Ultimate Guide to Side Milling: Processes & Applications Unveiled

What is Side Milling?

In side milling, a rotating cutter removes material from the side of a workpiece, resulting in various complex features like flat surfaces, shoulders, and grooves. Unlike slot milling, which cuts directly into the material, side milling utilizes the side teeth of the cutting tool to achieve these results. Particularly, this technique is useful when machining surfaces that traditional face milling cannot access.

How does Side Milling Work?

Several key steps ensure efficient and precise material removal in the side milling process. Below are the main steps:

1. Setup: First, mount a cutter—either a slab mill or an end mill—onto the spindle of the milling machine. Simultaneously, securely clamp the workpiece to the table of the milling machine. This step ensures accurate contact between the cutting tool and the material.
2. Material Removal: The edges of the cutting tool engage with the raw material to shape it according to the desired design. The cutter rotates perpendicular to the workpiece, efficiently removing material along the intended path. Additionally, the cutter moves perpendicular to the axis of the workpiece, accurately sculpting the side profile.
3. Climb vs. Conventional Milling: In side milling, you can choose between two primary methods: climb milling and conventional milling. During climb milling, the cutter advances in the same direction as the workpiece feed, effectively reducing cutting forces and enhancing the surface finish. In contrast, conventional milling moves the cutter against the feed direction, providing better control, especially when working with harder materials.
   • Cutting Parameters: Optimizing key parameters—such as radial depth of cut, axial depth of cut, feed per tooth, and material removal rate—is crucial for achieving precise and efficient cuts.
   • Radial Depth of Cut (ae): This parameter determines how much of the cutter’s diameter interacts with the workpiece. A smaller ae reduces cutting forces and tool deflection, which is particularly helpful for machining thin-walled parts or during finishing passes.
   • Axial Depth of Cut (ap): This measures how deeply the tool cuts along its axis. Deeper cuts can improve productivity; however, they require sufficient rigidity from both the machine and the tool.
   • Feed per Tooth (Fn): This factor affects chip load and tool wear. By optimizing Fn, you ensure efficient material removal while preventing excessive cutting forces.

Speeds and Feeds for Side Milling

Speeds and feeds are crucial parameter which is responsible for the efficiency, surface finish, and tool life of the process. Careful selection of these parameters is necessary based on the material being machined, the cutter type, and the capabilities of the milling machine.

Cutting Speed (vc):

The cutting speed, expressed in meters per minute (m/min) or surface feet per minute (SFM), refers to the speed at which the tool’s cutting edge moves relative to the workpiece. The appropriate cutting speed depends on the workpiece material. Softer materials, such as aluminum, can withstand higher speeds, while harder materials, like steel, require lower speeds.

For milling steels, cutting speeds typically range from 50 to 200 m/min.

Spindle Speed (n):

Spindle speed indicates the rotational speed of the cutter and is measured in revolutions per minute (RPM). It can be calculated using the cutting speed and the tool diameter.

Feed Rate (vf):

The feed rate is the speed at which the workpiece moves relative to the rotating cutter, measured in millimeters per minute (mm/min) or inches per minute (IPM). It is influenced by the number of teeth on the cutter (Z), the feed per tooth (fz), and the spindle speed.

Feed per Tooth (fz):

Feed per tooth is the distance the workpiece moves during one revolution of a single cutter tooth.

Depth of Cut:

The depth of cut includes both the axial depth of cut (ap) and the radial depth of cut (ae). Axial depth of cut affects vertical pressure on the tool, while radial depth involves horizontal pressure. Balancing these depths is essential for tooling life and surface integrity. For finish cuts, it is recommended that the radial depth of cut (ae) does not exceed 2% of the tool diameter (XD).​

Material Removal Rate (MRR):

The material removal rate is the volume of material removed per unit of time and is calculated using the axial depth, radial depth, and feed rate.

