CNC is one of the many subtractive machining processes for rapid part and prototype production. It uses various cutting tools from lathes to laser cutters to ensure precision tolerances and since everything is automated, how does CNC machining work? Where do you start with understanding CNC machining?
In this guide, you’ll understand how CNC technology can make complex parts, the need for automation in the manufacturing industry, and tips for getting started with your first CNC project.
Why Is CNC Important For Modern Manufacturing?
Current manufacturing processes require extreme accuracy, efficiency, and productivity. CNC is the only manufacturing process that combines these three qualities to produce parts at any scale.
CNC technology can integrate with other technologies like CAD in design and CAM in manufacturing. This means you can design something using computer-aided design software and optimize it for mass manufacturing using CAM software and a simple G-code output.
You can even, edit CNC programs directly to adjust angles, rotational direction, and depth of cuts at each step.
Plus, there are specialized CNC machines for particular operations like milling, drilling, and turning and some even combine these operations into one offering freedom of more than 3 – axes. That means the cutting tool can move in X, Y, and Z and rotate around X and Y directions.
Such customizability and versatility make machining custom parts easy and quick.
Start Here: What Is CNC Machining?
CNC machining parts are produced by removing material from a blank using single or multiple cutting tools. The tool operates using a micro-computer installed in the CNC machine which interprets CNC program language called G-code or M-code.
Computer Numerical Control (CNC)
CNCs operate via numerical control. It involves using a pre-programmed set of instructions using a language called G-code (Geometric code) to define the path and speed of the cutting tool.
CNC machining relies on a control unit that reads the coded instructions and sends signals to different components, turning them on and off, like the coolant supply.
Brief History of CNC Machining
CNC machining originated in the 1940s when John Parsons collaborated with MIT to produce magnetic punch cards to control machine movement. A punched tape had columns with holes in specific positions. Each column had a specific instruction, like movement in the Y axis, cutting speed, and orientation.
In the 1960s, to standardize different NC machines and punched tapes, with the help of microcomputers, numerical control changed to Computer Numerical Control or CNC.
By the 1980s, CNC technology employed CAD software for precise drawings and manufacturing.
How Does CNC Machining Works?
CNC machines work by interpreting the standardized G-code from 2D or 3D CAD programs to run the repetitive commands and cycles of material removal with no human involvement during the process.
It is also possible to load instructions or edit the pre-programmed instructions in the machine itself. A CNC machinist can easily add commands through manual control of the CNC machine.
A CNC machinist prefers a closed-loop system, which can determine any errors in coordinates and correct them. Closed-loop CNC routers usually have a sensing probe that touches a known coordinate on the bed to re-calibrate after a tool change.
Steps of CNC Machining Process
Whether you are using CNC mills, CNC lathes or multi-axes CNC machines, the CNC machining process is universal and mostly has the following sequence.
Start With a CAD File
You don’t have to learn CNC programming to understand the CNC process. Use a Computer Aided Design tool like Autocad to make your 2D/3D design file. This file should account for all details in machining like tight tolerances, dimensions, and shape of your part.
Using this file, you can generate a technical drawing or make a 2D drawing from scratch, this will inform the CNC operator about the machining operations and dimensions for quality checks.
Using CAM Software To Export CNC File
You can use Computer Aided Manufacturing software to create CNC-readable machining instructions as a G-code file. CNC machinists can upload this file to CNC machines and place a blank to start machining.
Creating Tool Path
It is generally, good practice to generate the tool path in the machine setup of your pre-programmed computer software (CAM) and select the cutting tool before making the G-code file. Computer Numerical Control machining allows you to alter the tool path or even control the tool path but this can introduce error at the machining stage.
Start Machining
After placing the workpiece blank in the holder, the CNC operator can simply tap the start button and execute the entire machining process. This is completely automated and the stopping instructions are also in the CNC program file (G-code).
Types of CNC Machines
There are many types of CNC machines, some of which are even hydraulic CNCs. The focus of this guide will be electrical CNC machines since they are the most common and efficient CNC machinery.
Most CNC machines are used for subtractive manufacturing or material removal from a standard blank. The difference in types of CNC machines is generally the cutting tool and axis of rotation.
3-Axis CNC Machine
These are the most common types of CNC machines. CNC turning and CNC milling operations generally use 3-axis CNC machining. The cutting tool or workpiece can take advantage of movement in the X, Y, and Z axes.
In other words, the tool can move in the horizontal and vertical directions and add depth. 3 axis machining is a versatile CNC manufacturing method that produces affordable parts for smaller businesses.
In most CNC equipment, the tool moves in 3 axis, which means the operation in 3 axis is mostly CNC milling.
5-Axis CNC Machine
In addition to the three translational axes, 5-axis CNC machining takes advantage of two additional rotational axes. This allows the tool, to move in three axes and the workpiece to rotate around 2 of the tool axes (usually X and Y).
Complex machinery like turbines or angled propellers for drones can make use of CNC manufacturing in 5 axis.
