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The helical cutting edge is the intersecting line or curve between the cylindrical outer surface of the cutter and a plane which contains the cutting edge itself. When rotating inserts with this cutting edge around the center line of the cylinder, the resulting machined surface is flat and perpendicular to the frontal face. The new inserts solve the main geometrical disadvantages of a straight-cutting-edge insert which is the lack of workpiece side wall straightness, flatness, and perpendicularity, saving additional finishing steps.
In addition the helical insert geometry of the rake and clearance faces provides constant rake and clearance angles on the tool for better tool life..
When using inserts with the helical configuration, each cutting edge penetrates gradually into the workpiece with a step-wise force increase, reaching a maximum value which is lower than that achieved with a straight cutting edge. When cutting edges overlap each other, the resultant cutting forces are lower, the tools are always under load, stability is improved, vibration reduced and required forces and machine power during the milling operation are lowered. Due to the use of larger radial rake angles and the unique geometry, the chips are easily deformed and the sidewalls remain perpendicular.
The rhombic type inserts with sloped-cutting-edges shown in Figure 2 with thicker frontal ends act to strengthen the cutter body and enable machining with higher loads and higher feeds. While the frontal edge is at maximum strength, the rear side has a smaller insert wedge angle, but at the same time is subjected to lower cutting forces. The inserts are also equipped with wiper flats which act on the frontal machined surface to improve surface quality. Figure 2 shows also square, multipurpose helical inserts for 90° shouldering, facing and slotting for improved economy and performance. These square inserts combine the helical cutting edge on all four edges with an additional wiper to perform for 90° side wall milling operations. The typical insert designs shown in Figure 2 have helical edges at the central part of each cutting edge, while sloping down- or up-wardly in the wiper area. The unique design with the wiper insures high surface quality and stable machining.
The multipurpose inserts are clamped with a relatively large axial angle on endmills, shoulder cutters, slotting cutters, facemills and also on milling cutters with 45° for chamfering operations as well as on drill mill cutters.The unique features of the square insert design offer the possibility of using each of the four corners for machining flat, straight, and perpendicular shoulders.
Clamping the inserts on heavy-duty cutters with multiple inserts provides full-effective helical cutting edges and the possibility to machine at large depths. The latest development is the unique square inserts designated QDMT or QPMT, mainly for machining shoulders, slots, and deep walls. Each of the new inserts with four helical cutting edges can be used for right- and left-hand milling directions, reducing stock requirements significantly. The inserts have reinforced cutting edges and cutting corners due to a unique corner design. Each corner is equipped with a wiper for right- and left-hand applications. A recess on each of the four clearances faces is designed to mount the insert in a selected position on the cutter periphery being able to select cutter width. Square inserts are normally available in 6, 10, and 16mm square shapes and corner radii of 0.9 to 3.2mm.
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