NC Machine: Definition, Parts, Types, Coordinate System, Pros, Cons, Apps [PDF]

In this article, I shall share knowledge about NC machines. I will explore its definition, parts, types, working principles, advantages, disadvantages, and applications. I have also given a PDF for the same.

What are NC Machines

An NC Machine stands for Numerical Control Machine it is the predecessor of CNC Machine. It is a manufacturing equipment wherein the Operator doesn’t manually adjust parameters. The parameters like Depth of the cut, Feed Rate, speed, etc. It isn’t software-driven but a more hardware-driven machine. It operates on coded instruction that consists of letters, symbols, numbers, etc.

These coded instructions are converted to electrical signals. These electrical signals are then used to control the machine motors or functions. This working principle allows the NC machines to be precise and automate various manufacturing processes.

These machines promote reduced time consumption, increased production efficiency, and minimized material wastage. Similarly, it also eliminates the need for manual skills and labor

Basically, NC is a concept of machine control through numerical instructions

What is NC Machine

NC Machine parts or Components

These are the various parts of the NC machine that help it perform its operation which include the following.

Program/ Set of instructions

A program of instructions is a step-by-step guide for a machine tool, telling it what to do. These instructions are typically stored on an input medium like L-in-wide tape. In the past, other media like punched cards, magnetic tape, and even 35mm film were used.

There are two other input methods: manual data input (MDI) for simple, one-time tasks, and direct numerical control (DNC) for computer-linked input. A part programmer creates this program, specifying how the machine tool should move relative to the workpiece. The program, in alphanumeric form, serves as input for the machine control unit (MCU).

MCU (Machine Control Unit)

The Machine Controller Unit, encompasses the electronics and hardware responsible for reading and interpreting the program of instructions, converting them into mechanical actions for the machine tools. This control unit manages tasks such as equipment movement, feeding, tool changes, and other functions.

Typical components found in a traditional NC controller unit comprise tape readers, a data buffer, signal channels for machine tools, and feedback channels from machine tools, all coordinated by series controls to ensure the smooth operation of these elements.

The key components of MCU are as follows:

  • Tape reader
  • Signal output unit
  • Sequence coordinator
Output Channel For Signals

These channels transmit instructions to the machine tool (servomotor), guiding it on what task to execute and how to execute it.

Parts of NC Machine
Components of NC Machine
Tape Reader

This device, known as a tape reader, is an electromechanical component designed to interpret the instructions encoded in a punched tape.

Sequence Coordinator

The sequence coordinator orchestrates and manages the order of operations for the machine control unit, ensuring tasks are carried out in the correct sequence and timing.

Data Buffer

It retrieves and processes the information stored in a tape reader.

Drive Units (Servo Motors)

The machine’s axes are powered by robust DC servo motors with preloaded ball bearings. Signals from the control unit activate these servomotors, enabling various slides to move, achieving the desired travel length and feed rate. Typically, the drive units employ hydraulic DC motors or stepping motors.

Feedback Unit

These channels transmit data back to the machine control unit, often referred to as the position feedback package. It relays information about the real-time position of movements to the control unit, which then compares it to the desired movements and triggers drive units for any needed corrections.

Machine Tools

This is the part of the NC machine responsible for carrying out specific operations. For instance, a drilling NC machine comprises components like spindles, motorized movement controls, cutting tools, work tables, fixtures, and supporting gear. These elements follow instructions from the controller unit to execute tasks such as drilling, cutting, tool changes, and rotation.

Control Panel

Within the NC system, the control panel, whether integrated with the controller unit or the machine tool, houses the dials and switches that the operator uses to operate the system. It may also feature data displays to provide information to the operator. While the NC system is primarily automated, the human operator is still essential for tasks like powering the machine on and off, tool changes, and loading and unloading the machine.

NC Machine Working Principle
Working Principle of NC Machine

types of NC machines

NC machines are classified into four main categories each with distinct characteristics which are as follows

Motion Control Classification

Under this classification, NC machines are categorized into three types:

Point-to-Point Mechanism

Moves between specific points, simple and cost-effective

Straight Cut Mechanism

The tool moves along an axis, suitable for milling and point-to-point tasks.

Contouring Mechanism

Complex, control multiple axes for intricate shapes

Classification According to Control Loops

NC machines are categorized into two types based on control loops:

Open Loop

Provides instructions but may lack precision, cost-effective for simpler tasks.

NC Machine types
Types of NC Machine
Closed Loop

Uses sensors for accuracy, more complex and costly.

Classification Based on Power Supply

NC machines can be classified into three categories based on their power supply:

Electric

Utilizes AC/DC motors for versatility

Hydraulic

Compact, high torque, ideal for rapid response

Pneumatic

Rarely used, less torque

Classification According to the Positioning System

According to the positioning system, NC machines are classified into two types:

Incremental Positioning

Determines position from the previous one

Absolute Positioning

Uses a fixed point as a reference, and calculates position independently.

NC Coordinate System

NC systems differ in their ability to control multiple motion instructions on a machine tool. In this coordinate system, each object can move in six ways: three translations along the X, Y, and Z axes, and three rotations clockwise or counterclockwise around these axes.

Commercial NC systems can simultaneously control two, two and a half, three, four, or five degrees of freedom (axes). A standard setup includes three linear translations (3-axis system) or three linear translations and one worktable rotation (4-axis system).

NC Coordinate system 
NC Machine Coordinate system

This coordinate system uniquely identifies positions within the machine’s workspace. Position data is always referenced to a calculated point with defined coordinates.

The machine manufacturer sets a permanent reference system called the machine coordinate system. Users can independently choose a coordinate system for each workpiece, with the control system understanding its position and origin relative to the machine coordinate system. This flexibility ensures the accurate application of position instructions from an NC program to the workpiece.

Advantages of NC Machine

  • High precision, less waste.
  • Versatile.
  • High machine utilization.
  • Easy complex programming.
  • Quick design changes.
  • Enhanced production control.
  • Space-efficient.
  • Speedy product development.
  • Skilled operators are not essential.
  • Efficient machine use.
  • Lower labor costs.
  • Automated settings, no manual adjustments.
NC Machine Pros & Cons

Disadvantages of NC Machine

  • High initial cost.
  • Programming expertise is needed.
  • Requires skilled programmers.
  • Increased maintenance expenses.
  • Demands higher-skilled operators.

Application of NC machine

  • Key in metalworking.
  • For metal cutting, milling, drilling, and more.
  • Used in punch presses and thermal cutting.
  • Boosts precision and efficiency.

Conclusion

I hope my blog on NC Machines Helped you understand the definition, parts, working, coordinate system, advantages, disadvantages, and application. Feel free to write to us in the comments if you have any doubts

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