In the "Tools" course, this part of the tool geometry angle is the focus of teaching. Because it is the basic knowledge of all types of tool design, selection, use, and sharpening. If you don't grasp the geometry of the tool, you won't be able to learn the follow-up course well. At the same time, the tool geometry is the teaching difficulty of the course. Because angle analysis is not easy to understand the concept of space; and there are many angles, each with its own function; there is a conversion relationship between angles. When teaching, students feel a lot of confusion and dazzling, which will cause fear. Some students may be discouraged and even give up studying and influence their studies.
In fact, the learning of the geometrical angle of the tool has its context and organization. As long as students master their internal laws, they will understand them in a certain way. It is possible to grasp the whole picture and essence of the geometrical angle of the tool from the inside and the inside, from the shallow to the deep, and thus from each other. To lay a solid foundation for future study and work.
First, understand the basic angle
——Understanding the angle, defining the auxiliary plane is the key
The basic angles are: the rake angle and the back angle in the orthogonal plane; the rake angle in the cutting plane; the main declination and the sub-deflection angle in the base plane. Many students feel that it is difficult to master at the time of teaching. The key is not to pay attention to and understand the concept of coordinate planes and measurement planes. It’s just a memorization of the angle of the rote, and the result is just a memory that stays on the surface.
In fact, it should be clear that the tool is placed in a certain measurement system to determine the angle. For example, the orthogonal plane measurement system includes a base surface, a cutting plane, an orthogonal plane, and the like. For the understanding of a plane, such as the base surface is defined: the selected point on the cutting edge, perpendicular to the plane of the assumed main motion direction. Two points must be grasped when understanding:
1) the base surface is a selected point on the cutting edge;
2) Vertical to the assumed main direction of motion.
The so-called main direction of motion is assumed to be the assumed height of the tool at the center of the workpiece. At this time, the main direction of motion is vertically downward. The base defined at this time is a horizontal plane passing through the selected point on the main cutting edge. Similarly, the cutting plane is a vertical plane that passes through a selected point on the main cutting edge and is perpendicular to the base surface. The orthogonal plane is a section that is perpendicular to both the base plane and the cutting plane. The three auxiliary planes are two or two perpendicular in space.
The orientation of the three auxiliary planes in space and the mutual positional relationship must be known. It is not difficult to understand the basic angle. For example, in an orthogonal plane: the angle between the rake face and the base surface is the rake angle; the angle between the flank face and the cutting plane is the relief angle. So the prerequisite for learning the basic angle is to understand the auxiliary plane.
Second, the derivation angle
- There is a clear connection between angles and functions
The derived angle is: the nose angle and the wedge angle. Because the sum of the rake angle, the back angle and the wedge angle is equal to 90°. The value of the wedge angle varies with the change of the rake angle and the back angle; and because the sum of the lead angle, the declination angle and the corner angle is equal to 180°. The value of the nose angle changes as the lead angle and the off angle change. This is the correspondence between the angle values. But both the wedge angle and the tip angle have their own meaning and function. It is by no means optional. For example, when turning a thread, the accuracy of the tool nose angle directly affects the tooth angle of the thread; also, the blade angle and the wedge angle have a great influence on the strength of the blade edge.
Third, the conversion angle
——The correspondence between the conversion angles between the measurement surfaces should be clear
The front or back angle can be defined in different measurement planes. For example, in the orthogonal plane, the normal plane, the depth of cut plane, and the feed plane, there are corresponding front and rear corners.
The angles defined in the different measurement planes have their independent meanings and functions. This is because the machining characteristics of the various tools are different and it is necessary to analyze the angles in different sections. For example, when turning the outer circle, the back angle of the turning tool is generally analyzed in an orthogonal plane; when drilling, it is necessary to analyze the back angle of the twist drill in the end section.
The angle of the same name in each measurement plane is also numerically related. Students must understand the similarities and differences. For example, the relationship between the orthogonal rake angle of the turning tool and the normal forward angle is as follows:
Γo = γn × cosλs ; When λs = 0°: γo = γn The forward angle of the method is the orthogonal rake angle.
When λs ≠0°, γo≠γn affects the machining accuracy of the workpiece during gear and thread machining.
Fourth, the working angle
——The working angle is the variable auxiliary plane changing with
The marking angle of the tool is a static angle and is uniquely determined. The dynamic angle, ie the working angle, varies with different working conditions.
For example: when turning the outer circle:
Working rake angle = γ0 + μ
Working back angle = α0-μ
The change in the μ value is now analyzed from the cutting motion alone.
Because there is a feed motion during actual turning (especially when machining large pitch threads). The base and the cutting plane should be defined by the synthetic cutting motion. Become the working base and the working cutting plane. The working base is defined as the plane perpendicular to the direction of the combined cutting speed by the cutting edge. The working cutting plane is defined as a plane that is tangent to the cutting edge by the cutting edge and perpendicular to the working base. The base and the cutting plane are inclined by an angle of μ relative to the original angle.
Thus, when turning a large pitch thread, the blade may not be able to cut into the workpiece due to the reduction of the working back angle.
V. Derivative perspective
1, the transition edge declination
A longer length transition edge is made on the main edge. That is, the transition blade and the main blade are formed as double blades. The main blade becomes a polygonal transition edge for part of the cutting task. The off-angle of the transition edge is typically half the value of the main declination. The purpose is to reduce the burden on the main blade while increasing the strength of the cutting portion of the cutter head. Therefore, the amount of cutting can be increased and the durability of the tool can be increased.
2, the wiper blade angle
Between the primary and secondary blades, the wiper can also be ground. In fact, the wiper blade is the extreme form of the secondary blade. The function of the wiper blade is similar to that of the sub-blade, but the wiper blade angle is generally 0°~3°, and the length is 2 times. Therefore, the roughness of the machined surface can be greatly reduced, and the processing quality can be improved.
3, negative chamfering front angle
Grinding a negative chamfer on the main edge. The chamfer angle is generally -15 ° ~ -20 °. The chamfer is on the main blade, but in the opposite direction of the rake angle, and belongs to the negative rake angle property. The goal is to increase the strength of the main cutting edge and increase tool durability. The selection should be considered together with the front corner.
When selecting and using the geometric angle of the tool, it is not to analyze an angle in isolation, but to consider the complementarity and constraint relationship of the relevant angle. Therefore, we need a comprehensive analysis of the tool geometry to maximize the potential of the tool. To achieve high quality, high yield, low consumption production requirements.
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Tag: Tools Tool durability Geometric angle Chamfer Xuzhou Institute of Architecture and Technology
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