Introduction, features and types of solid end mills

A milling cutter is a rotary tool with one or more teeth that is used for milling operations. It is mainly used for machining planes, steps, grooves, forming surfaces and cutting workpieces on milling machines.

Introduction to milling cutters

Milling cutters are multi-toothed rotary cutters, each of which is equivalent to a turning tool fixed to the rotating face of the milling cutter. The cutting edge is longer, there is no empty stroke and the Vc is higher, so the productivity is higher. There are many types of milling cutters with different structures and wide range of applications. According to their uses, they can be divided into three main categories: milling cutters for flat machining, milling cutters for groove machining and milling cutters for forming surfaces.

Milling tool is a highly efficient method of cutting workpieces using a rotary, multi-edge tool. The tool rotates during work (for the main motion), the workpiece moves (for the feed motion), and the workpiece can be fixed, but the rotating tool must also move (both the main motion and the feed motion). Tooling machines for milling are either horizontal or vertical milling machines, or large gantry milling machines. These can be regular tool machines, or they can be numerically controlled tool machines. Machining with a rotary milling cutter as a cutting tool. Milling is generally carried out on a milling machine or boring machine and is suitable for processing planes, grooves, various forming surfaces (e.g. flower milling keys, gears and threads) and special shapes of moulds.

Characteristics of the milling cutter

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

2. The cutting thickness of each tooth in the cutting process is variable.

3. Feed per tooth αf (mm/tooth), which indicates the relative displacement of the workpiece during the time that the milling cutter is turned over one tooth.

Type of milling cutter

1. Cylindrical end mills

Used for machining planes on horizontal milling machines. The cutter teeth are distributed on the circumference of the milling cutter and are divided into straight and spiral teeth according to their shape. There are two types of teeth: coarse and fine-toothed by number of teeth. Spiral tooth coarse-tooth milling cutters are suitable for rough machining because of their low number of teeth, high tooth strength and large chip tolerance; fine tooth milling cutters are suitable for finishing machining.

2. Face milling cutter

Used in vertical milling machines, face milling machines or gantry milling machines for machining planes with cutters on the face and circumference, as well as coarse and fine teeth. Its structure is available in three types: integral, toothed and indexable.

3. Solid carbide end mills

Used for machining grooves, step surfaces, etc., where the teeth are on the circumference and end surfaces and cannot be fed along the axis when working. Axial feed is possible when there are end teeth passing through the center on the end mill.

4. Three flute carbide end mills

It is used for machining all kinds of grooves and step surfaces with teeth on both sides and circumference.

5. Carbide end mills with different helix angle

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

6. Saw blade milling cutter

It is used for machining deep grooves and cutting workpieces with more teeth on the circumference. In order to reduce friction during milling, there is a sub-deflection angle of 15′~1° on both sides of the teeth. In addition, there are key groove end mills, dovetail groove end mills, T-groove end mills and various forming end mills.

7. T-shaped milling cutter

Used to mill T-slots.
Basic requirements for the cutting part of the material of the milling cutter

(1) High hardness and abrasion resistance:

At room temperature, cutting part of the material must have enough hardness to cut into the workpiece; with high abrasion resistance, the tool does not wear out, extending 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, both at high temperature can still maintain a higher hardness, can continue to cut performance, this has the property of high temperature hardness, also known as thermal hardness or red hardness.

(3) High strength and good toughness:

In the cutting process, the tool has to withstand a lot of impact, so the tool material should have a higher strength, otherwise it is easy to break and damage. Since the cutter is subject to shock and vibration, the cutter material should also have good toughness to prevent chipping and shattering.

Common materials used for milling cutters

1. High speed tool steel (HSS, FSS, etc.)

It's divided into general purpose and special purpose HSS. It has the following characteristics.

(1) The alloying elements tungsten, chromium, molybdenum and vanadium have higher content, and the quenching hardness can reach HRC62-70, which can maintain a higher hardness at 6000C.