Types of Side Milling Cutters

Side milling utilizes various types of cutters, each designed for specific applications and materials. Here are some common types:

• Plain Milling Cutters: Also known as straight-tooth cutters, these have teeth lined up in a single file and are suitable for creating flat surfaces.
• Staggered-Tooth Cutters: These cutters feature teeth that alternate along the circumference, reducing vibration and providing a smoother finish. They are ideal for heavy-duty operations and uneven surfaces.
• Side-and-Face Cutters: These cutters can be employed for both side milling and face milling.
• Slab Mill Cutters: Also known as surface milling cutters, these cutters have helical or straight teeth and are ideal for small-scale projects requiring light milling work. They cut on cylindrical or periphery mills flat surfaces parallel to the cutter axis.
• Concave Milling Cutter: This slitting saw is applied to produce a true convex radius, applying a seamless and smooth semi-circular shape to parts.
• Cylindrical Milling Cutter: Ideal for applications requiring a high rate of stock removal, this slitting saw has teeth on the peripheral surface only.
• End Mills: End mills are versatile tools that can cut in all directions, unlike drill tools that only cut axially. They can be used for tool steel cutting and various milling processes like plunging, reaming, slotting, drilling, face milling, and profile milling. Common types of end mills include:
  • Ball Nose End Mills: Feature a ball nose, making them ideal for milling contoured surfaces.
  • Square End Mills: Have a 90-degree profile and are used for all-around milling applications such as plunging, profiling, and slotting.
  • Radius End Mills: Feature rounded corners, preventing tool wear and prolonging tool life when cutting a specified radius.
  • Undercutting End Mills: Also known as lollipop cutters, these well-rounded tools are ideal for machining undercuts.
• Side Milling Cutters: These cutters often feature insert cutting edges for large or deep grooves or hard-to-machine materials.
• Tangential Side Milling Cutters: These cutters have fine tooth pitch through tangential insert design. In addition, it allows for very smooth cutting through left and right-hand inserts, with a secondary cutting edge positioned outside of the cutting zone. Face milling is also possible.
• Slot Milling Cutters: The GB18 is a standard milling cutter with double-cutting edge indexable inserts that are positively connected. Thus, it can slits and severs materials effectively.

Material Available for Precision Side Milling

Precision side milling is applicable to a wide array of materials, each requiring specific considerations. Here will explore two common materials:

• Aluminum: Side milling aluminum and its alloys, such as AL6061, ensure smooth cuts without material deformation. AL6061 is a common, general-purpose aluminum grade often used for automotive parts due to its good strength-to-weight ratio and natural resistance. Additionally, AL7075 is one of the highest-strength aluminum alloys available, making it ideal for high-strength applications.
• Stainless Steel: Side milling of stainless steel parts is ideal for applications requiring corrosion resistance. When milling 316 stainless steel, it is recommended to use a 3-flute endmill with a faster helix to reduce heat input and prevent work-hardening. Work hardening occurs if too much heat is introduced to the 316 stainless, turning it into something harder during the cut. For milling stainless steel, maximizing the tool’s flute length combined with the correct radial engagement can ease spindle load.

Pros and Cons of CNC Side Milling

CNC side milling offers several advantages, including versatility in producing complex shapes for both small and large parts. However, it also has some limitations:

Advantages

• Versatility: Capable of producing complex shapes and designs.
• High Precision: Achieves tight tolerances and accuracy, ensuring quality parts.
• Superior Surface Finish: Delivers excellent surface finishes, enhancing the aesthetic and functional quality of parts.
• Specific Textures: Able to create various textures on the surface of the workpiece.
• Effective for Hard Materials: Suitable for machining hard materials, providing durability and performance.
• Clean Edges: Ideal for creating slots and grooves with precise edges.
• Variety of Cutter Types: Different cutter options allow for adaptability to various applications.

Disadvantages

• Tool Wear: Significant tool wear can increase operational costs due to frequent tool replacement.
• Complexity: Programming and setup can be complex, requiring advanced skills and experience.
• Securing Workpieces: Securing irregular shapes can be tricky, complicating the setup process.
• Lateral Forces: There is a higher risk of issues due to lateral forces, which can affect the stability of the machining process.
• Thin Workpieces: Not suitable for very thin workpieces, as the cutting tools’ force could break or deform the material.
• Vibrations: Extreme vibration can lead to uneven cuts, affecting surface quality and tool longevity.

