What Is NC Machining?- Definition and Basic Guide

In today’s manufacturing precision, efficiency, and repeatability are key! Numerical Control (NC) machining is the foundational technology that changed how parts are built and introduced modern forms of automation.

Here this article will explain NC machining and give you a basic understanding of NC machining and what it involves.

Definition of NC Machining

NC (numerical control) machining is an automated manufacturing process where machine tools are controlled by programmed commands based on numbers, letters, and symbols on a storage medium.

NC machines differ from manually DNC or automatic machines whose movements are still under direct manual control by a human operator.

NC machines interpret the coded instructions, then machine operations (cutting, drilling, milling, turning, etc.) are performed with a high degree of repeatability and accuracy.

The “numerical” nature is in the alphanumeric codes itself. The machine tool will interpret alphanumeric (i.e. “numbers”, “letters”, and “symbols”) to perform designated functions such as tool path, cutting speed, feed rate definitions, tool change, etc.

What is NC Machining?

Numerical control (also called computer numerical control, and most commonly referred to as CNC) is the automated control of machining tools (for example, drills, lathes, mills, and 3D printers) by means of a computer.

A CNC machine processes a piece of material (for example, metal, plastic, wood, ceramic, or composite) in order to exact a specification, and does so by following the coded programmed instruction, without a manual operator directly controlling the machining operation.

A CNC machine refers to a motorized maneuverable tool and a motorized maneuverable platform, which are both controlled by a computer, according to specific input instructions.

Instructions are given to a CNC machine as a direct follow-on sequential program of machine control instructions (such as G-code and M-code) and then executed.

Programs can be written by a person, but far more likely, generated by graphical computer-aided design (CAD) software and/or computer-aided manufacturing (CAM) software.

When it comes to 3D printers, the part to be printed is “sliced” before instructions (or the program) are generated. 3D printers also use G-Code.

CNC is significant improvement over machine shops of the past which had to be manually controlled (using hand wheels, levers, etc.) or mechanically controlled (by pre-fabricated pattern guides, (i.e. cams).

Current CNC systems, the design of a mechanical part and its manufacturing program is largely automated;

The mechanical dimensions are defined in CAD and turned into manufacturing directives by CAM software.

When complete, the directives are turned (by “post processor” software) into the commands needed for a particular machine to produce the part, and loaded into the CNC machine.

Since a particular part can be made with a range of tools (drills, saws, etc.) contemporary machines often have multiple tools in one “cell”.

In other configurations, a number of machines are utilized with an external controller and operators, either human or robots, moving the part from machine to machine.

In either case, the series of steps needed to produce any part is highly automated and produces a part that closely matches the original CAD drawing.

How Does NC Machining Work?

NC machining (Numerically Controlled machining), is an automated method of manufacturing parts using a series of steps that are pre-programed with instructions from a computer.

Automated controls allow machines (machine tools) to execute precisely defined work processes to produce parts that meet continuous repeatable, and high quality production.

Here are the steps in the NC machining process:

#1. Programming the Machine.

The first step in NC machining is to program the machine with precise instructions.

The instructions are programmed using codes (e.g. G codes and M codes) that tell the machine how to perform the required operations desired in the programming.

Programming is completed using CAD and CAM software. This type of program helps to generate and ensure precision in the commands given to the machine tool.

#2. Setting Up the Machine Tool.

Once the machine program is ready to execute, it’s time to set up the machine tool. This step includes the installation of the cutting tools, as well as , choking the workpiece in position.

It is essential to take care of the set-up procedures properly and accurately so that no concerns are raised once the machining process starts , and that the product is made exactly to specifications.

#3. Executing the Machining Operation.

With the program loaded in and the machine tool ready to execute it’s commands, the machining operation begins.

The predetermined programming instructions allow the NC machine to effectively carry out the directed operation; drilling, milling, cutting etc.

All movements and operations at very precise and close tolerances, and repeatability, are controlled by only following the commands in the technology.

#4. Inspecting the Final Product.

When the machining operation is entirely finished, the final product is inspected to confirm the part meets the acceptable standards.

The inspection is done through measuring the dimensions of the part, searching for defects, and making actual comparisons with part specifications described in the product design.

What are the Key Components of an NC Machine?

Knowing what the major parts of a NC machine is important so that you can also understand how the machine works differently from modern CNC (computer numerical control) machines.

These eight major parts of NC machines are:

#1. Controller.

The controller is the most important part of the NC machine. It is often referred to as the brain of the machine. This is where the input directions are processed; the machine tools are directed to follow the input directions from the controller.

In CNC machines, this component is more sophisticated than NC machines; CNC controllers can run complex algorithms and process real-time data.

#2. Machine Tools.

