Basic knowledge of End Mill Series

1. Basic requirements for milling cutters to cut some materials

(1) High hardness and wear resistance: Under normal temperature, the cutting part of the material must have sufficient hardness to cut into the workpiece; with high wear resistance, the tool will not wear and extend the service life.

(2) Good heat resistance: The tool will generate a lot of heat during the cutting process, especially when the cutting speed is high, the temperature will be very high. Therefore, the tool material should have good heat resistance, even at high temperatures. It can still maintain high hardness and can continue cutting. This property of high temperature hardness is also called hot hardness or red hardness.

(3) High strength and good toughness: During the cutting process, the tool has to withstand a great impact, so the tool material must have high strength, otherwise it is easy to break and damage. Because the milling cutter is subject to impact and vibration, the milling cutter material should also have good toughness so that it is not easy to chip and chip.


2. Commonly used materials for milling cutters

(1) High-speed tool steel (referred to as high-speed steel, front steel, etc.), divided into general-purpose and special-purpose high-speed steel. It has the following characteristics:

a. The content of alloying elements tungsten, chromium, molybdenum and vanadium is relatively high, and the quenching hardness can reach HRC62-70. At 6000C high temperature, it can still maintain high hardness.

b. The cutting edge has good strength and toughness, strong vibration resistance, and can be used to manufacture tools with general cutting speed. For machine tools with poor rigidity, high-speed steel milling cutters can still be cut smoothly

c. Good process performance, forging, processing and sharpening are relatively easy, and tools with more complex shapes can also be manufactured.

d. Compared with cemented carbide materials, it still has the disadvantages of lower hardness, poor red hardness and wear resistance

(2) Cemented carbide: It is made of metal carbide, tungsten carbide, titanium carbide and cobalt-based metal binder through powder metallurgical process. Its main features are as follows:

It can withstand high temperature, and can still maintain good cutting performance at about 800-10000C. When cutting, the cutting speed can be 4-8 times higher than that of high-speed steel. High hardness at room temperature and good wear resistance. The bending strength is low, the impact toughness is poor, and the blade is not easy to sharpen.

Commonly used cemented carbides can generally be divided into three categories:

① Tungsten-cobalt cemented carbide (YG)

Commonly used grades YG3, YG6, YG8, where the numbers indicate the percentage of cobalt content, the more cobalt content, the better the toughness, the more impact and vibration resistance, but will reduce the hardness and wear resistance. Therefore, the alloy is suitable for cutting cast iron and non-ferrous metals, and can also be used for cutting rough and hardened steel and stainless steel parts with high impact

② Titanium-cobalt cemented carbide (YT)

Commonly used grades are YT5, YT15, YT30, and the numbers indicate the percentage of titanium carbide. After the cemented carbide contains titanium carbide, it can increase the bonding temperature of the steel, reduce the friction coefficient, and slightly increase the hardness and wear resistance, but it reduces the bending strength and toughness and makes the properties brittle. Therefore, the Class alloys are suitable for cutting steel parts.

③ General cemented carbide

Add appropriate amount of rare metal carbides, such as tantalum carbide and niobium carbide, to the above two hard alloys to refine their grains and improve their room temperature and high temperature hardness, wear resistance, bonding temperature and oxidation resistance , It can increase the toughness of the alloy. Therefore, this type of cemented carbide knife has better comprehensive cutting performance and versatility. Its brands are: YW1, YW2 and YA6, etc., because of its relatively expensive price, it is mainly used for difficult Processing materials, such as high-strength steel, heat-resistant steel, stainless steel, etc.


3. Types of milling cutters

(1) According to the material of the cutting part of the milling cutter:

a. High-speed steel milling cutter: This type is used for more complex cutters.

b. Carbide milling cutters: mostly welded or mechanically clamped to the cutter body.

(2) According to the purpose of the milling cutter:

a. Milling cutters for processing planes: cylindrical milling cutters, end milling cutters, etc.

b. Milling cutters for processing grooves (or step tables): end mills, disc milling cutters, saw blade milling cutters, etc.

c. Milling cutters for special-shaped surfaces: forming milling cutters, etc.

(3) According to the structure of the milling cutter

a. Sharp tooth milling cutter: The cut-off shape of the tooth back is straight or broken, easy to manufacture and sharpen, and the cutting edge is sharper.

b. Relief tooth milling cutter: the cut-off shape of the tooth back is an Archimedes spiral. After sharpening, as long as the rake angle remains unchanged, the tooth profile does not change, which is suitable for forming milling cutters.


4. The main geometric parameters and functions of the milling cutter

(1) The name of each part of the milling cutter

① Base plane: A plane passing through any point on the cutter and perpendicular to the cutting speed of that point

② Cutting plane: the plane passing through the cutting edge and perpendicular to the base plane.

③ Rake face: the plane where the chips flow out.

④ Flank surface: the surface opposite to the machined surface

(2) The main geometric angle and function of cylindrical milling cutter

① Rake angle γ0: The included angle between the rake face and the base surface. The function is to make the cutting edge sharp, reduce the metal deformation during cutting, and easily discharge the chips, thus saving labor in cutting.

