Каталог Dormer Pramet фрезерование 2021 - 2022 - страница 772

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axy RE axy0,05 H 9 MACHINED SURFACE ROUGHNESS One of the key criteria in finishing operations is the resulting segments, the rule of thumb is that the feed per revolution must be roughness of the machined surface. The following article will less than 80 % of the size of the smoothing segment. In larger (multi- therefore provide several tips on how to approach this issue. tooth) cutters, fulfilling this condition can sometimes be problematic, since the maximum feed value fz = 0.8.a/z may approach the lower Face Milling limit recommended for certain types of insert geometry (the feed When performing any milling operation, the machined surface is speed is lower than the width of the facet in the feed direction). Using shaped by multiple edges. The microgeometry of the surface is thus lower feed speeds usually results in an increase in cutting resistance, dependent on the axial runout of the individual edges of the milling leading to reduced tool life. cutter. The most axially protruding edges are the ones that shape the machined surface. The resulting roughness of the milled surface is, to a large extent, influenced by the design of the tip of the indexable in- sert. If the tip of the indexable insert has a radius, it creates imperfec- tions on the surface. The size of these imperfections is dependent on the corner radius and feed speed (fig.a). For inserts with smoothing R 6 5 4 3 2 1 frev < a frev 6fz5 frev > a frevfz 65 4 4 3 vf 3 vf 2 2 1 1 a a Cutting edge Cutting edge Cutting edge Cutting edge No. 4 rev. × n No. 4 rev. × n +1 No. 4 rev. × n No. 4 rev. × n +1 In that case, the best solution is to use a milling cutter with fewer teeth or to reduce the number of teeth on the milling cutter (only fit- ting an insert onto every other tooth of milling cutters with an even number of teeth). There is, however, a risk of reduced productivity. Another alternative is the use of so-called wiper inserts (if such in- serts are available for the given type of tool). Even this solution has its drawbacks, however. For milling cutters with a small diameter (ap- prox. 63 mm and less) the speed gradient is too high and there is a risk of tearing or smearing of the surface (edge build-up) towards the centre of the milling cutter when machining tough materials. Information about the size of smoothing segments can be found at the beginning of technical information in the catalogue section. a1 = n . a H As regards the majority of other types of milling operations, the ap- proximate maximum surface roughness can again be calculated. To fe do so, we can use the following formula, here accompanied by a graphical explanation. DC H= fe24 . DC fe = 4 . DC . H 771