Peripheral milling is a crucial machining operation employed by intermediate and professional manufacturers to enhance metal removal rates and extend tool life.
This guide explores various strategies, focusing on plain milling, standard milling, and the distinction between up-milling and down-milling.
So, if you’re opting for plain milling for your next production project, read on to learn all about peripheral milling operations – beyond the basics!
Peripheral Milling: A Brief Overview
Peripheral milling, commonly known as plain milling, is a milling operation that employs a rotating milling cutter with an axis parallel to the workpiece.
Unlike face milling, where the cutting tools are mounted perpendicular to the stock, in peripheral milling, the cutter’s cutting edges grind at the workpiece’s periphery, providing an efficient means to remove large amounts of surface material.
Types of Peripheral Milling
In plain milling, understanding the nuances of different techniques is crucial for optimizing machining processes. Let’s delve into two primary types: Up Milling and Down Milling (Climb Milling).
Up Milling
Up milling, or conventional milling, involves cutter teeth moving opposite the feed direction. This results in initially thin chips that gradually grow throughout the cut. The extended tool engagement leads to long chip formation.
However, it’s important to note that as the cutter exits, the workpiece may tend to lift, necessitating a sturdy fixture to maintain stability. Manufacturers should consider up-milling when seeking a robust cutting process, especially for materials where chip evacuation is critical.
Down Milling (Climb Milling)
In contrast, Down Milling, or Climb Milling, sees cutter teeth moving in the same direction as the feed. This produces shorter chips with decreasing thickness over the length of the cut. The reduced frictional forces contribute to minimized heat generation, extending tool life.
Tangential forces act downward, ensuring a steady cut and enabling an increased feed rate. Manufacturers should opt for down milling when prioritizing heat reduction, improved tool longevity, and a smoother machining experience, especially when high precision and finish are paramount.
Up Milling vs Down Milling
| Up Milling | Down Milling |
| Cutter direction opposite feed | The cutter direction is the same as the feed |
| Requires high-cutting power | Only requires less cutting power |
| Cutting forces act upwards | Cutting forces act downwards |
| Suitable for rough cutting | Suitable for surface finishing |
| High tool wear rate | Less tool wear rate |
| Chip thickness increases | Chip thickness decreases over the cut |
| Mostly used for ferrous metals | Mostly used for aluminum and alloys |
The Different Peripheral Milling Methods and Cutters
Understanding the ‘how’ and ‘when’ of peripheral milling methods and cutters is key when optimizing milling operations. As seasoned manufacturers, you’re already familiar with plain milling, so let’s delve into the nuances of these techniques and tools.
Peripheral Milling Methods
1. Slab Milling
- Overview: Slab milling involves using a plain milling cutter, usually wider than the workpiece, to shape flat surfaces or efficiently reduce part thickness.
- Usage: During slab milling, the cutter, wider than the workpiece, moves across, systematically removing material and creating a precisely flat surface or reducing thickness as needed.
- Ideal for: This method is ideal for applications where large, flat surfaces must be created or when efficiently reducing part thickness is a primary objective.
2. Slot Milling
- Overview: Slot milling utilizes a cutter with a width less than the part to create rectangular or round channels in the workpiece.
- Usage: In slot milling, the cutter’s width is strategically less than the part, allowing it to form slots during the pass, making it particularly effective for crafting channels of varying shapes.
- Ideal for: This method is ideal for applications requiring the creation of slots, especially when fine slots are needed for specific designs.
3. Side Milling
- Overview: Side milling involves machining a surface at a right angle to the cutter’s axis of rotation.
- Usage: The side milling cutter works by machining the side faces of the workpiece, creating a precisely flat vertical surface perpendicular to the cutter’s rotation axis.
- Ideal for: Ideal for situations where machining side faces or creating flat vertical surfaces is a primary requirement.
4. Gang Milling
Overview: Gang milling is an operation where more than one parallel vertical surface is machined in a single pass.
Usage: Multiple cutters are mounted on the same arbor, spaced apart based on the required width using spacers, enabling the machining of multiple surfaces simultaneously.
Ideal for: This method is ideal when the objective is to efficiently machine multiple parallel surfaces simultaneously.
5. Straddle Milling
- Overview: Straddle milling is similar to gang milling but has the unique feature of cutting two slots simultaneously.
