The cutting part is that part of a cutting tool that is effective during machining and on which the cutting wedges are located. The most important terms for its surfaces, cutting edges, reference systems and angles are standardized in DIN 6581.
The face of the cutting wedge over which the chip runs during machining is called the rake face . The other adjacent areas are referred to as open areas. The edge of the wedge, which lies on the rake face and points in the feed direction, is the main cutting edge ; the other is called the minor cutting edge.
These surfaces form different angles with one another and with the cutting and feed directions. In order to be able to describe them clearly, two important reference systems, which consist of several levels, have been defined and standardized. In the tool reference system, all planes are based on the vector of the cutting speed , whereas in the active reference system they are based on the active speed . It is the resultant of the cutting speed and the feed rate . The effective speed is actually important for the description of the machining processes, but its exact orientation in space and its amount are difficult to determine. However, since it differs only insignificantly in amount and direction from the easily determined cutting speed, the tool reference system based on it is usually selected.
Both systems consider any point on the main cutting edge. The basic plane of the tool reference system is the tool reference plane . Like all other planes, it contains the selected point and is perpendicular to the vector of the cutting speed. The tool setting angle ( Kappa ) and the corner angle lie in this plane . The following planes are perpendicular to the tool reference plane:
- The working plane : It contains the vectors of the feed rate and cutting speed. In this level, the are advancing direction angle and the effective direction angle indicating the angle between the vectors of the feed, cutting and molding speed.
- The tool cutting edge plane: It contains the main cutting edge. The angle of inclination lies in it
- The tool orthogonal plane: It is perpendicular to the tool cutting edge plane. It contains the clearance angle , the wedge angle and the rake angle that is important for chip formation .
Surfaces, edges and corners
The geometry of the cutting edges is standardized in Germany in DIN 6581 and DIN 6582 and internationally in ISO 3002/2
The rake face (index after the rake angle ) is the face over which the chip slides. Their position and orientation in space as well as their surface properties therefore essentially determine the chip formation and the power requirement. If it is chamfered , the part of the rake face that lies on the cutting edge is called the rake face. Its width has the formula symbol .
The free area is the area that faces the newly created workpiece area. It therefore depends on the kinematics (movement relative to the workpiece) with which a tool is used to decide which area is the free area. It is always inclined away from the workpiece to avoid friction. A distinction is made between two open spaces:
- The main open area is in the feed direction. In the idealized cutting wedge it forms a line of cut with the rake face: the main cutting edge . Real cutting edges, on the other hand, are often rounded (so-called cutting edge rounding), with a radius or chamfered.
- The secondary flank is not in the feed direction and forms the secondary cutting edge with the rake face .
If the open spaces are chamfered, their width is denoted by and .
The rake face, main and secondary flank form a wedge, the so-called cutting wedge. Its tip is called the cutting corner.
To define the different angles, two different reference systems were defined and standardized, which consist of clearly defined planes. The tool reference system is important for tool manufacture and maintenance. Its reference plane is perpendicular to the cutting speed. The knitting reference system, on the other hand, is based on the knitting speed, which is important for chip formation . Both systems are thus rotated against each other by the angle of effective direction. Since it is very small in most processes, the angles in both systems are also very similar. Formula symbols in the effective reference system are given the index “e” (from “effective”), those in the tool reference system do not have a special index. Both systems consider an (arbitrary) point on the cutting edge. If a point is selected on the secondary cutting edge, all designations are given an apostrophe (') as an addition in analogy to the secondary clearance area .
The tool reference system has the tool reference plane (r from English reference) as its basic plane . The following levels are perpendicular to it:
- The tool cutting edge plane ( cutting plane ) : It runs tangentially to the main cutting edge at the point under consideration .
- The tool orthogonal plane: It is perpendicular (o for orthogonal ) to the tool cutting edge plane . Previously, it was also called wedge measuring plane referred to as the wedge angle in it is measured.
- The (assumed) working plane (f for "feed" = feed): It lies parallel to the assumed feed direction. It is spanned by the feed and cutting direction.
- The tool back plane : It is perpendicular to the working plane .
The tool cutting edge normal plane : It is perpendicular ( normal ) to the tool cutting edge . It is therefore also identical to the effective cutting edge normal plane because it is not oriented to the tool reference plane.
Angles and radii
Different angles and radii are measured in the defined planes. They are given the index of the level in which they are measured for unambiguous determination. The tool orthogonal wedge angle is therefore measured in the tool orthogonal plane and the effective side rake angle in the working plane . The position of the surfaces on the cutting wedge is defined by the following three angles:
- The tool rake angle
- The tool entering angle
- The tool tilt angle
Tool orthogonal plane
The clearance angle , the wedge angle and the rake angle lie in the tool orthogonal plane . It applies . The rake angle can also be negative.
