How to Select Milling Cutter? (General Principles And Solutions to Common Problems in Milling)

When selecting milling cutter, it is necessary to consider many factors such as part shape, material, processing conditions and so on.

Affected by these factors, there are often some thorny problems in milling.

General principles for milling cutter selection

1. The selection process of milling cutter generally considers the following aspects for selection

(1) Part shape (considering the machining surface): the machining surface can generally be plane, deep, cavity and thread.

Different cutting tools are used for different machining surfaces.

For example, the fillet milling cutter can mill convex surfaces, but cannot mill concave surfaces.

(2) Material: consider its machinability, chip forming, hardness and alloy elements.

Tool manufacturers generally divide materials into steel, stainless steel, cast iron, non-ferrous metals, superalloys, titanium alloys and hard materials.

(3) Processing conditions: the processing conditions include the stability of the workpiece system of the machine tool fixture and the clamping of the tool handle.

(4) Stability of the machine tool fixture workpiece system: it is necessary to understand the available power of the machine tool, the type and specification of the spindle, the service life of the machine tool, etc., and in combination with the long overhang of the tool handle and its axial / radial circular runout.

(5) Machining category and subcategory:

This includes square shoulder milling, plane milling, profiling milling, etc., which need to be selected according to the characteristics of the tool.

2. Selection of geometric angle of milling cutter

(1) Selection of front corner.

The rake angle of milling cutter shall be determined according to the material of cutter and workpiece.

Milling often has impact, so it should ensure that the cutting edge has high strength.

Generally, the rake angle of milling cutter is smaller than that of turning tool;

High speed steel is larger than cemented carbide tools;

In addition, when milling plastic materials, due to the large cutting deformation, a larger rake angle should be taken;

When milling brittle materials, the rake angle should be smaller;

When processing materials with high strength and hardness, negative rake angle can also be used.

See table 4-1 for specific values of front corners.

Table 4-1 reference value of rake angle of milling cutter [unit: (°)]

Workpiece material

Rm/MPa

High speed steel milling cutter

Carbide blade

Steels

<600

20

15

600-1000

15

-5

>1000

12~10

-15~–10

Cast iron

5~5

-5~5

(2) Selection of blade inclination.

Cylindrical helix angle of end milling cutter and cylindrical milling cutter β Is the blade inclination λs.

This enables the cutter teeth to gradually cut in and out the workpiece, and improves the stability of milling.

By increasing β , the actual rake angle can be increased, the cutting edge is sharp, and the chips can be easily discharged.

For milling cutters with narrow milling width, it is of little significance to increase the helix angle β, so β=0 or smaller value is generally taken.

The specific value of helix angle β is shown in Table 4-2.

Table 4-2 reference value of external spiral angle of milling cutter [unit: (°)]

Milling cutter type

Helical tooth cylindrical milling cutter

End mill

Trihedral blade, double edged milling cutter

Sparse tooth

Dense tooth

Angle of helix

45~60

25~30

30~45

15~20

(3) Selection of main deflection angle and sub deflection angle.

The function of the main deflection angle of face milling cutter and its influence on the milling process are the same as that of turning tool in turning.

The commonly used main deflection angles are 45 °, 60 °, 75 ° and 90 °.

The rigidity of the process system is good, and the smaller value is taken;

On the contrary, take the larger value, and the selection of main deflection angle is shown in table 4-3.

The secondary deflection angle is generally 5 ° ~ 10 °.

The cylindrical milling cutter has only the main cutting edge and no auxiliary cutting edge, so there is no auxiliary deflection angle, and the main deflection angle is 90 °.

Table 4-3 selection of main deflection angle

90 ° principal deflection angle

45 ° principal deflection angle

Round blade cutter

90 ° principal deflection angle

45 ° principal deflection angle

Round blade cutter

1. thin wall parts;

2. clamping poor parts;

3. occasions requiring accurate 90 ° angle forming.