New: Multiple Axis CNC Machine
Multi-axis CNC equipment is a range of new CNC technology that have X, Y, Z, A, B, C, and additional rotary axes. This means CNC mills and CNC lathes no longer need to be a separate machine, making turn-mill machines with linear and rotational capabilities.
Most CNC machines are used for subtractive manufacturing or material removal from a standard blank. The difference in types of CNC machines is generally the cutting tool and axis of rotation.
CNC Milling Machine
In CNC mills, the cutting tool rotates using a spindle. The tool can translate into 3 axes and cut the material using the rotating spindle. The cutting tool can change, however, the rotation and axes movement do not change.
Some CNC mills can also use more axes of freedom, adding two more rotary axes for complex shapes. CNC mills are largely used in facing operations.
CNC Lathe
In CNC lathes, the cutting tool is stationary and the workpiece rotates at high speeds in the CNC lathe chuck. The CNC lathe is limited in its axes translation and most CNC lathes operate in the X and Z axis.
Modern CNC systems use turret CNC lathes which have multiple tools (up to 12) that allow swift tool change.
CNC Plasma Cutter
Plasma cutter works with conductive materials like metals. It uses a plasma torch that is made of flammable gas and an electrical arc. The sparks combined with the gas, create a jet of plasma that can cut metal.
CNC plasma cutters are widely used in the sheet metal industry to cut cross-sections quickly. Most CNC plasma cutters operate in the X and Y axes making them ideal to cut sheets of uniform thickness.
CNC Electric Discharge Machine
CNC EDMs use a sparking technique to remove material from a conductive material. Such CNC machining offers extreme accuracy and precision. The EDM process uses a conductive wire and a workpiece submerged in a di-electric fluid. It repeatedly generates tiny sparks with extreme temperatures that melt the material at micros levels and flush the chips out.
There is no direct contact between the electrode (wire) of the wire EDM machine which means minimal stress formation. CNC EDMs are generally reserved for specialized tooling and components.
CNC Laser Cutter
CNC laser cutters work through a powerful laser directed at the workpiece that melts away the material. You can use laser cutters for engravings and markings, but they are expensive to operate when cutting materials.
These laser cutters use a CO2 laser for non-metals like wood and plastics
Fiber lasers purely rely on amplified light doped in minerals to generate shorter wavelengths that can cut though metals like steel and aluminum.
CNC Machining Techniques
CNC machining is often categorized based on the cutting motion. In the manufacturing industry many times, CNC turning and milling are used interchangeably with CNC mills and CNC lathes. To completely, understand what is CNC machining , you should understand CNC operations.
CNC Turning
CNC turning is a lathe-based operation. Unlike manual lathes, which required spinning gears to control feed and adjusting cutting angles using readable markings, CNC turning involves using a rotating workpiece and a stationary cutting tool guided by translational movement along 2 or 3 axis.
The cutting tool moves in a linear or arc type movement to produce rounded endings on shafts, cylinders and cones.
CNC Milling
CNC milling involves a rotating cutting tool paired with a stationary workpiece. Apart from this, CNC machinists often uses squares or rectangular blanks for shaping in milling which is different from cylindrical blanks used in lathes.
Most CNC mills move along 3 axes but more capable CNC mills can move in 5 axis. CNC milling includes
Contour milling
Peripheral milling
Shoulder milling
Face milling
CNC Drilling
CNC drilling is also a type of milling operation but in the CNC manufacturing industry, there are dedicated CNC drills for solely making holes. It uses a drill bit rotating at high speeds that removes material from the workpiece leaving behind a hole. An end mill can also be used for this process.
CNC EDM
Electrical discharge machines work on the principle of eroding material from conductive materials by generating sparks using a wire. CNC EDM offer hughes precision in CNC machined parts and they are generally used for repetitive metal cutting for carbon hardened or heat treated components.
CNC Grinding
Grinding is a polishing operation to achieve a smooth surface finish. Here, CNC is computer numerical control in the grinding process to make it repeatable and ensure identical surface quality in products.
CNC Cutting
CNC cutting is a general term used to describe material trimming with high precision. This category is used for
CNC Laser Cutting: uses a high powered gas or fiber magnified laser to vaporize material.
CNC Water Jet Cutting: uses a pressurized stream of water to cut through material.
CNC Router Cutting: CNC routers are a semi manual type of CNC cutters. They come with a range of tools and primarily rely on a rotating cutting tool. CNC routers can drill, engrave, cut, mill, create profiles and grooves, and can even be modified for printing.
CNC Machining finishes
CNC parts already have a great surface finish and it’s hard to notice any uneven bumps or visible tool marks. Most anomalies are polished in CNC grinding, but some applications require resistance to weathering, enhanced durability or simply a color change.
To achieve this, CNC machined parts undergo many finishing processes depending on the material.
Anodizing
CNC parts especially aluminum aerospace components can undergo an electrolytic oxidation process to form a natural oxide layer which is tougher and more durable than standard aluminum surface.
Brushing
Brushing involves adding fine lines and thin grooves to the surface for aesthetic appeal. This is common for stainless steel metal parts.
