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Fundamentals of CNC

Fundamentals of CNC

Introduction

In the earliset efforts to attain automations, the general process of searching for improvement and elimination of wastage was resorted, so as to achieve reduction in the cost of production. The process is know as rationalization when it is coupled with mechanization
It leads to automation. The degree of mechanization may vary to suit the level of production.

Automation is a technology of working in which handling methods, process and design of products are integrated to utilize economically justifiable mechanization of thought and effort to achieve automatic and self-regulating chain of process.

Early automatic devices

Early automatic devices attempted gradual replacement of human labour by adopting mechanical electrical technologies capable of doing physical and even mental work as in numerical control or adap control machines.

Falcon Knitting Machine:

In the early 1700's, M. Falcon invented a perforated card controlled knitting machine. Each of these cards was chain-synchronized to the action of the knitting machine. Each hole in a given card set up a mechanical linkage which caused a needle associated with a particular column on the card to pull specific colour of thread through the cloth at that location. Falcon's invention was inherently limited to low production.

The Jacquard loom of 1801

In 1801, J.M. Jacquard invented improved controlled knitting and weaving machine permitting higher output and lower unit costs. Which continues to be widely used in modern production? This machine utilize like discs with patterns of peripheral teeth giving higher volume of production. Such machines are analogous to automatic screw machines or tracer machines in the metal cutting industries


Structure of NC & CNC Machines.

Objectives 

At the end of this chapter trainees will be able to
 
1.the open loop and close loop system.

2.NC & CNC Explain the major parts, major switches and its functions.

3.Explain the internal & external structures of the CNC machines.

4.Explain the limitation of NC & CNC machines.

SHORTCOMINGS OF CONVENTIONAL MANUFACTURING METHODS:

Better quality and quantity of manufacture can be achieved with conventional machine tools also.

however requires either of the following conditions:

i Conventional machine tools being operated by skilled and efficient operators using elaborate dedicated tooling. 
ii.Use of automats and or transfer lines.

It may be noted that the success of the system depends on availability of skilled individuals to a large extent. Moreover the volume of production should be sufficiently large to justify investment in elaborate The tooling The application of Automats and transfer lines makes the system very much constrained to cater to one particular type of production only.

MANUALLY CONTROLLED MACHINING.

The Operator produces the work piece manually, using information from the part drawing.

(POSITION CONTROL LOOP)- The procedure in which m/c slides are moved by means of hand wheels, feed lever, positions are controlled on the scales of the machines. In case of manual machining,

The operators control tool positions by observing the Scales on the machines.

The position control loop for controlling the machine slides consists of:

Control system- programmable control in the switch cabinet – feed motors - linear measuring systems.




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