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Introduction
In order to successfully achieve precision cutting on high-temperature alloys, it is necessary to use the correct tool geometry - an important factor in this being the cutting angles. The two angles associated with the cutting tool are the back and side angles, also referred to as the initial nose angle and the clearance angle. The initial nose angle is the angle formed by the face of the tool tip (or cutter) and the peripheral cutting edge. The clearance angle is the angle created by the side cutting edge and the flank of the tooth (or rake angle).
Both of these angles must be carefully selected for each specific cutting application and material, as they both have a major effect on the cutting performance and the life of the tool. Generally speaking, the more aggressive the cutting action required, the larger the nose and clearance angles tend to be. In contrast, when a low cutting force is needed, a smaller nose and clearance angle may be necessary.
Initial Nose Angle
The initial nose angle is the most important of the two angles, as it establishes the direction of the cutting force exerted on the material being cut. It has a direct influence on the depth of cut, the surface finish, and the tool life. For optimum cutting results, the initial nose angle must be selected based on the type of material being cut and the cutting process used.
For example, when cutting a steel material at high speed and high temperature, a wider initial nose angle may be used to reduce the cutting force and enable a greater depth of cut. On the other hand, when cutting a hardened material, a much sharper initial nose angle may be required to prevent chipping and excessive wear.
When selecting an initial nose angle for high-temperature alloys, it is recommended to start with an angle of around 8 degrees. This angle provides the necessary cutting force and chip carrying capacity, while also generating wear-resistant chips. If the initial nose angle is too wide, the cutting force required to achieve a correct cutting action will be too weak and the tool will produce a loud noise while cutting.
Clearance Angle
The clearance angle is the second of the two angles associated with the cutting tool, and its function is to direct the chips away from the cut face of the workpiece. The clearance angle also has a major influence on the overall cutting performance, as it helps to provide stability, which improves chip evacuation and reduces contact surface area. The best clearance angle is highly dependent upon the material being cut and the cutting speed.
In most cutting operations on high-temperature alloys, a clearance angle of around 10 degrees is generally suitable. This angle ensures chip evacuation and reduces the surface contact area between the cutting tool and the workpiece. Along with the initial nose angle, this provides the necessary cutting force for a successful cut.
Conclusion
The back and side cutting angles associated with machining high-temperature alloys are vitally important for successful cutting performance. The initial nose angle is the most important, as it establishes the direction of the cutting force and also provides wear-resistant chips. A suitable initial nose angle of around 8 degrees is generally recommended. The clearance angle is then used to provide stability, improve chip evacuation and reduce the contact surface area. A clearance angle of around 10 degrees is commonly used for machining high-temperature alloys. Together, the back and side angles will ensure a successful cut and long tool life.
