Characteristics of edge processing of PCBN tool and its influence on cutting

The correct selection and application of the tool edge treatment is considered one of the essential elements for the successful manufacture and proper use of hard turning tools. For different application conditions, cutting edge processing has different processing forms and parameters. Tool edge treatment refers to a process before the blade is finely ground and before coating (if any), by chamfering, passivating, leveling, polishing and other treatments on the cutting edge, so as to improve the quality of the tool and prolong the service life of the tool.

1. Forms and characteristics of edge treatment

Usually edge treatment can be divided into 4 categories: F type - not chamfered but not rounded, E type - blunt round without chamfering, T type - chamfered and not rounded, S type - chamfered and blunt rounded. The four types of edge treatments have their own physical and geometric characteristics, and have different effects on the force state, tool-chip friction, and chip shape during use.

1.1 F-type edge treatment. F-type edge treatment, that is, neither chamfering nor blunt rounding. This cutting edge treatment method is sharp, with small cutting force, small shear deformation, and low cutting heat, but the cutting edge strength is low, and the cutting edge has initial defects, so it is rarely used.

1.2 E-type edge treatment. E-type edge treatment, that is, not chamfered but blunt. The edge type adopts the blunt round process, which eliminates the machining micro-defects on the cutting edge, strengthens the cutting edge, and increases the resistance to chipping and cracking.

1.3 T-edge treatment. T-shaped edge treatment, that is, chamfered but not blunt. Through chamfering treatment, it has better impact resistance, and can replace the S-shaped edge in the case of reducing cutting force and high tolerance requirements.

1.4 S-shaped edge treatment. S-shaped edge treatment, that is, chamfer + blunt round. This form is the most common edge treatment and the preferred edge type in hard turning. It has higher strength than T-type, is more resistant to chipping and cracking, easier to predict tool life, and can produce more stable workpiece surface quality. Especially suitable for large depth of cut and intermittent machining.

2. Influence of S type edge treatment in cutting process

In S type In the cutting edge treatment, the angle of the chamfer has two sides. On the one hand, the increase of the angle can improve the strength of the tool and increase the impact resistance of the tool; but on the other hand, the tool becomes dull, which increases the cutting heat and resists wear on the rake face. unfavorable. This is because the increase of the angle is equivalent to a larger negative rake angle, so the shear angle becomes smaller, the deformation increases, and the deformation heat is high, so the wear on the rake face is accelerated. At the same time, the chamfering width should also be adapted to the setting of the processing parameters. If the width of the chamfer is too small, the chamfering effect will be weakened, and the friction between the chip and the rake face will wear quickly at the junction of the chamfer and the original rake face. If the edge width is too large, the cutting force will increase, and the friction distance between the chip and the rake face will be prolonged, which is not conducive to tool life. At the same time, the size, uniformity and machining method of the blunt circle will also have a certain influence on the performance of the tool.

PCBN tools are generally processed with negative rake angle and negative chamfering during hard turning, which can strengthen the cutting edge and improve the The wear resistance of the tool, when machining hardened steel or gray cast iron, provides the different machining edge strengths required for each. After being sharpened by a diamond grinding wheel, there are often microscopic gaps (ie, micro chipping and sawing) on ​​the cutting edge. During the cutting process, the microscopic notch of the tool edge is easy to expand, which accelerates the tool wear and damage. Through the design of negative rake angle and the fine grinding of negative chamfer, the strength of the tool is improved. At the same time, the blunt round treatment is adopted to eliminate the machining micro-defects on the cutting edge. The two treatment methods improve the impact strength of the tool and increase the wear resistance of the tool. properties, thereby extending tool life.