CNC Machine Definition, Advantages, Limitations and Classification:
Computer Numerical Control (CNC) is a specialized and versatile form of Soft Automation and its applications cover many kinds, although it was initially developed to control the motion operation of machine tools.
The definition of CNC given by Electronic Industry Association (EIA) is as follows:
“A system in which actions are controlled by the direct insertion of numerical data at some point. The system must automatically interpret at least some portion of this data.”
In a simple word, a CNC system receives numerical data, interpret the data then control the action accordingly.
Numerically control is a method employed for the controlling the motion of a machine tool slides and auxiliary functions with an input in the form of numerical data. A computer numerical control is a microprocessors based system to store and process the data for control of slide motions and auxiliary functions of the machine tools. The CNC system is the heart and brain of a CNC machine which enable the operation of the various machine members such as slides, spindles, etc. and also optimizes the machining with proper parameters involved in a machining operation.
CNC refers to a computer that is joined to the NC machine to make the machine versatile. Information can be stored in a memory bank. The programme is read from a storage medium such as the punched tape and retrieved to the memory of the CNC computer. Some CNC machines have a magnetic medium (tape or disk) for storing programs. This gives more flexibility for editing or saving CNC programs.
Advantages of CNC Machines:
1. Increased productivity.
2. High accuracy and repeatability.
3. Reduced production costs.
4. Reduced indirect operating costs.
5. Facilitation of complex machining operations.
6. Greater flexibility.
7. Improved production planning and control.
8. Lower operator skill requirement.
9. Facilitation of flexible automation.
Limitations of CNC Machines:
1. High initial investment.
2. High maintenance requirement.
3. Not cost-effective for low production cost.
Some common types of CNC machines and instruments used in industry are as following:
• Drilling Machine
• Lathe / Turning Centre
• Milling / Machining Centre
• Turret Press and Punching Machine
• Wirecut Electro Discharge Machine (EDM)
• Grinding Machine
• Laser Cutting Machine
• Water Jet Cutting Machine
• Electro Discharge Machine
• Coordinate Measuring Machine
• Industrial Robot
CNC machines can be divided into two groups
1) Milling Machines: A milling machine is a machine that has a spindle with a special tool that spins and cuts in various directions and moves in three different directions along the x, y and z axis.
2) Turning Machines: A turning machine is generally made up of a device that spins a work piece at a high speed and a tool (sharp edge) that shaves off the undesired material from the work piece (where the tool is moved back and forth and in and out until the desired form is achieved).
CNC Machining Centers
The machining centre, developed in the late 50’s is a machine tool capable of multiple machining operations on a work part in one setup under NC program control.
Machining centres are classified as vertical, horizontal, or universal. The designation refers to the orientation of the machine spindle.
A vertical machining centre (VMC) has its spindle on a vertical axis relative to the work table. A vertical machining centre is typically used for flat work that requires tool access from top. E.g. mould and die cavities, Large components of aircraft.
A horizontal machining centre (HMC) is used for cube shaped parts where tool access can be best achieved on the sides of the cube.
A universal machining centre (UMC) has a work head that swivels its spindle axis to any angle between horizontal and vertical making this a very flexible machine tool. E.g.: Aerofoil shapes, Curvilinear geometries.