When cutting metal, the tool cuts into the workpiece, the tool angle is an important parameter used to determine the geometry of the cutting part of the tool.
The composition of the cutting part of the lathe tool
The cutting part of the lathe tool consists of rake face, main flank face, secondary flank face, main cutting edge, secondary cutting edge and tool tip.
1) Rake face: The surface through which the chips on the tool flow.
2) Main flank face: the surface on the tool that opposes and interacts with the machined surface on the workpiece.
3) Secondary flank face: the surface on the tool opposite and interacting with the machined surface on the workpiece.
4) Main cutting edge: the intersection line between the rake face of the tool and the main flank.
5) Secondary cutting edge: the intersection line between the rake face of the tool and the counter flank.
6) Tool tip: the intersection of the main cutting edge and the secondary cutting edge. The tool tip is actually a small curve or straight line, which is also called the rounding tool tip and the chamfering tool tip.
Auxiliary plane for measuring the cutting angle of the lathe tool
In order to determine and measure the geometric angle of the lathe tool, three auxiliary planes need to be selected as the benchmark.
The three auxiliary planes are cutting plane, base plane and orthogonal plane.
1) Cutting plane
A plane that cuts at a selected point on the main cutting edge and is perpendicular to the base plane of the shank.
2) Base plane
A plane that passes through a selected point of the main cutting edge and is parallel to the bottom surface of the shank.
3) Orthogonal plane
A plane that is perpendicular to the cutting plane and perpendicular to the base plane.
It can be seen that these three coordinate planes are perpendicular to each other, forming a space rectangular coordinate system.
Main geometric angles and selection of lathe tools
1) Principle of rake angle (γ0 ) selection
The size of the rake angle mainly resolves the conflict between the firmness and sharpness of the bit.
Therefore, the first step is to choose a rake angle need to be base on the hardness of the hard-to-be-cut material.
If the hardness of the material to be processed is high, the rake angle takes a small value, while taking a large value on the opposite.
Secondly, according to the nature of the processing to consider the size of the front angle, the rake angle takes a small value when rough machining while a large value is taken in finishing machining.
The rake angle is generally selected between -5°and 25°.
Usually, the rake angle (γ0) is not made in advance when making lathe tools, but by grinding the chip discharge groove on the lathe tools to obtain.
The junk slot is also called chip-breaking groove, which is to break the chip without winding; control the outflow direction of chips to maintain the accuracy of the machined surface; reduce cutting resistance and extend tool life.
2) The principle of back angle (α0 ) selection
Firstly, the nature of the processing should be considered.
In finishing machining, the back angle takes a large value while taking a small in rough machining.
Secondly, the hardness of the processed material should be considered.
If the hardness of the machined material is high, the main back angle should take a small value to enhance the firmness of the cutter head; otherwise, the back angle should take a small value.
The back angle should not be zero degree or negative value, generally chosen between 6 °and 12 °.
3) Principle of cutting edge angle (Kr ) selection
Firstly, the rigidity of the turning process system composed of lathes, fixtures and tools should be considered.
If the rigidity of the system is good, the entering angle should be a small value, which will help increase the service life of the lathe tool, then improve the heat dissipation conditions and the roughness of the surface.
Secondly, the geometry of the workpiece to be processed should be considered.
When processing steps, the cutting edge angle should be 90°.
For workpieces cut in the middle, the cutting edge angle is generally 60°.
The cutting edge angle is generally between 30° and 90°, and the most commonly used are 45°, 75° and 90°.
4) The principle of the secondary deflection angle (Kr’) selection
Firstly, The lathe tool, workpiece, and clamp need to have sufficient rigidity to reduce the secondary deflection angle; otherwise, take a larger value; secondly, consider the nature of the processing.
When in finishing machining, the secondary deflection angle can be 10°- 15°while taking about 5° for rough machining.
5) The principle of inclination angle (λS) selection
It mainly depends on the nature of the machining.
During rough machining, the workpiece has a great impact on the lathe tool.
When taking λS ≤ 0°in finishing machining, the impact force of the workpiece on the lathe tool is small; when taking λS ≥ 0°, λS=0°is usually taken.
The inclination angle is generally selected between -10°and 5°.