Plane Milling: Characteristics, Contact Methods And Classification

Plane milling is mainly to process the surface of the workpiece, so that the precision and quality of the workpiece can meet the processing requirements.

Plane milling needs to consider the size of the processing plane, the specific position and the flatness of the processing surface.

In addition, the datum positioning, parallelism and perpendicularity of the workpiece processing surface shall be taken into account.

The processing content of plane milling is the basis of plane milling technology.

(1) Characteristics of plane milling process

In the process of plane milling, there are mainly two ways: end milling with end milling cutter and end milling with face milling cutter.

In plane operation, the efficiency and quality of face milling are high, so in general, face milling will be used in plane milling.

The characteristics of end milling are as follows:

(1) In face milling, the axis must be perpendicular to the surface of the workpiece.

The spindle axis of milling machine will directly affect the flatness of workpiece.

(2) The face milling cutter handle has good clamping performance during face milling, and the vibration amplitude is small and relatively stable.

(3) During face milling, the main cutting edge and the auxiliary cutting edge of the cutter teeth work at the same time, so that the surface quality of the machined workpiece is better.

Among them, the main cutting edge is responsible for cutting, and the auxiliary cutting edge plays the role of polishing.

(4) End milling can use alloy blades with good quality and accuracy to improve efficiency and quality.

(2) Plane milling contact mode

The cut in angle and cut out angle are shown in Fig. 4-7.

The angle (E) at which the tip of the face milling cutter cuts into the workpiece is called the cut in angle (bite in angle), and the angle (DE) at which the tip leaves from the workpiece is called the cut out angle (disengagement angle).

Cut in angle and cut out angle are the main factors that determine the impact on the tool at the beginning and end of cutting, and also related to the tool life.

cut in angle and cut out angle

Fig. 4-7 cut in angle and cut out angle

For some workpieces, the diameter and correction amount of the face milling cutter (the position relationship between the workpiece and the milling cutter) are determined, and the cut in angle and the cut out angle are also determined.

As shown in Fig. 4-8, the relationship between the face milling cutter cut in angle EA on the left and the face milling cutter cut in angle EB on the right is EA ≥ EB.

cut in angle comparison

Fig. 4-8 cut in angle comparison

The point of contact at which the cutting edge cuts in.

The tool life will vary with the position where the cutting edge cuts into the workpiece.

As shown in Fig. 4-9, the state before the cutting edge cuts into the workpiece.

The cut section is represented by STUV parallelogram.

cutting edge contact points

Fig. 4-9 cutting edge contact points

The contact between the cutting edge and the workpiece occurs within the stuv range, starting from any side of S, T, U, V or the whole plane at the same time.

The ways of contact are classified as follows:

(1) Point contact S, T, U, V.

(2) Line contact ST, TU, UV, VS.

(3) Face contact STUV.

The contact mode is determined by each angle and cutting angle of the face milling cutter.

The relationship between the 9 contact modes and each angle is shown in Fig. 4-10.

S-point contact starts from the weakest part of the tool tip, so it is easy to be damaged.

This method must be avoided, preferably U-point contact or V-point contact.

To achieve such a contact mode, it is necessary to determine the angles and relative installation positions of the face milling cutter.

In the figure, R is the radial edge inclination;

A is the axial blade angle;

E is the cut in angle;

CH is the residual angle of the cutting edge.

9 contact modes

a) Point contact

b) Line contact

c) Surface contact

Fig. 4-10 9 contact modes

(3) Face milling cutter and its classification for plane milling

Face milling cutters are divided into two categories.

The first category is to fix the cemented carbide blade on the cutter teeth by brazing, and then install the cutter teeth on the milling cutter body, which is called insert face milling cutter;

The second kind is to install the carbide blade directly on the milling cutter body, and then fix it with screws, which is called indexable machine clamp milling cutter.

The face milling cutter has two rake angles: axial rake angle and radial rake angle.

The direction of the two rake angles, i.e. positive, negative or zero, is selected according to the material of the machined object and the cutting conditions.

Plane milling methods are generally divided into the following types:

1. Ordinary face milling

Face milling (see Fig. 4-11) is the most common milling process, which can be carried out with many different tools.