Polishing
Many CNC parts are primarily for consumers, like paint brushes, smartphone cases, and rings. CNC machining makes intricate designs but they require polishing to remove marks and add luster. Steel jewelry commonly gets its silver look from polishing.
Electroplating
To protect parts from weather and water damage you can electroplate a layer of another metal like zinc or copper to your steel part for added chemical resistance. This also serves aesthetic and decorative purpose. For example, many CNC machined glass frames are electroplated in gold.
Powder Coating
Powder coating makes your part durable, rust resistant and tough. It can be applied to plastics, metals and various materials and uses a form of polyurethane or epoxy for exceptional hardness.
CNC Machining Applications
CNC technology developed because of demanding applications in aerospace and automobile industries. However, their applications are not limited to these.
Aerospace and Defense
This sector requires precision CNC machining because components like turbine blades can produce variations in airflow if the blades have a mismatch. Many aerospace parts are made of lightweight materials like aluminum and carbon fiber that are best machined using electric discharge machines.
Wing spars
Fuel system components like valves
Engine nozzles
Panels
Automotive
Automotive industry uses CNC technology more than any other industry. They produce millions of components every year and identical parts require the use of pre-programmed software to repeat tasks.
Engine blocks
Titanium brake calipers
Exhaust tips
Piston rods
Medical and Dental
Medical implants work with bio-compatible stainless steel and titanium. These metals are fairly hard to machine and most require small tools with high precision to produce custom implants that match contours of bones and dental cavities.
Bone plates
Bone screws
Forceps
Prosthetics
Construction and Architecture
Many architectural projects begin with CNC machining a smaller model to check decor elements, load bearing performance, and reviewing features.
Research and Development
CNC machining has also opened up a new sector in the industry called rapid prototyping. Since the process is standardized, you can use CNC services to craft intricate parts and have them delivered at your doorstep.
CNC Machining Materials
Materials are no longer a concern for CNC machining. In the past, it was a problem to machine tough metals like titanium but now there’s specialized machining tool access to carbide cutters which can glide through any metal.
Metals
There are many reasons for machining metals.
Stainless steel is durable, strong and works in many temperature ranges.
Aluminum is lightweight, durable and common material for prototyping metal parts
Brass is one of the few metals that does not spark from friction and CNC machining brass components for plumbing fittings and electronic connectors has aesthetic appeal.
Magnesium is part of soft metal materials and a simple tool change can lower the tool hardness and accurately machine magnesium electronic casings.
Plastics
Plastics do not confine to soft, malleable sheets, there are plastics which have very high strength and are used in the automotive industry like ABS. Most plastic parts are made using injection molding but many consumer electronics, nylon gears, and gaskets are made using CNC machining.
Composites and other material
Composites like carbon fiber, FRP, and foam are commonly used in part manufacturing in the automotive industry. They are strong and lightweight. The cutting process of these materials typically uses diamond coated tools because it maintains sharpness and has minimal delamination effect.
Benefits and Limitations
CNC machining offers unmatched precision and rapid part manufacturing. It is also easy to scale production when CNC machining because the process simply has to be repeated a given number of times.
Benefits of CNC Machining
Precision
CNC machining allows clients to get quality controlled parts and manufacturers have the freedom to use various methods to make tight tolerances. The automation removes any human error.
Cost Effective
CNC machines are now available in many bed frame sizes. Buying a CNC machine has a large initial cost, but it offers high volume production, precision, and overtime the cost effectiveness increases.
Various Materials
You don’t need different CNC machines to cut metals and plastics. You can simply change the cutting tool and work with different materials.
Limitations of CNC machining
Large Initial Investment
CNC machines have a high setup cost. As the number of axis increases, the cost of the CNC machine increases significantly. Plus, manufacturers have to hire CNC machinists to calibrate and maintain the CNC machines.
Most CNC come with a basic set of tool and specialized cutting requires you to invest in more tools.
Part Complexity
While CNC machines can produce many shapes, there are some shapes which are difficult to achieve using CNC. Components with internal features are not ideal for CNC machines and usually discharge machining is used for such parts.
Size Range
You CNC machine parts in an enclosure, because the coolant can be recycled and the chips don’t fly out everywhere. But this enclosure also limits the size of your part. For large parts especially large internal and external gears, casting and forging processes are employed.
Large parts need re-orientation, new setups, sectioned machining which adds time and cost to the part.
Tool Wear
The largest running expense of a CNC machine is the tool wear. While this depends on the material, feed rate, depth of cut, and speed, almost all tools wear out eventually and need replacement.
An amateur CNC operator can lead to quick tool burns and skilled operators add cost to manufacturing.
Conclusion
CNC machining is a versatile, precise, and repetitive manufacturing process widely accepted across various industries. It offers the benefits of high accuracy and low costs but produces material waste and can face challenges in internal part complexities.
Despite this, it is the best manufacturing process for prototyping small to large components and its efficiency makes it ideal for modern manufacturing.