(2) Good cutting edge strength and toughness, strong vibration resistance, can be used in the manufacture of cutting tools with average cutting speed, for the less steel tool machine, the use of high-speed steel cutter, can still cut smoothly.

(3) Good process performance, forging, processing and sharpening are relatively easy, and it is also possible to make more complicated shapes of tools.

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

2. Carbide:

It is made of metal carbide, tungsten carbide, titanium carbide and cobalt-based metal binder through powder and unmetallurgical process. Its main features are as follows.
It can withstand high temperature and maintain good cutting performance at about 800-10000C. It can choose 4-8 times higher cutting speed than HSS when cutting. Good abrasion resistance at room temperature and hardness. Low bending strength, poor impact toughness, not easy to sharpen the blade very sharp.

Commonly used carbide can generally be three major categories:

(1) Tungsten and cobalt carbide (YG)

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

(2) Titanium and cobalt carbide (YT)

Commonly used grades are YT5, YT15, YT30, and the numbers indicate the percentage of titanium carbide. Carbide alloys containing titanium carbide and beyond increase the bonding temperature of steel, reduce the coefficient of friction, and provide a slight increase in hardness and wear resistance, but reduce the bending strength and toughness, making the properties brittle, so this type of alloy is adapted to cutting steel-like parts.

(3) General carbide

The above two types of hard alloys have been added with the right amount of rare metal carbides, such as Tantalum Carbide and Niobium Carbide, etc., to make the die thinning, improve the room temperature hardness and high temperature hardness, wear resistance, bonding temperature and oxidation resistance, which can increase the toughness of the alloy, therefore, this type of hard alloy tool has better integrated cutting performance and versatility.

Types of end mills

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

(1) High speed steel end mills: These are used for more complicated tools.

(2) Carbide end mills: Most of them are welded or mechanically clamped to the cutter body.

2. According to the use of milling cutter.

(1) Milling cutters for processing plane: Cylindrical milling cutters, end mills, etc.

(2) Milling cutters for processing grooves (or stages): vertical milling cutters, disc milling cutters, saw blade milling cutters, etc.

(3) Milling cutters for special faces: Forming cutters, etc.

3. According to the construction of the cutter

(1) Pointed Tooth Mills: The truncated shape of the back of the tooth is straight or folded, easy to manufacture and sharpen, with a sharper edge.

(2) Shovel tooth milling cutter: The truncated shape of the back of the tooth is an Archimedean spiral. After sharpening this type of milling cutter, as long as the front angle remains unchanged and the shape of the tooth remains unchanged, it is suitable for forming the cutter.

Main geometrical parameters and functions of the milling cutter.

1. Name of each part of the milling cutter

Base surface:
A plane passing through any point on the cutter and perpendicular to the cutting speed of that point.
Cutting plane:
A plane that passes through the cutting edge and is perpendicular to the base.
Front blade surface:
the plane where the chips flow out.
Rear tool face:
the face opposite to the machined surface

2. The main geometric angle and function of cylindrical milling cutter

(1) Front angle γ0:
The angle between the front blade surface and the base surface. The purpose is to make the cutting edge sharp, reduce metal deformation during cutting, and reduce chip removal, thus saving cutting effort.
(2) Back angle α0:
The angle between the back cutting surface and the cutting plane. Its main function is to reduce the friction between the rear tool face and the cutting plane and reduce the surface roughness of the workpiece.
(3) Angle of rotation 0:
The angle between the tangent line on the spiral tooth cutting edge and the axis of the milling tool. The function is to allow the teeth to gradually cut into and out of the workpiece to improve cutting stability. Also, for cylindrical end mills, it has the effect of making the chips flow smoothly from the end face.

3. The main geometric angle and function of end mills

The end mill has an additional secondary cutting edge, so in addition to the front and rear corners there are.

