A milling cutter is a rotary tool used in milling operations, featuring one or more cutting edges, mainly used for machining planes, steps, grooves, forming surfaces and cutting parts on milling machines. Based on different classification standards, milling cutters can be divided into several types.
Firstly, categorized by use, cutters can be divided into three main types: cutters for flat machining, for grooving and for machining forming surfaces. This classification focuses on the fields of application of the cutters.
Secondly, from the structural point of view, cutters can be divided into cylindrical cutters, face cutters, three-sided cutters, integral welded tooth type and indexable type, among others. These categories reflect the different structural characteristics and manufacturing processes of cutters.
Furthermore, based on the tooth shape of the cutter, it can be divided into straight teeth and spiral teeth. This classification is based on the distribution shape of the cutter teeth, which affects the cutting efficiency and quality of the part during the milling process.
In addition, there are cutters specially designed for specific processing requirements, such as gear cutters. They are special tools for milling involute gears and, according to their shape, they can be divided into disc gear hobs and finger gear hobs. This demonstrates the professionalism and diversity of cutters in specific processing fields.
Grading standards for milling cutters
The classification standards for milling cutters mainly include the shape of the blade, the direction of the teeth, the shape of the back of the tooth and the structure. The following sections detail these classifications and their advantages and disadvantages.
By blade shape:
Based on the shape of the blade, cutters can be classified into flat cutters, ball end cutters and circular cutters. This classification method makes it easier to select the appropriate type of cutter for different machining requirements.
By the direction of the teeth:
They are classified into straight tooth cutters and spiral tooth cutters. Straight tooth cutters are suitable for machining flat surfaces or channels, while spiral tooth cutters are more suitable for machining complex profiles as they provide better adaptability to curvature.
By the shape of the posterior tooth:
They are classified into point-toothed cutters and spade-toothed cutters. Pointed tooth cutters are suitable for high-speed machining due to their lower cutting resistance; Spade tooth cutters are suitable for heavy cutting as they can withstand higher cutting forces.
By structure:
They are classified into integral, welded, carbide insert and interchangeable types. Integral milling cutters have a simple structure and lower cost, but their durability is not as good as other types; welded cutters present better performance in terms of durability and resistance, but at a higher cost; carbide insert cutters extend their service life by replacing teeth, making them suitable for mass production; Interchangeable burs offer the highest flexibility and cost-effectiveness as they allow users to replace specific teeth as needed.
Types of Milling Tools
To make milling a versatile machining process, there is a wide variety of cutters available on the market. These cutters come in different sizes, shapes and materials. Some cutters are made from high-speed steel (HSS), while others are made with carbide tips.
1. End mill:
The end mill is a cutting tool that has teeth on both sides. This tool is versatile and can be used for a variety of drilling operations. The term “end mill” is commonly used for flat-bottomed tools.
Unlike a drill, which cuts only in the axial direction, the end mill is capable of cutting in all directions. The end mill typically has one or more chip removal grooves and is used for various milling operations. It is made of high speed steel or hardened material.
There are two variations of end mill: one with cutting edges on both sides, known as center cutting, and another with cutting edge on only one side, called non-center cutting edge.
2. Roughing cutter:
The Rough End Mill cutter is also known as the “Pippa” cutter. These end mills offer excellent performance even under harsh operating conditions. They are used to remove a substantial amount of material from the workpiece. These tools typically have more wavy teeth and result in a rough surface finish with the production of smaller chips.
3. Peripheral milling cutter:
When the cutting teeth of the cutter are located on the circumference or periphery of the disc, they are called peripheral or circumferential cutters. These types of cutters can only be used on horizontal milling machines.
4. Side milling cutter:
Side milling cutter is a type of milling tool with cutting teeth present both on the periphery and on the face or end. It is typically used for side milling, face milling, and slot cutting operations. They are also effective in creating deep, narrow grooves.
5. Face milling cutter:
The front milling cutter consists of a large diameter cutting body with multiple mechanically fixed blades. Through its cutting stroke and deep radial and narrow axial cuts, it can remove a large amount of unwanted material.
