Introduction, characteristics, and types of milling cutters

what is a milling cutter?

 

what is a milling cutter, milling cutter

 

A milling cutter is a rotating tool with one or more teeth for milling operations. When working, each cutter tooth intermittently cuts off the allowance of the workpiece in turn. It is mainly used for machining planes, steps, grooves, forming surfaces and cutting off workpieces on milling machines.

A milling cutter is a high-efficiency processing method that uses a rotating multi-blade tool to cut a workpiece. When working, the tool rotates (for the main movement), the workpiece moves (for the feed movement), and the workpiece can also be fixed, but at this time the rotating tool must still move (to complete the main movement and the feed movement at the same time).

Machine tools for milling include horizontal milling machines or vertical milling machines, as well as large gantry milling machines. These machine tools can be ordinary machine tools or CNC machine tools. Cutting with a rotating milling cutter as a tool. Milling is generally carried out on a milling machine or a boring machine, which is suitable for processing planes, grooves, various forming surfaces (such as flower milling keys, gears and threads) and special surfaces of moulds.

 

Features of Milling Cutters

 

1. Each tooth of the milling cutter participates in intermittent cutting periodically.

2. The cutting thickness of each tooth changes during the cutting process.

3. Feed amount αf per tooth (mm/tooth), which means the relative displacement of the workpiece within the time when the milling cutter rotates one tooth.

How are milling cutters classified?

 

1. According to the material of the cutting part of the milling cutter:

 

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

(2) Carbide milling cutters: Most of them are fixed on the cutter body by welding or mechanical clamping.

 

2. According to the use of a milling cutter:

 

(1) Milling cutters for machining planes: cylindrical milling cutters, end milling cutters, etc.

(2) Milling cutters for processing grooves (or steps): end mills, disc milling cutters, saw blade milling cutters, etc.

(3) Milling cutters for special-shaped surfaces: forming milling cutters, etc.

 

3. According to the structure of the milling cutter

 

(1) Spike-tooth milling cutter: The truncation shape of the back of the tooth is a straight line or a broken line, which is easy to manufacture and sharpen, and the cutting edge is sharper.

(2) Shovel tooth milling cutter: The truncated shape of the back of the tooth is an Archimedes spiral. After sharpening, this kind of milling cutter is suitable for forming milling cutters as long as the rake angle remains unchanged and the tooth shape remains unchanged.

 

Types of milling cutters

 

Types of milling cutters

 

1. Cylindrical milling cutter

 

For machining flat surfaces on horizontal milling machines. The cutter teeth are distributed on the circumference of the milling cutter and are divided into two types: straight teeth and helical teeth according to the tooth shape. According to the number of teeth, there are two kinds of coarse teeth and fine teeth. The helical-toothed coarse-toothed milling cutter has fewer teeth, high tooth strength and large chip space, and is suitable for rough machining; the fine-toothed milling cutter is suitable for finishing.

 

2. Face milling cutter

 

It is used for machining planes on vertical milling machines, end milling machines or gantry milling machines. There are cutter teeth on the end face and the circumference, and there are coarse teeth and fine teeth. Its structure has three types: integral type, insert type and indexable type.

 

3. Endmills

 

It is used to process grooves and stepped surfaces, etc. The cutter teeth are on the circumference and end faces, and cannot be fed in the axial direction during work. Axial infeed is possible when the end mill has end teeth that pass through the centre.

 

4. Side and side milling cutter

 

It is used to process various grooves and stepped surfaces, and there are cutter teeth on both sides and circumferences.

 

5. Angle milling cutter

 

Used for milling grooves with a certain angle, there are two kinds of single-angle and double-angle milling cutters.

 

6. Saw blade milling cutter

 

It is used to process deep grooves and cut-off workpieces, and there are more cutter teeth on its circumference. In order to reduce friction during milling, there are 15′~1° secondary deflection angles on both sides of the cutter teeth. In addition, there are keyway milling cutters, dovetail milling cutters, T-slot milling cutters and various form milling cutters.

 

7. T-shaped milling cutter

 

For milling T-slots.

What are milling cutters made of?

 

1. The basic requirements for a milling cutter cutting some materials:

 

(1) High hardness and wear resistance: At room temperature, the cutting part must have sufficient hardness to cut into the workpiece; with high wear resistance, the tool will not wear and prolong 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, and the temperature will be very high. Therefore, the tool material should have good heat resistance, both at high temperatures It can still maintain a high hardness under high temperatures, and has the ability to continue cutting. This kind of high-temperature hardness is also called thermal hardness or red hardness.

(3) High strength and good toughness: During the cutting process, the tool has to bear a large impact force, so the material of the tool must have high strength, otherwise it is easy to break and damage. Since the milling cutter will be subject to shock and vibration, the material of the milling cutter should also have good toughness so that it is not easy to chip and chip.

 

2. Common materials for milling cutters:

 

1) high-speed tool steel (referred to as high-speed steel, front steel, etc.)