1. the first choice of ordinary process;

2. reduce the vibration of large overhang processing;

3. reduce chip thickness and improve productivity.

1. the toughest cutting edge with multiple indexation;

2. the chip is very thin, which is most suitable for heat-resistant alloy processing;

3. general tools.

3. Selection of blade groove

The selection of milling cutter blade groove shape (see table 4-4) is of great significance for chip breaking, surface performance and surface quality of machined surface.

Table 4-4 selection of blade groove shape

Light cutting groove-LCommon groove-MHeavy duty channel-H
Light cutting groove-L Common groove-M Heavy duty channel-H 
1. Sharp front corner cutting edge;
2. Stable cutting performance;
3. Low feed rate;
4. Low machine power;
5. Requirements for low cutting force.
1. common groove -m;
2. positive front corner groove for mixed processing;
3. medium feed rate.
For the highest safety requirements, large feed rate.

4. Selection of tooth number

The selection of the number of teeth of the milling cutter (see table 4-5) mainly considers the density of the tooth pitch, which has an important impact on the machining surface quality, chip removal and the impact resistance of the cutter teeth.

Table 4-5 selection of tooth number

Sparse pitchDense pitchSuper dense tooth
Sparse pitch Dense pitch Super dense tooth 
When stability and power are limited, in order to achieve maximum production efficiency, unequal tooth pitch can be used or the number of blades can be reduced.It can be used for long hanging deep tools and small machine tools, such as tool handles with a taper of 40 °.General milling and Hybrid MachiningMaximum number of blades to obtain the best productivity under stable working conditions, short chip materials, heat-resistant materials.

Solutions to common problems during milling

In the process of milling, due to the influence of workpiece material, cutting parameters and tool geometric parameters, tool wear, edge collapse and chip buildup often occur.

Table 4-6 shows the solutions to several common problems.

Table 4-6 solutions to common problems during milling

Question

Reason

Solution

Wear on the back surface

Excessive wear will result in poor or out-of-order surface quality.

Excessive wear will result in poor or out-of-order surface quality.

1. Cutting and elimination speed is too high

2. Lack of wear resistance

3. fz of feed per tooth is too low.

1. reduce the cutting speed Vc;

2. choose a more wear-resistant brand;

3. increase the feed rate fz per tooth.

Too much wear leads to short tool life.

Too much wear leads to short tool life.

1. vibration

2. cutting month before cutting

3. burrs formed on parts

4. poor surface quality

5. heat generation

6. excessive noise.

1. increase the feed rate fz of each tooth;

2. downward milling;

3. use compressed air for effective chip removal;

4. check the recommended cutting parameters.

Crescent depression wear

Excessive wear weakens the cutting edge.

Damage to the back edge of the cutting edge will result in a loss of surface quality.

Excessive wear weakens the cutting edge.

Diffusion wear is caused by high cutting temperature on the rake face.

1. Select Al2O3 coating grade;

2. Use positive front corner blade groove shape;

3. First reduce the cutting speed to reduce the temperature, and then reduce the feed.

plastic deformation 

The plastic deformation of the cutting edge, down collapse or back surface depression leads to poor chip control, poor surface quality and sharp blade breakage.

The plastic deformation of the cutting edge, down collapse or back surface depression leads to poor chip control, poor surface quality and sharp blade breakage.

Cutting temperature and pressure are too high.

1. Choose a more wearable (harder) brand;

2. Reduce the cutting speed Vc;

3. Reduce the feed per tooth fz.

cutting edge burst crack

Some cutting edges not involved in cutting are damaged by chip impact.

The upper face and support of the blade can be damaged, resulting in poor surface texture and excessive rear face wear.

The upper face and support of the blade can be damaged, resulting in poor surface texture and excessive rear face wear.

back to cutting edge

The chip retracts back to the cutting edge

Small chipping of the cutting edge results in poor surface quality and excessive wear of the back face.

Small chipping of the cutting edge results in poor surface quality and excessive wear of the back face.