Machine tools are the tools perform the actual cutting. Some examples of machine tools, are, drills, lathes, mills.

These machine tools are attached to the machine. They are moved according to the controller’s input directions.

In CNC machines, there is a greater degree of breadth and flexibility of machine tools. This means CNC machines can perform more intricate and precise machining operations.

#3. Input Devices.

Former NC machines relied on punched tapes to provide the machine with its input instructions. Input instructions to the NC machine are simply sequences of code that the NC machine reads and follows.

Unlike prior NC machines that used punched tapes, CNC machines utilize digital input devices to provide the machine with software input instructions.

The common input devices of digital input methods include computer-aided design (CAD) files and computer-aided manufacturing (CAM) software.

#4. Servo Motors.

These motors are responsible for the movement of the machine tools. They ensure that the correct movements are made with accuracy. The motors receive signals from the controller which tells them the correct movement to make.

CNC machines also utilize servo motors, but the motor used in a CNC machine can make smooth and fast movements.

#5. Feedback Systems.

Feedback systems are also responsible for watching the operations to make sure that the machine tools are operating as expected.

They transmit information back to the controller which may have to make adjustments to maintain accuracy.

Feedback systems primarily can be more robust in CNC machines. They also have the potential to be more precise on utilizing feedback and more control over the machining process.

#6. Drive System:

Is comprised of both motors (servo motors or stepper motors) and lead screws or ball screws that take the signals from the MCU and translate them into precise linear and rotary movements of the machine’s axes.

#7. Workholding Device:

This is what holds the raw material in place while machining occurs. Workholding devices come in many shapes/form to hold various shapes/forms of material. Popular examples are vises, clamps, and chucks.

#8. Tooling System:

This incorporates the many actual cutting tools (end mills, drills, inserts, etc.) that remove material from the working piece.

What Controls the Movements of NC Machines?

The movements of an NC machine depend on the combination of parts working together, and not all of the parts are hardware.

The hardware utilizes software components, and the software has parts to provide feedback to the control unit to ensure proper movement of the NC machine.

• Control Unit: This is the brain that controls the machine. Consists of a unit that reads programming that must often be in G code format, and translates those directions into signals to control the movement of the machine.
• Servo Motors: These motors receive signals from the control unit and are responsible for moving the machine tools to the correct position. Servo motors play a vital role in controlling speed and position precisely.
• Feedback Systems: Feedback systems (encoders and sensors) provide real-time data regarding all possible positions and movements in the machine. Information recorded by encoders and/or other sensors is sent back to the control unit. This information calculates how the machine should operate to ensure accuracy.

What Types of Sensors Are Used in NC Machines?

Sensors are very useful in ensuring the accuracy and efficiency of NC machines by providing real-time data allowing adaptive control and feedback systems.

• Position Sensors: These are encoders and resolvers which have the ability to observe the position of machine components to ensure accurate movements.
• Force Sensors: Force sensors can be installed to measure cutting force to ensure cutting force stays within limits to protect the tool and maintain an effective machining operation.
• Temperature Sensors: Temperature sensors measure the temperature of machine components and the workpiece. When appropriate temperatures are recorded, the operator can adjust to avoid damage or other problems and also maintain consistent material properties.
• Vibration Sensors: Vibration sensors determine if the machining process has extensive excess vibration that could cause machining problems affecting accuracy and tool life. The machine can then adjust machining parameters accordingly to avoid excess vibrations.

Types of NC Machining Operations

NC technology is used in various machining processes. Below are some examples of NC Machining Operations:

• Milling: A multi-point cutting tool rotates while material is removed from a workpiece that is stationary. Has the ability to machine flat surfaces, slots, holes, arcs, and complex 3-D contouring operations.
• Turning (Lathes): A lathe rotates a workpiece while a single-point cutting tool removes material to typically form cylindrical or conical shapes.
• Drilling: Use a rotating drill bit to create cylindrical holes in a workpiece.
• Grinding: Use a grinding wheel specifically for wear and finishing to remove small levels of material and becomes very high precision.
• Electrical Discharge Machining (EDM): Uses electrical sparks and hate to erode material from a workpiece. Ideal for very hard metals and complex geometry.
• Laser Cutting: Uses a focused laser beam to cut and/or engrave materials by melting or vaporizing them.
• Plasma Cutting: Cuts through electrical conductive materials using a high-velocity jet of ionized gas (plasma)
• Waterjet Cutting: Uses a high-pressure stream of water (often mixed with abrasive materials) to cut through a variety of materials.

Types of NC Machine

NC (Numerical Control) machines come in various types, each designed for specific applications and machining processes.

Understanding these types helps in selecting the right machine for a particular manufacturing task.