② Relief angle α0: The included angle between the flank surface and the cutting plane. Its main function is to reduce the friction between the flank face and the cutting plane and reduce the surface roughness of the workpiece.

③ Swivel angle 0: The angle between the tangent on the helical tooth blade and the axis of the milling cutter. The function is to make the cutter teeth gradually cut into and away from the workpiece, and improve the cutting stability. At the same time, for cylindrical milling cutters, it also has the effect of making chips flow out smoothly from the end face.

(3) The main geometric angle and function of the end mill

The end mill has one more secondary cutting edge, so in addition to the rake angle and the relief angle, there are:

① Entering angle Kr: The included angle between the main cutting edge and the machined surface. The change affects the length of the main cutting edge to participate in the cutting, and changes the width and thickness of the chip.

② Secondary deflection angle Krˊ: The included angle between the secondary cutting edge and the machined surface. The function is to reduce the friction between the secondary cutting edge and the machined surface, and affect the trimming effect of the secondary cutting edge on the machined surface.

③ Blade inclination λs: The included angle between the main cutting edge and the base surface. Mainly play the role of oblique blade cutting.


5. Forming cutter

The forming milling cutter is a special milling cutter used to process the forming surface. Its blade profile needs to be designed and calculated according to the profile of the workpiece to be processed. It can process complex-shaped surfaces on a general-purpose milling machine, ensuring that the shape is basically the same, and the efficiency is high. , It is widely used in batch production and mass production.

(1) Forming milling cutters can be divided into two types: pointed teeth and relief teeth

The milling and re-grinding of the sharp tooth forming milling cutter requires a special master, which is difficult to manufacture and sharpen. The tooth back of the shovel tooth profile milling cutter is made by shoveling and shovel grinding on a shovel tooth lathe. Only the rake face is sharpened during re-grinding. Because the rake face is flat, it is more convenient to sharpen. At present, the forming milling cutter mainly uses shovel Tooth back structure. The tooth back of the relief tooth should meet two conditions: ①The shape of the cutting edge remains unchanged after regrinding; ②Get the required relief angle.

(2) Tooth back curve and equation

An end section perpendicular to the axis of the milling cutter is made through any point on the cutting edge of the milling cutter. The intersection line between it and the tooth back surface is called the tooth back curve of the milling cutter.

The tooth back curve should mainly meet two conditions: one is that the relief angle of the milling cutter after each regrind is basically unchanged; the other is that it is easy to manufacture.

The only curve that can satisfy the constant clearance angle is the logarithmic spiral, but it is difficult to manufacture. The Archimedes spiral can satisfy the requirement that the clearance angle is basically unchanged, and it is simple to manufacture and easy to realize. Therefore, Archimedes spiral is widely used in production as the profile of the tooth back curve of the milling cutter.

From the knowledge of geometry, the vector radius ρ value of each point on the Archimedes spiral increases or decreases proportionally with the increase or decrease of the turning angle θ of the vector radius.

Therefore, as long as a combination of constant velocity rotational motion and constant velocity linear motion along the radius direction, an Archimedes spiral can be obtained.

Expressed in polar coordinates: when θ=00, ρ=R, (R is the radius of the milling cutter), when θ>00, ρ<r,< p=”"></r,<>

The general equation for the back of a milling cutter is:  ρ=R-CQ

Assuming that the blade does not retreat, then every time the milling cutter rotates an inter-tooth angle ε=2π/z, the tooth amount of the blade is K. To adapt to this, the elevation of the cam should also be K. In order to make the blade move at a constant speed, the curve on the cam should be an Archimedes spiral, so it is easy to manufacture. In addition, the size of the cam is only determined by the shovel sales K value, and has nothing to do with the number of teeth and the clearance angle of the cutter diameter. As long as the production and sales are equal, the cam can be used universally. This is also the reason why Archimedes spirals are widely used in tooth backs of relief tooth forming milling cutters.

When the radius R of the milling cutter and the cutting amount K are known, C can be obtained:

When θ=2π/z, ρ=R-K

Then R-K=R-2πC /z ∴ C = Kz/2π


6. Phenomena that will occur after the milling cutter is passivated

(1) Judging from the shape of the chips, the chips become thick and flaky. As the temperature of the chips rises, the color of the chips becomes purple and smokes.

(2) The roughness of the processed surface of the workpiece is very poor, and there are bright spots on the surface of the workpiece with gnawing marks or ripples.

(3) The milling process produces very serious vibration and abnormal noise.

(4) Judging from the shape of the knife edge, there are shiny white spots on the knife edge.

(5) When using cemented carbide milling cutters to mill steel parts, a large amount of fire mist will often fly out.

(6) Milling steel parts with high-speed steel milling cutters, such as oil lubrication and cooling, will produce a lot of smoke.

When the milling cutter is passivated, you should stop and check the wear of the milling cutter in time. If the wear is slight, you can sharpen the cutting edge with oilstone and then use it; if the wear is heavy, you must sharpen it to prevent excessive milling wear.

Post time: Jul-23-2021

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