The diameter of the face mill body typically depends on the length of the workpiece and the clearance available on both sides.
This cutting tool can also be used for profile milling operations and is known for its rigidity. The surface finish produced by the face mill depends on the feed rate and number of teeth on the tool.
6. Concave cutter:
The Concave Mill belongs to the category of forming mills. These are specially manufactured tools designed to create specific shapes on the workpiece. The Concave Mill is specifically designed to match the convex surface of a circular profile, which is generally equal to or smaller than a semicircle.
7. Woodruff Tool:
“Woodruff” cutting tools are typically used to cut keyways in wood materials. The edge of the tool has a slightly concave shape and its teeth are not designed for side cutting. The tool has two types of tooth profile: straight teeth and stepped teeth.
8. Thread milling cutter:
A thread milling cutter is a cutting tool used to cut the external and internal thread tooth profile of a workpiece. It is capable of processing single and variable pitch threads ranging from M2 to 1mm nominal diameter.
9. Ball end mill:
Ball end mills, also known as ball end mills, are named for their hemispherical cutting edges. They are used to reduce stress concentration during operation and are typically suitable for machining three-dimensional surface shapes of workpieces.
10. Flying Cutter:
The flying cutter consists of a main body with one or two cutting heads inserted. As the cutter head rotates, it can make narrower or wider cuts. Although face mills are more commonly used in many cases, they are also more expensive.
Flying mills, on the other hand, can perform the same processing tasks as face mills, but at a lower cost. However, its cutting efficiency is significantly lower compared to face mills.
What is a milling tool?
The cutter plays an important role in the milling machine. It is a rotary tool with one or more teeth for milling.
During operation, each tooth of the cutter cuts a portion of the workpiece.
The milling cutter is mainly used for tasks such as milling flat surfaces, steps, grooves, forming shapes, and cutting workpieces.
Meaning of Milling Tools
In typical milling operations, the tool on the mill moves perpendicular to its own axis, thus removing excess material from the workpiece around the tool.
The milling machine is a widely used device capable of performing a variety of machining operations. It is used to process and manufacture parts of different shapes and sizes, with the milling cutter being a fundamental tool in carrying out these tasks.
Material considerations
When selecting a router, it is essential to consider the material from which it is made. Different materials serve different applications and have unique properties. Four main materials commonly used in milling cutters are discussed below: high-speed steel, carbide, cobalt and diamond.
High speed steel
High speed steel (HSS) is a widely used material for milling cutters. HSS offers wear resistance and reasonable cutting speeds for a variety of applications. Due to their versatility, lower cost and ease of manufacturing, HSS cutters are a popular choice, especially for less demanding applications or small-scale operations.
Carbide
Carbide cutters are composed of a hard compound, usually tungsten carbide, and a metal binder. They offer greater wear resistance and cutting speeds compared to HSS. Although carbide cutters tend to be more expensive, their durability and efficiency make them suitable for high-volume production and machining harder materials. Some key properties of carbide cutters include:
- High wear resistance
- Faster cutting rates
- Longer tool life
- Improved surface finish
Cobalt
Cobalt cutters contain a significant amount of cobalt, increasing their hardness and wear resistance compared to standard HSS cutters. These cutters are suitable for machining tougher materials such as stainless steel and high temperature alloys. Although cobalt cutters are not as wear-resistant as carbide cutters, they offer an excellent balance between performance and cost, making them a reliable choice for many applications.
Diamond
Diamond cutters are another high-performance option, made from polycrystalline diamond (PCD) or natural diamond. These cutters feature exceptional hardness and wear resistance, allowing them to sustain sharp cutting edges for a long period. Diamond cutters are ideal for:
- Machining highly abrasive materials
- Providing a superior surface finish
- Achieving strict tolerances
However, diamond cutters have a higher cost compared to other materials and generally do not work well when machining ferrous materials. This limitation is due to the carbon found in ferrous materials, which forms hard carbides and reduces the effectiveness of the cutter.
