What Are CNC Machines And How Do They Work?
As technology and computers have evolved over the years, a new high precision computer manufacturing technique called CNC machining has appeared.
What Are CNC Machines
CNC Machines or Computer Numerically Controlled Machines, are electro-mechanical devices that can manipulate tools around different types of axis (usually three or five axis) with high precision being controlled by a computer program.
Using CNC machines, engineers, machinists or makers, have two ways to generate a physical part:
1. Using a CNC Machine and a computer design file.
2. Using a 3D Printing Machine (additive manufacturing).
The difference between these two manufacturing techniques is quite obvious.
CNC Machining
CNC Machining like other machining processes, is a manufacturing process where material is removed to create the final product.
3D Printing
3D Printing is a manufacturing process that works in reverse by adding material to create the final product.
Short History of the CNC Machines
The first generation of CNC machines was developed in the 1940s and 1950s, and they used punched tapes to control the machines.
The code used to control the machine was manually introduced (punched) in a data card that was then introduced into the system to read the instructions.
These early machines had limited functionality compared to the today’s machines.
The massive development of the CNC machining technologies was accelerated only in the late 20th century.
How Modern CNC Machines Work?
CNC machining is a manufacturing technique used to transform a piece of material such as Aluminum (Al), Steel (Fe) or Titanium (Ti), into a finished product or part.
CNC machines relied on digital instructions (G-Code) before modern programs were created to control the manufacturing process with the help of computer software (Fusion 360).
Before these programs, machinists used to manually write the G-Code to control the machines.
CAM programs are used today to create 3D models, and automatically generate the required G-Code, which will drive the CNC machine.
When comparing automated CNC machining with the manual alternative, we can rapidly see the difference, because CNC machines run faster, at higher precision and accuracy.
These machines allow the quick and precise transformation of a digital design into a physical part.
CNC machining services are used today to produce a very wide variety of precise parts.
CNC Machines are precise and their accuracy is measured in thousands of an inch (1 Thou = 1 Mil and is equal to 1⁄1000 of an inch).
Standard machines can provide tolerances on parts of ±0.005″ (±0.127 mm), fine machines can provide tolerances of about ±0.001″ (±0.0254 mm), and specialized processes can provide tolerances as tight as ±0.00005″ (±0.00127 mm).
Tools Used By CNC Machines
Specific machining processes and different designs require the use of multiple tools to make the cuts very precise.
One tool is never enough, and this is the reason why machinists often build digital tool libraries that interface with the physical CNC machine.
CNC machines can automatically switch the tools being directed by digital instructions, and this allows them to become the manufacturing work horses of the industry.
Basic CNC machining moves one or two axes referred to as the X-axis and the Y-axis.
There are 2.5 axis, 3 axis and 5 axis machines, and these numbers refer to the degree of freedom machine can make cuts in.
A 3-axis machine will move in the x, y and z axis, while a 5-axis machine will move in these three axis (x,y,z) along with two additional rotational axis.
The possibilities of production using 5-axis machines are practically endless.
Conventional Machining Technologies
There are three conventional machining technologies used to move material from the stock.
Drills
Drills work by spinning a drill bit and slowly moving into contact with a stationary stock.
Lathes
Lathes function in reverse to drilling, and they spin a block of material against a stationary cutter or drill bit to remove material in a fluid or circular path.
Lathes are more limited in creating shapes compared to other techniques, but modern technology does allow these machines to create things like square holes or non circular shapes.
Milling Machines
Milling machines are the most common CNC machines used today.
They involve the use of rotary cutting tools, which are perfect for the removal of material.
These machines work like drills, but their capabilities are broader.
Almost any material can be used in CNC machining, metals such as aluminum, brass, steel, titanium, etc., plastics such as Acrylics (PMMA), Acetal (POM), Polypropylene (PP), Polycarbonate (PC), and many others.
Each material can have different properties, so machinists and engineers have to alter machining variables such as: RPM, tool selection, coolant flow and feed rate, among other factors.
Conclusion
Parts created by CNC machines are all around us, they can be found in cars, appliances, and in many other places (even in space technology).
CNC machining is for sure the only way to produce high precision metal parts for engineering designs across the planet.