#1. Point-to-Point (PTP) Machines

Machines that specifically perform movement from one point to another discrete point in the workspace.

For instance, a point-to-point machine would be ideal for drilling, spot welding, and punching workpieces because the tool has to move to a specific place on the workpiece, perform an operation, and then move to another place.

The distinction of any point-to-point machine is the ability to make precise control of the tool’s position to accurately measure operations.

#2. Continuous Path (Contouring) Machines.

Continuous path machines are designed to perform complex movements along a unique path.

Contour machines are completely different than point-to-point (PTP) machines because PTP machine coordinates can only move from one unanimous coordinate to another, whereas, contour machines can move simultaneously in multiple axes.

This allows them to generate detailed and smooth surfaces, causing the machine to be suitable for purposes of milling and complicated cutting operations.

#3. Dedicated Machines.

These machines are built for one purpose and do not have the versatility of other machines.

The efficiency of these machines is very high because they are very good at repetitive operations.

Dedicated machinery, for example; each of these machines are made for a specific function; drilling, boring, cutting, they are made specifically to perform their function as effectively and as quick as possible.

#4. Modular Machines.

The major feature of modular machines is flexibility. They consist of machines which allow the user to change the machine to more than one task by simply adding modules or subtracting them.

This ability makes them very flexible and useful for various machining jobs.

#5. Adaptive Control Machines.

These machines use internal feedback processes which automatically update the operating parameters of the machine, depending on variables in real time.

This allows them to do a task more effectively, using less power and assigning less warp to the workpiece, if changes are made based upon feedback from variables in the machining task.

Types of NC Systems

NC systems have been created for a variety of manufacturing operations to produce product with precision, efficiency and automation.

The different NC systems can exist for various manufacturing requirements and to understand these helps to understand which type of system can accommodate each requirement.

#1. Point-to-Point (PTP) Systems.

These systems are designed to move the machine tool from one discrete point to another, stopping at each point it moves to with the purpose of performing an operation.

These systems are good for operations which use the machine to reposition the tool at points on the part, where the operations to do are not based on feeding the tool continuously along a path

Applications:

• Drilling: PTP systems are great for drilling operations where exact hole location is paramount.
• Spot Welding: PTP systems are excellent for spot welding, where the tool must be moved to specific points on the workpiece.
• Component Insertion: PTP is appropriate in automated assembly processes, where components must be put at precise locations.

#2. Contouring Systems.

Contouring systems (also known as continuous path systems) are designed to perform operations that are not limited to point-to-point; instead they follow a complex, continuous path.

Contouring systems are great for any operation where the machine tool is moving continuously and smoothly along a path. Milling and engraving are examples of such operations.

Applications:

• Milling: Contouring systems are ideal for milling operations where the tool needs to continuously mill along a path so as to create complex shapes.
• Engraving: Contouring systems are great for engraving a detailed and intricate design on a variety of materials when smooth and precise movements are necessary.
• Mold Making: Contouring systems are employed for creating precise and intiricate molds for manufacturing.

#3. Closed-Loop Systems.

Closed-loop systems utilize input from sensors as feedback to continuously monitor its movements, and correct the machine’s operation in a continuous manner.

The feedback system aims to ensure high precision and continuity when the machine deviates from the path.

Applications:

• Precision Machining: Closed-loop systems are used in applications needing high precision and accuracy. A typical example would be aerospace and medical device manufacturing.
• Complex Operations or Information gathering: Closed-loops systems are ideal for complex machining tasks that require the process to be continuously monitored and information to be gathered regarding the processes that will help continue to improve quality.
• Quality Control: Closed-loop systems are used in situations where it is necessary to maintain quality, so that the correct form and function is employed and that each part is within exact specifications.

#4. Open-Loop Systems.

Open-loop systems use no feedback which means they have a sequence of instructions and strictly follow those instructions without any feedback/change based on the surrounding environment.

Open-loop systems are very straightforward and inexpensive. Open-loop systems are appropriate for conducting operations where the feedback control is not very important.

Application:

• Basic machining operations that do not require precision. Such as a simple drilling operation or a simple mill cut.
• Education Use: they are quite common in education, so that students learn the basics of NC machining, without the complication of feedback.
• Low cost manufacturing: they are appropriate in a manufacturing environment when cost is the primary factor and the required precision is acceptable.

Difference Between NC and CNC Machine

Numerical Control (NC), and Computer Numerical Control (CNC) are two processes in which computer networks are used to control machine tools.

You have heard both of them, but, you are probably wondering what the difference is between NC vs CNC machines.

In general terms, NC machining is usable in simpler applications, and CNC machining is usable in more complex applications.

NC machines operate with an instruction set that is coded to tell the machine what operations to perform. These instruction sets are called G-codes.