- Usage: Multiple cutters on the same arbor create two slots in a single pass, making it efficient for projects requiring the creation of dual slots.
- Ideal for: Straddle milling is ideal for applications where dual slots must be created efficiently.
6. Form Milling
- Overview: Form milling involves using specially designed cutters to machine different patterns on the workpiece.
- Usage: Customized form milling cutters create intricate patterns like round recesses and beads on the workpiece, adding a unique touch to the machining process.
- Ideal for: This method is ideal for applications that require the creation of intricate patterns and contours on the workpiece.
Peripheral Milling Cutters
1. Slab Milling Cutter
- Overview: Slab milling cutters are circular discs with straight or spiral teeth on the periphery, designed for efficient material removal.
- Ideal for: Perfect for horizontal milling applications where the goal is to remove a large amount of material and produce flat surfaces.
2. Side Milling Cutter
- Overview: Side milling cutters have cutting teeth on one or both sides and teeth on the periphery, making them effective for straddle milling jobs and cutting slots.
- Ideal for: For situations where straddle milling is required, efficient cutting of slots is a primary objective.
3. Staggered Milling Cutter
- Overview: Staggered milling cutters are side milling cutters with teeth arranged in a zig-zag order.
- Ideal for: Suitable for milling slots where the depth is larger than the width, preventing interference with the cutting actions.
4. Concave & Convex Milling Cutter
- Overview: Concave and convex milling cutters can mill varying convex and concave contours on the workpiece surface based on the circular form’s diameter.
- Ideal for: Perfect for applications that require milling surfaces with varying convex and concave profiles.
5. Woodruff Milling Cutter
- Overview: Woodruff milling cutters have cutting teeth on the periphery of a disc connected to a straight shank.
- Ideal for: Essential for precise cutting of keyways in shafts.
6. Hobbing Cutter
- Overview: Hobbing cutters are cylindrical cutters with helical cutting teeth designed for cutting teeth in the workpiece.
- Ideal for: Used specifically for cutting splines and sprocket gears.
You can strategically enhance your machining processes by considering the characteristics and applications of each peripheral milling method and cutter.
Whether crafting intricate patterns or efficiently removing material, selecting the right method and cutter ensures optimal results in your manufacturing endeavors.
Key Parameters in Peripheral Milling
Chip Thickness to Width of Cut Ratio
An optimal combination of chip thickness and cut width is paramount for effective peripheral milling. And with a proper balance between these two, you can easily reduce the machining time and increase tool life. Notably, thin chip thickness on exit and small engagement arcs result in longer life for a particular cutting tool.
Workpiece Entry – Rolling into the Cut
Among the proposed cutting strategies, entry into the workpiece is critical. The rolling-in technique, where the cutter rotates on a pivot point, gradually entering until the nominal width of the cut is reached, proves advantageous.
This approach minimizes chip thickness during exit, reduces temperature, and eliminates vibrations compared to direct entry.
Cutting Force Model for Cutter Entry
Considering the different types of cutters and their usage, it’s important to introduce a new cutting force model for estimating the entry of the cutter into the workpiece until total engagement.
For this, three distinct zones are identified during cutter entry: the cuts start until the workpiece’s left corner is reached, cutting the top surface of the workpiece, and complete engagement.
The force profile varies in the first two zones, highlighting the variable cutting conditions. Once fully engaged, the force profile stabilizes.
Advantages of Rolling-In Entry
Comparing straight-in and rolling-in entries, the evolution of cutting forces, chip formation, and volume of metal removal are analyzed.
The rolling-in technique exhibits a more gradual increase in cutting forces, resulting in thinner chips exiting the cutter from the start of the machining process. The engagement arcs are shorter, leading to lower temperatures in the cutting flute and reduced tool wear.
Conclusion
In conclusion, effective peripheral milling approaches can significantly improve tool life and metal removal rates, particularly emphasizing the rolling-in entry technique.
The experimental data presented in this guide serves as a foundation for manufacturers seeking to enhance their milling strategies. By implementing these insights, professionals can optimize their processes, reduce tool wear, and achieve higher efficiency in peripheral milling operations.
Still have questions? Consult our professional manufacturers at Prototool.
