Overview of CNC Machining Process

Like most conventional mechanical CNC machining processes, the CNC machining process utilizes computerized controls to operate and manipulate machine tools which cut and shape stock material. In addition, the process follows the same basic production stages which all CNC machining processes do, including:

•      Designing a CAD model

•      Converting the CAD model into a CNC program

•      Setting up the CNC machining machine

•      Executing the machining operation

The CNC machining process begins with the creation of a 2D or 3D CAD part design. Then the completed design is exported to a CNC-compatible file format and converted by CAM software into a CNC machine program which dictates the actions of the machine and the movements of the tooling across the workpiece. Before the operator runs the CNC program, they prepare the CNC machining machine by affixing the workpiece to the machine’s work surface (i.e., worktable) or workholding device (e.g., vise), and attaching the machining tools to the machine spindle. The CNC machining process employs horizontal or vertical CNC-enabled machining machines—depending on the specifications and requirements of the machining application—and rotating multi-point (i.e., multi-toothed) cutting tools, such as mills and drills. When the machine is ready, the operator launches the program via the machine interface prompting the machine to execute the machining operation.

Once the CNC machining process is initiated, the machine begins rotating the cutting tool at speeds reaching up to thousands of RPM. Depending on the type of machining machine employed and the requirements of the machining application, as the tool cuts into the workpiece, the machine will perform one of the following actions to produce the necessary cuts on the workpiece:

1.    Slowly feed the workpiece into the stationary, rotating tool

2.    Move the tool across the stationary workpiece

3.    Move both the tool and workpiece in relation to each other

As opposed to manual machining processes, in CNC machining, typically the machine feeds moveable workpieces with the rotation of the cutting tool rather than against it. Machining operations which abide by this convention are known as climb machining processes, while contrary operations are known as conventional machining processes.

Generally, machining is best suited as a secondary or finishing process for an already machined workpiece, providing definition to or producing the part’s features, such as holes, slots, and threads. However, the process is also used to shape a stock piece of material from start to finish. In both cases, the machining process gradually removes material to form the desired shape and form of the part. First, the tool cuts small pieces—i.e., chips—off the workpiece to form the approximate shape and form. Then, the workpiece undergoes the machining process at much higher accuracy and with greater precision to finish the part with its exact features and specifications. Typically, a completed part requires several machining passes to achieve the desired precision and tolerances. For more geometrically complex parts, multiple machine setups may be required to complete the fabrication process.

Once the machining operation is completed, and the part is produced to the custom-designed specifications, the milled part passes to the finishing and post-processing stages of production.