(1) Main deflection angle Kr:
The angle between the main cutting edge and the machined surface. The change affects the length of the main cutting edge participating in the cut, changing the width and thickness of the chip.
(2) Sub-deflection angle Krˊ:
The angle between the sub-cutting edge and the machined surface. The effect is to reduce the friction between the secondary cutting edge and the machined surface and to affect the polishing effect of the secondary cutting edge on the machined surface.
(3) The angle of inclination of the cutting edge λs:
The angle between the main cutting edge and the base surface. It mainly serves the purpose of bevel cutting.

4. Forming milling cutter

Forming end mills are special end mills for machining formed surfaces, where the cutting edge profile is designed to be calculated according to the contour of the workpiece being machined.

(1) Forming cutters can be divided into two kinds of sharp teeth and spade teeth

Milling and resharpening of sharp-edged milling cutters requires special dies, which are more difficult to manufacture and sharpen. Shovel-tooth forming milling cutter back is shoveled and sharpened on the shovel bed, and only the front cutter face is sharpened during resharpening. Two conditions should be met: ①the shape of the cutting edge remains unchanged after resharpening; and ②the desired back angle is obtained.

(2) Dorsal curves and equations

An end profile perpendicular to the axis of the end mill is made at any point on the cutting edge of the end mill, and its intersection with the tooth back surface is called the tooth back curve of the end mill.

The back curve of the tooth should satisfy two main conditions: one is that the back corner of the mill remains essentially unchanged after each resharpening; the other is simple to manufacture.

The curves that satisfy the unchanging posterior angle are only logarithmic spirals, but they are difficult to produce. The Archimedes spiral satisfies that the rear corner remains essentially unchanged and is simple to manufacture and easy to implement. This is why Archimedes spirals are widely used in production as a back curve for forming milling cutters.

By geometric knowledge, the value of the vector radius ρ at points on the Archimedean helix line increases and decreases in equal proportion to the value of the angle θ of the vector radius.

Thus, an Archimedean spiral can be obtained as long as it consists of a combination of an equivocal rotational motion and an equivocal straight line motion along the radius.

Expressed in polar coordinates: when θ=00, ρ=R, (R is the milling cutter radius), when θ>00, ρ<r,< p=""></r,<>
The general equation for the back of a milling cutter tooth is: ρ=R-CQ

Assuming that the shovel is not returned, the end mill should have an interdental angle of ε=2π/z for each turn of the shovel, and the amount of shovel teeth should be K. To enable the shovel to move at equal speed, the curve on the cam should be an Archimedean spiral, and therefore easy to make. In addition, the cam size is determined only by the K value of the shovel sales volume and is not related to the number of teeth in the diameter of the milling cutter and the back angle. As long as production and sales are equal, the cam is universal. This is the reason why the Archimedes spiral is now widely used on the back of shovel-forming milling cutter teeth.

When the milling cutter radius R and the amount of shoveling K are known, it is possible to obtain C.
When θ=2π/z ρ=R-K
then R-K=R-2πC /z ∴ C= Kz/2π

5. Phenomena that occur after passivation of milling cutters

(1) From the shape of the flakes, the flakes become coarse and flaky in shape.
(2) The roughness of the workpiece surface is very poor, the workpiece surface has bright spots and gnawing knife marks or ripples.
(3) The milling process produces very severe vibrations and abnormal noise.
(4) Looking at the shape of the blade, there are shiny white spots on the blade.
(5) When milling steel parts with carbide cutters, a large amount of fire mist often flies out.
(6) When milling steel parts with HSS mills, a lot of smoke will be generated if they are cooled with oil lubrication.

Above, is the introduction, features, type and type of milling cutter. In the actual production application, when the milling cutter passivation, we should stop in time to check the milling cutter wear, if the wear is relatively minor, can be used to repair the cutting edge with oil stone, and then use; if the wear is heavier, must be sharpened to prevent excessive wear of the milling cutter.