A milling cutter is a rotary tool with one or more teeth for milling.
During operation, each cutter tooth cuts off the allowance of the workpiece intermittently.
Milling cutter is mainly used for milling upper plane, step, groove, forming surface processing and cutting workpiece.
Several common forms of milling cutter products are shown in Fig. 4-1.
Fig. 4-1 type of milling cutter
a) Cylindrical plane milling cutter
b) Face milling cutter
c) Slot milling cutter
d) Double edged milling cutter
e) Trihedral edge milling cutter
f) Staggered three face edge milling cutter
g) End milling cutter
h) Keyway milling cutter
i) Single angle milling cutter
j) Double angle milling cutter
k) Forming milling cutter
1. Classification of milling cutter
（1） Classification by function
1. Cylindrical milling cutter
It is used for machining plane on horizontal milling machine, and the cutter teeth are distributed on the circumference of the milling cutter.
According to the tooth profile, it can be divided into straight teeth and spiral teeth.
According to the number of teeth, it can be divided into sparse teeth and dense teeth.
Spiral and sparse tooth milling cutters have less teeth, high tooth strength and large chip holding space, which are suitable for rough machining;
The dense tooth milling cutter is suitable for finish machining.
2. Face milling cutter
It is used for machining plane on vertical milling machine, horizontal milling machine or gantry milling machine.
There are cutter teeth on the end face and circumference.
Face milling cutter also has coarse teeth and fine teeth, and its structure has three types: integral type, insert type and indexable type.
3. End milling cutter
It is used to process grooves and step surfaces.
The cutter teeth are on the circumference and end face.
Generally, it cannot be fed along the axial direction during operation. When the end milling cutter has teeth passing through the center, it can be fed axially.
4. Three edge milling cutter
It is used to process various grooves and step surfaces. There are cutter teeth on both sides and circumference.
5. Angle milling cutter
It is used for milling grooves with a certain angle, including single angle milling cutter and double angle milling cutter.
6. Saw blade milling cutter
It is used for machining deep grooves and cutting workpieces. There are many cutter teeth on the circumference.
In order to reduce the friction during milling, there are 15 ′~1 ° auxiliary deflection angles on both sides of the cutter teeth.
7. Die milling cutter
Die milling cutter is used to process die cavity or punch forming surface.
Die milling cutter is evolved from end milling cutter.
According to the shape of working part, it can be divided into three types: conical flat head, cylindrical ball head and conical ball head.
Cemented carbide die milling cutters are widely used.
In addition to milling various die cavities, they can also replace hand files and grinding wheel heads to clean the flash of cast, forged and welded parts, and finish some formed surfaces.
The milling cutter can be installed on pneumatic or electric tools, and its productivity and service life are dozens of times higher than those of grinding wheel and file.
8. Gear milling cutter
According to the different shapes, the cutting tools that work according to the profiling method or the non instantaneous center envelope method are divided into disk gear milling cutter and finger gear milling cutter.
9. Thread milling cutter
The tool for milling thread is realized through three-axis or more linkage machining centers.
In addition, there are keyway milling cutter, dovetail groove milling cutter, T-shaped groove milling cutter and various forming milling cutters.
（2） Classification by product structure
1. Integral type
The cutter body and the cutter teeth are integrated.
2. Integral welded tooth type
The cutter teeth are made of hard alloy or other wear-resistant cutter materials and brazed on the cutter body.
3. Insert type
The cutter teeth are fastened on the cutter body by mechanical clamping.
The replaceable cutter tooth can be a cutter head of the whole cutter material or a cutter head of the welding cutter material.
The milling cutter with the cutter head mounted on the cutter body for grinding is called the internal grinding milling cutter;
The cutter head is grinded separately on the fixture, which is called external grinding milling cutter.
2. Geometric angle of milling cutter
Although there are many types and shapes of milling cutters, they can be summarized into two basic forms: cylindrical milling cutter and face milling cutter.
Each cutter tooth can be regarded as a simple turning tool, but the difference is that the milling cutter has more rotation and cutter teeth.
Therefore, only through the analysis of one cutter tooth, we can understand the geometric angle of the whole milling cutter.
Taking face milling cutter as an example, the geometric angle of milling cutter is analyzed.
The marked angle of face milling cutter is shown in Fig. 4-2.
