vacuum bag moulding

9. Vacuum infusion moulding

10. Autoclave moulding

11. Pultrusion

12. Continuous laminating

Similar techniques are also utilised using preforms of reinforcing material, coating these preforms by immersion or applying resin by spray (or both) before and during positioning on the mould, to give optimum distribution of reinforcement.