What is a wiper insert.
The first wiper geometries were first introduced by Sandvik Coromant in 1997.The wiper technology for turning is based on a carefully developed series of radii that make up the cutting edge. On a conventional insert, the nose of the edge is just one radius. The wiper edge, however, is made up of a large, main radius complemented by several smaller radii.
When machining with a standard insert, the surface finish roughness is determined by the feed-rate in mm/revolution and the nose radius of the insert. These are in a direct relationship to the scallop height of the surface H see above figure. This means that the higher the feed, the rougher the surface generated by the edge of a given nose radius.
Wiper inserts have changed this through the effect of their specially developed edges that smooth the scalloped tops that would otherwise have been created. So we can say that turning with wiper inserts we create a surface roughness quality that is better than with a standard insert?
In the image above the geometry of the nose radius on the wiper insert is R=0.8mm, the same as the standard ISO insert nose radius which is also R=0.8mm. On the wiper insert you see clearly the wiper flats.
What advantages are there using wiper turning inserts?
The biggest advantage when using wiper inserts is productivity. Simply by increasing the feed rate we raise the MMR cm3/min (metal removal rate.). But how much do we have to increase the feed?
When talking about using wiper turning inserts there a 2 commonly noted key advantages.
1/. Double the feed rate per revolution with the wiper insert while still achieving the same surface finish as with the standard ISO radius insert. This means that the productivity will also be doubled. Doubling the feed rate in turn reduces the in cut time of the insert in the material, this will give us also beter tool life. The in cut time for a finishing insert is reduced bij 50% per component. Another advantage when using wiper inserts in finishing operation is that we can often increase the cutting speed 10-20%, depending on the depth of cut.
2/. Replacing a standard ISO radius geometry with a wiper geometry and keeping the same feed per revolution the same, the surface finish produced will be two times beter. For example, when turning with a standard ISO nose radius geometry with a feed rate of 0.25mm/rev what creates a surface roughness of 1.6Ra, with the feed rate the same when using a wiper insert the workpiece will have a surface roughness of 0.8Ra.
There is no special tooling needed to use wiper inserts, the turning tool holders used standard inserts can also be used for wiper inserts.
Restrictions and points to consider when using wiper turning inserts.
The lead angle is important when using wiper inserts. The wiper effect will be lost if the lead angle deviates around the 2 to5 degrees. An example of this is when turning chamfers, profiling and conical components.
The wiper geometry will not work effectively on the red marked surfaces in the above drawing. The surface roughness on these surfaces will not be as smooth as on the green marked surfaces. To achieve a good surface roughness on red marked surfaces we have to reduce the feed per revolution.
It is important to understand that visually the surface of the component turned with a wiper insert looks different to that turned with a standard insert. Also we have to take into consideration that the corner radius when using wiper inserts is different than when using a normal ISO radius.
When copying with a D- or T-style High feed insert, adjustments must be made for dimensional deviations.
Nowadays the developments of cutting tool manufacturers have come a long way since the beginning of the introduction in 1997.
Today there are not only finishing application for wiper inserts but also for roughing operations in many materials, and not to forget turning operations in hard turning, materials up to 65HRC can be machined using PCBN wiper inserts. In many operations grinding can be replaced by turning with wiper inserts.