What Is CNC Machining?

A computer numerical control machine (CNC) is a tool that shapes stock materials into precise forms to meet manufacturing requirements and component specifications. CNC machines utilize pre-programmed software to guide the motions of advanced machinery, such as grinders, lathes, mills, and other cutting tools that remove material.

These computer-aided manufacturing methods can handle a variety of intricate and accurate CNC machining tasks, producing components for industries like automotive, defense, and aerospace, among others.

While 3D printing and other additive manufacturing techniques are at the forefront of producing components from soft materials in the 21st century, the majority of everyday products are still created through highly automated subtractive machining processes.

Plastic water bottles are formed using molds created through the CNC die sinking method, and the individual components that make up a car's drive system are precisely milled to ensure all moving parts fit together smoothly for optimal mechanical performance.

"Chances are, nearly everything you interact with in your daily life has been touched by a machine tool at some point," says University of Tennessee Knoxville engineering professor Tony Schmitz. "If you've ever flown on an airplane — like a Boeing 747, for instance — over a million individual components were machined and assembled to make that aircraft airborne."

How Does a CNC Machine Tool Work?

CNC machine tools are as adaptable and dynamic as the variety of products they produce. Yet, most CNC machinery operates within two primary systems: an open-loop or a closed-loop configuration.

In open-loop CNC systems, the operator creates the computer numerical control for the specific task and generates the g-code or work file using computer-aided design (CAD) software. The computer then sends the correct instructions to the controller and its connected servo motors.

These motors guide cutting tools such as lathes or grinders across at least two axes (X and Y), though more advanced CNC machines can enhance versatility and precision by moving CNC mills and other components across multiple additional axes.

Closed-loop CNC systems offer feedback to the monitor, allowing adjustments to correct any inconsistencies as the CNC machine moves along the material. This continuous motor-monitor communication enables real-time adjustments to the velocity, position, and feed rate of turning machines and other CNC tools.

5 Key Functions of CNC Machines

Below are some of the most prevalent industrial uses of CNC machinery:

1. Cutting

CNC machines are top-tier tools for tasks requiring precise and rapid cutting speeds. They can also handle two of the most advanced cutting methods: sinker EDM (electric discharge machining) and wire EDM.

A sinker EDM employs thermal erosion through the interaction of two electrodes — one attached to the tool (typically copper or graphite), while the other is the dielectric fluid that surrounds the material. Remarkably, the tool and the material never come into direct contact. Wire EDM follows a similar process, but it uses wire electrodes as the cutting tools for precise results.

2. Drilling

This accurate hole-making method utilizes a rotating cutting tool, often drill bits or high-pressure water jets, to create round holes in a stationary material. These holes are typically designed to house screws and bolts for assembly purposes.

3. Grinding

CNC machines are often equipped with abrasive wheels that deliver almost perfect surface finishes. This subtractive grinding method significantly outperforms any additive manufacturing technique and can minimize imperfections to tolerances as small as 1/10th the width of a human hair.

4. Milling

A CNC mill, much like traditional mills and hand-operated milling machines, utilizes lathes, water jets, or turning tools to remove material from a stationary piece of stock. CNC mills are capable of moving along multiple axes, enabling operators to execute horizontal, vertical, angled, and face milling operations with pinpoint accuracy. The ability to move in multiple directions enhances the efficiency of manufacturing complex wood, metal, and plastic parts, as it reduces the need to adjust and reposition the stock material frequently.

5. Turning

This CNC machining process resembles milling, but instead of securing the material on a fixed workstation, the stock is attached to a rotating mechanism that spins at high speeds. A machinist using a lathe or a similar CNC tool will gradually remove small amounts of material to shape the stock into the desired form.

What Is Computer-Aided Manufacturing Software?

Computer-aided manufacturing (CAM) software is a vital part of CNC machining. It acts as the translator and coordinator between human inputs and automated processes during every phase of production.

For example, designers use computer-aided design (CAD) software to craft 3D models of their designs, which are then imported into CAM. CAM interprets these models and generates machine codes like m-code or g-code, turning the design into CNC programming language. As the CNC machine performs its tasks, it transmits data back to CAM, alerting the operator to any changes or factors that could impact the final product's quality.

A Brief History of CNC Machine Tools

The origins of CNC machining can be traced back to the technological advancements during the Industrial Revolution in the mid-1800s, when manufacturers began utilizing cam-operated lathes and milling tools to mass-produce firearms, factory equipment, and everyday objects. By the mid-20th century, the advent of m-code punch cards introduced basic forms of numerical control machining that automated tasks previously carried out manually by teams of workers.

The growth of digital computers and software in the 1970s and '80s enabled the automation of more manufacturing tools, boosting both production speed and operational efficiency.

In the 21st century, CAD and CAM software, coupled with state-of-the-art CNC machines, offer small production teams a cost-effective method to produce large volumes of intricate parts. As artificial intelligence and machine learning continue to evolve, the manufacturing sector is poised to further optimize and automate its processes.

What Will the Future CNC Machining Process Look Like?

While it might be tempting to imagine a future where robots handle all tasks during the AI revolution, both machining experts and engineering scholars agree that the CNC machining process still relies on skilled operators to ensure optimal performance.

"Computer Numerical Control (CNC) machining remains a critical element in manufacturing that isn't going anywhere anytime soon," says Schmitz. He further explains that additive and subtractive methods will eventually merge, with hybrid manufacturing representing the future of CNC processes.

Schmitz adds that hybrid manufacturing will start with an additive component as the base or starting point, followed by precise machining to achieve a smooth surface finish that additive processes alone cannot replicate.

One of the significant obstacles in the future of CNC machining is the ongoing shortage of skilled machinists familiar with CNC programming. This issue is expected to worsen as experienced professionals retire, with few newcomers entering the field to fill the gap.

In the U.S., the Department of Defense, alongside other federal agencies, recognizes the urgent need to rejuvenate a failing national manufacturing program and adopt advanced manufacturing methods that will restore global competitiveness in the industry.

"Machining has traditionally been seen as a craft, requiring years of training and practical experience to produce quality parts," says Schmitz. "However, we're moving toward a more automated environment. While jobs will remain, they will look very different from those that existed when CNC technology first emerged in the 1940s and '50s."