By understanding the qualities of different materials, an informed decision can be made when selecting cutters for specific applications.
Cutter selection principle
1. Selection of cutter diameter
Cutter diameter selection can vary greatly based on the specific product and production batch. The choice of tool diameter depends mainly on the equipment specifications and the size of the part to be machined.
Flat cutter
When selecting the diameter of the face milling tool, it is important to consider that the power required by the tool must be within the power capacity range of the machine tool. Alternatively, it can be selected based on the machine tool spindle diameter.
A commonly used method for determining face mill diameter is to use the formula D = 1.5d, where d is the spindle diameter.
For mass production, the tool diameter can also be selected based on 1.6 times the width of the part to be cut.
And second mill
The selection of end mill diameter should mainly consider the processing size requirements of the workpiece to ensure that the power requirements of the end mill are within the rated power range of the machine tool.
For small diameter end mills, the main concern should be whether the maximum machine tool revolutions can reach the tool's minimum cutting speed (60m/min).
For slotting cutters, the diameter and width must be selected based on the size of the part being machined, ensuring that the cutting power remains within the allowable power range of the machine tool.
2. Selection of cutter blade
The. For finishing, it is best to use a grinder blade. This type of blade has good dimensional accuracy, which guarantees the positioning accuracy of the cutting edge, providing better machining precision and surface roughness.
B. For rough machining, it is better to use a pressing blade, which reduces the processing cost. Although the dimensional accuracy and sharpness of a pressing blade are worse than that of a grinding blade, its edge strength is better. It is resistant to impacts during rough machining and can handle large cutting depths and high feeds.
w. Large, sharp rake blades are ideal for milling viscous materials such as stainless steel. The sharp edge reduces friction between the blade and the workpiece, allowing chips to move away from the front of the blade more quickly during the cutting process.
3. Selection of cutter blade
(a) The number of teeth must be considered when selecting a cutter. The tooth pitch size will determine the number of cutter teeth involved in cutting at the same time and will affect the smoothness of the cut and the requirements for the cutting speed of the machine tool. Rough tooth milling cutters are mainly used for rough machining because of their large chip removal slot. The cutting load per tooth of a coarse-toothed cutter is greater than that of a dense-toothed cutter at the same feed rate.
(b) For finish milling, with a shallow cutting depth of generally 0.25-0.64mm, it is recommended to select a dense tooth cutter.
(c) During heavy rough milling, excessive cutting force can cause chatter in machine tools with low rigidity, causing edge collapse of carbide blades and shortening tool life. Using a coarse-toothed milling cutter can reduce the power requirement of the machine tool. Therefore, when the spindle hole size is small (such as R8, 30#, 40# tapered holes), rough tooth milling cutters can be used effectively for milling.
Latest technological trends in milling cutters
The latest technological developments in milling cutters are mainly concentrated in the following areas:
Innovation in materials composition: One of the recent advances in top drill technology is innovation in materials engineering, particularly the use of ultrafine carbide grains. This helps improve performance and extend tool life.
Advances in coating technology: Innovations in material selection, tool design and coating technology will further enhance cutter performance.
Improvements in geometric shapes: The progression of technology from drills to end mills also includes improvements in geometric shapes to improve performance and extend tool life.
Application of CNC Milling Machines and Development Towards Intelligence and Digitalization: The use of CNC milling machines not only increases manufacturing efficiency and product quality, but also pushes the industry towards intelligence and digitalization. This suggests that the evolution of milling technology will adapt to these trends.
Market demand driven by rapid development in new industrial fields: Rapid growth in some emerging industrial sectors brings new market demands for milling cutters, driving constant innovations in milling cutter technology to meet these needs.
Conclusion
When choosing a cutter for a CNC milling machine or a conventional milling machine, it is important to consider several factors such as the material and hardness of the workpiece and the specifications of the cutter such as cutting edge length, tool length, cutting edge diameter and rod diameter. High-speed steel cutters are typically used with conventional milling machines, while carbide cutters are preferred for use with CNC milling machines.