1. The blade is too brittle.

2. The slot of the blade is too weak.

3. bue

.

1. Choose a brand with better toughness;

2. Choose a stronger cutting knife blade;

3. Improve the cutting speed Vc

4. Select positive front corner groove;

5. Reduce the feed at the beginning of cutting;

6. Improve stability.

Groove wear

Groove wear can cause surface quality degradation and cutting edge fracture.

Groove wear can cause surface quality degradation and cutting edge fracture.

1. Work hardening materials;

2. Skin and rust.

1. Reduce the cutting speed Vc;

2. Choose a brand with better toughness;

3. Improve the cutting speed Vc.

Thermal cracking

A small crack perpendicular to the cutting edge will cause the blade to crumble and the surface quality to be degraded.

A small crack perpendicular to the cutting edge will cause the blade to crumble and the surface quality to be degraded.

The thermal crack caused by temperature change is caused by intermittent machining and periodic supply of cutting fluid.

1. select the toughness grade that can resist thermal shock;

2. cutting fluid shall be supplied adequately or dry cutting shall be adopted.

BUE

The BUE will reduce the surface quality, and the cutting edge will collapse when the BUE is removed.

The BUE will reduce the surface quality, and the cutting edge will collapse when the BUE is removed.

1. the temperature in the cutting area is too low;

2. materials easy to bond, such as low carbon steel, stainless steel and aluminum;

1. increase the cutting speed VC;

2. replace the more suitable blade groove.

Workpiece material bonded to cutting edge

Workpiece material bonded to cutting edge

1. the cutting speed Vc is low;

2. the feed rate fz of each tooth is low;

3. negative front corner groove;

4. poor surface quality.

1. improve cutting speed;

2. increase the feed rate fz of each tooth;

3. select positive front corner groove;

4. use oil mist or cutting fluid.

vibration

vibration

Fixture rigidity difference

1. analyze the direction of cutting force and provide sufficient support or improve the fixture;

2. reduce the back cutting amount AP;

3. select cutting tools with positive rake angle, sparse teeth and unequal tooth pitch;

4. select l-groove with small fillet radius and small parallel cutter belt.

Poor axial rigidity of workpiece

1. square shoulder cutter with groove shape of positive rake angle (90 main deflection angle);

2. select the blade with L groove;

3. reduce the axial cutting force;

4. low back cutting amount, small fillet radius and parallel blade belt;

5. select the sparse tooth cutter with unequal tooth pitch.

Tool overhang

1. minimize the overhang;

2. use sparse cutters with unequal tooth pitch;

3. balance radial and axial cutting forces;

4. increase the feed rate of each tooth;

5. use light cutting blade slot l/m;

6. reduce the axial back feed tool amount AP;

7. use up milling in finishing.

Milling square shoulder with poor rigidity spindle

1. select the tool diameter as small as possible;

2. select positive rake angle and light cutting tool and blade;

3 try milling up.

The vibrations at the rounded corners

Large fillet radius is used in programming to reduce the feed rate.

Chip blockage

There are usually obstacles during full slot milling, especially when machining long chip materials.

There are usually obstacles during full slot milling, especially when machining long chip materials.

1. edge collapse and fracture;

2. chip re cutting;

1. use cutting fluid or compressed air to improve chip removal;

2. reduce the feed rate fz of each tooth;

3. divide the deep cutting into several tool runs;

4. try upward milling in deep groove processing;

5. use a tooth thinning tool.

It occurs in full groove milling and machining of cavities, especially in titanium alloy materials.

This is often the case when milling deep cavities and recesses on vertical machine tools.

This is often the case when milling deep cavities and recesses on vertical machine tools.

1. the cutting edge is broken;

2. damage to tool life and safety

3. chip blockage.

1. use compressed air or sufficient cutting fluid to remove chips;

2. change the tool position and tool path;

3. reduce the feed rate fz of each tooth;

4. divide the deep cutting into several tool runs.

Scroll to Top