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.