The cutting tool for machining plane workpiece is mainly face milling cutter, and its cutting edge is full of circumference and end face.
The cutting edge of the end face is a secondary cutting edge.
The diameter of face milling cutter is large, so the cutter teeth and cutter body are usually separated when selecting the cutter, so as to achieve the purpose of long-term use.
1. Selection of face milling cutter diameter
The selection of face milling cutter diameter is mainly divided into three cases:
(1) The machining plane area is small. When selecting tools, pay attention to selecting tools or milling cutters with diameter larger than the plane width, so as to realize single plane milling.
When the width of the plane milling cutter reaches 1.3 ~ 1.6 times of the width of the machining surface, it can effectively ensure the good formation and discharge of chips.
(2) When the machining plane area is large, it is necessary to select a milling cutter with appropriate diameter to mill the plane several times.
Among them, the diameter of milling cutter will be limited due to the limitations of machine tool, cutting depth and width, and the size of blade and tool.
(3) When the machining plane is small and the workpieces are scattered, the end milling cutter with smaller diameter shall be selected for milling.
In order to maximize the processing efficiency, the milling cutter should have 2 / 3 of the diameter in contact with the workpiece, that is, the milling cutter diameter is equal to 1.5 times of the milled width.
During forward milling, the rational use of the ratio of tool diameter to cutting width will ensure that the milling cutter has a very suitable angle when cutting into the workpiece.
If it is uncertain whether the machine tool has enough power to maintain the cutting of the milling cutter at such a ratio, the axial cutting thickness can be completed twice or more, so as to maintain the ratio of the milling cutter diameter to the cutting width as much as possible.
2. Selection of tooth number of milling cutter
When selecting a milling cutter for machining, the number of teeth of the milling cutter needs to be considered.
For example, a sparse tooth milling cutter with a diameter of 100mm has only 6 teeth, while a dense tooth milling cutter with a diameter of 100mm can have 8 teeth.
The density of cutter teeth will affect the production efficiency and product quality.
If the cutter teeth are dense, the production efficiency will be improved and the quality of the processed workpiece will be better, but the dense cutter teeth will also lead to the inconvenience of chip discharge.
According to the diameter of cutter teeth, they can be divided into sparse teeth, fine teeth and dense teeth.
Sparse teeth are used for rough machining of workpieces.
1 ~ 1.5 blades are used for every 25.4mm diameter, with large chip holding space.
This tool is used for cutting soft materials that can produce continuous chips.
Long blades and large width are selected for cutting.
Dense teeth are conducive to machining under stable conditions. They are generally used for rough machining of cast iron.
They are also suitable for shallow cutting, narrow cutting of superalloys and cutting without chip space.
Dense teeth are used in finish milling.
The axial back cutting amount is 0.25 ~ 0.64mm.
The cutting load of each tooth is small and the required power is small.
For example, it is used for the processing of thin-walled materials.
The tooth pitch will determine the number of cutter teeth involved in cutting at the same time during milling.
At least one blade shall be cutting during cutting to avoid milling impact, resulting in tool damage and machine tool overload.
In addition, the selection of the number of blade teeth must make the chips curl properly and leave the cutting area easily.
Improper chip holding space will lead to chip holding, damage the cutting edge and possibly damage the workpiece.
At the same time, the blade shall have sufficient density to ensure that at least one blade is cutting at any time during cutting.
If this cannot be guaranteed, it will cause severe impact, which will lead to the fracture of cutting edge, tool damage and overload of machine tool.
3. Selection of tool angle
The cutting angle of the tool can be positioned as positive rake angle, negative rake angle and zero rake angle relative to the radial plane and axial plane.
Because zero rake angle will cause the whole cutting edge to impact with the workpiece at the same time, it is generally not used.
The selection of face milling cutter angle has an impact on the plane milling contact mode.
In order to minimize the impact on the cutter, reduce the damage degree of the cutter and avoid the face contact mode of stuv, the geometric angle of the face milling cutter should also be taken into account while considering the cutting angle of the cutter.
The combination of radial and axial rake angle determines the cutting angle.
The common basic combination methods include:
Radial negative rake angle and axial negative rake angle;
Radial positive rake angle and axial positive rake angle;
Radial negative rake angle and axial positive rake angle;
Radial positive rake angle and axial negative rake angle.
The tools with negative axial and radial forward angles (hereinafter referred to as “double negative”) are mostly used for rough machining of cast iron and cast steel, but the machine tool requires high power and enough rigidity.
The “double negative” blade has high cutting edge strength and can withstand large cutting load. The tool with negative double angles also needs high rigidity of machine tool, workpiece and fixture.
The cutting tools with positive axial and radial forward angles (hereinafter referred to as “double positive”) increase the cutting angle, so the cutting is light and the chip removal is smooth, but the strength of the cutting edge is poor.
This combination is suitable for processing soft materials and stainless steel, heat-resistant steel, ordinary steel and cast iron.
This combination should be preferred when low-power machine tools, insufficient rigidity of process system and chip accumulation tumor occur.
The combination of radial negative rake angle and axial positive rake angle, the negative radial rake angle improves the strength of the cutting edge, and the positive axial rake angle produces a shear force.
This combined method has strong impact resistance and sharp cutting edge, so it is suitable for large surplus milling of steel, cast steel and cast iron.
The radial positive rake angle and axial negative rake angle make the broken chips move below the center, so the chips will scratch the machined surface, so the chip removal is poor.
4. Selection of milling insert
The selection of milling insert preparation is also a consideration in plane milling.
In some processing occasions, it is more appropriate to select the pressed blade, and sometimes it is also necessary to select the ground blade.
It is better to select the pressed blade for rough machining, which can reduce the processing cost.
The dimensional accuracy and edge sharpness of the pressing blade are worse than those of the grinding blade, but the edge strength of the pressing blade is better.
For rough milling, it is resistant to impact and can withstand large back feed and feed.
There is a chip curling groove on the rake face of the pressed blade, which can reduce the cutting force, reduce the friction with the workpiece and chips, and reduce the power demand.
However, the pressed blade surface is not as close as the ground blade, and the dimensional accuracy is poor.
There is a large difference in the height of each tool tip on the milling cutter body.
Because the pressing blade is cheap, it is widely used in production.
For finish milling, it is best to select grinding blade, which has good dimensional accuracy, so the positioning accuracy of cutting edge in milling is high, and higher machining accuracy and lower surface roughness value can be obtained.
In addition, the development trend of grinding milling insert used in finish machining is to grind out chip curl groove to form a large positive rake cutting edge, allowing the blade to cut with small feed and small back draft.
When the carbide blade without sharp rake angle is processed with small feed and small back draft, the tool tip will rub the workpiece and reduce the tool life.