 

There are two types of general-purpose and special-purpose high-speed steel. It has the following characteristics:

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

(2) The edge strength and toughness are good, and the vibration resistance is strong. It can be used to manufacture tools with average cutting speed. For machine tools with poor rigidity, high-speed steel milling cutters can still cut smoothly.

(3) The process performance is good, forging, processing and sharpening are relatively easy, and knives with complex shapes can also be manufactured.

(4) Compared with cemented carbide materials, there are still disadvantages such as lower hardness, red hardness and poor wear resistance.

 

2) cemented carbide

 

Cemented carbide is made of metal carbide, tungsten carbide, titanium carbide and cobalt-based metal binder through a powder metallurgy process. Its main features are as follows:

It can withstand high temperatures, and can still maintain good cutting performance at around 800-10000C. When cutting, you can choose a cutting speed that is 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.

The main geometric parameters and functions of the milling cutter:

 

1. The name of each part of the milling cutter

 

Base plane: A plane that passes through any point on the cutting tool and is perpendicular to the cutting speed at that point.

Cutting plane: The plane passes through the cutting edge and is perpendicular to the base surface.

Rake face: The plane from which chips flow out.

Flank: The face opposite the machined surface

 

2. The main geometric angles and functions of cylindrical milling cutters

 

(1) Rake angle γ0: The angle between the rake face and the base face. The function is to sharpen the blade, reduce metal deformation during cutting, and easily discharge chips, thus saving cutting effort.

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

(3) Rotation angle 0: The angle between the tangent line on the helical tooth blade and the milling cutter axis. The function is to make the cutter teeth cut into and out of the workpiece step by step, so as to 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. Main geometric angles and functions of end mills

 

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

(1) Main declination Kr: the angle between the main cutting edge and the machined surface. Its change affects the length of the main cutting edge participating in the cutting, changing the width and thickness of the chip.

(2) Secondary deflection angle Krˊ: The 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 smoothing effect of the secondary cutting edge on the machined surface.

(3) Blade inclination λs: the angle between the main cutting edge and the base surface. It mainly plays the role of bevel cutting.

 

4. Forming milling cutter

 

Forming milling cutter is a special milling cutter used to process the formed 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, which can ensure that the shape is basically consistent and has high efficiency. , are widely used in mass production and mass production.

 

(1) Form milling cutters can be divided into sharp teeth and shovel teeth

 

The milling and regrinding of the tine form milling cutter require a special profile, which is difficult to manufacture and sharpen. The tooth back of the shovel tooth forming milling cutter is shovelled and shovelled on a shovel tooth lathe. When regrinding, only the rake face is ground. Because the rake face is flat, it is more convenient to sharpen. At present, the form milling cutter mainly uses a shovel Tooth structure. The back of the shovel tooth should meet two conditions: ①The shape of the cutting edge remains unchanged after regrinding; ②Obtain the required relief angle.

 

(2) Tooth back curve and equation

 

The end section perpendicular to the axis of the milling cutter is made through any point on the cutting edge of the milling cutter, and the intersection line with 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 clearance angle of the milling cutter is basically unchanged after each regrinding; the other is that the manufacturing is simple.

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

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

Therefore, the Archimedes spiral can be obtained as long as the constant rotational motion and the constant linear motion along the radial direction are combined.

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 of the tooth back of the milling cutter is:  ρ=R-CQ

Assuming that the shovel does not return, the amount of shovel teeth of the shovel is K every time the milling cutter rotates through an inter-tooth angle ε=2π/z, and accordingly, the amount of cam lift 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 cam size is only determined by the shovel volume K value and has nothing to do with the diameter of the milling cutter and the number of teeth and the relief angle. As long as the production and sales are equal, the cams can be used universally. This is also the reason why the Archimedes helix is widely used in tooth backs of shovel tooth forming milling cutters.

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

When θ=2π/z, ρ=R-K

Then R-K=R-2πC /z ∴ C= Kz/2π

 

5. The phenomenon that will appear after the passivation of the milling cutter

 

(1) From the shape of the chip, the chip becomes thick and flakes. Due to the increase in the temperature of the chip, the colour of the chip turns purple and smokes.

(2) The roughness of the machined 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 serious vibration and abnormal noise.
(4) Judging from the shape of the knife edge, there are bright white spots on the knife edge.
(5) When milling steel parts with cemented carbide milling cutters, a large amount of fire mist often flies out.
(6) When milling steel parts with high-speed steel milling cutters, if they are lubricated and cooled with oil, a lot of smoke will be produced.

The above is the introduction, characteristics, and types of milling cutters. In actual production and use, when the milling cutter is passivated, we should stop the machine in time to check the wear of the milling cutter. If the wear is slight, use the oil stone to grind the cutting edge and then use it again; if the wear is serious, it must be sharpened, to prevent excessive wear of the milling cutter.

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