Introduction: Milling is a common machining process in modern manufacturing. By using a rotating cutter, it shapes materials into precise parts. According to the workpiece geometry and machining requirements, milling operations can be categorised into face milling, end milling, side milling, slot milling, square shoulder milling and other types. This article will explore these milling types in detail.
Common milling operations
Milling operations encompass multiple types, each method serving a distinct purpose in achieving specific surface finishes and dimensional accuracy.
Face Milling
Face milling is a machining process where the cutter’s axis is perpendicular to the work surface. Material is removed as the tool moves parallel to the surface, producing a flat and smooth finish.
This operation primarily uses the end edges of the cutting tool and is commonly used for machining large flat surfaces, stepped faces, and end faces.Face milling enables large-area cutting in a single pass, resulting in highly efficient machining.
End Milling
End milling is a milling process that uses both the end cutting edges and the peripheral flutes of the cutter to remove material. In simple terms, it can flatten surfaces as well as cut into the material. During machining, the tool feeds axially into the workpiece, allowing efficient machining of grooves, pockets, and profile contours.
Side Milling
Side milling primarily uses the side edges of the milling cutter to machine the workpiece. In this operation, the tool moves parallel to the surface of the workpiece, cutting along its sides to produce parallel vertical faces. It is commonly used for machining external contours, guideways, and other similar features.
Slot Milling
Slot milling refers to the process of machining open or closed grooves on a workpiece using a rotating cutter.During this operation, both the end and peripheral cutting edges of the tool are engaged simultaneously, forming a recessed slot structure, as shown below.
Slot milling can produce grooves of various widths and depths, including straight slots, keyways, T-slots, and circular or curved grooves.
Square Shoulder Milling
Square shoulder milling refers to the process of machining a 90-degree angle structure (resembling an L-shape) in a single pass using a milling cutter. This operation employs both the face cutting edge and peripheral cutting edge of the cutter to simultaneously mill two surfaces. When executed without deviation, it produces a smooth, precisely 90-degree plane. It is commonly employed for milling features such as steps on workpieces.
Angle Milling
Angle milling is a process that employs specialised milling cutters to machine specific angular features (not 90°) on workpieces. It is commonly used for machining structures such as inclined surfaces, chamfers, or V-shaped grooves.
Thread Milling
Thread machining refers to the process of using the tool to produce workpieces with threaded features, including internal and external threads. In this process,the tool rotates and moves in a circular path around the hole, while simultaneously advancing axially by one thread pitch per revolution. This coordinated motion produces a helical cutting path that forms the thread.
Gear Milling
Gear milling, as the name suggests, is a process specifically designed for manufacturing gears. This procedure employs a hob (a cutting tool whose profile perfectly matches the gear’s tooth form) to machine the workpiece, thereby forming the gear’s tooth profile and tooth form.
Form Milling
Form milling refers to a process employing specialised cutting tools to produce specific shapes. These tools are typically custom-designed to meet product requirements, enabling the single-pass machining of surfaces with defined contours. Form milling facilitates the one-off machining of complex geometries, reducing steps such as multiple tool changes and thereby enhancing efficiency. However, owing to the necessity for bespoke tool design and debugging, form milling incurs higher unit costs during small-batch production.
Profile Milling
Profile milling is a process in which the cutter follows the outline or contour of a workpiece to remove material along its path.The operation requires selecting the appropriate tool based on the contour geometry and precisely controlling machining parameters to ensure accuracy.
It is mainly used for producing complex profiles such as curves, arcs, and irregular shapes on the surface of a part.
Straddle Milling
Straddle milling refers to the method of mounting two milling cutters on the same spindle to simultaneously machine the planar surfaces on both sides of a workpiece. A distinctive feature of straddle milling is that the tools straddle the workpiece, as illustrated below:
Gang Milling
Gang milling, also known as combination milling, is a process in which multiple milling cutters are mounted on the same spindle to machine several surfaces in a single pass. This setup allows simultaneous cutting of multiple planes or features, significantly improving production efficiency.
Gang milling is commonly used for machining multi-faced components or parts with complex slot and surface structures.
Summary
To provide a clearer understanding and comparison of different milling types, we have compiled the following table:
| Milling Type | Tool Axis Orientation | Cutting Area / Edge | Typical Applications |
|---|---|---|---|
|
Face Milling |
Perpendicular to the workpiece |
End cutting edges |
Machining flat surfaces and faces |
|
End Milling |
Perpendicular to the workpiece |
End and peripheral edges |
Machining steps, slots, and cavities |
|
Side Milling |
Parallel to the workpiece |
Peripheral edges |
Machining vertical or side surfaces, guideways |
|
Slot Milling
|
Perpendicular or parallel to the workpiece |
End and side edges
|
Cutting grooves, keyways, and channels
|
|
Square Shoulder Milling |
Perpendicular to the workpiece |
End and peripheral edges |
Producing 90° steps or shoulders |
|
Angle Milling
|
Inclined at a specific angle |
Angle cutter
|
Machining inclined surfaces, chamfers, or tapers |
|
Thread Milling |
Helical feed motion |
Thread milling cutter |
Cutting internal and external threads |
|
Gear Milling
|
Parallel to the gear profile |
Form cutter |
Machining gear teeth profiles |
|
Profile Milling |
Parallel or inclined |
Peripheral edges |
Machining external contours or 2D shapes |
|
Form Milling |
Parallel or inclined |
Form-shaped cutter |
Producing shapes matching the cutter profile |
|
Contour / Surface Milling |
Multi-axis |
Multi-axis cutting |
Machining complex 3D surfaces or structures |
|
Straddle Milling |
Parallel to the workpiece |
Two cutters simultaneously |
Machining two parallel surfaces at once |
|
Gang Milling |
Parallel to the workpiece |
Multiple cutters in sequence |
Machining multiple surfaces or slots simultaneously |
In essence, different types of milling operations are simply varied combinations of the cutter’s end and peripheral edges applied in different directions.Processes such as face milling, end milling, and side milling are commonly used for flat and vertical surfaces, while form and contour milling represent more advanced methods for complex, freeform surfaces.
Understanding these milling types is only the first step — choosing the right process is what truly improves product quality and production efficiency. If you’re unsure which milling method best suits your part, contact us today for a free process evaluation and quotation.
FAQ
What is the most precise milling operation?
The accuracy of milling depends on several factors, including machine performance, cutter type, and process control. Among the various milling operations mentioned above, profile (or contour) milling stands out as a typical high-precision process, as it often requires multi-axis coordination to machine complex geometries with exceptional accuracy.
What is the most cost-effective milling operation?
Among common milling types, face milling is generally the most economical. This process uses large-diameter, multi-edge cutters capable of removing a wide area of material in each pass, which results in high machining efficiency. In addition, face milling requires less demanding machine setups and lower-cost tooling, making it the most cost-effective method for rough machining flat surfaces.
What is the most expensive milling operation?
Among all milling operations, surface (or contour) milling is typically the most expensive. This is because it involves machining complex geometries, which demand advanced equipment, precise programming, and specialized cutting tools.
Within this category, 3D surface milling is the most costly, as it requires multi-axis machining, longer cycle times, and tight accuracy control throughout the process.