The clearance angle is measured between the cutting plane and the flank. Large clearance angles (between 6 ° and 15 °) reduce the friction between workpiece and tool and are mainly used for materials that tend to stick and for tools made of tough hard metals such as P40, M40 or K40. Large clearance angles also worsen the heat dissipation from the tool and, with otherwise the same conditions, result in larger wear mark widths . They also weaken the size of the wedge angle and therefore lead to greater wear .
Small clearance angles (2 ° to 5 °) enable a more stable cutting wedge and thus reduce tool wear and vibration . Vibrations can lead to rattling . However, small clearance angles also increase the friction between the tool and the workpiece. They are used for materials with a strength of over 700 N / mm 2 .
The wedge angle is measured between the flank face and the rake face. It should be large for hard and brittle materials and small for soft, tough materials. A rather large wedge angle is also chosen for roughing . It is usually set first. For tools made of high-speed steel (HSS) or carbide , it takes values between 60 ° and 120 °.
The rake angle is measured between the rake face and the tool reference plane. It can also be negative. Large positive rake angles (+ 6 ° to + 25 °) reduce the cutting force, improve the chip flow, reduce the friction between chip and tool, reduce chip compression , improve the surface and reduce the drive power required for the machines. However, the chips tend to form continuous chips and thus to long chips that can get tangled in the machine. Negative rake angles are mainly used for machining hard, brittle materials, as well as for roughing and scraping .
Tool reference plane
The tool setting angle ( Kappa ) and the corner angle are located in the tool reference plane .
Tool setting angle
The tool setting angle lies between the working plane and the tool cutting edge plane . It determines the position of the main cutting edge to the workpiece, and determines at a given depth of cut the cutting width . The smaller the setting angle, the larger the chip width and the longer the area of the main cutting edge that is in contact with otherwise the same chip cross-section . Therefore, the cutting force is distributed over a greater length and the cutting edge is subject to a lower line load, which leads to less wear . In addition, a small setting angle reduces the required feed force and power. On the other hand, it increases the passive force , so that large setting angles are used, especially with unstable workpieces. With a value of the passive force disappears completely. Values between 35 ° and 100 ° are used. Too small a setting angle can also have a negative effect on the cutting edge and cause severe chatter marks. For roughing it should be> 25 ° and <90 °; for finishing turning, an angle of 90 to 97 ° is preferable because of corner machining.
The corner angle lies between the main cutting edge and the secondary cutting edge . It determines the stability of the cutting edge and should be chosen as large as possible. Small corner angles (around 50 °) are used for finishing and copy turning, since the tool is only lightly stressed here. Usually it is 90 °. Particularly large corner angles of around 130 ° are used for heavy roughing. When turning, radii in common sizes between 0.2 mm and 2 mm are ground onto the turning tools, with high-speed steel (HSS) often individually by hand. The larger the radius, the higher the surface quality.
Tool cutting edge plane: The angle of inclination
In the tool cutting edge plane, the angle of inclination lies between the tool reference plane and the main cutting edge .
A negative angle of inclination means a rising edge. The cutting then does not take place on the weak tool tip, but on the main cutting edge, which increases the tool life . However, it also worsens the chip flow and increases the cutting force. Due to the shock loads, planes have angles of inclination of up to −10 °, while −3 ° to −8 ° are common. They are used for roughing and milling. Positive angles of inclination have the opposite effect and are therefore mainly used for materials that tend to stick and are up to + 6 °. With a negative angle of inclination, the chip can also run onto the workpiece surface and thus lead to poor surfaces, which is more likely to be avoided with positive angles. Negative angles of inclination also increase passive strength.
According to the angle of inclination, the insert holders are also designed to be positive and negative. Negative indexable inserts often have the advantage that they can be used on both sides, whereas positive ones can only be used on one side. With HSS turning tools i. d. Usually only positive angles of inclination are used, with indexable inserts made of ceramic often negative and with PCD, coated carbide and CBN indexable inserts made of hard metal as base carrier negative and positive angles of inclination.
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- Heisel, Klocke, Uhlmann, track: Handbuch Spanen , Hanser, 2014, ISBN 978-3-446-42826-3 , pp. 73-77.
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- Wilfried König, Fritz Klocke: Manufacturing process 1: turning, drilling, milling. 8th edition. Springer 2008, ISBN 978-3-540-23458-6 , p. 4f.
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