While CNC machines operate using a set of computer generated instructions, which are called programs. These programs can be used from a CAM (Computer-Aided Manufacturing) system.

NC vs CNC Machine

Numerical Control (NC)	Computer Numerical Control (CNC)
Stands for Numerical Control.	Stands for Computer Numerical Control.
Uses punch tapes and punch cards for input.	Uses keyboards for input.
Alteration in operation parameters is not possible.	Alteration in operation parameters is possible.
No memory for storing instructions.	Memory exists to store instructions.
Less expensive than CNC.	More expensive than NC.
Maintenance cost is low.	Maintenance cost is high.
Requires highly skilled operators.	Requires less skilled operators.
Less flexible than CNC.	More flexible than NC.
Less accurate than CNC.	High accuracy.
Execution of jobs takes more time.	Execution of jobs takes less time.
Cannot run continuously.	Can run continuously for 24 hours a day.
Limited machine control.	Advanced machine control capabilities.
Programming changes are difficult.	Easy to update and modify programming.
Limited to a basic set of instructions.	Can execute a complex set of instructions.
Lower precision.	High precision in operations.
Less capability for intricate tasks.	Greater capability for intricate and complex tasks.

The Evolution: From NC to CNC

Although the term NC machining is often sufficiently interchangeable with regard to CNC machining, they are not the same.

Early NC (1940s-1960s):

The first NC machines were developed back in the late 1940s by a group led by John T. Parsons.

The first NC machines used punched paper tapes or punched cards to store instructions which were then translated mechanically by the machines to execute the original design.

The NC systems were revolutionary but limited as far as flexibility and would also take a lot of time to modify. Any change in design would be a new tape.

CNC (1970s+):

Digital computers were developed in the 1970s which aided the migration of NC systems to CNC systems.

Today, the CNC systems use a computer (usually an onboard controller) which directly interprets the programming language that runs the machine, there is no longer a necessity for tapes or cards to convey information.

CNC systems allow simpler program storage and editing and allow for more complex machining operations. Today, the vast majority of NC machines are actually CNC machines.

For the purposes of this guide, I will be addressing both NC and CNC and will also note that the vast majority of implementations today are CNC.

Applications of numerical control technology

Numerical control technology has applications in a variety of production operations such as automatic drafting, inspection, assembly, welding, machining, spot welding, metal machining, machining, etc.

In the end, we essentially all agree that the majority of NC applications or examples occur within metal machining processes. NC can execute virtually all processes associated with removing metal. (i.e. Turning, sawing, Grinding, Milling, Drilling).

The production operations in which numerical control machines are appropriate are summarized below.

• Numerical control technology is appropriate if workpiece and/or processes involves multiple machining operations.
• The geometry of the job is complicated and value-added. Making errors during machining means there are more ways to have a high-value part wasted.
• The expectation of future design changes to the engineering.
• The volume of material to be removed.
• A requirement to inspect the work piece is 100%.
• To have close tolerances to the dimensions on the job workpiece.
• There are many operations to be machined when machining parts and therefore they are typically machined in batches of small lot sizes.

Advantages of NC Machine

• More flexibility of manufacture. It is easy to adapt NC machines to design engineering changes let alone a change in production scheduling.
• Reduced lead time in manufacture. It is easy to set up the job using NC which makes production quick and simple.
• Fewer non-productive times. NC helps reduce non-productive time where machining is complex. It eliminates the set-up and handling time between workpeices, plus it speeds up automated tool changing.
• Fewer fixturing. Fixturing requirements in NC operations are less complicated, and less expensive to what they would in conventional shops. In NC tapes, fixturing and parts jigs are not necessary, the NC tape provides positional reference.
• Fewer inventories. The fewer setups and lead times are functions of inventories affected by much more infrequent, albeit planned, events
• Quality assurance. Zero risk of human error. Produces the part to a level of accuracy that removes or significantly decreases the amount of man-hours put into the inspection.
• Greater operator safety.
• Less scrap. NC technology increases accuracy from fittings to scrap size material.
• Less floor space used. Every standard NC machine can provide a variety of processes or will offer the opportunity to combine lightweight products into one machine; standard NC gives success to less space.

Disadvantages of NC Machine

• Capital and costs of maintenance. More sophisticated and complex technology always costs more than conventional machine technology.
• Requires trained operators. Finding and training NC personnel is at issue in itself.
• The constants breaking and wear of tape punches; unreliable tape punch elements.
• Errors in part programming to punched tapes.
• Not having optimal feeds or speeds for cutting. Conventional NC machines disallow swaps for feed rates and cutting speeds during the operations. This is useful to have more precise and rapid feeds to improve effectiveness.

FAQs

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