One tooth of a face milling cutter is equivalent to a trolley cutter. Its geometric angle is basically similar to that of a cylindrical turning cutter.
The difference is that there is only one base surface for each tooth of the milling cutter, that is, the base surface is the plane jointly determined by the tool tip and the axis of the milling cutter.
Therefore, each tooth of face milling cutter has four basic angles: rake angle, rake angle, main deflection angle and blade inclination angle.
(1) Front angle γο : the angle between the front and the base, measured in an orthogonal plane.
(2) Back angle αo: the angle between the back and the cutting plane, measured in the orthogonal plane.
(3) Main deflection angle κr: the included angle between the main cutting plane and the assumed working plane, measured in the base plane.
(4) Edge inclination λs: the angle between the main cutting edge and the base surface.
The relevant angles of the face milling cutter in the main profile system are shown in Fig. 4-2. During design, manufacturing and grinding, the relevant angles in the profile system of feed and back feed, as well as the radial front angle and axial front angle, are also required.
Fig. 4-2 geometric angle of face milling cutter
3. Milling method
（1） Milling mode of end milling
When machining a plane with a face milling cutter, it can be divided into three milling methods according to the different relative positions between the milling cutter and the machined surface of the workpiece (or the cutting relationship): symmetric milling, asymmetric reverse milling and asymmetric forward milling, as shown in Fig. 4-3.
Fig. 4-3 three milling methods of end milling
a) Symmetrical milling
b) Asymmetric reverse milling
c) Asymmetric forward milling
1. Symmetrical milling
The axis of the milling cutter is located at the symmetric center of the milling arc length, that is, when the cutting thickness is the same during cutting in and cutting out, it is symmetric milling.
This milling method has a large average cutting thickness.
When milling hardened steel with a small feed per tooth, symmetrical milling should be used to make the cutter teeth cut into the workpiece beyond the cold layer.
2. Asymmetric reverse milling
The cutting thickness at cut in is less than that at cut out, which is asymmetric reverse milling.
When milling carbon steel and general alloy steel, using this milling method can reduce the impact during cutting and increase the service life of carbide face milling cutter by more than twice.
3. Asymmetric forward milling
The cutting thickness at cut in is greater than that at cut out, which is asymmetric forward milling.
It has been proved that asymmetric forward milling can reduce the spalling wear of cemented carbide and increase the cutting speed by 40% ~ 60% when it is used to process stainless steel and heat-resistant alloy.
（2） Milling mode of circular milling
According to the different changing rules of cutting layer parameters during milling, circular milling has two forms: up milling and down milling.
During up milling (see Fig. 4-4), the cutting speed direction when the milling cutter cuts into the workpiece is opposite to the feed direction of the workpiece.
This milling method is called up milling.
During reverse milling, the cutting thickness of the cutter teeth increases gradually from zero.
At the beginning of cutting, due to the influence of the blunt radius of the cutting edge, the cutter teeth slip, squeeze and friction on the working surface, resulting in serious cold and hard layer on this surface.
When sliding to a certain extent (i.e. cutting thickness ≥ cutting edge blunt radius), the cutter teeth can cut into the workpiece.
When the next cutter tooth cuts in, it squeezes and slides on the cold hard layer, so that the cutter tooth is easy to wear and the workpiece surface roughness value increases.
In addition, when the contact angle is greater than a certain value during reverse milling, the vertical milling component is upward, which is easy to loosen the clamping of the workpiece and cause vibration.
Fig. 4-4 reverse milling of circular milling
As shown in Fig. 4-5, the cutting speed direction when the milling cutter cuts into the workpiece is the same as the feed direction of the workpiece.
This milling method is called forward milling.
During the forward milling, the cutting thickness of the cutter teeth is the maximum when cutting in, and then gradually decreases, avoiding the squeezing, sliding and scraping phenomena when cutting in the reverse milling, and the cutting distance of the cutter teeth is short.
The wear of milling cutter is small, its service life can be 2 ~ 3 times higher than that of reverse milling, and the machined surface quality is also good.
Especially for hard to machine materials with strong milling hardening trend, the effect is more obvious.
The vertical component of the front acting on the cutting layer is always downward, so the vertical component of the whole milling cutter acting on the workpiece is large, and the workpiece is always pressed on the fixture to avoid the vibration of the workpiece, which is safe and reliable.
Fig. 4-5 forward milling of circular milling