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Drilling and Associated Cutting Tool Technology Industrial Handbook_5

Tham khảo tài liệu 'drilling and associated cutting tool technology industrial handbook_5', kỹ thuật - công nghệ, điện - điện tử phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Drilling and Associated Technologies 123 The insert s substrate - if cemented carbide - requires some thought as if it is too hard this type of insert may chip via the effects of machining vibrations this is particularly so if the tool geometry has an extra-positive and sharp insert cutting edge. It might be more prudent to initially choose a medium-hard cemented carbide grade as it tends to cope with a poten tial edge-chipping condition more readily then if this proves successful a harder grade may be selected. Cutting Parameters - Decisions Two complementary cutting parameters are the insert s nose radius and the influence it has on the DOC. For a Typical length-to diameter ratios for boring bars Figure 62. Interchangeable cutting heads for machining internal features. Courtesy of Sandvik Coromant 124 Chapter 3 example when a finish boring operation is required then it is recommended that both a small nose radius and DOC is used. This smaller boring insert nose radius minimises contact between the workpiece and insert resulting in lower tangential and radial cutting forces. For fine-boring applications a good start point is to choose an insert with a 0.4 mm nose radius with a 0.5 mm DOC. It should be noted that the DOC ought to be larger than the nose radius this is because if it was the other way around cutting forces would be directed in a radial direction - increasing potential vibrational bar-bending i.e. push-off42 problems. Feedrates should be identical regardless of tool s overhang as any feed selection is normally based upon the insert s chip-breaking capabilities. Avoidance of very high feedrates when rough boring is necessary as it can significantly increase the tangential cutting force component. For finish boring operations it is normally the workpiece s surface texture requirement that dictates the maximum feedrate that can be utilised. More will be mentioned on the machined cusp height s effect on surface texture this being created by the remnants .