Summary of CNC Milling operation,techniques,benefits

What is milling? It’s is a type of machining that uses cutters to shape a workpiece, often on a moveable tabletop, although some milling machines also feature movable cutters. Milling started out as a manual task performed by humans, but most milling these days is done by a CNC mill, which utilizes a computer to oversee the milling process.

CNC milling offers higher precision, accuracy, and production rates, but there are still some situations when manual milling comes in useful. Manual milling, which requires a lot of technical skill and experience, offers shorter turnaround times. It also has the added benefit that manual mills are cheaper and the user doesn’t need to worry about programming the machine.

Overview of CNC Milling Process

Like most conventional mechanical CNC machining processes, the CNC milling 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 milling machine
Executing the milling operation

The CNC milling 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 milling machine by affixing the workpiece to the machine’s work surface (i.e., worktable) or workholding device (e.g., vise), and attaching the milling tools to the machine spindle.

The CNC milling process employs horizontal or vertical CNC-enabled milling machines—depending on the specifications and requirements of the milling 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 milling operation.

Once the CNC milling process is initiated, the machine begins rotating the cutting tool at speeds reaching up to thousands of RPM. Depending on the type of milling machine employed and the requirements of the milling 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:

Slowly feed the workpiece into the stationary, rotating tool
Move the tool across the stationary workpiece
Move both the tool and workpiece in relation to each other
As opposed to manual milling processes, in CNC milling, typically the machine feeds moveable workpieces with the rotation of the cutting tool rather than against it. Milling operations which abide by this convention are known as climb milling processes, while contrary operations are known as conventional milling processes.

Generally, milling 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 milling 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 milling 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 milling 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.

Here are the most common CNC milling methods:

Plain milling. Also known as surface milling, this milling process uses a cutting tool to remove material along the surface of the workpiece. In plain milling, the rotation axis is parallel to the workpiece.
Face milling. Face milling uses a rotational axis perpendicular to the material’s surface. The cutting or grinding tool faces down against the workpiece surface to remove material.

Angular milling. This milling method positions the cutting tool’s rotary axis at an angle to the workpiece surface to produce angular cuts as specified by the design, such as grooves or dovetails.
Form milling. Form milling makes non-flat cuts, such as contours, curves, and radii. Each type of curve will require a specific cutting tool to create an accurate form cut.

Types of CNC Milling Machines

CNC milling machines are highly versatile and may be used to facilitate a variety of cuts and machining operations. In general, however, the workpiece remains stationary while the cutting tool moves and rotates to remove material and realize the design. Different CNC milling machines will have varying spindle configurations that hold and move the workpiece in different ways.

Horizontal Milling: A spindle with a mounted cutting tool is oriented horizontally as it presses against the workpiece. Horizontal milling can handle deeper and heavier cuts using thicker and shorter cutting tools.
Vertical milling: A vertically-oriented spindle moves a rotating cutting tool up and down to remove material from a stationary workpiece. The turret-style milling machine features a spindle and table that moves both perpendicular and parallel to the axis.

Multi-axis milling: 4-axis and 5-axis CNC mills facilitate highly detailed or complex machine operations. Multi-axis milling machines move on the X, Y, and Z axes, in addition to rotating on the A and B axes. This allows the workpiece to be approached from any direction, often facilitating multiple operations simultaneously.

CNC Milling Applications

The benefits of CNC milling include its ability to cut a wide range of materials and produce custom-designed parts much faster than conventional machining. CNC milling can be used to machine parts from a variety of materials, such as:

Metals
Aluminum,Beryllium,Brass,Bronze alloys,Carbon steel,Copper,Iron,Nickel,Stainless steel,Steel alloys,Titanium

Plastics
ABS,Acetal,Acrylic,Fiber-reinforced plastics,Nylon,Phenolic,Polycarbonate,Polyetherketone,PTFE,PVC,Teflon

CNC milling can be used with any industry that requires precise components, including complex industries such as aerospace and military. No matter what your component geometry or material, MF Engineering offers the right CNC milling process to meet your needs. To learn more about our capabilities, please contact us or request a quote.