The tools with 45 ° main deflection angle are most commonly used, but circular blade milling cutter, square shoulder milling cutter and three face edge milling cutter are also used under some working conditions, as shown in table 4-7.

cutting state of common face milling

Fig. 4-11 cutting state of common face milling

Table 4-7 selection of common face milling tools

Blade classificationBlade illustrationscope of application
45 ° tool 1. preferred for general use2. reduce vibration of long overhang3. chip thinning to improve productivity
90 ° tool90 ° tool 1. thin wall parts;2. clamp parts with poor rigidity;3. occasions requiring 90 ° angle forming.
Round blade cutterRound blade cutter 1. general tools;2. high cutting edge strength;3. each blade has multiple cutting edges;4 applicable to heat-resistant alloy processing;5. gentle cutting effect.

Note:

1. For face milling of thin-walled and deformed parts, the direction of main cutting force shall be considered for the stability of workpiece and fixture.

When milling parts with poor axial rigidity, 90 ° square shoulder milling cutter shall be used because it leads the main part of cutting force to the axial direction.

Light cutting face milling cutter can also be used to avoid the use of axial back cut of 0.5~2mm to minimize the axial force.

The use of sparse tooth cutter can minimize the number of cutting edges cut in.

The use of sharp positive rake cutting edge can reduce the cutting force, which is suitable for face milling of thin-walled and deformed parts.

2. For thin-wall edge milling with face milling cutter, place the cutter at the eccentric position to carry out face milling on the thin-wall edge.

In this way, the cutting becomes smoother and the cutting force is transmitted evenly along the thin wall, thus reducing the risk of vibration.

Select the tool pitch used in these processes to keep one blade eating.

Use the blade groove as light as possible (light instead of medium load, or medium load instead of heavy load).

Select a smaller blade radius and a shorter parallel blade belt to reduce the risk of vibration in thin-walled parts.

Use low cutting parameters, small back feed ap and low feed per tooth fz.

These applications include rough milling of heavy forged or hot rolled materials, castings and welded structures on large gantry milling machines, high-power milling machines or machining centers.

2. Large feed milling

For large feed milling (see Fig. 4-12), when using a tool with a small main deflection angle or a round blade tool, due to the thin chip effect, the face milling can be carried out with a very high feed per tooth (up to 4mm/z).

Although the back feed is limited to within 2mm, the great feed makes it a high productivity milling method. The required tool selection is shown in table 4-8.

large feed cutting status

Fig. 4-12 large feed cutting status

Table 4-8 selection of large feed milling tools

Blade type  Matters needing attention
Round blade cutterWhen large feed milling technology is applied with round blade tools, the back feed should be kept low (up to 10% of the blade diameter), otherwise the thin chip effect will be reduced.
Tool with small main deflection angleThe maximum chip thickness can be significantly reduced by using a small principal deflection angle.This allows a very high feed rate to be used without overloading the blade.

3. Heavy load face milling

Generally speaking, heavy-duty face milling (see Fig. 4-13) needs to remove a large amount of materials and generate high temperature and high cutting force at the same time.

The main cutting edge of the face milling cutter bears heavy load at the full back draft.

When the back draft is close to zero, the abrasive scale will wear the fillet.

heavy load cutting status

Fig. 4-13 heavy load cutting status

When a magnetic worktable is used to clamp the workpiece, a large amount of chips will usually stay around the tool, which will lead to interruption or partial chip removal, and chip re cutting, which will endanger the tool life.

To avoid this, keep the machining range free of chips.

By increasing the back draft, the vulnerable tip is prevented from rubbing with the abrasive skin and oxide skin, and the surface contact point is moved to the stronger main cutting edge on the blade.

4. Unequal pitch milling cutter

Unequal teeth means that the cutting edges of face milling cutters are intentionally set according to different sizes (see Fig. 4-14).

For example, the bisection of a 6-edge milling cutter should have a spacing of 60 °, while the bisection method is to set the segmentation angle to 65 °, 56 °, 59 °, 65 °, 56 °, 59 °.

The reason why unequal tooth milling cutters are widely used is that during high-speed cutting, due to the high-speed rotation of the main shaft, if there is an imbalance in the tool, the centrifugal force generated by it will impose periodic loads on the main shaft bearings and machine tool components, resulting in vibration, which will have an adverse impact on the main shaft bearings, tool life and machining quality.

The unequal pitch end milling cutter is a new type of high-performance cutting tool, which can effectively suppress chatter and improve the quality of the machined surface.

Fig. 4-14 unequal pitch milling cutter

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