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Wiper CBN Inserts |
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Positive Inserts with the Wiper Geometry
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Further developments in the wiper concept resulted in the positive CCMT wiper inserts. These inserts are providing high stability machining with minimum vibration, high surface quality and a decrease in machining costs, including in internal turning applications.
The CCMT shaped ISO turning inserts with 0.4 mm and 0.8 mm corner radii are equipped with a deep chipformer to control chip flow and reduce forces in semi-finishing conditions with a relatively high feed rate. For example, when using CCMT 120408-WG inserts at a feed rate of up to 0.45mm/rev, the surface roughness Ra is better than 1µm, compared to a surface roughness of Ra=3-5µm when standard CCMT inserts are used.
The Basic Wiper Geometry Concept
The surface quality and precision of the finished part are both functions of the tool design, the cutting edge geometry and the machining conditions.
When using standard ISO inserts, the surface profile - the PTV (peak to valley) surface roughness (Rt) and therefore the average surface roughness (Ra) - depends mainly on the insert’s nose radius, the approach angle and the feed. In general, improving the surface finish requires either slower feeds or a larger nose radius. Iscar’s new machining concept and the new WG corner configuration for turning inserts has resulted in the surface quality depending only to a small extent on two of these parameters, namely the radius and the feed. Based on this unique wiper concept, Iscar applied for a patent back in 1991 (the patent has been subsequently granted). The patent describes the wiper geometry, which is a new cutting tool configuration especially in the nose corner area of the insert.
The wiper edge L is designed basically as a tangent line to the nose radius or as a very large curved section, shown in Figure 3. The length of the wiper "L" is always designed significantly larger than the maximum feed "f" in order to ensure the high surface quality.
The wiper is positioned at a very slight lead angle - almost 0˚ - in relation to the axis of rotation.
The angle between the corner sections of the "W" (trigon-shaped) or the "C" (rhombic) wiper insert configurations (as shown in Figure 3B) is nearly 90˚ whereas the corner edge angle B on standard inserts
(Figure 3A) is normally 80˚.
In all machining applications the selected feed "f" is smaller than the wiper length "L", thereby producing an excellent surface quality of Rt2 and Ra2 (Figure 3B). The design of this wiper geometry is combined with an optimized chip deflector to provide good chip control and high machining stability when using small, medium and even high feed values.
Iscar offers two different chipformers. The standard WG type covers most workpiece materials and semi-finishing operations. The new WF type with a very narrow chip deflector covers smaller feeds, smaller depths of cut and particularly soft carbon steel alloys. The diagram in Figure 4 shows the effective chipbreaking range using the WG and WF types in turning of low to medium carbon steel types.
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