Understanding Numerical Control

Introduction to Numerical Control

• Numerical control involves utilizing a computer to manage and observe the actions of a machine tool, whether stationary or portable.

Principles

• The rapid industrial growth since the start of the 20th century, along with the extensive use of machinery powered by motor energy, mandated a continuous search for more efficient processes.
• Industries faced the task of adapting to technological progress by automating manufacturing processes, aiming to design machines proficient in autonomously executing all manual tasks previously done by an operator, during the first part of the 20th century.
• CNC originated in the 1950s at the Massachusetts Institute of Technology (MIT) with the automation of a large milling machine for the first time.
• Early computers were large, often consuming more space than the machinery they controlled.

Definition of Numerical Control

• Numerical Control is due to the commands being indicated through numerical codes that are given to the machine.
• For example, if a machine must move a tool describing a 10mm square, the appropriate codes would provided.

Advantages of CNC

• Automates machine movements.
• Offers flexible automation through easily modifiable programs.
• Allows for unattended machine operation.
• Diminishes the impact of operator skill on machine operation.
• Enhances movement precision and speed.

CNC Machine Types

• Turning centers available.
• Machining Centers available.
• Hybrid machines exist.
• Grinding machines available.
• Machines such as electroerosion, laser cutting, and water jet cutting.

The structure of CNC

• The structure includes input devices, CNC program, controller, processing unit, closed circuit unit, monitor, G and M codes, feedback of position and speed, actuation system, and a machine tool.

Functions of CNC

• All CNC machines share the following similar characteristic: have two or more programmable directions of movement referred to as axes.
• A axis of movement can be linear (straight line) or rotary (on a circular path).
• Movement can be controlled through absolute values (G90 code) or incremental values (G91 code).
• Optional accessories include an automatic tool changer, spindle speed and activation, and coolant features.
• CNC Program: Is a sequential series of instructions.
• CAM: CNC programs are sometimes difficult to write due to complexities, that a CAM program solves.
• DNC System: The CNC program must be loaded into the controller using a numerical control distribution system (DNC), whether from CAM or manually.
• CNC Controller: Interprets the program, activates commands, initiates movements and overall, adheres to program instructions.

Programming examples

• Various manufacturers that provide specification of programming codes for their machines are, General Electric, Fanuc, Anilam, Mazatrol, Siemens, Milacron, Denford, and Heidenhain.

• Numerical codes for G, X, Y, Z, etc, include:

  • Auxiliary functions
  • Tool number
  • Spindle Speed
  • Feed Rate
  • Axis Coordinates

• As an example, a machine can move a tool to describe a 10 mm square through the following steps.

Absolute Value (G90)

• Absolute coordinates means that distances are referenced from the origin (0,0) with X and Y axes.
• Use absolute coordinates when the X and Y coordinate values are available.

Incremental Value (G91)

• Each point is relative to another, measuring the distance/increment between two points.

G Codes

• They describe machine movement functions such as rapid movements, feed rates, or cycles.

M Codes

• Describe the miscellaneous functions required for machining a part, but do not correspond to movements of the machine.
• Examples include tool change, coolant activation, and program stop.