What Is CNC Machining?
A computer numerical control machine (CNC) is a machining tool that forms stock material to a desired shape that will fulfill manufacturing directives and component requirements. CNC machines use pre-programmed software to control the movements of complex machinery, including grinders, lathes, mills and other cutting tools used to remove material.
These computer-aided manufacturing techniques can perform a wide range of complex and precise CNC machining tasks to create manufactured products and specifically designed parts for the automotive, defense and aerospace industries.
Although 3D printing and other additive manufacturing processes take center stage in the 21st-century production of components made with soft materials, most everyday items are still the result of highly automated subtractive machining techniques.
Plastic water bottles are produced from molds using the CNC die sinking technique, and individual drive system components of any car on the road are milled to accurate dimensions to allow all moving gears to fit together seamlessly for optimal mechanical performance.
"Chances are, nearly everything you touch in your day-to-day life was at some point touched by a machine tool," says University of Tennessee Knoxville engineering professor Tony Schmitz. "If you've ever traveled in an airplane — a Boeing 747, for example — over a million separate components were machined and then assembled to get that plane off the ground."
CNC machine tools are as versatile and dynamic as the multitude of items they create. However, most CNC machinery works within two frameworks: An open-loop or closed-loop system.
In open-loop CNC systems, the operator will develop the computer numerical control for the task at hand and generate the g-code or work file using computer-aided design (CAD) software. The computer then relays the proper steps to the controller and its connected servo motors.
These motors manipulate cutting tools, like lathes or grinders, along at least two axes (X and Y), although high-end CNC machines can increase versatility and accuracy by moving CNC mills and other accessories around several additional axes.
Closed-loop CNC systems provide feedback data to the monitor to address inconsistencies while CNC machines move around the material. This motor-monitor communication allows closed-loop systems to alter the velocity, position and feed rate of turning machines and other CNC machine tools in real time.
Here are a few of the most common industrial applications for CNC machinery:
CNC machines are excellent tools for projects that require a precise and efficient cutting speed and they can accommodate two of the most advanced cutting techniques: sinker EDM (electric discharge machine) and wire EDM.
A sinker EDM uses a thermal erosion from interaction between two electrodes — one attached to the tool in the form of copper or graphite. The other is the dielectric fluid that the material is bathed in. Amazingly enough, the tool and workpiece never come into direct contact during production. Wire EDM works in the same fashion, except it utilizes wire electrodes as accurate cutting tools.
This precise hole-punching process uses a rotating cutting tool, typically drill bits or high-velocity water jets, to produce round holes in a stationary workpiece. These holes often accommodate assembly screws and bolts.
CNC machines are often equipped with abrasive wheels that produce nearly flawless surface finishes. This subtractive grinding technique greatly surpasses the accuracy of any additive manufacturing process and can reduce imperfections to tolerances as small as 1/10th the width of a human hair.
A CNC mill, similar to basic mills and other hand-milling machines, uses lathes, water jets, or turning tools to remove material from a stationary stock piece. CNC mills can move along multiple axes, allowing operators to perform horizontal, vertical, angled and face milling tasks with absolute precision. These multi-angled capabilities increase efficiency in the manufacturing process of intricate wood, metal and plastic parts since the machinist can adjust and resecure the stock material fewer times.
This CNC machine process works similarly to milling; however, instead of securing the stock to a workstation, it is attached to turning mechanism that rotates at high speeds. A worker using a lathe, or a CNC with a similar attachment, will then remove small amounts of material until they form the stock to the desired shape.
Computer-aided manufacturing (CAM) software is an essential component of the CNC machining process. It is the mediator and interpreter of any computer-aided machining operation because it manages both human and automated inputs and outputs of every stage in production.
For instance, designers create 3D models of their project in computer-aided design (CAD) software and upload the file in CAM. CAM will then interpret the model and act as an m-code or g-code generator, translating the project goal into the language of CNC programming. As the CNC machine works on the project, it sends back data to CAM and informs the operator of any variables that may affect the outcome of the product.
CNC machining is rooted in technological advances during the Industrial Revolution in the mid-19th century, when manufacturing companies started using cam-based lathes and milling tools in the mass production of firearms, factory equipment and everyday items. By the 1940s and '50s, rudimentary numerical control machining in the form of m-code punch cards began to automate several manufacturing tasks that were originally manually controlled by a team of workers.
As digital computers and computer software improved in the 1970s and '80s, more manufacturing tools could be automated to improve production speed and overall efficiency.
Now in the 21st century, CAM and CAD software and cutting-edge CNC machines allow small production teams a cost-effective strategy for manufacturing large quantities of complex parts. As machine learning and artificial intelligence continues to advance, the manufacturing industry will likely continue to optimize and automate processes.
It can be easy to daydream about a world where robots do all the work as we enter the first stages of the artificial intelligence revolution, however, machining professionals and engineering academics both understand that the CNC machining process requires skilled workers to ensure that everything performs as it should.
"It [computer numerical control machining] is a cornerstone capability that's not going away any time soon," Schmitz says. Instead, Schmitz argues that additive and subtractive manufacturing actually complement each other to the point where "hybrid manufacturing" will become the future CNC machining process.
Schmitz also says this hybrid manufacturing will "begin with an additive part that is the pre-form or staring condition, and then we'll use limited machining to produce a smooth surface finish that you can't achieve with additive."
However, one of the most challenging hurdles facing the future of CNC machining is the current labor shortage of qualified machinists who are familiar with CNC programming. This shortage will only exacerbate as veteran CNC professionals retire and few enter the industry to take their place.
In the United States, the Department of Defense and various other federal agencies have realized the need to revive a failing national manufacturing program and implement cutting-edge manufacturing processes that will make the country competitive in the industry.
"While historically, machining has been thought of as a craft — where someone needs years and years of training and hands-on experience before they can create the parts they want — I believe we'll move away from that to a more automated machining environment," Schmitz says. "There will still be jobs, but they'll be drastically different from what they were when CNC technology started in the 1940s and '50s."
The United States was a manufacturing powerhouse that led the world in innovative technologies after World War II. The U.S. then began outsourcing manufacturing in the 1960s and '70s, which led to a stronger reliance on foreign-made goods. Industry leadership and federal organizations agree that the country is in dire need of increased self-reliance and a revival of the American machining industry in the 21st century. As the workforce dwindles, with less people entering than leaving the CNC technology field, it has never been a better time to join this high-demand profession.