CNC milling (computer numerical control milling)

Computer numerical control milling, commonly known as CNC milling, is a precision process used in industrial machining to create customized products or parts. It uses computer-programmed code to relay instructions to production machines, which then execute the instructions to yield objects with the desired physical and functional characteristics. CNC milling is compatible with numerous commonly used raw materials, including glass, metal, plastic, and wood. By definition, CNC milling alters the raw material, known as “workpieces,” by removing substances from it via machine-powered cutting.

The systems and equipment used to program and control CNC milling machines work through computer interactions. Technicians use specialized software to enter numerical code, which is then relayed to the machine as Cartesian coordinates. The machine then uses those coordinates to carry out the assigned task. CNC milling is one of multiple types of precision computer numerical control machining, with others including CNC lathing, turning, grinding, lasering, waterjet cutting, plasma cutting, sheet metal stamping, and electrical discharging.

Brief History

Milling is an industrial process that deploys rotating cutting equipment to remove material from a workpiece and shape it into a finished product or part. During the early stages of the Industrial Revolution in the 19th century, workers performed milling tasks manually using a technique known as hand-filing. Milling machines first appeared when rudimentary industrial technologies began to evolve during the early nineteenth century. Surveys of machining history note that it is not known exactly when the first milling machines were invented, as many independent industrial manufacturers developed and used their own systems on small scales. Machine-assisted milling became a common feature of industrial production beginning in the 1840s, and a major advance occurred in 1861 when the Providence, Rhode Island-based Brown & Sharpe company introduced its Universal Milling Machine. The Universal Milling Machine quickly became a widely used standard, leading competitors to create refined systems capable of more precise movements.

CNC milling was preceded by a noncomputerized technology known as numerical control (NC) milling. NC milling arose to address persistent production errors arising from the high volume of input required of manual machinists. Its invention is credited to the American industrial developer John T. Parsons (1913–2007), who pioneered a system of using punched tape to relay instructions to automated machines in the late 1940s. The punched tape contained numerical data, which was interpreted by specialized tape readers and relayed to machines, which then carried out the assigned task according to the submitted instructions. NC machining was initially limited to the manufacture of aviation and aerospace equipment and products, but slowly expanded into other industries over the course of the 1950s.

During the 1960s, improvements in data storage capabilities propelled significant advancements in emerging computer technologies and allowed automated tools to replace human workers in many processes. NC machining evolved into CNC machining through advances in computing and control systems, with the initial generations of computer-aided design (CAD) software, an advancement attributed to the French engineer Pierre Bézier (1910–1999), who created an early CAD system known as UNISURF for the Renault automobile company in 1968. As the capabilities of CAD software continued to expand, it became able to interpret complex three-dimensional blueprints and relay specifications to milling machines. CNC milling matured further during the 1970s, and became increasingly common in automated industrial production.

Overview

Contemporary CNC milling systems have the capability and data capacity to carry out highly complex and large-scale milling processes with extreme precision. Their basic structure links a computer running CAD software to a production machine with cutting tools affixed to rotating spindles. A technician places a workpiece of raw material into the cutting machine, and the CAD software then relays instructions that tell the machine exactly where, when, and how to cut the workpiece. The machine then carries out the commands, selectively removing material from the workpiece until it matches final specifications. Simple CNC milling systems operate on a single, flat plane, but more complex examples mount workpieces on tables, which then rise, tilt, or rotate at various angles to facilitate cutting on multiple planes.

Manufacturers can use CNC milling in many ways. It has become a common way to cut workpieces into specified shapes, but CNC milling systems also create holes, notches, pockets, slots, and other precision characteristics. Exact manufacturing instructions can be entered in two-dimensional or three-dimensional formats, which CAD software converts into a set of commands readable by the cutting machine. These commands are then exported, and the CNC machine selectively activates its cutting tools as needed to create a product or part that matches the original instructions. In shaping workpieces, the CNC milling machine’s cutting tools spin at extremely fast rates, guiding raw materials into their final forms with great speed and efficiency.

Industrial manufacturers use four main types of CNC milling processes: plain, face, angular, and form milling. Plain milling, sometimes called slab milling or surface milling, brings cutting tools into contact with workpieces at a flat, parallel angle. In face milling, the cutting tool’s rotary axis is perpendicular to the workpiece. Angular milling straddles plain and face milling, positioning the cutting tool’s rotary axis in positions that are neither parallel nor perpendicular. Form milling is the most complex type, yielding curved, concave, or convex products and parts with no flat surfaces. These four primary CNC milling techniques can be deployed to create many different types of manufactured goods, but they are most commonly used to make precision instruments or product components, furniture and cabinetry, sculpted objects, signage, and industrial prototypes. Five-axis CNC milling systems have become increasingly common because they improve precision, reduce setup times, and enable the manufacture of highly complex parts used in industries such as aerospace, medical devices, and energy production.

Human operators still participate in various phases of the process. Some CNC milling machines have removable tools, allowing technicians to choose and place the specific implements necessary to complete the task at hand. Machinists also place and secure the unformed workpieces, then initiate the production process by manually enabling the programmed task with the CNC machine’s interface. However, advancements in machine learning (ML), artificial intelligence (AI), and robotics technologies continue to drive CNC milling processes toward complete automation. AI technologies are increasingly being used for toolpath optimization, adaptive machining, predictive maintenance, and digital-twin-based process control. Hybrid manufacturing systems that combine additive manufacturing (3D printing) and CNC milling have also become increasingly common in advanced industrial applications, allowing parts to be built and machined within a single machine environment. Researchers have also identified emerging cybersecurity concerns in CNC manufacturing, including the potential exposure of machine-operation data through industrial monitoring systems.

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