Applications of Side Milling

CNC side milling plays a vital role across various industries due to its precision and versatility. Here are some key sectors where side milling is particularly beneficial:

In the aerospace industry, side milling is crucial for manufacturing precise wing sections and structural components that meet the stringent quality and tolerance requirements of the sector.

Within the electronics sector, side milling enables the creation of intricate features and contours on components such as circuit boards and connectors, ensuring a seamless fit and reliable functionality.

The medical field relies on side milling for the production of components like implants and surgical instruments, where high precision and flawless surface finishes are imperative to meet healthcare standards. Titanium, known for its corrosion resistance and compatibility with the human body, is often used in these medical devices.

In automotive manufacturing, side milling assists in creating various components, including car body panels, frames, and exhaust parts, contributing to the overall quality and safety of vehicles.

Side Milling vs. End Milling vs. Plain Milling

These milling techniques serve distinct purposes, each contributing to the efficiency and quality of the manufacturing process in various applications.

Side Milling

As we mentioned before, side milling employs the side teeth of a cutter to remove material from the sides of a workpiece, allowing for the creation of features such as slots, keyways, vertical surfaces and complex contours. Furthermore, side milling finds applications across various industries, including construction, aerospace, and automotive.

End Milling

On the other hand, end milling utilizes tools that rotate around their axis while moving axially along the surface of a workpiece to remove material. This versatile process can perform both axial and lateral cuts, making it capable of creating pockets, slots, recesses, shoulders, profiles, and cavities. With a variety of sizes and shapes, including ball nose, square, tapered, and corner radius, end mills can cater to different machining requirements. Although end milling can handle face milling tasks, it typically does not achieve the same level of surface finish quality.

Plain Milling

Also known as surface milling, plain milling is utilized for fabricating flat surfaces, particularly in situations where high accuracy and productivity are essential. This process focuses on the creation of planar surfaces, ensuring that the milled parts meet stringent precision standards. In addition, the cutter’s helical or spiral design allows for engagement with the workpiece’s multiple teeth, promoting smoother operations and minimizing vibrations during the milling process.

Tips for Efficient Side Milling

To ensure efficiency and precision in side milling, consider the following strategies:

Cutting Tool Selection

Select the right tool material based on the requirements of the workpiece. Carbide cutters are the industry standard for side milling due to their hardness and wear resistance, making them suitable for high-speed cutting and for machining hard materials. Coatings like titanium nitride (TiN) can enhance the hardness and wear resistance of cutting tools.

Cutting Parameters

Optimize cutting parameters, such as cutting speed, feed rate, and both axial and radial depths of cut, to strike a balance between productivity and tool life. Measuring the tool’s edge movement through the material in surface feet per minute or meters per minute helps determine the ideal cutting speed. Properly balancing feed rate with cutting speed is essential to minimize wear while maximizing productivity.

Machine Rigidity and Stability

Ensure that machine rigidity is maintained for successful side milling. The workpiece should be securely clamped, and the machine along with the tool holder must be stable to prevent vibration and movement during the milling process. Reducing the radial engagement angle and applying advanced stabilization methods can further enhance cutting stability.

Chip Evacuation

Effective chip evacuation is crucial to prevent tool clogging, especially during deeper cuts. Implement machining strategies such as trochoidal or helical tool paths to avoid chip congestion. High-pressure coolant systems are also beneficial for chip removal and maintaining thermal control, which helps ensure a smoother machining process.

Workpiece Material

Side milling can be applied to various materials, including metals, plastics, and composites. Special care is required when machining titanium; using specialized tools and cooling systems is essential to manage heat generation, ensuring precision and extending tool life.

Conclusion

By understanding the various types of cutters, materials, and best practices involved, manufacturers can significantly improve the efficiency, quality, and cost-effectiveness of their milling operations. Moreover, with the right tool selection and strategies, side milling can produce smooth finishes and maintain tight tolerances.

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